Muscle physiology and muscles of facial expressions & mastication

MUSCLE PHYSIOLOGY,
MUSCLES OF FACIAL
EXPRESSIONS &
MASTICATION
Dr. KUNAAL AGRAWAL
PG STUDENT
DEPT. OF ORTHODONTICS
GDCRI, BANGALORE
1

CONTENTS
• Introduction
• Classification of muscles
• Functions of muscles
• Anatomy of muscles
• Muscle proteins
• Contraction of muscles
• Embryology of muscles of head
• Muscles of facial expressions
• Muscles of mastication
• Physical examination of muscles of mastication
• Overview of mastication
• Bibliography
2

INTRODUCTION
 Muscles constitute 40-50% of total body weight. Muscular
strength reflects the prime function of muscle i.e. changing
chemical energy into mechanical energy to generate force,
performing work and producing movements.
 In addition, muscle tissue stabilizes the body’s position,
regulates organ volume and also generates heat.
3

CLASSIFICATION OF MUSCLES
• Basis of classification:
• The basis of these classifications is as follows:
1. DEPENDING UPON THE PRESENCE OR ABSENCE OF
STRIATIONS,
2. DEPENDING UPON THE CONTROL, AND
3. DEPENDING UPON THE FUNCTION
4

• Depending upon presence or absence of striations:
 Under this, the muscles are divided into two groups namely,
 STRIATED MUSCLE
 NON STRIATED MUSCLE
STRIATED MUSCLE
 Under light microscope, in each muscle cell, a large number of cross
striations (transverse lines) are seen at regular interval.
 Skeletal and cardiac muscles are striated.
NON-STRIATED MUSCLE
 The muscle without cross striations are called non striated muscle or
muscle.
 Eg. Smooth muscles.
5

• Depending upon control:
 VOLUNTARY MUSCLE, AND
 INVOLUNTARY MUSCLE
VOLUNTARY MUSCLE
 They are innervated by neurons that are part of the somatic division of
nervous system.
E.g. Skeletal muscles
INVOLUNTARY MUSCLE
 Their action is involuntary, either by autonomic nervous system or by
hormones selected by the endocrine system.
E.g. Cardiac and smooth muscles, and some skeletal muscles like
which cause contraction and relaxation of the diaphragm.
6

• Depending upon function:
 SKELETAL MUSCLE,
 CARDIAC MUSCLE, AND
 SMOOTH MUSCLE
SKELETAL MUSCLE
 These muscles are in association with bones forming the skeletal
 They constitute 40% of body mass.
 These are about 600 skeletal muscles identified.
7

CARDIAC MUSCLE
 This muscle group forms the musculature of the heart.
SMOOTH MUSCLE
 These are the muscles, which are in association with viscera.
 So they are also called visceral muscles.
 They form the contractile units of walls of the various visceral organs and
are present in the following structures like:
 Walls of organs of G.I.T. like oesophagus, stomach and intestine.
 Ducts of digestive glands.
 Trachea, bronchial tube and alveolar ducts of respiratory tract.
 Walls of the blood vessels.
8

FUNCTIONS OF MUSCLES
 Through sustained contraction or alternating contractions and
relaxations, muscle tissue has five key functions:
1. Producing body movements
2. Stabilizing body positions
3. Regulating organ volume
4. Producing heat
5. Moving substances within the body
9

• Producing body movements:
• Total body movements such as walking and running, and
movements such as nodding the head, rely on the integrated
of bones, joints and skeletal muscles.
• Stabilizing body position:
 Skeletal muscle contractions stabilize joints and help maintain
positions like standing or sitting.
 Postural muscles contract continuously when a person is
E.g. Sustained contractions in neck muscles hold the head
10

• Regulating organ volume:
 Sustained contractions of ring-like bands of smooth
(sphincters) may prevents outflow of the contents of a
organ.
E.g. Temporary storage of food in the stomach or urine in
urinary bladder.
• Producing heat:
 As muscle tissue contracts, it also produces heat.
 Much of this heat is used to maintain body temperature.
11

• Moving substances within the body:
 Cardiac muscle contractions pump blood through the blood
 Skeletal muscle contractions promote flow of lymph and aid
return of blood to the heart.
 Smooth muscle contractions moves food and substances such
and enzymes through the G.I.T.
 Contraction and relaxation of smooth muscles in the walls of
vessels help adjust their diameter and thus regulate the rate of
flow.
12

CONNECTIVE TISSUE COMPONENTS:
 Connective tissue surrounds muscle fibers and whole muscles.
 FASCIA  sheet or broad band of fibrous connective tissue which is
the skin and surrounds muscles and other organs.
 Superficial fascia or subcutaneous layer – separates muscle from
 It is composed of areolar connective tissue and adipose tissue.
 This provides a pathway for the nerves and blood vessels to enter
muscles.
14

 DEEP FASCIA  is a dense, irregular connective tissue which holds
muscles with similar functions together.
 Allows free movement of muscles at carrier nerves and blood and lymphatic
vessels and fill the spaces between muscles.
 Three layers of connective tissue from deep fascia extend to further protect
and strengthen skeletal muscles.
 EPIMYSIUM  it is the outermost layer encircling the whole muscle.
 PERIMYSIUM  surrounds groups of 10 to 100 or more individual muscle
fibers, separating them into bundles called fascicles. Epimysium and
perimysium are dense irregular connective tissue.
15

