NEET MDS Lessons
Anatomy
Extrinsic Muscles of the Tongue (p. 746)
The Genioglossus Muscle
- This is a bulky, fan-shaped muscle that contributes to most of the bulk of the tongue.
- It arises from a short tendon from the genial tubercle (mental spine) of the mandible.
- It fans out as it enters the tongue inferiorly and its fibres attach to the entire dorsum of the tongue.
- Its most inferior fibres insert into the body of the hyoid bone.
- The genioglossus muscle depresses the tongue and its posterior part protrudes it.
The Hyoglossus Muscle
- This is a thin, quadrilateral muscle.
- It arises from the body and greater horn of the hyoid bone and passes superoanteriorly to insert into the side and inferior aspect of the tongue.
- It depresses the tongue, pulling its sides inferiorly; it also aids in retrusion of the tongue.
The Styloglossus Muscle
- This small, short muscle arises from the anterior border of the styloid process near its tip and from the stylohyoid ligament.
- It passes inferoanteriorly to insert into the side and inferior aspect of the tongue.
- The styloglossus retrudes the tongue and curls its sides to create a trough during swallowing.
The Palatoglossus Muscle
- Superior attachment: palatine aponeurosis.
- Inferior attachment: side of tongue.
- Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.
- This muscle, covered by mucous membrane, forms the palatoglossal arch.
- The palatoglossus elevates the posterior part of the tongue and draws the soft palate inferiorly onto the tongue.
The External Nose
- Noses vary considerably in size and shape, mainly as a result of the differences in the nasal cartilages and the depth of the glabella.
- The inferior surface of the nose is pierced by two apertures, called the anterior nares (L. nostrils).
- These are separated from each other by the nasal septum (septum nasi).
- Each naris is bounded laterally by an ala (L. wing), i.e., the side of the nose.
- The posterior nares apertures or choanae open into the nasopharynx.
- Bones begin to form during the eighth week of embryomic life in the fibrous membranes (intramembranous ossification) and hyaline cartilage (endochondral ossification)
CARTILAGE
There are 3 types:
Hyaline cartilage
Elastic cartilage
Fibrocartilage
Matrix is made up by: Hyaluronic acid
Proteoglycans
- In cartilage the protein core of the proteoglycan molecule binds through a linking protein to hyaluronic acid to form a proteoglycan aggregate which binds to the fibres
- In the matrix there are spaces, lacunae in which one to three of the cells of cartilage, chondrocytes, are found
- The matrix around the lacuna is the territorial matrix
- Type II collagen fibrils are embedded in the matrix
- The type of fiber depends on the type of cartilage
- Cartilage is surrounded by perichondrium which is a dense CT
- Apositional growth takes place in the perichondrium
- The fibroblasts of the perichondrium change to elliptic chondroblasts which later change to round chondrocytes
- Interstitial growth takes place around the lacunae
- Nutrients diffuse through the matrix to get to the chondrocytes this limits the thickness of cartilage
Hyaline cartilage
Found: Rib cartilage, articulating surfaces, nose, larynx, trachea, embryonic skeleton, Articulating cartilage has no perichondrium
Bluish-white and translucent
Contains type II collagen that is not visible
Elastic cartilage
Found: external auditory canal, epiglottis
Similar to hyaline except that it contains many elastic fibres ,Yellow in colour, Can be continuous with hyaline
Fibrocartilage
Found: Intervertebral disk, symphysis pubis
Always associated with dense CT, Many collagen fibres in the matrix, No perichondrium
- Chondrocytes tend to lie in rows, Can withstand strong forces
Muscles of the larynx
Extrinsic muscles
suprahyoid: raise larynx, depress mandible for swallowing
infrahyoid: lower larynx for swallowing
both stabilize hyoid for tongue movements
The Temporalis Muscle
- This is an extensive fan-shaped muscle that covers the temporal region.
- It is a powerful masticatory muscle that can easily be seen and felt during closure of the mandible.
- Origin: floor of temporal fossa and deep surface of temporal fascia.
- Insertion: tip and medial surface of coronoid process and anterior border of ramus of mandible.
- Innervation: deep temporal branches of mandibular nerve (CN V3).
- The temporalis elevates the mandible, closing the jaws; and its posterior fibres retrude the mandible after protrusion.
The Auditory Ossicles
The Malleus
- Its superior part, the head, lies in the epitympanic recess.
- The head articulates with the incus.
- The neck, lies against the flaccid part of the tympanic membrane.
- The chorda tympani nerve crosses the medial surface of the neck of the malleus.
- The handle of the malleus (L. hammer) is embedded in the tympanic membrane and moves with it.
- The tendon of the tensor tympani muscle inserts into the handle.
The Incus
- Its large body lies in the epitympanic recess where it articulates with the head of the malleus.
- The long process of the incus (L. an anvil) articulates with the stapes.
- The short process is connected by a ligament to the posterior wall of the tympanic cavity.
The Stapes
- The base (footplate) of the stapes (L. a stirrup), the smallest ossicle, fits into the fenestra vestibuli or oval window on the medial wall of the tympanic cavity.
Functions of the Auditory Ossicles
- The auditory ossicles increase the force but decrease the amplitude of the vibrations transmitted from the tympanic membrane.