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INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

www.indiandentalacademy.com
NEURO ANATOMY AND
PHYSIOLOGY OF
MASTICATORY SYSTEM
 The

function of masticatory system is
complex
 Discriminatory contr...
A

highly refined neurologic control system
regulates and coordinates the activities of the
entire masticatory system .
...
 Activation

of neuron – Motor end plate is
stimulated to release small amounts of
acetylcholine-

 initiates

depolaris...
 Fewer

muscle fibers /motor neuron-more precise
movement
 Eg.ciliary muscles(2or3fibers/neuron-controls of
eye-1neuron/...
 In

contrast-masseter-large no of muscle
fibers/motor neuron-more gross functions of
providing the force necessary durin...
 To

understand the effect of these muscles
one must observe the basic skeletal
relationships of head and neck.
 The sku...
 Some

of the muscles that serve this function
are the
trapezius,sternocliedomastoid,splenus
capitus and long capitus mus...
– Muscle function: motor unit can carry out only

one action I.contraction or shortening
– Muscle –3 potential functions
–...
 Isometric

contraction-when proper no of
motor units contract opposing a given
force,the resultant function of muscle to...
 By

control of this decrease in motor unit
stimulation,a precise muscle lengthening
can occur that allows smooth and del...
 Therefore

muscles may act as primary
movers of part,they may act in a stabilizing
manner so that a movement will be
coo...
 Eccentric

contraction-which occurs during
certain conditions-which is injurious to the
muscle tissue.
 It refers to th...
 However

the impact is great,the sudden
change in the inertia of head causes it to
move while the muscles contract tryin...
www.indiandentalacademy.com
 Neurologic

structures:the basic structural
unit of the nervous system is the neuron.
 Neuron-composed of a mass of pro...
 Many

neurons are grouped together to form a
nerve fiber.
 These neurons are capable of transmitting
electrical and che...
 Efferent

neurons-conducts it peripherally
also called as motor neurons-which convey
impulses from c.n.s to effector org...
 Synapse-where

the process of two neurons
are in close proximity-consists of section of
terminal end of the axon of one ...
 Two

types of receptors:
 Exteroreceptors-which mediate sensation of
touch.light,pressure,pain,cold,heat etc.
 Nocirec...
 Interoreceptors-

they carry information
regarding the status of the internal organs.
 Constant input received from all...
 Masticatory

system-utilizes four major
types of sensory receptors to monitor the
status of its structures.
 Muscle spi...
 Muscle

spindles-primarily monitor muscle

length
 Skeletal muscle consists of two types of
muscle fibers that is extra...
 Primarily

monitor tension within the
skeletal muscles.
 They are interspersed through the muscles
and aligned parallel...
 There

are two types of afferent fibers that supply
the intrafuasal fibers which are classified
according to their diame...
 Since

the intrafusal fibers of the muscle
spindles are aligned parallel to the
extrafusal fibers of the muscles,the
int...
 Muscle

stretch
 Activation of annulospiraland flower spray
endings
 Afferent neurons carry these neural
impulses to t...
www.indiandentalacademy.com
 The

intrafusal fibers receive efferent
innervations by way of fusimotor nerve
fibers.
 The extrafusal fibers receive i...
 Golgi

tendon organs-they are located in the
muscle tendon between the muscle fibers
and their attachment to the bone.
...
 Tension

on the tendon stimulates the
receptors in the golgi tendon organ.
 Therefore contraction of muscle also
stimul...
 Pacinian

corpuscles these are large oval organs
made up of concentric lamella of concentric
connective tissue .
 These...
 Nociceptors:

these are sensory receptors
that are stimulated by injury and transmit
injury information to the c.n.s by ...
the nociceptors primarily function to
monitor the condition,position and
movement of the tissues in the masticatory
system...
 Reflex

action-it is the response resulting
from a stimulus that passes as an impulse
along an afferent neuron to a post...
A polysynaptic reflex is present when the
afferent neuron stimulates one or more
interneurons in the CNS which in turn
sti...
 Myotactic

reflex-it is monosynaptic jaw reflex
 When a skeletal muscle is quickly stretched,this
protective reflex is ...
 Afferent

