Nervous System Question Paper

Section A: Multiple Choice Questions (MCQ) - 100 Questions

How many pairs of cranial nerves are there? a) 10 pairs b) 12 pairs c) 14 pairs d) 16 pairs
Sensory nerves carry signals from: a) Brain to muscles b) Sense organs to brain c) Muscles to brain d) Brain to glands
The main part of a neuron containing the nucleus is called: a) Axon b) Dendrite c) Cell body d) Synapse
How many pairs of spinal nerves are there? a) 29 pairs b) 31 pairs c) 33 pairs d) 35 pairs
Motor nerves carry signals from: a) Sense organs to brain b) Brain to muscles and glands c) Muscles to brain d) One neuron to another
Mixed nerves contain: a) Only sensory fibers b) Only motor fibers c) Both sensory and motor fibers d) Neither sensory nor motor fibers
The control center of the nervous system is: a) Spinal cord b) Brain c) Cranial nerves d) Spinal nerves
Branch-like extensions that receive signals from other neurons are called: a) Axons b) Cell bodies c) Dendrites d) Receptors
A reflex action is: a) Voluntary movement b) Involuntary and nearly instantaneous movement c) Slow response d) Conscious decision
The long projection that carries signals away from the cell body is: a) Dendrite b) Axon c) Cell body d) Nucleus
Cranial nerves emerge directly from: a) Spinal cord b) Brain c) Muscles d) Sense organs
The spinal cord extends from the medulla oblongata to: a) Cervical region b) Thoracic region c) Lumbar region d) Sacral region
A stimulus is: a) A response to an event b) A thing that evokes a reaction c) A nerve signal d) A muscle contraction
An organ that responds to external stimuli and transmits signals is a: a) Effector b) Receptor c) Motor neuron d) Sensory neuron
The signal transmitted along a nerve fiber is called: a) Stimulus b) Response c) Impulse d) Reflex
An effector is: a) A stimulus detector b) An organ that acts in response to a stimulus c) A nerve fiber d) A brain region
Which is an example of reflex action? a) Writing b) Reading c) Blinking when something comes close to eye d) Speaking
The CNS consists of: a) Brain only b) Spinal cord only c) Brain and spinal cord d) All nerves
Withdrawing hand from hot object is an example of: a) Voluntary action b) Reflex action c) Motor action d) Sensory action
The reaction to a stimulus is called: a) Impulse b) Response c) Receptor d) Effector
Spinal nerves emerge from: a) Brain b) Spinal cord c) Muscles d) Sense organs
The nervous system's main function is: a) Digestion b) Circulation c) Control and coordination d) Respiration
A neuron is: a) A muscle cell b) A nerve cell c) A blood cell d) A bone cell
The space between two neurons is called: a) Gap junction b) Synapse c) Axon terminal d) Node
Sensory neurons are also called: a) Motor neurons b) Afferent neurons c) Efferent neurons d) Interneurons
Motor neurons are also called: a) Sensory neurons b) Afferent neurons c) Efferent neurons d) Receptor neurons
The protective covering around the brain is: a) Skull b) Meninges c) Vertebrae d) Cartilage
The basic unit of nervous system is: a) Brain b) Nerve c) Neuron d) Synapse
Reflexes help in: a) Conscious thinking b) Protection from harm c) Voluntary movements d) Memory formation
The part of brain that controls reflexes is: a) Cerebrum b) Cerebellum c) Medulla oblongata d) Hypothalamus
Nerve impulses are: a) Chemical signals b) Electrical signals c) Both electrical and chemical d) Mechanical signals
The myelin sheath around axons helps in: a) Slowing impulses b) Speeding up impulses c) Stopping impulses d) Creating impulses
Which type of nerve fiber is myelinated? a) All nerve fibers b) Only sensory fibers c) Only motor fibers d) Long nerve fibers
The direction of nerve impulse in a neuron is: a) Dendrite to axon b) Axon to dendrite c) Cell body to dendrite d) Random
Neurotransmitters are released at: a) Cell body b) Dendrites c) Axon terminals d) Nucleus
The autonomic nervous system controls: a) Voluntary actions b) Involuntary actions c) Reflexes only d) Sensory functions
The somatic nervous system controls: a) Involuntary actions b) Voluntary actions c) Heart rate d) Digestion
Pain receptors are called: a) Photoreceptors b) Mechanoreceptors c) Nociceptors d) Chemoreceptors
Temperature receptors are called: a) Thermoreceptors b) Photoreceptors c) Chemoreceptors d) Mechanoreceptors
Light receptors are called: a) Thermoreceptors b) Photoreceptors c) Chemoreceptors d) Mechanoreceptors
The knee-jerk reflex involves: a) Brain processing b) Spinal cord only c) Voluntary control d) Conscious thought
Gray matter in spinal cord contains: a) Myelinated axons b) Cell bodies c) Blood vessels only d) Cerebrospinal fluid
White matter in spinal cord contains: a) Cell bodies b) Myelinated axons c) Gray matter d) Blood only
The reflex arc involves: a) 3 components b) 4 components c) 5 components d) 6 components
In a reflex arc, the correct sequence is: a) Effector→Receptor→CNS b) Receptor→CNS→Effector c) CNS→Receptor→Effector d) Receptor→Effector→CNS
The fastest type of nerve fiber is: a) Unmyelinated b) Thinly myelinated c) Thickly myelinated d) All are same speed
Sensory receptors convert stimuli into: a) Mechanical energy b) Chemical energy c) Electrical impulses d) Heat energy
The peripheral nervous system includes: a) Brain only b) Spinal cord only c) Brain and spinal cord d) All nerves outside CNS
Cranial nerve I is: a) Optic nerve b) Olfactory nerve c) Auditory nerve d) Trigeminal nerve
The vagus nerve is cranial nerve: a) VIII b) IX c) X d) XI
The optic nerve is cranial nerve: a) I b) II c) III d) IV
Facial expressions are controlled by cranial nerve: a) V b) VI c) VII d) VIII
The trigeminal nerve is cranial nerve: a) III b) IV c) V d) VI
Hearing and balance are controlled by cranial nerve: a) VII b) VIII c) IX d) X
The spinal cord is protected by: a) Skull b) Ribs c) Vertebral column d) Sternum
Cerebrospinal fluid is found in: a) Blood vessels b) Ventricles and subarachnoid space c) Muscles d) Bones
The blood-brain barrier protects: a) Heart b) Lungs c) Brain d) Liver
Neurons communicate through: a) Direct contact b) Chemical messengers c) Electrical connection d) All of the above
The resting potential of a neuron is approximately: a) +70mV b) -70mV c) 0mV d) +35mV
Action potential is: a) Resting state b) Active state c) Damaged state d) Dead state
Saltatory conduction occurs in: a) Unmyelinated fibers b) Myelinated fibers c) All fibers d) Damaged fibers
Nodes of Ranvier are found in: a) Cell bodies b) Dendrites c) Myelinated axons d) Synapses
The refractory period prevents: a) Impulse generation b) Backward flow of impulse c) Forward flow of impulse d) Synapse formation
Excitatory neurotransmitters: a) Inhibit nerve impulses b) Promote nerve impulses c) Block nerve impulses d) Have no effect
Inhibitory neurotransmitters: a) Promote nerve impulses b) Inhibit nerve impulses c) Speed up impulses d) Create new impulses
Acetylcholine is a: a) Hormone b) Enzyme c) Neurotransmitter d) Receptor
The neuromuscular junction is between: a) Two neurons b) Neuron and muscle c) Two muscles d) Muscle and bone
Muscle contraction is initiated by: a) Hormones b) Nerve impulses c) Blood flow d) Oxygen
The sympathetic nervous system: a) Slows heart rate b) Increases heart rate c) Has no effect on heart d) Stops the heart
The parasympathetic nervous system: a) Increases heart rate b) Slows heart rate c) Stops digestion d) Increases breathing
Fight or flight response is controlled by: a) Parasympathetic system b) Sympathetic system c) Somatic system d) Central system
Rest and digest response is controlled by: a) Sympathetic system b) Parasympathetic system c) Somatic system d) Sensory system
Reflex actions are important for: a) Learning b) Memory c) Survival d) Growth
The simplest reflex involves: a) 2 neurons b) 3 neurons c) 4 neurons d) 5 neurons
Conditioned reflexes are: a) Inborn b) Learned c) Automatic d) Unconscious
Unconditioned reflexes are: a) Learned b) Inborn c) Voluntary d) Conscious
The pupillary reflex controls: a) Eye movement b) Pupil size c) Blinking d) Focusing
The patellar reflex tests: a) Arm function b) Leg function c) Spinal cord function d) Brain function
Withdrawal reflex is: a) Protective b) Harmful c) Voluntary d) Learned
Reflexes can be: a) Only spinal b) Only cranial c) Both spinal and cranial d) Neither
The stretch reflex maintains: a) Blood pressure b) Muscle tone c) Heart rate d) Breathing
Golgi tendon organs detect: a) Muscle length b) Muscle tension c) Muscle temperature d) Muscle color
Muscle spindles detect: a) Muscle tension b) Muscle length c) Muscle strength d) Muscle fatigue
Proprioceptors provide information about: a) External environment b) Body position c) Temperature d) Pain
The vestibular system controls: a) Vision b) Hearing c) Balance d) Taste
Sensory adaptation means: a) Increased sensitivity b) Decreased sensitivity c) No change d) Loss of function
Phantom limb sensation occurs due to: a) Damaged receptors b) Brain interpretation c) Muscle memory d) Blood circulation
Cross-over of nerve fibers occurs at: a) Spinal cord b) Medulla oblongata c) Cerebrum d) Cerebellum
The left brain controls: a) Left side of body b) Right side of body c) Both sides equally d) No specific side
Nerve regeneration is possible in: a) CNS only b) PNS only c) Both CNS and PNS d) Neither CNS nor PNS
Wallerian degeneration occurs in: a) Healthy nerves b) Damaged nerves c) Growing nerves d) All nerves
Schwann cells are found in: a) CNS b) PNS c) Both CNS and PNS d) Neither
Oligodendrocytes are found in: a) PNS b) CNS c) Both CNS and PNS d) Neither
The largest cranial nerve is: a) Optic b) Trigeminal c) Vagus d) Facial
Bell's palsy affects: a) Trigeminal nerve b) Facial nerve c) Optic nerve d) Auditory nerve
Carpal tunnel syndrome affects: a) Ulnar nerve b) Radial nerve c) Median nerve d) All arm nerves
Sciatica involves: a) Femoral nerve b) Sciatic nerve c) Tibial nerve d) All leg nerves
Multiple sclerosis affects: a) Myelin sheath b) Cell bodies c) Dendrites d) Synapses
Parkinson's disease involves: a) Excess dopamine b) Lack of dopamine c) Excess acetylcholine d) Lack of serotonin
Alzheimer's disease primarily affects: a) Spinal cord b) Peripheral nerves c) Brain d) Muscles

