Spinal Disorders - Physiology

Question 1

Describe the effects on motor function and peripheral nerves if there is denervation in the:

a) Upper motor neurone
b) Lower motor neurone

Answer 1

Upper motor neurone

• Spasticity – patients will have stiff muscles with brisk tendon reflexes
• Normal peripheral nerves

Lower motor neuron – start at anterior horn cell body

• Flaccid paralysis, lost tone, and power
• Loss of axons or peripheral nerve cell body

Question 2

Describe the two types of sensory function including the type of nerve fibres they’re provided by

Answer 2

• Discriminitive touch - ability to distinguish objects, shapes, surfaces, textures with skin. Provided by large, myelinated nerve fibres (A-beta)
• Pain and temperature - provided by small, unmyelinated fibers (A-delta and C)

Question 3

What are the most common effects of denervation

Answer 3

• Loss of function in root distribution
• Loss of function in distribution of named nerve

Question 4

Describe the effects of denervation

Answer 4

Sensory nerve - altered sensation

• Numbness
• Pain due to loss of axons supplying discriminative touch
• Parathesia - axons that are hyperexcitable

Motor nerve

• Atrophy
• Weakness
• Paralysis

Question 5

Describe the effects of denervation in muscle

Answer 5

• Begins to waste- atrophy
• Begins to generate spontaneous motor activity e.g., fibrillation and fasciculations,cramps
• Muscles remain viable for up to 2 years without a nerve supply after which they fibrose and can’t return to normal function

Question 6

What are the types of pathology of peripehral nerves that result in denervation

Answer 6

• Pathology of myelin, if severe enough will lead to secondary axon damage
• Pathology of axons
• Inflammation of blood vessels e.g., vasculitis can also damage axons

Question 7

Describe causes of damage to axons and provide examples

Answer 7

a)

Trauma

• Axonotmesis
• Neurotmesis
• Compression e.g., carpal tunnel syndrome, ulnar nerve compression at elbow, ivd prolapse
• Transection e.g., knife wound
• Stretching

Disease - periperal neuropathy

• Diabetes, B12 deficiency
• Inflammation, autoimmune
• Infection, HIV, leprosy
• Drugs and toxins
• Inherited

Question 8

In terms of peripheral neuropathy. Explain the following terms:

a) Length dependant
b) Non-length dependant
c) Mono-neuropathy
d) Radiculopathy

Answer 8

a) Length dependant - denervation and loss of function affects most distal parts of body first
b) Non-length dependant - loss of function occurs in patches and can affect short and long nerves
c) Mono-neuropathy - named nerve damage
d) Radiculopathy - damaged nerve root

Question 9

Explain the terms:

a) Axonotmesis
b) Neurtmesis

Answer 9

a) Damage to few axons, can recover but slow and may be incomplete
b) Complete transection of nerves,recovery requires grafting transected ends

Question 10

a) What is neuropoxia
b) What are the effects of demyelination
c) After removal of cause, how long does myelin damage take to recover

Answer 10

a) Damage to nerve in the form of myelin, temporary and reversible
b) Slow conduction, conduction block
c) 8-12 weeks

Question 11

Describe wallerian degeneration

Answer 11

1. When an axon has been cut, calpain gets released which is activated and breaks down the components of nerve over 3 day s
2. Macrophages move in an clear debris
3. Reinnervation - the ends of the axon still attached to the cell body will start to regenerate