NEET MDS Lessons
Anatomy
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. |
The Tongue
- The tongue (L. lingua; G. glossa) is a highly mobile muscular organ that can vary greatly in shape.
- It consists of three parts, a root, body, and tip.
- The tongue is concerned with mastication, taste, deglutition (swallowing), articulation (speech), and oral cleansing.
- Its main functions are squeezing food into the pharynx when swallowing, and forming words during speech.
Gross Features of the Tongue
- The dorsum of the tongue is divided by a V-shaped sulcus terminalis into anterior oral (presulcal) and posterior pharyngeal (postsulcal) parts.
- The apex of the V is posterior and the two limbs diverge anteriorly.
- The oral part forms about 2/3 of the tongue and the pharyngeal part forms about 1/3.
Oral Part of the Tongue
- This part is freely movable, but it is loosely attached to the floor of the mouth by the lingual frenulum.
- On each side of the frenulum is a deep lingual vein, visible as a blue line.
- It begins at the tip of the tongue and runs posteriorly.
- All the veins on one side of the tongue unite at the posterior border of the hyoglossus muscle to form the lingual vein, which joins the facial vein or the internal jugular vein.
- On the dorsum of the oral part of the tongue is a median groove.
- This groove represents the site of fusion of the distal tongue buds during embryonic development.
The Lingual Papillae and Taste Buds
- The filiform papillae (L. filum, thread) are numerous, rough, and thread-like.
- They are arranged in rows parallel to the sulcus terminalis.
- The fungiform papillae are small and mushroom-shaped.
- They usually appear are pink or red spots.
- The vallate (circumvallate) papillae are surrounded by a deep, circular trench (trough), the walls of which are studded with taste buds.
- The foliate papillae are small lateral folds of lingual mucosa that are poorly formed in humans.
- The vallate, foliate and most of the fungiform papillae contain taste receptors, which are located in the taste buds.
The Pharyngeal Part of the Tongue
- This part lies posterior to the sulcus terminalis and palatoglossal arches.
- Its mucous membrane has no papillae.
- The underlying nodules of lymphoid tissue give this part of the tongue a cobblestone appearance.
- The lymphoid nodules (lingual follicles) are collectively known as the lingual tonsil.
Muscles of the Tongue
- The tongue is divided into halves by a medial fibrous lingual septum that lies deep to the medial groove.
- In each half of the tongue there are four extrinsic and four intrinsic muscles.
- The lingual muscles are all supplied by the hypoglossal nerve (CN XII).
- The only exception is palatoglossus, which is supplied by the pharyngeal branch of the vagus nerve, via the pharyngeal plexus.
Extrinsic Muscles of the Tongue
The Genioglossus Muscle
- This is a bulky, fan-shaped muscle that contributes to most of the bulk of the tongue.
- It arises from a short tendon from the genial tubercle (mental spine) of the mandible.
- It fans out as it enters the tongue inferiorly and its fibres attach to the entire dorsum of the tongue.
- Its most inferior fibres insert into the body of the hyoid bone.
- The genioglossus muscle depresses the tongue and its posterior part protrudes it.
The Hyoglossus Muscle
- This is a thin, quadrilateral muscle.
- It arises from the body and greater horn of the hyoid bone and passes superoanteriorly to insert into the side and inferior aspect of the tongue.
- It depresses the tongue, pulling its sides inferiorly; it also aids in retrusion of the tongue.
The Styloglossus Muscle
- This small, short muscle arises from the anterior border of the styloid process near its tip and from the stylohyoid ligament.
- It passes inferoanteriorly to insert into the side and inferior aspect of the tongue.
- The styloglossus retrudes the tongue and curls its sides to create a trough during swallowing.
The Palatopharyngeus Muscle
- Superior attachment: hard palate and palatine aponeurosis.
- Inferior attachment: lateral wall of pharynx.
- Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.
- This thin, flat muscle is covered with mucous membrane to form the palatopharyngeal arch.
- It passes posteroinferiorly in this arch.
- This muscle tenses the soft palate and pulls the walls of the pharynx superiorly, anteriorly and medially during swallowing.