fibers synapse in trigeminal motor
nucleus with efferent motor neurons.
 Efferent fibers carry information to...
 In

masticatory system, this reflex becomes
active when a hard object is suddenly
encountered during mastication.
 Unex...
 These

interneurons travel to the trigeminal
motor nucleus
 Afferent information from the sensory
receptors reaches the...
 Excitatory

interneurons leading to efferent
neurons in trigeminal motor nucleus of the jaw
opening muscles are stimulat...
www.indiandentalacademy.com
 The

myotactic reflex protects the masticatory
system from sudden stretching of a muscle.
 The nociceptive reflex prote...
Influence from higher centers
in brain
 Main

sensory nucleus trigeminal nerve Sensory nerve impulses arise from oral re...
 Mesencephalic

nucleus of trigeminal nerve Changes in tension stimulate proprioceptive
receptors in periodontal membran...
 Motor

cortex of cerebrum-impulses arising
in the cerebral cortex are carried by nerve
fibers to the motor nucleus and a...
Major functions of the
masticatory system
 The

neuroanatomy and physiology that has been
discussed provide a mechanism b...
 Mastication-

it is defined as the act of
chewing foods.
 This act is made up of rhythmic,well
controlled separation an...
 It

can be divided into an opening phase and
closing phase
 Closing phase –crushing phase and grinding
phase.
 Opening...
 Closing

phase- the first phase of closure traps the
food between the teeth and is called as crushing
phase.
 As teeth ...
 As

mandible continues to close,the bolus of
food is trapped between the teeth which
begins the grinding phase of closur...
 Tooth

contact during mastication When food is initially introduced into the
mouth, few contacts occur.
 As the bolus ...
www.indiandentalacademy.com
 Gliding

contact-which occurs as the cuspal
inclines pass by each other during the
 Amount of lateral movement is great...
 Factors

affecting mandibular movements during
chewing stroke Amount of lateral movement is greater when
food is introd...
 Tall

cusps and deep fossa-promote
predominantly vertical chewing strokes
where as flattened cut worn out teeth
encourag...
 Persons

with t.m.j disorders-strokes are
shorter and slower and have an irregular
pathway but repeatable pathways relat...
www.indiandentalacademy.com
Thank you
For more details please visit
www.indiandentalacademy.com

www.indiandentalacademy.com
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Neuro anatomy and physiology of masticatory system /certified fixed orthodontic courses by Indian dental academy

