Case 1 - PBL Flashcards
what is included in the voluntary phase of swallowing
mastication: leads to a bolus of food being produced, during this stage the back of the tongue is elevated and the soft palate pulled anteriorly against it. this keeps the food within the oral cavity and allows the airway to remain open
what happens after mastication in the voluntary phase
inspiration is inhibited and the bolus of food is moved to the pharynx by the tongue. this leads to the stimulation of the swallowing reflex
what is the nerve involved in the voluntary phase
the trigeminal nerve
what happens in the pharyngeal phase
Once the bolus has been moved to the pharynx, pressure receptors are activated in the palate and the anterior pharynx. This signals the swallowing centre in the brain stem which:
inhibits respiration
Raises the larynx
Closes the glottis
Opens the upper oesophageal sphincter
Levator and tensor veli palatini
what else happens to prevent aspiration
the true vocal cords are closed
what happens after the vocal cords are closed and the soft palate is elevated
the bolus is moved towards the oesophagus via peristalsis of the pharyngeal constrictor muscles. Gravity makes very little contribution to this process and the main factors affecting the speed of this are the viscosity and volume of the bolus.
what is the upper third of the oesophagus
voluntary skeletal muscle
what are the lower two thirds of the oesophagus
involuntary smooth muscle
what muscle prevents reflux
the larynx lowers, returning to its normal position. the cricopharyngeus muscle then contracts to prevent reflux and respiration begins again
what happens after this
The bolus is moved down the oesophagus via peristalsis, which is coordinated by extrinsic nerves. Each area of muscle systematically relaxes to allow food through and contracts afterwards to propel it further. The bolus is propelled at a rate of around 3-5cm per second and so the transit time to the stomach takes around 9 seconds.
digram showing swallowing
what are long periods of low flow of saliva broken by
short periods of high flow, which is stimulated by taste and mastication
what is the nerve mediated salivary reflex modulated by
nerve signals from other centres in the central nervous system, which is most obvious as hyposalivation at times of anxiety
what does circadian rhythm affect
salivary flow and ionic composition
what evokes salivary secretion
Cholinergic parasympathetic and adrenergic sympathetic autonomic nerves evoke salivary secretion, signalling through muscarinic M3 and adrenoceptors on salivary acinar cells and leading to secretion of fluid and salivary proteins.