Section B: One Mark Short Questions - 100 Questions

Define sensory nerves.
What are motor nerves?
How many cranial nerves are there?
Name the main parts of a motor neuron.
What is the function of dendrites?
What does CNS stand for?
Define reflex action.
What is a stimulus?
Give one example of reflex action.
What is an impulse?
Define receptor.
What is an effector?
How many spinal nerves are there?
What are mixed nerves?
Name the two main parts of CNS.
What is the function of axon?
Where do cranial nerves emerge from?
What is a response?
Give another example of reflex action.
What contains the nucleus in a neuron?
What is the control center of nervous system?
From where do spinal nerves emerge?
What type of fibers do mixed nerves contain?
What is the basic unit of nervous system?
Name the protective covering of brain.
What is myelin sheath?
What are neurotransmitters?
Define synapse.
What is autonomic nervous system?
What is somatic nervous system?
Name the pain receptors.
What are thermoreceptors?
What detects light?
What is gray matter?
What is white matter?
How many components are in reflex arc?
What is resting potential?
What is action potential?
What are nodes of Ranvier?
Name one excitatory neurotransmitter.
What is neuromuscular junction?
Which system controls fight or flight?
What is withdrawal reflex?
What do muscle spindles detect?
What system controls balance?
What is sensory adaptation?
Where does crossover occur?
What are Schwann cells?
Name the largest cranial nerve.
What is Bell's palsy?
What is the direction of impulse in neuron?
What is saltatory conduction?
What is refractory period?
Name one inhibitory neurotransmitter.
What initiates muscle contraction?
Which system slows heart rate?
What are conditioned reflexes?
What is pupillary reflex?
What is stretch reflex?
What do Golgi tendon organs detect?
What are proprioceptors?
What is phantom limb sensation?
Which side does left brain control?
What is Wallerian degeneration?
Where are oligodendrocytes found?
What does carpal tunnel syndrome affect?
What nerve is involved in sciatica?
What does multiple sclerosis affect?
What is lacking in Parkinson's disease?
What does Alzheimer's primarily affect?
What is the function of cerebrospinal fluid?
What protects the brain from toxins?
What is the speed of nerve impulse?
What type of neuron carries signals to muscles?
What type of neuron carries signals from senses?
What connects two neurons?
What covers long nerve fibers?
What releases neurotransmitters?
What receives neurotransmitters?
What type of response is blinking?
What protects spinal cord?
What fluid surrounds brain and spinal cord?
What is the charge inside resting neuron?
What happens during action potential?
What speeds up nerve conduction?
What prevents backward flow of impulse?
What type of junction is between nerve and muscle?
What controls involuntary actions?
What controls voluntary actions?
What is the simplest nervous pathway?
What type of reflex is knee-jerk?
What detects muscle stretch?
What maintains muscle tone?
What provides body position sense?
What causes adaptation in receptors?
What helps in nerve regeneration?
What cells make myelin in PNS?
What cells make myelin in CNS?
What is affected in nerve damage?
What is neural plasticity?

Section C: Two Marks Questions - 50 Questions

Differentiate between sensory and motor nerves.
Explain the structure of a motor neuron with a labeled diagram.
List the components of Central Nervous System and their functions.
Define reflex action and give two examples.
Explain the difference between cranial and spinal nerves.
What are mixed nerves? Give their significance.
Describe the basic terms related to reflex action.
Compare voluntary and involuntary actions.
Explain the pathway of a simple reflex arc.
What is the importance of reflex actions in daily life?
Describe the structure and function of dendrites.
Explain the role of axon in nerve impulse transmission.
What is the significance of cell body in a neuron?
Differentiate between CNS and PNS.
Describe any two cranial nerves and their functions.
Explain the protective mechanisms of the nervous system.
What happens when you touch a hot object? Explain the reflex.
Describe the components involved in blinking reflex.
Explain the concept of stimulus and response with examples.
What are the different types of neurons? Explain briefly.
Describe the structure of a typical nerve.
Explain the importance of myelin sheath.
What is a synapse? Describe its structure.
Differentiate between excitatory and inhibitory neurons.
Explain the process of nerve impulse transmission.
What are neurotransmitters? Give examples.
Describe the autonomic nervous system.
Explain the somatic nervous system.
What are the different types of sensory receptors?
Describe the reflex arc with suitable examples.
Explain the concept of sensory adaptation.
What is the role of spinal cord in reflexes?
Describe the structure of spinal cord.
Explain the difference between gray and white matter.
What are the characteristics of nerve impulse?
Describe the resting and action potential.
Explain saltatory conduction.
What is the refractory period? Why is it important?
Describe the neuromuscular junction.
Explain the sympathetic nervous system.
Describe the parasympathetic nervous system.
What are conditioned and unconditioned reflexes?
Explain the stretch reflex mechanism.
Describe the withdrawal reflex.
What is the role of proprioceptors?
Explain the vestibular system.
Describe nerve regeneration process.
What are the common nervous system disorders?
Explain the concept of neural plasticity.
Describe the blood-brain barrier and its functions.

Section D: Three Marks Broad Questions - 50 Questions

Draw a well-labeled diagram of a motor neuron and explain the function of each part in detail.
Describe the classification of the nervous system with a flowchart. Explain the functions of each division.
Explain the mechanism of reflex action with the help of a labeled diagram. Use the example of withdrawal of hand from a hot object.
Compare and contrast the Central Nervous System and Peripheral Nervous System in terms of structure, location, and functions.
Describe the structure and functions of cranial nerves. Explain any three cranial nerves with their specific functions.
Explain the concept of nerve impulse transmission. Describe the events that occur during the generation and propagation of an action potential.
What are synapses? Describe the structure of a synapse and explain the mechanism of synaptic transmission.
Describe the autonomic nervous system. Explain the differences between sympathetic and parasympathetic divisions with examples.
Explain the different types of sensory receptors with examples. How do they convert stimuli into nerve impulses?
Describe the structure of the spinal cord. Explain its role in reflex actions and as a pathway for nerve impulses.
What is myelin sheath? Explain its structure, formation, and significance in nerve impulse conduction.
Describe the process of nerve regeneration. What factors affect the regeneration of damaged nerves?
Explain the concept of neurotransmitters. Describe their classification and functions with specific examples.
What are reflexes? Classify different types of reflexes and explain their importance in maintaining homeostasis.
Describe the mechanism of muscle contraction as controlled by the nervous system. Include the role of motor neurons and neuromuscular junction.
Explain the sensory pathways in the nervous system. Describe how sensory information travels from receptors to the brain.
What is neural plasticity? Explain its types and significance in learning, memory, and recovery from brain injuries.
Describe the protective mechanisms of the nervous system including meninges, cerebrospinal fluid, and blood-brain barrier.
Explain the development of the nervous system. Describe the major stages of neurogenesis and neural development.
What are the common disorders of the nervous system? Describe the causes, symptoms, and effects of any three neurological disorders.
Describe the electrical properties of neurons. Explain resting potential, action potential, and the factors that influence them.
Explain the concept of sensory adaptation. Why is it important and how does it occur at the cellular level?
Describe the pain pathway in the nervous system. Explain how pain signals are transmitted, processed, and modulated.
What is the role of the nervous system in maintaining homeostasis? Provide specific examples of homeostatic control mechanisms.
Explain the integration function of the nervous system. How does the nervous system process and integrate multiple inputs?
Describe the motor pathways in the nervous system. Explain how voluntary movements are initiated and controlled.
What are the effects of aging on the nervous system? Describe the structural and functional changes that occur with age.
Explain the relationship between the nervous system and the endocrine system. How do they work together to control body functions?
Describe the sleep-wake cycle and its neural control mechanisms. What brain regions and neurotransmitters are involved?
What is the role of the nervous system in behavior and emotions? Explain the neural basis of behavior with examples.
Describe the memory formation and storage mechanisms in the nervous system. What are the different types of memory?
Explain the neural control of respiration. Describe the respiratory centers and their regulation mechanisms.
What is the neural control of heart rate and blood pressure? Describe the cardiovascular control centers and their functions.
Explain the neural control of digestion. Describe the enteric nervous system and its relationship with the CNS.
What are neurodegenerative diseases? Describe the pathophysiology of Alzheimer's disease and Parkinson's disease.
Describe the neural basis of vision. Explain the pathway from photoreceptors to visual cortex.
Explain the neural basis of hearing. Describe the auditory pathway from cochlea to auditory cortex.
What is the neural control of movement? Describe the motor cortex, basal ganglia, and cerebellum in motor control.
Explain the concept of lateralization in the brain. What are the functional differences between left and right hemispheres?
Describe the limbic system and its functions. How does it control emotions and motivation?
What is the blood-brain barrier? Explain its structure, functions, and clinical significance.
Describe the glial cells and their functions. How do they support neuronal function?
Explain the concept of neuroplasticity in learning and memory. How do synapses change during learning?
What are the effects of drugs on the nervous system? Describe the mechanisms of action of common psychoactive drugs.
Describe the neural control of temperature regulation. How does the body maintain thermal homeostasis?
Explain the neural mechanisms of stress response. What is the role of the hypothalamic-pituitary-adrenal axis?
What is the neural basis of consciousness? Describe the current theories about consciousness and awareness.
Describe the neural control of circadian rhythms. What is the role of the suprachiasmatic nucleus?
Explain the neural mechanisms of addiction. How do addictive substances affect the reward pathways in the brain?
What are the applications of neuroscience in medicine? Describe modern techniques for studying and treating nervous system disorders.

