Neuro muscular function saquib/prosthodontic courses

NEURO MUSCULAR
FUNCTION OF MASTICATORY
APPARATUS
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INDIAN DENTAL ACADEMY
Leader in continuing Detal Education

INTRODUCTION
The functions of masticatory systems is complex.
Discriminatory contraction of various head and neck muscle
is necessary to move the mandible precisely and allow effective
functioning. A highly refined neurologic control system regulates
and co-ordinates the activities of entire masticatory system. It
consists primarily of nerves and muscles; hence the term
Neuromuscular system.
A basic understanding of anatomy and functions of
neuromuscular system is essential to understand the influence that
tooth contact and other conditions have on mandibular movement.

Neuromuscular System
The neurologic system The muscle system

Nervous System
It has three basic functions
 Sensory
 Integrative
 Motor
Sensory functions - Nervous system senses changes (stimuli)
both within the body and outside the body.
Integrative functions:- It analysis the sensory information,
stores some of its aspect and make decision for
appropriative behavior.
Motor functions: - It responds to stimuli by musculature
contraction or glandular secretion.

NERVOUS
SYSTEM
DIVISION

PERIPHERAL NERVOUS SYSTEM
A. Somatic nervous system
B. Autonomic nervous system
Sympathetic
Parasympathetic
Somatic Nervous System: - These convey sensory neurons
from cutaneous of head, body wall and extremities to CNS
and motor neurons from CNS conducts to skeletal muscles
only. This is self controlled and hence voluntary.
Autonomic Nervous System:-These convey sensory neurons
from viscera to CNS and motor neurons from CNS conduct
to smooth muscle, cardiac muscle and glands.

NEURON
It is functional
and
anatomical
unit of
nerve.
It has three
parts.
Cell body
Axion
Dendrites

NEUROPHYSIOLOGY
Communication of neurons depend upon two factors
• There is electrical voltage called resting membrane potential
(RMP) across membrane.
• Plasma membrane has variety of ion channels that may close or
open.
Resting membrane potential
There is equal distribution of negative charge just inside the
membrane and positive outside the membrane.
In neurons resting membrane potential ranges from -40 to -90 mV.
A typical value is -70mV.
The minus sign indicates that
the inside is negative to the
outside.
Because of phospholipids
bilayer plasma membrane is
good insulator. www.indiandentalacademy.com

Distribution of ions across plasma membrane
Extra cellular fluid is reaching Na+
& Ca++
and intra cellular fluid
is rich in K+
and Cl-
.
Permeability to K+
is 50-100 times more than that of Na+
in
resting neuron.

ION CHANNEL:
may be :
Voltage gated
Chemical gated
Voltage gated ion channel; responds to direct change in membrane
potential. The presence of voltage gated ion channel in nerve and
muscle plasma membrane of the cell is the property of excitability i.e.
the ability to respond certain stimuli by producing impulse.
Chemical gated ion channel; responds to chemical stimuli such as
neurotransmitters, hormones, ions like H+
and Ca++
.

ION CHANNELS

Action Potential (Impulse)
During action potential two types of voltage, gated channels
open and then close.
1. Opening of Na+
channel (Depolarisation)
2. Opening of K+
channel and
closing of Na+
channel
(Repolirasation)
3. Recovery of
resting
membrane
potential.

Depolarisation
If action potential is above critical level (threshold about –55mV) the
voltage gated channel open.
This leads to activation of Na+
channel & it opens causing Na+
influx
As depolarisation increases the membrane potential changes from
-70mV towards 0, then to +30mV.
Na channel has two gates activation gate and inactivation gate.
Repolarisation
As the action potential peaks, during depolarization to +30mV the
repolarisation begins.
By opening voltage gated K+
channel.
As K+
channel open Na+
channel are closing
The membrane potential thus changes from +30mV to 0 then o -70
mV.
Repolarisation restores resting membrane potential and allows
inactivated Na+
channel to revert to resting stage.www.indiandentalacademy.com

Refractive Period
Period of time were excited cell cannot generate another action
potential is called refractive period.
Absolute Refractive Period
Time period where excited cell cannot generate another action
potential even with very strong stimuli.

