Glial Cells and Nervous System Organization

Glial Cells and Nervous System Organization

Introduction

  • This lecture introduces glial cells and the organization of the nervous system.
  • It references figures from Chapter 12, specifically 12.32 and 12.33, illustrating important pathways.
  • Students should be able to draw, describe, and understand the common names and functions of these pathways: spinocerebellar, dorsal column medial lemniscus, spinothalamic, and lateral corticospinal.

Nervous System Functions

  • The nervous system performs three main functions:
    • Sensory Input: Detecting environmental stimuli through various receptors (vision, hearing, taste, smell, touch, chemical and mechanical receptors).
    • Integration: Processing sensory information within the central nervous system (spinal cord and brain).
    • Motor Output: Generating a response via muscle contraction (skeletal or smooth), glandular secretion, or inaction.

Organization of the Nervous System

  • The nervous system is divided into two major divisions:
    • Central Nervous System (CNS): Brain and spinal cord, responsible for integration and conscious thought.
      • Composed of neurons and glial cells.
    • Peripheral Nervous System (PNS): Cranial and spinal nerves that transmit information to and from the CNS.
Peripheral Nervous System Subdivisions
  • Further divided into sensory (afferent) and motor (efferent) divisions.
Sensory (Afferent) Division
  • Carries information toward the CNS.
  • Subdivided into:
    • Somatic: From the body surface (soma).
    • Visceral: From organs (viscera).
Motor (Efferent) Division

  • Carries information away from the CNS.

  • Targets include skeletal muscle, smooth muscle, and glands.

  • Subdivided into:

    • Somatic: Voluntary control of skeletal muscles.
    • Autonomic: Involuntary control of organ function, glandular secretion, smooth muscle, and cardiac muscle.
Autonomic Nervous System Subdivisions
  • Sympathetic: "Fight or flight" response.
  • Parasympathetic: "Rest and digest;" conserves energy, lowers heart rate.

Glial Cells (Neuroglia)

  • Supporting cells in the nervous system that enhance neuron function.
  • Six types of neuroglial cells:
    • CNS: Astrocytes, Microglia, Ependymal Cells, Oligodendrocytes
    • PNS: Satellite Cells, Schwann Cells
Glial Cells of the Central Nervous System (CNS)
Astrocytes
  • Star-shaped cells that regulate nutrient access to neurons, provide structural support, and maintain the neuronal environment.
  • Regulate capillary permeability by controlling tight junctions.
  • Help hold the nervous system together by providing structure to blood vessels and neurons.
  • Help regulate the constituents of the interstitial fluid, particularly potassium
Microglia
  • Act as immune cells; phagocytize debris and injured neurons.
  • Function similarly to dendritic cells, sounding the alarm through phagocytosis.
Ependymal Cells
  • Line ventricles and spaces within the CNS (e.g., cerebral aqueduct, central canal of the spinal cord).
  • Cilia facilitate CSF movement.
  • Associated with the choroid plexus, which produces CSF.
  • Tight junctions vary in tightness depending on location.
Oligodendrocytes
  • Produce myelin in the CNS, which insulates axons.
  • Myelin sheath speeds up action potential conduction.
  • Demyelination, as seen in multiple sclerosis, results from the loss of oligodendrocytes.
Glial Cells of the Peripheral Nervous System (PNS)
Satellite Cells
  • Similar in function to astrocytes.
  • Regulate the environment and nutrient access for neurons in the PNS.
  • Helps hold and bind structures together.
Schwann Cells
  • Produce myelin in the PNS, similar to oligodendrocytes.
  • Wrap around axons to speed up action potential conduction.
  • Degeneration of Schwann cells is seen in ALS (Amyotrophic Lateral Sclerosis).

Neurons

  • Excitable cells responsible for transmitting signals in the nervous system.
  • Long-lived and generally amitotic.
  • Require a high amount of energy to maintain.
Neuron Classifications
  • Refer to Table 11.1 for the three basic classifications of neurons.
    • Multipolar, Bipolar, and Unipolar.

Summary

  • The nervous system perceives, integrates, and responds to information via motor output.
  • Two major cell types: glial cells and neurons.