Nervous System - Answer Key

Section A: Multiple Choice Questions

b) 12 pairs
b) Sense organs to brain
c) Cell body
b) 31 pairs
b) Brain to muscles and glands
c) Both sensory and motor fibers
b) Brain
c) Dendrites
b) Involuntary and nearly instantaneous movement
b) Axon
b) Brain
c) Lumbar region
b) A thing that evokes a reaction
b) Receptor
c) Impulse
b) An organ that acts in response to a stimulus
c) Blinking when something comes close to eye
c) Brain and spinal cord
b) Reflex action
b) Response
b) Spinal cord
c) Control and coordination
b) A nerve cell
b) Synapse
b) Afferent neurons
c) Efferent neurons
b) Meninges
c) Neuron
b) Protection from harm
c) Medulla oblongata
c) Both electrical and chemical
b) Speeding up impulses
d) Long nerve fibers
a) Dendrite to axon
c) Axon terminals
b) Involuntary actions
b) Voluntary actions
c) Nociceptors
a) Thermoreceptors
b) Photoreceptors
b) Spinal cord only
b) Cell bodies
b) Myelinated axons
c) 5 components
b) Receptor→CNS→Effector
c) Thickly myelinated
c) Electrical impulses
d) All nerves outside CNS
b) Olfactory nerve
c) X
b) II
c) VII
c) V
b) VIII
c) Vertebral column
b) Ventricles and subarachnoid space
c) Brain
b) Chemical messengers
b) -70mV
b) Active state
b) Myelinated fibers
c) Myelinated axons
b) Backward flow of impulse
b) Promote nerve impulses
b) Inhibit nerve impulses
c) Neurotransmitter
b) Neuron and muscle
b) Nerve impulses
b) Increases heart rate
b) Slows heart rate
b) Sympathetic system
b) Parasympathetic system
c) Survival
a) 2 neurons
b) Learned
b) Inborn
b) Pupil size
c) Spinal cord function
a) Protective
c) Both spinal and cranial
b) Muscle tone
b) Muscle tension
b) Muscle length
b) Body position
c) Balance
b) Decreased sensitivity
b) Brain interpretation
b) Medulla oblongata
b) Right side of body
b) PNS only
b) Damaged nerves
b) PNS
b) CNS
b) Trigeminal
b) Facial nerve
c) Median nerve
b) Sciatic nerve
a) Myelin sheath
b) Lack of dopamine
c) Brain

Section B: One Mark Short Questions

Sensory nerves carry signals from sense organs to the brain.
Motor nerves carry signals from the brain to muscles and glands.
There are 12 pairs of cranial nerves.
A motor neuron consists of a cell body, dendrites, and an axon.
Dendrites receive signals from other neurons.
CNS stands for Central Nervous System.
A reflex action is an involuntary and nearly instantaneous movement in response to a stimulus.
A stimulus is an event or thing that evokes a reaction.
Withdrawing your hand from a hot object is a reflex action.
An impulse is an electrical signal transmitted along a nerve fiber.
A receptor is an organ or cell that detects stimuli.
An effector is a muscle or gland that responds to a stimulus.
There are 31 pairs of spinal nerves.
Mixed nerves contain both sensory and motor fibers.
The two main parts of the CNS are the brain and the spinal cord.
The axon carries signals away from the cell body.
Cranial nerves emerge from the brain.
A response is a reaction to a stimulus.
Blinking when an object approaches the eye is a reflex action.
The cell body contains the nucleus in a neuron.
The brain is the control center of the nervous system.
Spinal nerves emerge from the spinal cord.
Mixed nerves contain both sensory and motor fibers.
The neuron is the basic unit of the nervous system.
The meninges are the protective coverings of the brain.
The myelin sheath is a fatty layer that insulates the axon.
Neurotransmitters are chemical messengers that transmit signals across a synapse.
A synapse is the junction between two neurons.
The autonomic nervous system controls involuntary actions.
The somatic nervous system controls voluntary actions.
Nociceptors are pain receptors.
Thermoreceptors detect changes in temperature.
Photoreceptors detect light.
Gray matter consists mainly of neuronal cell bodies.
White matter consists of myelinated axons.
A reflex arc has 5 components: receptor, sensory neuron, interneuron, motor neuron, effector.
Resting potential is the electrical potential of a neuron at rest.
Action potential is the change in electrical potential associated with the passage of an impulse.
Nodes of Ranvier are gaps in the myelin sheath of an axon.
Acetylcholine is an example of an excitatory neurotransmitter.
The neuromuscular junction is the synapse between a motor neuron and a muscle fiber.
The sympathetic nervous system controls the fight or flight response.
The withdrawal reflex is a protective reflex that pulls a body part away from a painful stimulus.
Muscle spindles detect changes in muscle length.
The vestibular system in the inner ear controls balance.
Sensory adaptation is the process by which sensory receptors become less responsive to a constant stimulus.
Crossover of nerve fibers (decussation) occurs in the medulla oblongata.
Schwann cells produce the myelin sheath in the Peripheral Nervous System (PNS).
The trigeminal nerve (Cranial Nerve V) is the largest cranial nerve.
Bell's palsy is a condition that causes temporary weakness or paralysis of the muscles in one side of the face, affecting the facial nerve.
The impulse in a neuron travels from the dendrites to the cell body and then down the axon.
Saltatory conduction is the rapid transmission of a nerve impulse along a myelinated axon, where the impulse jumps from one Node of Ranvier to the next.
The refractory period is a brief period after an action potential during which a neuron cannot be stimulated again.
GABA (gamma-aminobutyric acid) is an example of an inhibitory neurotransmitter.
A nerve impulse from a motor neuron initiates muscle contraction.
The parasympathetic nervous system slows the heart rate.
Conditioned reflexes are learned responses to a previously neutral stimulus.
The pupillary reflex is the constriction or dilation of the pupil in response to light.
The stretch reflex is a muscle contraction in response to stretching within the muscle.
Golgi tendon organs detect changes in muscle tension.
Proprioceptors are sensory receptors that provide information about the position and movement of the body.
Phantom limb sensation is the feeling that an amputated limb is still attached to the body.
The left side of the brain controls the right side of the body.
Wallerian degeneration is the process of degeneration of the axon distal to a point of injury.
Oligodendrocytes are found in the Central Nervous System (CNS).
Carpal tunnel syndrome affects the median nerve in the wrist.
The sciatic nerve is involved in sciatica.
Multiple sclerosis affects the myelin sheath of neurons in the CNS.
Parkinson's disease involves a lack of the neurotransmitter dopamine.
Alzheimer's disease primarily affects the brain, causing memory loss and cognitive decline.
Cerebrospinal fluid cushions the brain and spinal cord and provides nutrients.
The blood-brain barrier protects the brain from harmful substances and toxins in the blood.
The speed of a nerve impulse can range from 0.5 to 120 meters per second.
Motor neurons carry signals to muscles.
Sensory neurons carry signals from sense organs.
A synapse connects two neurons.
The myelin sheath covers long nerve fibers.
Axon terminals release neurotransmitters.
Dendrites of the postsynaptic neuron receive neurotransmitters.
Blinking is a reflex response.
The vertebral column protects the spinal cord.
Cerebrospinal fluid surrounds the brain and spinal cord.
The inside of a resting neuron is negatively charged relative to the outside.
During an action potential, the charge inside the neuron briefly becomes positive.
The myelin sheath speeds up nerve conduction.
The refractory period prevents the backward flow of an impulse.
The neuromuscular junction is the junction between a nerve and a muscle.
The autonomic nervous system controls involuntary actions.
The somatic nervous system controls voluntary actions.
The reflex arc is the simplest nervous pathway.
The knee-jerk reflex is a stretch reflex.
Muscle spindles detect muscle stretch.
The stretch reflex maintains muscle tone.
Proprioceptors provide a sense of body position.
Continuous stimulation of receptors causes sensory adaptation.
Schwann cells in the PNS help in nerve regeneration.
Schwann cells make myelin in the PNS.
Oligodendrocytes make myelin in the CNS.
The axon is primarily affected in nerve damage.
Neural plasticity is the brain's ability to reorganize itself by forming new neural connections.

