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Orthodontics > Exam 2 - Control of Mastication (Part One) > Flashcards

Exam 2 - Control of Mastication (Part One) Flashcards

1
Q

What are the three recording techniques of mastication in human subjects?

A
  1. cineradiography
    - take x-rays like picture frames of a movie and you will see moving objects on radiographs
  2. tracking devices (i.e., light source marker applied to teeth and movements recorded in 3D)
  3. electrmyography (EMG) - records changes in electrical potential in activated muscle fibers during contraction most important
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2
Q

What 2 experiments in animals observe mastication?

A
  1. metal markers bonded to skeletal structures or teeth to track movements
  2. direct recordings from neural pathways involved or experimental ablation of these neural pathways
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3
Q

The pattern of movements and muscle activity of the masticatory muscles depend on

A
  1. species
  2. type of food
  3. individual variation
    - jaw opening
    - jaw closing
    - contralateral balance
    - variable lateral and A/P jaw movements
    - tongue movemments
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4
Q

What are the three jaw closer muscles?

A
  1. masseter
  2. temporalis
  3. medial pterygoid

*pterygoid and masster form a muscle sling

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5
Q

What is the jaw opening muscle?

A

anterior and posterior digastric

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6
Q

Which two muscles form the masticatory sling?

A

medial pterygoid and masseter

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7
Q

What is the function of the lateral pterygoid?

A
  • attaches to the condyle of the mandible
  • stabilizing the condyle during mastication
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8
Q

How many heads does the lateral pterygoid have?

A

2
- superior and inferior

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9
Q

What are the 4 phases of mammalian masticatory movement during one ingestion ‘cycle’?

A
  1. fast closing
  2. slow closing
  3. slow opening
  4. fast opening
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10
Q

EXAM QUESTION How many phases are there in a masticatory cycle?

A

4

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11
Q

True or false: The relative time spent in the 4 phases of mastication varies with species and consistency of food.

A

True

**slow closing would be barely there when ingesting soft food

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12
Q

Compare and contrast the masticatory cycles in hard food and soft food

A

Hard food:
1. profile of jaw movement
- extended slow closing phase (power stroke) which will bite down and crush the food

Soft food:
1. profile of jaw movement
- no extended slow closing phase
- its hard to detect the slow closing phase

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13
Q

What does the tongue do during mastication?

A
  1. FAST OPENING AND CLOSING
    - tongue retracts to allow food into mouth
  2. SLOW CLOSING & SLOW OPENING
    - tongue moves forward and elongates below food
  3. MAINLY DURING OPENING
    - styloglossi and genioglossus act together to form a longitudinal trough in the dorsal surface of the tongue that:
    –> either pushes food to the posterior oral cavity (if both SG contract together)
    –> pushes food towards the cheek for further processing if food not ready for swallowing (if one SG contracts)
  4. PRE-SWALLOWING
    - tongue presses food against the hard palate, squeezing it posteriorly
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14
Q

If you contract the right styloglossus and relax the left, where will the bolus go?

A

left posterior occlusal surface of the teeth

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15
Q

Inverted V***

A

Answer

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16
Q

Describe an EMG of the complete masticatory sequence

A

Mvt - Jaw tracking in three planes of space
- vertical
- lateral
- anterior/posterior

Op - Opening
RDIG = right digastric
LDIG = left digastric

Cl - Closing
RDMA = right masseter
LDMA = left masseter

RPTE = right pterygoid

Stage one transport = food from incisal surfaces to posterior occlusal surfaces

Stage two transport = oral cavity to oralpharyngeal space to initiate a swallow

**staggered action potentials between closer muscles and opener muscles

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17
Q

What is the hallmark muscle seen on an EMG which shows initiation of a swallow?

A

thyrohyoid muscle

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18
Q

What is the innervation of the thyrohyoid?

A

1st cervical nerve

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19
Q

What is the function of the thyrohyoid muscle?

A

stabilizes hyoid bone

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20
Q

What is the function of the anterior and posterior digastric muscles?

A

elevates hyoid bone and depresses mandible

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21
Q

What is the innervation of the anterior and posterior digastric muscles?

