NEET MDS Lessons
Anatomy
- This is the second cranial nerve (CN II) and is the nerve of sight.
- 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.
Veins of the Face
The Supratrochlear Vein
- This vessel begins on the forehead from a network of veins connected to the frontal tributaries of the superficial temporal vein.
- It descends near the medial plane with its fellow on the other side.
- These veins diverge near the orbits, each joining a supraorbital vein to form the facial vein near the medial canthus (angle of the eye).
The Supraorbital Vein
- This vessel begins near the zygomatic process of the temporal bone.
- It joins the tributaries of the superficial and middle temporal veins.
- It passes medially and joins the supratrochlear vein to form the facial vein near the medial canthus.
The Facial Vein
- This vein provides the major venous drainage of the face.
- It begins at the medial canthus of the eye by the union of the supraorbital and supratrochlear veins.
- It runs inferoposteriorly through the face, posterior to the facial artery, but takes a more superficial and straighter course than the artery.
- Inferior to the margin of the mandible, the facial vein is joined by the anterior branch of the retromandibular vein.
- The facial veins ends by draining into the internal jugular vein.
The Superficial Temporal Vein
- This vein drains the forehead and scalp and receives tributaries from the veins of the temple and face.
- In the region of the temporomandibular joint, this vein enters the parotid gland.
The Retromandibular Vein
- The union of the superficial temporal and maxillary veins forms this vessel, posterior to the neck of the mandible.
- It descends within the parotid gland, superficial to the external carotid artery but deep to the facial nerve.
- It divides into an anterior branch that unites with the facial vein, and a posterior branch that joins the posterior auricular vein to form the external jugular vein.
Muscles Moving the Auditory Ossicles
The Tensor Tympani Muscle
- This muscle is about 2 cm long.
- Origin: superior surface of the cartilaginous part of the auditory tube, the greater wing of the sphenoid bone, and the petrous part of the temporal bone.
- Insertion: handle of the malleus.
- Innervation: mandibular nerve (CN V3) through the nerve to medial pterygoid.
- The tensor tympani muscle pulls the handle of the malleus medially, tensing the tympanic membrane, and reducing the amplitude of its oscillations.
- This tends to prevent damage to the internal ear when one is exposed to load sounds.
The Stapedius Muscle
- This tiny muscle is in the pyramidal eminence or the pyramid.
- Origin: pyramidal eminence on the posterior wall of the tympanic cavity. Its tendon enters the tympanic cavity by traversing a pinpoint foramen in the apex of the pyramid.
- Insertion: neck of the stapes.
- Innervation: nerve to the stapedius muscle, which arises from the facial nerve (CN VII).
- The stapedius muscle pulls the stapes posteriorly and tilts its base in the fenestra vestibuli or oval window, thereby tightening the anular ligament and reducing the oscillatory range.
- It also prevents excessive movement of the stapes.
Intrinsic Muscles of the Tongue
The Superior Longitudinal Muscle of the Tongue
- The muscle forms a thin layer deep to the mucous membrane on the dorsum of the tongue, running from its tip to its root.
- It arises from the submucosal fibrous layer and the lingual septum and inserts mainly into the mucous membrane.
- This muscle curls the tip and sides of the tongue superiorly, making the dorsum of the tongue concave.
The Inferior Longitudinal Muscle of the Tongue
- This muscle consists of a narrow band close to the inferior surface of the tongue.
- It extends from the tip to the root of the tongue.
- Some of its fibres attach to the hyoid bone.
- This muscle curls the tip of the tongue inferiorly, making the dorsum of the tongue convex.
The Transverse Muscle of the Tongue
- This muscle lies deep to the superior longitudinal muscle.
- It arises from the fibrous lingual septum and runs lateral to its right and left margins.
- Its fibres are inserted into the submucosal fibrous tissue.
- The transverse muscle narrows and increases the height of the tongue.
The Vertical Muscle of the Tongue
- This muscle runs inferolaterally from the dorsum of the tongue.
- It flattens and broadens the tongue.
- Acting with the transverse muscle, it increases the length of the tongue.
The Orbital Vessels
- The orbital contents are supplied chiefly by the ophthalmic artery.
- The infraorbital artery, the continuation of the maxillary, also contributes blood to this region.
- Venous drainage is through the superior orbital fissure to enter the cavernous sinus.
The Ophthalmic Artery
- This artery arises from the internal carotid artery as it emerges from the cavernous sinus.
- It passes through the optic foramen within the dural sheath of the optic nerve and runs anteriorly, close to the superomedial wall of the orbit.
The Central Artery of the Retina
- This is the one of the smallest but most important branches of the ophthalmic artery.
- It arises inferior to the optic nerve until it approaches the eyeball.
- It then pierces the optic nerve and runs within it to emerge through the optic disc.
- The central artery of the retina spreads over the internal surface of the retina and supplies it.
The Ophthalmic Veins
The Superior Ophthalmic Vein
- The superior ophthalmic vein anastomoses with the facial vein.
- It has no valves and blood can flow in either direction.
- It crosses superior to the optic nerve, passes through the superior orbital fissure and ends in the cavernous sinus.
The Inferior Ophthalmic Vein
- This begins as a plexus on the floor of the orbit.
- It communicates with the inferior orbital fissure with the pterygoid plexus, crosses inferior to the optic nerve, and ends in either the superior ophthalmic vein or the cavernous sinus.
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.