NEET MDS Lessons
Anatomy
- This is the second cranial nerve (CN II) and is the nerve of sight.
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
Initially, four clefts exist; however, only one gives rise to a definite structure in adults.
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1st pharyngeal cleft |
Penetrates underlying mesenchyme and forms EAM. The bottom of EAM forms lateral aspect of tympanic cavity. |
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2nd pharyngeal cleft |
Undergoes active proliferation and overlaps remaining clefts. It merges with ectoderm of lower neck such that the remaining clefts lose contact with outside. Temporarily, the clefts form an ectodermally lined cavity, the cervical sinus, but this disappears during development. |
MUSCLE
Types:
Skeletal (voluntary)
Cardiac (involuntary)
Smooth (involuntary)
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Pharyngeal Arch |
Arch Artery |
Cranial Nerve |
Skeletal elements |
Muscles |
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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
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Muscles of mastication (temporalis, masseter, and pterygoids), mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini (originate from cranial somitomere 4) |
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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) |
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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) |
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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) |
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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 Soft Palate
- This is the posterior curtain-like part, and has no bony support. It does, however, contain a membranous aponeurosis.
- The soft palate, or velum palatinum (L. velum, veil), is a movable, fibromuscular fold that is attached to the posterior edge of the hard palate.
- It extends posteroinferiorly to a curved free margin from which hangs a conical process, the uvula (L. uva, grape).
- The soft palate separates the nasopharynx superiorly and the oropharynx inferiorly.
- During swallowing the soft palate moves posteriorly against the wall of the pharynx, preventing the regurgitation of food into the nasal cavity.
- Laterally, the soft palate is continuous with the wall of the pharynx and is joined to the tongue and pharynx by the palatoglossal and palatopharyngeal folds.
- The soft palate is strengthened by the palatine aponeurosis, formed by the expanded tendon of the tensor veli palatini muscle.
- This aponeurosis attaches to the posterior margin of the hard palate.
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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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