NEET MDS Lessons
Anatomy
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Skull
Cranium
o Superior portion formed by the frontal. parietal, and occipital bones
o Lateral portions formed by the temporal and sphenoid bones
o Cranial base formed by the temporal. sphenoid, and ethmoid bones
o Fontanels-soft spots in which ossification is incomplete at birthFrontal bone
o Forms the forehead
o Contains the frontal sinuses
o Forms the roof of the orbits
o Union with the parietal bones forms the coronal sutureParietal bones
o Union with the occipital bone forms the lambdoid suture
o Union with the temporal bone forms the squamous suture
o Union with the sphenoid bone forms the coronal sutureTemporal bones
o Contains the external auditory meatus and middle and inner ear structures
o Squamous portion-above the meatus: zygomatic process-articulates with the zygoma
o to form the zygomatic arch• Petrous portion
o Contains organs of hearing and equilibrium
o Prominent elevation on the floor of the cranium• Mastoid portion
o Protuberance behind the earo Mastoid process
• Glenoid fossa-articulates with the condyle on the mandible
• Styloid process-anterior to the mastoid process; several neck muscles attach here
• Stylomastoid foramen-located between the styloid and mastoid processes; facial nerve emerges through this opening
• Jugular foramen-located between the petrous portion and the occipital bone: cranial nerves IX. X, and XI exit
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.
Initially, four clefts exist; however, only one gives rise to a definite structure in adults.
|
1st pharyngeal cleft |
Penetrates underlying mesenchyme and forms EAM. The bottom of EAM forms lateral aspect of tympanic cavity. |
|
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. |
The Nose
- The nose is the superior part of the respiratory tract and contains the peripheral organ of smell.
- It is divided into right and left nasal cavities by the nasal septum.
- The nasal cavity is divided into the olfactory area and the respiratory area.
A. Anatomic position-erect body position with the arms at the sides and the palms upward
B. Plane or section
1. Definition-imaginary flat surface formed by an extension through an axis
2. Median plane-a vertical plane. that divides a body into right and left halves
3. Sagittal plane
- Any plane parallel to the median plane
- Divides the body into right and left portions
4. Frontal plane
- Vertical plane that forms at right angles to the sagittal plane
- Divides the body into anterior and posterior sections
- Synonymous with the term coronal plane
5. Transverse plane
- Horizontal plane that forms at right angles to the sagittal and frontal planes
- Divides the body into upper and lower portions
- Synonymous with the term horizontal plane
C. Relative positions
1. Anterior
- Nearest the abdominal surface and the front of the body
- Synonymous with the term ventral
- In referring to hands and forearms, the terms palmar and Volar are used
2. Posterior
- Back of the body
- Synonymous with the term dorsal
3. Superior
- Upper or higher
- Synonymous with the term cranial (head)
4. Inferior
- Below or lower
- Synonymous with the term caudal (tail)
- In referring to the top of the foot and the sole of the foot. the terms dorsal and plantar are used respectively
5. Medial-near to the median plane
6. Lateral-farther away from the median plane
7. Proximal-near the source or attachment
8. Distal-away from the source or. attachment
9. Superficial-near the surface
10. Deep-away from the surface
11. Afferent-conducting toward a structure
12. Efferent-conducting away from a structure
The Paranasal Sinuses
- These sinuses are air-filled extensions of the respiratory part of the nasal cavity.
- They are in the following bones, frontal, ethmoid, sphenoid and the maxilla.
The Frontal Sinuses
- These are located between the outer and inner tables of the frontal bone, posterior to the superciliary arches.
The Ethmoidal Sinuses
- These comprise of several small cavities, called ethmoidal air cells, within the ethmoidal labyrinth (G. labyrinthos, a maze) of the lateral mass of the ethmoid bone.
The Sphenoidal Sinuses
- These occupy a variable amount in the body of the sphenoid bone and may extend into the wings.
The Maxillary Sinuses
- These are the largest pair of paranasal sinuses.
- They are pyramidal-shaped cavities that may occupy the entire bodies of the maxillae.
- The six muscles rotate the eyeball in the orbit around three axes (sagittal, horizontal and vertical).
- The action of the muscles can be deduced by their site of insertion on the eyeball.
| Muscle | Action(s) on the Eyeball | Nerve Supply |
| Medial Rectus | Adducts | CN III |
| Lateral Rectus | Abducts | CN VI |
| Superior Rectus | Elevates, adducts, and medially rotates | CN III |
| Inferior Rectus | Depresses, adducts, and laterally rotates | CN III |
| Superior Oblique | Depresses, abducts, and medially rotates | CN IV |
| Inferior Oblique | Elevates, abducts, and laterally rotates | CN III |