Mastication Flashcards
Is matiscation voluntary or involunatary? conscious or unconscious?
opening your mouth depressing your jaw is voluntary. But the chewing is patterned into the brain stem.
It is voluntary but it begins to become involuntary. When you’re not paying attention to it it starts going again.
Chewing can be conscious but most times we don’t think about it.
BECAUSE OF THIS IF YOU CHANGE ANYTHING IN THE ORAL CAVITY YOU CAN DAMAGE SOMETHING BECAUSE YOUR PATTERN GENERATORS ARE GOING TELLING YOU HOW TO CHEW.
what is a persons chewing pattern like?
It’s different for everyone but similar as you chew for each individual person.
What are the four main muscles of mastication?
medial pterygoid, lateral pterygoid, temporalis, masseter
What elevates the mandible?
masseter, medial pterygoid, temporalis
these are much stronger than the opening muscle
What muscle depresses the mandible?
lateral pterygoid. accessory muscles: mylohyoid, digastric (opening)
What muscles protrude the mandible and do not laterally deviate?
masseter, medial pterygoid
What muscles protrude the mandible and laterally deviate?
lateral pterygoid
What muscle retrudes the mandible and is involved in lateral deviation?
temporalis
so what two muscles are involved in lateral deviation?
lateral pterygoid, temporalis
So what is the main movement in the jaw? what are two other types of movement?
. Main movement is a rhythmic opening and closing - (separation & apposition) of the jaws (depression and elevation)
closing muscles = masseter, temporalis, medial pterygoids)
Opening muscles = lateral pterygoids, digastric, mylohyoid
- Also small protrusive and retrusive movements
- Lateral deviation (extrusion) used in grinding
What is the so-called “Bennett” movement?
Lateral movement results in lateral displacement of condoyles -
the so-called “Bennett” movement
In most individuals, all of these movements results in chewing that is mainly (approx) symmetrical
In about one third of normal chewing strokes, how is the bolus of food chewed? where is the remained concentrated?
Bolus of food only chewed equally on both sides in about one third of normal chewing strokes
Remainder concentrated on one side (primarily left in most patients) although bolus transferred to other side after several strokes
What are three factors that affect symmetrical chewing patterns?
Factors that affect symmetrical chewing patterns
sore tooth
inflamed periodontal ligament
missing teeth
what’s the most common pattern for chewing?
- Food initially cut/torn by incisors & canines
- Broken up into smaller pieces in premolar/anterior molar regions
- Comminuted (grinding action) by the molars (includes lateral movements)
does the mandible move a constant speed or force?
no
What are the two main phases of chewing? what are the sub phases to make four total phases of chewing?
opening versus closing.
SLOW OPENING (SO) FAST OPENING (FO) FAST CLOSING (FC) SLOW CLOSING (POWER STROKE) SC (PS)
Chewing cycles differ with species but patterns are similar within species. WHY?
Chewing patterns will differ depending on whether you are doing a lot of grinding (herbivore) vs. shearing (omnivore) as well as the position of the tongue (the food eaten likely directs the chewing cycle pattern)
Which muscles are active during each phase of chewing ( beginning at the point of minimal opening) ?
SO = __mylohyoids, digastric, lat. pterygoid____________
FO = ___mylohyoid, digastrics, lat. Pterygoids. __________
FC= __med. Pterygoids, masster, temporalis____________
PS = __masseter, temporalis, med. Pterygoids. __________
during chewing, when does the mandible reach its greatest speed?
toward the end of opening and beginning of closing
When do chewing cycles (or cycle time) vary?
Chewing cycles vary depending on what is being ingested Cycle time (especially the opening phase) is increased for tough sticky foods Eg., carrots = 0.58 sec peanut butter = 0.77 sec
When else does the cycle time vary?
Cycle time also varies as we comminute the food in the oral cavity.
ie., the time/forces used at the beginning of the cycle for chewing a piece of crunchy carrot are not the same as those at the end (just before we swallow it)
What changes to make the time/forces used at the beginning of the cycle for chewing a piece of crunchy carrot not the same as those at the end?
the mechanoreceptor activity will change
For opening and closing muscles the RA/SA fire when?
RA/SA:
Fire when teeth in contact,
may still
fire at any time there is input
For closing, are the opening muscles inhibited? For opening are the closing muscles inhibited?
Opening muscles are at 0 when closing, so they are not inhibited. The closing muscles are hyperpolarized or below zero and are therefore inhibited. The closing muscles are inhibited. This is because the closing muscles are very strong and will overried what is happening with the opening muscles.
What is the direct sequence of action for opening and closing?
Also there is a direct sequence of activation
- Opening - mylohyoids, digastrics, lat.pterygoids
- Closing - med. Pterygoids, masseter, temporalis
What receptors modulate the output from the chewing centers of the CNS with respect to the forces that are eliminated by the mandible?
Feedback control from the sensory receptors such as pulpal receptors, periodontal receptors, receptors in the surrounding bone and soft tissue and even TMJ receptors plays a role in modulating the output from the chewing centres of the CNS with respect to the forces that are elicited by the mandible
What are the normal forces of mastication for north americans?
Normal forces are in the 7 - 15 kg per tooth load
Total load developed can be much greater
Inuit population - 50 - 150 kg per tooth
Where is the force of biting hte greatest?
your third molar has a little less but it is highest on your second molar and decreases until you get to your incisors.
what factors affect forces of mastication?
pain, exercise, diet (strength)
pain - you get inhibition to bite down
exercise - you can train people who have had strokes for example to chew.
What are the muscles of mastication controlled by?
- the trigeminal motor nucleus (V)
- the sensory nuclei –
- mesencephalic;
- main sensory nucleus
- descending spinal trigeminal nucleus
- the reticular formation - pattern generators (in pons) + higher centers
What is the jaw closing reflex?
The Jaw Closing reflex (jaw-jerk). MONOSYNAPTIC.
Tap chin = stretch muscle spindle = afferent information
to cell bodies in mesencephalic nucleus = monosynaptic
synapse on alpha motor neuron which closes the jaw
What is the jaw opening reflex?
Stimulate intraoral mucosal receptors –> afferent info
to trigeminal nucleus–> synapse on interneuron –>
activate alpha motor neuron (digastric)–> open jaw
For smooth rhythmic chewing patterns where do these come from?
These all form the substrates for smooth rhythmic chewing patterns
sensory receptors - reflexes
pattern generators (in pons)
higher centers - cerebral cortex, basal ganglia, hypothalamus, cerebellum
