Lecture 3 Upper and Lower Motor Neuron Pathology

Question 1

what is the axon, function, and activation of the muscle spindle?

Answer 1

Axon: 1a
Function: Monitors the length and velocity of a muscle. Detects tension in the tendon.
Activation: Tendon reflex

Question 2

what is the axon, function, and activation of the gamma motor neurons?

Answer 2

Axon: II (Motor)
Function: Reset the muscle spindle after activation
Activation: he brain modulates (controls) the muscle spindle to stretch

Question 3

what is the axon, function, and activation of the GTO?

Answer 3

Axon: 1b (sensory)
Function: Monitor and regulate the tension of muscle force.
Distributes workload so all motor units are working efficiently
Activation: Inverse Stretch Reflex

Question 4

what is the axon, function, and activation of the alpha motor neuron?

Answer 4

Axon: Alpha (motor)
Function: Activates muscle
Activation: Force production

Question 5

What are GTOs?

Answer 5

GTOs are encapsulated receptors (proprioceptors) located in the tendon adjacent to the musculotendinous junction.

Question 6

How do GTOs lie about skeletal muscle fibers? When are they discharged?

Answer 6

GTOs lie in series with extrafusal fibers and are discharged during passive stretching of the muscle as well as when the tendon is stretched during a forceful contraction of the muscle
Extrafusal fibers are skeletal muscle fibers innervated by alpha motor neurons that generate tension by contracting which allows for skeletal movement

Question 7

How many GTOs are there per muscle?

Answer 7

3-50 GTOS per muscle

Question 8

How are GTOs innervated? (what type of axon)

Answer 8

GTOs are innervated by afferent 1b axons (sensory neurons) {sensory information from the outside world to the brain}
Each GTO is innervated by a single myelinated 1B afferent sensory axon

Question 9

How do GTOs function? What do they regulate? How are they task dependent?

Answer 9

GTOs will detect small changes in muscle contraction (<1g force)
When the muscle is fatigued, the GTOs will compensate and activate different motor units
GTOs can inhibit muscle contractions to prevent injury, they can also facilitate contraction
GTOs regulate alpha motor neurons (muscle activation)
GTOs are context/task dependent. They will provide the right amount of force and velocity for accuracy when completing a task

Question 10

What is autogenic inhibition/ inverse stretch reflex?

Answer 10

The inverse stretch reflex is the same as autogenic inhibition
The job of the GTOs (they are mechanoreceptors) is to maintain muscle tension within an optimal range to prevent excessive force and damage.
Excessive muscle tension will cause the inhibition of the motor neuron and reduce the rate of muscle contraction.
Autogenic inhibition occurs when the tension of a muscle and tendon stimulates and innervates 1b axons at the musculotendinous junction. When there is too much force in a muscle, inhibitory interneurons inhibit muscle contraction.

Question 11

Explain the steps of the inverse stretch reflex with an example

Answer 11

1. The Golgi tendon senses excessive tension
2. The sensory neuron (1b) conducts an action potential to the spinal cord
3. The sensory neuron (1b) synapses interneurons on the posterior spinal cord.
4. The Interneuron relays information from the brain on the amount of force the muscle should produce. There is an alpha motor neuron sent to the quads to inhibit contraction while there is an alpha motor neuron sent to the hamstrings that stimulates contraction
5. The hamstrings contract and the quads relax

Question 12

what are the classic signs of UMN syndrome?

Answer 12

weakness, spasticity, decreased muscle control, hyperreflexia or exaggerated DTR, and clonus

Question 13

What is hypertonia?

Answer 13

Hypertonia is the increase is passive muscle tightness. It is the abnormal increase in resistance to an external force about a joint.

Question 14

What are the classifications of hypertonia? (3)

Answer 14

1. Spasticity: A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes (muscle tone). There are exaggerated tendon jerks as there is hyperexcitability of the stretch reflex. In spasticity, the gamma motor neuron is not working to reset the muscle spindle after activation.
2. Rigidity: A significant increase in resistance to multidirectional external force about a joint. Movement in any direction will present with tightness.
3. Dystonia: A state of abnormal muscle tone resulting in muscular spasms and abnormal posture. Dystonia is typically due to a neurological disease or a side effect of drugs. Tone can fluctuate from rigid to spastic and typically involves the basal ganglia.

Question 15

What are the common upper limb postures or joint positions for UMN syndrome?

Answer 15

Flexed elbow, bent wrist, pronated forearm, clenched fist, and thumb in palm

Question 16

What is flexor synergy? What is extensor synergy?

