Anatomy & Physiology of Mastication & Deglutition

mastication

• Process of grinding and crushing food

• Prepares food for swallowing

deglutition

• Complex process of moving a bolus from oral cavity -> pharynx -> esophagus

• Requires precise coordination of multiple systems

Key structures involved in mastication

• Lips and facial muscles

• Tongue (intrinsic & extrinsic muscles)

• Velum (soft palate)

• Pharyngeal muscles

• Larynx

• Respiratory system (you cannot swallow while breathing*)

Jaw closure (elevation)

• Masseter

• Temporalis

• Medial (internal) pterygoid

Jaw opening (depression)

• Anterior belly of digastric

• Mylohyoid

• Geniohyoid

• Platysma

Jaw protrusion & side to side

Lateral pterygoid

Masseter

the main muscle to elevate mandible

Temporalis

elevate & retract mandible (if protruded)

Medial (internal) pterygoid

elevate mandible & assist with lateral movement

Lateral pterygoid

protrudes mandible & assist with lateral movement

Platysma

Tenses skin of neck and assists in depressing mandible

Stages of swallowing

1. Oral stage (preparation and transport)

2. Pharyngeal stage (pharyngeal swallow)

3. Esophageal stage (esophageal transit)

Oral stage (Oral preparation)

• Prepare food for swallowing and form bolus

• Not technically a stage of swallow

• Food is broken down through the coordinated activity of the lingual muscles and muscles of mastication

• The tongue continuously repositions food within the oral cavity for effective chewing

• Facial muscles (*buccinator) keep food on the teeth and prevent it from collecting in the cheeks

Oral stage (Transport)

• bolus is transmitted to the pharynx

• Can be voluntary or automatic

• Typically, the velum elevates to seal away the nasal cavity

• Lasts 0.1 to 0.25 seconds.

Pharyngeal stage

• move bolus through pharynx while protecting the airway

• Involuntary

• During this phase respiration briefly ceases

• Lasts about 1 second

This stage is triggered when the front of bolus:

• passes between the anterior faucial pillars OR

• the bolus crosses the posterior of the dorsum of the tongue OR

• physical presence of adequate bolus in the oropharynx

Esophageal Phase

• transport bolus from esophagus → stomach

• Involuntary

• Lasts about 10 to 20 seconds

• Influenced by gravity