The mouth is an oval-shaped cavity inside the skull. The two main functions of the mouth are eating and speaking. Parts of the mouth include the lips, vestibule, mouth cavity, gums, teeth, hard and soft palate, tongue and salivary glands. The mouth is also known as the oral cavity or the buccal cavity.
The digestive tract begins at the mouth. Digestion starts when food is taken into the mouth, ground up by the teeth and moistened with saliva. Saliva has an enzyme called amylase that starts to break down carbohydrates into sugars. Movements of the tongue help to push the wet, soft mass of food to the back of the mouth where it can be swallowed. A flap of skin called the epiglottis closes over the windpipe (trachea) to ensure that food is directed into the oesophagus – the tube that leads to the stomach.
Talking requires a complex series of events to occur in exactly the right order. Expelled air runs through the vocal cords in the larynx. The vocal cords vibrate, which produces sound. The type of sound depends on the tightness of the vocal cords and the force of the expelled air. Movements of the tongue and lips help to shape the sounds. Other mouth structures involved in the production of sounds include the hard and soft palates and the nose.
The main structures of the mouth include:
- Lips – two mobile and muscular structures that form the entrance to the mouth. The lips mark the transition from skin to moist mucous membrane.
- The vestibule – the space between the soft tissue (lips and cheeks), and the teeth and gums. The vestibule is kept moist by secretions from the parotid salivary glands, which are located in front of the ears and behind the angle of the jaw.
- Mouth cavity – the mouth cavity is bounded by several structures. The alveolar arches (bony structures that contain the teeth) surround the mouth cavity at the front and on the sides – overhead are the hard and soft palates and below is the tongue. The mouth cavity is kept moist by secretions from the submaxillary and sublingual salivary glands located in the floor of the mouth beneath the tongue.
- Gums – are made up of the fibrous and dense tissue that lines the alveolar arches and hugs the teeth.
- Teeth – a person has two sets of teeth over the course of a lifetime. The average child has their full set of 20 primary (or milk or baby) teeth by the age of three years. The primary teeth start to fall out between the ages of about six and seven years, and are gradually replaced by permanent (or secondary or adult) teeth. By about 21 years, the average person has 32 permanent teeth – 16 in the upper jaw and 16 in the bottom jaw.
- Palate – consists of the hard and soft palates. The hard palate is the bony roof of the mouth. The soft palate is a fold of membrane that hangs between the mouth cavity and the back of the throat. The little dangling bit you can see when you stick out your tongue and say ‘ah’ is called the uvula.
- Tongue – the tongue is made up almost entirely of muscle fibres. It is divided into an oral portion (tip, blade, front, centre and back) and a pharyngeal (throat) section. The tongue helps us to taste, speak and swallow.
- Minor salivary glands – make the clear fluid (saliva) that keeps the mouth moist and contains enzymes to break down food. These glands are found in various locations around the mouth, including the inner cheeks.
The trigeminal nerve is the major nerve of the face. Its roles include sensation and some motor functions such as biting, chewing and swallowing. Also known as the fifth cranial nerve, it has three main branches, including:
- Upper branch – services the scalp and forehead.
- Middle branch – services the cheeks, top lip, upper jaw, top teeth and gums, some areas of the nose.
- Lower branch – services the bottom lip, bottom jaw, bottom teeth and gums.
Some disorders of the mouth include:
- Infections such as thrush, herpes (cold sore) or tonsillitis
- Mouth ulcers
- Mouth cancer
- Cleft palate and cleft lip
- Halitosis (bad breath)
- Dry mouth syndrome
- Tongue problems such as a cracked or coated surface
- Tooth problems such as dental caries (cavities) or impacted wisdom teeth
- Speech problems such as lisping.
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