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Neuro anatomy and physiology of masticatory system /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. NEURO ANATOMY AND PHYSIOLOGY OF MASTICATORY SYSTEM  The function of masticatory system is complex  Discriminatory contraction of the various head and neck muscles is necessary to move the mandible precisely and allow effective functioning. www.indiandentalacademy.com
  3. 3. A highly refined neurologic control system regulates and coordinates the activities of the entire masticatory system .  It consist of primarily nerves and muscles hence the term neuromuscular system.  Muscles:  Motor unit: It is the basic component of neuromuscular system –consist of number of muscles fibers that are innervated by6 one motor neuron .  Each neuron joins with the muscle fiber at the motor end plate www.indiandentalacademy.com
  4. 4.  Activation of neuron – Motor end plate is stimulated to release small amounts of acetylcholine-  initiates depolarisation of muscle fibers –  muscle fibers to shorten or contract.  Number of muscle fibers innervated by one motor neuron varies greatly according to the function of motor unit. www.indiandentalacademy.com
  5. 5.  Fewer muscle fibers /motor neuron-more precise movement  Eg.ciliary muscles(2or3fibers/neuron-controls of eye-1neuron/1oomuscle fibers-rectus femorus in leg)  Similarly muscles of mastication  The inferior lateral pterygoid muscle has relatively low muscle fiber-motor neuron ratio therefore capable of doing more precise adjustments in length needed to adopt to horizontal changes in mandibular position www.indiandentalacademy.com
  6. 6.  In contrast-masseter-large no of muscle fibers/motor neuron-more gross functions of providing the force necessary during mastication  Muscle:  Hundred to thousand of motor units along blood vessels and nerves are bundled together by connective tissue and fascia to make up muscle. www.indiandentalacademy.com
  7. 7.  To understand the effect of these muscles one must observe the basic skeletal relationships of head and neck.  The skull is supported in position by cervical spine in fact cervical spine alone cannot support the head so far this muscles are needed to balance it.  If the head is to be maintained in an upright position so one can see forward’,the muscles that attach the posterior aspect of skull to the cervical spine and shoulder region must contract. www.indiandentalacademy.com
  8. 8.  Some of the muscles that serve this function are the trapezius,sternocliedomastoid,splenus capitus and long capitus muscles.  It is possible, however for these muscles to over contract and direct the line of vision too far upward.  To counteract this action,an antagonistic group of muscles exists in anterior region of the head –masseter (joins mandible to skull),suprahyoid muscles and infrahyoid muscles. www.indiandentalacademy.com
  9. 9. – Muscle function: motor unit can carry out only one action I.contraction or shortening – Muscle –3 potential functions – Isotonic contraction-when large no of motor units in the muscle rare stimulated –contraction or an overall shortening of muscle occurs-this type of shortening under a constant load – Eg.isotonic contraction occurs in the masseter muscle when the mandible is elevated .forcing the teeth through bolus of food. www.indiandentalacademy.com
  10. 10.  Isometric contraction-when proper no of motor units contract opposing a given force,the resultant function of muscle to hold or stabilize the jaw. This contraction without shortening is called isometric contraction eg.it occurs in masseter muscle when an object is held between the teeth (pipe or pencil)  Controlled relaxation:when stimulation of motor unit is discontinued,the fibers of motor unit relax and return to their normal length. www.indiandentalacademy.com
  11. 11.  By control of this decrease in motor unit stimulation,a precise muscle lengthening can occur that allows smooth and deliberate movement.  Eg.masseter muscle when the mouth opens to accept a new bolus of food during mastication.  When these three functions are used, the muscles of head and neck maintain a constant desirable head position www.indiandentalacademy.com
  12. 12.  Therefore muscles may act as primary movers of part,they may act in a stabilizing manner so that a movement will be coordinated or smooth or they may act as a fixer of a part so that the part can be maintained firmly in a given position.  These three types of muscle activities are present during routine function of head and neck. www.indiandentalacademy.com
  13. 13.  Eccentric contraction-which occurs during certain conditions-which is injurious to the muscle tissue.  It refers to the lengthening of muscle at the same time that it is contracting.  Eg.it occurs with the tissue damage associated during an extension-flexion injury(whip-lash injury)  At the precise movement of motor vehicle accident the cervical muscles contract to support the head and resist movement. www.indiandentalacademy.com
