Nerve and Muscle: Degeneration and Re-innervation Flashcards
1
Q
What is a motor unit?
A
Aggregation of a motor neuron axon and all the muscle fibers it innervates
2
Q
What to efferent neurones do?
A
- Leave ventral horn
- Into peripheral nervous
- Innervates muscles
3
Q
Difference between small and large motor units?
A
level of force. Small=low
4
Q
What spinal tract supplies skeletal muscles?
A
Corticospinal
5
Q
What will neurons in the motor system supply
A
- Skeletal muscles
- Smooth muscles
- Glands
- Other neurons
6
Q
What is neurapraxia?
A
- Structure still intact
- Ion pump dysfunction
- Ischaemia following trauma, traction or pressure
- Motor function is lost but can be fully recovered over time
7
Q
Axonotmesis?
A
- Schwann cells remain intact
- Axonal death
- Damage to axon and possibly myelin
- Surrounding endoneurium remains intact and can guide regrowth
- Complete loss of function
- Degeneration of distal axon
8
Q
Neurotmesis?
A
- Loss of nerve fibre continuity
- Total severance of peripheral nerve
- Axon, myelin, endoneurium all divided
- Total loss of function and no guiding structures
- Surgical intervention
9
Q
Process of injury to neuron and re-growth?
A
- Neurons can regenerate if cell body remains intact
- Schwann cells phagocytose the distal axon and myelin
- Muscle fibre undergoes wasting
- Cell body undergoes cromatolysis
- Axons sprout from the damaged end to restore innervation of the muscle
- Muscle regrows where possible to reach and innervate original tissue/organ
10
Q
Muscle response to injury
A
- Dependent of muscle type
- Smooth and cardiac are myogenic and are not initiated by nerves
- Initial paralysis
- Progression depends on whether the upper or lower motor neuron was damaged
- Atrophy/wasting occurs
- Leads to muscle death and fibrosis
