Neuroglial Cells

Neuroglial Cells: Support Cells of the Nervous System

Terminology

• Nerve:

  • Found only in the peripheral nervous system (PNS).

  • Groups of axons wrapped together in connective tissue, providing a pathway for nerve impulses. These bundles are essential for transmitting signals throughout the body.

• Ganglia:

  • Found in the peripheral nervous system (PNS).

  • Collections of neuron cell bodies grouped together in masses, often appearing as swellings along nerve pathways. These ganglia serve as relay stations for nerve signals.

Neuroglial Cells: Support and Protection

• Neuroglial cells are support cells for neurons, providing essential services that neurons cannot perform themselves.

• They protect the health and life of neurons, which need to last a lifetime, as neurons are generally non-renewable.

Neuroglial Cells of the Peripheral Nervous System (PNS)

• Schwann Cells:

  • Composed of a fatty myelin sheath, which is critical for the efficient transmission of nerve signals.

  • Wrap around the axon to insulate and protect it, preventing signal loss and interference.

  • Increase the speed of nerve impulses through saltatory conduction.

• Node of Ranvier

  • Gaps or nodes in between the Schwann cells or myelin sheath, exposing the axon membrane.

• Saltatory Conduction:

  • Electrical impulse jumps from one node of Ranvier to the next, rather than traveling continuously along the axon.

  • Much faster than the electrical signal traveling the entire length of the axon, significantly increasing nerve conduction velocity.

  • Enables quick communication between neurons, vital for daily functioning and rapid responses.

Neuroglial Cells of the Central Nervous System (CNS)

• Ependymal Cells:

  • Circulate cerebrospinal fluid (CSF), aiding in the movement and distribution of this critical fluid.

  • Cerebrospinal Fluid:

    • Specialized clear fluid only found in the brain and spinal cord, providing a unique protective environment.

    • Protects the brain and spinal cord from physical impacts and injuries.

    • Enables the brain to float, preventing it from hitting the skull and reducing pressure on neural tissues.

  • Ventricles of the brain produce CSF, and ependymal cells line these ventricles to facilitate CSF circulation.

  • Ependymal cells facilitate fluid exchange between the brain, spinal cord, and CSF; act as a filtering system, helping to maintain a stable environment.

• Oligodendrocytes:

  • Act as insulation for central nervous system (CNS) axons, analogous to Schwann cells in the PNS.

  • One cell can cover multiple neurons, enhancing the efficiency of signal transmission across multiple axons.

  • Have multiple extensions to cover various places, allowing a single oligodendrocyte to myelinate several axons.

• Astrocytes:

  • Control the chemical environment of neurons, maintaining the optimal conditions for neuronal function.

  • Neurons need a very specific chemical environment to function and conduct electrical impulses; astrocytes ensure this balance.

  • Wrap around blood capillaries, forming a critical interface between the circulatory system and neural tissue.

  • Create the blood-brain barrier.

    • Physical barrier that only allows the passage of certain substances, protecting the brain from harmful compounds and pathogens.

    • $O_2$ is critical, neurons can only survive minutes without it, highlighting the importance of regulated substance transport.

• Microglial Cells:

  • Protect the central nervous system (CNS) from dead cells and pathogens, acting as the primary immune defense in the brain and spinal cord.

  • Phagocytize (eat up) dead cells and pathogens inside the brain and spinal cord, preventing inflammation and tissue damage.

Summary of Neuroglial Cells in the CNS

• Capillary: Blood supply to the brain, delivering essential nutrients and oxygen.

• Astrocytes: Wrap around capillaries, creating the blood-brain barrier and regulating nutrient supply.

• Oligodendrocytes: Wrap around axons for insulation, speeding up signal transmission.

• Microglia: Clean up and remove dead cells, maintaining a healthy neural environment.

• Ependymal Cells: Circulate cerebrospinal fluid inside the brain and spinal cord, providing cushioning and nutrient transport.