L2: mastication & deglutition Flashcards
Function of mastication
First stage of digestion
Mash and crush food so it is small enough to swallow - bolus
Mixes food with saliva
Increases SA for enzymes
What part of the mouth does it involve?
Mandible moves up and down - incisors bite food
Molars side to side to crush food into bolus
Tongue
What does chewing do?
Generates a lot of saliva
Muscles of mastication - jaw closing
Temporalis
Masseter
Medial pterygoid
Muscles of mastication - jaw opening
Lateral pterygoid
What are the muscles of mastication innervated by?
The mandibular division of the trigeminal nerve (CNV)
How do we know mastication is controlled?
Because the bite required is different for different foods e.g., for jelly, cracker or steak different bites are needed
Central pattern generator - ‘chewing centre’
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.
How does the chewing centre allow control of jaw movements?
- controls jaw opening and jaw closing
- generates a basic rhythm
- brought about by neuronal network in the brainstem - rhythm generating neurones
How does the chewing centre control bite?
- 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
How does the sensory feedback in the chewing centre work?
- 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.
What factors affect pattern of chewing?
Pattern of chewing varies according to age, gender, food
Which centres communicate with each other?
Respiratory CPG and swallowing CPG communicate with each other and the masticatory CPG, so it is all coordinated.
Difference between the rhythm generator and the burst generator
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.
How does dental/periodontal disease affect mastication?
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
What is deglutition?
Swallowing
Lasts a few second
Requires 25 muscles
Coordinated by stalling centre in medulla
What are the three phases of deglutition?
Oral - voluntary
Pharyngeal - involuntary
Oesophageal - involuntary
What kind of reflex is deglutition?
All or none reflex - once it is started it cannot be stopped
Pharyngeal phase of deglutition
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)
Oesophageal phase of deglutition
8-20 seconds
Sphincters at both ends (upper and lower oesophageal sphincter, UOS and LOS)
Peristaltic action pushes food down
Controlled by swallowing centre
Structure of the muscular oesophageal tube
Upper third: skeletal muscle
Middle third: skeletal and smooth muscle
Terminal third: smooth muscle
How do the oesophageal sphincters work?
Ensure food doesn’t come back up from the stomach
LOS opens to allow food into the stomach
How does oesophageal peristalsis work?
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
What is oesophageal peristalsis controlled by?
Extrinsic vagal nerves
Intrinsic enteric nerves (within the alimentary tract)
