Detailed Notes on the Nervous System and Functionality

Overview of the Central Nervous System

• The nervous system can be classified into two major divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).

• The CNS includes the brain and spinal cord. The PNS consists of all sensory and motor nerves outside the CNS.

Types of Nerves

• Sensory Nerves:

  • Also known as afferent nerves.

  • Function: Carry impulses toward the CNS.

  • Input: Received from sensory organs like eyes, ears, skin, and tongue, traveling up the spinal cord to the brain.

• Motor Nerves:

  • Known as efferent nerves.

  • Function: Carry signals away from the CNS to effectors (muscles and glands).

The Motor Division

• Divisions of Motor Nerves:

  • Somatic Nervous System:

  • Involves voluntary control of skeletal muscles (e.g., biceps, lats, trapezius).

  • Autonomic Nervous System:

  • Controls involuntary functions (e.g., heart rate, digestion).

  • Further divided into:

    • Sympathetic Division:

    • Associated with stress and 'fight or flight' responses.

    • Parasympathetic Division:

    • Controls 'rest and digest' functions.

Supporting Cells in the CNS

• Astrocytes:

  • Most abundant supporting cells in the CNS.

  • Functions:

  • Provide support and stability to neurons.

  • Form the blood-brain barrier to regulate substance permeability to the brain.

• Blood-Brain Barrier:

  • A selective barrier that protects the brain from harmful substances.

  • Permeable to: Alcohol and nicotine can cross this barrier, affecting coordination and brain function.

• Microglial Cells:

  • Function: Act as the immune response in the CNS; they perform phagocytosis.

• Oligodendrocytes:

  • Function: Insulate neurons with myelin sheaths in the CNS.

Myelin and Neuron Structure

• Myelin Sheath:

  • Whitish material formed by Schwann cells in the PNS or oligodendrocytes in the CNS.

  • Function: Increases the speed of electrical impulses along the nerve fibers (axons).

Gray and White Matter

• In the CNS:

  • Gray Matter:

  • Forms the H-shaped structure in the spinal cord.

  • Contains nerve cell bodies and is involved in processing information.

  • White Matter:

  • Composed of myelinated axons, carrying signals up and down the spinal cord.

Spinal Cord H Structure

• The spinal cord has 'horns' (posterior and anterior).

• Posterior Gray Horn:

  • Receives afferent sensory signals from the body.

• Anterior Gray Horn:

  • Sends efferent motor signals to muscles or glands.

Reflex Arc Example

• A reflex arc involves:

  • A stimulus (e.g., stretching of an ankle) triggers sensory input, which travels to the spinal cord.

  • The signal is processed, and an efferent response is sent to the muscles, leading to a reaction (e.g., muscle contraction or relaxation).

  • Reflex actions can prevent injuries, such as sprains, by responding before injury occurs.