NEET MDS Lessons
Anatomy
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 tongue is divided into halves by a medial fibrous lingual septum that lies deep to the medial groove.
- In each half of the tongue there are four extrinsic and four intrinsic muscles.
- The lingual muscles are all supplied by the hypoglossal nerve (CN XII).
- The only exception is palatoglossus, which is supplied by the pharyngeal branch of the vagus nerve, via the pharyngeal plexus.
The Paranasal Sinuses
- These sinuses are air-filled extensions of the respiratory part of the nasal cavity.
- They are in the following bones, frontal, ethmoid, sphenoid and the maxilla.
The Frontal Sinuses
- These are located between the outer and inner tables of the frontal bone, posterior to the superciliary arches.
The Ethmoidal Sinuses
- These comprise of several small cavities, called ethmoidal air cells, within the ethmoidal labyrinth (G. labyrinthos, a maze) of the lateral mass of the ethmoid bone.
The Sphenoidal Sinuses
- These occupy a variable amount in the body of the sphenoid bone and may extend into the wings.
The Maxillary Sinuses
- These are the largest pair of paranasal sinuses.
- They are pyramidal-shaped cavities that may occupy the entire bodies of the maxillae.
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| Motor Innervation | All muscles by hypoglossal nerve (CN XII) except palatoglossus muscle (by the pharyngeal plexus) | ||
| General Sensory Innervation |
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| Special Sensory Innervation |
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Muscles Around the Nose
The Nasalis Muscle
- This muscle consists of a transverse (compressor naris) and alar (dilator naris) parts.
- It is supplied by the buccal branch of the facial nerve.
- 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 |
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.