INJURY AND REPAIR OF THE NERVOUS SYSTEM

Question 1

What is anterograde axoplasmic transport?

Answer 1

Motion from the center of the cell to the periphery (axon terminals)

Question 2

What is retrograde axoplasmic transport?

Answer 2

Motion from the periphery to the center of the cell (carries signals back towards the cell body)

Question 3

What are the functions of anterograde and retrograde transport?

Answer 3

Cycles neurotransmitters and structural cell elements back and forth between the cell body and the axonal tip

Question 4

What does axoplasmic mean?

Answer 4

Axoplasm is the cytoplasm within the axon of a neuron (nerve cell).
-In axonal transport (also known as axoplasmic transport) materials are carried through the axoplasm to or from the soma.

Question 5

What occurs if there is a break or defect in the axonal or neuronal bilayer?

Answer 5

Irreversible cascade of programmed cell death or an automatic attempt at repair

Question 6

What is the most important factor of the repair of a damaged nerve?

Answer 6

The level of schwann cell damage

• It is the main glial cell essential for the survival and function of neurons
• Axons are myelinated by Schwann cells

Question 7

What occurs during transection of a nerve?

Answer 7

Substances produced in the cell body can only reach where the nerve has been injured, axonal transport mechanism is disrupted
-Spread of damage also occurs to distal sites

Question 8

Define anterograde degeneration

Answer 8

Anterograde degeneration refers to the process in which an axon is damaged, followed by secondary anterograde degeneration, subsequently progressing away from the cell body (soma). This is also called Wallerian degeneration.
-Distal segments degenerates

Question 9

Define retrograde degeneration

Answer 9

When proximal segments degenerates

• Axonal “dieback”
• Usually in the next node of ranvier

Question 10

What are fascicles?

Answer 10

A muscle fascicle is a bundle of skeletal muscle fibers surrounded by perineurium, a type of connective tissue.

Question 11

What is the perineurium?

Answer 11

The perineurium is a protective sheath that surrounds a nerve fascicle. This bundles together axons targeting the same anatomical location. The perineurium is composed from fibroblasts.

Question 12

What is an endoneurium?

Answer 12

The connective tissue around an individual nerve axon i

Question 13

What is the epineurium?

Answer 13

A connective tissue layer that surrounds groups of fascicles within a peripheral nerve

Question 14

What happens when a peripheral nerve is cut?

Answer 14

The distal part is disconnected from its cell body and degenerates
1. Macrophages engulf the degenerated axon

2. The distal schwann cells unwrap themselves from the dead fragments and divide to form a continuous line of cells lining the distaal endoneurial sheaths
3. The proximal cut ends form growth cones and start to grow back down inside the sheaths, guided by chemical factors like cell adhesion molecules of the surface of schwann cells
4. As the regenerating nerve fibres extend into distal sheaths, schwann cells proliferate and start to wrap myelin around them

Question 15

Define neuropraxia

Answer 15

Temporary loss of motor and sensory function due to blockage of nerve conduction

• Mild
• Eg. damage to the myelin sheath

Question 16

Define axonotmesis

Answer 16

A disruption of axons, resulting from severe crush or contusion

• Moderate
• Leads to wallerian degeneration (axons distal to site of injury)

Question 17

Define neurotmesis

Answer 17

Both the axons and nerve sheath are disrupted

• Severe
• No connective tissue to guide axon regeneration
• Causes permanent damage

Question 18

What does the success of nerve repair depend on?

Answer 18

1. Severity of initial injury (Primary damage)
   - What has been damaged
   - How much has been damaged
2. The extent of secondary damage