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Anatomy > muscles of mastication (A22) > Flashcards

muscles of mastication (A22) Flashcards

1
Q

mastication definition

A

chewing

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2
Q

why is the process of mastication important

A
  • breakdown of foodstuffs:
  • > to prepare for swallowing
  • > to increase the surface area for chemical digestion (digestion minorly starts in the mouth as enzymes in saliva start the breakdown, however it mainly occurs by the enzymes in the stomach/GI tract)
  • > release of chemicals for sense of taste
  • stimulates salivary flow
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3
Q

why is sense of taste so important

A

-important in selection of food, eg. toxic foods taste more bitter therefore sense of taste acts as a safety mechanism

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4
Q

saliva

A
  • lubricant that cleans the mouth
  • acts as a buffer to regulate pH to clean the teeth
  • > therefore chewing gum is good as it stimulates saliva flow which has a buffering effect and counteracts acid
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5
Q

location of masticatory movements

A

-temporomandibular joint (TMJ)

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6
Q

TMJ

A
  • temporomandibular joint
  • joint between mandibular condyle/condylar head of mandible and glenoid fossa (of temporal bone)
  • TMJ is within the temporal bone
  • TMJ/mandible has 2 joints/the two TMJ joints are joined, therefore if one TMJ moves, the other TMJ must be doing something
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7
Q

glenoid fossa

A
  • depression of temporal bone where condylar head of mandible sits
  • position of TMJ joint
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8
Q

articular eminence

A

=bump/eminence on temporal bone that limits movement of mandibular condyle during jaw opening etc, if condyle moves infront of articular eminence, jaw will lock open

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9
Q

clicking jaw

A

-as the EAM is directly behind the glenoid fossa on temporal bone, the patient can hear the “clicking jaw” sound more significantly

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10
Q

movement of TMJ involved in jaw opening

A

hinge movement

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11
Q

movement of TMJ involved in WIDE jaw opening

A

hinge AND slide movement (sticking of jaw occurs during sliding movement and is the cause of the ‘clicking jaw’)

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12
Q

movement of TMJ involved in protrusion

A

sliding movement

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13
Q

movement of TMJ during lateral excursion (jaw moves to one side)

A
  • TMJ on side you are moving jaw away from ‘translates’ (moves forward)
  • TMJ on opposite side/ side that jaw is moving towards rotates around vertical axis (in order to move jaw to the side) then moves laterally
  • > if lateral pterygoid is activated unilaterally it causes lateral excursion (jaw moves to the opposite side of that, that you contracted)
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14
Q

muscles INVOLVED in mastication

A
  • as mastication is a complex movement it requires a complex arrangement of muscles to produce the movement
  • 3 groups of muscles involved in mastication:
  • > the main group are the muscles between the skull and mandible in varying directions which act across the temporomandibular joint (TMJ) aka ‘muscles of mastication’
  • > the muscles between the mandible and the hyoid bone
  • > the hyoid stabilizing muscles
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15
Q

hyoid bone

A
  • floating bone
  • sits among tissue
  • in order to be functional, the hyoid bone must be stabilized
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16
Q

‘muscles of mastication’ between the skull and mandible

A
  • > = biggest and most important muscles that are involved in mastication
  • masseter
  • temporalis
  • medial pterygoid
  • lateral pterygoid
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17
Q

masseter muscle

A

-there are 2 types of masseter muscle fibres:
->superficial masseter (fibres run more forward)
->deep masseter (fibres run more vertical), deep masseter is exposed if you cut off the superficial masseter
(form a sling)

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18
Q

superficial masseter muscle attachments

A
  • origin = zygomatic bone and onto zygomatic arch (outer aspect of arch)
  • insertion = angle/ramus of mandible (outer aspect of mandible)
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19
Q

function/action of superficial masseter muscle

A
  • main role = jaw closing/elevation

- minor role = protrusion (pulls jaw forward as the fibres face forward)

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20
Q

innervation of superficial masseter muscle

A

motor root of mandibular division of trigeminal nerve (motor root of Vc)

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21
Q

hypertrophy of masseter muscle

A
  • as it is major muscle of mastication, people who grind there teeth can have enlarged masseter muscle/hypertrophy of masseter muscle
  • botox can be used to treat this
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22
Q

deep masseter muscle attachments

A
  • origin = inner aspect of zygomatic arch (deep part of arch)
  • insertion = angle/ ramus of mandible (underneath the superficial masseter)
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23
Q

function/action of the deep masseter muscle

A

jaw elevation/ closing, as there is no forward movement of the muscle fibres (like the superficial masseter), the deep masseter is NOT involved in protrusive movement/movement of jaw forward

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24
Q

innervation of deep masseter muscle

A

motor root of mandibular division of trigeminal (Vc motor root)

