NEET MDS Lessons
Anatomy
The Layers of the Pharyngeal Wall
- The pharyngeal wall is composed of 5 layers. From internal to external, they are as follows.
- Mucous membrane: this lines the pharynx and is continuous with all chambers with which it communicates.
- Submucosa
- Pharyngobasilar fascia: this is a fibrous layer that is attached to the skull.
- Muscular layer: this is composed of inner longitudinal and outer circular parts.
- Buccopharyngeal fascia: this is a loose connective tissue layer.
- This fascia is continuous with the fascia covering the buccinator and pharyngeal muscle.
- It contains the pharyngeal plexus of nerves and veins.
- 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 |
- Bones begin to form during the eighth week of embryomic life in the fibrous membranes (intramembranous ossification) and hyaline cartilage (endochondral ossification)
The Arteries of the Face
- The superficial arteries are derived from the external carotid arteries.
The Facial Artery
- This is the chief artery of the face.
- It arises from the external carotid artery and winds its way to the inferior border of the mandible, just anterior to the masseter muscle.
- It hooks around the inferior border of the mandible and grooves the bone. Here the artery is superficial, just beneath the platysma and its pulsation can be felt.
- In its course over the face to the medial angle of the eye, the facial artery crosses the mandible, buccinator muscle, and maxilla.
- It lies deep to the zygomaticus major.
- The facial artery ends by sending branches to the lip and side of the nose.
- The part of the artery that runs along the side of the nose to supply the eyelids is called the angular artery.
The Superficial Temporal Artery
- This artery is the smaller of the two terminal branches of the external carotid artery (the other is the maxillary artery).
- It begins deep to the parotid gland, posterior to the neck of the mandible, and ascends superficial to the posterior end of the zygomatic process of the temporal bone. It then enters the temporal fossa.
- The superficial temporal artery ends in the scalp by dividing into the frontal and parietal branches.
- Pulsation of this artery can be felt by compressing the root of the zygomatic process of the temporal bone.
The Transverse Facial Artery
- This small artery arises from the superficial temporal artery before it emerges from the parotid gland.
- It crosses the face superficial to the masseter muscle, about a fingerbreadth inferior to the zygomatic arch.
- It divides into numerous branches that supply the parotid gland and duct, the masseter muscle, and the skin of the face.
- It anastomoses with branches of the facial artery.
MUSCLE
Types:
Skeletal (voluntary)
Cardiac (involuntary)
Smooth (involuntary)
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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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Nerve Supply of the Muscles of the Orbit (pp. 715-6)
- Three cranial nerves supply the muscles of the eyeball; the oculomotor (CN III), trochlear (CN IV) and abducent (CN IV) nerves.
- All three enter the orbit via the superior orbital fissure.
- The trochlear nerve supplies the superior oblique muscle.
- The abducent nerve supplies the lateral rectus muscle.
- The oculomotor nerve supplies everything else.
- A mnemonic that is used is this formula for this strange sulfate: SO4(LR6)3