Intrinsic Muscles of the Tongue
The Superior Longitudinal Muscle of the Tongue
- The muscle forms a thin layer deep to the mucous membrane on the dorsum of the tongue, running from its tip to its root.
- It arises from the submucosal fibrous layer and the lingual septum and inserts mainly into the mucous membrane.
- This muscle curls the tip and sides of the tongue superiorly, making the dorsum of the tongue concave.
The Inferior Longitudinal Muscle of the Tongue
- This muscle consists of a narrow band close to the inferior surface of the tongue.
- It extends from the tip to the root of the tongue.
- Some of its fibres attach to the hyoid bone.
- This muscle curls the tip of the tongue inferiorly, making the dorsum of the tongue convex.
The Transverse Muscle of the Tongue
- This muscle lies deep to the superior longitudinal muscle.
- It arises from the fibrous lingual septum and runs lateral to its right and left margins.
- Its fibres are inserted into the submucosal fibrous tissue.
- The transverse muscle narrows and increases the height of the tongue.
The Vertical Muscle of the Tongue
- This muscle runs inferolaterally from the dorsum of the tongue.
- It flattens and broadens the tongue.
- Acting with the transverse muscle, it increases the length of the tongue.
EPITHELIUMS
Epithelial Tissue Epithelial tissue covers surfaces, usually has a basement membrane, has little extracellular material, and has no blood vessels. A basement membrane attaches the epithelial cells to underlying tissues. Most epithelia have a free surface, which is not in contact with other cells. Epithelia are classified according to the number of cell layers and the shape of the cells.
- Epitheliums contain no blood vessels. There is normally an underlying layer of connective tissue
- Almost all epitheliums lie on a basement membrane.The basement membrane consists of a basal lamina and reticular lamina. The reticular lamina is connected to the basal lamina by anchoring fibrils. The reticular lamina may be absent in which case the basement membrane consist only of a basal lamina. The basal lamina consists of a - lamina densa in the middle (physical barrier) with a lamina lucida on both sides (+charge barrier),The basement membrane is absent in ependymal cells.The basement membrane is not continuous in sinusoidal capillaries.
- Epitheliums always line or cover something
- Epithelial cells lie close together with little intercellular space
- Epithelial cells are strongly connected to one another especially those epitheliums that are subjected to mechanical forces.
Functions of Epithelium:
→ Simple epithelium involved with diffusion, filtration, secretion, or absorption
→ Stratified epithelium protects from abrasion
→ Squamous cells function in diffusion or filtration
Appendicular Skeleton
Upper extremity
• Shoulder-clavicle and scapula
Clavicle
Articulates with the manubrium at the sternal end
Articulates with the scapula at the lateral end
Slender S-shaped bone that extends horizontally across the upper part of the thorax
Scapula
Triangular bone with the base upward and the apex downward
Lateral aspect contains the glenoid cavity that articulates with the head of the humerus
Spine extends across the upper part of the posterior surface; expands laterally and
forms the acromion (forms point of shoulder)
Coracoid process projects anteriorly from the upper part of the neck of the scapula
Arm (humerus)
Consists of a shaft (diaphysis) and two ends (epiphyses)
Proximal end has a head that articulates with the glenoid fossa of the scapula
Greater and lesser tubercles lie below the head
Intertubercular groove is located between them; long tendon of the biceps attaches here
Surgical neck is located below the tubercles
o Radial groove runs obliquely on the posterior surface; radial nerve is located here
o Deltoid muscles attaches in a V-shaped area in the middle of the shaft. called the deltoid tuberosity
Distal end has two projections. the medial and lateral epicondyles
Capitulum-articulates with the radius
Trochlea-articulates with the ulqa
Forearm
Radius
Lateral bone of the forearm
Radial tuberosity is located below the head on the medial side
Distal end is broad for articulation with the wrist: has a styloid process on its lateral side
Ulna
Medial side of the forearm
Conspicuous part of the elbow joint (olecranon)
Curved surface that articulates with the trochlea of the humerus is the trochlearnotch
Lateral ide is concave (radial notch); articulates with the head of the radius Distal end contains the styloid process
Distal end contains the styloid process
Hand
Carpal bones (8)
Aranged in two rows of four
Scaphoid. lunate. triquetral. and pisiform proximal row); trapezium. trapezoid.
