Lecture 4: PNS Injury and Repair

Question 1

where are upper motor neurons?

Answer 1

originate in the cerebral cortex and brainstem and govern the activity of lower motor neurons

Question 2

where are lower motor neurons

Answer 2

once it reaches the anterior horn of the spinal cord

Question 3

what are the 2 types of lower motor neurons

Answer 3

alpha motor neurons

gamma motor neurons

Question 4

what are alpha motor neurons

Answer 4

LMNs that innervate extrafusal muscle fibres for muscle contraction

Question 5

what are gamma motor neurons

Answer 5

LMNs that innervate intrafusal muscle fibres (muscle spindles)

Question 6

what is a motor unit

Answer 6

The alpha motor neuron and the skeletal muscle fibres it innervates

Question 7

do we have more alpha motor neurons or muscle fibres in the body

Answer 7

way more muscle fibres

Question 8

Spinal nerves are made up of which two types of roots

Answer 8

posterior (sensory Afferent ) roots

anterior (motor efferent) roots

Question 9

if a spinal nerve is injured, would there be motor or sensory issues

Answer 9

both

Question 10

what do Spinal nerves split to become

Answer 10

posterior and anterior rami

Question 11

what is a dermatome

Answer 11

an area of skin that is mainly supplied by afferent nerve fibres from the dorsal root of a spinal nerve

Question 12

what is a peripheral nerve

Answer 12

terminal branches of the PNS

Mixed (motor and sensory)

Question 13

where is the damage in an Upper Motor Neuron Syndrome

Answer 13

Damage to the descending tract before it synapses in the anterior horn of the spinal cord

Question 14

where is the damage in a Lower Motor Neuron Syndrome

Answer 14

Damage to alpha motor neuron at or distal to the anterior horn

Question 15

what are 3 symptoms of an upper motor neurone lesion

Answer 15

(proximal to anterior horn)

hypertonia

hyperreflexia

positive babinski and Hoffman’s test

Question 16

what are the 6symptoms of a lower motor neuron lesion

Answer 16

(at or distal to the anterior horn)

Weakness/paralysis/paresis

hypotonia

hyporeflexia

negative babinski and Hoffman’s test

a lot of atrophy

abnormal nerve conduction tests and EMG

Question 17

if there was a lesion on the right side of the brain in the cerebral cortex or the brain stem, what would we excect to see

Answer 17

spastic paresis (hypertonia) on the opposite side (contralateral) and below lesion

Question 18

what would we expect to see if there was a lesion on the spinal cord

Answer 18

hypertonia on the same side (ipsilateral) and below lesion

Question 19

what would we see if the lesion was at the lower motor neuron or the muscle?

Answer 19

flaccid paralysis (hypotonia) ipsilaterally (same side) at the level of injury

Question 20

what type of neuron is injured during a stroke

Answer 20

upper motor lesion

Question 21

what are the 4 symptoms of stroke

Answer 21

Usually have some paresis

positive Babinski/Hoffman’s

• Hyperreflexia
• Hypertonia

Question 22

what type of neuron is injured during a spinal cord injury

Answer 22

primary upper motor neuron, but can have Lower motor neurons or mixed depending on location of injury

Question 23

what are the 4 symptoms of a spinal cord injury

Answer 23

Hypertonia and hyperreflexia

Weakness below level of lesion (often bilateral)

Sensory loss below level of lesion

Bladder and bowel involvement

Question 24

what is Amyotrophic Lateral Sclerosis (ALS) (3 things)

Answer 24

Destroys both UMNs and LMNs

dramatic ↓ Number of motor units

negative prognosis (death)

Question 25

what is an Alpha Motor Neuron Injury

Answer 25

LMN syndrome Wasting and weaknes no sensory involvement

Question 26

what is a Spinal Nerve Injury

Answer 26

Weakness in distribution of nerve root Associated sensory symptoms in same distribution (dermatome)

Question 27

what is Peripheral Nerve Injury

Answer 27

LMN Weakness and sensory loss in distribution of affected nerve(s)

Question 28

what is Guillain-Barre Syndrome (GBS)

Answer 28

peripheral nerve issue, lower motor neurone presentation Preceded by acute infectious illness Destruction of myelin sheath with axonal damage Rapidly progressing motor and sensory impairments

Question 29

what are the 3 classifications of peripheral nerve injuries

Answer 29

neuropraxia axonotmesis neurotmesis

Question 30

what is neuropraxia

Answer 30

Focal myelin injury axon is intact most mild

Question 31

what is axonotmesis

Answer 31

Injury to axon and myelin but supporting connective tissue intact crush injury

Question 32

what is neurotmesis

Answer 32

Injury to myelin, axon and supporting connective tissue Complete nerve laceration