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25
Q

temporalis muscle attachments

A
  • origin = inferior temporal line and fascia

- insertion = coronoid process of mandible

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26
Q

function/action of temporalis muscle

A

-jaw elevation (muscle fibres travelling in the upwards direction are responsible for this movement)
-retrusion/pull the jaw in backwards direction (fibres travelling posteriorly)
->as the temporalis muscle is a large fan shaped muscle, it has fibres travelling in different directions(some point up, some point backwards) therefore can carry out more than 1 movement
(->in extended Q, just saying that the temporalis muscle is a jaw closer isn’t enough and would be wrong as it suggests you don’t understand the direction of the fibres fanning out)

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27
Q

innervation of temporalis muscle

A

motor root of mandibular division of trigeminal (motor root of Vc)

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28
Q

lateral pterygoid muscle

A

has an upper and lower head (upper head is smaller than the lower head)

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29
Q

attachments of upper head of lateral pterygoid muscle

A
  • origin = infratemporal surface of greater wing of the sphenoid
  • insertion = capsule and articular disc of TMJ
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30
Q

attachments of lower head of lateral pterygoid muscle

A
  • origin = lateral aspect of the lateral pterygoid plate

- insertion = pterygoid

31
Q

is the lateral pterygoid muscles described as ‘jaw openers’

A
  • DO NOT DESCRIBE AS JAW OPENER
  • involved in initial opening of jaw, when hinge is in lower joint space and the condyle stays in place as jaw opening is initially just a hinge movement therefore lateral pterygoids do not assist in this process, HOWEVER, as wide jaw opening involves a hinge AND slide movement (anterior and inferior translation/movement of condyle), the lateral pterygoid assists in this process
  • > when jaw slides on wide opening, the condyle moves forward towards articular eminence (?) therefore lateral pterygoid helps pull the jaw forward (which is a part of jaw opening)
  • > if the lateral pterygoid contracts alone, it only pulls the condyle forward therefore only assists in jaw opening
32
Q

capsule and articular disc of TMJ

A
  • capsule is attached to disc

- disc is between two joints

33
Q

innervation of lateral pterygoid muscle

A

motor root of mandibular division of trigeminal (motor root of CNVc)

34
Q

function/action of the lateral pteryoid muscle (inferior and superior head/ upper and lower head)

A
  • very complex
  • inferior head:
  • > pulls the condyle forwards
  • > if activated bilaterally, causes: protrusion, ASSISTS opening
  • > if activated unilaterally, causes: lateral excursion
  • superior head:
  • > pulls disc forward/stabilizes the disc
  • > active during retrusion and closing
35
Q

lateral and medial pterygoid muscles

A
  • lateral pterygoid attaches to lateral aspect of lateral pterygoid plate
  • medial pterygoid attaches to the medial aspect of lateral pterygoid plate
36
Q

medial pterygoid muscle attachments

A
  • origin = medial aspect of lateral pterygoid plate on inner aspect of skull AND maxillary tuberosity on outer aspect of skull (therefore forms a sling)
  • insertion = medial aspect of ramus/angle of mandible
37
Q

pterygoid fovea

A

= a depression on the anteromedial side of the neck of the condylar process of the mandible, giving attachment to the lateral pterygoid muscle

38
Q

function/action of medial pterygoid muscle

A
  • jaw elevation/closing
  • assists protrusion and lateral excursions (when activated unilaterally/if you contract one medial pterygoid, jaw moves to opposite side)
39
Q

innervation of medial pterygoid muscle

A

motor root of mandibular division of trigeminal (motor root of CNVc)

40
Q

movement of articular disc of TMJ during contraction of muscles of mastication

A
  • when condyle moves backwards during jaw closing, the upper head of lateral pterygoid contracts (just to stabilize the disc?)
  • the disc adjusts to the condylar head and moves with it, does not require contracting of muscle to move the disc forward
41
Q

elevators

A

aka jaw closers

42
Q

depressors

A

aka jaw openers

43
Q

muscles between the mandible and hyoid bone (that are INVOLVED in mastication)

A
  • geniohyoid muscle
  • mylohyoid muscle
  • digastric muscle (anterior belly)
44
Q

true jaw openers/depressors

A
  • geniohyoid muscle
  • mylohyoid muscle
  • digastric muscle (anterior belly)
  • > lateral pterygoid only assists during wide opening of jaw
45
Q

attachments of geniohyoid muscle

A
  • hyoid bone

- lower mental spine/genial tubercle

46
Q

function/action of geniohyoid muscle

A
  • if the hyoid bone is fixed:
  • > jaw opening (and retrusion)/ contracts and pulls jaw open and back
  • if the hyoid bone is not fixed and the geniohyoid muscle contracts it:
  • > raises and brings hyoid bone forwards (this is why hyoid stabilizers/stabilizing muscles are significantly important)
47
Q

innervation of geniohyoid muscle

A

C1 (with hypoglossal)

48
Q

attachments of mylohyoid muscle

A
  • hyoid bone
  • median raphe/mylohyoid line on medial aspect of mandible
  • itself (as it forms the floor of the mouth/FOM)
49
Q

function/action of mylohyoid muscle

A
  • if hyoid bone is fixed:
  • > when mylohyoid contracts it causes jaw opening/pulls mandible down
  • if hyoid bone is not fixed
  • > when the mylohyoid muscle contracts it raises the hyoid bone and the floor of the mouth (FOM)
50
Q

muscle which forms the floor of the mouth (FOM)