Propagation and conduction of nerve

Propagation of conduction
Continuous Conduction:- this is property of unmylinated nerves.
As depolarization increases there is increase in Na= ,influx, this
depolarization opens voltage gated sodium channel at adjacent
patch of membrane.
It is self- propogatory from trigger zone.
2.Saltatory conduction :-
This is the property of mylinated nerves.
Myelin sheath acts as an insulator
Myelin sheath is interrupted at node of Ranvier which has
high density of Na channel
Thus, the impulse appears to jump from node to node to cause
depolarization.

Large
fibres
A fibres Myelinated 5-20µm
thick
12-130
m/s
Medium
fibres
B fibres Myelinated 3-10 µm
thick
15-30
m/s
Small
fibres
C fibres Unmyelinated 0.5-1.5
µm thick
1-4 m/s
TYPES OF NERVE FIBRES

MUSCULAR SYSTEM
Although bones and joints form frame worth of body, they cannot
move by themselves. Motion results from alternate contraction
and relaxation of muscles
Muscles constitute 40-50% body weight.
Function of muscles
 Motion: Movements like walking, running localized movement
example grasping pencil or nodding of head
 Stabilising body position to regulating organ volume
Maintains posture
Prevent outflow of contents of hollow organs
 Thermogenesis: skeletal muscle contract to perform work and
by product is heat. Heat released by muscle maintains body
temperature. www.indiandentalacademy.com

TYPES OF MUSCLES
Skeletal muscle tissue
Primarily attached to bones and move parts of skeletal system.
They are striated muscles because alternate light and dark bands
when seen under microscope
Is voluntary and can be made contract and relax by conscious
control.
Cardiac muscle tissue
Forms most of the heart
It is also striated but is involuntary i.e. its contraction is usually not
under conscious control. It can built it own rhythm and is called
autorhythimicity
Smooth muscle tissue
It is located in walls of hollow internal structures such as blood
vessels, stomach, intestine as well as most other obdominal
organs. It also in skin attached to hair follicle.
Under microscope they are nonstraited or smooth
These are involuntary.

Characteristics of muscle tissues
Excitability: ability to respond to stimuli by producing action
potential.
Contractility: ability of muscle to shorten and thicken thus
generating force to do work. Muscle contract in response to
one or more muscle action potential.
Extensibility: Muscles can be extended without damaging the
tissue
Elasticity: Muscle tends to return to original shape after
contraction or extension.

NEUROMUSCULAR JUNCTIONS
Term neuromuscular junction includes junction
between axion terminal of neuron to motor and plate of
muscle fiber.
Synapses is the contact between two neurons or neurons
and muscle fibers and neurons to grandular cells.
At most synapses a small gap is present called synaptic
gap.
Muscle fiber at the end of axion terminal of neuron is
called motor end plate.
Neurons communicate with motor end plate by releasing
a chemical called neuro transmitter

MICROSCOPIC ANATOMY OF MUSCLE
Functional unit of muscle is muscle fibers
Fibers and arranged parallel to each other having 10-100 µ m. in
diameter and 100 µ m. –30 cms long
Plasma membrane is called sarcolemma and is surrounded by
cytoplasm or sarcoplasm

MYOFIBRILS
Myofibrils are contractile elements of skeletal muscle
They are 1 to 2 µ m. in diameter and contains 3 types of filaments
1. Thick filament: about 16 nm diameter – it has contractile
protein called myosin
2. Thin filament – about 8 nm diameter – it has contractile
protein called as actin
3. Elastic filament: It has protein called as titin – this titin
anchors thick filaments Z discs and thereby helps stabilize
the position of thick filaments.
 Myofibrils in muscles fibers are arranged in compartments
called as sarcomere
 Z line separate one sarcomere from another
 ‘A’ band (dark or anisotropic) extends from one end to other
end of thick band
 I band (Light band) contains thin filamentwww.indiandentalacademy.com

Regulation of contraction of muscle
In 1950 Jean Hanson and Huge Huxley gave mechanism of muscle
contraction by their model known as sliding filament mechanism.

