Download Oral Cavity

Oral Cavity
• Objectives:
• Describe the boundaries of the oral
cavity.
• Describe the normal anatomical
structures of the oral cavity.
• Describe teeth and their structure.
• Describe the tongue and its
structure.
• Understand the innervation of the
oral cavity.
• The roof of the oral cavity consists of the
hard and soft palates. The floor is formed
mainly of soft tissues, which include a
muscular diaphragm and the tongue. The
lateral walls (cheeks) are muscular and
merge anteriorly with the lips. The posterior
aperture of the oral cavity is the
oropharyngeal isthmus, which opens into the
oral part of the pharynx. The oral cavity is
separated into two regions:
• 1- The outer oral vestibule.
• 2- the inner oral cavity proper
• The walls of the oral cavity are formed
by the cheeks. Each cheek consists of
fascia and a layer of skeletal muscle
sandwiched between skin externally and
oral mucosa internally. The thin layer of
skeletal muscle within the cheeks is
principally the buccinator muscle.
Buccinator muscle holds the cheeks
against the alveolar arches and keeps
food between the teeth when chewing.
• The floor of the oral cavity proper is formed
mainly by three structures:
• 1- A muscular diaphragm, which fills the Ushaped gap between the left and right sides
of the body of the mandible and is composed
of the paired mylohyoid muscles.
• 2- Two cord-like geniohyoid muscles above
the diaphragm, which run from the mandible
in front to the hyoid bone behind.
• 3- The tongue, which is superior to the
geniohyoid muscles.
• The tongue is a muscular structure that
forms part of the floor of the oral cavity and
part of the anterior wall of the oropharynx.
The apex is directed anteriorly and sits
immediately behind the incisor teeth. The
root of tongue is attached to the mandible
and the hyoid bone. The superior surface of
the oral or anterior two-thirds of the tongue
is oriented in the horizontal plane. The
pharyngeal surface or posterior one-third of
the tongue curves inferiorly.
• The superior surface of the oral part of the
tongue is covered by papillae. The inferior
surface lacks papillae, but have mucosal
folds. A single median fold (the frenulum of
tongue) is continuous with the mucosa of the
floor of the oral cavity. On each side of the
frenulum is a lingual vein. The mucosa of the
pharyngeal surface of the tongue is irregular
because of the nodules of lymphoid tissue in
the submucosa (the lingual tonsil). There are
no papillae on the pharyngeal surface.
• The superior surface of the oral part of the
tongue is covered by papillae. The inferior
surface lacks papillae, but have mucosal
folds. A single median fold (the frenulum of
tongue) is continuous with the mucosa of the
floor of the oral cavity. On each side of the
frenulum is a lingual vein. The mucosa of the
pharyngeal surface of the tongue is irregular
because of the nodules of lymphoid tissue in
the submucosa (the lingual tonsil). There are
no papillae on the pharyngeal surface.
• The bulk of the tongue is composed of muscle.
There are intrinsic and extrinsic lingual muscles.
The intrinsic muscles of the tongue originate and
insert within the substance of the tongue. They are
divided into superior longitudinal, inferior
longitudinal, transverse, and vertical muscles, and
they alter the shape of the tongue. Working in
pairs or one side at a time the intrinsic muscles of
the tongue contribute to precision movements of
the tongue required for speech, eating, and
swallowing.
• Extrinsic muscles of the tongue originate
from structures outside the tongue and
insert into the tongue. There are four major
extrinsic muscles on each side, the
genioglossus, hyoglossus, styloglossus, and
palatoglossus. These muscles protrude,
retract, depress, and elevate the tongue.
Except for the palatoglossus, which is
innervated by the vagus nerve [X], all
muscles of the tongue are innervated by the
hypoglossal nerve [XII].
• Innervation:
• General sensory innervation is carried
predominantly by branches of the trigeminal nerve
[V]. The upper parts of the cavity, including the
palate and the upper teeth, are innervated by
branches of the maxillary nerve [V2].
• The lower parts, including the teeth and oral part
of the tongue, are innervated by branches of the
mandibular nerve [V3].
• Taste (special afferent-SA) from the oral part or
anterior two-thirds of the tongue is carried by
branches of the facial nerve [VII], which join and
are distributed with branches of the trigeminal
nerve [V].
• Parasympathetic fibers to the glands within
the oral cavity are also carried by branches of
the facial nerve [VII], which are distributed
with branches of the trigeminal nerve [V].
• Sympathetic fibers in the oral cavity
ultimately come from spinal cord level T1,
synapse in the superior cervical sympathetic
ganglion, and are eventually distributed to
the oral cavity along branches of the
trigeminal nerve [V] or directly along blood
vessels.
• The Teeth:
• The teeth are collectively called the
dentition. Adults normally have 16
teeth in the mandible and 16 in the
maxilla.
• On each side of the midline, there
are two incisors, a canine,two
premolars, and three molars in each
jaw.
• The incisors are chisel-like cutting
teeth used to bite off a piece of food.
The canines are more pointed and
act to puncture and shred it. The
• premolars and molars have relatively
broad surfaces adapted to crushing
and grinding.
• Teeth develop beneath the gums and
erupt (emerge) in predictable order.
Twenty deciduous teeth (milk teeth
or baby teeth) erupt from the ages
of 6 to 30 months, beginning with
the incisors. Between 6 and 25 years
of age, these are replaced by the 32
permanent teeth.
Human Deciduous and Permanent Teeth
Structure of
Tooth
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