  14. 14.  However the impact is great,the sudden change in the inertia of head causes it to move while the muscles contract trying to support it.  Results in sudden lengthening of muscles while they are contracting which results in injury www.indiandentalacademy.com
  15. 15. www.indiandentalacademy.com
  16. 16.  Neurologic structures:the basic structural unit of the nervous system is the neuron.  Neuron-composed of a mass of protoplasm termed cell body and protoplasmic process from the nerve cell body called axons and dendrites.  Axon-it is the central core that forms the essential conducting part of a neuron and it is an extension of cytoplasm from a nerve cell. www.indiandentalacademy.com
  17. 17.  Many neurons are grouped together to form a nerve fiber.  These neurons are capable of transmitting electrical and chemical impulses along their axis enabling information to pass both in and out of the c.n.s  Neurons are classified as-(depending on their location and function)  Afferent neurons-conducts impulse towards C.N.S also called AS sensory or receptors –which receive and convey impulses from receptor organs. www.indiandentalacademy.com
  18. 18.  Efferent neurons-conducts it peripherally also called as motor neurons-which convey impulses from c.n.s to effector organ to produce muscular or secretary effects.  Internuncial neurons or interneurons-they provide for alternate or distant connections with many of the cells of the nervous system.  Receptors-they are structures that detect changes in environment within the body and transmit information to c.n.s. www.indiandentalacademy.com
  19. 19.  Synapse-where the process of two neurons are in close proximity-consists of section of terminal end of the axon of one neuron with the dendrite zone or cell body of another neuron.  It can be monosynaptic or polysynaptic.  Sensory receptors-these are neurologic structures or organs located in all body tissues that provide information regarding the status of these  tissues to c.n.s by way of the afferent neuron. www.indiandentalacademy.com
  20. 20.  Two types of receptors:  Exteroreceptors-which mediate sensation of touch.light,pressure,pain,cold,heat etc.  Nocireceptors-specific for discomfort and pain.  Proprioceptors-provide information regarding the position and movement of mandible and associated oral structures.  Mechanoreceptors-respond at a higher frequency to innocous stimuli than to thermal or noxious stimulation they are tactile receptors www.indiandentalacademy.com
  21. 21.  Interoreceptors- they carry information regarding the status of the internal organs.  Constant input received from all these receptors allows the cortex and the brain stem to coordinate action of individual muscles or muscle groups to create appropriate response in the individual. www.indiandentalacademy.com
  22. 22.  Masticatory system-utilizes four major types of sensory receptors to monitor the status of its structures.  Muscle spindles-specialized receptors organs found in the muscle tissues  Golgi tendon organs-located in tendons  Pacinian corpuscles-located in the tendons.joints.periosteum.fascia and subcutaneous tissues.  Nociceptors-found generally through all the tissues of the masticatory system www.indiandentalacademy.com
  23. 23.  Muscle spindles-primarily monitor muscle length  Skeletal muscle consists of two types of muscle fibers that is extrafusal and intrafusal fibers.  Extrafusal fibers-they are contractile and makeup the bulk of the muscle  Intrafusal fibers-minutely contractile.  A bundle of intrafusal fibers bound by connective sheath is called muscle spindle. www.indiandentalacademy.com
  24. 24.  Primarily monitor tension within the skeletal muscles.  They are interspersed through the muscles and aligned parallel with the extrafusal fibers.  Within each spindle,the nuclei of intrafusal fibers are arranged in two distinct fashions  Chain like(nuclear type)  Clumped(nuclear bag type) www.indiandentalacademy.com
  25. 25.  There are two types of afferent fibers that supply the intrafuasal fibers which are classified according to their diameters .  The larger fibers conduct impulses at a higher speed and have lower thresholds.  Primary endings(annulospiral endings)- they end central region of the intrafusal fibers which are larger (1a,a-alpha)  Secondary ending (flower spray endings)- those that end in the poles of spindle away from central region,which are smaller.(2,a-beta) www.indiandentalacademy.com
  26. 26.  Since the intrafusal fibers of the muscle spindles are aligned parallel to the extrafusal fibers of the muscles,the intrafusal fibers are stretched as the muscle is stretched.  This stretch is monitored at the nuclear chain and nuclear bag region. www.indiandentalacademy.com
  27. 27.  Muscle stretch  Activation of annulospiraland flower spray endings  Afferent neurons carry these neural impulses to the C.N.S.  (the afferent neurons originating in the muscle spindles of muscles of mastication have their cell bodies in the trigeminal mesencephalic nucleus) www.indiandentalacademy.com
  28. 28. www.indiandentalacademy.com
