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Muscles of MasticationMuscles of Mastication
Alex ForrestAssociate Professor, Forensic OdontologyForensic Science Research & Innovation Centre, Griffith UniversityConsultant Forensic Odontologist, Queensland Health Forensic and Scientific Services, 39 Kessels Rd, Coopers Plains, Queensland, Australia 4108
Oral Biology
COMMONWEALTH OF AUSTRALIA
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The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may
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Information or excerpts from this material may be used for the purposes of private study, research, criticism or review as permitted under the Act, and
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Do not remove this notice
Learning ObjectivesLearning Objectives
You should be able to explain the embryological origin of the muscles of mastication, and to explain the resulting common
motor nerve supply.
You should be able to explain the various systems by which the muscles of mastication can be classified, and to
demonstrate their ability to differentiate between the major and accessory groups of these muscles.
You should be able to demonstrate knowledge of the origins, insertions and the functions of each of the major muscles
during normal masticatory function.
Muscles of MasticationMuscles of Mastication
As we talk about the muscles of mastication, we will involve ourselves in a discussion about bones, muscles and the
structures that ensure their viability and continued function.
We will be thinking about the functions of these muscles in a dynamic way, and trying to gain an appreciation of their
role in the living, moving head and neck.
Muscles of MasticationMuscles of Mastication
When thinking about anatomy, remember that the bones provide crucial clues to us about the soft tissues. Recall
that the soft tissue structures were there first, and that the bones formed around them.
Recall also that the bones are part of a dynamic system called the musculoskeletal system.
This system is responsive to change. Enlarge the muscles and the bones alter accordingly. Re-attach the muscles
surgically in a different place, and the forces on bones are different following the procedure.
Muscles of MasticationMuscles of Mastication
DefinitionDefinition
The Muscles of Mastication are defined as the muscles immediately concerned with the movements of the
mandible in mastication and speech.
Some texts include the digastric muscle as a muscle of mastication, based on its function, and there are some
arguments in favour of this approach.
Other texts define the muscles based on their nerve supply, and include only the anterior belly of digastric as such a muscle. Many such texts include the mylohyoid
also as a muscle of mastication.
DefinitionDefinition
We will include only the following muscles which are directly responsible for movements of the mandible at the TMJ:
Masseter
Temporalis
Medial Pterygoid
Lateral Pterygoid
DefinitionDefinition
We will include the following muscles as accessory muscles of mastication:
DefinitionDefinition
Digastric
Mylohyoid
MasseterMasseter
The masseter muscle is
quadrilateral in shape, and
consists of three layers which
blend anteriorly.
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 1121
MasseterMasseter
It is covered by a strong layer of fascia
called the parotid fascia. This is derived
from the deep cervical fascia, and is firmly attached to the
surface of the muscle.
MasseterMasseter
Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 451.
The masseter originates from the zygomatic process
and zygomatic arch, and inserts onto the
ramus of the mandible in three layers which leave
distinct oblique marks on the bone.
MasseterMasseter
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 281
It arises from the zygomatic process of the maxilla and lower border of the body of the zygomatic bone,
and anterior two-thirds of the lower border of the zygomatic arch.
MasseterMasseter
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 257.
Copyright A. Forrest
It passes downwards and backwards to insert into the angle and much of the superficial surface
of the ramus of the mandible.
MasseterMasseter
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 281
The Superficial Layer is the largest layer, and arises by a thick aponeurosis from
the zygomatic process of the maxilla and lower border of the body of the zygomatic bone, and anterior two-thirds of the lower
border of the zygomatic arch. Its fibres pass downwards and backwards to insert
into the angle and lower half of the superficial surface of the ramus of the
mandible.
Note that intramuscular tendinous septa in this layer are responsible for ridges on the
bony surface.
MasseterMasseter
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 281
Copyright A. Forrest
The Middle Layer arises from the deep surface of the anterior two-thirds
of the zygomatic arch, and from the lower border of the posterior third.
It inserts on the middle of the ramus of the mandible.
The Deep Layer arises from the deep surface of the zygomatic arch. It
inserts into the upper part of the ramus of the mandible and into the coronoid
process.
