N23-masticaton 2

Question 1

what is the masticatory system?

Answer 1

– Complex muscle‐joint system

– Symmetrical or asymmetrical jaw movements

Question 2

what forces can the masticatory system produce?

Answer 2

• Maximum bite forces: 500‐700N between molars

* Up to 150N during mastication

Question 3

what replaces golgi tendon organs in the mastication system?

Answer 3

role replaced by the periodontal ligament which direct control on teeth affects mastication

Question 4

what are 3 levels of control of mastication?

Answer 4

• reflex
• pattern generator
• voluntary

Question 5

if there is a unilateral signal , is activation unilateral or bilateral?

Answer 5

bilateral

Question 6

what nucleus controls mastication?

Answer 6

V motor nucleus

Question 7

what can act on the V motor nucleus?

Answer 7

• reflexes i.e jaw jerk reflex

- chewing centre

Question 8

what does chewing centre control?

Answer 8

takes over rhymical chewing motion

Question 9

what controls voluntary mastication?

Answer 9

higher centres which can act on chewing centre and V motor nucleus

Question 10

what is a reflex?

Answer 10

Predictable response to a given stimulus

Question 11

Describe stretch reflexes.

Answer 11

- Simple
- Usually mono‐synaptic  Examples:
– Knee Jerk Reflex
– Jaw Jerk Reflex

Question 12

Describe the knee-jerk reflex.

Answer 12

-stimulus: stretch (via patellar tendon tap)
-Receptor: muscle spindle
-Synapses: 1
-Effect -contraction of quadriceps Femoris
Latency: 19-24ms

Question 13

Describe the jaw-jerk reflex.

Answer 13

Stimulus: stretch (via chin tap)
Receptor:muscle spindle
Synapses(s): 1 in V motor nucleus
Effect: contraction of master muscle
Latency: 7-8ms

(the trigeminal mesencephalic nucleus acts on the trigeminal motor nucleus)

Question 14

what is the tonic role of stretch reflexes?

Answer 14

– Resist gravity

– Help maintain posture

Question 15

what position remains reproducible throughout life in both dentate and edentulous subjects?

Answer 15

rest/postural position

Question 16

how is rest/postural position maintained?

Answer 16

• minimal muscle activity

- is ot governed by muscle elasticity

Question 17

what is the phasic role of stretch reflexes?

Answer 17

– Load compensation during chewing

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

Question 18

Describe protective reflexes.

Answer 18

• Polysynaptic (>1 synapse) Reflexes
  - Often a response to a noxious stimulus 
  Examples:
  – Limb: Flexion Withdrawal Reflex
  – Jaw: Jaw “Opening”

Question 19

what happens in the flexion-withdrawal reflex?

Answer 19

• excitatory interneurone causes contraction in bicep

- inhibitory interneurone prevents contraction of tricep

Question 20

what is the stimulus for jaw “opening reflexes”.

Answer 20

– Intra‐oral mechanical or noxious

– Extra‐oral noxious

Question 21

what is the jaw opening reflex response in sub-primates?

Answer 21

Activation of jaw depressors

Question 22

what is the jaw opening reflex response in primates (humans)?

Answer 22

– Inactivation of jaw closers
– i.e. cessation of closing
– Inhibitory Jaw Reflexes

Question 23

what is the jaw opening response and latency with a stimulus of a gentle tap to the tooth?

Answer 23

Response: early inhibition
Latency: 10ms

Question 24

what is the jaw opening response and latency with a stimulus of a harder tap to the tooth?

Answer 24

Response: Early and late reflex
Latency: 10 and 40ms

Question 25

what is the jaw opening response and latency with a stimulus of a painful stimulus to lip?

Answer 25

Response: late reflex
Latency: 40ms

Question 26

what is latency?

Answer 26

time for stimulus to effect

Question 27

what is conduction time?

Answer 27

neurones speed and distance

Question 28

what is the minimum synaptic delay?

Answer 28

0.2ms per synapse

Question 29

what makes singals from nociceptors slower?

Answer 29

• slower C fibres

- several synapses (reticular formation)

Question 30

what is the jaw opening response with an electrical stimulus to the tooth?

Answer 30

response: early and late fused reflex

Question 31

what is the response of inhibitory jaw reflexes?

Answer 31

– inactivation of jaw closing muscles

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

Question 32

what is the role of inhibitory jaw reflexes?

Answer 32

– Prevent overloading of the masticatory system
– Facilitate opening:
• Expel noxious material
• Minimise damage to intra‐/peri‐oral structures

Question 33

what causes delay of signal on the ECG after being told to clench hard when you see light?

Answer 33

reflex response time

Question 34

what tooth movement is enough to produce inhibitory reflex effects in the master muscle?

Answer 34

9 micrometers

Question 35

what is the stimulus for jaw unloading reflex?

Answer 35

– Sudden closure following hard biting

– e.g. a hard/brittle food breaks

Question 36

what is the response of jaw unloading reflex?

Answer 36

– Inactivation of jaw closing muscles

– Activation of jaw opening muscles

Question 37

what is the result of jaw unloading reflex?

Answer 37

Teeth do not crash together

Question 38

what are types of control of mastication:reflexes?

Answer 38

– Stretch reflexes
– Inhibitory reflexes
– Unloading reflexes

Question 39

what are the functional roles of control of mastication?

Answer 39

– Modulate voluntary and pattern generated motor neuron
drive
– Fine control/compensatory
– Protective

Question 40

Describe the central pattern generator theory of mastication.

Answer 40

• higher centres (cerebral cortex) to..
• central neural pattern generator (pontine reticular formation) to..
• “masticatory “ muscle motoneurons to..
• “masticatory”muscles

(peripheral influences act as jaw reflexes on “masticatory” muscle motorneurons)