Mastication and its control Flashcards
Protective reflex
> 1 synapse (polysynaptic)
in response to a noxious stimulus
e.g. jaw “opening” reflex
Pulling hand away from a hot pan in response to noxious stimulus triggers…
flexion-withdrawal reflex
involves excitatory interneurone and inhibitory interneurone that work together.
What stimulus initiates jaw “opening” reflex?
Intra-oral: mechanical or noxious
Extra-oral: noxious
How does jaw “opening” reflex differ in humans and sub-primates?
Humans don’t activate the “openers” of the jaw, they inhibit the “closers”.
Sub-primates: Activate jaw depressors
To the teeth: why would a small stimulus have a faster reflex than a hard harmful stimulus?
They take different pathways which effects latency
What is the role of inhibitory jaw reflex?
The chewing cycle
0.5-1.2 sec duration
Opening, fast closing, slow closing, intercuspal phases
Lateral movements like this for…
Tough foods
Lateral movements like this for…
Brittle foods
Lateral movements like this…
are “abnormal”
“Opening” muscles in the chewing cycle
- Mylohyoid
- Digastric
- Lateral pterygoid
“Closing” muscles in the chewing cycle…
- Temporalis
- Masseter
- Medial pterygoid
(Lateral pterygoid also active)
Control of mastication: sensory system within components?
- PDL: mechanoreceptors
- Muscles: spindle fibres
- TMJ: receptors
Control of mastication: 3 levels of control
- Reflex
- Pattern generator
- Voluntary
What allows the “jaw-jerk reflex” to occur when being stimulated by a tap?
Stimulus: stretch (via chin tap)
Receptor: Muscle spindle
Synapses in V motor of nucleus
Effect: contraction of masseter muscle.
Latency: ~7-8ms
Electromyography
Measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle.
What is the role of stretch reflexes?
Resist gravity
Help maintain jaw posture
Load compensation during chewing
Stabilises jaw during vigorous head movements - e.g. during running.
When the teeth are at “rest” they sit apart - why is this?
Minimal muscle activity
Or… governed by muscle elasticity?
Protective reflexes
Polysynaptic reflexes
Often in response to a noxious stimulus (e.g. jaw “opening” reflexes).
Jaw unloading reflex
Sudden closure following hard biting (e.g hard/brittle food breaks)
—> Inactivation of jaw closing muscles
—> Activation of jaw opening muscles
Prevents teeth crashing together.
Control of mastication: centres
- Higher centres (e.g. cerebral cortex)
- Central neural pattern generator (“chewing centre”)
- Mastication muscle motorneurones
- Masticatory muscles
