neuro-muscular function saquib / orthodontic courses by indian dental academy

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NEURO MUSCULAR FUNCTION OF

MASTICATORY APPARATUS

“Nothing is more fundamental to treating patients than knowing the

anatomy.”-JPO

Presented by:Dr. Saquib A. Shaikh


INTRODUCTION

“You cannot successfully treat dysfunction unless you understand function.”

-JPOThe 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 SystemIt 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 systemB. 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 AxionDendrites


NEUROPHYSIOLOGYCommunication 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 potentialThere 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 membraneExtra 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.


DepolarisationIf 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+ influxAs depolarisation increases the membrane potential changes from -70mV towards 0, then to +30mV. Na channel has two gates activation gate and inactivation gate.

RepolarisationAs 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 PeriodPeriod of time were excited cell cannot generate another action potential is called refractive period.

Absolute Refractive PeriodTime period where excited cell cannot generate another action potential even with very strong stimuli.


Propagation and conduction of nerve


Propagation of conductionContinuous 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 posturePrevent 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.


TYPES OF MUSCLESSkeletal 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 microscopeIs voluntary and can be made contract and relax by conscious

control.

Cardiac muscle tissueForms most of the heartIt 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 smoothThese 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 fibersFibers and arranged parallel to each other having 10-100 m. in diameter and 100 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 m. in diameter and contains 3 types of filaments1. 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 actin3. 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 muscleIn 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 nerveIt contains both sensory and motor fibers


It is attached to the lateral part of pons by its two roots – sensory and motor rootsSensor root arises from samilunar ganglion located in mickles cavity.Sensory roots has three nucleus

Main sensory nucleusMesencephalic 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 divisionMaxillary divisionMandibular divisionwww.indiandentalacademy.com

DISTRIBUTION AREAS OF TRIGEMINAL NERVEwww.indiandentalacademy.com

OPHTHALMIC NERVE

It is first branch of trigeminal nerveIt is sensory nerveIt 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 nerveExternal nasal branch www.indiandentalacademy.com

MAXILLARY DIVISION

Maxillary division is entirely sensory in functionOriginates: In middle of trigeminal ganglion and continues forward in lower part of cavernous sinusIt leaves cranial fossa through foramen rotundum and enters pterygopalatine fossaFrom 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 regionA. Middle cranial fossa

1. Middle meningeal nerveB. Branch in pterygopalatine fossa

Zygomatico facial nerve1.Zygomatic nerve

Zygomatico temporal nerve

2.Pterygopalatine nervea. Orbital branchb. Nasal branch

Anterior palatinec. 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 division1. Inferior palpable branch2. Lateral nasal branch3. Superior labial branch


MANDIBULAR NERVEThis is largest of three divisions of trigeminal nerve. It has both sensory and motor fibers

CourseBegins in middle cranial fossa through large sensory root and small motor rootSensory 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 trunkAfter short course, the main trunk divides into small anterior and large posterior division.


Branches:1. From main trunk

Meningeal branchNerve to medial pterygoid

2. From anterior trunkSensory branch: Buccal nerveMotor branch:

Messeteric nerveDeep temporal nerveNerve to lateral pterygoid

3. Posterior trunkAuriculotemporal nerveLingual nerveInferior alveolar nerve

a. Mylohyoid branch b. Mental branchwww.indiandentalacademy.com

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

Mandibular neuralgia


Peripheral nerve input in spinal cordThroughout 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 oralisb. Sub nucleus inter polarisc. 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.

OriginSuperficial 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.InsertionThe 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 SupplyMasseteric nerve, a branch of anterior division of

mandibular nerve.Action

Muscle elevate the mandible to close the mouth and clench the teeth.


The TemporalisThis muscle fills the temporal fossa.

OriginTemporal fossa excluding the zygomatic bone/Temporal fascia


InsertionThe fibres of the muscle coverage and pass through the gap

deep to the zygomatic arch. They are inserted intoThe 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.

ActionElevates 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 SupplyA branch from the anterior division of mandibular nerve.

ActionsDepress 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.

OriginSuperficial head: from tuberosity of the maxilla and adjoining

bone.Deep head from medial surface of lateral pterygoid plate and

adjoining part of palatine bone.

InsertionThe 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 receptorsMuscle spindle – special receptors found in muscle tissuesgolgi tendon organs – located in tendonspacinian corpuscle : located in tendons joints periosteum and

faciaNociceptors – found generally in all tissue of masticatory

system


Muscle spindle Skeletal muscle consist of 2 types of fibersExtrafusal fibers and intrafusal fibersExtrafusal fibers which are contractile and make the bulk of muscleIntrafusal fibers minutely contractile intrafusal fibers bound by connective tissue sheath is called muscle spindleMuscle 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 CNSIntern 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.NocicepotorsAre 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.


Reflex actionReflex is a mechanism by which “sensory impulse is automatically

converted into a motor effect through involvement of central nervous system.

This definition implies1. 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

automaticAlthough information is sent to higher centers response is independent of

will and with no brain stem influenceReflex action may be (a) monosynaptic (b) poly synaptic Monosynaptic – occurs when afferent fibers directly stimulates with

efferent fibers in CNSPolysynaptic – 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 reflexIt 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 systemMastication Swallowing Speech

MasticationIt 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 patternIt 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 chaudariiwww.indiandentalacademy.com

neuro-muscular function saquib / orthodontic courses by indian dental academy

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