capitate. and hamate (distal row)
Metacarpal bones (5)
Framework of the hand
Numbered 1 to 5 beginning on the lateral side
Phalanges (14)
Fingers
Three phalanges in each finger; two phalanges in the thumb
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
BONE
A rigid form of CT, Consists of matrix and cells
Matrix contains:
organic component 35% collagen fibres
inorganic salts 65% calcium phosphate (58,5%), calcium carbonate (6,5%)
2 types of bone - spongy (concellous)
compact (dense)
Microscopic elements are the same
Spongy bone consists of bars (trabeculae) which branch and unite to form a meshwork
Spaces are filled with bone marrow
Compact bone appears solid but has microscopic spaces
In long bones the shaft is compact bone
And the ends (epiphysis) consists of spongy bone covered with compact bone
Flat bones consists of 2 plates of compact bone with spongy bone in-between
Periosteum covers the bone
Endosteum lines marrow cavity and spaces
These 2 layers play a role in the nutrition of bone tissue
They constantly supply the bone with new osteoblasts for the repair and growth of bone
Microscopically
The basic structural unit of bone is the Haversian system or osteon
An osteon consists of a central Haversian canal
- In which lies vessels nerves and loose CT
- Around the central canal lies rings of lacunae
- A lacuna is a space in the matrix in which lies the osteocyte
- The lacunae are connected through canaliculi which radiate from the lacunae
- In the canaliculi are the processes of the osteocytes
- The canaliculi link up with one another and also with the Haversian canal
- The processes communicate with one another in the canaliculi through gap junctions
- Between two adjacent rows of lacunae lie the lamellae, 5-7µm thick
- In three dimensions the Haversian systems are cylindrical
- The collagen fibres lie in a spiral in the lamellae
- Perpendicular to the Haversian canals are the Volkman's canals
- They link up with the marrow cavity and the Haversian canals
- Some lamellae do not form part of a Haversian system
- They are the:
- Inner circumferential lamellae - around the marrow cavity
- Outer circumferential lamellae - underneath the outer surface of the bone
- Interstitial lamellae - between the osteons
Endosteum
Lines all cavities like marrow spaces, Haversian- and Volkman's canals
Consists of a single layer of squamous osteoprogenitor cells with a thin reticular CT layer underneath it
Continuous with the inner layer of periosteum
Covers the trabeculae of spongy bone
Cells differentiate into osteoblasts (like the cells of the periosteum)
Periosteum
Formed by tough CT
2 layers
Outer fibrous layer: Thickest, Contains collagen fibres,
Some fibres enter the bone - called Sharpey's fibres
Contains blood vessels.
Also fibrocytes and the other cells found in common CT
Inner cellular layer
Flattened cells (continuous with the endosteum)
Can divide and differentiate into osteoprogenitor cells
spindle shaped
little amount of rough EPR
poorly developed Golgi complex
play a prominent role in bone growth and repair
Osteoblasts
Oval in shape, Have thin processes, Rough EPR in one part of the cell (basophilic)
On the other side is the nucleus, Golgi and the centrioles in the middle, Form matrix
Become trapped in the matrix
Osteocytes
Mature cells, Less basophilic than the osteoblasts, Lie trapped in the lacunae, Their processes lie in the canaliculi, Processes communicate with one another through gap junctions, Substances (nutrients, waste products) are passed on from cell to cell
Osteoclasts
Very large, Multinucleate (up to 50), On inner and outer surface of bone, Lie in depressions on the surface called Howships lacunae, The cell surface facing the bone has short irregular processes
Acidophylic
Has many lysosomes, polyribosomes and rough EPR
Lysosomal enzymes are secreted to digest the bone
Resorbs the organic part of bone
Histogenesis
Two types of bone development.
- intramembranous ossification
- endochondral ossification
In both these types of bone development temporary primary bone is deposited which is soon replaced by secondary bone. Primary bone has more osteocytes and the mineral content is lower.