17 Questions
Which type of glial cell is responsible for producing the myelin sheath in the peripheral nervous system?
Schwann cells
What is the name given to the spaces between adjacent sections of myelin where the axon's plasma membrane is exposed to extracellular fluid?
Nodes of Ranvier
Which type of motor protein is primarily responsible for the anterograde transport of materials from the cell body to the axon terminals?
Kinesins
Which harmful agents can invade the central nervous system through retrograde transport?
Tetanus toxin and the herpes simplex virus
What is the primary function of the myelin sheath surrounding axons?
To facilitate the rapid transmission of electrical signals
Which process is responsible for the degeneration of the distal portion of an axon following injury or disease?
Wallerian degeneration
What is the primary role of ependymal cells in the brain and spinal cord?
To produce and regulate the flow of cerebrospinal fluid
How do the properties of Schwann cells in the peripheral nervous system (PNS) compare to glial cells in the central nervous system (CNS)?
Schwann cells have most of the same properties as CNS glial cells
What is the primary function of satellite cells in the peripheral nervous system?
To regulate the chemical environment and detect/respond to injury
What is the time frame for the key events of Wallerian degeneration?
Separation of proximal and distal nerve ends within 30 minutes, myelin clearance within 7 days
How does the rate of myelin clearance during Wallerian degeneration differ between the central nervous system (CNS) and peripheral nervous system (PNS)?
The clearance rate is slower in the CNS compared to the PNS
What is the purpose of the axonal sprouts that form during Wallerian degeneration?
To allow for nerve regeneration following the lesion
What is the main role of oligodendrocytes in the central nervous system?
Facilitate the formation of myelin sheath around axons
What happens to a neuron if its cell body is damaged?
It cannot regenerate, except if the injury occurs at the end of the axon
What is the function of neurotrophins in the nerve regeneration process?
Promote regeneration by providing growth support
Where are ganglia primarily located in the nervous system?
Grouped together in the peripheral nervous system
What happens to the distal segment of an axon during Wallerian degeneration?
Undergoes granular disintegration and cytoplasmic element accumulation
Study Notes
Glial Cells
- Ependymal cells line the fluid-filled cavities within the brain and spinal cord and regulate the production and flow of cerebrospinal fluid.
- Schwann cells, the glial cells of the PNS, produce the myelin sheath of the axons of peripheral neurons and have most of the properties of CNS glia.
- Satellite cells help transport several neurotransmitters, regulate the chemical environment, detect and respond to injury and inflammation.
Wallerian Degeneration
- Wallerian degeneration is an active process of antegrade degeneration of axons and their accompanying myelin sheaths following proximal axonal or neuronal cell body lesions (7-21 days after the lesion occurs).
- Axon degeneration: within approximately 30 minutes of injury, there is a separation of the proximal and distal ends of the nerve.
- Axonal sprouts form (< a day) allowing for nerve regeneration.
- Myelin clearance: macrophages are signaled by Schwann cells to clean up axonal and myelin debris by the 7th day.
Myelin and Axonal Transport
- Axons are covered by sheaths of myelin (20-200 layers) of highly modified plasma membrane wrapped around the axon by a nearby supporting cell.
- Oligodendrocytes (in the brain and spinal cord) and Schwann cells (in the PNS) are responsible for myelin production.
- Nodes of Ranvier: spaces between adjacent sections of myelin where the axon's plasma membrane is exposed to extracellular fluid.
- Axonal transport: movement of various organelles and materials between the cell body and axon terminals using specialized motor proteins (kinesins and dyneins).
Maintenance of Neurons
- Kinesin transport: anterograde, moving nutrient molecules, enzymes, mitochondria, neurotransmitter-filled vesicles, and other organelles from the cell body towards the axon terminals.
- Dynein movement: retrograde, carrying recycled membrane vesicles, growth factors, and other chemical signals that can affect the neuron's morphology, biochemistry, and connectivity.
Functional Classes of Neurons
- Oligodendrocytes inhibit regeneration in the CNS.
- Neuronal regeneration occurs only if the injury is at the end of the axon, not if the cell body is damaged.
- Regeneration is assisted by the release of neurotrophins produced by astrocytes and other structures innervated by neuron-like nerve growth factor released by target cells.
Nervous System Structure
- Neurons are the structural and functional units of the nervous system.
- Nerves: collection of axons from neuron cell bodies running outside CNS.
- Nerve tracts: collection of axons from neuron cell bodies running within CNS.
- Nuclei: cell bodies grouped together in CNS.
- Ganglia: cell bodies grouped together in PNS.
Test your knowledge on the functions of neuroglia cells such as ependymal cells, Schwann cells, and satellite cells in the brain and spinal cord. Learn about their roles in regulating cerebrospinal fluid, producing myelin sheath, and maintaining the chemical environment.
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