 ENDOMYSIUM  a thin sheath of areolar connective tissue
which penetrates the interior of each fascicle and separates the
individual fibers.
 All these three connective tissue layers may extend beyond the
muscle fibers to form a tendon.
 TENDON  is a cord of dense regular connective tissue that
attaches a muscle to the periosteum of a bone.
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 The plasma membrane of the muscle fiber is called as
“sarcolemma”.
 The multiple nuclei of a skeletal muscle fiber are located just
beneath the sarcolemma.
 Sarcolemma consists of thousands of tiny invaginations from the
surface towards the center of each muscle fiber, called as “T
(transverse) tubules”.
 T-tubules are open to the outside of the fiber and thus are filled with
extracellular fluid.
 Muscle action potentials propagate along the sarcolemma and
through the T-tubules spreading throughout the muscle fiber.
18

 SARCOPLASM, the cytoplasm of a muscle fiber is present within the
sarcolemma.
 Sarcoplasm consists of large amount of glycogen which is used for ATP
synthesis. At also contains myoglobin, a red colored oxygen binding protein,
found only in muscle fibers.
 MITOCHONDRIA lie in rows throughout the muscle fiber.
 MYOFIBRILS which are the contractile elements of the skeletal muscle are
present in the sarcoplasm and are seen under high magnification.
 Myofibrils are about 2 m in diameter and extend through the entire length of
the muscle fiber.
 Prominent striations of these myofibrils gives the muscle its striated appearance.
20

 SARCOPLASMIC RETICULUM or the fluid filled system of
membranous sacs encircles each myofibril.
 This is similar to endoplasmic reticulum in non-muscle cells.
 Dilated end sacs of the sarcoplasmic reticulum are called terminal
cisternae which butt against T-tubules from both sides.
 This SR stores the Ca2+ ions. Muscle contraction occurs if these Ca2+
ions are released from the terminal cisternae.
 Within myofibrils are two types of even smaller structures called
filaments.
 They are only 1-2 m long.
21

 When the muscle is in resting position, the length of the
sarcomeres is 2m.
 Sarcomeres are separated from one another by a plate-shaped
region of dense material called Z-disc.
 Actin and myosin filaments are interdigitated partially, thus
filament causes the myofibril to have alternate dark and light
bands.
22

 The light band contains actin filaments and are called I-bands
because they are isotropic to the polarized light.
 The dark band contains myosin filaments and ends of actin
filaments, where they overlap the myosin, are called dark bands or A-
bands.
 This band is anisotropic to polarized light.
 A narrow H-zone in the center of the each A-band contains thick
filaments.
 M-line is present in the center of the sarcomere, holding the thick
filaments together with the help of supporting proteins.
23

MUSCLE PROTEINS
 Myofibrils are made up of three kinds of proteins.
 Contractile proteins
 Generates force during contraction.
 Regulatory proteins
 Regulates the process of contraction.
 Structural proteins
 Keep the filaments in alignment, give the myofibril its elasticity and
extensibility, link the myofibrils to the sarcolemma and extracellular
matrix.
27

1. Contractile Proteins
• MYOSIN:
 Functions as a motor protein in all the three types of muscles.
 300 molecules of myosin forms a single thick filament.
 The myosin molecule is composed of six polypeptide chains,
heavy chains each with a molecular weight of about 200,000
light chains with molecular weight of about 20,000 each.
 Two heavy chains wrap spirally around each other to form a
helix, which is called the tail of the myosin molecule.
 One end of each of these chains is folded into a globular
structure called the myosin head.
28

 These heads lie side by side at one end.
 The 4 light chains are also parts of the myosin heads, two for each head.
 Part of each myosin molecule hangs to the side along with the head, thus
providing an arm that extends the head outward from the body.
 The protruding arms and heads together are called cross-bridges.
 Each cross-bridge is flexible and is attached to the myosin filament with the
help of hinges.
 This hinged arm allows the head to be extended far outwards from the body
of the myosin filament or to be brought close to the body.
 Thus it helps in contraction process.
29

• ACTIN:
 Actin is the main component of the thin filament.
 Actin filament is a double-stranded F-actin protein molecule,
is 1 micrometer long.
 Each strand of F-actin helix is composed of polymerized G-
molecules with molecular weight of about 42,000.
 There are 13 molecules in each revolution of each strand of
 One molecule of ADP is attached to one G-actin molecule
the active site on actin myosin filament where the cross-bridges
myosin filament interact to cause muscle contraction.
31

2. Regulatory Proteins
• TROPOMYOSIN:
 Tropomyosin, a regulatory protein, is present on the actin
 Its molecular weight is 70,000; length is 40nm.
 Tropomyosin molecules are wrapped around the sides of the
helix.
 When the muscle is resting, the tropomyosin molecules lie on
the active sites of the actin filament, and does not allow the
filament to bind with the actin filament and thus not allowing the
contraction to occur.
33

• TROPONIN:
 Troponin molecules are attached along the sides of the
tropomyosin molecules.
 Troponin is made up of three subunits
 Troponin I – strong affinity for actin
 Troponin T – strong affinity for tropomyosin
 Troponin C – strong affinity for calcium ions.
 This complex helps in attachment of tropomyosin to
 The affinity for Ca2+ ions initiates the contraction process.
34

