Nervous System

The nervous system is the body's intricate command center, a complex network that coordinates actions, transmits signals between different parts of the body, and responds to both internal and external stimuli. It regulates everything from basic bodily functions to complex processes like thought and emotion.

Divisions of the Nervous System

The nervous system is divided into two main parts:

• Central Nervous System (CNS): The CNS is the primary control center, consisting of the brain and spinal cord. It is protected by the skull and vertebrae, as well as a three-layered membrane system called the meninges.
  • Brain: The control center of the nervous system, responsible for intelligence, learning, memory, and emotions.
  • Spinal Cord: A long, thin, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It relays information to and from the brain and mediates reflex actions.
• Peripheral Nervous System (PNS): The PNS is a vast network of nerves that extend from the CNS to all other parts of the body, including organs, limbs, and skin. It relays information to and from the CNS.
  • Somatic Nervous System: This part controls voluntary movements and relays sensory information from the skin, muscles, and joints to the CNS.
  • Autonomic Nervous System: This system regulates involuntary bodily functions such as heart rate, digestion, and breathing. It is further subdivided into the sympathetic (which prepares the body for "fight or flight" responses) and parasympathetic (which controls "rest and digest" functions) nervous systems.

Cells of the Nervous System

The nervous system is composed of two main types of cells:

• Neurons: These are the primary functional units of the nervous system. They are specialized cells that transmit electrical and chemical signals. A typical neuron consists of a cell body, dendrites (which receive signals), and an axon (which sends signals).
• Glial Cells (Glia): These cells are the supporting cast of the nervous system. They outnumber neurons and provide physical and metabolic support.

Types of Nerves

• Sensory Nerves: Nerves that carry signals from the sense organs to the brain.
• Motor Nerves: Nerves that carry signals from the brain to the muscles and glands.
• Mixed Nerves: Nerves that contain both sensory and motor fibers.

Cranial and Spinal Nerves

• Cranial Nerves: Nerves that emerge directly from the brain.
  • Number: 12 pairs
• Spinal Nerves: Nerves that emerge from the spinal cord.
  • Number: 31 pairs

Structure of a Motor Neuron

• Cell Body: The main part of the neuron, which contains the nucleus.
• Dendrites: Branch-like extensions that receive signals from other neurons.
• Axon: A long, slender projection that carries signals away from the cell body.

Reflex Action

• Definition: An involuntary and nearly instantaneous movement in response to a stimulus.
• Basic Terms:
  • Stimulus: A thing or event that evokes a specific functional reaction in an organ or tissue.
  • Response: A reaction to a stimulus.
  • Impulse: A signal that is transmitted along a nerve fiber.
  • Receptor: An organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve.
  • Effector: An organ or cell that acts in response to a stimulus.
• Common Examples:
  • Withdrawing your hand from a hot object.
  • Blinking when something comes close to your eye.