Page 26 - Edited - Webster HEAD AND NECK - part 2-Merge PDF

HN 224

ORAL EPITHELIUM AND INNERVATIONS

The oral cavity is lined with stratified squamous epithelium (“wear and tear”). Anteriorly this
epthelium continues over the lips to become continuous with facial skin: the vermillion part of the lips is not
true skin since it lacks both sebaceous and sweat glands; it is also only lightly keratinized, which is, why in
Caucasians the “lips” appear red. As in the oral cavity (and oro-pharynx) this thin, poorly or un-keratinized
epithelium allows ready access to neurotropic viruses. These are spread by contact (as in kissing) and reside in
the sensory ganglion cells innervating the epithelia of the lips, oral cavity and oro-pharynx. Those known as
“herpes simplex, type l” replicate from time to time, and are transported down the peripheral axons
(highjacking the anterograde transport mechanism). This causes tingling in the lips, followed by a vesicular
eruption or “cold sore”. The fluid of these intra-epithelial vesicles is packed with virus particles waiting to be
kissed. Similar viruses cause intra-oral mouth ulcers or “aphthous ulcers”.

Except on the upper and lateral surfaces of the tongue and the inferior surface of the palate, the intra-
oral epithelium is everywhere poorly keratinized. The upper surface of the oral tongue (the “anterior two-
thirds”, or pre-sulcal tongue - the tongue in front of the sulcus terminalis) has most evidence of keratin
because of the presence of filiform papillae in large numbers. Here, the keratin extends as threads (“filum” - a
thread), and this surface of the tongue has a whitish, roughened appearance which is enhanced during illness
when the appetite is diminished: the lack of rubbing normally encountered during mastication enables these
threads to elongate, and the general layer of keratin to thicken.

When it completes mucous membrane over bone (i.e. over the hard palate and the maxillary and
mandibular alveolar margins) the epithelium and its collagenous submucosa is bound down very firmly to the
bone - hence the unpleasant nature of receiving hypodermic injections in the immediate neighbourhood of
teeth. Around the teeth, the mucous membrane is referred to as the gingiva, which covers the bony alveolar
margins or gums.

Taste & Taste Buds – See HN 225.

Sensory Innervations

These subserve either general sensation (touch, pain, temperature), or taste.

General Sensation

Notice that

A. General sensation of the oral cavity proper is subserved by the trigeminal (Vth cranial) nerve (HN
222 & 245). This nerve has, on each side, three major divisions (“trigeminal” means “triplets”) viz:

(1) the ophthalmic (“ophthalmos” - “seeing”) division (or V 1) innervates the upper face including the
conjunctiva of the eye (HN 49);
(2) the maxillary division (or V 2) innervates facial skin over the maxilla (HN 49);

(3) the mandibular division (or V 3) innervates facial skin over the mandible (HN 49);

Observe in HN 245 that the sensory fields of the maxillary and mandibular divisions continue into
the oral cavity where they innervate:

(i) the upper lip, gingiva, teeth and palate, as well as part of the buccal (cheek) wall of the vestibule
(maxillary division);

NewCMedPhysSc\29 HN 224 OralEpithel&lnnerv.