A

anterior digastric: trigemenal cranial nerve (5)
posterior digastric: facial cranial nerve (7)

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22
Q

True or false: The thyrohyoid muscle is innervated by a cranial nerve.

A

False, its innervated by the 1st cervical nerve.

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23
Q

EXAM QUESTION What is the motor innervation of the jaw-closers?

A

trigeminal (V)

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24
Q

EXAM QUESTION What is the motor innervation of the digastric muscles?

A

anterior digastric - trigeminal (V or 5)
posterior digastric - cranial (VII or 7)

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25
Q

EXAM QUESTION What is the motor innervation of the intrinsic tongue muscles?

A

hypoglossal XII

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26
Q

EXAM QUESTION What is the motor innervation of the extrinsic tongue muscles?

A

hypoglossal XII

*with one exception (palatoglossus muscle)

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27
Q

What is the exception to the innervation of the extrinsic tongue muscles?

A

palatoglossus is innervated by vagus cranial nerve X (or 10)

28
Q

Memorize the path of mastication

A
29
Q

Describe the afferent and efferent activities during one chewing cycle.

A

EFFERENT - from brainstem to oral cavity
opener EMG = opener (i.e., anterior digastric)
closer EMG = closer (i.e., temporalis)

AFFERENT = from oral cavity in opposite direction to brainstem for sensation
periodontal ligament:
cutaneous (mucosa): receptors on the skin that are sensing anything touching the skin (i.e., food touching the cheeks)

*RA –> rapidly adopting action potentials (initial burst which it adjusts to)
*SA –> slowly adopting action potentials (continuous sensation)

30
Q

What are the periodontal mechanoreceptors?

A
  • mylenated and unmylenated
  • ruffini-like endings

*allow CNS to know that the root of tooth being displaced in the socket between the root and alveolar bone

31
Q

Describe the oral and mucosal mechanoreceptors.

A
  • slowly or rapidly adapting to stimuli
  • have specific structural & physiological adaptations depending on area/function
32
Q

Afferent feedback from oral function comes from other mechanoreceptors such as

A
  • muscle spindles
  • golgi tendon organs
  • periodontal ligament receptors
33
Q

True or false: Different textures and properties of food are detected by mucosal mechanoreceptors, to enable modulation of the masticatory pattern according to food consistency.

A

True

34
Q

What type of receptive field and adaptive response is good for detecting hard lumpy foods?

A
  • small receptive field
  • rapidly-adapting response
35
Q

What type of receptive field and adaptive response is good for detecting soft, spreading foods?

A
  • large receptive field
  • slowly-adapting response
36
Q

Proprioceptors that lie in the muscle in parallel with muscle fibers

A

muscle spindles

37
Q

What happens when the spindle (intrafusal) fibers are stretched?

A

deforms sensory afferent endings, causing them to fire APs

38
Q

How is the sensitivity of the spindles to stretch adjusted?

A

gamma (fusimotor) efferents supplying the intrafusal fibers

39
Q

In afferent innervation, what do the group Ia afferents singal?

A

change in length

40
Q

In afferent innervation, what do group II afferents singal?

A

absolute length

41
Q

What are the two functions of gamma motor (fusimotor) supply?

A
  1. used to adjust sensitivity of afferents to length changes
  2. in load compensation, i.e., detection of and compensation for, unexpected alterations to a movement predicted or planned by the CNS (ex. when food is harder than expected)
42
Q

What are the 2 brainstem structures involved in mastication?

A
  1. motor - various cranial motor nuclei
  2. sensory - trigeminal sensory nucleus - a column or neurons which extend along the lateral borders of the brain stem from the pons to the first two segments of the spinal cord
43
Q

Primary afferents that detect the peripheral signal will have their cell bodies in 2 places, what are they?

A
  1. trigeminal ganlia
  2. trigeminal mesencephalic sensory nucleus
44
Q

Secondary afferents are the next step in the afferent pathway, where are their cell bodies located and where do they project?