Section C: Two Marks Questions

Sensory vs. Motor Nerves: Sensory nerves (afferent) carry impulses from sensory receptors towards the CNS. Motor nerves (efferent) carry impulses away from the CNS to muscles and glands (effectors).
Structure of a Motor Neuron: A motor neuron has a cell body with a nucleus, dendrites that receive signals, and a long axon that transmits signals away from the cell body to an effector. The axon is often covered by a myelin sheath.
CNS Components: The Central Nervous System consists of the brain, which is the main control center for thought, memory, and emotion, and the spinal cord, which relays messages and controls reflexes.
Reflex Action: A reflex is a rapid, involuntary response to a stimulus. Examples include the withdrawal of a hand from a hot object and the knee-jerk reflex.
Cranial vs. Spinal Nerves: Cranial nerves emerge directly from the brain (12 pairs) and primarily serve the head and neck. Spinal nerves emerge from the spinal cord (31 pairs) and serve the rest of the body.
Mixed Nerves: These nerves contain both sensory and motor fibers, allowing them to transmit signals in both directions. Their significance lies in enabling a two-way communication between the CNS and a particular body part.
Terms in Reflex Action:
- Receptor: Detects the stimulus.
- Effector: The muscle or gland that responds.
- Stimulus: The change that triggers the reflex.
- Response: The action performed by the effector.
Voluntary vs. Involuntary Actions: Voluntary actions are consciously controlled by the brain (e.g., writing). Involuntary actions are not under conscious control and are regulated by the autonomic nervous system or reflexes (e.g., heartbeat, digestion).
Reflex Arc Pathway: The pathway is: Receptor → Sensory Neuron → Interneuron (in spinal cord) → Motor Neuron → Effector. This allows for a rapid response without involving the brain for decision-making.
Importance of Reflexes: Reflexes are crucial for survival as they provide rapid, protective responses to potentially harmful stimuli, such as pulling away from a sharp object or blinking to protect the eye.
Dendrites: These are short, branched extensions of a neuron that receive electrochemical signals from the axon terminals of other neurons and transmit them towards the cell body.
Axon: This is a long, slender projection of a neuron that conducts electrical impulses, known as action potentials, away from the neuron's cell body to transmit the signal to other neurons, muscles, or glands.
Cell Body (Soma): The cell body is the neuron's core. It contains the nucleus and other organelles and is responsible for maintaining the life of the cell and integrating incoming signals.
CNS vs. PNS: The Central Nervous System (CNS) consists of the brain and spinal cord and is the main processing center. The Peripheral Nervous System (PNS) consists of all the nerves outside the CNS and connects the CNS to the rest of the body.
Two Cranial Nerves:
- Optic Nerve (II): A sensory nerve that transmits visual information from the retina to the brain.
- Vagus Nerve (X): A mixed nerve that controls a wide range of functions, including heart rate, digestion, and sweating.
Protective Mechanisms: The nervous system is protected by bone (skull and vertebral column), meninges (three layers of protective tissue), and cerebrospinal fluid (which provides cushioning).
Touching a Hot Object: When you touch a hot object, temperature and pain receptors in your skin send a signal via a sensory neuron to the spinal cord. An interneuron relays the signal to a motor neuron, which instructs muscles in your arm to contract and pull your hand away.
Blinking Reflex: When an object rapidly approaches the eye, photoreceptors or mechanoreceptors detect the stimulus. A signal is sent via the optic or trigeminal nerve to the brainstem, which then sends a motor command via the facial nerve to the eyelid muscles (orbicularis oculi) to contract, causing a blink.
Stimulus and Response: A stimulus is any change that can be detected (e.g., light, sound, heat). A response is the reaction of the organism to that stimulus (e.g., pupils constricting in bright light).
Types of Neurons:
- Sensory (Afferent) Neurons: Transmit signals from receptors to the CNS.
- Motor (Efferent) Neurons: Transmit signals from the CNS to effectors.
- Interneurons: Connect sensory and motor neurons within the CNS.
Structure of a Nerve: A nerve consists of a bundle of axons (nerve fibers) from multiple neurons, held together by connective tissue. Each nerve is supplied with blood vessels.
Importance of Myelin Sheath: The myelin sheath is a fatty insulating layer that surrounds the axon. It speeds up the transmission of nerve impulses through saltatory conduction and prevents the electrical signal from dissipating.
Synapse: A synapse is the specialized junction where a neuron communicates with another cell. It includes the axon terminal of the presynaptic neuron, the synaptic cleft (a small gap), and the membrane of the postsynaptic cell.
Excitatory vs. Inhibitory Neurons: Excitatory neurons release neurotransmitters that cause depolarization in the postsynaptic neuron, making it more likely to fire an action potential. Inhibitory neurons cause hyperpolarization, making it less likely to fire.
Nerve Impulse Transmission: An impulse (action potential) is an all-or-nothing electrical signal that travels down an axon. It is generated by the rapid influx of sodium ions across the neuron's membrane, causing a temporary reversal of charge.
Neurotransmitters: These are chemical messengers released from axon terminals into the synaptic cleft to transmit a signal to the next cell. Examples include acetylcholine (muscle control) and dopamine (mood and pleasure).
Autonomic Nervous System (ANS): The ANS is a division of the PNS that controls involuntary bodily functions such as heart rate, digestion, respiratory rate, and pupillary response. It has two main branches: the sympathetic and parasympathetic systems.
Somatic Nervous System: This is the part of the PNS associated with the voluntary control of body movements via skeletal muscles. It consists of sensory nerves and motor nerves.
Types of Sensory Receptors:
- Mechanoreceptors: Respond to mechanical pressure or distortion (touch, sound).
- Thermoreceptors: Respond to changes in temperature.
- Photoreceptors: Respond to light.
- Chemoreceptors: Respond to chemical stimuli (taste, smell).
- Nociceptors: Respond to damaging or painful stimuli.
Reflex Arc Example: In the knee-jerk reflex, tapping the patellar tendon stretches the quadriceps muscle. Stretch receptors (muscle spindles) are stimulated, sending a signal via a sensory neuron to the spinal cord. It synapses directly with a motor neuron, which causes the quadriceps to contract, kicking the leg forward.
Sensory Adaptation: This is a decrease in sensitivity to a constant level of stimulation. For example, when you first put on a watch, you feel it, but you soon become unaware of it because the touch receptors adapt.
Spinal Cord's Role in Reflexes: The spinal cord acts as a reflex center, processing simple reflexes without involving the brain. This allows for extremely fast responses to stimuli, which is crucial for protection.
Structure of Spinal Cord: The spinal cord is a long, thin tube of nervous tissue. In cross-section, it has a central H-shaped region of gray matter (containing cell bodies) surrounded by white matter (containing myelinated axons).
Gray vs. White Matter: Gray matter consists of neuronal cell bodies, dendrites, unmyelinated axons, and glial cells; it is where synaptic integration occurs. White matter is composed mainly of myelinated axons that transmit signals over longer distances.
Characteristics of Nerve Impulse: A nerve impulse (action potential) is an "all-or-none" event, meaning it either fires at full strength or not at all. It is self-propagating and travels in one direction down the axon without losing strength.
Resting and Action Potential: Resting potential is the negative charge (~ -70mV) inside a neuron at rest. An action potential is a brief, rapid reversal of this charge that occurs when a neuron is stimulated, allowing it to transmit an electrical signal.
Saltatory Conduction: This is the "jumping" of an action potential from one Node of Ranvier to the next along a myelinated axon. This process is much faster than the continuous conduction seen in unmyelinated axons.
Refractory Period: This is a short period after an action potential when the neuron cannot fire another one. It is important because it ensures that the nerve impulse travels in only one direction (forward) and limits the firing rate of the neuron.
Neuromuscular Junction: This is a specialized synapse between a motor neuron and a skeletal muscle fiber. The motor neuron releases acetylcholine, which binds to receptors on the muscle fiber, causing it to depolarize and contract.
Sympathetic Nervous System: This division of the ANS prepares the body for "fight or flight" situations. It increases heart rate, blood pressure, and glucose levels, while diverting blood flow to the muscles.
Parasympathetic Nervous System: This division of the ANS controls "rest and digest" functions. It slows the heart rate, stimulates digestion, and conserves energy.
Conditioned vs. Unconditioned Reflexes: An unconditioned reflex is an inborn, automatic response (e.g., salivating at the sight of food). A conditioned reflex is a learned response to a previously neutral stimulus (e.g., Pavlov's dogs salivating at the sound of a bell).
Stretch Reflex: This is a monosynaptic reflex that maintains muscle tone and posture. When a muscle is stretched, its muscle spindles are activated, causing a reflexive contraction of the same muscle to resist the stretch.
Withdrawal Reflex: This is a polysynaptic, protective reflex. When a painful stimulus is detected, sensory neurons activate interneurons in the spinal cord, which in turn activate motor neurons to cause contraction of flexor muscles, pulling the limb away from the stimulus.
Role of Proprioceptors: Proprioceptors (like muscle spindles and Golgi tendon organs) are sensory receptors located in muscles, tendons, and joints. They provide the brain with information about the position, movement, and force of the body's limbs and trunk.
Vestibular System: Located in the inner ear, this system is responsible for providing our sense of balance and spatial orientation. It detects changes in head position and movement, sending signals to the brain to help maintain balance and coordinate eye movements.
Nerve Regeneration: In the PNS, if a nerve is severed, the axon distal to the injury degenerates. However, the Schwann cells can form a regeneration tube, guiding the growth of a new axon from the proximal stump back to the target tissue. Regeneration is very limited in the CNS.
Common Nervous System Disorders: Common disorders include neurodegenerative diseases (Alzheimer's, Parkinson's), demyelinating diseases (Multiple Sclerosis), stroke (damage due to lack of blood flow), epilepsy (seizures), and peripheral neuropathies (nerve damage).
Neural Plasticity: This is the brain's ability to change and adapt its structure and function in response to experience, learning, or injury. It involves the formation of new synapses, the strengthening or weakening of existing ones, and the reorganization of neural pathways.
Blood-Brain Barrier (BBB): The BBB is a highly selective semipermeable border of endothelial cells that prevents solutes in the circulating blood from non-selectively crossing into the extracellular fluid of the CNS. Its function is to protect the brain from toxins and pathogens while allowing essential nutrients to pass through.

