L2: mastication & deglutition

Question 1

Function of mastication

Answer 1

First stage of digestion
Mash and crush food so it is small enough to swallow - bolus
Mixes food with saliva
Increases SA for enzymes

Question 2

What part of the mouth does it involve?

Answer 2

Mandible moves up and down - incisors bite food
Molars side to side to crush food into bolus
Tongue

Question 3

What does chewing do?

Answer 3

Generates a lot of saliva

Question 4

Muscles of mastication - jaw closing

Answer 4

Temporalis
Masseter
Medial pterygoid

Question 5

Muscles of mastication - jaw opening

Answer 5

Lateral pterygoid

Question 6

What are the muscles of mastication innervated by?

Answer 6

The mandibular division of the trigeminal nerve (CNV)

Question 7

How do we know mastication is controlled?

Answer 7

Because the bite required is different for different foods e.g., for jelly, cracker or steak different bites are needed

Question 8

Central pattern generator - ‘chewing centre’

Answer 8

Chewing is a repetitive and rhythmical motor activity controlled by the ‘chewing centre’
Masticatory central pattern generator (CPG). A neural network in the brain stem.

Question 9

How does the chewing centre allow control of jaw movements?

Answer 9

• controls jaw opening and jaw closing
• generates a basic rhythm
• brought about by neuronal network in the brainstem - rhythm generating neurones

Question 10

How does the chewing centre control bite?

Answer 10

• great variability
• regulated by food type
• brought about by sensory feedback to the brain stem
  Type of chewing is modified by:
• cortex - voluntary control
• sensory feedback from dental/periodontal receptors

Question 11

How does the sensory feedback in the chewing centre work?

Answer 11

• dental (tooth pulp) /periodontal mechanoreceptors send information on the food to the brain stem/CPG
• fine tune rhythmic jaw movements
• prevents excessive force being applied to the tooth
• if biting force increases, jaw closing is inhibited (so you don’t chomp too hard)
• adapts to the food type - motor output becomes appropriate for food viscosity, size, temperature etc.

Question 12

What factors affect pattern of chewing?

Answer 12

Pattern of chewing varies according to age, gender, food

Question 13

Which centres communicate with each other?

Answer 13

Respiratory CPG and swallowing CPG communicate with each other and the masticatory CPG, so it is all coordinated.

Question 14

Difference between the rhythm generator and the burst generator

Answer 14

Rhythm generator - generates the basic masticatory rhythm
Burst generator - adapts rhythm according to sensory inputs from the oral cavity so that the movement becomes appropriate for the food bonus, size, viscosity and temperature. Fine tunes rhythmic jaw movements.

Question 15

How does dental/periodontal disease affect mastication?

Answer 15

Edentulism (no teeth) - some sensory feedback in the teeth is lost
Periodontal disease - inflammation means sensors won’t work as well
Dental caries - teeth are rotting, so nerves within them will have trouble working
Dentures - loss of sensory feedback and fine tuning ability

Question 16

What is deglutition?

Answer 16

Swallowing
Lasts a few second
Requires 25 muscles
Coordinated by stalling centre in medulla

Question 17

What are the three phases of deglutition?

Answer 17

Oral - voluntary
Pharyngeal - involuntary
Oesophageal - involuntary

Question 18

What kind of reflex is deglutition?

Answer 18

All or none reflex - once it is started it cannot be stopped

Question 19

Pharyngeal phase of deglutition

Answer 19

1 second
Food activated pressure receptors in palate/pharynx
Impulses to the swallowing centre in brainstem:
- lifts soft palate and seals nasal cavity
- raises larynx
- closes glottis (opening of trachea) by lowering epiglottis over trachea - can’t breath
- inhibits respiration
The upper oesophageal sphincter opens, it closes once the food passes and the glottis opens again.
(Refer to pic at min 35)

Question 20

Oesophageal phase of deglutition

Answer 20

8-20 seconds
Sphincters at both ends (upper and lower oesophageal sphincter, UOS and LOS)
Peristaltic action pushes food down
Controlled by swallowing centre

Question 21

Structure of the muscular oesophageal tube

Answer 21

Upper third: skeletal muscle
Middle third: skeletal and smooth muscle
Terminal third: smooth muscle

Question 22

How do the oesophageal sphincters work?

Answer 22

Ensure food doesn’t come back up from the stomach

LOS opens to allow food into the stomach

Question 23

How does oesophageal peristalsis work?

Answer 23

Gravity is not only thing that moves food down
Wave-like smooth muscle contractions and relaxation:
- response to wall distension by bolus
- contracts behind bolus
- relaxes in front of bolus

Question 24

What is oesophageal peristalsis controlled by?

Answer 24

Extrinsic vagal nerves

Intrinsic enteric nerves (within the alimentary tract)