NEET MDS Lessons
Anatomy
The Nasal Mucosa
- Mucosa lines the entire nasal cavities except for the vestibule of the nose.
- The nasal mucosa is firmly bound to the periosteum and perichondrium of the supporting structures of the nose.
- It is continuous with the adjoining cavities to which the nasal cavity communicates (e.g., the nasopharynx and paranasal sinuses).
- The inferior 2/3 of the nasal mucosa is called the respiratory area and air passing over this is warmed and moistened before it passes into the lungs.
- The superior 1/3 is called the olfactory area.
The Olfactory Area of Nasal Mucosa
- This area contains the peripheral organ of smell.
- Sniffing draws air into this area
- Olfactory receptor cells (from the olfactory nerve, CN I, are located in the mucosa of this area in the nose.
Nerves to the Respiratory Area of Nasal Mucosa
- The inferior 2/3 of the nasal mucosa are supplied chiefly by the trigeminal nerve (CN V).
- The mucous membrane of the nasal septum is supplied chiefly by the nasopalatine nerve, a branch of the maxillary nerve (CN V2).
- Its anterior portion is supplied by the anterior ethmoidal nerve (a branch of the nasociliary nerve) which is derived from the ophthalmic nerve (CN V1).
- The lateral walls of the nasal cavity are supplied by branches of the maxillary nerve (CN V2); the greater palatine nerve, and the anterior ethmoidal nerve.
Arteries of the Nasal Mucosa
- The blood supply of the mucosa of the nasal septum is derived mainly from the maxillary artery.
- The sphenopalatine artery, a branch of the maxillary, supplies most of the blood of the nasal mucosa.
- It enters by the sphenopalatine foramen and sends branches to the posterior regions of the lateral wall and to the nasal septum.
- The greater palatine artery, also a branch of the maxillary, passes through the incisive foramen to supply the nasal septum.
- The anterior and posterior ethmoidal arteries, branches of the ophthalmic artery, supply the anterosuperior part of the mucosa of the lateral wall of the nasal cavity and nasal septum.
- Three branches of the facial artery (superior labial, ascending palatine, and lateral nasal) also supply the anterior parts of the nasal mucosa.
Veins of the Nasal Mucosa
- The veins of the nasal mucosa form a venous network of plexus in the connective tissue of the nasal mucosa.
- Some of the veins open into the sphenopalatine vein and drain to the pterygoid plexus.
- Others join the facial and infraorbital veins.
- Some empty into the ophthalmic veins and drain into the cavernous sinus.
The Sublingual Glands
- These are the smallest of the three paired salivary glands and the most deeply situated.
- They are almond-shaped and lie in the floor of the mouth between the mandible and the genioglossus muscle.
- The paired glands unite to form a horseshoe-shaped glandular mass around the lingual frenulum.
- Numerous small ducts (10 to 12) open into the floor of the mouth.
- Sometimes one of the ducts opens into the submandibular duct.
- The nerves the accompany the submandibular and sublingual glands are derived from the lingual and chorda tympani nerves and from the sympathetic nerves.
- The parasympathetic secretomotor fibres are from the submandibular ganglion.
Genioglossus Muscle
- Origin: Mental spine of the mandible.
- Insertion: Dorsum of the tongue and hyoid bone.
- Nerve Supply: Hypoglossal nerve (CN XII).
- Arterial Supply: Sublingual and submental arteries.
- Action: Depresses and protrudes the tongue.
The Lips
- These are mobile muscular folds that surround the mouth, the entrance of the oral cavity.
- The lips (L. labia) are covered externally by skin and internally by mucous membrane.
- In between these are layers of muscles, especially the orbicularis oris muscle.
- The upper and lower lips are attached to the gingivae in the median plane by raised folds of mucous membrane, called the labial frenula.
Sensory Nerves of the Lips
- The sensory nerves of the upper and lower lips are from the infraorbital and mental nerves, which are branches of the maxillary (CN V2) and mandibular (CN V3) nerves.
- This is the second cranial nerve (CN II) and is the nerve of sight.
Stylohyoid Muscle
- Origin: Posterior border of the styloid process of the temporal bone.
- Insertion: Body of the hyoid bone at the junction with the greater horn.
- Nerve Supply: Facial nerve (CN VII).
- Arterial Supply: Muscular branches of the facial artery and muscular branches of the occipital artery.
- Action: Elevates the hyoid bone and base of the tongue.
Muscles Around the Eyelids
- The function of the eyelid (L. palpebrae) is to protect the eye from injury and excessive light. It also keeps the cornea moist.
The Orbicularis Oculi Muscle
- This is the sphincter muscle of the eye.
- Its fibres sweep in concentric circles around the orbital margin and eyelids.
- It narrows the eye and helps the flow of tears from the lacrimal sac.
- This muscle has 3 parts: (1) a thick orbital part for closing the eyes to protect then from light and dust; (2) a thin palpebral part for closing the eyelids lightly to keep the cornea from drying; and (3) a lacrimal part for drawing the eyelids and lacrimal punta medially.
- When all three parts of the orbicularis oculi contract, the eyes are firmly closed and the adjacent skin becomes wrinkled.
- The zygomatic branch of the facial nerve (CN VII) supplies it.
The Levator Palpebrae Superioris Muscle
- This muscle raises the upper eyelid to open the palpebral fissure.
- It is supplied by the oculomotor nerve (CN III).