Answer 16

Flexor synergy refers to the muscle “drawing in” making the muscle feel tight, stiff, and immovable.
Extensor synergy refers to the muscle “pushing away” from the midline of the body.
With synergy, there is a loss of selective motion. Volitional movements (movements that are intended and purposeful) are interrupted due to damaged motor pathways.

Question 17

What movement-based problems arise with damaged associated brain structures? (cerebellum)

Answer 17

When the cerebellum is injured, ataxia can occur. Ataxia is when there is loss of coordination, tremors, overshooting, and loss of velocity.

Question 18

What movement-based problems arise with damaged associated brain structures?
(basal ganglia)

Answer 18

When the basal ganglia is injured, bradykinesia can occur. Bradykinesia is the slowness of movement and speed with progressive hesitation or halts. It is commonly seen in people with Parkinson’s disease.

When the basal ganglia is injured, dystonia can occur. Dystonia is a state of abnormal muscle tone resulting in muscular spasms and abnormal posture. Commonly seen in Huntington’s Chorea. In this disease, there is a continuous stream of slow, flowing, writing involuntary movements that typically affect the hands, feet, and facial expressions.

Question 19

What movement-based problems arise with damaged associated brain structures? (brain stem)

Answer 19

When the brainstem is injured, there is a severe disruption to sensory and motor pathways. All limbs are “fixed” in a posture with limited limb movement, there is also increased rigidity.
Decerebrate rigidity (extension posturing) is when there is extension in both the UE and LE.
Decorticate rigidity (abnormal flexion) is when the UE is in flexion and the LE is in ext and IR.

Question 20

what happens to movement when there is a CVA or stroke?

Answer 20

When there is a CVA or stroke, a person is initially flaccid. Not too long after, the person develops spasticity (hypertonia) and reflexes become hyperactive. There is the presence of clonus, sensory loss, loss of joint position sense, changes in vision and facial strength, and bladder changes.
Typically, people will have UE flexor synergy and LE extensor synergy.

Question 21

What are hyperactive reflexes?

Answer 21

UMN syndrome typically presents with clonus. There is an increase in the reflex response. Typically, when one body part is moving another limb will move involuntarily.

Question 22

What are contractures? how does it relate to UMN syndrome?

Answer 22

A contracture is a fixed tightening (shortening) of muscles, tendons, ligaments, or skin that causes a deformity.

In UMN syndrome, the is a loss of selective movement accompanied by muscle hyper-reflexia and hypertonia. If left alone, the loss of ROM can lead to a contracture.

Contractures are associated with loss of proprioception, loss of light touch, loss of pin prick.
It is essential to prevent contractures with movement and splints

Question 23

What is a typical spinal cord injury?

Answer 23

Fractures of the vertebrae are typical in high-speed collisions. Pieces of the shattered vertebrae will travel and jam into the spinal cord causing an injury.

Question 24

What are the types of incomplete spinal cord injuries (SCI)? (Anterior cord syndrome)

Answer 24

Anterior cord syndrome is when the anterior spinal cord is affected and the posterior column is spared.
Motor and sensory pathways including touch, pain, and temperature are affected.

Question 25

What are the types of incomplete spinal cord injuries (SCI)? (brown sequard)

Answer 25

Brown sequard is when a hemisection of the spinal cord is affected.
There are ipsilateral (belonging to the same side of the body), UMN syndrome signs below the level of the lesion because the corticospinal tract is damaged.
There is ipsilateral loss of tactile, vibration, and proprioception sense 1-2 levels below the level of the lesion.
There is ipsilateral loss of all sensation at the level of the lesion.
There is contralateral pain and temperature loss below the level of the lesion due to the spinothalamic tract being damaged.

Question 26

What are the types of incomplete spinal cord injuries (SCI)? (central cord syndrome)

Answer 26

Central cord syndrome is when there is a large lesion caused to the cervical spinal cord. This injury typically occurs with forceful hyperextension of the neck.
There is pain and temperature sense loss as the spinothalamic tract is damaged.

