NEET MDS Lessons
Anatomy
- The forehead is formed by the smooth, broad, convex plate of bone called the frontal squama.
- In foetal skulls, the halves of the frontal squama are divided by a metopic suture.
- In most people, the halves of the frontal bone begin to fuse during infancy and the suture between is usually not visible after 6 years of age.
- The frontal bone forms the thin roof of the orbits (eye sockets).
- Just superior to and parallel with each supraorbital margin is a bony ridge, the superciliary arch, which overlies the frontal sinus. This arch is more pronounced in males.
- Between these arches there is a gently, rounded, medial elevation called the gabella; this term derives from the Latin word glabellus meaning smooth and hairless. In most people, the skin over the gabella is hairless.
-The slight prominences of the forehead on each side, superior to the superciliary arches, are called frontal eminences (tubers).
- The supraorbital foramen (occasionally a notch), which transmits the supraorbital vessels and nerve is located in the medial part of the supraorbital margin.
- The frontal bone articulates with the two parietal bones at the coronal suture.
-It also articulates with the nasal bones at the frontonasal suture. At the point where this suture crosses the internasal suture in the medial plane, there is an anthropological landmark called the nasion . The depression is located at the root of the nose, where it joins the cranium.
- The frontal bone also articulates with the zygomatic, lacrimal, ethmoid, and sphenoid bones.
In about 8% of adult skulls, a remnant of the inferior part of the metopic (interfrontal) suture is visible. It may be mistaken in radiographs for a fracture line by inexperienced observers.
- The superciliary arches are relatively sharp ridges of bone and a blow to them may lacerate the skin and cause bleeding.
- Bruising of the skin over a superciliary arch causes tissue fluid and blood to accumulate in the surrounding connective tissue, which gravitates into the upper eyelid and around the eye. This results in swelling and a "black eye".
- Compression of the supraorbital nerve as it emerges from its foramen causes considerable pain, a fact that may be used by anaesthesiologists and anaesthetists to determine the depth of anaesthesia and by physicians attempting to arouse a moribund patient.
The Lips
- These are mobile muscular folds that surround the mouth, the entrance of the oral cavity.
- The lips (L. labia) are covered externally by skin and internally by mucous membrane.
- In between these are layers of muscles, especially the orbicularis oris muscle.
- The upper and lower lips are attached to the gingivae in the median plane by raised folds of mucous membrane, called the labial frenula.
Sensory Nerves of the Lips
- The sensory nerves of the upper and lower lips are from the infraorbital and mental nerves, which are branches of the maxillary (CN V2) and mandibular (CN V3) nerves.
Muscles Around the Eyelids
- The function of the eyelid (L. palpebrae) is to protect the eye from injury and excessive light. It also keeps the cornea moist.
The Orbicularis Oculi Muscle
- This is the sphincter muscle of the eye.
- Its fibres sweep in concentric circles around the orbital margin and eyelids.
- It narrows the eye and helps the flow of tears from the lacrimal sac.
- This muscle has 3 parts: (1) a thick orbital part for closing the eyes to protect then from light and dust; (2) a thin palpebral part for closing the eyelids lightly to keep the cornea from drying; and (3) a lacrimal part for drawing the eyelids and lacrimal punta medially.
- When all three parts of the orbicularis oculi contract, the eyes are firmly closed and the adjacent skin becomes wrinkled.
- The zygomatic branch of the facial nerve (CN VII) supplies it.
The Levator Palpebrae Superioris Muscle
- This muscle raises the upper eyelid to open the palpebral fissure.
- It is supplied by the oculomotor nerve (CN III).
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 Ear
- The ear contains the vestibulocochlear organ and consists of three main parts: external, middle, and internal.
- It has two functions, balance and hearing.
- The tympanic membrane (eardrum) separates the external ear from the middle ear.
- The auditory tube joins the middle ear or tympanic cavity to the nasopharynx.
->The sides and base of the skull are formed partly by these bones.
->Each bone consists of four morphologically distinct parts that fuse during development (squamous, petromastoid, and tympanic parts and the styloid process).
->The flat squamous part is external to the lateral surface of the temporal lobe of the brain.
->The petromastoid part encloses the internal ear and mastoid cells and forms part of the base of the skull.
->The tympanic part contains the bony passage from the auricle (external ear), called the external acoustic meatus. The petromastoid part also forms a portion of the bony wall of the tympanic cavity (middle ear). The meatus and tympanic cavity are concerned with the transmission of sound waves.
->The slender, pointed styloid process of the temporal bone gives attachment to certain ligaments and muscles (e.g., the stylohyoid muscle that elevates the hyoid bone).
->The temporal bone articulates at sutures with the parietal, occipital, sphenoid, and zygomatic bones.
->The zygomatic process of the temporal bone unites with the temporal process of the zygomatic bone to form the zygomatic arch. The zygomatic arches form the widest part of the face.
->The head of the mandible articulates with the mandibular fossa on the inferior surface of the zygomatic process of the temporal bone.
->Anterior to the mandibular fossa is the articular tubercle.
->Because the zygomatic arches are the widest parts of the face and are such prominent facial features, they are commonly fractured and depressed. A fracture of the temporal process of the zygomatic bone would likely involve the lateral wall of the orbit and could injure the eye.
Innervation of the Pharynx
- The motor and most of the sensory supply of the pharynx is derived from the pharyngeal plexus of nerves on the surface of the pharynx.
- The plexus is formed by pharyngeal branches of the vagus (CN X) and glossopharyngeal (CN IX) nerves, and by sympathetic branches for the superior cervical ganglion.
- The motor fibres in the pharyngeal plexus are derived from the cranial root of accessory nerve (CN XI), and are carried by the vagus nerve to all muscles of the pharynx and soft palate.
- The exceptions are stylopharyngeus (supplied by CN IX) and the tensor veli palatini (supplied by CN V3).