A&P

The common carotid artery

Internal carotid artery and External carotid artery

• Structures of the cranium and Eye and related structures
• (supplies blood to the eye)

• Superficial areas of the head and neck
• Small portion of the circulation to the ocular adnexa

• 1- Enters the skull through the carotid canal
• 2- Then immediatly enters the cavernous sinus
• 3- As it emerges, it branches to the opthalmic artery (fist major branch)

The Opthalmic Artery

• 1- Enters the orbit within the dural sheath of the optic nerve
• 2- Passes through the optic canal (below and lateral to the nerve)
• 3- In the orbit it runs inferolateral to the optic nerve for a short distance
• 4- Then crosses either above or below the nerve (20% below)

• 1- Central Retinal Artery
• 2- Lacrimal Artery
• 3- Ciliary Arteries - 2 
• 4- Ethmoid arteries - 2
• 5- Supraorbital Artery
• 6- Muscular Arteries - 2
• 7- Sup and Inf Medial Palpebral arteries
• 8- Supratrochlear artery
• 9- Dorsonasal artery

• 1- The smallest branch
• 2- Leaves the opthalmic artery as it lies below the optic nerve
• 3- Enters the meningeal sheath of the nerve about 10-12 mm behind the globe
• 4- Supplies the inner retina

• In the optic nerve, the CRA provides the collateral branches ( to the nerve and pia mater)
• The CRA passes through the lamina cribose and enters the optic disk nasal to center branching into the Superior and Inferior.
• The S and I branches divide further into nasal and temporal branches
• These vessels continue to bifurcate
• 2 capillary networks are formed, the deep capillary plexus and the Superficial capillary plexus
• No blood vessels are found in the macula or fovea

The Opthalmic Artery from the Internal Carotid Artery

• Short Ciliary Arteries (10-20)
• Long Ciliary Arteries (2)

• Arise as one or two branches, then form 10-20 branches
• Enter the scelera in a ring around the optic nerve and from the arterial network within the choroidal stroma
• Divide to form posterior choriocapillaris
• Other branches form the Circle of Zinn
• Supplies the Optic nerve of the head (external part of retina)

Nourishes retina as far anteriorly as equator

Encircles the optic nerve at the choriod

The uveal vessels 

• 2
• One enters nasally one temporally
• Near the optic nerve
• Give 3-5 branches at the ora serrata and passes directly back to form the anterior choriocapillaris.
• These capillaries nourish retina from the equator forward.
• Run between the sclera and choroid anterior globe.
• Enter the ciliary body and branch superiorly and inferiorly
• Anastomose with each other and with the anterior ciliary arteries and form the major arterial circle of the iris.

• Located in the ciliary stroma
• Is the source of the radial vessels found in the iris

• Branch from the vessels that supply the rectus muscles
• Exit the muscles near the insertions, run along the tendons
• Then loop inward to pierce the sclera (just outer to the limbus)
• Before entering the scelera, they send branches into the conjunctiva, forming a network of vessels in the limbal conjunctiva.
• Other branches enter the episcelera to form a network of vessels before entering the uvea, then enter the ciliary body and anastomose with the branches of the long posterior ciliary arteries (major circle of the iris)
• Generally, 2 emanate from each of the rectus muscles, wih exception of the lateral muscle (only 1)

 The conjunctiva, episclera, ciliary body, and iris

• Receive blood from the anterior conjuntiva, limbal archades, anterior episcleral veins, and perforating scleral veins. 
• Then form the anterior ciliary veins (leave the globe anteriorly over the rectus muscles)

Posteriorly 4-7 vortex veins drain the venous system ( the choriod, cilary body, and iris) into the superior and inferior opthalmic veins

• 33% larger then CRA
• Drains into the superior opthalmic vein and/or the cavernous sinus

The perfusion pressure (PP), the pressure that drives blood through the vessel, and the resistance (R) generated by the vessels.

Reduction of arterial pressure or increase in intraocular pressure.

