Neuroanatomy of Cortical Cells and Peripheral Nerves

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Questions and Answers

Where are pyramidal cells mainly found in the cortical fields?

Layers 3, 5, and 6 (correct)

Layers 2 and 4

Layer 1

Layers 7 and 8

What is the function of the perineurium in peripheral nerves?

To tie the axons of each fascicle together (correct)

To provide a barrier against the surrounding connective tissue

To serve as a matrix between individual axons

To produce myelin

What is the process of Wallerian degeneration characterized by?

A calcium-mediated process that occurs distal to the injury site (correct)

A calcium-mediated process that occurs proximal to the injury site

A potassium-mediated process that occurs at the injury site

A sodium-mediated process that occurs at the injury site

What is the hallmark of acute neuronal injury or ischemic cell change?

Acute shrinkage and homogeneous eosinophilia of the cytoplasm Signup and view all the answers

What is the term for the affected cells in acute neuronal injury or ischemic cell change?

All of the above Signup and view all the answers

What is the minimum time required for acute neuronal injury or ischemic cell change to occur?

6-12 hours Signup and view all the answers

What is the term for the process that occurs in second-degree injuries?

Axonotmesis Signup and view all the answers

What is the primary mechanism of injury in first-degree injuries?

Conduction block Signup and view all the answers

What is the term for the degeneration of neurons and axons following injury to cells with which they synapse?

Trans-synaptic degeneration Signup and view all the answers

Which of the following is an example of retrograde trans-synaptic degeneration?

Degeneration of neurons of the inferior olivary nuclei Signup and view all the answers

What is the direction of degeneration in dying-back degeneration?

From the distal to the proximal end of the axon Signup and view all the answers

Which of the following is a site of trans-synaptic neuronal atrophy?

The lateral geniculate bodies Signup and view all the answers

What is the role of Schwann cells in regeneration of injured nerve fibers?

Guidance of the regenerating nerve fiber Signup and view all the answers

What is the time period for full recovery of injured nerve fibers?

3-6 months Signup and view all the answers

Which of the following is a condition for regeneration of injured nerve fibers?

If the injury was slight and/or away from the cell body Signup and view all the answers

What happens during the regeneration of injured nerve fibers?

The nissl granules reappear and the nucleus resumes its central position Signup and view all the answers

What is the primary function of Schwann cells during Wallerian degeneration?

To remove degenerated axonal and myelin debris Signup and view all the answers

What occurs in the neuronal body during central chromatolysis?

The cytoplasm becomes smooth and the nucleus is displaced towards the periphery Signup and view all the answers

What is the rate of proximal stump elongation following axonal transection?

1 to 3 mm per day Signup and view all the answers

What is the characteristic of stage 2 of Wallerian degeneration?

Rapid destruction of myelin protein fragments Signup and view all the answers

What is the result of trans-synaptic degeneration?

Neuronal injury spreads to previously uninjured neurons Signup and view all the answers

What is the time frame for stage 3 of Wallerian degeneration?

>14 weeks Signup and view all the answers

What is the result of a neuron losing its chief or only afferent connection?

Neuronal atrophy Signup and view all the answers

What is the duration of stage 1 of Wallerian degeneration?

0-4 weeks Signup and view all the answers

Study Notes

Cerebral Cortex

Pyramidal cells are found in layers 3, 5, and 6, while stellate cells are mainly found in layers 2 and 4.
The mix of pyramidal and stellate cells varies in different cortical fields and correlates with cortical function.

Peripheral Nerve Anatomy

Peripheral nerves consist of fascicles that contain myelinated and unmyelinated axons.
Endoneurium is the small amount of matrix present between individual axons.
Perineurium is a sheath of special, fiber-like cells that ties the axons of each fascicle together.
Epineurium is the connective tissue that surrounds the entire nerve trunk and gives off vascular connective tissue septa that traverse the nerve and separate fascicles from one another.

Pathophysiology of Nerve Degeneration

Neural response to injury involves a series of degenerative processes that must take place before regeneration of nerve fibers can occur.
Pathological changes are mild or absent in first-degree injuries, where the mechanism is conduction block alone.
In second-degree injuries (axonotmesis), there is little histological change at the injury site or proximal to it, but distal to the injury site, Wallerian degeneration occurs.

Acute Neuronal Injury

Neurons are quickly injured by hypoxia or ischemia.
After 6-12 hours, acute shrinkage, angularity, and homogeneous eosinophilia of the cytoplasm occur, followed by changes in the nucleus.
Affected cells are called ischemic neurons or red neurons or eosinophilic neurons.

Trans-Synaptic Neuronal Atrophy

Particular sites of trans-synaptic neuronal atrophy include the lateral geniculate bodies, the mammillary body, and the neurons of the gracile and cuneate nuclei of the medulla.
Trans-synaptic degeneration occurs when neurons and axons degenerate following injury to cells with which they synapse.

Retrograde Trans-Synaptic Degeneration

Degeneration of neurons and axons following injury to cells with which they synapse can occur in postsynaptic neurons (anterograde) or in presynaptic neurons (retrograde).
For example, the neurons of the inferior olivary nuclei atrophy when the Purkinje cells in the contralateral cerebellar cortex have degenerated.

Dying-Back Degeneration

Degeneration of the axons begins in their distal ends and progresses toward the neurons of their origin.
Dying-back degeneration results from metabolic, toxic, or degenerative disorders.

Regeneration

Regeneration of injured nerve fibers occurs in two cases: if the injury was slight and/or away from the cell body, or if the injured nerve fiber was part of the PNS.
The process of regeneration involves the reformation of the endoneural tube, guided by Schwann cells, and the regrowth of axons.

Wallerian Degeneration

Wallerian degeneration is the degenerative change that the distal segment of a peripheral nerve fiber undergoes when its continuity with its cell body is interrupted by a focal lesion.
Changes occur in the neuronal body, including central chromatolysis and the activation of protein synthesis.
The process is classified into four stages: degeneration of axons and myelin sheaths, rapid destruction of myelin protein fragments, gliosis, and atrophy of white matter tracts.

Schwann Cells in Wallerian Degeneration

Schwann cells play a key role in Wallerian degeneration by removing degenerated axonal and myelin debris and passing it on to macrophages.

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Description

This quiz covers the anatomy of cortical cells, including pyramidal and stellate cells, and the structure of peripheral nerves, including fascicles and axons.