A

mylohyoid muscle

51
Q

innervation of the mylohyoid muscle

A

motor root of mandibular division of trigeminal (CNVc motor root) via nerve to mylohyoid which is a branch of the inferior alveolar nerve

52
Q

inferior alveolar nerve

A
  • one of the terminal branches of the mandibular division of trigeminal/CNVc
  • supplies mandibular teeth
  • important for administrating nerve block
53
Q

attachments of anterior belly of digastric

A
  • from digastric fossa (on the inner aspect of the mandible)
  • to the intermediate tendon
  • > attaches to hyoid bone via the fibrous loop that the intermediate tendon runs through
  • the intermediate tendon connects/attaches the anterior belly of digastric muscle (ABD) and the posterior belly of digastric muscle (PBD)
54
Q

function/action of anterior belly of digastric (ABD)

A
  • if the ABD contracts whilst the hyoid bone is fixed:
  • > jaw opening/jaw is pulled open
  • if the ABD contracts when the hyoid bone is not fixed:
  • > it raises the hyoid bone
55
Q

innervation of anterior belly of digastric (ABD)

A

motor root of mandibular division of trigeminal (CNVc motor root) via nerve to mylohyoid which is a branch of the inferior alveolar nerve

56
Q

hyoid stabilizing muscles

A
  • infrahyoids (thyrohyoid, omohyoid, sternohyoid)
  • posterior belly of digastric (PBD)
  • stylohyoid
57
Q

other muscles involved in mastication

A
  • tongue (involved in movement of food from teeth to cheek)
  • orbicularis oris (=oral sphincter, keeps mouth closed and stops food from falling out)
  • buccinators (cheek muscle, helps direct food back to teeth from cheek -> along with the tongue, helps control the bolus of food and direct it to the posterior teeth)
58
Q

sphincter of mouth

A

orbicularis oris

59
Q

sphincter of eye

A

orbicularis oculi

60
Q

buccinator muscle

A
  • cheek muscle
  • helps direct food back to teeth from cheek
  • > along with the tongue, helps control the bolus of food and direct it to the posterior teeth
61
Q

where does trigeminal motor root exit brainstem

A

pons

62
Q

what is the trigeminal motor root fibres carried within

A

mandibular division of trigeminal (CNVc)

63
Q

where does the mandibular division of trigeminal nerve exit skull/cranial cavity

A

foramen ovale

64
Q

what does the mandibular division of trigeminal nerve supply

A
  • muscles involved in mastication:
  • masseter muscle
  • temporalis muscle
  • lateral and medial pterygoids
  • mylohyoid (including ABD/anterior belly of digastric)
  • > also supplies: tensor palatini and tensor tympani
65
Q

summary of masseter muscle (innervation, bilateral action and unilateral action)

A
  • innervation = Vc motor
  • bilateral movement = jaw close, assists protrusion
  • unilateral movement = assists lateral movement
66
Q

summary of temporalis muscle (innervation, bilateral action and unilateral action)

A
  • innervation = Vc motor
  • bilateral movement = jaw close, retrude
  • unilateral movement = retrude
67
Q

summary of medial pterygoid muscle (innervation, bilateral action and unilateral action)

A
  • innervation = Vc motor
  • bilateral movement = jaw close, assists protrusion
  • unilateral movement = lateral excursion
68
Q

summary of lateral pterygoid muscle (innervation, bilateral action and unilateral action)

A
  • innervation = Vc motor
  • bilateral movement = protrude, assist wide opening
  • unilateral movement = lateral excursion
69
Q

what produces the masticatory forces

A

the masticatory muscles

70
Q

physiological masticatory/chewing forces

A
  • 70-150N (N=kg x gravity and gravity is essentially 10 therefore 150N = 15kg) = dentate , this is the reason why biting tongue/cheek causes so much pain
  • 4-55N = edentulous
71
Q

maximum masticatory clenching forces

A
  • 500-700N between molars

- record = 4,345N by a 37 year old male bruxist (teeth grinder) with hypertrophied masseter and temporalis muscles

72
Q

summary of geniohyoid muscle (innervation, action when hyoid is fixed and action when hyoid is not fixed)

A
  • innervation = C1
  • action when hyoid is fixed = jaw open, retrude
  • action when hyoid is not fixed = raise (+forward) hyoid
73
Q

summary of mylohyoid muscle (innervation, action when hyoid is fixed and action when hyoid is not fixed)

A
  • innervation = Vc motor
  • action when hyoid is fixed = jaw open
  • action when hyoid is not fixed = raise hyoid and floor of mouth
74
Q

summary of anterior belly of digastric muscle (innervation, action when hyoid is fixed and action when hyoid is not fixed

A
  • innervation = Vc motor
  • action when hyoid is fixed = jaw open, retrude
  • action when hyoid is not fixed = raise hyoid bone

Anatomy (21 decks)

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