  29. 29.  The intrafusal fibers receive efferent innervations by way of fusimotor nerve fibers.  The extrafusal fibers receive innervations by way of efferent motor neurons(most of these have their cell bodies in the trigeminal motor nucleus)  Stimulation of these neurons therefore the group of extrafusal fibers (motor unit )to contraction  Muscle contraction www.indiandentalacademy.com
  30. 30.  Golgi tendon organs-they are located in the muscle tendon between the muscle fibers and their attachment to the bone.  They primarily monitor tension.  They occur in series with the muscle spindles.  Afferent fibers enter near the middle of the organ and spread out over the the extent of fibers. www.indiandentalacademy.com
  31. 31.  Tension on the tendon stimulates the receptors in the golgi tendon organ.  Therefore contraction of muscle also stimulates the organ.  Likewise,an overall stretching of the muscle creates tension in the tendon and stimulates the organ. www.indiandentalacademy.com
  32. 32.  Pacinian corpuscles these are large oval organs made up of concentric lamella of concentric connective tissue .  These are widely distributed because of their frequent location in the joint structures.  They are considered to serve principally for the perception of movement and firm pressure.  They are found in tendons,joints,periosteum,tendinous insertions,fascia and subcutaneous tissue. www.indiandentalacademy.com
  33. 33.  Nociceptors: these are sensory receptors that are stimulated by injury and transmit injury information to the c.n.s by way of the afferent nerve fibers.  They are located throughout most of the tissues in the masticatory system.  Several types exist.  Some respond exclusively to noxious, mechanical and thermal stimuli,others respond to wide range of stimuli,from tactile sensations to noxious injury etc. www.indiandentalacademy.com
  34. 34. the nociceptors primarily function to monitor the condition,position and movement of the tissues in the masticatory system  When conditions exist that are either potentially harmful or actually cause injury to the tissues, the nociceptors relay this information to c.n.s as sensations of discomfort or pain.  www.indiandentalacademy.com
  35. 35.  Reflex action-it is the response resulting from a stimulus that passes as an impulse along an afferent neuron to a posterior root or its cranial equivalent;where it is then transmitted to an efferent neuron leading back to the skeletal muscle.  A reflex action may be monosynaptic or polysynaptic  A monosynaptic reflex occurs when the afferent fiber directly stimulates the efferent fiber in the CNS. www.indiandentalacademy.com
  36. 36. A polysynaptic reflex is present when the afferent neuron stimulates one or more interneurons in the CNS which in turn stimulate the efferent nerve fibers. Two general reflex actions are important in masticatory system. Myotactic reflex Nociceptic reflex www.indiandentalacademy.com
  37. 37.  Myotactic reflex-it is monosynaptic jaw reflex  When a skeletal muscle is quickly stretched,this protective reflex is elicited and brings about a contraction of the stretched muscle.  Sudden stretching of muscle  Afferent activity from the spindles  Afferent impulses pass into the brain stem to the trigeminal motor nucleus by way of the trigeminal mesencephalic nucleus where the primary afferent cell bodies are located. www.indiandentalacademy.com
  38. 38.  Afferent fibers synapse in trigeminal motor nucleus with efferent motor neurons.  Efferent fibers carry information to extrafusal fibers  Muscle contraction  Nociceptive reflex- it is a polysynaptic reflex to noxious stimuli and hence considered to be protective.  www.indiandentalacademy.com
  39. 39.  In masticatory system, this reflex becomes active when a hard object is suddenly encountered during mastication.  Unexpected biting on hard object  Sudden noxious stimulus is generated by over loading the periodontal structures (the primary afferent nerve fibers carry information to the trigeminal spinal tract nucleus,where they synapse with interneurons) www.indiandentalacademy.com
  40. 40.  These interneurons travel to the trigeminal motor nucleus  Afferent information from the sensory receptors reaches the interneurons,two  distinct actions occur.  They synapse with efferent neurons in the trigeminal spinal tract nucleus www.indiandentalacademy.com
  41. 41.  Excitatory interneurons leading to efferent neurons in trigeminal motor nucleus of the jaw opening muscles are stimulated  Causes muscle to contract  At the same time-the afferent fibers stimulate inhibitory interneurons,which cause jaw- elevating muscles to relax.  The overall result is that the jaw quickly drops and teeth are pulled away from the object causing noxious stimuli-this process is called antagonistic inhibition www.indiandentalacademy.com
  42. 42. www.indiandentalacademy.com
  43. 43.  The myotactic reflex protects the masticatory system from sudden stretching of a muscle.  The nociceptive reflex protects the teeth and supportive structures from damage created by sudden and unusually heavy functional forces .  These are very complex and controlled in higher centers.  Reflex actions play major role in functioning. eg.mastication,swallowing,gagging .coughing,speaking. www.indiandentalacademy.com