SLIDING FILAMENT MECHANISM OF MUSCLE
CONTRACTION

EVENTS OF CONTRACTION
AND RELAXATION

It is largest cranial nerve
It contains both sensory and motor fibers

It is attached to the lateral part of pons by its two roots – sensory
and motor roots
Sensor root arises from samilunar ganglion located in mickles
cavity.
Sensory roots has three nucleus
Main sensory nucleus
Mesencephalic nucleus arising from mesencephalic
root
Spinal tract nucleus
Motor root origin in motor nucleus which is located in
upper pons
Three large division proceed from convex border of
semilunar ganglion
Ophthalmic division
Maxillary division
Mandibular division

DISTRIBUTION AREAS OF
TRIGEMINAL NERVEwww.indiandentalacademy.com

OPHTHALMIC NERVE
It is first branch of trigeminal nerve
It is sensory nerve
It is the smallest division, it passes forward to enter
orbits through superior orbital fissure. It gives the
following branches
Branches
Lacrimal nerve
Supra orbital branch
Frontal nerve
Supra trochlear branch
Infra trochlear branch
Nasociliary nerve
External nasal branchwww.indiandentalacademy.com

MAXILLARY DIVISION
Maxillary division is entirely sensory in function
Originates: In middle of trigeminal ganglion and continues
forward in lower part of cavernous sinus
It leaves cranial fossa through foramen rotundum and enters
pterygopalatine fossa
From there it enters orbital cavity through inferior orbital fissure,
here it turns laterally in infra orbital groove and emerges on
anterior surface of maxilla through infraorbital foramen.
It supplies
Lower eyelid, side of the nose, upper lip, all maxillary teeth and
gingiva, hard and soft palate part of tonsillar region and pharynx
near opening of auditory tube

It branches in four region
A. Middle cranial fossa
1. Middle meningeal nerve
B. Branch in pterygopalatine fossa
Zygomatico facial nerve
1.Zygomatic nerve
Zygomatico temporal nerve
2.Pterygopalatine nerve
a. Orbital branch
b. Nasal branch
Anterior palatine
c. Palatine branch middle palatine
Posterior palatine
3. Posterior superior alveolar branch

C. Branches in infra orbital groove and canal
1. Anterior superior alveolar nerve (supplying
incisors and canine)
2. Middle superior alveolar nerve (supplying
premolars and mesial root of first molar)
D. Terminal branch of maxillary division
1. Inferior palpable branch
2. Lateral nasal branch
3. Superior labial branch

MANDIBULAR NERVE
This is largest of three divisions of trigeminal nerve.
It has both sensory and motor fibers
Course
Begins in middle cranial fossa through large sensory root and small
motor root
Sensory root arises from lateral part of trigeminal ganglion and
leaves cranial cavity through foramen ovale.
Motor root lies deep to trigeminal ganglion and sensory root. It
also passes through foramen ovale and joint sensory root just below
foramen to form main trunk
After short course, the main trunk divides into small anterior and
large posterior division.

Branches:
1. From main trunk
Meningeal branch
Nerve to medial pterygoid
2. From anterior trunk
Sensory branch: Buccal nerve
Motor branch:
Messeteric nerve
Deep temporal nerve
Nerve to lateral pterygoid
3. Posterior trunk
Auriculotemporal nerve
Lingual nerve
Inferior alveolar nerve
a. Mylohyoid branch
b. Mental branch

Applied anatomy
Motor part of mandibular nerve is tested by asking patient to
clench his teeth, and feel contraction of masseter muscle on
two side
If one masseter is paralyzed jaw deviates to paralyzed side.
Mandibular neuralgia

Peripheral nerve input in spinal cord
Throughout the body first order neurons synapse with second order
neurons in dorsal horn of spinal cord.
Sensory receptor – first order neuron synapses – dorsal horn of
spinal cord – interneurons – second order neurons – cross the spinal
cord to anterior lateral spinothalamic pathway – to higher centers

But face and oral structures do not enter spinal cord, they are
carried by trigeminal nerve directly in brain stem in the region
of pons to synapse in trigeminal nucleus.
Trigeminal nucleus
1. Main sensory nucleus (more rostrally located)
2. Spinal track nucleus (caudally located )
a. Sub nucleus oralis
b. Sub nucleus inter polaris
c. Sub nucleus caudalis
3. Mesencephalic nucleus
4. Motor nucleus