A

location: trigeminal main sensory nuclus
projection to: CPG and sensory cortex

45
Q

Describe the trigeminal neurophysiology diagram

A
  • Mucosal mechanoreceptors found in the mesencephalic sensory nucleus (in CNS)
    **monosynaptic: can be direct
  • PDL mechanoreceptors found in both the mesencephalic sensory nucleus and in the trigeminal ganglion*
    *trigeminal ganglion is external to CNS
    **need an interneuron b/c external
46
Q

Where does the trigeminal mesencephalic sensory nucleus lie?

A

rostral (near the front) to main sensory nucleus

47
Q

The trigeminal mesencephalic sensory nucleus contains primary afferent cell bodies from what three things?

A
  1. spindles of jaw-closing muscles
  2. periodontal ligament mechanoreceptors
  3. gingival and palatal mechanoreceptors
48
Q

The primary afferent neurons send collaterals to which nerve to form the basis fr masticatory reflexes?

A

motor nucleus of trigeminal (Vth or 5th) nerve

49
Q

The only part of the CNS with primary afferent cell bodies is

A

gingival and palatal mechanoreceptors

50
Q

The ____ contains cell bodies of alpha and gamma motorneurons which innervate the jaw muscles.

A

trigeminal motor nucleus

51
Q

How are jaw-opening alpha motorneurons excited?

A

inputs from the central pattern generator that drives chewing

52
Q

How are jaw-closing alpha motorneurons excited?

A
  1. inputs from the central pattern generator that drives chewing
  2. by inputs from muscle spindles
53
Q

How are jaw-closing alpha motorneurons inhibited?

A

by strong stimuli to mucosal & periodontal ligament afferents

54
Q

The temporalis muscle is located mostly ___ on the trigeminal motor nucelus?

A

dorsal

*jaw closing

55
Q

The diagstric muscle is located mostly ___ on the trigeminal motor nucleus?

A

ventral

*jaw opening

56
Q

What are two other motor nuclei that have to be coordinated with the trigeminal motor nuclei during mastication?

A
  1. hypoglossal motor nucleus
    - crossover to contralateral side
    - inputs from CPG (tongue movements during opening/closing)
  2. facial motor nucleus
    - facial muscles: buccinator and obicularis oris need to contain food during mastication
    - posterior digastric (needs to contract with anterior digastric)
57
Q

What is patterning the trigeminal motor nuclei to produce movements of opening/closing?

A
  • MOST IMPORTANT: CPG (central pattern generator) responsible for most chewing
  • by a reflex (opening or closing)
58
Q

Where is the CPG located?

A

brainstem

59
Q

It’s activity is influence by drive from motor cortex and peripheral receptors

A

CPG

60
Q

Describe how the CPG “patterns” movement

A

electrical recording of
- dorsal masseter skeletal muscle fibers
- ventral on anterior digastric muscles

CLOSING
- inhibitory patterns sent for digastric (ventral motor neuron)
- activation patterns sent for masseter (dorsal motor neuron)

OPENING
- inhibitory patterns sent for masseter (dorsal motor neuron)
- activation patterns sent for digastric (ventral motor neuron)

61
Q

sterotyped nervous system response to a stimulus

A

reflex

62
Q

A reflex can be altered in ____ but not ____

A

strength (quantitatively)
kind of response (quality)

63
Q

True or false: Reflexes are ALWAYS unconscious/automatic/innate.

A

False, they are often but not ALWAYS.

For example, they can be consciously suppressed or learned

64
Q

What is the jaw-opening reflex?

A
  • main sensory Vth and spinal sensry Vth nuclei
  • protective functions for tongue, face, and jaw (i.e., overlad on one tooth with inflamed PDL will inhibit jaw closing)
  • usually di-synaptic within CNS and fast
65
Q

What is the jaw-closing reflex?

A
  • mesencephalic nucleus
  • jaw-jerk reflex: monosynaptic reflex elicited by stretching closer muscles, causing the jaw to close
66
Q

True or false: The jaw closing (jaw jerk) reflex is a di-synaptic reflex.

A

False, it is monosynpatic.

Orthodontics (7 decks)

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