Section D: Three Marks Broad Questions

Motor Neuron Diagram and Function:
- Diagram: A clear, labeled diagram showing the cell body (soma), nucleus, dendrites, axon, myelin sheath, Schwann cells, Nodes of Ranvier, and axon terminals.
- Functions:
  - Dendrites: Receive signals from other neurons.
  - Cell Body (Soma): Contains the nucleus and organelles; integrates incoming signals.
  - Axon: Transmits the electrical impulse (action potential) away from the cell body.
  - Myelin Sheath: Insulates the axon and dramatically speeds up impulse transmission.
  - Axon Terminals: Release neurotransmitters into the synapse to communicate with the next cell (e.g., a muscle fiber).
Classification of Nervous System:
- Flowchart:
  - Nervous System
    - Central Nervous System (CNS)
      - Brain
      - Spinal Cord
    - Peripheral Nervous System (PNS)
      - Somatic Nervous System (Voluntary)
      - Autonomic Nervous System (Involuntary)
        
        Sympathetic Division (Fight or Flight)
        
        Parasympathetic Division (Rest and Digest)
- Functions:
  - CNS: Integration and command center.
  - PNS: Carries messages to and from the CNS.
  - Somatic: Controls voluntary movements of skeletal muscles.
  - Autonomic: Controls involuntary functions of glands and internal organs.
Mechanism of Reflex Action (Withdrawal Reflex):
- Diagram: A labeled diagram of a reflex arc showing a cross-section of the spinal cord and the pathway from receptor to effector.
- Explanation:
  1. Stimulus: Touching a hot object.
  2. Receptor: Pain/temperature receptors in the skin are activated.
  3. Sensory Neuron: An impulse travels along a sensory neuron to the spinal cord.
  4. Integration Center: In the spinal cord, the sensory neuron synapses with an interneuron.
  5. Motor Neuron: The interneuron synapses with a motor neuron.
  6. Effector: The motor neuron sends an impulse to the biceps muscle (effector), causing it to contract and pull the hand away. This happens before the pain signal reaches the brain.
CNS vs. PNS:
- Structure: CNS is the brain and spinal cord. PNS is the network of cranial and spinal nerves branching out from the CNS.
- Location: CNS is encased in bone (skull, vertebrae). PNS extends throughout the body.
- Functions: CNS is the primary integration and control center, responsible for processing information, thought, and coordinating actions. PNS connects the CNS to the limbs and organs, essentially serving as the communication relay between the brain/spinal cord and the rest of the body.
Cranial Nerves:
- Description: There are 12 pairs of cranial nerves that emerge directly from the brain and brainstem. They are part of the PNS and can be sensory, motor, or mixed.
- Examples:
  1. Olfactory Nerve (I): Purely sensory; responsible for the sense of smell.
  2. Facial Nerve (VII): Mixed nerve; controls the muscles of facial expression (motor) and carries taste sensations from the front of the tongue (sensory).
  3. Vagus Nerve (X): Mixed nerve; the main nerve of the parasympathetic nervous system, controlling a vast range of functions including heart rate, digestion, and speech.
Nerve Impulse Transmission (Action Potential):
- Resting State: The neuron maintains a resting potential (~ -70mV) with a higher concentration of K+ inside and Na+ outside, maintained by the Na+/K+ pump.
- Depolarization: A stimulus causes voltage-gated Na+ channels to open. Na+ rushes into the cell, causing the membrane potential to rapidly become positive (~ +30mV). This is the action potential.
- Repolarization: The Na+ channels inactivate, and voltage-gated K+ channels open. K+ rushes out of the cell, restoring the negative charge inside.
- Propagation: This depolarization/repolarization process creates a wave of electrical activity that travels down the axon to the axon terminal. The "all-or-none" principle means the action potential fires at full strength or not at all.
Synaptic Transmission:
- Structure: A synapse includes the presynaptic terminal (axon terminal), the synaptic cleft (the gap), and the postsynaptic membrane (on the dendrite of the next neuron). The presynaptic terminal contains vesicles filled with neurotransmitters.
- Mechanism:
  1. An action potential arrives at the presynaptic terminal.
  2. This causes voltage-gated calcium channels to open, and Ca2+ flows into the terminal.
  3. The influx of Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft (exocytosis).
  4. Neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane.
  5. This binding opens ion channels on the postsynaptic neuron, causing either an excitatory or inhibitory potential in the next cell.
Autonomic Nervous System (ANS):
- Description: The ANS is the involuntary division of the PNS that regulates visceral functions like heart rate, digestion, and glandular secretion.
- Differences:
  - Sympathetic Division: Prepares the body for "fight or flight." It increases heart rate, dilates pupils, inhibits digestion, and mobilizes energy stores. Its neurons originate in the thoracic and lumbar regions of the spinal cord.
  - Parasympathetic Division: Promotes "rest and digest" activities. It slows the heart rate, constricts pupils, stimulates digestion, and conserves energy. Its neurons originate in the brainstem and sacral region of the spinal cord. These two divisions generally have opposite effects on target organs.
Sensory Receptors:
- Description: Sensory receptors are specialized cells or nerve endings that detect changes in the internal or external environment (stimuli) and convert this energy into electrical signals (transduction).
- Types and Examples:
  - Mechanoreceptors: Detect pressure, vibration, stretch (e.g., touch receptors in skin, hair cells in the ear).
  - Thermoreceptors: Detect heat and cold.
  - Photoreceptors: Detect light (e.g., rods and cones in the retina).
  - Chemoreceptors: Detect chemicals (e.g., taste buds, olfactory receptors).
  - Nociceptors: Detect pain/tissue damage.
- Transduction: The stimulus causes a change in the receptor's membrane potential (a receptor potential). If this potential reaches a certain threshold, it triggers an action potential in the associated sensory neuron, which then travels to the CNS.
Spinal Cord Structure and Role:
- Structure: A cylindrical bundle of nerve fibers extending from the brainstem. It is protected by the vertebral column and meninges. A cross-section reveals a central, H-shaped area of gray matter (cell bodies and synapses) surrounded by white matter (myelinated axons forming ascending and descending tracts).
- Roles:
  1. Reflex Center: It is the integration center for many reflexes, allowing for rapid responses without direct involvement of the brain.
  2. Conduction Pathway: The white matter tracts act as a two-way highway, carrying sensory information up to the brain and motor commands down from the brain to the peripheral nerves.
Myelin Sheath:
- Structure: A multi-layered sheath of lipid and protein that wraps around the axons of many neurons. In the PNS, it is formed by Schwann cells, with each cell wrapping a segment of one axon. In the CNS, it is formed by oligodendrocytes, which can myelinate segments of multiple axons. Gaps between the myelin are called Nodes of Ranvier.
- Formation: The glial cell (Schwann or oligodendrocyte) repeatedly wraps its plasma membrane around the axon.
- Significance: Myelin acts as an electrical insulator, preventing ion leakage across the axon membrane. This forces the action potential to "jump" from one Node of Ranvier to the next (saltatory conduction), which dramatically increases the speed of nerve impulse transmission.
Nerve Regeneration:
- Process: Regeneration is possible in the PNS but very limited in the CNS.
  1. Injury: When an axon is cut, the distal part (separated from the cell body) undergoes Wallerian degeneration and is cleaned up by macrophages.
  2. Schwann Cell Role: The Schwann cells that formed the myelin sheath survive and form a "regeneration tube" along the path of the original axon.
  3. Regrowth: The axon stump on the proximal side begins to sprout, and one sprout grows down the regeneration tube, guided by growth factors secreted by the Schwann cells.
- Factors: Successful regeneration depends on the severity of the injury, the distance between the severed ends, and the absence of scar tissue. The presence of inhibitory molecules and lack of a supportive environment prevent significant regeneration in the CNS.
Neurotransmitters:
- Concept: Chemical messengers used by neurons to transmit signals across the synaptic cleft to another neuron or to a muscle or gland cell.
- Classification & Functions:
  - Excitatory: Cause depolarization of the postsynaptic membrane, promoting an action potential (e.g., Acetylcholine at the neuromuscular junction, Glutamate in the CNS).
  - Inhibitory: Cause hyperpolarization of the postsynaptic membrane, inhibiting an action potential (e.g., GABA is the main inhibitory neurotransmitter in the brain, Glycine in the spinal cord).
  - Modulatory: Some neurotransmitters can have more complex effects, modulating the cell's response to other neurotransmitters (e.g., Dopamine, Serotonin are involved in mood, reward, and cognition).
Reflexes Classification and Importance:
- Definition: A reflex is a rapid, predictable, and involuntary response to a stimulus.
- Classification:
  - By Development: Innate (inborn) reflexes are genetically determined (e.g., withdrawal reflex). Acquired (conditioned) reflexes are learned through experience (e.g., salivating at the sound of a bell).
  - By Processing Site: Spinal reflexes are processed in the spinal cord (e.g., knee-jerk). Cranial reflexes are processed in the brainstem (e.g., pupillary light reflex).
  - By Complexity: Monosynaptic reflexes have one synapse (sensory neuron to motor neuron). Polysynaptic reflexes involve one or more interneurons.
- Importance: Reflexes are essential for survival and homeostasis. They provide rapid protection from harm, control involuntary functions like breathing and blood pressure, and maintain posture and balance.
Neural Control of Muscle Contraction:
- Motor Neuron Role: Voluntary muscle contraction is initiated by a command from the motor cortex in the brain. This signal travels down the spinal cord and out along a motor neuron.