3. Structural Proteins
• TITIN:
 It is the third most plentiful protein after actin and myosin in
muscle.
 Titin anchors a thick filament to both, Z-disc and the M-line,
helps in stabilizing the position of the thick filament.
 It extends from Z-disc to the beginning of thick filaments.
 It can stretch atleast 4 times its resting length and then spring
unharmed.
 Thus it helps in elasticity and extensibility of myofibrils.
36

• MYOMESIN:
 This forms the M-line in the middle of the sarcomeres.
 This binds to titin and also connects adjacent thick filaments to one
• NEBULIN:
 It is a large but inelastic protein and lies alongside the thin filament.
 It is also attached to the Z-disc.
 It helps maintain alignment of thin filaments in the sarcomeres.
• DYSTROPHIN:
 It is a cytoskeletal protein that links thin filaments of the sarcomeres to
membrane proteins of the sarcolemma.
 Dystrophin reinforces the sarcolemma and helps transmit the tension
by sarcomeres to the tendon.
37

CONTRACTION OF MUSCLES
 In the mid 1950’s, Jean Hanson and Hurdey had a revolutionary
insight into the mechanism of muscle contraction.
 They examined the first electron micrographs of skeletal muscle and
found that the length of the thick and thin filaments were the same in
both relaxed and the contracted muscle.
 Later on, the researches discovered that skeletal muscle shortens
during contraction because the thick and thin filaments slide past one
another.
 This model, which describes the contraction of muscle, is known as
the sliding filament mechanism.
38

The Contraction Cycle
 At the onset of contraction, the sarcoplasmic reticulum releases Ca2+
ions which bind to Troponin.
 This moves the Troponin-Tropomyosin complexes away from the
myosin binding sites on actin. When these sites are free, the
contraction cycle occurs that causes the filaments to slide.
 This contractions cycle occurs in four steps:
I. ATP Hydrolysis
II. Attachment of myosin to actin to form cross-bridges
III. Power stroke
IV. Detachment of myosin from actin
39

Action potential through motor nerve fiber
AXON TERMINAL
Opening of voltage gated
calcium channels
Entry of calcium ions
from ECF
Opening of vesicles
and release of ACh
SYNAPTIC
CLEFT
Passage of
ACh
44

POSTSYNAPTIC MEMBRANE
Binding of Ach with receptors and formation of
Ach-receptor complex
Opening of ligand gated sodium
channels and entry of Na+ from ECF
Development of end-plate
potential
MUSCLE FIBRE
Generation of action
potential
Excitation-
contraction
coupling
Muscular
contraction
45

EMBRYOLOGY OF MUSCLES OF
HEAD - Mesodermal
MESODERM
Lateral Part Intermediate Part
Forms wall of
Visceral organs
Paraxial Mesoderm
SomitesContribute to the
formation of
Visceral organs
Somitomeres
46

Somitomeres
• Also called pre-occipital / preotic somites
• The paraxial mesoderm, along the side of the notochord,
forms a rostral condensation of incomplete segments
• Supplied by III, IV and VI cranial nerves
• 1 to 7 in number
Somites
• Paraxial mesoderm, divides caudally into a series of
segmental blocks
47

SOMITES
Occipital
Somites
Cervical Somites
Intermediate
Part
Forms muscles
of tongue
Ventro-Medial
Part
Lateral Part
Known as
Myotomes
Known as
Dermotomes
Known as
Sclerotomes
Dermis of
the skin
Muscles of
orofacial region
Surrounds the Neural
tube and forms the
vertebral column
48

1st & 2nd
Somitomers
Four extrinsic ocular
muscles (Superior,
medial, inferior rectus &
inferior oblique)
Oculomoter nerve
(3rd cranial nerve)
3rd Somitomers Superior oblique
(Extrinsic ocular muscle)
Trochlear Nerve
(4th cranial nerve)
4th Somitomers
with 1st branchial
arch
Muscles of mastication
(Masseter, Temporalis,
Medial & Lateral
Pterygoid)
Trigeminal nerve (5th
cranial nerve)
5th Somitomers Lateral rectus (Extrinsic
ocular muscle)
Abducent nerve
(6th cranial nerve)
6th Somitomers
with 2nd branchial
arch
Muscles of facial
expression
Facial nerve (7th
cranial nerve)
49

7th Somitomers
with 3rd branchial
arch
Stylopharyngeus muscle Glossopharyngeal
nerve (9th cranial
nerve)
1st, 2nd, 3rd & 4th
Occipital Somites
with 4th, 5th & 6th
branchial arches
Extinsic & intrinsic
laryngeal muscles
Vagal and spinal
accessory nerve (10th
& 11th cranial nerve)
1st, 2nd, 3rd & 4th
Occipital Somites
Intrinsic and extrinsic
tongue muscles
Hypoglossal nerve
(12th cranial nerve)
3rd, 4th, 5th, 6th &
7th Occipital
Somites
Sternocleidomastoid and
trapezius
Spinal accessory
(11th cranial nerve)
50

MUSCLES OF FACIAL EXPRESSIONS
• A group of muscles in head have in common their
superficial arrangement & especially their attachment to,
or their influence on, the skin.
• Muscles can be divided into several groups.
• Embryologically – from mesoderm of 2nd branchial arch.
• Topographically –
• Scalp muscles
• Auricle muscles
• Eyelids muscles
• Nose muscles
• Muscles around mouth
• Neck muscles
51

