Control of mastication

Question 1

How is mastication controlled?

Answer 1

-pattern generator in the brain stem allows chewing to happen semi-automicatically

Question 2

How is mastication voluntary?

Answer 2

• we can control the jaw movement

- we can chose to start/stop/ alter jaw movements

Question 3

what is the reflex control?

Answer 3

• rapid

- automatic control

Question 4

what is a reflex?

Answer 4

Predictable response to a given stimulus

Question 5

what are 3 examples of reflexes?

Answer 5

• masticatory- salivary reflex
• knee jerk reflex
• jaw jerk reflex

Question 6

what type of nerves are afferent standard reflexes ?

Answer 6

sensory nerves

Question 7

what is the reflex pathway?

Answer 7

stimulus > receptor > afferent neurone (from periphery to CNS) > synapse > efferent neurone (from CNS to periphery) > effector > response

Question 8

what type of reflex is the jaw jerk reflex?

Answer 8

stretch reflex

Question 9

what type of reflex is the inhibitory jaw reflex?

Answer 9

Protective reflex

Question 10

what type of reflex is the jaw unloading reflex?

Answer 10

unloading reflex

Question 11

Describe stretch reflexes

Answer 11

• simple
• usuallly mono-synaptic
• i.e jaw jerk reflex

Question 12

what factors effect reflex latency ( time from stimulus to effect)?

Answer 12

• conduction time of the neurones

- synaptic delay

Question 13

why is the jaw jerk reflex latency smaller than the knee jerk latency?

Answer 13

shorter pathway

Question 14

what are the roles of the jaw jerk reflex?

Answer 14

• 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

Question 15

Describe protective reflexes

Answer 15

• polysynaptic
• often a response to a noxious (damaging) stimulus
• jaw opening reflexes

Question 16

what are the types of stimuli for jaw opening reflexes?

Answer 16

• intra-oral mechanical or noxious

- extra-oral noxious

Question 17

what type of receptors are there in jaw “opening” reflexes?

Answer 17

• mechanoreceptors

- nociceptors

Question 18

what are the responses of the inhibitory jaw reflex?

Answer 18

• inactivation of jaw closing muscles

- two phases - early (10-30ms) , late (40-90ms)

Question 19

what is the role of inhibitory jaw reflexes?

Answer 19

• 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

Question 20

what is the jaw unloading reflex stimulus?

Answer 20

sudden closure following hard biting e.g hard/brittle food breaks

Question 21

what are the responses jaw unloading reflex?

Answer 21

• inactivation of jaw closing muscles

- activation of jaw opening muscles

Question 22

what is the result of jaw unloading reflex?

Answer 22

Teeth do not crash together

Question 23

what is the pathway of mastication?

Answer 23

Higher centres (cerebral cortex) > central neural pattern generator “chewing centre” > masticatory muscle motorneurones > masticatory muscles