5 - Motor system 1 Flashcards
In which part of the grey matter of the spinal cord, do UMN’s synapse with LMNs?
Ventral horn
Give some reasons why you may be unable to elicit a knee jerk reflex in a patient:
- Faulty technique
- Patient unconscious
- Damage @ spinal level
- Sensory neuropathy
- UMN cell death ie stroke
- UMN damage
- LMN damage
- Neuromuscular junction disease ie myasthenia gravis
- Muscle damage ie late muscular dystrophy
If you are unable to elicit a knee jerk in a patient and you suspect its because they are overly conscious, what technique can you try?
How do you perform it?
Jendrassik manœuvre
- Ask patient to clench jaw and lock hands together and pull hard as you tap their quadriceps tendon
How does the Jendrassik manoeuvre increase the reflex response?
- Removes some of the normal descending inhibition on the LMN
- May prevent some unconscious inhibition
Why do people with UMN lesions have hyperreflexia?
UMN’s carry descending inhibition, regulating the LMN’s which elicit the reflex.
UMN lesion = less descending inhibition, which increases the excitability of the LMN, increasing the reflex response
Why do people with UMN lesions have hypertonia?
UMN’s carry descending inhibition, regulating the LMN’s which elicit the reflex.
UMN lesion = less descending inhibition, which increases the excitability of the LMN, increasing the reflex response
Where is the cell body of a LMN located?
Ventral horn of the spinal cord (CNS)
Where is the cell body of an UMN located?
Cerebral cortex or brainstem
NOT basal ganglia or cerebellum
What is meant by the positive signs of an UMN lesion? Give some examples?
Excessive normal resting state signs:
- Hypertonia
- Hyperreflexia
- Positive Babinski sign
- Clonus
What is meant by the positive signs of a LMN lesion? Give some examples?
Excessive normal resting state signs:
- Fasciculations
What is meant by the negative signs of a LMN lesion? Give some examples?
Loss of normal resting state signs:
- Hyporeflexia
- Hypotonia
- Weakness
Which motor neurones can be affected in motor neurone disease?
Upper +/- lower
Why does LMN damage lead to wasting of the target muscle?
LMN’s provide growth factors to maintain muscle fibres
What is spasticity?
Spasticity is increased, involuntary, velocity-dependent muscle tone that causes resistance to movement.
^velocity of passive movement = ^resistance
Why do people with UMN lesions have clonus?
UMN’s carry descending inhibition, regulating the LMN’s which elicit the stretch reflex.
UMN lesion = less descending inhibition, which increases the excitability of the LMN, increasing the stretch reflex
Why do people with LMN lesions have fasciculation’s?
Damaged LMNs spontaneously fire APs causing involuntary muscle contractions/twitch
Why do people with LMN lesions have hypotonia?
Tone is produced by low level contraction of muscles, if LMN to muscle is damaged, muscle cannot contract.
Why do people with LMN lesions have areflexia/hyporeflexia?
Efferent portion of reflex arc damaged = reflex will be absent/reduced
What are the causes of hypotonia?
- LMN lesion
- Muscle degeneration ie muscular dystrophy
- Lesion of sensory afferent in skeletal muscle
- Cerebral/spinal shock
- Cerebellar lesions
What are some example causes of LMN lesions?
- Traumatic injury
- Peripheral neuropathy
- Motor neurone disease
Damage to which motor neurone causes early wasting of muscles?
LMN - loss of growth factors to muscle
Damage to which motor neurone causes late wasting of muscles?
UMN - late-disuse atrophy
Damage to which motor neurone can cause fasciculations?
LMN - damaged motor neurone fires spontaneous APs = muscle twitch
What is meant by ‘clasp-knife’ reflex? What type of UMN lesions is it seen in?
In a hypertonic muscle: following a sudden increase in resistance there is a swift decrease in tone of a muscle, allowing the muscle to easily be stretched.
- due to Golgi tendon reflex
