Muscles of Mastication

Muscle of Mastication

Lateral Pterygoid

Medial Pterygoid

Muscles of Mastication

Muscle of Mastication

Temperalis

cavities

The pharynx (throat);• the paranasal sinuses (small hollow spaces around

the nose, lined with cells that secrete mucus, which keeps the nose from drying out);

• the nasal cavity (the passageway just behind the nose, through which air passes on the way to the throat during breathing);

• the larynx ("Adam's apple" or voice box);

• salivary glands (which secrete saliva, the fluid released into the mouth to keep it moist and to help dissolve food).

Assessing the Oral cavity

Swallowing

3. Throat muscles squeeze food down

2. Soft palate seals Nose

4. Vocal cords close

5. Oesophagus opens

Vocal cords• Airway function requires that the vocal cords move

away from each other when air is flowing into the lungs, while voice production requires the vocal cords to move toward each other when air is flowing out of the lung.

• The intact vocal cords can perform these dual functions of airway and voice production because they can automatically open and close the airway as needed.

• If the vocal cords cannot move away, the patient will have difficulty breathing but can speak. On the other hand, if the vocal cord(s) cannot come together, the patient can breathe but may not be able to speak.

Cranial Nerves in Chewing & Swallowing

CN V -- Trigeminal - sensory and motor fibres that innervate the face - important in chewing located at the level of the pons

CN VII -- Facial - sensory and motor fibres important for sensation of oropharynx & taste to anterior 2/3 of tongue

CN IX -- Glossopharyngeal

- sensory and motor fibres important for taste to posterior tongue, sensory and motor functions of the pharynx

CN X -- Vagus - sensory and motor fibres important for taste to oropharynx, and sensation and motor function to larynx and laryngopharynx. - important for airway protection

• CN XII -- Hypoglossal - motor fibres that primarily innervate the tongue

SWALLOWING

• There are three stages

• Oral

• Pharyngeal

• Oesophageal

Stage 1- to chew – to masticate• The is triggered by both the presence of food in the mouth and by

voluntary control • Contraction of a group of mussels allows us to masticate food.

These include muscles of the lips, lower jaw, cheek and the tongue. These muscles create exceptional pressure forces: this can rise to as much as 75 mmhg or 10kPa (Rutishauser 1996)

• The aim of chewing is to mix food with saliva and to make a bolus. This helps both digestion of food and swallowing.

• The stimulus for saliva secretion comes from the saliva centre (located between the medulla and the pons). Parasympathetic nerves increase the activity of the centre; while sympathetic nerves decrease the firing rate of this centre. Higher brain centres such as smell, vision, hearing and thought also bring about saliva release. Reflexes from the stomach and the small intestine also increase salivation (part of the Gastro-colic reflex).

Stage 2 and stage 3–deglutition• First the pharyngeal stage

• This is a reflex action

• What is a reflex action

• When food is swallowed, it enters the throat (oropharynx) and then the laryngopharynx. Swallowing starts off as a voluntary action. This involves pushing the food to the back of the mouth into the oropharynx. The tongue is used to move the food backwards. The swallowing reflex starts as food enters the back of the mouth. This stimulates receptors situated around the pharynx, the soft palate, the tonsils, the epiglottis and the base of the tongue. These receptors further stimulate cells of the medulla (swallowing centre).

The swallowing centre controls the contraction of several muscles

• The soft palate closes off the nasopharynx (levator and tensor palati muscles- interestingly, these muscles also open the Eustachian tube which helps to relieve discomfort in the ears when swallowing)

• The vocal cords of the larynx are moved up and forward to causing the epiglottis to close over the glottis (to protect the respiratory tract)

• This also widens to space available for the bolus• Pharyngeal muscles also produce peristaltic action.• It takes around 4-8 seconds for food to enter the upper

oesophagus. Reflexes then conveyed by the vagus and myenteric nerves produce peristaltic action in skeletal and smooth muscle. These contractions propel the bolus towards the stomach

Oesophagus

• The oesophagus is a muscular tube that carries the food from the back of the throat to the stomach. It must contract in a very co-ordinated fashion so we don't regurgitate our food or feel that our meals are sticking as we swallow.

• It is inflammation within the oesophagus that gives the sensation of heartburn.

Dysphagia

• Emotional tension can cause the cricopharyngeal muscle may go into spasm. This gives the sensation of a lump in the throat even though the swallow reflex if intact.

• Oesophageal cancer or peptic ulcer may cause obstruction, through growths or inflammation. This can cause both increased peristalsis (leading to chest pain) and obstruction to the bolus - dysphagia.

• Disruption of cranial nerve activity through brain haemorrhage, or trauma such as head injury or stroke may disrupt the co-ordination of the reflex.