Lecture 4: PNS Injury and Repair Flashcards
where are upper motor neurons?
originate in the cerebral cortex and brainstem and govern the activity of lower motor neurons
where are lower motor neurons
once it reaches the anterior horn of the spinal cord
what are the 2 types of lower motor neurons
alpha motor neurons
gamma motor neurons
what are alpha motor neurons
LMNs that innervate extrafusal muscle fibres for muscle contraction
what are gamma motor neurons
LMNs that innervate intrafusal muscle fibres (muscle spindles)
what is a motor unit
The alpha motor neuron and the skeletal muscle fibres it innervates
do we have more alpha motor neurons or muscle fibres in the body
way more muscle fibres
Spinal nerves are made up of which two types of roots
posterior (sensory Afferent ) roots
anterior (motor efferent) roots
if a spinal nerve is injured, would there be motor or sensory issues
both
what do Spinal nerves split to become
posterior and anterior rami
what is a dermatome
an area of skin that is mainly supplied by afferent nerve fibres from the dorsal root of a spinal nerve
what is a peripheral nerve
terminal branches of the PNS
Mixed (motor and sensory)
where is the damage in an Upper Motor Neuron Syndrome
Damage to the descending tract before it synapses in the anterior horn of the spinal cord
where is the damage in a Lower Motor Neuron Syndrome
Damage to alpha motor neuron at or distal to the anterior horn
what are 3 symptoms of an upper motor neurone lesion
(proximal to anterior horn)
hypertonia
hyperreflexia
positive babinski and Hoffman’s test
what are the 6symptoms of a lower motor neuron lesion
(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
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
spastic paresis (hypertonia) on the opposite side (contralateral) and below lesion
what would we expect to see if there was a lesion on the spinal cord
hypertonia on the same side (ipsilateral) and below lesion
what would we see if the lesion was at the lower motor neuron or the muscle?
flaccid paralysis (hypotonia) ipsilaterally (same side) at the level of injury
what type of neuron is injured during a stroke
upper motor lesion
what are the 4 symptoms of stroke
Usually have some paresis
positive Babinski/Hoffman’s
- Hyperreflexia
- Hypertonia
what type of neuron is injured during a spinal cord injury
primary upper motor neuron, but can have Lower motor neurons or mixed depending on location of injury
what are the 4 symptoms of a spinal cord injury
Hypertonia and hyperreflexia
Weakness below level of lesion (often bilateral)
Sensory loss below level of lesion
Bladder and bowel involvement
what is Amyotrophic Lateral Sclerosis (ALS) (3 things)
Destroys both UMNs and LMNs
dramatic ↓ Number of motor units
negative prognosis (death)
what is an Alpha Motor Neuron Injury
LMN syndrome
Wasting and weaknes
no sensory involvement
what is a Spinal Nerve Injury
Weakness in distribution of nerve root
Associated sensory symptoms in same distribution (dermatome)
what is Peripheral Nerve Injury
LMN
Weakness and sensory loss in distribution of affected nerve(s)
what is Guillain-Barre Syndrome (GBS)
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
what are the 3 classifications of peripheral nerve injuries
neuropraxia
axonotmesis
neurotmesis
what is neuropraxia
Focal myelin injury
axon is intact
most mild
what is axonotmesis
Injury to axon and myelin but supporting connective tissue intact
crush injury
what is neurotmesis
Injury to myelin, axon and supporting connective tissue
Complete nerve laceration
what is Wallerian degeneration
when a nerve fiber is cut or crushed (axonotmesis or neurotmesis) and part of the distal axon degenerates
can happen with axonotmesis or neurotmesis
what are the 2 types of peripheral nerve recovery
Axonal Repair and Regrowth
Collateral Sprouting
what does regrowth of the axon result in
reinnervation of the target muscle
Regeneration is faster closer to injury site and slower further away
what are the 2 key players in axonal regrowthand their function
Macrophages clear away degenerating parts
Schwann cells act as a guide and stimulate regrowth
How do Schwann cells support axonal regrowth?
Growth cone extends to search for target
Provide a framework to help guide growing axons
Secrete neurotrophic signals that promote axon growth
do Crush injury (axonotmesis) always result in Wallerian degeneration
no but its always in neurotmesis
why do crush injuries (axonotmesis) not always result in wallerian degeneration
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
how are severed nerves reconnected
if severe, surgery is needed
are Schwann cells unable to regrow with extensive damage
no. new Schwann cells can regrew
what happens if there is a severe injury and distal end is not available for reapposition
outcomes tend to be poor
who is Henry Head
he Surgically transected his own radial nerve
Can We Fast-Track peripheral nerve regeneration?
not good enough evidenve to suggest a positive effect of exercise on nerve regeneration
what is collateral sprouting
motor unit sprouts new axons to reinnervate damaged muscle fibres, so motor unit increase in size
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?
lower motor neuron
hyperreflexia
weakness
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?
Guillain-Barre Syndrome (GBS)
where do we see damage with polio
anterior horn cells
what was recovery with polio due to
motor unit collateral sprouting
true or false
Damage to the post-central gyrus would impact upon an individual’s ability to perceive tactile sensation.
true
true or false:
Peripheral nerves, such as the median nerve, are branches from multiple spinal cord levels
true
do Nerve bundles consist of motor neurons only, A single axon, or a collection of motor and sensory neurons
a collection of motor and sensory neurons
A lesion affecting the lateral aspect of the post-central gyrus would most likely produce what
Impairment in contralateral sensory function for the face and neck
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?
A lesion of the anterior white commissure at the level of the cervical spinal cord
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
Compression to a peripheral nerve
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:
Left (ipsilateral) posterior column medial lemniscus (PCML) tract/dorsal column
If an individual experienced compression to their right thoracic 10th (T10) spinal nerve, you would expect to see:
Motor and sensory impairments consistent with a myotome and dermatome distribution
Axonotmesis refers to:
Nerve crush
A client has had a stroke affecting the left internal capsule. What would you be most likely to observe?
Spastic paralysis of the right arm
As a result of collateral sprouting, the following changes occur to the motor unit:
The motor unit size increases
