Terms in this set (22)
A pure motor response that occurs after the CMAP. Called "F" because it was first discovered in the foot. Derived from antidromic travel up the nerve to the AHC, backfiring of a small population of AHCs resulting in orthodromic travel back down the nerve to the muscle being recorded.
Normal persistence of F waves (%)
80-100%, always above 50% with exception of the peroneal F response
A measure of the difference between the minimal and maximal F wave latencies.
Normal is up to 4 ms in the UEs and 6 ms in the LEs
A technique that helps prime the AHCs while trying to obtain F responses. Should only be done if Fs are difficult to obtain
Abnormal F wave difference comparing side to side
Upper limit of normal for UE F wave latencies
Upper limit of normal for LE F wave latencies
The Hoffman reflex; it is a true reflex with a sensory afferent, a synapse, and a motor efferent segment. Beyond the age of 2 it can only be elicited by stimulating the tibial nerve in the popliteal fossa and recording from the gastroc-soleus muscle.
Circuitry of the H reflex
Involves Ia muscle spindles as sensory afferents, and the alpha motor neurons and their axons as efferents.
Normal latency difference for side to side H reflex comparisons
Normal H/M ratio difference (%)
< 50%. This often increases with UMN lesions.
Tibial H reflex correlate
S1 tendon ankle reflex. If the ankle reflex is not present, the H reflex may still be but may be prolonged
Prolonged H reflex differentials
Proximal tibial and sciatic neuropathy
Lesions of the S1 nerve root
The axon reflex; A late response often seen during the recording of F responses, usually occurring in between M waves and F waves. They are identical in latency and morphology with each successive stimulation. Typically seen in reinnervated nerves, especially with submaximal stimulation. Not a true reflex
A true reflex involving the trigeminal and facial cranial nerves, along with their connections in the pons and medulla.
Which branch of the trigeminal nerve is involved in the blink reflex?
Sensory fibers of the supraorbital branch of the opthalamic division (V1)
What produces the R1 response of the blink reflex?
When the stimulus follows the afferent volley along the trigeminal nerve to the main sensory nucleus of the trigeminal nerve found within the mid-pons (Vm)
What produces the R2 response of the blink reflex?
After the stimulus has passed through the trigeminal nucleus within the spinal tract of the lower pons and medulla (Vs), the nerve impulse then travels to the ipsi and contralateral facial nuclei
Normal R1 latency of a blink reflex
< 13 ms
Normal ipsilateral R2 latency of a blink reflex
< 41 ms
Normal contralateral R2 latency of a blink reflex
< 44 ms
Normal differences for side to side comparisons of a blink reflex
<1.2 ms between R1s
< 5 ms between ipsilateral R2s
< 7 ms between contralateral R2s
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