MasseterMasseter
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 281
Copyright A. Forrest
The insertions of the separate layers can be seen on the mandible, and are separated by vague oblique lines on
the external surface of the ascending ramus.
You should examine a variety of mandibles, holding them in such a way that light falling across them casts a
shadow from these lines to make them visible.
Do not use a plastic skull for this purpose. A good-quality real skull will be needed.
MasseterMasseter
The masseter is supplied by the masseteric nerve, a motor branch of the anterior trunk of the mandibular
division of V3.
MasseterMasseter
The masseteric nerve passes from the
infratemporal fossa through the posterior part of the mandibular notch
along with the masseteric artery which is a branch of the maxillary artery, and
both then run into the deep surface of the muscle.
MasseterMasseter
Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 455.
Masseter is active during closure, and most active during clenching and during the forceful phase of a
chewing cycle.
It is primarily an elevator of the mandible.
MasseterMasseter
TemporalisTemporalis
The temporalis muscle is covered superficially by the temporal fascia. This is firmly attached
to the superficial surface of the muscle, and indeed the muscle
arises partly from it.
If followed upwards, the fascia attaches along the superior temporal
line.
TemporalisTemporalis
Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 453.
The temporalis muscle is fan-shaped, and originates from the whole of the temporal fossa (except the part formed by the zygomatic bone), and from the deep
surface of the temporalis fascia.
TemporalisTemporalis
Its fibres converge and descend in a tendon which
passes through the gap between the zygomatic arch and the side of the skull, to
insert upon the medial (deep) surface, apex, anterior and
posterior borders of the coronoid process of the
mandible, and the anterior border of the ramus of the
mandible down nearly as far as the third molar.
TemporalisTemporalis
Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 455.
It is supplied by deep temporal branches of the
anterior trunk of V3, passing through the mandibular notch.
The vessels and nerve to masseter pass behind the
tendon of the temporalis.
TemporalisTemporalis
Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 455.
Temporalis is an elevator of the mandible. It is also a retrudor of the mandible.
During closure, the posterior, more horizontal, fibres are the first of the elevators to activate, followed by the
oblique middle group, and then by the anterior vertical group - a wave of contraction starting posteriorly and
ending anteriorly in the muscle.
TemporalisTemporalis
It is not a particularly powerful elevator compared to others, but is nonetheless most important.
It is believed to be functional mainly in the anteroposterior positioning of the mandible, and in the
maintenance of its posture.
TemporalisTemporalis
Lateral PterygoidLateral Pterygoid
This muscle is short and thick,
and arises by two distinct heads.
Lateral PterygoidLateral Pterygoid
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 502.
The upper head originates from the infratemporal
surface of the greater wing of sphenoid, between foramen ovale and the infratemporal crest, and
from the infratemporal crest of the sphenoid (greater
wing).
Lateral PterygoidLateral Pterygoid
Modified from Grays Anatomy, 35th Ed,
Longman, London 1973, p. 268
The lower headoriginates of the lateral surface of
the lateral pterygoid plate of sphenoid.
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 502.
Lateral PterygoidLateral Pterygoid
At their origins, the two heads are
separated by a slight space through which
the buccal nerve passes, and also the
second part of the maxillary artery if it lies deep to lateral
pterygoid.
Lateral PterygoidLateral Pterygoid
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 502.
The fibres of the upper head are
horizontal in direction, pass beneath the
articular eminence, and are attached to
the front of the articular disk of the temporomandibular
joint.
Lateral PterygoidLateral Pterygoid
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 502.
The fibres of the lower head run
upwards, backwards, and slightly outwards,
to attach to a small fossa on the anterior surface of the neck of
the mandibular condyle.
Lateral PterygoidLateral Pterygoid
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 502.
It is generally a depressor muscle. Specifically it is a protrudor. Only a small component of its fibres are angled
enough away from horizontal to produce a depressive action.
Lateral PterygoidLateral Pterygoid
http://www.drjimboyd.com/lateralpteygoidsworktogether.jpg
The lateral pterygoid muscles from both sides acting together protrude the mandible.
One muscle, acting alone on one side, helps pull the condyle forwards, downwards and medially, swinging the mandible to
the opposite side.
