Chewing Has two functions

1. Mixes food with saliva

• Lubricate and facilitate swallowing 

• Expose starch in food to salivary amylase 

2. Reduce the size of food particles

• Facilitate swallowing 
• The act of chewing both voluntary an involuntary

• Most of the time proceeds by the reflex actions void of conscious input 
• Liquids – propelled immediately from the mouth and the oropharynx and swallowed 

Swallowing 

• Swallowing is initiated voluntarily 
• Occurs in 3 stages 

1. Voluntary stage (oral stage )

• Food bolus is propelled towards the pharynx by the tongue 
• Soft palate is elevated and closes off the entrance to the nasal passage 

2. Pharyngeal stage

• Pharyngeal stage is the beginning of involuntary reflex activity 
• At the start vocal cords approximate and close the glottis 
• Respiration is inhibited and the larynx is pulled upwards 
• The bolus pushes the epiglottis back over the glottis 
• Prevent food entering the respiratory tract 

Oral stage and Pharyngeal stages are brief ( last < 1 Sec )

• Stimulation of pharyngeal receptors 
• Carries impulse through vagaus and glossopharengial nerve 
• To swallowing center 
• Evoke a coordinated sequential output of efferent activity via the nucleus ambiguous and nuclei of 5,7,12 cranial nerves 
• Sequentially activates the muscles of the pharynx and esophagus 
• Receptors in the pharynx and oesophagus 
• Feedback information to the swallowing center causes further coordination of muscle contraction 

2. Oesophageal stage

• Commence with contraction of the pharyngeal constrictor muscle . 
• This initiate a peristaltic wave that pushes the bolus into the oesophagus 
• Relaxation of the upper osephageal sphincter 
• Bolus passes down into the oesphagus 
• Initiates a peristaltic wave in the oesophagus 
• Propels the bolus into the stomach 
• Fuids pass down the oesophagus ahead of the peristaltic wave due to the effect gravity