1. Platysma
• Origin: Upper parts of pectoral & deltoid fasciae. Fibers
run upwards & medially.
• Insertion: Anterior fibers to base of the mandible.
Posterior fibers to skin of lower face & lip.
• Nerve supply: Facial nerve
• Actions:
• It releases pressure of skin on subjacent veins.
• Depresses mandible.
• It pulls angle of mouth downwards as in horror or surprise.
53

2. Levator Labii Superioris (Quadratus)
• Origin: Maxillary body in a line paralleling the infraorbital
margin & slightly below it.
• Insertion: In an area below nasolabial sulcus.
• Nerve supply: Facial nerve.
• Action: Elevator of upper lip & raises the corner of the
mouth.
55

3. Levator Labii Superioris Alaeque Nasi
• Origin: Frontal process of maxilla at the level of medial
palpebral ligament.
• Insertion: Into skin of wing of nose into upper lip (close to
philtrum) interweaving with orbicularis oris.
• Action: Elevates the upper lip & nasal wing.
57

4. Zygomaticus Minor
• Origin: Height of zygomatic bone in front of origin of major
zygomatic muscle. It courses medially & downwards.
• Insertion: Fibers overlap to variable degree, those which
elevate the upper lip & end in skin of upper lip at a
variable distance from midline.
• Actions:
• Elevates upper lip.
• The three muscles, levator labii superioris, levator labii
superioris alaeque nasi and zygomaticus minor, together
form three heads of quadratus labii superioris.
59

5. Zygomaticus Major
• Origin: Behind that of zygomaticus minor muscle,
temporal process of zygomatic bone. It runs downward &
forward.
• Insertion: Corner of mouth, where it is divided by caninus
muscle into superficial & deep part.
• Actions: Pulls corner of the mouth upward & laterally.
• Posed or Social smile (reasonably reproducible and is the
one that is presented to the world routinely). Focus of
attention in orthodontic diagnosis.
61

6. Risorius
• Origin: Fascia of masseter muscle behind its anterior
border. It is directed horizontally.
• Insertion: Muscle is triangular in shape. It is inserted
lateral to corner of the mouth, most of the fibers pass into
tendinous node (modiolus), partly interlacing with fibers of
other muscles.
• Nerve supply: Facial nerve
• Action: Pulls the corner of the mouth laterally, as in
grinning.
• Enjoyment smile (or Duchenne smile, varies with emotion
being displayed)
63

7. Levator Anguli Oris (Caninus)
• Origin: On anterior surface of maxillary body from canine
fossa below infraorbital foramen. It is directed downward
& laterally.
• Insertion: Above & lateral to corner of the mouth. Fibers
enter tendinous node (modiolus) after crossing & often
dividing zygomaticus major muscle.
• Action: Elevates corner of the mouth & pulls it medially.
64

8. Depressor Anguli Oris (Triangularis)
• Origin: Outer surface, above the lower border of mandible
& just above the line to which fibers of platysma are
attached.
• Insertion: Muscle forms triangular plate with its posterior
border ascending vertically to the corner of mouth & its
anterior border can be followed obliquely upward &
backward.
• Action: Pulls corner of the mouth downwards and laterally.
66

9. Depressor Labii Inferioris
• Origin: Uppermost level of rough line that serves as the
attachment of platysma & triangularis muscle. It is
directed upwards & medially.
• Insertion: Skin of lower lip above mentolabial fold, skin of
chin & mucous membrane of lower lip.
• Action: Pulls the lower lip downward & laterally.
68

10. Mentalis
• Origin: Mental fossa.
• Insertion: Fibers interlace with those of contralateral
muscle, after crossing midline, in the skin of the chin. Only
lateral fibers insert in skin of the same side.
• Action: Elevates skin of chin, lift & roll of lower lip
outwards, renders lower vestibule shallow on contraction.
• Hyperactive Mentalis – Class II Division 1 malocclusion.
• Deep mentolabial sulcus.
70

11. Buccinator
• Origin: Upper fibers from maxilla opposite molar teeth,
lower fibers from mandible, opposite molar teeth, middle
fibers from pterygomandibular raphe.
• Insertion: Upper fibers to upper lip, lower fibers to lower
lip & middle fibers decussate before passing to the lips.
• Actions:
• It flattens the cheek against gums & teeth.
• It prevents the accumulation of food in vestibule, pulls the
corner of mouth laterally & posteriorly.
• It maintains the necessary tension of cheek so that cheek is
prevented from folding & bitten by teeth.
72

THE BUCCINATOR
MECHANISM:
• Force exerted by the lip
musculature anteriorly and
buccinator, and muscles of
the cheek posteriorly is
counteracted by the force
exerted by the tongue. Thus
balanced force is
transmitted to the teeth and
supporting bone.
• Superior Constrictor
Muscle
• Buccinator Muscle
• Orbicularis Oris
74

THE NEUTRAL ZONE
CONCEPT:
• Buccinator mechanism is
like a continuous band of
muscles that encircles the
dentition and is anchored
by the pharyngeal tubercle.
• Opposing this mechanism
is a powerful muscle, the
tongue.
• These two muscles act in
opposite direction and
maintain the position of the
teeth.
75

THE TRIANGULAR FORCE
CONCEPT:
• The three major groups of
muscles affecting occlusion
during the act of
swallowing are:
• The Tongue
• Masseter and Buccinator
• The Orbicularis Oris
76