THE MASSETER
This is a quadrilateral muscle which covers the lateral surface of
the ramus of the mandible. Its fibres are arranged in three layers.
Origin
Superficial layer from anterior 2/3 of the lower border of the
zygomatic arch and from the zygomatic process of the maxilla.
Middle layer : from the anterior 2/3 of the deep surface and posterior
1/3 of the lower border of zygomatic arch.
Deep layer: from the deep surface of zygomatic arch.
Insertion
The superfacial fibres pass downwards and backwards at the angle of
450 They are inserted into the lower part of the lateral surface of
the ramus of mandible.
The middle and the deep fibres, pass vertically downwards. The
middle fibres are inserted into the middle part of the ramus the
deep fibres into the upper part of the ramus and into coronoid
process.

Nerve Supply
Masseteric nerve, a branch of anterior division of
mandibular nerve.
Action
Muscle elevate the mandible to close the mouth and clench
the teeth.

The Temporalis
This muscle fills the temporal fossa.
Origin
Temporal fossa excluding the zygomatic bone/
Temporal fascia

Insertion
The fibres of the muscle coverage and pass through the gap
deep to the zygomatic arch. They are inserted into
The margin and deep surface of the coronoid process.
The anterior border of the ramus of mandible.
Nerve Supply
Deep temporal branch from anterior division of mandibular
nerve.
Action
Elevates the mandible.
Posterior fibres retract the protruded mandible

THE LATERAL PTERYGOID
This muscle has upper and lower heads.
Origin
Both heads arises from sphenoid bone.
The upper head is small. It arises from infratemporal surface
and crest of greater wing of sphenoid bone.
The lower head is large. It arises from lateral pterygoid plate.
Insertion
The fibres run backwards and laterally and coverage to
insert into
Pterygoid fovea on the anterior surface of the neck of the
mandible
Anterior margin of articular disc and capsule of the
temporomandibular joint.

Nerve Supply
A branch from the anterior division of mandibular nerve.
Actions
Depress the mandible to open the mouth
The lateral and medial pterygoid muscle of both side act together to
protrude the mandible.
The medial and lateral pterygoid on both side contract alternately
to produce side to side movement of mandible (chewing).

THE MEDIAL PTERYGOID
This is quadrilateral muscle having small superficial head
and large deep head which forms major part of the muscle.
Origin
Superficial head: from tuberosity of the maxilla and adjoining
bone.
Deep head from medial surface of lateral pterygoid plate and
adjoining part of palatine bone.
Insertion
The fibres run downwards, backwards and laterally to be
inserted into the roughened area on medial surface of angle
and adjoining part of ramus of mandible, below and behind
mandibular foramen and mylohyoid groove.www.indiandentalacademy.com

Applied Anatomy

SENSORY RECEPTORS OF MASTICATORY SYSTEM
Sensory receptors are organs located in all body tissue and
provide information to central nerve system (CNS) by
afferent neurons
Masticatory system has 4 types of sensory receptors
Muscle spindle – special receptors found in muscle tissues
golgi tendon organs – located in tendons
pacinian corpuscle : located in tendons joints periosteum and
facia
Nociceptors – found generally in all tissue of masticatory
system

Muscle spindle
Skeletal muscle consist of 2 types of fibers
Extrafusal fibers and intrafusal fibers
Extrafusal fibers which are contractile and make the bulk of muscle
Intrafusal fibers minutely contractile
intrafusal fibers bound by connective tissue sheath is called muscle
spindle
Muscle spindle acts as length monitoring system by feed back
mechanism to CNS.
When muscle is stretched suddenly its both extrafusal and intrafusal
fibers elongate. This stimulates nuclear chain and nuclear bag fiber
from which afferent nerves group 1A and group II relay the stimulus
to CNS
Intern α efferent motor fibers are stimulated, extrafusal fibers contract
and muscle shortens. This shortening decreases the afferent output of
muscle spindle.

