Lecture Notes on the Human Nervous System

Summary

The lecture focuses on the structure and function of the human nervous system, detailing its two main parts: the central and the peripheral nervous systems. It describes the anatomy and roles of various components like the spinal cord, nerve fibers, and the process of synaptic transmission. The discussion extends to the types of receptors and nerve cells involved in transmitting sensory and motor impulses.

Central and Peripheral Nervous Systems

• Central Nervous System (CNS): Consists of the brain and spinal cord, protected by the skull and spinal column.

  • Spinal Cord:
    • Enclosed in three membranes: dura mater, arachnoid mater, and pia mater.
    • Contains nerve fibers and blood vessels.

• Peripheral Nervous System (PNS): Extends throughout the body.

  • Spinal Nerves:
    • Connect to the spinal cord.
    • Comprise afferent nerve fibers (carry impulses to the CNS) and efferent nerve fibers (carry impulses to effectors like muscles and glands).

Nerve Cells and Fibers

• Structure:

  • Covered by a connective tissue layer and Schwann cells.
  • Axons wrapped by Schwann cells to increase impulse conduction speed, with nodes of Ranvier facilitating this increase.

• Synaptic Transmission:

  • Occurs at synaptic terminals or terminal buttons of axons.
  • Involves the release of neurotransmitters through exocytosis triggered by calcium ions.
  • Post-synaptic cells possess receptors that convert neurotransmitters back into electrical impulses.

Spinal Cord and Ganglia

• Spinal Ganglion/Dorsal Root Ganglion:
  • Contains the cell bodies of sensory neurons, leading to its thicker appearance.
  • Neurons here are pseudo-unipolar with axons that bifurcate toward the periphery (e.g., skin) and the central nervous system.

Types of Neurons and Nerve Fibers

• Unmyelinated Nerve Fibers:

  • Without Schwann cell wrapping, lacking increased conduction speed.

• Sensory Reception and Transmission:

  • Mechanical stimuli are converted to electrical impulses by sensory nerve fibers.
  • The impulses travel through the afferent pathway to another neuron in the spinal cord and onwards to the brain.

Receptors in the Skin

• Types of Mechanoreceptors:
  • Meissner's Corpuscles: Rapidly adapting; respond to changes in pressure.
  • Merkel Cells: Slowly adapting; respond to dynamic and sustained pressure.
  • Ruffini Corpuscles: Respond to skin stretch; slowly adapting.

Processing and Reflex Action

• Spinal Cord Processing:
  • Transmits sensory information from the receptors through nerve fibers to the brain.
  • Impulses can be processed directly in the spinal cord to initiate reflex actions like muscle contraction in response to pain.

This lecture on the human nervous system provides insights into the intricate network of nerve cells and fibers, highlighting how bodily responses to environmental stimuli are generated and managed.