12. Orbicularis Oris
• Origin: It is divided into 2 main
parts, the extrinsic part & the
intrinsic part.
• Extrinsic part:
Thickest middle stratum from
buccinator.
Superficial stratum from elevator &
depressor of angle of the lips.
• Intrinsic part:
Deepest stratum
Superior incisivus – from maxilla
Inferior incisivus – from mandible
• Insertion: Angle of the mouth.
• Action: Closes & purses the mouth.
77

13. Nasalis
• Origin: Alveolar eminence of lateral incisor & canine of
upper jaw.
• Insertion: The fibers diverge upwards & medially toward
wing of nose:
• Alar part or inferior part
• Transverse part
• Action: Transverse part compresses the nasal aperture &
alar part dilates it.
• Atrophied in chronic mouth breathers.
78

14. Orbicularis Oculi
• Origin:
Orbital part: Medial part of medial palpebral ligament &
adjoining bone
Palpebral part: Lateral part of medial palpebral ligament
Lacrimal part: Lacrimal fascia & lacrimal bone
• Insertion:
Orbital part forms concentric rings & returns to the point of
origin.
Palpebral part into the lateral palpebral raphe.
Lacrimal part into upper & lower tarsi.
• Actions:
• Orbital part closes lids tightly.
• Palpebral part closes lids gently.
• Lacrimal part dilates lacrimal sac.
80

15. Corrugator Supercilli
• Origin: Medial end of supercilli arch.
• Insertion: Skin of middle of the eyebrow.
• Action: Vertical wrinkling of forehead, frowning.
82
16. Procerus
• Origin: Nasal bone close to midline, it runs straight & upwards.
• Insertion: In skin of head & forehead in glabellar region.
• Action: Depresses middle wider part of the skin over bridge of
nose.

17. Frontalis
• Origin: Anterior border of galea aponeurotica.
• Insertion: Skin of eyebrow & root of nose. Many of its
fibers interlace with the fibers of adjacent muscles.
• Action: It produces horizontal wrinkles of the forehead.
84
18. Depressor Septi
• Origin: Mucosa above the central incisor.
• Insertion: Mobile part of the nasal septum.
• Action: Assists alar part in dilating nasal aperture during
deep inspiration.

MUSCLES OF MASTICATION
• EMBRYOLOGY: 1st
Pharyngeal Arch
• INNERVATION: Mandibular
nerve (a branch of
Trigeminal Nerve, Cranial
Nerve V) and its supplying
branches
• Mandibular Nerve
branches have
proprioceptive fibers,
helping in correct NM co-
ordination involved in
correct timings of
mandibular movements
86

The Masticatory Apparatus
• Maxilla, Mandible, Teeth, Muscles and Ligaments of mandible
• Masticatory somatic functions voluntarily controlled
• PRIMARY MUSCLES:
1. Masseter
2. Temporalis
3. Pterygoideus Externus (Lateral Pterygoid)
4. Pterygoideus Internus (Medial Pterygoid)
• SECONDARY MUSCLES:
1. Digastric
2. Mylohyoid
3. Geniohyoid
Suprahyoid group of muscles,
antagonists to the elevators
87

1. The MASSETER
• Strongest, covering a wide
area
• EXTENT: Zygomatic arch to
ramus and body of mandible
• Covered partly by parotid
gland tissue
• 3 layers: Superficial, Middle,
Deep; Superficial largest
• Distinctly distinguished
superficial layer from deeper
layers at posterior upper part
of the muscle
88

• ORIGIN:
1. Superficial layer: A thick aponeurosis from maxillary
process of zygomatic bone and from anterior two-thirds of
inferior border of zygomatic bone
2. Middle layer: Medial aspect of anterior two-thirds of
zygomatic arch and lower border of its posterior one-third
3. Deep layer (or Zygomaticomandibular Muscle): Deep
surface of zygomatic arch
• INSERTION:
1. Superficial layer: Fibers run downwards and
backwards; insert in angle and lower posterior half of
lateral surface of ramus
2. Middle layer: Central part of ramus
3. Deep layer (or Zygomaticomandibular Muscle): Upper
part of the ramus and its coronoid process
89

• VASCULAR SUPPLY:
1. Masseteric branch of 2nd part of Maxillary Artery
2. Facial Artery
3. Transverse Facial Branch of Superficial Temporal Artery
• INNERVATION: Masseteric branch of anterior trunk of
Mandibular nerve
• ACTIONS:
1. Elevation (without contact or resistance) of mandible to
occlude teeth in mastication
2. Minimal effect in side-to-side movements, protraction (with
teeth in occlusion, with pterygoid muscles) and retraction
3. Antagonist to posterior fibers of Temporalis
4. Synergist for Lateral Pterygoid in grinding movements
• SUBMASSETERIC SPACE INFECTIONS: Around mandibular
3rd molar tracks backwards, lateral to ramus. Abscess forms
deep to attachment of masseter in submasseteric tissue space.
Muscle spasm and limited jaw opening. Plus, little visible
swelling
91

2. The TEMPORALIS
• Fan shaped, covered by
temporal fascia
• EXTENT: Fills up the temporal
fossa up to inferior temporal
line
• ORIGIN:
From deep surface of
temporal fascia; fibers
converge and descend into a
tendon passing through gap
between zygoma and side of
skull
• INSERTION:
Medial surface, apex, anterior
and posterior borders of
coronoid process and anterior
border of ramus up to 3rd
molar
92