  44. 44. Influence from higher centers in brain  Main sensory nucleus trigeminal nerve Sensory nerve impulses arise from oral receptors travel to the sensory nucleus of trigeminal nerve.  From nerve, the impulses are transmitted to the motor nucleus of trigeminal nerve and to the cerebral cortex.  Those transmitted directly to the motor nucleus are responsible for involuntary movement. www.indiandentalacademy.com
  45. 45.  Mesencephalic nucleus of trigeminal nerve Changes in tension stimulate proprioceptive receptors in periodontal membrane,tmj,and muscles of mastication.  Sensory impulses travel to the mesencephalic nucleus in the pons.  From here impulses are transmitted to the motor nucleus and are responsible for involuntary jaw movements. www.indiandentalacademy.com
  46. 46.  Motor cortex of cerebrum-impulses arising in the cerebral cortex are carried by nerve fibers to the motor nucleus and are responsible for voluntary jaw movements.  Globus palladius of corpus striatum-this center is responsible for postural adjustments and automatic movements  Cerebellum-impulses from cerebellum go to the motor nucleus and result in synergism of various muscles taking part in functional movements. www.indiandentalacademy.com
  47. 47. Major functions of the masticatory system  The neuroanatomy and physiology that has been discussed provide a mechanism by which important functional movements of the mandible can be executed  The functional movements are Mastication  Swallowing  Speech  Respiration  Aimless contact movements www.indiandentalacademy.com
  48. 48.  Mastication- it is defined as the act of chewing foods.  This act is made up of rhythmic,well controlled separation and closure of the maxillary and mandibular teeth.  Each opening and closing movement of mandible represents a chewing stroke.  The complete chewing stroke has a movement pattern described as tear shaped www.indiandentalacademy.com
  49. 49.  It can be divided into an opening phase and closing phase  Closing phase –crushing phase and grinding phase.  Opening phase-the mandible drops downward from the inter cuspal position to a point where incisal edges of the teeth are about 16 to 18 mm apart.  The mandible then moves laterally 5- 6mm from midline as the closing movement begins. www.indiandentalacademy.com
  50. 50.  Closing phase- the first phase of closure traps the food between the teeth and is called as crushing phase.  As teeth approaches each other ,the lateral displacement is lessened so that when the teeth or only 3mm apart the jaw occupies a position only 3-4mm lateral to the starting position of the chewing stroke.  At this point teeth are so positioned that the buccal cusps of mandibular teeth are almost directly under buccal cusps maxillary teeth on the side to which the mandible has been shifted. www.indiandentalacademy.com
  51. 51.  As mandible continues to close,the bolus of food is trapped between the teeth which begins the grinding phase of closure stroke.  Grinding phase-the mandible is guided by the occlusal surfaces of teeth back to the inter cuspal position,which causes the cuspal inclines of teeth to pass across each other permitting shearing and grinding of bolus of food. www.indiandentalacademy.com
  52. 52.  Tooth contact during mastication When food is initially introduced into the mouth, few contacts occur.  As the bolus is broken down,the frequency of tooth contact increases.  In the final stages of mastication,just prior to swallowing contacts occur during every stroke.  Two types of contact have been identified. www.indiandentalacademy.com
  53. 53. www.indiandentalacademy.com
  54. 54.  Gliding contact-which occurs as the cuspal inclines pass by each other during the  Amount of lateral movement is greater when food is introduced and then becomes less as the food is broken down opening and grinding phases of mastication.  Single contact-which occurs during maximum intercuspal position. www.indiandentalacademy.com
  55. 55.  Factors affecting mandibular movements during chewing stroke Amount of lateral movement is greater when food is introduced and then becomes less as the food is broken down.  Consistency of food-hard foods –greater amount of lateral movement.  Soft foods-lesser lateral movements eg.chewing on a carrot creates a broader stroke than while chewing on a cheese. www.indiandentalacademy.com
  56. 56.  Tall cusps and deep fossa-promote predominantly vertical chewing strokes where as flattened cut worn out teeth encourage a broader chewing stroke.,  Malocclusion produces an irregular and less repeatable chewing stroke  Normal persons with good occlusion masticate with chewing stroke that are well rounded that have definite borders and less repeated. www.indiandentalacademy.com
  57. 57.  Persons with t.m.j disorders-strokes are shorter and slower and have an irregular pathway but repeatable pathways related to altered functional movement of the condyle around which the pain is centered. www.indiandentalacademy.com
  58. 58. www.indiandentalacademy.com
  59. 59. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

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