23 CLINICAL REFLEXES AND MUSCLE TONE Flashcards
What is the role of Gamma motoneurons
Gamma motoneurons regulate how sensitive the stretch reflex is by tightening or relaxing the fibers within the spindle.
Describe the myotactic reflex physiology
1a afferent sensory fibres innervate muscle spindles which fire when the muscle stretches. In the SC they synapse with alpha motoneuron that innervates the muscle being stretched so it contracts. The 1a afferents also give off slips to inhibitory interneurons which inhibit alpha motoneurons of opposing muscle groups.
What are some characteristics of the stretch reflex
Involuntary, non-fatiguing, response determined by stimuli strength
Where are some typical locations to test the stretch reflex and what spinal/cranial nerve are you testing
Jaw V, biceps and brachioradialis (C5/C6), triceps (C7), finger (C8), knee (L3/4) and ankle (S1)
How to grade reflexes
0- absent \+ normal \++ normal brisk \+++ exaggerated \++++ clonus (repeated contraction)
How to assess muscle tone
Passive flexion and extension of limbs at varying speeds. Elbow, pronate/supinate arm, flew/extend wrist rapidly.
What will you see in the wrist with an UMN problem
Cogwheel rigidity due to spastic catches.
Describe the tendon jerk reflex
Myotactic reflex. Hit hammer on tendon see contraction of same muscle. Eg in quadriceps tendon (knee jerk) quads will contract and knee extend.
Where can you check for the tendon jerk reflex
Biceps, brachioradialis, triceps, ankle
Describe Babinski’s reflex
Run key along lateral aspect of foot increasing pressure as you move along. Should cause flexion of toes.
What dose a positive babinski sign entail and suggest
Extension of toes, UMN pathology
What will reflex’s and tone show in UMN and LMN pathology
UMN increased reflexes (contralateral), spasticity
LMN decreased reflexes (ipsilateral), hypotonia
What will reflexes and tone show in basal ganglia path
no change, rigidity