• FIBER DIRECTION:
1. Anterior Fibers: Vertical orientation
2. Intervening Fibers: Intermediate degree of obliquity
3. Posterior Fibers: Almost horizontal
• VASCULAR SUPPLY: Deep Temporal branches from 2nd
part of Maxillary artery
1. Anterior Deep Temporal Artery: 20% muscle anteriorly
2. Middle Deep Temporal Artery: middle 40% muscle
3. Posterior Deep Temporal Artery: 40% muscle
posteriorly
• INNERVATION: Deep Temporal branches of the anterior
trunk of Mandibular Nerve
93

• ACTIONS: Variety of actions owing to differential orientation of
muscle fibers:
1. Principal positioner of mandible during elevation (against
some external resistance)
2. Posterior part retracts the mandible (without occlusal
contact)
3. Anterior part active during clenching (upward pull);
clenching requires both upward and backward pull, because
condylar head rests on articular eminence when the mouth is
open
4. Anterior part acts synergistically with masseter in clenching
5. Posterior part acts antagonistically to masseter in
retracting the jaw
6. Lateral movement of mandible by ipsilateral posterior and
middle fibers
94

3. The PTERYGOIDEUS EXTERNUS
• Short, thick muscle
• Not pennate, unlike other
muscles of mastication, nor
does it have sufficient
number of Golgi Tendon
Organs
• One of the main muscular
components of
infratemporal fossa, along
with some mandibular
ligaments and neuro-
vasculature of the region
• Consists of two parts:
1. Superior or Upper head
2. Inferior or Lower head
95

• ORIGIN:
1. Upper Head: Infratemporal
surface and infratemporal crest of
greater wing of sphenoid bone
2. Lower Head: Lateral surface of
the lateral pterygoid plate (part of
sphenoid bone)
• INSERTION:
1. From the two origins, fibers
converge, and pass backwards and
laterally, to be inserted into a
depression on the front of neck of
mandible (pterygoid fovea)
2. A part of upper head may be
attached to the capsule of
temporomandibular joint and to
anterior and medial borders of
articular disc
96

1. Pterygoid branches from 2nd part of Maxillary Artery
2. Ascending Palatine branch of Facial Artery
• INNERVATION: Branches from anterior trunk of
Mandibular Nerve
1. Buccal nerve branch: Upper head and lateral part of
lower head
2. Medial part of lower head receives a branch directly
from anterior trunk of Mandibular Nerve
97

• ACTIONS:
1. Superior head: Jaw closing movements, stabilizes
condylar head and disc against articular eminence during
jaw closing
2. Inferior head: Jaw opening and protrusion, assists in
translation of condyle downward, anteriorly and
contralaterally during jaw opening
3. Anatomically suited for protraction, depression and
contralateral abduction
4. Jaw rotates about a vertical axis passing through
opposite condyle and is pulled medially towards opposite
side, if one muscle of one side contracts. This, plus
adjacent medial pterygoid provides strong medially
directed force, used for grinding food between teeth of the
ipsilateral side
5. Contralateral muscle initiates a lateral transversion
98

4. The PTERYGOIDEUS INTERNUS
• Thick, quadrilateral muscle
• One of the main muscular
components of
infratemporal fossa, along
with some mandibular
ligaments and neuro-
vasculature of the region
99

• ORIGIN: Two heads of origin:
1. Deep Head: Medial surface of lateral pterygoid plate of
sphenoid bone; deep to lower head of lateral pterygoid
2. Superficial Head: Maxillary tuberosity and pyramidal
process of palatine bone; lies on lower head of lateral pterygoid
• INSERTION:
Fibers descend postero-laterally and are attached by a strong
tendinous lamina to postero-inferior part of the medial surface
of ramus and angle of mandible, as high as mandibular
foramen and as far forwards as mylohyoid groove
• VASCULAR SUPPLY: Pterygoid branches of 2nd part of the
Maxillary Artery
• INNERVATION: Medial Pterygoid branch of main trunk of
Mandibular Nerve
100

• ACTIONS:
1. Elevates the mandible (against resistance)
2. When acting in synchrony with lateral pterygoid, it
protrudes the mandible against external resistance
3. Movement to left side against resistance and with
occlusal contact by contralateral contraction of medial
pterygoid and masseter
4. Alternating contractions help in side-to-side
movements helping in trituration of the food
• PTERYGOSPINOUS LIGAMENT:
Stretches between spine of sphenoid and posterior border
of lateral pterygoid plate near its upper end. Sometimes
ossified, completing a foramen, which transmits branches
of mandibular nerve to respective muscles
102

1. The DIGASTRIC
• Main muscular component of Digastric triangle of Anterior
triangle of the neck
• Two parts:
1. Anterior Belly: From 1st pharyngeal arch, so
innervated by branch to Mylohyoid, given off by Inferior
Alveolar Nerve just prior to its entry into the mandibular
foramen; a branch of Mandibular nerve (VIII). Attaches at
lower border of mandible near midline
2. Posterior Belly: From 2nd pharyngeal arch, so
innervated by Digastric branch of Facial Nerve (VII).
Attaches at anterior border and lateral surface of mastoid
process of temporal bone of the skull
103

• A tendon between two parts; attached by a loop-like strip
of cervical fascia to hyoid
1. Anterior Belly: Submental branch of facial artery
2. Posterior Belly: Posterior auricular and occipital
arteries
• ACTIONS:
1. Depresses mandible when hyoid is fixed
2. Elevates hyoid when mandible is fixed
3. Posterior belly active during deglutition and
mastication
104