Lateral PterygoidLateral Pterygoid
http://www.drjimboyd.com/lateralpteygoidsworktogether.jpg
The muscle is active during the power phase of a chewing cycle, as it exerts control over the anteroposterior position of
the mandible.
Lateral PterygoidLateral Pterygoid
Medial PterygoidMedial Pterygoid
The medial pterygoid is also a thick, quadrilateral
muscle.
It also arises by two heads.
Medial PterygoidMedial Pterygoid
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 502.
The larger arises from the medial surface of the lateral pterygoid plate of the sphenoid bone, and the smaller
from the lateral surface of the
pyramidal process of the palatine bone and the tuberosity of the
maxilla.
Medial PterygoidMedial Pterygoid
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 502.
It inserts onto the lower and posterior parts of
the deep surface of the mandibular ramus, as
far upwards as the mandibular foramen,
and to the deep surface of angle of the
mandible.
Medial PterygoidMedial Pterygoid
Modified from: Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 459.
The medial pterygoid is
supplied by a branch from
the mandibular nerve V3.
Medial PterygoidMedial Pterygoid
Modified from: http://www.drjimboyd.com/TENSaccessibility.html
Medial Pterygoid is an elevator. It becomes highly active towards the end of a closing movement, and even more so
during clenching of the teeth.
In a chewing stroke, it assists in directing the mandible towards the contralateral side.
Medial PterygoidMedial Pterygoid
The masseter and medial pterygoid are active together in protrusive movements, and in lateral mandibular
movements, particularly so in movements towards the opposite side.
In both of these movements they maintain elevation of the anterior part of the mandible, whilst the condyle is
depressed.
Medial PterygoidMedial Pterygoid
Accessory Muscles of Mastication
Accessory Muscles of Mastication
DigastricDigastric
The digastric muscle is so-called because it has two bellies. This is an anatomist’s idea of a joke. They may not get out
much.
DigastricDigastric
Modified from: http://www.drjimboyd.com/TENSaccessibility.html
The muscle stretches between the mastoid
process of the cranium to the mandible at the
chin, and part-way between, it becomes a tendon which passes through a tendinous
pulley attached to the hyoid bone.
DigastricDigastric
Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 455.
Because the hyoid is a mobile bone, not
attached to the skeleton directly at any point, the
action of the digastric can be modified by the
position of the bone, and therefore the position of
the sling, which determines where in space the tendon is.
DigastricDigastric
Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 455.
The posterior belly of the muscle attaches in a
deep notch just medial to the mastoid process on
the temporal bone called the digastric notch.
DigastricDigastric
Modified from Grays Anatomy, 35th Ed, Longman, London 1973, p. 268
The posterior belly runs forward below the
mandible, and often beneath the cover of the superficial belly of
the submandibular gland, it starts to
become tendinous again.
DigastricDigastric
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 1210.
The tendon passes through the pulley which
originates as a thick band of fascia from the
greater cornu of the hyoid bone, and then it starts to form a second
muscle belly.
DigastricDigastric
Clemente CD, Anatomy, A Regional Atlas of the Human Body, Munich, Urban & Shwarzenberg, 1975, Diagram 455.
The anterior belly of the digastric muscle originates from the first branchial arch, and therefore gains its motor supply from the mandibular division of the trigeminal nerve (V3), while the posterior belly originates from the second branchial arch and
therefore is supplied by the Facial Nerve (VII).
DigastricDigastric
The anterior belly attaches to the
mandible on the internal aspect at the
digastric fossa, slightly to the side of the
midline near the base of the mandible,
inferior to the genial tubercles.
DigastricDigastric
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 281
As it passes down towards the fascial sling, the tendon of the posterior belly of the digastric is surrounded by the tendon of the stylohyoid muscle, which splits around it, before attaching
to the hyoid bone slightly forward of the attachment of the digastric sling.
DigastricDigastric
Modified from Grays Anatomy,
35th Ed, Longman,
London 1973, p. 507.
If the hyoid bone is held down by the infrahyoid strap muscles, then contraction of the digastric causes the mandible to be
pulled inferiorly, opening the mouth.
If the mandible is held in the closed position, then the digastric muscles elevate the hyoid and therefore the larynx, as in
swallowing.
