OCB04-2015

Question 1

What factors affect chewing in humans?

Answer 1

Dentition

Salivary flow

Muscle strength

Food consistency/structure

Question 2

What muscles are involved in jaw closing?

Answer 2

Masseter

Temporalis

Medial pterygoid

Question 3

What muscles are involved in jaw opening?

Answer 3

Digastric (pulls against hyoid)

Sub-hyoid muscles help in stabilisation

Question 4

What are the four phases of mammalian masticatory movement?

Answer 4

1. Fast closing
2. Slow closing
3. Slow opening
4. Fast opening

Question 5

Which phase of masticatory movement is not present when ingesting soft foods?

Answer 5

2. Slow closing

Question 6

What factors affect the time spent in each phase of masticatory movement?

Answer 6

Species

Food consistency

Question 7

How does the tongue move during the phases of masticatory movement?

Answer 7

Fast opening and closing = retraction to allow food into mouth

Slow closing and opening = protraction (elongates below food)

1. Fast closing = retraction

2, Slow closing = protraction

3. Slow opening = protraction
4. Fast opening = retraction

Question 8

What do the styloglossi and genioglossus do during the opening stages of mastication?

Answer 8

Form the longitudinal trough in tongue dorsum

Can push food to posterior oral cavity if both styloglossi contract

Can push food towards teeth if one styloglossus contracts

Question 9

What does the tongue do pre-swallowing?

Answer 9

Tongue presses food against hard palate, squeezing it posteriorly

Question 10

What detects the texture and properties of food?

Answer 10

Mucosal mechanoreceptors (gingival, PDL, etc)

Principally on soft palate to the back of the throat

Question 11

Which neurons innervate the jaw muscles?

Answer 11

α and β motoneurons of trigeminal motor nerve

Question 12

What are jaw-opening α-motoneurons primarily excited by?

Answer 12

Inputs from central pattern generator that drives chewing

Question 13

What are jaw-closing α-motoneurons excited/inhibited by?

Answer 13

Excited by inputs from central pattern generator that drives chewing and the muscle spindles

Inhibited by strong stimuli to mucosal and PDL afferents (ie very hard food)

Question 14

Describe the hypoglossal motor nucleus function in masticatory movement.

Answer 14

Controls tongue

Some crossover to contralateral sides allows asymmetrical movement

Some input from central pattern generator to coordinate tongue movement with jaw opening/closing

Question 15

Describe the facial motor nucleus function in masticatory movement.

Answer 15

Controls facial muscles including buccinator and circum-oral muscles needed to contain food in the mouth

Controls posterior digastric which needs to contract with the anterior digastric during jaw opening

Question 16

What is the origin of the signals that elicit muscle activity in chewing?

Answer 16

Reflex

Central pattern generator in brainstem

Question 17

What is the masticatory CPG influenced by?

Answer 17

“Drive” from motor cortex and peripheral receptors

Question 18

What is the masticatory CPG?

Answer 18

Interconnected neural circuits producing a neural oscillatory network capable of generating simple patterns of masticatory movement

Has rhythm and pattern generator functions

Question 19

Where is the masticatory CPG located?

Answer 19

Probably in the reticular formation and parts of the pons that contain the trigeminal nucleus

Question 20

How does a CPG work?

Answer 20

2 pathways/circuits interconnected by inhibitory pathways

Bias where one circuit starts after receiving a signal

Mutually reinforcing circuits help to propagate and maintain signal for each circuit

Active circuit sends an inhibitory signal to prevent second circuit from working at the same time

Circuit works for a while before tiring which decreases the inhibitory signal to allow the second circuit to work

Question 21

Why is a CPG alone insufficient for normal life?

Answer 21

Basic rhythmical movement cannot be modulated by higher centres and afferent input to meet the variety challenges involved in normal mastication (eg hard foods)

Question 22

What role does the cortex have in mastication?

Answer 22

Initiate feeding and tongue posture

Motor cortex essential for coordination and modulation of all motor systems in response to afferent input

Question 23

What is stage 1 transport in mastication and swallowing?

Answer 23

On tongue to molars to assess whether bolus is suitable for swallowing or needs further chewing

Question 24

How many chews is typically required before swallowing?

Answer 24

7-10

Question 25

What is stage 2 transport in mastication and swallowing?

Answer 25

Transport to back of tongue and swallowing

Question 26

What phase of masticatory movement is elongated during stage 2 transport?

Answer 26

Longer slower opening to allow time for pharyngeal swallow

Question 27

What is swallowing?

Answer 27

Sequence of muscle contractions and relaxations which move material from oral cavity to stomach ~2mins

Question 28

How many swallows does the average adult do per day? How many of these are done with eating?

Answer 28

Up to 1000/day ~150 swallows with eating

Question 29

What are the 3 main stages of swallowing?

Answer 29

1. Oral 2. Pharyngeal 3. Oesophageal

Question 30

Describe the oral stage of swallowing.

Answer 30

Conscious/voluntary Food bolus moved back to a "glossopharyngeal-innervated" area

Question 31

Describe the pharyngeal stage of swallowing.

Answer 31

Reflex/involuntary (can be controlled a little) Elicited by bolus stimulation of glossopharyngeal receptors

Question 32

Is the oesophageal stage of swallowing conscious or reflex?

Answer 32

Reflex/involuntary

Question 33

In what order do the pharyngeal muscles contract during a swallow?

Answer 33

Superior constrictor --> middle constrictor --> inferior constrictor

Question 34

What muscles pull on the hyoid to change tongue position during swallowing?

Answer 34

Anterior and posterior bellies of digastric Sternohyoid

Question 35

What is the vallecula?

Answer 35

Pouch between base of tongue and epiglottis

Question 36

What role does the vallecula have in swallowing?

Answer 36

Highly innervated so when food or saliva touches this space, it will help to elicit a swallow and suppress respiration

Question 37

Which parts of the brainstem control the stages of swallowing?

Answer 37

Higher centres for preparatory and oral phases Brainstem for pharyngeal and oesophageal stages

Question 38

Where is the CPG for swallowing?

Answer 38

Brainstem - nucleus tractus solitarius = dorsal swallowing group - nucleus ambiguus = ventral swallowing group

Question 39

Describe what happens in the CPG for swallowing.

Answer 39

Dorsal swallowing group (NTS) receives inputs from higher centres and peripheral afferents to generate the trigger, shape and timing of the rhythmic swallowing patterns Ventral swallowing group (NA) contains cell bodies of motoneurons that are activated by dorsal swallowing group and directly innervate the muscles

Question 40

What reflexes can interrupt swallowing?

Answer 40

Sneezing Coughing Gagging Choking

Question 41

What are the 4 mechanisms that protect the lower airway?

Answer 41

Closure of glottis (prevents aspiration) Flexionof epiglottis over laryngeal inlet Interruption of respiration Swallows times to occur near end of inspiration

Question 42

Why are swallows naturally timed to occur near the end of inspiration?

Answer 42

Ensures that if an object is aspired: - there is an escape of air at first opening of the glottis to help clear the laryngeal opening - there would be an adequate volume of air in the lungs to permit a forceful cough to dislodge the object

Question 43

What medical conditions interfere with swallowing and reflexes that protect the airway?

Answer 43

Stroke Parkinson's disease Myaesthenia gravis Motor neuron disease Recurrent laryngeal, superior laryngeal or main vagus nerve palsies Severe chronic obstructive pulmonary disease (COPD)