mastication Flashcards
what are the main 4 muscles involved in mastication
masseter (in posterior aspect of cheek)
temporalis (felt on side of head)
medial pterygoid
lateral pterygoid
which of the two muscles are more superficial
masseter
temporalis
what do these muscles move
1 bone (mandible) around TMJs
which nerve controls the muscles of mastication
trigeminal
what has to occur for normal functioning to be achieved
actions on one side have to be co-ordinated with actions on the other side
which three of the muscles are involved in elevation of the mandible (generates biting forces)
masseter
temporalis
medial pterygoid
what do the actions of the tmj include
- not fully understood
- rotation
- anteroposterior translation (sliding) of mandibular condylar head
what is the function of the fibrocartilagenous disc (articular disc of fibre cartridge)
- sits on top of head of mandible
- separated the tmj capsule into 2 completely separate joint spaces (a superior and inferior compartment)
how do muscles of mastication move the mandible around
work around the TMJ
attach to the mandible and to the cranium
so when they shorten (contract) they move the mandible round
how can the masseter be felt from the outside
if we clench our teeth together
feel it contracting in cheek (a few cm in front of the ear)
where does the masseter run from
most superficial
from zygomatic arch
runs down and backwards to insert into external / superficial surface of mandibular ramus near the angle which is fixed in position (so masseter elevates it by contracting, increasing biting forces)
what happens when the masseter contracts
- because the zygomatic arch is fixed and the mandible is mobile
- pulls / rotates the mandible upwards
- masseter is responsible for elevating mandible for generating biting forces
what forces are generated between the teeth when theyre occluded
biting forces (as theyre clenched together)
which nerve supplies the masseter muscle
- the nerve to masseter
- branch of mandibular division (V3) of trigeminal nerve
how can the temporalis be felt from the outside
contracting on side of head when clench teeth
where does the temporalis run
between temporal fossa on side of skull
inserts into the coronoid process of the mandible
what type of insertion does the temporalis have into the coronoid process and why
- extensive
- part of it runs all way down anterior surface of coronoid process to where it stops behind 3rd molar
- needs this because it is a large powerful muscle so needs to stay attached to bone its working on when it contracts
which types of fibres does the temporalis have
- vertical
- horizontal
- oblique
what do the vertical fibres do
- elevate the mandible when they get shorter
- contributing to biting forces
what do the horizontal fibres do
- retract the condylar head of the mandible when they get shorter
what do the oblique fibres do
contribute to both elevation and retraction
what is the nerve supply to the temporalis
- the deep temporal nerves - branch of mandibular division (V3) of trigeminal nerve
why does the mandible move forward and backward
its head is covered by the capsule of the tmj
which muscle contracts as the mouth is being opened
digastric
other than rotating how else does the mandibular head move
- anteriorly then posteriorly as the mouth opens and closes
where does the medial pterygoid muscle lie
- infratemporal foss (area posterior to maxilla and medial to mandibular ramus)
why is the sphenoid bone relevant to the medial and lateral pterygoid muscles
they take origin from the lateral wings/plates of the bone (ones that stick downwards)
so their names come from these wing like projections - the medial and lateral pterygoid plates
where does the word pterygoid come from
greek for ‘wing’
what are the wings of the sphenoid bone attached to
the body of the bone in the centre
what are the 3 parts of the unpaired spenoid bone
- wings (greater and lesser)
- a body
- medial and lateral pterygoid plates (downward projections)
where do the two heads of the medial pterygoid muscle originate from
1) from posterior surface of maxilla
2) medial surface of lateral pterygoid plate (larger of the 2) of the sphenoid bone
where does the medial pterygoid muscle run
- downwards + backwards (inferoposteriorly)
- outwards
- the two heads merge together
- to insert into the deep surface of the mandibular ramus adjacent to the angle
what is the main function of the medial pterygoid muscle
elevate mandible (assist in closing mouth and biting) when they contract
what lesser function does the medial pterygoid muscle have and how
assists in side-to-side movements and protrusion of mandible (grinding motion)
as it has anterior to posterior angulation of muscle fibres which pull side of mandible forward when they contract
if only one side drawn forward and other just rotated around the tmj
the anterior part of the mandible will swing towards opposite side
SO then have to contract the other side so anterior part swings back
which nerve supplies the medial pterygoid muscle
- nerve to medial pterygoid
- branch of mandibular division (V3) of trigeminal nerve
where does the mandibular nerve run to give off branches to the masseter, temporalis and medial pterygoid muscles
through foramen ovali in sphenoid bone into the infratemporal fossa
why is the lateral pterygoid the most complex muscle of mastication
- has 2 heads which have different functions
- upper (superior) head
- lower (inferior) head
where does the upper (superior) head of the lateral pterygoid muscle run
originates on outer surface of greater wing of sphenoid
runs posteriorly
inserts into the capsule and articular disc of the tmj
where does the lower (inferior) head of the lateral pterygoid muscle run
originates on lateral surface of lateral pterygoid plate of the sphenoid bone
runs posteriorly
inserts into the neck of the condylar process of mandible
so what happens when the inferior head contracts
pulls condylar process forward onto articular eminence
important movement as mouth is opening
depresses the mandible
what other functions does the lateral pterygoid muscle have
- key role in elevation (does NOT contribute directly to biting force generation)
- side-to-side movement of mandible when the 2 heads act alternatively instead of together
what is the theory on the function of the upper head when the mouth is closing
controls position of articular disc of the tmj
which nerve supplies the lateral pterygoid muscle
- nerve to lateral pterygoid
- branch of mandibular division (V3) of trigeminal nerve
which other muscle has a role in opening the mouth but IS NOT one of the muscles of mastication
digastric muscle
where does the digastric muscle run
originates at mastoid process of temporal bone (attached to it anteriorly)
passes through a loop of connective tissue that ties it to the hyoid bone
inserts into deep surface of mandible near chin
what feature does the digastric have
- two bellies (posterior and anterior)
connected by an intermediate tendon (runs through a loop of connective tissue ATTACHED to hyoid bone allowing it to slide as mouth opens and closes)
why is the digastric often not needed
gravity plays larger part in opening the mouth
what functions does the digastric muscle have when it contracts
- depress/ pull mandible down (only if muscles of mastication are relaxed and muscles below hyoid bone contract to hold the hyoid in place)
- OR pull the hyoid bone upwards (important in early stages of swallowing)
why doesnt the digastric muscle work if the muscles of mastication are being used
muscles of mastication are MORE powerful
when these are being used the effect of the digastric is to pull hyoid bone up
what happens when the hyoid bone is pulled upwards
- tongue pushed into mouth
- tip of tongue rolled against hard palate
- pushes food backwards into pharynx
describe the mandibular nerve (V3)
3rd division of trigeminal nerve (5th cranial nerve - V)
only division that transmits motor nerve fibres
has major sensory functions (supplies lower teeth + their supporting structures)
supplies ALL muscles of mastication
what movements does the head of the mandible undergo when mouth opens
rotation
sliding anteriorly
The mandibular fossa is located on the inferior surface of which bone
temporal
