NEET MDS Lessons
Anatomy
The External Ear
- The auricle (L. auris, ear) is the visible, shell-like part of the external ear.
- It consists of a single elastic cartilage that is covered on both surfaces with thin, hairy skin.
- The external ear contains hairs, sweat glands, and sebaceous glands.
- The cartilage is irregularly ridged and hollowed, which gives the auricle its shell-like form.
- It also shapes the orifice of the external acoustic meatus.
The Ear Lobule
- The ear lobule (earlobe) consists of fibrous tissue, fat and blood vessels that are covered with skin.
- The arteries are derived mainly from the posterior auricular artery and the superficial temporal artery.
- The skin of the auricle is supplied by the great auricular and auriculotemporal nerves.
- The great auricular nerve supplies the superior surface and the lateral surface inferior to the external acoustic meatus with nerve fibres from C2.
- The auriculotemporal nerve supplies the skin of the auricle superior to the external acoustic meatus.
The External Acoustic Meatus
- This passage extends from the concha (L. shell) of the auricle to the tympanic membrane (L. tympanum, tambourine). It is about 2.5 cm long in adults.
- The lateral 1/3 of the S-shaped canal is cartilaginous, whereas its medial 2/3 is bony.
- The lateral third of the meatus is lined with the skin of the auricle and contains hair follicles, sebaceous glands, and ceruminous glands.
- The latter glands produce cerumen (L. cera, wax).
- The medial two-thirds of the meatus is lined with very thin skin that is continuous with the external layer of the tympanic membrane.
- The lateral end of the meatus is the widest part. It has the diameter about that of a pencil.
- The meatus becomes narrow at its medial end, about 4 mm from the tympanic membrane.
- The constricted bony part is called the isthmus.
- Innervation of the external acoustic meatus is derived from three cranial nerves:
- The auricular branch of the auriculotemporal nerve (derived from the mandibular, CN V3).
- The facial nerve (CN VII) by the branches from the tympanic plexus.
- The auricular branch of the vagus nerve (CN X).
The Tympanic Membrane
- This is a thin, semi-transparent, oval membrane at the medial end of the external acoustic meatus.
- It forms a partition between the external and middle ears.
- The tympanic membrane is a thin fibrous membrane, that is covered with very thin skin externally and mucous membrane internally.
- The tympanic membrane shows a concavity toward the meatus with a central depression, the umbo, which is formed by the end of the handle of the malleus.
- From the umbo, a bright area referred to as the cone of light, radiates anteroinferiorly.
- The external surface of the tympanic membrane is supplied by the auriculotemporal nerve.
- Some innervation is supplied by a small auricular branch of the vagus nerve (CN X); this nerve may also contain some glossopharyngeal and facial nerve fibres.
Classified on functional Basis
Secretion ,Protection and waterproofing, Absorbtion, Transport, Sensory
Secretion
Glandular epithelium’s 3 types:
- Exocrine - with ducts
- endocrine - without ducts
- mixed exo-endocrine
Exocrine glands: One cell
- goblet cells
- In lining epitheliums of respiratory tract and GIT
- Secretes musin (protein) Musin + water = mucus, Mucus is a lubricant
More than one cell
Simple: Has a single duct,
- Acinar - mucus glands of the penile urethra
- Tubular - cripts of Lieberkuhn
- Coiled tubular - sweat gland
- Spiral tubular - Gland of Moll
- Branched tubular - mucous glands of the pyloric region
- Branched acinar - sebaceous gland in the skin
Compound
- Consists of a branched duct with numerous secretory end organs
- Compound tubular - Brünners glands
- Compound alveolar - mammary, prostate, pancreas, parotid
- Compound tubuloalveolar - submandibular-, sublingual salivary glands
Endocrine glands
Secrete directly into the blood
One cell : mast cells, in soft CT, near capillaries,
secrete - heparin - histamine
More than one cell
Cells can be arranged in the following ways:
- Cords - adrenal glands, parathyroid, anterior pituitary
- anastomosing cords with dilated blood capillaries in-between
- Isles - pancreas
- Follicles - thyroid
- cells line a follicle filled with non-cellular material
Superior Constrictor Muscle
- Origin: Hamulus, pterygo-mandibular raphe, and mylohyoid line of the mandible.
- Insertion: Median raphe of the pharynx.
- Nerve Supply: Vagus nerve via the pharyngeal plexus.
- Arterial Supply: Ascending pharyngeal artery, ascending palatine artery, tonsillar branch of the facial artery, and dorsal branch of the lingual artery.
- Action: Constricts the wall of the pharynx during swallowing.
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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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Internal Muscles of the Pharynx
- The internal, chiefly longitudinal muscular layer, consists of 3 muscles: stylopharyngeus, palatopharyngeus, and salpingopharyngeus.
- They all elevate the larynx and pharynx during swallowing and speaking.
The Stylopharyngeus Muscle
- This is a long, thin, conical muscles that descends inferiorly between the external and internal carotid arteries.
- It enters the wall of the pharynx between the superior and middle constrictor muscles.
- Origin: styloid process of temporal bone.
- Insertion: posterior and superior borders of thyroid cartilage with palatopharyngeus muscle.
- Innervation: glossopharyngeal nerve (CN IX).
- It elevates the pharynx and larynx and expands the sides of the pharynx, thereby aiding in pulling the pharyngeal wall over a bolus of food.
The Palatopharyngeus Muscle
- This is a thin muscle and the overlying mucosa form the palatopharyngeal arch.
The Salpingopharyngeus Muscle
- This is a slender muscle that descends in the lateral wall of the pharynx.
- The over lying mucous membrane forms the salpingopharyngeal fold.
- Origin: cartilaginous part of the auditory tube.
- Insertion: blends with palatopharyngeus muscle.
- Innervation: through the pharyngeal plexus.
- It elevates the pharynx and larynx and opens the pharyngeal orifice of the auditory tube during swallowing.
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.
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"