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 Articular Capsule
- The capsule of this joint is loose.
- The thin fibrous capsule is attached to the margins of the articular area on the temporal bone and around the neck of the mandible.
- The six muscles rotate the eyeball in the orbit around three axes (sagittal, horizontal and vertical).
- The action of the muscles can be deduced by their site of insertion on the eyeball.
| Muscle | Action(s) on the Eyeball | Nerve Supply |
| Medial Rectus | Adducts | CN III |
| Lateral Rectus | Abducts | CN VI |
| Superior Rectus | Elevates, adducts, and medially rotates | CN III |
| Inferior Rectus | Depresses, adducts, and laterally rotates | CN III |
| Superior Oblique | Depresses, abducts, and medially rotates | CN IV |
| Inferior Oblique | Elevates, abducts, and laterally rotates | CN III |
The Soft Palate
- This is the posterior curtain-like part, and has no bony support. It does, however, contain a membranous aponeurosis.
- The soft palate, or velum palatinum (L. velum, veil), is a movable, fibromuscular fold that is attached to the posterior edge of the hard palate.
- It extends posteroinferiorly to a curved free margin from which hangs a conical process, the uvula (L. uva, grape).
- The soft palate separates the nasopharynx superiorly and the oropharynx inferiorly.
- During swallowing the soft palate moves posteriorly against the wall of the pharynx, preventing the regurgitation of food into the nasal cavity.
- Laterally, the soft palate is continuous with the wall of the pharynx and is joined to the tongue and pharynx by the palatoglossal and palatopharyngeal folds.
- The soft palate is strengthened by the palatine aponeurosis, formed by the expanded tendon of the tensor veli palatini muscle.
- This aponeurosis attaches to the posterior margin of the hard palate.
The Auditory Tube
- This is a funnel-shaped tube connecting the nasopharynx to the tympanic cavity.
- Its wide end is towards the nasopharynx, where it opens posterior to the inferior meatus of the nasal cavity.
- The auditory tube is 3.5 to 4 cm long; its posterior 1/3 is bony and the other 2/3 is cartilaginous.
- It bony part lies in a groove on the inferior aspect of the base of the skull, between the petrous part of the temporal bone and the greater wing of the sphenoid bone.
- The function of the auditory tube is to equalise pressure of the middle ear with atmospheric pressure.
Skull bones
- 26 bones: 22 bones + hyoid (small bone in neck for swallowing) + 3 auditory ossicles (middle ear: incus, malleus, stapes)
- 21 bones: tightly connected; mandible is freely mobile at temperomandibular joint (synovial)
- connective-tissue interface b/w bones = suture
- bones – mandible = cranium
- cranium
- neurocranium: covers brain anteriorly, laterally and posteriorly
- brain supported by bones of basicranium
- also contributes to interorbital region; b/w eyes and superior to nasal passages
- viscerocranium/splanchnocranium: bones of face
- sutures
- coronal: separates frontal from parietals
- sagittal: separates two parietal bones
- lambdoidal: separates parietal form occipital
- squamosal: b/w temporal and parietal; overlapping sutures
- At birth: 2 frontal bones which eventually fuse; metopic suture disappears
Cranial Cavities: 5 major cavities
Endocranial, left and right orbits, nasal cavities, oral cavity, middle ear cavities
Endocranial cavity
- contains brain, meninges, cerebrospinal fluid, brain’s vascular supply and most proximal portion of cranial nerves
- enclosed by neurocranium and basicranium
- basicranium: foramina for neurovascular bundles
- foramen magnum: spinal cord exit
- floor of endocranial cavity divide into fossae
- anterior: frontal lobes of brain
- middle: pair temporal lobes
- posterior: cerebellum and brainstem
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.