NEET MDS Lessons
Anatomy
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 Inferior Wall of the Orbit
- The thin inferior wall of the orbit or the floor is formed mainly by the orbital surface of the maxilla and partly by the zygomatic bone, and orbital process of the palatine bone.
- The floor of the orbit forms the roof of the maxillary sinus.
- The floor is partly separated from the lateral wall of the orbit by the inferior orbital fissure.
Skeletal Muscle: 1-40 cm long fibres, 10- 60 µm thick, according to myoglobin content there are:
Red fibres: lots of myoglobin, many mitochondriam slow twitching - tire slowly
White fibres: less myoglobin, less mitochondria, fast twitching - tire quickly
Intermediate fibres:
mixture of 2 above
Most muscles have all three - in varying ratios
Structure of skeletal muscle:
Light Microscopy: Many nuclei - 35/mm, Nuclei are oval - situated peripheral, Dark and light bands
Electron Microscopy: Two types of myofilaments
Actin
- 5,6 nm
3 components:
-actin monomers,
-tropomyosin - 7 actin molecules long
- troponin
actin monomers form 2 threats that spiral
- tropomyosin - lie in the groove of the spiral
- troponin - attach every 40 nm
- one end attach to the Z line
- other end goes to the middle of the sarcomere
- Z line consists of á actinin
Myosin:
- 15 nm
- 1,6 µm long
- The molecule has a head and a tail
- tails are parallel
- heads project in a spiral
- in the middle is a thickening
- thin threats bind the myosin at thickening (M line)
Contraction:
A - band stays the same, I - band, H - bands become narrower
Myosin heads ratchet on the actin molecule
Sarcolemma: 9 nm thick, invaginate to form T-tubule,
myofibrils - attach to the sarcolemma
Sarcoplasmic Reticulum:
specialized smooth EPR, Consists of T-tubules, terminal sisternae and sarcotubules
It is speculated that there are gap junctions between the T-tubule and terminal sisterna
An impulse is carried into the fiber by the T-tubule from where it goes to the rest of the sarcoplasmic reticulum
Connective tissue coverings of the muscle
Endomycium around fibres, perimycium around bundles and epimycium around the whole muscle
Blood vessels and nerves in CT
CT goes over into tendon or aponeurosis which attaches to the periosteum
Nerves:
The axon of a motor neuron branches and ends in motor end plates on the fiber
Specialized striated fibres called spindles (stretch receptors) form sensory receptors in muscles telling the brain how far the muscle has stretched
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.
|
Pharyngeal Arch |
Arch Artery |
Cranial Nerve |
Skeletal elements |
Muscles |
|
1 |
Terminal Branch of maxillary artery |
Maxillary and mandibular division of trigemenial (V) |
Derived from arch cartilages (originating from neural crest): From maxillary cartilages: Alispenoid, incus From mandibular: Mackel’s cartilage, malleus
Upper portion of external ear (auricle) is derived from dorsal aspect of 1st pharyngeal arch.
Derived by direct ossification from arch dermal mesenchyme: Maxilla, zygomatic, squamous portion of temporal bone, mandible
|
Muscles of mastication (temporalis, masseter, and pterygoids), mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini (originate from cranial somitomere 4) |
|
2 |
Stapedius artery (embryologic) and cortiotympanic artery (adult) |
Facial nerve (VII) |
Stapes, styloid process, stylohyoid ligament, lesser horns and upper rim of hyoid (derived from the second arch cartilage; originate from neural crest).
Lower portion of external ear (auricle) is derived from 2nd pharyngeal arch. |
Muscles of facial expression (orbicularis oculi, orbicularis oris, auricularis, platysma, fronto-ooccipitalis, buccinator), posterior belly of digastric, stylohyoid, stapedius (originate from cranial somitomere 6) |
|
3 |
Common carotid artery, most of internal carotid |
Glossopharyngeal (IX) |
Lower rim and greater horn of hyoid (derived from the third arch cartilage; originate from neural crest cells) |
Sytlopharyngeus (originate from cranial somitomere 7) |
|
4 |
Left: Arch of aorta; Right: Right subclavian artery; Original sprouts of pulmonary arteries |
Superior laryngeal branch of vagus (X) |
Laryngeal cartilages (Derived from the 4th arch cartilage, originate from lateral plate mesoderm) |
Constrictors of pharynx, cricothyroid, levator veli palatine (originate from occipital somites 2-4) |
|
6 |
Ductus arteriosus; roots of definitive pulmonary arteries |
Recurrent laryngeal branch of vagus (X) |
Laryngeal cartilages (derived from the 6th-arch cartilage; originate from lateral plate mesoderm) |
Intrinsic muscles of larynx (originate from occipital somites 1 and 2) |
The Hard Palate
- The anterior bony part of the palate is formed by the palatine process of the maxillae and the horizontal plates of the palatine bones.
- Anteriorly and laterally, the hard palate is bounded by the alveolar processes and the gingivae.
- Posteriorly, the hard palate is continuous with the soft palate.
- The incisive foramen is the mouth of the incisive canal.
- This foramen is located posterior to the maxillary central incisor teeth.
- This foramen is the common opening for the right and left incisive canals.
- The incisive canal and foramen transmit the nasopalatine nerve and the terminal branches of the sphenopalatine artery.
- Medial to the third molar tooth, the greater palatine foramen pierces the lateral border of the bony palate.
- The greater palatine vessels and nerve emerge from this foramen and run anteriorly into two grooves on the palate.
- The lesser palatine foramen transmits the lesser palatine nerve and vessels.
- This runs to the soft palate and adjacent structures.
Muscles of the larynx
Extrinsic muscles
suprahyoid: raise larynx, depress mandible for swallowing
infrahyoid: lower larynx for swallowing
both stabilize hyoid for tongue movements