Neuroscience Lecture 23: Nerve Injury & Repair

Is central or peripheral nerve regeneration possible?

Only peripheral

What is the ability of the brain to change throughout an individual's life called?

Neuroplasticity

What is recovery of function associated with?

Diminishing brain activation

Why is there diminished brain activation with recovery of function?

Increasingly efficient neural circuitry

What is the outermost layer of dense, irregular connective tissue surrounding a peripheral nerve?

Epineurium

What is the protective sheath covering nerve fascicles?

Perineurium

What is the layer of connective tissue that surrounds axons?

Endoneurium

Which grade of Sunderland's classification of nerve injuries has temporary interruption of myelin sheath without loss of axonal continuity?

Grade I

Which grade of Sunderland's classification has loss of continuity of the axon and its myelin sheath?

Grade II

Which grade of Sunderland's classification has the axon and the endoneurium damaged, but not the perineurium?

Grade III

Which grade of Sunderland's classification has the axon, endoneurium and perineurium damaged, but the epineurium preserved?

Grade IV

Which grade of Sunderland's classification has the nerve completely transected?

Grade V

What trauma does Grade I of Sunderland's classification most often correspond to?

Peripheral nerve compression

What does a positive Tinel's sign refer to?

Tingling sensation when nerve is tapped

What are the two immediate peripheral axon reactions to injury?

1. Synaptic transmission off

2. Cut ends pull apart

What are the two peripheral axon reactions to injury after hours?

1. Synaptic terminal degenerates

2. Astroglia surround terminal normally

What are the three peripheral axon reactions to injury after days?

1. Myelin break up

2. Wallerian degeneration of axon

3. Chromatolysis

What is the cascade of stereotypical cellular and molecular events that causes neuroinflammation called?

Wallerian degeneration

On which section of an axon does Wallerian degeneration occur?

Distal to site of injury

What are the four steps for axonal repair?

1. Axon fragmented

2. Macrophages clean dead axon

3. Axon sprouts grow

4. Myelin sheath forms

Which cells create the regeneration tube and myelin sheaths for axon repairment?

Schwann Cells

How do neuron cell bodies react to peripheral nerve injury proximal to the injury?

Expression of growth-related genes

For motor nerve reinnervation, what path is taken for axon repair?

Similar guidance cues from muscle to original location

What is released by Schwann cells that initiate the injury responses for peripheral nerve injuries?

ATP

What are the two results of hypoxia/ischemia?

1. Apoptosis

2. Necrosis

What is the first apoptosis regulator makes the this signal transduction cascade irreversible?

Bcl-2

For which two reasons does regeneration fail in the CNS?

1. Mature neurons don't grow as well

2. Glial scars have growth inhibitory molecules

What kind of brain damage induces neurogenesis?

Ischemic

Stem cells located where are responsible for neurogenesis in an adult mammalian brain?

Lateral wall of lateral ventricle

Which zone of the lateral ventricle are neural stem cells located?

Subventricular zone

Which two ways can stem cells migrate from the lateral ventricle to other brain regions?

1. RMS pathway

2. Glial supports

What are the four factors preventing neurogenesis in CNS?

1. Inhibition by neuroglial cells

2. Absence of growth stimulating factors

3. Lack of neurolemmas

4. Rapid formation of scar tissue