Functional neuroanatomy and physiology of masticatory system

Preeti Kalia3rd year PG student

Department of ProsthodonticsAECS Maaruti College of Dental

Sciences

“You cannot successfully treat dysfunction unless you understand function”

Functional neuroanatom

y and physiology of masticatory

system

Neuromuscular system

Muscle Nerve

Neuromuscular

function

Pain

Neuromuscular system

Neurological structure

Muscles

Muscles

Muscle functionIsotonic contraction

Isometric contraction

Relaxation

Muscle function

Muscle function

Eccentric contraction

Neurological structure

Types of neurons Afferent neurons

Efferent neurons

Reticular formation

Thalamus

Hypothalamus

Limbic structure

Cerebral cortex

Sensory receptors

Nociceptors

Propriceptors

Muscle spindle

Golgi organ

Pacinian corpuscle

Muscle spindles

Golgi tendon receptor

Pacinian corpuscles

Nociceptors

Neuromuscular function

Reflex action:

It is response resulting from a stimulus that passes as an impulse along afferent neurons to a

posterior nerve root or its cranial equivalent

Monosynaptic reflex

Polysynaptic reflex

Myotatic reflex

Nociceptive reflexIt is a polysynaptic reflex

Seen when hard food substances are taken in the mouth

Reciprocal innervationThe controlling mechanism of antagonistic group of

muscles

Regulation of muscle activityGamma charge keeps the alpha motor neuron reflex

prepared to receive impulses

Influence of higher centers

Major function of masticatory system

Mastication

Swallowing Speech

MasticationDefined as act of chewing food

Chewing cycle

Mascles activity

OpeningStart from static intercuspal

position

muscle activity begins in the ipsilateral inferior head of the lateral pterygoid muscle approximately half way through the period of tooth contact.

Follow closely by the action of the contralateral inferior lateral pterygoid muscles.

Both superior and inferior head of th lateral pterygoid muscle are active during the opening phase.

OpeningEarly in the opening phase,

digastric muscles become active and remain until maximum opening position

During the opening phase, masseter, temporalis, medial pterygoid, and superior head of lateral pterygoid muscles are inactive.

Closing initiation of jaw closing

the inferior heads of the lateral pterygoid muscle ceases their functioning and activity

initiated in the contralateral medial pterygoid muscle

ClosingContralateral medial pterygoid controls the upward and lateral

positions of the mandible Activity increases in the anterior and posterior temporalis muscle, in

the deep and superficial masseter muscles, and in the ipsilateral medial pterygoid muscle

anterior and posterior temporalis muscle, in the deep and superficial masseter muscles, and in the ipsilateral medial pterygoid muscle activity declines in activity at the onset of intercuspation.

There appears to be reciprocal action between the inferior head of the lateral pterygoid muscle and the medial pterygoid muscle in same subject

Tooth contact during masticationGliding contacts

Single contact

Average time for tooth contact is 194 minutes

60% Gliding contacts seen during grinding

56% gliding contacts seen during opening

Forces of masticationMaximum biting force in females 70 to 99 pounds

Males 118 to 142 pounds

Maximum bite force for molar 91 to 198 pounds

Central incisors 29 to 51 pounds

SwallowingSeries of coordinated muscle movements that

moves bolus from oral cavity through esophagus to stomach

Somatic swallow

Visceral swallow

Stages

Frequency of swallowing590 times in 24 hours

146 cycles during eating

394 in between meals

50 cycles during sleep

SpeechImportant sounds formed by the lip are m,band p

Teeth are important in saying s

Tongue and palate are essential in forming d

Tongue touches maxillary incisors to form th

Lower lip touches maxillary incisors to form f and v

PainUnpleasant sensation perceived in the cortex as a

result of incoming nociceptive input.

Modulation of pain

Non painful cutaneous nerve stimulation

Intermittent painful stimulation

Psychological modulation

Types of pain

Central pain

Projected pain

Referred pain

Central excitatory effectExplains the mechanism of referred pain

“Pain is inevitable. Suffering is optional.

ReferencesOkeson.J.P, Temporomandibular disorders and

occlusion,6th edition , 2008, Mosby publication, St Louis, United States of America, pp:25-57