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.

Connective Tissue

Functions of Connective tissue:

→ joins together other tissues

→ supporting framework for the body (bone)

→ fat stores energy

→ blood transports substances

Connective tissue is usually characterized by large amounts of extracellular materials that separate cells from each other, whereas epithelial tissue is mostly cells with very little extracellular material. The extracellular substance of connective tissue consists of protein fibers which are embedded in ground substance containing tissue fluid.

Fibers in connective tissue can be divided into three types:

→ Collagen fibers are the most abundant protein fibers in the body.

→ Elastic fibers are made of elastin and have the ability to recoil to original shape.

→ Reticular fibers are very fine collagen fibers that join connective tissues to other tissues.

Connective tissue cells are named according to their functions:

 → Blast cells produce the matrix of connective tissues

→ Cyte cells maintains the matrix of connective tissues

→ Clast cells breaks down the matrix for remodeling (found in bone)

The Skeleton of the Nose

• The immovable bridge of the nose, the superior bony part of the nose, consists of the nasal bones, the frontal processes of the maxillae, and the nasal part of the frontal bones.

• The movable cartilaginous part consists of five main cartilages and a few smaller ones.
• The U-shaped alar nasal cartilages are free and movable.
• They dilate and constrict the external nares when the muscles acting on the external nose contract.

The Nasal Cavities

• The nasal cavities are entered through the anterior nares or nostrils.
• They open into the nasopharynx through the choanae.

The Roof and Floor of the Nasal Cavity

• The roof is curved and narrow, except at the posterior end.

• The floor is wider than the roof.
• It is formed from the palatine process of the maxilla and the horizontal plate of the palatine bone.

The Walls of the Nasal Cavity

• The medial wall is formed by the nasal septum; it is usually smooth.

• The lateral wall is uneven owing to the three longitudinal, scroll-shaped elevations, called the conchae (L. shells) or turbinates (L. shaped like a top).
• These elevations are called the superior, middle and inferior conchae according to their position.

• The superior and middle conchae are parts of the ethmoid bone, whereas the inferior conchae are separate bones.

• The inferior and middle conchae project medially and inferiorly, producing air passageways called the inferior and middle meatus (L. passage). Note: the plural of "meatus" is the same as the singular.
• The short superior conchae conceal the superior meatus.
• The space posterosuperior to the superior concha is called the sphenoethmoidal recess.

The skull, the skeleton of the head, is the most complex bony structure in the body because it:

1. Encloses the brain, which is irregular in shape;
2. Houses the organs of special senses for seeing, hearing, tasting, and smelling; and
3. Surrounds the openings in to the digestive and respiratory tracts.

• In the anatomical position, the skull is oriented so that the inferior margin of the orbit (eye socket) and the superior margin of the external acoustic meatus (auditory canal) are horizontal. This is called the orbitomenial plane (Frankfort plane).

• The term cranium (L. skull) is sometimes used when referring to the skull without the mandible (lower jaw), but the cranium is often used when referring to the part of the skull containing the brain.
• The superior part is the box-like structure called the calvaria (cranial vault, brain case); the remainder of the cranium, including the maxilla (upper jaw), orbits (eyeball sockets) and nasal cavities, forms the facial skeleton.
• The term skullcap (calotte) refers to the superior part of the calvaria, which is removed during autopsies and dissections. The inferior aspect of the cranium is called the cranial base.

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

The Eye and Orbit

• The orbit (eye socket) appears as a bony recess in the skull when it is viewed from anteriorly.
• It almost surrounds the eye and their associated muscles, nerves and vessels, together with the lacrimal apparatus.

• The orbit is shaped somewhat like a four-side pyramid lying on its side, with its apex pointing posteriorly and its base anteriorly.