Golgi tendon organ
They are located in muscle tendons
They monitor muscle tension
Tension on tendons (because of contraction of muscles) stimulates the
receptors in golgi tendons and again by feed back mechanism it causes
relaxation.
Pacinian organs
They are large oval organs made up of concentric lamila of connective
tissues. They are widely distributed in joints periosteum, tendons,
facia sub connective tissue. Pressure applied to these tissues deforms
the organ and stimulate the nerve fibers.
Nocicepotors
Are generally sensory receptors which responds to wide range of
stimuli from tactile to noxous injury also called as machanorceptors
giving sensation to touch pressure, hair follicle movements.
Noceceptors primarily function to monitor the condition, position and
movement of tissue in masticatory system.www.indiandentalacademy.com

Reflex action
Reflex is a mechanism by which “sensory impulse is automatically
converted into a motor effect through involvement of central nervous
system.
This definition implies
1. There must be a sensory stimulus from sensory receptors
There must be a motor effect. Motor effect may be contraction of muscle
(skeletal, cardiac, and smooth muscles) or secretion of exocrine gland
The integration (i.e. conversion of afferent into efferent) must be
automatic
Although information is sent to higher centers response is independent of
will and with no brain stem influence
Reflex action may be (a) monosynaptic (b) poly synaptic
Monosynaptic – occurs when afferent fibers directly stimulates with
efferent fibers in CNS
Polysynaptic – reflex presents when afferent neurons stimulate one or
more inter neurons in CNS which interns stimulate efferent nerve
fibers. www.indiandentalacademy.com

Two general reflexes are important in masticatory system.
They are ,
Myostatic reflex
&
Nociceptive reflex
Myostatic reflex or stretch reflex
It is only monosynaptic jaw reflex. When skeletal muscle is quickly
stretched, this protective reflex is elicited and brings about contraction
of stretch muscles
It is activated by sudden application of downward force to chin with
rubber hammer, which results in sudden contraction of elevator
muscles.

Nociceptive reflex or flexor reflex: It is polysynaptic reflex to
noxious stimulus and hence considered protective e.g. sudden
withdrawal of hand touching by touching hot object.

Reciprocal innervations: It is control of antagonist muscles. Each
muscle that supports the head and control functions has an
antagonist that counteracts its activity.
If certain muscle elevates the mandible other group of muscle
depresses it
For mandible to be elevated by temporalis, medial pterygoid and
massetric muscle, the supra hyoid muscle should relax and
lengthen. Likewise, for mandible to be depressed the suprahyoid
muscles should contract and elevator muscle should relax and
lengthen
This neurologic control for antagonist muscle is called reciprocal
innervation.

Major function of masticatory system
Mastication
Swallowing
Speech
Mastication
It is the act of chewing food
It is a complex function that uses the muscle, teeth, periodontal
supporting structures, lips, cheek, tongue, palate and salivary
glands.
The functional activity is generally automatic and involuntary.
However when desired it can be brought under voluntary
control.

Chewing stroke
Mastication is made up of rythemic and well control separation and
closure of maxillary and mandibular teeth. This is the under the
control of central pattern generator in brainstem.
Complete chewing stroke is tear shape movement pattern
It is divided in to –
Opening and closing movement
Closing movement is further subdivided into crushing phase and
grinding phase

In frontal view of chewing stroke the following happens
In opening phase, it drops downwards from maximal
intercuspal position to point where incisal edges are 16-18 mm
apart. Then it moves laterally 5-6 mm. from midline and the
closing movement begins. In first phase of closing movement
food is trapped in teeth and is called crushing phase, as teeth
approach each other lateral displacement is lessened and when
teeths are 3mm apart jaw is 3-4 mm lateral to starting point.
At this point both maxillary and mandibular buccal cusp are
directly under each other. As mandibular continues to close
food is trapped between teeth this begins grinding phase of
closure stroke. During grinding phase mandibular is guided
by occlusal surface of teeth to maximum intercuspal position,
cuspal inclines cross across each other permitting sharing and
grinding of food bolus.

