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describe the different types of contractions

Isotonic Contraction: when many motor units are activated and the muscle is shortened
Force of contraction greater than opposing force
Occurs when masseter elevates the mandible to crush the bolus of food

Isometric Contraction: when an adequate # of motor units are activated to resist an opposing force ~ results in no motion
Force opposing = force of contraction
When the masseter contracts to hold something between the teeth

Controlled Relaxation: when controlled relaxation of different motor units allow a controlled lengthening of the muscle unit
Dictated by a smooth movement, smoothly decreasing the number of active motor units
Happens when you open the mouth to accept more food
Contraction of the muscle controlling depression—lateral pterygoid and

Eccentric contraction--muscles contracts while simultaneously lengthening


what are the parts of the STN?

Subnucleus oralis – pulp afferent
Subnucleus interpolaris – pulp afferent & oral pain
Subnucleus caudalis – pulp afferent & trigeminal nociceptive (is especially nociceptive)
Pulp has a lot of nociceptive afference, very important for homseostasis; this is why tooth pain is one of the most painful experiences


purpose of motor nucleus

Interpret impulses demanding motor response
Also act as center for motor reflexes of the face (as spinal reflexes in the rest of the body)


purpose of ret form?

interneurons pass through
Nuclei here are centers for various functions:
monitor impulses entering brainstem
Controls brain activity by ↑ or ↓ impulses to higher centers
Activates or inhibits
*****Influences pain and other sensory info


purpose of thalamus

Thalamus evaluates and directs impulses to appropriate higher centers
It drives the Cortex to act
It allows the Cortex to communicate with other centers


study slide 23



describe golgi tendon organs

Located in the tendon (between muscle and bone) and monitor tension in the tendon
Seem to be more active in ‘reflex’ actions during normal fn (rather than acting like Muscle Spindles as was once believed)

Work in series with the Extrafusal Muscle fibers
Tendinous fibers surrounded by lymph spaces, enclosed in a fibrous capsule
Afferent fibers enter near the center and spread branches throughout the internal fiber network
Is actually in the tendon
Can sense both stretch and contraction in a tendon
Whether the tension is from outside sources or muscle


study slide 37 & 38



describe the myotactic stretch reflex

The only monosynaptic jaw reflex
When skeletal muscle is quickly stretched – this reflex elicits a contraction response
Protective mechanism
Prevents gravity from pulling jaw down
Ex. – Masseter quickly stretched → muscle spindles activate afferent neurons → brainstem (trigeminal motor neuron) → synapse with α efferent neuron (Ia) → contraction of the masseter muscle via extrafusal fibres

Counteracts the effects of gravity on the mandible
Without muscular action – the TMJ would dislocate when not in function
Muscle tonus – slight contraction maintained by this reflex

As gravity pulls down on the mandible, muscle spindles are stretched → reflex controlled activation of the elevator muscle → maintains muscle tonus and mandibular position
Muscle tonus also influenced by other sensory receptors (skin, oral mucosa, etc.)


describe the nociceptive reflex

Also called the Flexor reflex = Polysynaptic
Also inhibition of current movemente.g. touch something hot, immediately pull hand away
Ex: Chewing and biting a hard object (antagonistic inhibition)
Noxious stimulus generated by periodontal structures → afferent fibers to the Trigeminal Spinal Tract Nucleus & synapse with interneurons → interneurons to Trigeminal motor nucleus
Trigeminal motor nucleus → coordinates several muscle groups at once
Inhibition of the elevator muscles
Activation of depressor muscles


what is CPG and what is it related to?

collection of neurons in brainstem that control rhythmic muscular activities (walking, breathing, chewing)


Chewing stroke sequence:
Opening movement/opening phase
mnd drops down (incisal edges are ~ 16 – 18 mm apart)
Lateral movement ~ 5 -6 mm off midline

Closing movement – 2 phases
Crushing phase – food bolus trapped, mnd is elevated and moved back towards midline
When incisors are ~ 3 mm apart, the mnd is only 3-4 mm off midline
Mx & mnd Buccal cusps aligned on working side
Grinding phase – with food bolus trapped, teeth are guided into intercuspation by occlusal surfaces of the teeth



study slide 51



study slide 54



study slide 53



what are the two types of contacts?

Gliding – on opening and grinding phases (~60% for 194 ms)

Single – in max intercuspal position

Tooth morphology determines broadness of chewing stroke (guidance in grinding phase)


Molars can accept more force (41.3-89.8 kg) than can incisors (13.2-23.1 kg) … < 1/3
Biting force increases from childhood to adolescence
Food may impact a person’s biting force (Inuit people have ‘unusually’ high biting forces)



role of soft tissue in chewing?

Lips – guide and control intake, also seal the oral cavity
Maneuvers food onto chewing surfaces
Initial breakdown – forces food against hard palate
Divides food into portions that need more chewing
Cleans teeth
Buccinator – repositions food onto teeth


type of swallowing?

somatic--posterior teeth contact and provide stability
Somatic swallowing – teeth contact for ~683 ms @ ~ 65 lbs.

visceral--infants or those without teeth … tongue thrust forward between arches (until molars erupt)
Still allow mandible to stabilize itself
If a child does not grow out of this, the tongue can procline the teeth outwards when they grow in


describe the stages of swallowing

stage 1--– voluntary
Food bolus divided into appropriately sized portion by tongue
Bolus is placed on dorsum of tongue, and tongue pressed lightly to hard palate
Lips sealed – teeth into IP

Presence of food on dorsum initiates a reflex wave of contraction in tongue – forces food back from tongue into pharynx

stage 2--Once in the pharynx – a peristaltic wave of pharyngeal constrictors carries food down to esophagus
Soft palate rises to touch post. pharyngeal wall = sealing nasal cavity
Epiglottis blocks the trachea
Activity of constrictors opens pharyngeal orifices of Eustachian tubes

Activity of stage 1 & 2 ~ 1 sec

Third Stage
Esophagus to Stomach – via peristaltic waves ~ 6 sec
Cardiac sphincter relaxes, and bolus enters stomach

Upper esophagus – muscles are ‘voluntary’ – can return food to the mouth if more mastication is needed
Lower esophagus is involuntary


swallowing facts Frequency - ~590 x per day
~ 146 cycles during eating
~ 394 cycles between meals (awake)
~50 times during sleep (decreased saliva)



how can pain be modulated?

non-painful cutaneous stimulation (e.g. TENS)--subpainful stimulation that stims larger muscle fibre and blocks input of the smaller fibres to CNS

- intermittent painful stimulation (i.e. via endorphins)-->painful stim at a site away from the source/site

- psychological modulation (e.g. distraction)


- protective co-contraction (“muscle splinting”) = example of the central excitatory effect on efferent neurons which causes contraction of antagonistic muscles when pain is present thereby limiting function and causing fatigue
- sometimes trigger points, localized areas of hypersensitivity, are developed in response to prolonged deep pain
- as such, pain can become self-perpetuating and is often termed “cyclic”
- testing for unilaterality is the best way to confirm any sort of central excitatory effect



study slide 7



study slide 10



study slide 22



study slide 31



Gamma efferents can sustain a muscle contraction (by ‘tricking’ the CNS into believing that a muscle group is no longer contracting)
Can cause muscle spasm-->if efferents are slacked, says muscle is relaxednot calibrated properlythinks muscle isn’t contracted so it tells it to contract (cramp)
Gamma efferents – ‘sensitize’ the muscle spindle, keeping it activated to monitor muscle status
Gamma efferents – not present in all M.O.M.s, but very active in ‘reflex’ actions