NS23 mastication 2

Question 1

what is the maximum bite force between molars?

Answer 1

500-700N

Question 2

what is a reflex?

Answer 2

predicted response to a given stimulus

Question 3

are stretch receptors monosynaptic?

Answer 3

usually

ex) knee jerk reflex
jaw jerk reflex

Question 4

describe the jaw jerk reflex

Answer 4

• stimulus: stretch
• receptor: muscle spindle
• synapse (s): 1 in V motor
  nucleus
• effect: contraction of
  masseter muscle
• latency : around 7- 8ms

Question 5

what is the role of stretch reflex?

Answer 5

tonic

• resists gravity
• helps maintain posture?

phasic:

• loads compensation for chewing
• stabilises jaw during vigorous head movements - eg during running

Question 6

what is the rest/postural position?

Answer 6

• at ‘‘rest’’ teeth apart
• maintained through minimal muscle activity or it is governed by muscle elasticity
• it remains reproducible thoughout life in both dentate and edentulous subjects
• important with complete dentures

Question 7

protective reflexes

Answer 7

polysynaptic reflexes
often response to a noxious stimulus
examples: limb: flexion withdrawal reflex

Question 8

describe the jaw opening reflex

Answer 8

stimuli:

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

response in primates (inc humans)

• inactivation of jaw closers
• ie cessation of closing
• inhibitory Jaw reflexes

Question 9

what does latency mean?

Answer 9

time from stimulus to effect

Question 10

what is the sequence of the reflex latency?

Answer 10

receptor –> afferent neurone –> synapse(s) –> efferent neurone –> effector

Question 11

how long is the minimum synaptic delay?

Answer 11

0.2ms per synapse

Question 12

what is the role of the inhibitory jaw reflex?

Answer 12

• prevent overloading of the masticatory system
• facilitate opening:
  to expel noxious material
  minimise damage to intra-/perio-oral structures

Question 13

why is it a sensitive system?

Answer 13

a tooth movement of only 9microns is enough to produce inhibitory reflex effects in the masseter muscle

Question 14

what is the response of the inhibitory jaw reflex?

Answer 14

• inactivation of jaw closing muscles

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

Question 15

what is the jaw unloading reflex?

Answer 15

stimulus:

• sudden closure following hard biting
• hard/brittle food breaks

response

• inactivation of jaw closing muscles
• activation of jaw opening muscles

result : teeth do not crash together

Question 16

what are the functional roles of the controls of mastication?

Answer 16

• modulate voluntary and pattern generated motor neuron drive
• fine control/ compensatory
• protective

Question 17

what is the central neural pattern generator?

Answer 17

pontine reticular formation