NEET MDS Lessons
Anatomy
Walls of the Tympanic Cavity or Middle Ear
- This cavity is shaped like a narrow six-sided box that has convex medial and lateral walls.
- It has the shape of the biconcave lens in cross-section (like a red blood cell).
The Roof or Tegmental Wall
- This is formed by a thin plate of bone, called the tegmen tympani (L. tegmen, roof).
- It separates the tympanic cavity from the dura on the floor of middle cranial fossa.
- The tegmen tympani also covers the aditus ad antrum.
The Floor or Jugular Wall
- This wall is thicker than the roof.
- It separates the tympanic cavity from the superior bulb of the internal jugular vein. The internal jugular vein and the internal carotid artery diverge at the floor of the tympanic cavity.
- The tympanic nerve, a branch of the glossopharyngeal nerve (CN IX), passes through an aperture in the floor of the tympanic cavity and its branches form the tympanic plexus.
The Lateral or Membranous Wall
- This is formed almost entirely by the tympanic membrane.
- Superiorly it is formed by the lateral bony wall of the epitympanic recess.
- The handle of the malleus is incorporated in the tympanic membrane, and its head extends into the epitympanic recess.
The Medial or Labyrinthine Wall
- This separates the middle ear from the membranous labyrinth (semicircular ducts and cochlear duct) encased in the bony labyrinth.
- The medial wall of the tympanic cavity exhibits several important features.
- Centrally, opposite the tympanic membrane, there is a rounded promontory (L. eminence) formed by the first turn of the cochlea.
- The tympanic plexus of nerves, lying on the promontory, is formed by fibres of the facial and glossopharyngeal nerves.
- The medial wall of the tympanic cavity also has two small apertures or windows.
- The fenestra vestibuli (oval window) is closed by the base of the stapes, which is bound to its margins by an annular ligament.
- Through this window, vibrations of the stapes are transmitted to the perilymph window within the bony labyrinth of the inner ear.
- The fenestra cochleae (round window) is inferior to the fenestra vestibuli.
- This is closed by a second tympanic membrane.
The Posterior or Mastoid Wall
- This wall has several openings in it.
- In its superior part is the aditus ad antrum (mastoid antrum), which leads posteriorly from the epitympanic recess to the mastoid cells.
- Inferiorly is a pinpoint aperture on the apex of a tiny, hollow projection of bone, called the pyramidal eminence (pyramid).
- This eminence contains the stapedius muscle.
- Its aperture transmits the tendon of the stapedius, which enters the tympanic cavity and inserts into the stapes.
- Lateral to the pyramid, there is an aperture through which the chorda tympani nerve, a branch of the facial nerve (CN VII), enters the tympanic cavity.
The Anterior Wall or Carotid Wall
- This wall is a narrow as the medial and lateral walls converge anteriorly.
- There are two openings in the anterior wall.
- The superior opening communicates with a canal occupied by the tensor tympani muscle.
- Its tendon inserts into the handle of the malleus and keeps the tympanic membrane tense.
- Inferiorly, the tympanic cavity communicates with the nasopharynx through the auditory tube.
->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.
The Walls of the Orbit
- Each orbit has four walls: superior (roof), medial, inferior (floor) and lateral.
- The medial walls of the orbit are almost parallel with each other and with the superior part of the nasal cavities separating them.
- The lateral walls are approximately at right angles to each other
->The two parietal bones (L. paries, wall) form large parts of the walls of the calvaria.
->On the outside of these smooth convex bones, there are slight elevations near the centre called parietal eminences.
->The middle of the lateral surfaces of the parietal bones is crossed by two curved lines, the superior and inferior temporal lines.
->The superior temporal line indicates an attachment of the temporal fascia; the inferior temporal line marks the superior limit of the temporalis muscle.
->The parietal bones articulate with each other in the median plane at the sagittal suture. The medial plane of the body passes through the sagittal suture.
->The inverted V-shaped suture between the parietal bones and the occipital bones is called the lambdoid suture because of its resemblance to the letter lambda in the Greek alphabet.
->The point where the parietal and occipital bones join is a useful reference point called the lambda. It can be felt as a depression in some people.
->In addition to articulation with each other and the frontal and occipital bones, the parietal bones articulate with the temporal bones and the greater wings of the sphenoid bone.
->In foetal and infant skulls, the bones of the calvaria are separated by dense connective tissue membranes at sutures.
->The large fibrous area where several sutures meet are called fonticuli or fontanelles.
->The softness of these bones and looseness of their connections at these sutures enable the calvaria to undergo changes of shape during birth called molding. Within a day or so after birth, the shape of the infant’s calvaria returns to normal.
->The loose construction of the new-born calvaria also allows the skull to enlarge and undergo remodelling during infancy and childhood.
->Relationships between the various bones are constantly changing during the active growth period.
->The increase in the size of the cranium is greatest during the first 2 years, the period of most rapid postnatal growth of the brain.
->The cranium normally increases in capacity until about 15 or 16 years of age; thereafter the cranium usually increases only slightly in size as its bones thicken for 3 to 4 years.
Classified on functional Basis
Secretion ,Protection and waterproofing, Absorbtion, Transport, Sensory
Secretion
Glandular epithelium’s 3 types:
- Exocrine - with ducts
- endocrine - without ducts
- mixed exo-endocrine
Exocrine glands: One cell
- goblet cells
- In lining epitheliums of respiratory tract and GIT
- Secretes musin (protein) Musin + water = mucus, Mucus is a lubricant
More than one cell
Simple: Has a single duct,
- Acinar - mucus glands of the penile urethra
- Tubular - cripts of Lieberkuhn
- Coiled tubular - sweat gland
- Spiral tubular - Gland of Moll
- Branched tubular - mucous glands of the pyloric region
- Branched acinar - sebaceous gland in the skin
Compound
- Consists of a branched duct with numerous secretory end organs
- Compound tubular - Brünners glands
- Compound alveolar - mammary, prostate, pancreas, parotid
- Compound tubuloalveolar - submandibular-, sublingual salivary glands
Endocrine glands
Secrete directly into the blood
One cell : mast cells, in soft CT, near capillaries,
secrete - heparin - histamine
More than one cell
Cells can be arranged in the following ways:
- Cords - adrenal glands, parathyroid, anterior pituitary
- anastomosing cords with dilated blood capillaries in-between
- Isles - pancreas
- Follicles - thyroid
- cells line a follicle filled with non-cellular material
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. |
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