Jaw Reflexes Flashcards
What is a reflex
Predictable response to a given stimulus Eg Knew jerk Jaw jerk Pupillary reflex Gag reflex Salivary reflex
Give the reflex pathway
Stimulus Receptor Afferent neurone Synapse Efferent neurone Effector Response
What are stretch reflexes
Simple
Mono synaptic
Knee or jaw jerk
Explain the knee jerk
Stimulus - stretch by hit with patellar tendon
Receptor - muscle spindles
1 synapse
Effect causes contraction of quadriceps femoris
Latency 19-24 ms
What is the reflex latency
The time for the stimulus to have an effect
What si the minimum synaptic delay
0.2ms per synapse
Explain the jaw jerk reflex
Stimulus - stretch via chin tap Receptor muscle spindle Synapse 1 in v motor nucleus Effect contraction of masseter muscle Latency 7-8ms
What are the roles of the jaw jerk
Tonic - resist gravity and maintain posture
Phasic - load compensation during chewing
Stabilises jaw during vigorous head movements
Clinical - test integrity of trigeminal nerve
What are protective reflexes
Poly synaptic reflexes
Often a response to a noxious stimulus
Eg limb flexion withdrawal reflex
What are the jaw opening reflexes
Stimuli - intra oral mechanical or noxious or extra oral noxious
Receptor - mechanoreceps or nociceptors
Response to sub primates - activating of jaw depressors
Response in primates - inactivatin of jaw closers
Cessation of closing
Inhib jaw reflexes
What happens in electromyograms when clench or relax
When clench it is high close stroes
What happens and the latency when:
Gentle tap on tooth
Harder Tap
Painful stimulus to lip
Gentle tap ~ early inhibition latency 10ms
Harder ~ early and late reflex latency 10-40ms
Painful ~ late reflex latency 40ms
What are the inhibitory jaw reflexes
Responses - inactivation of jaw closers
2 phases - early 10-30ms and late 40-90 Ms
Role. - prevent overloading of masticatory system
And facilitate opening expel noxious material, minimise damage to intra oral structures
What si the jaw unloading reflex
Stimulus - sudden closure following hard biting - hard or Brittle food breaks
Response - inactivation of jaw closers but activation of jaw openers
Result - teeth do not crash together
How is mastication controlled
Voluntary - we can control jaw movements, start/stop, can alter the pattern of jaw movements
Pattern generator - chewing hallens semi-automatic, pattern generator programming centre
Reflex - rapid, automatic control