CHEWING STROKE IN
SAGITTAL PLANE OF
WORKING SIDE
CONDYLE

CHEWING STROKE IN
SAGITTAL PLANE OF
NON WORKING SIDE
CONDYLE

CHEWING STROKE WITH VARIATION OF TYPE OF
FOOD (FRONTAL VIEW)

CHEWING STROKE WITH VARIATION OF TYPE OF
OCCLUSION (FRONTAL VIEW)

Forces of mastication
Biting force applied to teeth varies from individual to
individual.
Biting force in male is more than that of females.
In males it ranges from 118-142 pounds (53.6-64.4 kgs) and in
females it ranges from 79-99 pounds (35.8-44.9 kgs)
Maximum force applied is at molar region and it was found to
be 91-198 pounds (41.3-89.8 Kgs) whereas in anterior region
29-51 pounds (13.2-23.1 Kgs).
During chewing greatest amount of force is placed on first
molar region.
The biting force with complete denture is only one fourth that
of subjects with natural teeth i.e. 30-35 pounds in males and
20-25 pounds in females.

NEUROMUSCULAR REGULATION OF
MANDIBULAR MOTION

Neuromuscular regulation of mandibular motion.
Muscles that move, hold or stabilize the mandible can do so
because they receive impulses from central nervous system.
Impulses that regulate mandibular motion may arise at
consicious level and results in voluntary mandibular
activities. Impulses may also arise from subconcious level
as a result of stimulation of oral or muscle receptors.
Subconscious impulse produce involuntary movement.
Cell body of motor nerve may influence inhibition or
excitation. When closing movement occurs then neurons to
the closing muscles are excited and those to that of opening
muscles (Antagonist muscles) are inhibited.
Impulses from subconscious level also regulates the muscle
tone which plays the primary role in physiology rest
position of mandible.

Some receptors in muscle membrane of oral cavity stimulated by
touch, pain, pressure are nociceptors and other receptors present
in periodontal ligament, mandibular muscles and mandibular
ligament which provides informations as to the location of
mandible in space are called as proprioceptors.
Nociceptors travels to sensory nucleus and proprioceptors
to mesencephalic nucleus.
Impulses are transmitted in following ways:-
l) From sensory cortex & motor cortex conscious level.
to produce voluntary change in position of mandible.
2)By the way of reflex arch to motor nuclei of trigeminal nerve
and directly back to mandibular muscles to cause involuntary
movement of mandible.
3)By combination of these to under the influence of subcortical
areas, involuntary movement of mandible take place away.

Neuromuscular in parafunctional activities
Parafunctional habit involving repeated or sustained
occlusion of teeth which can be harmful to teeth and other
component of masticatory system.
The neuromuscular basis and mechanism of bruxism
have been studied and is explained by increase in tonic activity
in jaw muscles. Emotion or neuron tension, pain or discomfort,
stress, occlusal interferences are the factors that increase
muscle tonus and lead to nonfunctional gnashing and clenching.

Physiology of vertical jaw relation
Vertical dimension of rest (or physiological rest or
postural position of mandible) is established by muscles and
gravity.
There are two hypothesis of postural rest position of
mandible.
One is active and other is passive hypothesis
By active hypothesis this position is assumed only when
muscle that close the jaw and those that open the jaw are in the
state of minimal contraction to maintain the posture of
mandible.
Passive hypothesis holds that elastic element of jaw
musculature and not any muscle activity balances the influence
of gravity.

CONCLUSION
Mastication is a complex physiologic phenomenon and is
performed by series of highly coordinated functions involving
various parts of stomatognathic system. Therefore inspite of
volumionous recent work on functions of elemental structures of
stomatognathic system, systematic studies on mechanisms and
effectiveness of mastication as a whole are most essential.
As per this philosophical standpoint prosthodontist must
reaffirm importance of mastication and consider the practical
application of recent physiological concept to dental practice.

References
• 1) Grays anatomy: Peter L Williams, Roger Warwick, 37th
edition
• 2)B.D Chaurasias; Human Anatomy; regional and applied volume three, third edition
• 3)Tortora Grabowskai :Principals of anatomy and physiology 7th
edition
• 4)Review of medical physiology : William f Ganong 17th
edition
• 5)Bouchers Prosthodontic treatment for edentulous patients 7th
edition
• 6)Management of Temperomandibular disorders and occlusion 5th
edition ; Jeffrey p
Okeson
• 7)Evaluation diagnosis and treatment plan of occlusal problem 2nd
edition Peter E
Dawson
• 8)Concised medical physiology 2nd
edition sujit chaudarii

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