The Neuromuscular Determinant

Lecture given on 9/4/2025

motor unit

the basic component of the neuromuscular system, consists of a number of muscle fibers that are innervated by one motor neuron

t/f 1 neuron can control 2/3 muscle fibers for precise control or 100 muscle fibers for gross function

true

muscle sensory receptors

neurologic structures or organs located in all body tissues that provide information to the CNS by way of the afferent neurons regarding the status of these tissues

provide feedback

What is the role of sensory receptors in the human body?

A. They transmit signals from the CNS to muscles for movement.

B. They store nutrients in tissues for later use.

C. They provide information to the CNS via afferent neurons about the status of body tissues.

D. They regulate hormone production in glands.

C. They provide information to the CNS via afferent neurons about the status of body tissues

nociceptors

tissues of masticatory system for painful stimulus, stimulated when there is an injury, they relay the information to the CNS

muscle spindle

found in elevator muscles, sends information regarding the changes in the muscle length

send signals to contract to oppose the gravity force

golgi tendon

found in the junction of the muscle and tendon, primarily monitor tension of the muscle

pacinian corpuscle

found in tendon, joint, fascia, periosteum

responsible for the perception of movement and firm pressure

Which of the following best describes the role of nociceptors in the masticatory system?

A.They detect and relay painful stimuli to the central nervous system (CNS).

B.They control muscle movement in the jaw.

C.They are responsible for taste sensation.

D.B & C

A. They detect and relay painful stimuli to the central nervous system (CNS).

myotatic reflex in the masseter

when a sudden downward force is applied to the chin, muscle spindles are activated and the masseter contracts

this is important in determining the resting position of the jaw

nociceptive reflex in the masticatory system

activated when unexpectedly biting on a hard object

protective

elevators stop contracting and depressors start contracting to open the jaw

Which sensory receptor are stimulated when there is an injury (painful stimulus)?

A. Muscle Spindles

B. Nociceptors

C. Golgi tendon

B. Nociceptors

t/f the main function of the myotatic reflex in the masticatory system is maintaining muscle tonus and jaw rest position.

true

What occurs during the nociceptive reflex in the masticatory system when an individual accidentally bites on a hard object?

A. Continuous contraction of the masseter muscle to maintain occlusion

B. Inhibition of jaw-closing muscles and activation of jaw-opening muscles to prevent damage

C. Enhanced salivary secretion to allow the passage of the object

D. Increased activation of jaw-closing muscles to stabilize the bite

B. Inhibition of jaw-closing muscles and activation of jaw-opening muscles to prevent damage

what are the 3 major functions of the masticatory system?

mastication, swallowing, speech

mastication

the act of chewing foods, is the initial stage of digestion, it is involuntary but it can be brought under voluntary

chewing stroke

an opening and closing movement of the mandible, tear shaped, starts and ends in MIP

how large is the opening phase of a chewing stroke?

16-18 mm

what happens during the closing phase of a chewing stroke?

crushing and grinding

what kind of chewing stroke will someone with tall cusps and deep fossae have?

vertical chewing stroke

what kind of chewing stroke will someone with flattened or worn teeth have?

broader chewing stroke

what kind of chewing stroke will someone with malocclusion have?

irregular, less repeatable chewing strokes

in the sagittal view, what happens during the opening phase of the chewing stroke?

the mandible moves slightly anteriorly

in the sagittal view, what happens during the closing phase of the chewing stroke?

the mandible follows a slightly posterior pathway, ending in an anterior movement back to the maximum intercuspal position

Which of the following tooth characteristics is most associated with a vertical chewing stroke?

A. Worn teeth

B. Tall cusps and deep fossae

C. Malocclusion

D. Missing teeth

B. Tall cusps and deep fossae

how much force can males bite with?

118-142 lbs

how much force can females bite with?

79-99 lbs

what is the maximum force that can be applied to a first molar, compared to the central incisors?

91-198 lbs compared to 29-51 lbs

which type of teeth are structurally better suited to withstand higher bite forces?

first molars

what is the greatest maximum biting force reported?

