Mastication and its control

Question 1

Protective reflex

Answer 1

> 1 synapse (polysynaptic)
in response to a noxious stimulus
e.g. jaw “opening” reflex

Question 2

Pulling hand away from a hot pan in response to noxious stimulus triggers…

Answer 2

flexion-withdrawal reflex

involves excitatory interneurone and inhibitory interneurone that work together.

Question 3

What stimulus initiates jaw “opening” reflex?

Answer 3

Intra-oral: mechanical or noxious
Extra-oral: noxious

Question 4

How does jaw “opening” reflex differ in humans and sub-primates?

Answer 4

Humans don’t activate the “openers” of the jaw, they inhibit the “closers”.

Sub-primates: Activate jaw depressors

Question 5

To the teeth: why would a small stimulus have a faster reflex than a hard harmful stimulus?

Answer 5

They take different pathways which effects latency

Question 6

What is the role of inhibitory jaw reflex?

Answer 6

Question 7

The chewing cycle

Answer 7

0.5-1.2 sec duration
Opening, fast closing, slow closing, intercuspal phases

Question 8

Lateral movements like this for…

Answer 8

Tough foods

Question 9

Lateral movements like this for…

Answer 9

Brittle foods

Question 10

Lateral movements like this…

Answer 10

are “abnormal”

Question 11

“Opening” muscles in the chewing cycle

Answer 11

1. Mylohyoid
2. Digastric
3. Lateral pterygoid

Question 12

“Closing” muscles in the chewing cycle…

Answer 12

1. Temporalis
2. Masseter
3. Medial pterygoid

(Lateral pterygoid also active)

Question 13

Control of mastication: sensory system within components?

Answer 13

1. PDL: mechanoreceptors
2. Muscles: spindle fibres
3. TMJ: receptors

Question 14

Control of mastication: 3 levels of control

Answer 14

1. Reflex
2. Pattern generator
3. Voluntary

Question 15

What allows the “jaw-jerk reflex” to occur when being stimulated by a tap?

Answer 15

Stimulus: stretch (via chin tap)
Receptor: Muscle spindle

Synapses in V motor of nucleus
Effect: contraction of masseter muscle.
Latency: ~7-8ms

Question 16

Electromyography

Answer 16

Measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle.

Question 17

What is the role of stretch reflexes?

Answer 17

Resist gravity

Help maintain jaw posture

Load compensation during chewing

Stabilises jaw during vigorous head movements - e.g. during running.

Question 18

When the teeth are at “rest” they sit apart - why is this?

Answer 18

Minimal muscle activity

Or… governed by muscle elasticity?

Question 19

Protective reflexes

Answer 19

Polysynaptic reflexes

Often in response to a noxious stimulus (e.g. jaw “opening” reflexes).

Question 20

Jaw unloading reflex

Answer 20

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.

Question 21

Control of mastication: centres

Answer 21

1. Higher centres (e.g. cerebral cortex)
2. Central neural pattern generator (“chewing centre”)
3. Mastication muscle motorneurones
4. Masticatory muscles