M+O 7 - masticatory control

Question 1

Why do we need to breakdown foodstuffs via mastication?

Answer 1

• preparation for swallowing
• increase surface area for chemical digestion
• release of chemicals for sense of taste
• stimulation of salivary flow
• growth and maintenance of oro-facial tissues

Question 2

During mastication, what are jaw movements for?

Answer 2

chewing cycles

Question 3

During mastication, what are cheek movements for?

Answer 3

directing food

Question 4

During mastication, what are tongue movements for?

Answer 4

• directing food
• crushing food
• mixing food and saliva

Question 5

During mastication, what are lip movements for?

Answer 5

• (accepting food)
• retaining food: anterior oral seal
• directing food

Question 6

How long does the chewing cycle last?

Answer 6

0.5-1.2 secs

Question 7

What are the phases of the chewing cycle?

Answer 7

• opening
• fast closing
• slow closing
• intercuspal phases
  (note: many alternative terminologies used)

Question 8

During what phases of the chewing cycle is food broken down?

Answer 8

slow closing and intercuspal

Question 9

During the chewing cycle, what is the sequence of muscle activation?

Answer 9

mylohyoid —> digastric —> lateral pterygoid —> temporalis —> masseter —> medial pterygoid

Question 10

What muscles are activated during opening?

Answer 10

mylohyoid —> digastric —> lateral pterygoid

Question 11

What muscles are activated during closing?

Answer 11

temporalis —> masseter —> medial pterygoid
(lateral pterygoid also active)

Question 12

What force can be produced during mastication?

Answer 12

up to 150N

Question 13

What is the maximum bite force?

Answer 13

500-700N between molars

Question 14

What are the 3 levels of control of mastication?

Answer 14

• reflex
• pattern generator
• voluntary

Question 15

What produces pattern of activity for mastication?

Answer 15

chewing centre

Question 16

What are the 4 parts of the trigeminal nucleus?

Answer 16

• trigeminal main sensory nucleus (top)
• trigeminal nucleus oralis
• trigeminal nucleus interpolaris
• trigeminal nucleus caudalis (bottom)

Question 17

What is a reflex?

Answer 17

predicable response to a given stimulus

Question 18

What is a stretch reflex?

Answer 18

• simple
• usually monsynaptic

examples:
- knee jerk reflex
- jaw jerk reflex

Question 19

What gives the conduction time of a reflex?

Answer 19

neurones speed and distance

Question 20

What is the minimum synaptic delay?

Answer 20

0.2ms per synapse

Question 21

What is the stimulus and the receptor of the knee jerk reflex?

Answer 21

stimulus: stretch (via patellar tendon tap)

receptor: muscle spindle

Question 22

What is the stimulus and the receptor of the jaw jerk reflex?

Answer 22

stimulus: stretch (via chin tap)

receptor: muscle spindle

Question 23

How many synapses are there in the knee jerk reflex, and what is the latency of the reflex?

Answer 23

synapses: 1

latency: 19-24ms

Question 24

How many synapses are there in the jaw jerk reflex, and what is the latency of the reflex?

Answer 24

synapses: 1 in V motor nucleus

latency: ~7-8ms

Question 25

What is the effect of the knee jerk reflex?

Answer 25

contraction of quadriceps femoris

Question 26

What is the effect of the jaw jerk reflex?

Answer 26

contraction of masseter muscle

Question 27

What are the tonic roles of stretch reflexes?

Answer 27

- resist gravity - help maintain jaw posture?

Question 28

How is the rest/postural position maintained?

Answer 28

- minimal muscle activity? or… - is it governed by muscle elasticity? it remains reproducible throughout life in both dentate and edentulous subjects

Question 29

What are the phasic roles of stretch reflexes?

Answer 29

- load compensation during chewing - stabilises jaw during vigorous head movements e.g. during running

Question 30

How many synapses are involved in protective reflexes?

Answer 30

polysynaptic reflexes >1 synapse

Question 31

What are protective reflexes often a response to?

Answer 31

a noxious stimulus examples: - limb: flexion withdrawal reflex - jaw: jaw “opening” reflex

Question 32

What are the stimuli for the jaw “opening” reflexes?

Answer 32

- intra-oral mechanical or noxious - extra-oral noxious

Question 33

What is the jaw “opening’’ reflex response in **sub-primates** (e.g. cats)?

Answer 33

activation of jaw depressors

Question 34

What is the jaw “opening’’ reflex response in **humans**?

Answer 34

- inactivation of jaw closers - i.e. **cessation** of closing - **inhibitory jaw reflexes** In humans jaw openers not as powerful and jaw closers - can’t compete so jaw closers inhibited

Question 35

What are the phases of inhibitory jaw reflexes?

Answer 35

early (10-30ms) and late (40-90ms) these phases will merge together and get bigger is the stimulus is bigger

Question 36

What is the role of inhibitor jaw reflexes?

Answer 36

- prevent overloading of the masticatory system - facilitate opening: - expel noxious material - minimise damage to intra-/peri-oral structures - faster than a voluntary reaction

Question 37

What proves that inhibitory jaw reflexes are a sensitive system?

Answer 37

- they are produced every time our teeth contact - a tooth movement of only ~9um is enough to produce inhibitory reflex effects in the masseter muscle

Question 38

What is the stimulus of the jaw unloading reflex?

Answer 38

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

Question 39

What is the response of the jaw unloading reflex?

Answer 39

- inactivation of jaw closing muscles - activation of jaw opening muscles

Question 40

What is the result of the jaw unloading reflex?

Answer 40

teeth do not crash together

Question 41

What is the ‘series of reflexes’ theory of mastication (historical)?

Answer 41

Sir Charles Sherrington (1917) - e.g. reflex chain theory - sequence of jaw opening and closing reflexes - too simplistic - can’t explain all movements - e.g. lateral movements, changing sides etc…

Question 42

What are the 4 areas for control of mastication in the brain/body?

Answer 42

higher centres (e.g. cerebral cortex) —> central neural pattern generator (“chewing centre”) —> masticatory muscle motorneurones (only these just jaw reflexes) —> masticatory muscles