Control of Mastication

Question 1

What are the two stages of mastication?

Answer 1

Stage 1 = assessing the food and starting to chop it up

Stage 2 = bolus is formed and food is swallowed

Question 2

What are the 4 main factors which affect chewing?

Answer 2

1. Dentition (number and quality of teeth)
2. Salivary flow
3. Muscle strength/age
4. Food consistency/structure

Question 3

What does the pattern of jaw movement depend on?

Answer 3

Species (jaw morphology)
Type of food
Individual variation

Question 4

What are the main muscles for a)closing and b)opening the jaw?

Answer 4

a) masseter, temporalis, pterygoid

b) digastric, intrinsic and extrinsic tongue muscle, sub-hyoid muscles

Question 5

What are the 4 masticatory movements in an ingestion cycle?

Answer 5

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

Question 6

How how the tongue is affected in the 4 masticatory stages?

Answer 6

Fast closing = retraction of tongue

Slow closing = retraction of tongue

Slow opening = protraction of tongue (to rearrange bits of food to align with teeth)

Fast opening = retraction of tongue

Question 7

Explain some afferent and efferent activity during the masticatory cycle

Answer 7

Main receptor activity from:

• Opener motor neurons
• Closer motor neurons
• Periodontal receptors
• Cuntaneous receptors (mucosal receptors)

Question 8

What happens to the tongue during pre-swallowing?

Answer 8

Tongue presses food against the hard palate, squeezing it posteriorly

Question 9

How does our body know when to stop chewing?

Answer 9

Texture of food is detected by mucosal mechanoreceptors, to enable modulation of the masticatory pattern according to food consistency.

Question 10

What cranial nerve from the brain is important in jaw opening and closing?
Explain this further

Give the other two cranial nerve nuclei which give some input into opening and closing too

Answer 10

The trigeminal nerve.

It consists of alpha and gamma motoneurons which innervate the jaw muscle.

Jaw opening = alpha motoneurons are excited primarily by inputs from the central pattern generator that drives chewing.

Jaw closing = alpha motor neurones are excited by inputs from the central pattern generator and inhibited by strong signals to periodontal ligament.

Hypoglossal motor nucleus and facial motor nucleus.

Question 11

What are the two ways that muscle activity to the jaw can be elicited?

Answer 11

By a reflex or by the central pattern generator.

Question 12

Give some details on the masticatory central pattern generator

Answer 12

• Interconnected neural circuits producing a neural oscillatory network capable of generating simple patterns of masticatory movements
• Probably located in the reticular formation, and parts of the Pons that contain the trigeminal nuclei
• It has both rhythm generator and pattern generator functions
• Its output to mastictory motoneurons may be modified by input from afferent and central areas

Question 13

How does a central pattern generator work?

Answer 13

2 pathways interconnected by inhibitory connections.
1 circuit starts first once receiving signals. At this point, inhibitory fibres are sent to the second circuit to prevent the two operating at the same time e.g. one to open the jaw and one to close the jaw.

Once circuit one has slowed down, the inhibition to circuit 2 is reduced and then this circuit will then become activated.

Question 14

What influences do the higher senses give to mastication?

Answer 14

• In dysfunction of masticatory area of the motor cortex, there is generally failure to fully recover normal mastication
• Cortex initiates feeding and tongue posture in adults
• Motor cortex is essential for co-ordination and modulation of all the motor systems in response to afferent input

Question 15

What happens to the 4 stages to allow for swallowing?

Answer 15

The slow opening phase lengthens to allow time for the pharyngeal swallow.

Question 16

Define swallowing and explain why less of it happens during sleep

Answer 16

Swallowing is a sequence of muscle contraction and relaxation which move material from the oral cavity to the stomach.

Less swallows when asleep because less salivary flow is occurring.

Question 17

What are the 3 stages of swallowing?

Answer 17

1. Oral
2. Pharyngeal
3. Oesophageal

1 = conscious phase 
2 = reflex movement with some conscious control
3 = no conscious control

Question 18

What is the tongue base position controlled by?

Answer 18

Tongue base is controlled by the hyoid bone. The hyoid bone is attached via sternohyoid muscles to the sternum.

Question 19

In what order do the pharyngeal muscles contract?

Answer 19

Superior constrictor, middle constrictor then inferior constrictor.

Question 20

What is the valleculae and what is the importance of it?

Answer 20

When we start chewing, some of the food may move down into the pouch called the vallacula.
This is highly innervated with nerves.
When this pouch overflows, a swallow is triggered and respiration is suppressed.

Question 21

How is swallowing controlled?

Answer 21

Preparatory and oral phases = voluntary control from higher CNS centres

Pharyngeal and oesophageal phases = involuntary control from the brain stem

The whole system involves:

• Large areas of brain stem
• Several cranial nerves
• Numerous muscles
• Many afferent receptors

Question 22

How does the swallowing central pattern generator work?

Answer 22

Signals come from both the primary motor cortex and from the afferent inputs (from the mouth).

The CPG is located in the brainstem for the pharyngeal and oesophageal phases (involuntary phases)

Dorsal swallowing group = receives inputs from higher genres and from peripheral afferents to generate the rhythmic swallowing patterns.

Ventral swallowing group = these contain the cell bodies of the motoneurons that are activated by the dorsal swallowing centre and directly innervate the muscles.

Question 23

What reflexes interrupt swallowing?

Answer 23

• Sneezing
• Coughing
• Gagging
• Choking

Question 24

How is the lower airway protected when swallowing?

Answer 24

• Closure of the glottis
• Flexion of the epiglottis over the laryngeal inlet
• Interruption of respiration
• The swallow is timed to occur near the end of inspiration (to ensure there is air in the lungs to allow for a cough)