2. The GENIOHYOID
• Superior to Mylohyoid and adjacent to midline
• ORIGIN: Mental spine and inferior genial tubercles on
posterior aspect of symphysis menti
• INSERTION: Anterior surface of hyoid
• VASCULAR SUPPLY: Sublingual branch of Lingual Artery
• INNERVATION: C1, C2 through hypoglossal nerve
• ACTIONS:
1. When mandible is fixed, hyoid drawn forward and upward
2. When hyoid is fixed, mandible is depressed
105

3. The MYLOHYOID
• Muscle forming floor of oral cavity, triangular
• ORIGIN: Mylohyoid line of mandible, from symphysis to
last molar region
• INSERTION:
1. Anterior and Middle fibers decussate in median
fibrous raphe (from symphysis menti to hyoid)
2. Posterior fibers in front of body of hyoid
1. Sublingual branch of Lingual Artery
2. Mylohyoid branch of Inferior Alveolar Artery
3. Submental branch of Facial Artery
107

• INNERVATION: Mylohyoid branch of Inferior Alveolar
Nerve of Mandibular Nerve (VIII)
• ACTIONS:
1. Elevates floor of mouth in 1st stage of deglutition
2. Elevates hyoid and depresses mandible
108

4. The SPHENOMANDIBULAR
LIGAMENT
• Recently added as 5th
muscle of mastication
• Accessory ligament of TMJ
• ORIGIN: From spine of
sphenoid bone
• INSERTION: Lingula of
mandible
• Vestige of the dorsal end of
Meckel's cartilage
• ACTION: Stabilizes the
mandible during maximum
protrusion and retrusion
109

PHYSICAL EXAMINATION OF
MUSCLES OF MASTICATION
• The condition that brings about compromise or unhealthy
muscle tissue may be muscle overuse or physical trauma
such as overstretching or receiving a blow to the muscle
tissue itself.
• Increased muscle tonicity or hyperactivity, can lead to a
decrease in blood flow to the muscle tissues, lowering the
inflow of nutrient substances needed for normal cell
function while accumulating metabolic waste products.
• This accumulation of metabolic waste products and of
other algogenic substances is thought to cause the
muscle pain.
110

• In its early stages myalgia is noticed only during function
of the muscle. If sustained hyperactivity continues, it can
be long lasting and result in dull aching pain that often
radiates over the entire muscle.
• The muscle can be examined by direct palpation or by
functional manipulation.
111

Muscle Palpation
• A widely accepted method of determining muscle tenderness
and pain is by digital palpation. A healthy muscle does not elicit
sensations of tenderness or pain when palpated. Deformation
of compromised muscle tissue by palpation can elicit pain.
• Therefore if a patient reports discomfort during palpation of a
specific muscle, it can be deduced that the muscle tissue has
been compromised by either trauma or fatigue.
• Palpation of the muscle is accomplished mainly by the palmar
surface of the middle finger, with the index finger and forefinger
testing the adjacent areas. Soft but firm pressure is applied to
the designated muscles, with the fingers compressing the
adjacent tissues in a small circular motion. A single firm thrust
of 1 or 2 seconds’ duration is usually better than several light
thrusts.
112

• When a muscle is palpated, the patient’s response is
placed in one of four categories:
• A zero (0) is recorded when the muscle is palpated and there is no
pain or tenderness reported by the patient.
• A number 1 is recorded if the patient responds that the palpation is
uncomfortable (tenderness or soreness).
• A number 2 is recorded if the patient experiences definite
discomfort or pain.
• A number 3 is recorded if the patient shows evasive action or eye
tearing or verbalizes a desire not to have the area palpated again.
• A thorough muscle examination should identify not only
generalized muscle tenderness and pain but also the
small hypersensitive trigger points associated with
myofascial pain.
• To locate trigger points, the examiner palpates the entire
body of each muscle.
113

1. The Temporalis
• The temporalis is divided into three functional areas, and
therefore each area is independently palpated.
• The anterior region is palpated above the zygomatic arch and
anterior to the TMJ (fibers run vertically)
• The middle region is palpated directly above the TMJ and superior
to the zygomatic arch (fibers run obliquely)
• The posterior region is palpated above and behind the ear (fibers
run horizontally)
114

• When evaluating the
temporalis muscle, it is also
important to palpate its
tendon.
• The tendon of the
temporalis is palpated by
placing the finger of one
hand intraorally on the
anterior border of the ramus
and the finger of the other
hand extraorally on the
same area. The intraoral
finger is moved up the
anterior border of the ramus
until the coronoid process
and the tendon are
palpated.
116

2. The Masseter
• The masseter is palpated bilaterally at its superior and
inferior attachments.
• First, the fingers are placed on each zygomatic arch (just
anterior to the TMJ).
• They are then dropped down slightly to the portion of the
masseter attached to the zygomatic arch, just anterior to
the joint.
• Once this portion (the deep masseter) has been palpated,
the fingers drop to the inferior attachment on the inferior
border of the ramus.
• The area of palpation is directly above the attachment of
the body of the masseter (i.e., the superficial masseter).
117

118
Palpation of the masseter muscles at
their superior attachment to the
zygomatic arches
Palpation of the superficial masseter
muscles near the lower border of
the mandible