Question 33

what is Wallerian degeneration

Answer 33

when a nerve fiber is cut or crushed (axonotmesis or neurotmesis) and part of the distal axon degenerates can happen with axonotmesis or neurotmesis

Question 34

what are the 2 types of peripheral nerve recovery

Answer 34

Axonal Repair and Regrowth Collateral Sprouting

Question 35

what does regrowth of the axon result in

Answer 35

reinnervation of the target muscle Regeneration is faster closer to injury site and slower further away

Question 36

what are the 2 key players in axonal regrowthand their function

Answer 36

Macrophages clear away degenerating parts Schwann cells act as a guide and stimulate regrowth

Question 37

How do Schwann cells support axonal regrowth?

Answer 37

Growth cone extends to search for target Provide a framework to help guide growing axons Secrete neurotrophic signals that promote axon growth

Question 38

do Crush injury (axonotmesis) always result in Wallerian degeneration

Answer 38

no but its always in neurotmesis

Question 39

why do crush injuries (axonotmesis) not always result in wallerian degeneration

Answer 39

Schwann cell framework less disrupted which help guide the regenerating proximal segment Recovery is often more rapid (and complete) in a crush vs. cut injury

Question 40

how are severed nerves reconnected

Answer 40

if severe, surgery is needed

Question 41

are Schwann cells unable to regrow with extensive damage

Answer 41

no. new Schwann cells can regrew

Question 42

what happens if there is a severe injury and distal end is not available for reapposition

Answer 42

outcomes tend to be poor

Question 43

who is Henry Head

Answer 43

he Surgically transected his own radial nerve

Question 44

Can We Fast-Track peripheral nerve regeneration?

Answer 44

not good enough evidenve to suggest a positive effect of exercise on nerve regeneration

Question 45

what is collateral sprouting

Answer 45

motor unit sprouts new axons to reinnervate damaged muscle fibres, so motor unit increase in size

Question 46

progressive muscle weakness, hyporeflexia, and paralysis. She suddenly developed weakness and tingling sensations in her legs and arms that gradually progressed over the course of a few days. She eventually found it difficult to walk and perform her ADLs. Do you think this is an UMN or LMN condition?

Answer 46

lower motor neuron hyperreflexia weakness

Question 47

progressive muscle weakness, hyporeflexia, and paralysis. She suddenly developed weakness and tingling sensations in her legs and arms that gradually progressed over the course of a few days. She eventually found it difficult to walk and perform her ADLs. What condition do you think Emily has?

Answer 47

Guillain-Barre Syndrome (GBS)

Question 48

where do we see damage with polio

Answer 48

anterior horn cells

Question 49

what was recovery with polio due to

Answer 49

motor unit collateral sprouting

Question 50

true or false Damage to the post-central gyrus would impact upon an individual's ability to perceive tactile sensation.

Answer 50

true

Question 51

true or false: Peripheral nerves, such as the median nerve, are branches from multiple spinal cord levels

Answer 51

true

Question 52

do Nerve bundles consist of motor neurons only, A single axon, or a collection of motor and sensory neurons

Answer 52

a collection of motor and sensory neurons

Question 53

A lesion affecting the lateral aspect of the post-central gyrus would most likely produce what

Answer 53

Impairment in contralateral sensory function for the face and neck

Question 54

A patient presents with selective loss of pain and temperature sensations of both hands. Other sensory modalities and voluntary motor activity is intact. What is the most likely cause of this problem?

Answer 54

A lesion of the anterior white commissure at the level of the cervical spinal cord

Question 55

An individual is experiencing muscle weakness with no sensory dysfunction. Even with this limited clinical information, you would NOT expect the patient to have: An anterior root injury Compression to a peripheral nerve A myopathy (disease affecting muscle tissue) Damage to lower motor neuron cell bodies

Answer 55

Compression to a peripheral nerve

Question 56

Henry is able to detect pain in his left lower extremity, but is unable to perceive light (discriminative) touch in his left lower extremity. If Henry has no damage above/superior to his medulla, he most likely has a lesion affecting his:

Answer 56

Left (ipsilateral) posterior column medial lemniscus (PCML) tract/dorsal column

Question 57

If an individual experienced compression to their right thoracic 10th (T10) spinal nerve, you would expect to see:

Answer 57

Motor and sensory impairments consistent with a myotome and dermatome distribution

Question 58

Axonotmesis refers to:

Answer 58

Nerve crush

Question 59

A client has had a stroke affecting the left internal capsule. What would you be most likely to observe?

Answer 59

Spastic paralysis of the right arm

Question 60

As a result of collateral sprouting, the following changes occur to the motor unit:

Answer 60

The motor unit size increases