Control of mastication Flashcards
How is mastication controlled?
-pattern generator in the brain stem allows chewing to happen semi-automicatically
How is mastication voluntary?
- we can control the jaw movement
- we can chose to start/stop/ alter jaw movements
what is the reflex control?
- rapid
- automatic control
what is a reflex?
Predictable response to a given stimulus
what are 3 examples of reflexes?
- masticatory- salivary reflex
- knee jerk reflex
- jaw jerk reflex
what type of nerves are afferent standard reflexes ?
sensory nerves
what is the reflex pathway?
stimulus > receptor > afferent neurone (from periphery to CNS) > synapse > efferent neurone (from CNS to periphery) > effector > response
what type of reflex is the jaw jerk reflex?
stretch reflex
what type of reflex is the inhibitory jaw reflex?
Protective reflex
what type of reflex is the jaw unloading reflex?
unloading reflex
Describe stretch reflexes
- simple
- usuallly mono-synaptic
- i.e jaw jerk reflex
what factors effect reflex latency ( time from stimulus to effect)?
- conduction time of the neurones
- synaptic delay
why is the jaw jerk reflex latency smaller than the knee jerk latency?
shorter pathway
what are the roles of the jaw jerk reflex?
- tonic - resists gravity and helps maintain jaw rest position
- Phasic - load compensation during chewing and stabilises jaw during vigorous head movements
- Clinical- test integrity of trigeminal nerve
Describe protective reflexes
- polysynaptic
- often a response to a noxious (damaging) stimulus
- jaw opening reflexes
what are the types of stimuli for jaw opening reflexes?
- intra-oral mechanical or noxious
- extra-oral noxious
what type of receptors are there in jaw “opening” reflexes?
- mechanoreceptors
- nociceptors
what are the responses of the inhibitory jaw reflex?
- inactivation of jaw closing muscles
- two phases - early (10-30ms) , late (40-90ms)
what is the role of inhibitory jaw reflexes?
- prevent overloading of the masticatory system
- facilitate opening to expel noxious material and minimise damage to intra and peri-oral structures
- short latency - acts faster than a voluntary response
what is the jaw unloading reflex stimulus?
sudden closure following hard biting e.g hard/brittle food breaks
what are the responses jaw unloading reflex?
- inactivation of jaw closing muscles
- activation of jaw opening muscles
what is the result of jaw unloading reflex?
Teeth do not crash together
what is the pathway of mastication?
Higher centres (cerebral cortex) > central neural pattern generator “chewing centre” > masticatory muscle motorneurones > masticatory muscles
