• 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.

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

Initially, four clefts exist; however, only one gives rise to a definite structure in adults.

Muscles of the larynx

Extrinsic muscles
    suprahyoid: raise larynx, depress mandible for swallowing
    infrahyoid: lower larynx for swallowing
    both stabilize hyoid for tongue movements

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.

Blood Supply to the Head and Neck

• Most arteries in the anterior cervical triangle arise from the common carotid artery or one of the branches of the external carotid artery.
• Most veins in the anterior cervical triangle are tributaries of the large internal jugular vein.

The Common Carotid Arteries

• The right common carotid artery begins at the bifurcation of the brachiocephalic trunk, posterior to the right sternoclavicular joint.
• The left common carotid artery begins arises from the arch of the aorta and ascends into the neck, posterior to the left sternoclavicular joint.

• Each common carotid artery ascends into the neck within the carotid sheath to the level of the superior border of the thyroid cartilage.
• Here it terminates by dividing into the internal and external carotid arteries. 

The Internal Carotid Artery

• This is the direct continuation of the common carotid artery and it has no branches in the neck.
• It supplies structures inside the skull.
• The internal carotid arteries are two of the four main arteries that supply blood to the brain.

• Each artery arises from the common carotid at the level of the superior border of the thyroid cartilage.
• It then passes superiorly, almost in a vertical plane, to enter the carotid canal in the petrous part of the temporal bone.

• A plexus of sympathetic fibres accompany it.

• During its course through the neck, the internal carotid artery lies on the longus capitis muscle and the sympathetic trunk.
• The vagus nerve (CN X) lies posterolateral to it.

• The internal carotid artery enters the middle cranial fossa beside the dorsum sellae of the sphenoid bone.
• Within the cranial cavity, the internal carotid artery and its branches supply the hypophysis cerebri (pituitary gland), the orbit, and most of the supratentorial part of the brain. 

The External Carotid Arteries 

• This vessel begins at the bifurcation of the common carotid, at the level of the superior border of the thyroid cartilage.
• It supplies structures external to the skull.

• The external carotid artery runs posterosuperiorly to the region between the neck of the mandible and the lobule of the auricle.
• It terminates by dividing into two branches, the maxillary and superficial temporal arteries.
• The stems of most of the six branches of the external carotid artery are in the carotid triangle. 

The Superior Thyroid Artery

• This is the most inferior of the 3 anterior branches of the external carotid.
• It arises close to the origin of the vessel, just inferior to the greater horn of the hyoid.
• The superior thyroid artery runs anteroinferiorly, deep to the infrahyoid muscles and gives off the superior laryngeal artery. This artery pierces the thyrohyoid membrane in company with the internal laryngeal nerve and supplies the larynx.

The Lingual Artery

• This arises from the external carotid artery as it lies on the middle constrictor muscle of the pharynx.
• It arches superoanteriorly, about 5 mm superior to the tip of the greater horn of the hyoid bone, and then passes deep to the hypoglossal nerve, the stylohyoid muscle, and the posterior belly of digastric muscle.

• It disappears deep to the hyoglossus muscle.
• At the anterior border of this muscle, it turns superiorly and ends by becoming the deep lingual artery.

The Facial Artery

• This arises from the carotid artery either, in common with the lingual artery, or immediately superior to it.
• In the neck the facial artery gives off its important tonsillar branch and branches to the palate and submandibular gland.
• The facial artery then passes superiorly under the cover of the digastric and stylohyoid muscles and the angle of the mandible.

• It loops anteriorly and enters a deep groove in the submandibular gland.

• The facial artery hooks around the inferior border of the mandible and enters the face. Here the pulsation of this artery can be felt (anterior to the masseter muscle).

The Ascending Pharyngeal Artery

• This is the 1^st or 2^nd branch of the external carotid artery.
• This small vessel ascends on the pharynx, deep to the internal carotid artery.
• It sends branches to the pharynx, prevertebral muscles, middle ear and meninges.

The Occipital Artery

• This arises from the posterior surface of the external carotid near the level of the facial artery.
• It passes posteriorly along the inferior border of the posterior belly of digastric.
• It ends in the posterior part of the scalp.
• During its course, it is superficial to the internal carotid artery and three cranial nerves (CN IX, CN X and CN XI).

The Posterior Auricular Artery

• This is a small posterior branch of the external carotid artery.
• It arises from it at the superior border of the posterior belly of the digastric muscle.
• It ascends posteriorly to the external acoustic meatus and supplies adjacent muscles, the parotid gland, the facial nerve, structures in the temporal bone, the auricle, and the scalp. 

The Internal Jugular Vein

• This is usually the largest vein in the neck.
• The internal jugular vein drains blood from the brain and superficial parts of the face and neck.
• Its course corresponds to a line drawn from a point immediately inferior to the external acoustic meatus to the medial end of the clavicle.

• This large vein commences at the jugular foramen in the posterior cranial fossa, as the direct continuation of the sigmoid sinus.

• The dilation at its origin is called the superior bulb of the internal jugular vein.
• From here it runs inferiorly through the neck in the carotid sheath.

• The internal jugular vein leaves the anterior triangle of the neck by passing deep to the SCM muscle.
• Posterior to the sternal end of the clavicle, it unites with the subclavian vein to form the brachiocephalic vein.
• Near its termination is the inferior bulb of the jugular vein contains a bicuspid valve similar to that of the subclavian vein.

• The deep cervical lymph nodes lie along the course of the internal jugular vein, mostly lateral and posterior.

Tributaries of the Internal Jugular Vein

• This large vein is joined at its origin by the: inferior petrosal sinus, the facial, lingual, pharyngeal, superior and middle thyroid veins, and often the occipital vein.