NEET MDS Lessons
Anatomy
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
Gross anatomy-study of structures that can be identified with the naked eye; usually involves the use of cadavers
- Microscopic anatomy (histology)-study of cells that compose tissues and organs; involves the use of a microscope to study the details of the species
- Developmental anatomy (embryology)-study of an individual from beginning as a single cell to birth
- Comparative anatomy -comparative study of the animal structure in regard to similar organs or regions
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.
Sternum
o Forms the medial part of the anterior chest wall
o Manubrium (upper part)-clavicle and first rib articulate with the manubrium .
o Body (middle blade)-second and tenth ribs articulate with the body via the costal cartilages
o Xiphoid (blunt cartilaginous tip)
Ribs (12 pairs)
o Each rib articulates with both the body and the transverse process of its corresponding
o thoracic vertebra
o The second to ninth ribs articulate with the body of the vertebra above'
o Ribs curve outward, forward, and then downward
o Anteriorly, each of the first seven ribs joins a costal cartilage that attaches to the sternum
o Next three ribs (eighth to tenth) join the cartilage of the rib above
o Eleventh and twelfth ribs do not attach to the sternum; are called "floating ribs"
The Tongue
- The tongue (L. lingua; G. glossa) is a highly mobile muscular organ that can vary greatly in shape.
- It consists of three parts, a root, body, and tip.
- The tongue is concerned with mastication, taste, deglutition (swallowing), articulation (speech), and oral cleansing.
- Its main functions are squeezing food into the pharynx when swallowing, and forming words during speech.
Eye
At week 4, two depressions are evident on each of the forebrain hemispheres. As the anterior neural fold closes, the optic pits elongate to form the optic vesicles. The optic vesicles remain connected to the forebrain by optic stalks.
The invagination of the optic vesicles forms a bilayered optic cup. The bilayered cup becomes the dual layered retina (neural and pigmented layer)
Surface ectoderm forms the lens placode, which invaginates with the optic cup.
The optic stalk is deficient ventrally to contain choroids fissure to allow blood vessels into the eye (hyaloid artery). The artery feeds the growing lens, but will its distal portion will eventually degenerate such that the adult lens receives no hyaloid vasculature.
At the 7th week, the choroids fissure closes and walls fuse as the retinal nerve get bigger.
The anterior rim of the optic vesicles forms the retina and iris. The iris is an outgrowth of the distal edge of the retina.
Optic vesicles induces/maintains the development of the lens vesicle, which forms the definitive lens. Following separation of the lens vesicle from the surface ectoderm, the cornea develops in the anterior 1/5th of the eye.
The lens and retina are surrounded by mesenchyme which forms a tough connective tissue, the sclera, that is continuous with the dura mater around the optic nerve.
Iridopupillary membrane forms to separate the anterior and posterior chambers of the eye. The membrane breaks down to allow for the pupil
Mesenchyme surrounding the forming eye forms musculature (ciliary muscles and pupillary muscles – from somitomeres 1 and 2; innervated by CN III), supportive connective tissue elements and vasculature.
Eyelids
Formed by an outgrowth of ectoderm that is fused at its midline in the 2nd trimester, but later reopen.
The Middle Ear
- This part of the ear is in a narrow cavity in the petrous part of the temporal bone.
- It contains air, three auditory ossicles, a nerve and two small muscles.
- The middle ear is separated from the external acoustic meatus by the tympanic membrane.
- This cavity includes the tympanic cavity proper, the space directly internal to the tympanic membrane, and the epitympanic recess, the space superior to it.
- The middle ear is connected anteriorly with the nasopharynx by the auditory tube.
- Posterosuperiorly, the tympanic cavity connects with the mastoid cells through the aditus ad antrum (mastoid antrum).
- The tympanic cavity is lined with mucous membrane that is continuous with the mucous membrane of the auditory tube, mastoid cells, and aditus ad antrum.
Contents of the Tympanic Cavity or Middle Ear
- This cavity contains the auditory ossicles (malleus, incus and stapes); the stapedius and tensor tympani muscles; the chorda tympani nerve (a branch of the facial nerve, CN VII); and the tympanic plexus of nerves.