975 lbs

what do lips do during mastication?

guide and control intake, seal off the oral cavity

what does the tongue do during mastication?

taste, maneuvering the food within the oral cavity for sufficient chewing, repositions the partially crushed food onto the teeth for further breakdown, and sweeps the teeth to remove any food residue

what does the buccinator do during mastication?

pushes food onto the teeth for further breakdown

deglutation

series of coordinated muscular contractions that moves a bolus of food from the oral cavity through the esophagus to the stomach

which phases of deglutation are involuntary

pharyngeal and esophageal phase

what happens during the oral phase of deglutation?

masticate food into a bolus

place bolus on the dorsum of the tongue and press lightly against the hard palate

lips are sealed, teeth are brought together into MIP, stabilizes the mandible

reflex wave of contraction initiates in the tongue that presses the bolus backward to the pharynx

what happens during the pharyngeal phase of deglutation?

starts with stimulation of the tactile receptors in the oropharynx, reflexes are triggered to push the food down while preventing the food from going mouth, nose, larynx, and lungs

tongue blocks oral cavity

soft palate blocks nasopharynx

vocal cord closes to protect air to lungs

larynx closes up with epiglottis covers larynx to prevent food entry to trachea

what happens during the esophageal phase of deglutation?

bolus passes through the esophagus with peristaltic waves

larynx moves down

What is the primary action that occurs during the oral phase of swallowing?

A. The bolus enters the esophagus

B. The vocal cords close

C. Food is chewed and formed into a bolus

D. The soft palate rises

C. Food is chewed and formed into a bolus

how is speech created?

the release of air from the lungs

expiration is prolonged, allowing a series of syllables, words, or phrases to make a sound

what helps to articulate sounds?

relationships of the lips and tongue to the palate and teeth

what sounds are formed by the lips?

/m/, /b/, /p/

What stage of respiration is responsible for the

creation of sound during speech?

A.Circulation

B. Expiration

C.Inhalation

D.A & C

B. Expiration

when the condyles are rotating, how far can the mandible open, and what limits the rotation?

20-25 mm, TM ligament tightening

after rotating, when the condyles are translating, how far can the mandible open, and what limits the translation?

40-60 mm, capsular ligament

what creates the opening movement?

gravity, relaxation of the elevator muscles, and combined action of the lateral pterygoid, geniohyoid, mylohyoid, and digastric muscles

what creates the closing movement?

masseter, temporal, and medial pterygoid muscles

the disc and condyle move back

which muscles help protrude the jaw?

primarily the inferior lateral pterygoid muscle, but also superficial masseter and medial pterygoid muscle

what is protrusion limited by?

posterior portion of the joint capsule

is the temporalis active during protrusion?

no

disclusion

the separation of the teeth

the steeper the eminence, the more the condyle is forced to move inferiorly as it shifts anteriorly, this results in…

greater vertical movement of the condyle, mandible, and mandibular teeth

interference

any tooth contact that prevents, or hinders harmonius mandibular movement

the steeper the condylar angle, the more allowable cuspal angle, the ____ the cusps, and the ____ the fossae

longer, deeper

how far can you typically retrude the mandible from full intercuspidation?

1-2 mm

what limits retrusion?

capsular and TM ligament

when in the maximimally protruded position, what muscles help to retrude the mandible?

posterior and middle temporalis

what happens to the right condyle during left lateral movement of the mandible?

condyle is pulled forward, downward, and medially along the articular eminence (bennet angle)

what happens to the left condyle during left lateral movement of the mandible?

lateral pole of the condyle can move backward only about 1-2 mm until restricted by the deep horizontal band of the TM ligament

which muscles are active during left lateral movement of the mandible?

right lateral and medial pterygoid muscles

the middle portion of the left temporalis and masseter muscles assist to stabilize the condyle

During left lateral movement which masticatory muscles are active on the right side?

A. Lateral Pterygoid

B. Medial Pterygoid

C. Both

C. Both

Q: Which muscles initiate mandibular opening?

A: Gravity, relaxation of elevator muscles, and action of lateral pterygoid, geniohyoid, mylohyoid, and digastric muscles

Q: Which muscle primarily pulls the condyles and discs forward in protrusion?

A: Inferior lateral pterygoid

Q: Which ligament tightens to limit condyle

A: TM ligament

Q: Which muscles execute closing of the mandible?

A: Masseter, temporalis, and medial pterygoid muscles

Q: What structures limit retrusion of the mandible?

A: TM ligament and capsular ligament