N23-masticaton 2 Flashcards
what is the masticatory system?
– Complex muscle‐joint system
– Symmetrical or asymmetrical jaw movements
what forces can the masticatory system produce?
- Maximum bite forces: 500‐700N between molars
* Up to 150N during mastication
what replaces golgi tendon organs in the mastication system?
role replaced by the periodontal ligament which direct control on teeth affects mastication
what are 3 levels of control of mastication?
- reflex
- pattern generator
- voluntary
if there is a unilateral signal , is activation unilateral or bilateral?
bilateral
what nucleus controls mastication?
V motor nucleus
what can act on the V motor nucleus?
- reflexes i.e jaw jerk reflex
- chewing centre
what does chewing centre control?
takes over rhymical chewing motion
what controls voluntary mastication?
higher centres which can act on chewing centre and V motor nucleus
what is a reflex?
Predictable response to a given stimulus
Describe stretch reflexes.
- Simple
- Usually mono‐synaptic Examples:
– Knee Jerk Reflex
– Jaw Jerk Reflex
Describe the knee-jerk reflex.
-stimulus: stretch (via patellar tendon tap)
-Receptor: muscle spindle
-Synapses: 1
-Effect -contraction of quadriceps Femoris
Latency: 19-24ms
Describe the jaw-jerk reflex.
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)
what is the tonic role of stretch reflexes?
– Resist gravity
– Help maintain posture
what position remains reproducible throughout life in both dentate and edentulous subjects?
rest/postural position
how is rest/postural position maintained?
- minimal muscle activity
- is ot governed by muscle elasticity
what is the phasic role of stretch reflexes?
– Load compensation during chewing
– Stabilises jaw during vigorous head movements – e.g. during running
Describe protective reflexes.
- Polysynaptic (>1 synapse) Reflexes
- Often a response to a noxious stimulus
Examples:
– Limb: Flexion Withdrawal Reflex
– Jaw: Jaw “Opening”
what happens in the flexion-withdrawal reflex?
- excitatory interneurone causes contraction in bicep
- inhibitory interneurone prevents contraction of tricep
what is the stimulus for jaw “opening reflexes”.
– Intra‐oral mechanical or noxious
– Extra‐oral noxious
what is the jaw opening reflex response in sub-primates?
Activation of jaw depressors
what is the jaw opening reflex response in primates (humans)?
– Inactivation of jaw closers
– i.e. cessation of closing
– Inhibitory Jaw Reflexes
what is the jaw opening response and latency with a stimulus of a gentle tap to the tooth?
Response: early inhibition
Latency: 10ms
what is the jaw opening response and latency with a stimulus of a harder tap to the tooth?
Response: Early and late reflex
Latency: 10 and 40ms