- Neuromuscular Junction (NMJ): The axon of the motor neuron forms a synapse with a muscle fiber at the NMJ.
- Mechanism:
  1. The nerve impulse arrives at the axon terminal of the motor neuron.
  2. This triggers the release of the neurotransmitter acetylcholine (ACh) into the synaptic cleft.
  3. ACh binds to receptors on the muscle fiber's membrane (the sarcolemma).
  4. This binding opens ion channels, causing a wave of depolarization (an action potential) to spread across the muscle fiber.
  5. This electrical signal triggers the release of calcium from the sarcoplasmic reticulum within the muscle fiber, initiating the process of muscle contraction.
Sensory Pathways:
- Description: Sensory pathways are chains of neurons that transmit sensory information from receptors to the cerebral cortex for processing. These pathways typically consist of first, second, and third-order neurons.
- Pathway:
  1. First-Order Neuron: The sensory receptor (or a cell it synapses with) detects the stimulus. Its axon carries the signal into the CNS (spinal cord or brainstem).
  2. Second-Order Neuron: The first-order neuron synapses with a second-order neuron in the spinal cord or brainstem. This neuron's axon decussates (crosses over) to the opposite side and ascends to the thalamus.
  3. Third-Order Neuron: In the thalamus, the second-order neuron synapses with a third-order neuron, which then projects to the specific area of the somatosensory cortex in the cerebrum where the information is consciously perceived.
Neural Plasticity:
- Concept: Neural plasticity, or neuroplasticity, is the brain's remarkable ability to reorganize itself by forming new neural connections throughout life. This allows the neurons to compensate for injury and disease and to adjust their activities in response to new situations or changes in their environment.
- Types & Significance:
  - Structural Plasticity: The brain's ability to change its physical structure as a result of learning (e.g., growing new dendritic spines).
  - Functional Plasticity: The brain's ability to move functions from a damaged area of the brain to other undamaged areas.
- Significance: It is the basis for learning and memory. It is also crucial for recovery of function after brain injury, such as a stroke.
Protective Mechanisms of the CNS:
- Bone: The brain is protected by the rigid skull, and the spinal cord is protected by the vertebral column.
- Meninges: These are three layers of connective tissue membranes that lie between the bone and the nervous tissue:
  1. Dura Mater: The tough, outermost layer.
  2. Arachnoid Mater: The web-like middle layer.
  3. Pia Mater: The delicate inner layer that clings to the surface of the brain and spinal cord.
- Cerebrospinal Fluid (CSF): Found in the subarachnoid space (between the arachnoid and pia mater) and within the ventricles of the brain. CSF acts as a liquid cushion, absorbing shock, providing buoyancy to reduce the brain's effective weight, and circulating nutrients and waste products.
- Blood-Brain Barrier (BBB): A highly selective barrier that separates the circulating blood from the brain's extracellular fluid, protecting it from toxins and pathogens.
Development of the Nervous System:
- Neurulation: The process begins early in embryonic development when the neural plate folds to form the neural tube, which will become the CNS (brain and spinal cord).
- Neurogenesis: A massive proliferation of neurons occurs from progenitor cells lining the neural tube.
- Migration: Newly formed neurons migrate from their birthplace to their final positions in the brain.
- Differentiation & Synaptogenesis: Neurons differentiate into specific types and extend axons and dendrites to form trillions of synaptic connections.
- Synaptic Pruning & Myelination: In late development and adolescence, unused synapses are eliminated (pruning), and axons are myelinated to increase the efficiency of neural transmission.
Common Neurological Disorders:
1. Alzheimer's Disease: A progressive neurodegenerative disease characterized by memory loss, cognitive decline, and personality changes. It is caused by the accumulation of amyloid plaques and tau tangles in the brain, leading to neuronal death.
2. Parkinson's Disease: A motor system disorder caused by the loss of dopamine-producing neurons in the substantia nigra of the brain. Symptoms include tremors, rigidity, slow movement (bradykinesia), and postural instability.
3. Multiple Sclerosis (MS): An autoimmune disease where the body's immune system attacks the myelin sheath of neurons in the CNS. This disrupts communication between the brain and the body, leading to a wide range of symptoms including fatigue, numbness, muscle weakness, and vision problems.
Electrical Properties of Neurons:
- Resting Potential: This is the baseline electrical charge of an inactive neuron, typically around -70 millivolts (mV). It is established and maintained by the Na+/K+ pump, which actively transports 3 Na+ ions out for every 2 K+ ions in, and by the differential permeability of the membrane to these ions (more permeable to K+).
- Action Potential: This is a rapid, temporary, all-or-nothing reversal of the membrane potential that occurs when a neuron is stimulated past its threshold. It involves the opening and closing of voltage-gated Na+ and K+ channels, allowing the neuron to transmit a signal down its axon.
- Factors: The resting potential is influenced by the ion concentrations and the Na+/K+ pump. The action potential's propagation speed is influenced by axon diameter (larger is faster) and the presence of a myelin sheath (myelinated is much faster).
Sensory Adaptation:
- Concept: A phenomenon where sensory receptors become less responsive to a constant, unchanging stimulus over time. This results in a decreased frequency of action potentials being sent to the brain, leading to a diminished perception of the stimulus.
- Importance: It is crucial because it allows the nervous system to ignore constant, unimportant background information (like the feeling of clothes on the skin) and remain sensitive to new and changing stimuli, which are more likely to be important or dangerous.
- Cellular Level: It can occur through various mechanisms, such as changes in the receptor protein itself, depletion of intracellular signaling molecules, or feedback inhibition within the sensory pathway.
Pain Pathway (Nociception):
- Transmission:
  1. Transduction: Nociceptors (pain receptors) in the periphery are activated by noxious stimuli (mechanical, thermal, or chemical).
  2. Transmission: The signal travels along first-order sensory neurons (A-delta fibers for sharp pain, C fibers for dull, aching pain) to the spinal cord.
  3. Modulation: In the spinal cord, the signal can be modulated (amplified or suppressed) by interneurons before being relayed to second-order neurons.
- Processing: The second-order neurons cross over to the opposite side of the spinal cord and ascend via the spinothalamic tract to the thalamus. From the thalamus, third-order neurons project to various brain regions, including the somatosensory cortex (for localization of pain) and the limbic system (for the emotional response to pain).
Nervous System in Homeostasis:
- Role: The nervous system acts as the primary rapid control system for maintaining homeostasis (a stable internal environment). It detects changes, integrates information, and makes adjustments via nerve impulses.
- Examples:
  1. Thermoregulation: The hypothalamus detects changes in blood temperature. If the body is too hot, it initiates responses like sweating and vasodilation. If too cold, it triggers shivering and vasoconstriction.
  2. Blood Pressure Control: Baroreceptors in blood vessels detect changes in blood pressure and send signals to the medulla oblongata, which adjusts heart rate and vessel diameter via the autonomic nervous system.
  3. Breathing Rate: Chemoreceptors detect levels of CO2 and O2 in the blood, and the respiratory center in the medulla adjusts the breathing rate accordingly.
Integration Function of the Nervous System:
- Concept: Integration is the process by which the nervous system processes and interprets sensory information and makes decisions about what should be done at each moment. This occurs at multiple levels within the CNS.
- Mechanism: A single neuron, especially in the brain, can receive thousands of inputs from other neurons simultaneously. These inputs can be excitatory (EPSPs) or inhibitory (IPSPs). The neuron integrates these signals through a process called summation. If the sum of all excitatory and inhibitory inputs at the axon hillock reaches the threshold, the neuron will fire an action potential. This allows the nervous system to process complex information and make nuanced decisions rather than just reacting to single stimuli.
Motor Pathways:
- Description: Motor pathways are descending tracts of nerves that carry motor commands from the brain to the muscles and glands.
- Initiation and Control:
  1. Initiation: The decision to move is made in the prefrontal cortex and other association areas.
  2. Planning: The premotor cortex and supplementary motor area plan the sequence of muscle contractions.
  3. Execution: The primary motor cortex sends the primary commands down through the pyramidal (corticospinal) tracts. These tracts cross over in the medulla, so the left motor cortex controls the right side of the body, and vice versa.
  4. Coordination: The basal ganglia and cerebellum act as crucial modulators. The cerebellum ensures movements are smooth, coordinated, and accurate, while the basal ganglia help to select appropriate movements and suppress unwanted ones.
Effects of Aging on the Nervous System:
- Structural Changes: There is a modest loss of neurons in certain brain regions, a decrease in brain weight and volume, and a thinning of the cerebral cortex. The myelin sheath can also begin to break down, and the number of synaptic connections may decrease.
- Functional Changes:
  - Slower Processing: Nerve impulse conduction slows, leading to slower reaction times and cognitive processing.
  - Memory: Short-term memory and the ability to learn new information can decline.
  - Sensory & Motor: Senses like vision and hearing may become less acute, and motor control can become less precise, affecting balance and coordination.
