OCB04-2015 Flashcards
What factors affect chewing in humans?
Dentition
Salivary flow
Muscle strength
Food consistency/structure
What muscles are involved in jaw closing?
Masseter
Temporalis
Medial pterygoid
What muscles are involved in jaw opening?
Digastric (pulls against hyoid)
Sub-hyoid muscles help in stabilisation
What are the four phases of mammalian masticatory movement?
- Fast closing
- Slow closing
- Slow opening
- Fast opening
Which phase of masticatory movement is not present when ingesting soft foods?
- Slow closing
What factors affect the time spent in each phase of masticatory movement?
Species
Food consistency
How does the tongue move during the phases of masticatory movement?
Fast opening and closing = retraction to allow food into mouth
Slow closing and opening = protraction (elongates below food)
- Fast closing = retraction
2, Slow closing = protraction
- Slow opening = protraction
- Fast opening = retraction
What do the styloglossi and genioglossus do during the opening stages of mastication?
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
What does the tongue do pre-swallowing?
Tongue presses food against hard palate, squeezing it posteriorly
What detects the texture and properties of food?
Mucosal mechanoreceptors (gingival, PDL, etc)
Principally on soft palate to the back of the throat
Which neurons innervate the jaw muscles?
α and β motoneurons of trigeminal motor nerve
What are jaw-opening α-motoneurons primarily excited by?
Inputs from central pattern generator that drives chewing
What are jaw-closing α-motoneurons excited/inhibited by?
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)
Describe the hypoglossal motor nucleus function in masticatory movement.
Controls tongue
Some crossover to contralateral sides allows asymmetrical movement
Some input from central pattern generator to coordinate tongue movement with jaw opening/closing
Describe the facial motor nucleus function in masticatory movement.
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
What is the origin of the signals that elicit muscle activity in chewing?
Reflex
Central pattern generator in brainstem
What is the masticatory CPG influenced by?
“Drive” from motor cortex and peripheral receptors
What is the masticatory CPG?
Interconnected neural circuits producing a neural oscillatory network capable of generating simple patterns of masticatory movement
Has rhythm and pattern generator functions
Where is the masticatory CPG located?
Probably in the reticular formation and parts of the pons that contain the trigeminal nucleus
How does a CPG work?
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
Why is a CPG alone insufficient for normal life?
Basic rhythmical movement cannot be modulated by higher centres and afferent input to meet the variety challenges involved in normal mastication (eg hard foods)
What role does the cortex have in mastication?
Initiate feeding and tongue posture
Motor cortex essential for coordination and modulation of all motor systems in response to afferent input
What is stage 1 transport in mastication and swallowing?
On tongue to molars to assess whether bolus is suitable for swallowing or needs further chewing
How many chews is typically required before swallowing?
7-10
What is stage 2 transport in mastication and swallowing?
Transport to back of tongue and swallowing
What phase of masticatory movement is elongated during stage 2 transport?
Longer slower opening to allow time for pharyngeal swallow
What is swallowing?
Sequence of muscle contractions and relaxations which move material from oral cavity to stomach
~2mins
How many swallows does the average adult do per day? How many of these are done with eating?
Up to 1000/day
~150 swallows with eating
What are the 3 main stages of swallowing?
- Oral
- Pharyngeal
- Oesophageal
Describe the oral stage of swallowing.
Conscious/voluntary
Food bolus moved back to a “glossopharyngeal-innervated” area
Describe the pharyngeal stage of swallowing.
Reflex/involuntary (can be controlled a little)
Elicited by bolus stimulation of glossopharyngeal receptors
Is the oesophageal stage of swallowing conscious or reflex?
Reflex/involuntary
In what order do the pharyngeal muscles contract during a swallow?
Superior constrictor –> middle constrictor –> inferior constrictor
What muscles pull on the hyoid to change tongue position during swallowing?
Anterior and posterior bellies of digastric
Sternohyoid
What is the vallecula?
Pouch between base of tongue and epiglottis
What role does the vallecula have in swallowing?
Highly innervated so when food or saliva touches this space, it will help to elicit a swallow and suppress respiration
Which parts of the brainstem control the stages of swallowing?
Higher centres for preparatory and oral phases
Brainstem for pharyngeal and oesophageal stages
Where is the CPG for swallowing?
Brainstem
- nucleus tractus solitarius = dorsal swallowing group
- nucleus ambiguus = ventral swallowing group
Describe what happens in the CPG for swallowing.
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
What reflexes can interrupt swallowing?
Sneezing
Coughing
Gagging
Choking
What are the 4 mechanisms that protect the lower airway?
Closure of glottis (prevents aspiration)
Flexionof epiglottis over laryngeal inlet
Interruption of respiration
Swallows times to occur near end of inspiration
Why are swallows naturally timed to occur near the end of inspiration?
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
What medical conditions interfere with swallowing and reflexes that protect the airway?
Stroke
Parkinson’s disease
Myaesthenia gravis
Motor neuron disease
Recurrent laryngeal, superior laryngeal or main vagus nerve palsies
Severe chronic obstructive pulmonary disease (COPD)