Functional Manipulation
• Three muscles that are basic to jaw movement but impossible or
nearly impossible to palpate are the inferior lateral pterygoid,
superior lateral pterygoid, and medial pterygoid.
• Although the medial pterygoid can be palpated by placing the
finger in the lateral aspect of the pharyngeal wall of the throat, this
palpation is difficult and sometimes uncomfortable for the patient.
• Principle of Functional Manipulation: as a muscle becomes
fatigued and symptomatic, further function only elicits pain.
• Thus a muscle that is compromised by excessive activity is painful
both during contraction and when being stretched.
• During functional manipulation each muscle is contracted and then
stretched. If the muscle is a true source of pain, both activities will
increase the pain.
119

1. The Inferior Lateral Pterygoid
• Contraction:
• By having the patient make a
protrusive movement because
this muscle is the primary
protruding muscle.
• It is also active during opening,
but so are other muscles, which
adds confusion to the findings.
• The most effective manipulation
therefore is to have the patient
protrude against resistance
provided by the examiner.
• If the inferior lateral pterygoid is
the source of pain, this activity
will increase the pain.
120

• Stretching:
• The inferior lateral pterygoid stretches when the teeth are in
maximum intercuspation.
• Therefore if it is the source of pain when the teeth are clenched, the
pain will increase.
• When a tongue blade is placed between the posterior teeth, the
intercuspal position (ICP) cannot be reached and therefore the
inferior lateral pterygoid does not fully stretch.
• Consequently, biting on a separator does not increase the pain but
may even decrease or eliminate it.
• The Pterygoid Reflex
121

2. The Superior Lateral Pterygoid
• Contraction:
• It contracts especially during
a power stroke (clenching).
• Therefore if it is the source of
pain, clenching will increase
the pain.
• If a tongue blade is placed
between the posterior teeth
bilaterally and the patient
clenches on the separator,
pain again increases with
contraction of the superior
lateral pterygoid.
122

• Stretching:
• As with the inferior lateral pterygoid, stretching of the superior
lateral pterygoid occurs at maximum intercuspation.
• Therefore stretching and contracting of this muscle occur during the
same activity, clenching.
• If the superior lateral pterygoid is the source of pain, clenching will
increase it.
• Superior lateral pterygoid pain can be differentiated from elevator
pain by having the patient open wide. This will stretch the elevator
muscles but not the superior lateral pterygoid.
• If opening elicits no pain, then the pain of clenching is from the
superior lateral pterygoid.
• If the pain increases during opening, then both the superior lateral
pterygoid and the elevators may be involved.
123

3. The Medial Pterygoid
• Contraction:
• If it is the source of pain,
clenching the teeth together
will increase the pain.
• When a tongue blade is
placed between the posterior
teeth and the patient
clenches against it, the pain
is still increased because the
elevators are still contracting.
• Stretching:
• If it is the source of pain,
opening the mouth wide will
increase pain.
124

OVERVIEW OF MASTICATION
• DEFINITION: Process in
which ingested food is
cut/crushed into smaller
bits, mixed with saliva and
formed into a bolus in
preparation for deglutition
• An interruption in intraoral
transport process when
the ingested material is not
of a consistency suitable
for further onward
transport
127

• Primary function of teeth,
tongue, jaws and masticatory
muscles
• Possible due to variety of
movements at Temporo-
Mandibular Joint
• Preprogramming
• Combined vertical, lateral,
protrusive and retrusive
movements of mandible form
an ‘envelope of motion’
• Efficiency determined by:
1. Correct occlusal table
2. Masticatory stresses generated
by intercuspal contacts of opposing
teeth
128

CHEWING:
1. Chewing pattern viewed in frontal plane
2. Vertical movement dimensions: 16 to 20 mm
3. Lateral movement dimensions: 3 to 5 mm
4. Chewing cycle duration: 0.6 to 1 sec
5. After complete trituration of bolus, occlusal contacts occur in
centric occlusion
6. Contact gliding seen with each closing and opening
movement
7. Chewing force reaches its peak in centric occlusion and lasts
for 40 to 170 msec
8. Corresponding electromyographic activity of masseter and
temporalis lasts for 41 ± 26 msec
9. Jaw remains stationary in intercuspal position for 100 msec
before next cycle commences
10. A point located between incisal edges of mandibular incisors,
if traced during chewing cycle, exhibits a very complex envelope of
movement in the frontal plane
129

THE CHEWING CYCLE:
Mastication is a repetitive sequence of jaw opening and
closing with a profile in the vertical plane called the
chewing cycle. The human chewing cycle consists of
three phases:
1. Opening phase: The mouth is opened and the
mandible is depressed
2. Closing phase: The mandible is raised towards the
maxilla
3. Occlusal or intercuspal phase: The mandible is
stationary and the teeth from both upper and lower arches
approximate
133

MASTICATION MOTOR PROGRAM:
1. Mastication is primarily an unconscious act, but can
be mediated by higher conscious input. The motor
program for mastication is a hypothesized central nervous
system function by which the complex patterns governing
mastication are created and controlled
2. It is thought that feedback from proprioceptive nerves
in teeth and the temporomandibular joints govern the
creation of neural pathways, which in turn determine the
duration and force of individual muscle activation (and in
some cases, muscle fiber groups as in the masseter and
temporalis)
3. The motor program continuously adapts to changes
in food type or occlusion
134

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