Question 27

What are the signs of a Lower motor neuron (LMN) lesion?(6)

Answer 27

1. Loss of muscle function which causes weakness and flaccidity. Can range from weakness to paralysis. Weakness will typically be segmental or follow a peripheral nerve pattern depending on the lesion.
2. Loss of sensory functioning because of nerve damage. Proprioception, touch (discriminative and light touch), pain, temperature, vibration are all affected due to peripheral nerve damage.
3. Hyporeflexia means there is no response or a weak response to a tendon tap. There is low tone in the muscle and it is difficult to elicit a reflex response.
4. Fibrillations which is muscular twitching involving individual muscle fibers acting without coordination
5. Fasciculations are worm like contractions caused by increased receptor concentration on muscle to compensate for a lack of innervation.
6. Hypotonia or atonia

Question 28

How can you test for a LMN injury? (peripheral nerve injury vs spinal nerve root injury)

Answer 28

To test for a peripheral nerve injury:
Locate the injury at a specific location. The nerve injury will follow the pathway of the peripheral nerve.
Conduct a tinel test
There will be muscle and sensory loss below the level of the injury
Check for weakness or hyporeflexia

To test for a spinal nerve root injury:
An injury at the spinal nerve root will follow the dermatome and myotome pattern

Question 29

What are forms of peripheral nerve injury?
(3)

Answer 29

1. Neuropraxia is when there is a loss of myelination. It is characterized by focal segmental demyelination at the site of injury without disruption of axon continuity and its surrounding connective tissues. This condition results in blockage of nerve conduction and transient weakness or paresthesia.
2. Axonotmesis is when there’s a loss of the axon and myelination. There is weakness, atrophy, and sensory loss.
3. Neurotmesis is a complete transection of the nerve. Neurotmesis will produce complete sensory and motor deficits to the skin and muscles innervated by the injured nerve. It is much more difficult to recover due to neuroma (benign tumor of nerve tissue) formation.

Question 30

What are the common injuries to the peripheral nerve?
(herniated disc)

Answer 30

Herniated disk will cause a peripheral nerve root injury as the spinal nerve is being compressed.

Question 31

What are the common injuries to the peripheral nerve? (carpal tunnel)

Answer 31

Carpal tunnel syndrome is when the median nerve is compressed at the wrist. Muscles involved include the flexor pollicis brevis, opponens pollicis, abductor pollicis brevis.
There is weakness or paralysis
Pain following the nerve pattern
Numbness along the nerve pattern
Sensory loss along the nerve pattern (light touch or positional sense)
Loss of ROM

Question 32

What are the common injuries to the peripheral nerve? (deep fibular nerve)

Answer 32

Injury to the deep fibular (peroneal) nerve involves the fibularis longus, fibularis brevis, anterior tibialis, extensor hallucis longus, and extensor digitorum longus.
There is numbness and tingling
Shooting pain along the nerve pattern
Pain with nerve tapping as well as pain at rest.
Clinically, people will present with hypo-reflexia, muscular weakness along the nerve pattern and sensory loss along the nerve distribution.

Question 33

What are the common injuries to the peripheral nerve? (cervical nerve root)

Answer 33

Injury to the cervical nerve root (specifically C5-C6 nerve root injury)(radiculopathy) involves the biceps, brachioradialis, and extensor carpi radialis.
There is numbness, tingling, pain, sensory loss, weakness, hyporeflexia, and decreased DTR following the C6 dermatomal pattern.

Question 34

What are the common injuries to the peripheral nerve? (diabetic neuropathy)

Answer 34

Diabetic neuropathy can have different presentations such as glove and stocking or polyneuropathy. Typically, the first symptoms will be present in the feet.
With diabetes, the blood vessels are diseased. Once the blood vessels disappear, the nerve will shrivel up.

Question 35

How do you examine a peripheral nerve injury?

Answer 35

To begin with, you muscle test the uninvolved side. You then test the involved side. You also test muscle adjacent to the peripheral nerve.
In the case of carpal tunnel syndrome, you would test the ulnar and radial nerve as they are adjacent to the median nerve.
You also conduct sensory testing. You ask about their type of pain and location, followed by a test of sensation bilaterally (uninvolved first) (light touch/pin prick), followed by a sensation test to adjacent peripheral nerves.
You should always check the nerve above the level of the lesion as well as the nerves that run parallel to the lesion to see if neuropathy spreads.

Question 36

How do UMN lesions and LMN lesions differ in how they affect muscle strength, tone, reflex strength, muscle wasting, and causes?

Answer 36

LMN
Muscle strength: weakness of paralysis
Muscle Tone: decreased or absent muscle tone
Reflex Strength: decreased or absent reflex
Muscle Wasting: rapid muscle wasting
Causes: polio, peripheral nerve dysfunction, muscular dystrophy, spinal cord injury at a segmental level
UMN
Muscle strength: weakness or paralysis
Muscle Tone: increased muscle tone
Reflex Strength: increased reflex strength + babinksi sign
Muscle Wasting: muscle mass is maintained
Causes: stroke, spinal cord injury