It seems that the digastric muscles always work together on both sides, rather than separately, and this makes sense,
given their function.
DigastricDigastric
MylohyoidMylohyoid
The mylohyoid muscles are best thought of as the
muscles forming the floor of the mouth, sometimes better
referred to as the oral diaphragm.
MylohyoidMylohyoid
http://sprojects.mmi.mcgill.ca/larynx/notes/anat/naview072.htm
They form a muscular floor to the
entire oral cavity which suspends the tongue and helps
position it vertically.
MylohyoidMylohyoid
http://sprojects.mmi.mcgill.ca/larynx/notes/anat/naview072.htm
The muscles themselves are
triangular sheets attached along the mylohyoid ridges or
lines of the mandible, and to the anterior part of the body of the hyoid
bone.
MylohyoidMylohyoid
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 281
Because the hyoid bone lies posterior to
the mandible, the muscles meet in front
of the hyoid in the midline in a tendinous raphe which continues all the way forwards to
the mandible.
MylohyoidMylohyoid
Jamieson, EB. Illustrations of Regional Anatomy, Section II. Edinburgh, E & S Livingstone, 8th Ed. P.81.
The digastric muscles attach to the mandible in the digastric fossae
inferior to the mylohyoid, and the geniohyoid muscles attach to the inferior
genial tubercles superiorly to the
mylohyoid.
MylohyoidMylohyoid
Jamieson, EB. Illustrations of Regional Anatomy, Section II. Edinburgh, E & S Livingstone, 8th Ed. P.81.
If you follow the mylohyoid lines forwards to the
midline on the mandible, you will see that the muscle
attaches to the mandible quite highly posteriorly, and
becomes progressively more inferior as one works
forwards, until the mylohyoid lines meet in the
midline, below the genial tubercles and above the
digastric fossae.
MylohyoidMylohyoid
From Grays Anatomy, 35th Ed, Longman, London 1973, p. 281
The mylohyoid muscles also form from the first branchial arch tissue, and therefore they are provided with motor innervation by the mandibular division of the trigeminal
nerve (V3).
MylohyoidMylohyoid
The mylohyoid again has its function determined partly by the position of both the mandible and the hyoid bone.
MylohyoidMylohyoid
Where the mandible is fixed in position, it elevates the hyoid bone on contraction, and also elevates the tongue,
as in the first stage of swallowing.
Elevation of the hyoid bone is also important in closing the laryngeal inlet in swallowing.
If the hyoid bone is held down by the infrahyoid strap muscles, then the mylohyoid causes the mandible to be
depressed, opening the mouth.
MylohyoidMylohyoid
We have briefly described the muscles that control the position of the mandible, separating them into Muscles of
Mastication and Accessory Muscles.
You should correlate their origins and insertions with their functions to try and get a dynamic view of the way in which the position of the mandible is controlled, and integrate this with your knowledge of the movements of which the TMJ is
capable.
ConclusionConclusion
Normal SwallowingNormal Swallowing
In the mouth, the lips, teeth and tongue help prepare the bolus (food mass) for further stages of swallowing.
http://www.mdausa.org/publications/Quest/q64dysphagia.html
Normal SwallowingNormal Swallowing
Access between the nasal cavity and mouth closes as the bolus moves into the pharynx (throat).
http://www.mdausa.org/publications/Quest/q64dysphagia.html
Normal SwallowingNormal Swallowing
The bolus is propelled toward and into the oesophagus as the oesophagus entrance opens and the epiglottis helps guard against access to the lungs.
http://www.mdausa.org/publications/Quest/q64dysphagia.html
Normal SwallowingNormal Swallowing
The airway reopens and the oesophagus entrance closes as muscle contractions move the bolus toward the stomach.
http://www.mdausa.org/publications/Quest/q64dysphagia.html
Learning ObjectivesLearning Objectives
You should be able to explain the embryological origin of the muscles of mastication, and to explain the resulting common
motor nerve supply.
You should be able to explain the various systems by which the muscles of mastication can be classified, and to
demonstrate their ability to differentiate between the major and accessory groups of these muscles.
You should be able to demonstrate knowledge of the origins, insertions and the functions of each of the major muscles
during normal masticatory function.
The End