  - Neurotransmitters: Levels of some neurotransmitters, like dopamine, may decrease.
Nervous and Endocrine System Relationship:
- Cooperation: These two systems are the body's main control systems and work together to regulate physiology. The nervous system provides rapid, short-term control, while the endocrine system provides slower, long-lasting control.
- Integration: The hypothalamus is the primary link between the two. It is part of the brain but also controls the pituitary gland, the master gland of the endocrine system. For example, the hypothalamus can receive neural signals (e.g., stress) and respond by releasing hormones that trigger the pituitary to release its own hormones, initiating a body-wide endocrine response (like the HPA axis stress response).
- Direct Control: The nervous system directly controls some endocrine glands, such as the adrenal medulla, which is stimulated by the sympathetic nervous system to release adrenaline.
Sleep-Wake Cycle Control:
- Brain Regions: The sleep-wake cycle is controlled by a complex interplay between arousal systems and sleep-promoting centers.
  - Arousal System: The reticular activating system (RAS) in the brainstem projects to the thalamus and cortex, promoting wakefulness and alertness.
  - Sleep-Promoting Center: The ventrolateral preoptic nucleus (VLPO) in the hypothalamus inhibits the RAS, promoting sleep.
- Neurotransmitters:
  - Wakefulness: Promoted by neurotransmitters like acetylcholine, norepinephrine, serotonin, and histamine.
  - Sleep: Promoted by the inhibitory neurotransmitter GABA, released by the VLPO.
- Regulation: The cycle is regulated by the circadian rhythm (controlled by the suprachiasmatic nucleus) and homeostatic sleep drive (adenosine builds up during wakefulness, promoting sleep).
Nervous System in Behavior and Emotions:
- Neural Basis: Behavior and emotions are complex phenomena that arise from the activity of distributed neural circuits in the brain.
- Key Structures:
  - Limbic System: This is the primary emotional center of the brain. The amygdala is crucial for processing fear and threat. The hippocampus is involved in memory formation, including emotional memories. The hypothalamus translates emotions into physical responses (e.g., increased heart rate).
  - Prefrontal Cortex: This area is responsible for the conscious experience and regulation of emotions, as well as decision-making and social behavior. It allows us to inhibit impulsive emotional responses.
- Example: When you see a threat, the amygdala is rapidly activated, triggering a fear response via the hypothalamus. The prefrontal cortex then processes the situation more slowly, allowing you to decide whether the threat is real and how to respond.
Memory Formation and Storage:
- Types of Memory:
  - Short-Term (Working) Memory: A temporary storage system that holds a small amount of information for immediate use. It is thought to rely on transient patterns of neural activity in the prefrontal cortex.
  - Long-Term Memory: A more permanent storage system. It is divided into explicit (declarative) memory (facts, events) and implicit (procedural) memory (skills, habits).
- Mechanisms: The process of converting short-term memories into long-term memories is called consolidation. This process relies heavily on the hippocampus. The underlying neural mechanism is believed to be long-term potentiation (LTP), a long-lasting strengthening of synapses based on recent patterns of activity. Over time, memories are thought to be transferred from the hippocampus to be stored in a distributed manner across the cerebral cortex.
Neural Control of Respiration:
- Respiratory Centers: The basic rhythm of breathing is controlled by respiratory centers located in the medulla oblongata and pons of the brainstem.
  - Medulla: Contains the ventral respiratory group (VRG), which is the primary rhythm generator, and the dorsal respiratory group (DRG), which integrates sensory input.
  - Pons: Contains centers that help to smooth the transition between inspiration and expiration.
- Regulation: The rate and depth of breathing are modified based on the body's needs. Chemoreceptors (central receptors in the medulla and peripheral receptors in the aorta and carotid arteries) are the primary regulators. They monitor the levels of CO2, O2, and pH in the blood and send signals to the respiratory centers to adjust breathing accordingly. For example, a rise in blood CO2 is the most powerful stimulus to increase breathing.
Neural Control of Heart Rate and Blood Pressure:
- Cardiovascular Control Center: The primary control center is located in the medulla oblongata.
- Autonomic Nervous System Role: This center receives sensory input and directs output via the autonomic nervous system to control heart rate and blood vessel diameter.
  - Parasympathetic (Vagus Nerve): Decreases heart rate.
  - Sympathetic: Increases heart rate and the force of contraction, and causes vasoconstriction of most blood vessels, which increases blood pressure.
- Sensory Input: The control center receives input from:
  - Baroreceptors: Stretch receptors in the aorta and carotid arteries that monitor blood pressure.
  - Chemoreceptors: Monitor blood levels of O2 and CO2.
  - Higher Brain Centers: The hypothalamus and cerebral cortex can also influence heart rate and blood pressure in response to stress or emotions.
Neural Control of Digestion:
- Enteric Nervous System (ENS): Often called the "second brain," the ENS is a vast network of neurons located within the walls of the gastrointestinal tract. It can function independently to control local reflexes like peristalsis and secretion.
- Relationship with CNS: While the ENS can act alone, it is also regulated by the autonomic nervous system (ANS).
  - Parasympathetic Stimulation (via the Vagus Nerve): Generally stimulates digestive activities. It increases motility, relaxes sphincters, and promotes the secretion of digestive juices.
  - Sympathetic Stimulation: Generally inhibits digestion. It decreases motility, constricts sphincters, and reduces blood flow to the gut. This is why digestion is suppressed during a "fight or flight" response.
Neurodegenerative Diseases:
- Concept: These are incurable and debilitating conditions that result in the progressive degeneration and/or death of nerve cells.
- Alzheimer's Disease:
  - Pathophysiology: Characterized by the extracellular accumulation of amyloid-beta plaques and the intracellular accumulation of neurofibrillary tangles (made of hyperphosphorylated tau protein). These pathologies lead to synaptic dysfunction, inflammation, and widespread neuronal death, particularly in the hippocampus and cerebral cortex.
- Parkinson's Disease:
  - Pathophysiology: Caused by the death of dopamine-producing neurons in a part of the midbrain called the substantia nigra. The lack of dopamine disrupts the function of the basal ganglia, which are crucial for controlling movement. This leads to the characteristic motor symptoms of the disease.
Neural Basis of Vision:
- Pathway:
  1. Photoreceptors: Light entering the eye is focused on the retina, where it is detected by photoreceptor cells (rods for low light, cones for color and detail).
  2. Retinal Processing: Photoreceptors synapse with bipolar cells, which in turn synapse with ganglion cells. Horizontal and amacrine cells provide lateral processing.
  3. Optic Nerve: The axons of the ganglion cells bundle together to form the optic nerve (cranial nerve II), which exits the back of the eye.
  4. Optic Chiasm: At the optic chiasm, fibers from the nasal half of each retina cross over to the opposite side.
  5. Thalamus & Cortex: The optic tracts project to the lateral geniculate nucleus (LGN) of the thalamus. From the LGN, neurons project to the primary visual cortex in the occipital lobe, where conscious perception of vision begins.
Neural Basis of Hearing:
- Pathway:
  1. Cochlea: Sound waves are converted into mechanical vibrations by the eardrum and ossicles, which cause fluid waves in the cochlea of the inner ear.
  2. Hair Cells: These fluid waves bend the stereocilia of hair cells (the mechanoreceptors for hearing) within the cochlea.
  3. Auditory Nerve: The bending of the hair cells generates a nerve impulse that is transmitted to the cochlear nerve, which is part of the vestibulocochlear nerve (cranial nerve VIII).
  4. Brainstem & Thalamus: The signal travels through several nuclei in the brainstem (e.g., cochlear nuclei, superior olivary nucleus) to the medial geniculate nucleus (MGN) of the thalamus.
  5. Auditory Cortex: From the thalamus, the signal is relayed to the primary auditory cortex in the temporal lobe for conscious perception of sound.
Neural Control of Movement:
- Motor Cortex: The primary motor cortex is the main command center for initiating voluntary movements. The premotor cortex and supplementary motor area are involved in planning and sequencing movements.
- Basal Ganglia: A group of subcortical nuclei that are crucial for motor control. They help to select and initiate appropriate movements while suppressing unwanted or competing movements. Dysfunction of the basal ganglia is the cause of Parkinson's and Huntington's diseases.
- Cerebellum: Located at the back of the brain, the cerebellum is the key coordinator of movement. It receives sensory information about the body's position and motor commands from the cortex. It compares the intended movement with the actual movement and sends corrective signals to ensure that movements are smooth, accurate, and coordinated. It is also essential for motor learning.
Brain Lateralization:
- Concept: Lateralization is the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other. While the two hemispheres are in constant communication via the corpus callosum, they are not symmetrical in function.
- Functional Differences:
  - Left Hemisphere: Typically dominant for language (speech production in Broca's area, language comprehension in Wernicke's area), logic, analytical thought, and mathematical skills.
  - Right Hemisphere: Typically dominant for spatial abilities, facial recognition, visual imagery, music, and processing and expressing emotions.
- Note: This is a generalization, and the degree of lateralization can vary between individuals. Both hemispheres are involved in almost all tasks.
Limbic System:
