NEET MDS Lessons
Anatomy
The Scalp
- The scalp consists of five layers of soft tissue.
- It extends from the superior nuchal line on the posterior aspect of the skull of the supraorbital margins.
- Laterally, the scalp extends into the temporal fossa to the level of the zygomatic arches.
Layers of the Scalp
- The scalp proper is composed of three fused layers. It is separated from the pericranium by loose connective tissue.
- Because of this potential areolar cleavage plane, the scalp is fairly mobile.
- Each letter of the word "S C A L P" serves as a memory key for one of the layers of the scalp: Skin, Connective Tissue, Aponeurosis Epicranialis, Loose Areolar Tissue and Pericranium.
Layer 1: Skin
- Hair covers the scalp in most people.
- The skin of the scalp is thin, especially in elderly people, except in the occipital region.
- The skin contains many sweat and sebaceous glands and hair follicles.
- The skin of the scalp has an abundant arterial supply and good venous and lymphatic drainage systems.
Layer 2: Connective Tissue
- This is a thick, subcutaneous layer of connective tissue and is richly vascularised and innervated.
- It attaches the skin to the third layer of the scalp.
- Fat is enclosed in lobules between the connective fibres.
Layer 3: Aponeurosis Epicranialis
- This is a strong membranous sheet that covers the superior aspect of the cranium.
- This aponeurosis is the membranous tendon of the fleshy bellies of the epicranius muscle.
- The epicranius muscle consists of four parts: two occipital bellies, occipitalis and two frontal bellies, frontalis that are connected by the epicranial aponeurosis.
Layer 4: Loose Areolar Tissue
- This is a subaponeurotic layer or areolar or loose connective tissue.
- It is somewhat like a sponge because it contains innumerable potential spaces that are capable of being distended by fluid.
- It is this layer that allows free movement of the scalp proper, composed of layers 1-3.
Layer 5: Pericranium
- This is a dense layer of specialised connective tissue.
- The pericranium is firmly attached to the bones by connective tissue fibres called Sharpey’s fibres, however, they can be fairly easily stripped from the cranial bones of living persons, except where they are continuous with the fibrous tissues of the cranial sutures.
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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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Muscles of the larynx
Extrinsic muscles
suprahyoid: raise larynx, depress mandible for swallowing
infrahyoid: lower larynx for swallowing
both stabilize hyoid for tongue movements
The Meatus of the Nose
Sphenopalatine Recess
- This space is posterosuperior to the superior concha.
- The sphenoidal sinus opens into this recess.
Superior Meatus
- This is a narrow passageway between the superior and middle nasal conchae.
- The posterior ethmoidal sinuses open into it by one or more orifices.
Middle Meatus
- This is longer and wider than the superior one.
- The anterosuperior part of this meatus lead into a funnel-shaped opening, called the infundibulum, through which the frontonasal duct leads to the frontal sinus.
- There is one duct for each frontal sinus and since there may be several, there may be several frontonasal ducts.
- When the middle concha is removed, rounded elevation called the ethmoidal bulla (L. bubble), is visible
- The middle ethmoidal air cells open on the surface of the ethmoidal bulla.
- Inferior to this bulla is a semicircular groove called the hiatus semilunaris.
- The frontal sinus opens into this hiatus anterosuperiorly.
- Near the hiatus are the openings of the anterior ethmoid air cells.
- The maxillary sinus also opens into the middle meatus.
Inferior Meatus
- This is a horizontal passage, inferolateral to the inferior nasal concha.
- The nasolacrimal duct opens into the anterior part of this meatus.
- Usually, the orifice of this duct is wide and circular.
The Temporomandibular Joint
- This articulation is a modified hinge type of synovial joint.
- The articular surfaces are: (1) the head or condyle of the mandible inferiorly and (2) the articular tubercle and the mandibular fossa of the squamous part of the temporal bone.
- An oval fibrocartilaginous articular disc divides the joint cavity into superior and inferior compartments. The disc is fused to the articular capsule surrounding the joint.
- The articular disc is more firmly bound to the mandible than to the temporal bone.
- Thus, when the head of the mandible slides anterior on the articular tubercle as the mouth is opened, the articular disc slides anteriorly against the posterior surface of the articular tubercle
Muscles Moving the Auditory Ossicles
The Tensor Tympani Muscle
- This muscle is about 2 cm long.
- Origin: superior surface of the cartilaginous part of the auditory tube, the greater wing of the sphenoid bone, and the petrous part of the temporal bone.
- Insertion: handle of the malleus.
- Innervation: mandibular nerve (CN V3) through the nerve to medial pterygoid.
- The tensor tympani muscle pulls the handle of the malleus medially, tensing the tympanic membrane, and reducing the amplitude of its oscillations.
- This tends to prevent damage to the internal ear when one is exposed to load sounds.
The Stapedius Muscle
- This tiny muscle is in the pyramidal eminence or the pyramid.
- Origin: pyramidal eminence on the posterior wall of the tympanic cavity. Its tendon enters the tympanic cavity by traversing a pinpoint foramen in the apex of the pyramid.
- Insertion: neck of the stapes.
- Innervation: nerve to the stapedius muscle, which arises from the facial nerve (CN VII).
- The stapedius muscle pulls the stapes posteriorly and tilts its base in the fenestra vestibuli or oval window, thereby tightening the anular ligament and reducing the oscillatory range.
- It also prevents excessive movement of the stapes.
CARTILAGE
There are 3 types:
Hyaline cartilage
Elastic cartilage
Fibrocartilage
Matrix is made up by: Hyaluronic acid
Proteoglycans
- In cartilage the protein core of the proteoglycan molecule binds through a linking protein to hyaluronic acid to form a proteoglycan aggregate which binds to the fibres
- In the matrix there are spaces, lacunae in which one to three of the cells of cartilage, chondrocytes, are found
- The matrix around the lacuna is the territorial matrix
- Type II collagen fibrils are embedded in the matrix
- The type of fiber depends on the type of cartilage
- Cartilage is surrounded by perichondrium which is a dense CT
- Apositional growth takes place in the perichondrium
- The fibroblasts of the perichondrium change to elliptic chondroblasts which later change to round chondrocytes
- Interstitial growth takes place around the lacunae
- Nutrients diffuse through the matrix to get to the chondrocytes this limits the thickness of cartilage
Hyaline cartilage
Found: Rib cartilage, articulating surfaces, nose, larynx, trachea, embryonic skeleton, Articulating cartilage has no perichondrium
Bluish-white and translucent
Contains type II collagen that is not visible
Elastic cartilage
Found: external auditory canal, epiglottis
Similar to hyaline except that it contains many elastic fibres ,Yellow in colour, Can be continuous with hyaline
Fibrocartilage
Found: Intervertebral disk, symphysis pubis
Always associated with dense CT, Many collagen fibres in the matrix, No perichondrium
- Chondrocytes tend to lie in rows, Can withstand strong forces