- Description: The limbic system is a complex set of brain structures located on both sides of the thalamus, right under the cerebrum. It is not a separate system but a collection of structures from the cerebrum, diencephalon, and midbrain.
- Functions: It is the primary neural basis for emotion and motivation. It is also heavily involved in memory formation and olfaction.
- Key Structures:
  - Amygdala: The emotional center, especially for fear, anxiety, and aggression.
  - Hippocampus: Crucial for converting short-term memory to long-term memory.
  - Hypothalamus: Links the limbic system to the endocrine system and autonomic nervous system, translating emotions into physical responses (e.g., racing heart).
  - Thalamus: The relay station for sensory information.
Blood-Brain Barrier (BBB):
- Structure: The BBB is not a single wall but a dynamic interface formed by the specialized endothelial cells that line the brain's capillaries. These cells are joined together by tight junctions, which are much more restrictive than those in other parts of the body. The barrier is further supported by the foot processes of astrocytes (a type of glial cell).
- Functions: Its primary function is to maintain a stable and protected environment for the brain. It strictly regulates the passage of substances from the blood into the brain, protecting it from circulating toxins, pathogens, and fluctuations in hormones and ions.
- Clinical Significance: While protective, the BBB also poses a major challenge for treating brain disorders, as it blocks many potentially therapeutic drugs from reaching the brain. Researchers are developing strategies to bypass or temporarily open the BBB to deliver medications.
Glial Cells:
- Description: Glial cells (or neuroglia) are non-neuronal cells in the nervous system that do not produce electrical impulses. They are more numerous than neurons and provide essential support and protection.
- Functions & Types:
  - Astrocytes (CNS): Star-shaped cells that provide structural support, help form the blood-brain barrier, regulate the chemical environment, and are involved in synaptic transmission.
  - Oligodendrocytes (CNS): Form the myelin sheath around axons in the CNS.
  - Microglia (CNS): Act as the brain's immune cells, cleaning up debris and dead cells.
  - Schwann Cells (PNS): Form the myelin sheath around axons in the PNS and aid in nerve regeneration.
  - Satellite Cells (PNS): Surround neuron cell bodies in ganglia and regulate their chemical environment.
Neuroplasticity in Learning and Memory:
- Concept: Learning and memory are not stored in a single location but are distributed across neural networks. The process of learning physically changes the brain by altering the strength of synaptic connections between neurons. This is the essence of neuroplasticity.
- Synaptic Changes:
  - Long-Term Potentiation (LTP): A long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is a key mechanism for memory formation and involves increasing the number and sensitivity of neurotransmitter receptors on the postsynaptic neuron.
  - Long-Term Depression (LTD): A long-lasting decrease in synaptic strength, which is important for clearing old memory traces.
  - Structural Changes: Learning can also lead to physical changes, such as the growth of new dendritic spines, the formation of new synapses, and even the birth of new neurons (neurogenesis) in the hippocampus.
Effects of Drugs on the Nervous System:
- Mechanism: Most psychoactive drugs exert their effects by altering synaptic transmission. They can act as agonists (mimicking or enhancing the effect of a neurotransmitter) or antagonists (blocking the effect of a neurotransmitter).
- Examples:
  - Stimulants (e.g., Cocaine, Amphetamines): Increase the levels of dopamine and norepinephrine in the synapse, leading to increased alertness, energy, and euphoria.
  - Depressants (e.g., Alcohol, Benzodiazepines): Enhance the effect of the inhibitory neurotransmitter GABA, leading to reduced anxiety, sedation, and impaired coordination.
  - Opioids (e.g., Heroin, Morphine): Mimic the body's natural endorphins by binding to opioid receptors, leading to pain relief and euphoria.
  - Antidepressants (e.g., SSRIs): Block the reuptake of serotonin, increasing its levels in the synapse, which can help to regulate mood.
Neural Control of Temperature Regulation:
- Control Center: The primary thermoregulatory control center is the hypothalamus, specifically the preoptic area.
- Sensory Input: The hypothalamus receives input from:
  - Central Thermoreceptors: Located within the hypothalamus itself, they monitor the temperature of the blood.
  - Peripheral Thermoreceptors: Located in the skin and other parts of the body, they provide information about the external temperature.
- Efferent Responses: The hypothalamus integrates this information and orchestrates responses via the autonomic nervous system, somatic nervous system, and endocrine system to maintain core body temperature around 37°C (98.6°F).
  - If Too Hot: Initiates sweating (evaporative cooling) and vasodilation of skin blood vessels (to radiate heat).
  - If Too Cold: Initiates shivering (involuntary muscle contractions to generate heat), vasoconstriction of skin blood vessels (to conserve heat), and release of hormones like thyroxine to increase metabolic rate.
Neural Mechanisms of Stress Response:
- Concept: The stress response is a coordinated physiological reaction to a perceived threat.
- Two Main Pathways:
  1. Sympathetic-Adrenal-Medullary (SAM) System (The Fast Pathway): The hypothalamus activates the sympathetic nervous system. This directly stimulates the adrenal medulla to release epinephrine (adrenaline) and norepinephrine (noradrenaline). This causes the immediate "fight or flight" response: increased heart rate, blood pressure, and glucose mobilization.
  2. Hypothalamic-Pituitary-Adrenal (HPA) Axis (The Slow Pathway): The hypothalamus secretes corticotropin-releasing hormone (CRH). CRH stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH). ACTH travels to the adrenal cortex and stimulates the release of cortisol. Cortisol helps to mobilize energy stores and has anti-inflammatory effects, sustaining the body's response to a prolonged stressor.
Neural Basis of Consciousness:
- Concept: Consciousness is one of the most complex and least understood aspects of neuroscience. It involves awareness of oneself and the environment, and the ability to have subjective experiences.
- Current Theories: There is no single accepted theory, but research points to the importance of widespread, coordinated brain activity rather than a single "consciousness center."
  - Global Workspace Theory: Suggests that consciousness arises from the broadcasting of information from a specific neural network (the "global workspace") to many other specialized brain regions. This workspace is thought to involve a network of neurons in the prefrontal cortex and parietal lobe.
  - Integrated Information Theory (IIT): Proposes that consciousness is a measure of a system's capacity to integrate information. A system is conscious to the extent that it is a single, integrated entity with a large repertoire of possible states.
- Key Structures: The thalamus, cortex, and the connections between them (thalamocortical loops) are considered critical for consciousness.
Neural Control of Circadian Rhythms:
- Concept: Circadian rhythms are biological processes that display an endogenous, entrainable oscillation of about 24 hours. The sleep-wake cycle is the most prominent example.
- The Master Clock: The central pacemaker that controls circadian rhythms is the suprachiasmatic nucleus (SCN), a small group of neurons located in the hypothalamus.
- Entrainment: The SCN has its own intrinsic rhythm, but it is synchronized (entrained) to the 24-hour day primarily by light. Specialized ganglion cells in the retina detect light and send signals directly to the SCN via the retinohypothalamic tract.
- Output: The SCN then coordinates the rhythms of the rest of the body by sending out neural and hormonal signals. For example, it controls the release of melatonin from the pineal gland, which is suppressed by light and released in darkness to promote sleep.
Neural Mechanisms of Addiction:
- Reward Pathway: Addiction is a disease of the brain's reward system. The key pathway is the mesolimbic dopamine pathway, which connects the ventral tegmental area (VTA) to the nucleus accumbens. This pathway is normally involved in motivating behaviors essential for survival, like eating and sex, by releasing dopamine, which produces feelings of pleasure.
- Drug Effects: Addictive drugs hijack this system. They cause a massive and rapid surge of dopamine in the nucleus accumbens, far greater than that produced by natural rewards. This intense pleasure reinforces the drug-taking behavior.
- Brain Changes: With repeated use, the brain adapts to the dopamine surges. It may reduce the number of dopamine receptors or produce less natural dopamine. This leads to tolerance (needing more of the drug to get the same effect) and anhedonia (the inability to feel pleasure from normal activities). These changes create a powerful drive to continue using the drug, leading to addiction.
Applications of Neuroscience in Medicine:
- Neuroimaging: Techniques like MRI (Magnetic Resonance Imaging) and fMRI (functional MRI) allow doctors to visualize brain structure and activity, helping to diagnose tumors, strokes, and other structural abnormalities, and to understand brain function.
- Pharmacology: Understanding neurotransmitter systems has led to the development of drugs to treat a wide range of neurological and psychiatric disorders, including depression (SSRIs), Parkinson's disease (L-DOPA), and epilepsy (anticonvulsants).
- Neurosurgery & Stimulation:
  - Deep Brain Stimulation (DBS): Involves implanting electrodes in specific brain regions to treat movement disorders like Parkinson's disease and dystonia.
  - Gamma Knife Radiosurgery: Uses focused beams of radiation to treat brain tumors and vascular malformations without invasive surgery.
- Neurorehabilitation: Applying principles of neuroplasticity to help patients recover function after a stroke or brain injury through targeted physical and cognitive therapy.

Nervous System

On this page