That property of a vascular bed that permits constant or nearly constant blood flow throughout a wide range of perfusion pressures

Primary metabolic needs, especially the need for oxygen

More blood production

Vessels dilate

Vessels constrict

Ones that maintain the body in rest

• Used to make body aware for emergencies
• - Lowers the blood flow

P arteries (intering tissue) - P veins (leaving tissue)/ Resistance

65 mmHg

around 15mmHg

• The numeric value that indicates how easily blood can pass through a tissue.
• Is approx 50 mmHg (diff between A and veins)

Perfusion presssure

• OPP
• - Research is showing that glaucoma patients with low OPP are 1.5 x more likely to develop progressive nerve damage from ischemia.

• Ocular perfusion pressure
• Diastolic bp-intraocular bp

• High IOP will infringe on CRA which leads to:
• reduction in blood supply to the retinal tissue and:
• retinal vessels increase their vessel diameter to allow more blood flow (autoregulation).

CRA will obtain its critical closing pressure and shut down.

Critical closing pressure

IOP increases- which reduces the artieral pressure entering the retina

CRAO occurs, PP decreases = hypoxia retina

CRAO- Central Retinal Artery Occlusion

• IOP
• To drain into the trabecular meshwork and into the venous system.

• The perfusion pressure of the retinal and uveal arteries.
• Allows nutrients to be delivered from the choriocapillaris to the retina.

• Capillaries that contain pores that span the endothelial lining,
• These pores permit the rapid exchange of water and solutes

• The majority of blood flow in the ocular vessels is always in the choriocapillaris (60%)
• Capillaries have huge fenestration- they provide the outer retina with oxygen, glucose, vitamen A, etc.

Has Fenestrated capillaries

Iris and renal capillaries are non-fenestrated

• Arise either from the vessels entering the choriod or from the Circle of Zinn.
• Arise from the ciliary circulaton and not from the retinal supply
• Occur 15-50% of the population
• Supply the macular area
• ORA direct blood supply to the macular area will be maintained in those individuals with such a cilioretinal artery

• Dual blood supply
• Blood retinal barrier

• Central retinal artery= inner retina
• Choriocapilaris (choriod)= outer retina

Barrier formed by tight junctions between endothelial cells lining the retinal vessels as well as between RPE cells.

Prevents damage cause blood is toxic to the retina

• Vessel walls are transparent (colomn of blood within the vessel can be seen)
• Lighter colored blood is the oxygenated blood of the artery.
• Venous deoxyenated blood is slightly darker.
• The artery generally lies superficial to the vein

This anatomical position predisposes to thrombus formation in the CRV by various factors, including slowing the blood stream, changes in the vessel wall, and changes in the blood.

An increase of the blood supply to the affected areas, causing hyperemia.

• Conjunctivitis
• Uveitis

• The superficial blood vessels are injected, giving the conjunctiva a bright red color that often increases toward the fornix.
• The vessels move with conjunctivial movement and can be blanched with a topical vasoconstrictor.

• The deeper scleral and episcleral vessels are injected, giving the circumlimbial area a pirplish or rose-pink color
• These vessels fo not move with the conjunctiva and are not blanched with a topical vasoconstrictor.

By Sympathetic and Parasympathetic Innervation

• Vasoconstriction of the blood vessels
• Maintaining a resonable blood flow through the uvea during sudden spikes in blood pressure.
• Helps autoregulation to maintain the intraocular flow and constant volume.

• Vasodilation of the blood vessels
• Maitains high ocular blood flow during loss of systemic blood pressure.
• Mediates increase blood flow in response of increase retinal activity.

• 12 pairs
• The nucleus are found in the brain stem, except 1st and 2nd pair.
• Some are Sensoral, some Motor, some Both

• The midbrain, the pons, and the medulla oblongata
• Lies over the basilar portion of the occipital bone, with slight inclination

• 2-8
• Optic, Occlomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibularcochlear

• Mostly a motor (efferent) nerve, but has parasympathetic innervation and some sensorial (affarent) functions
• The Sensoral functions are in the anterior 2/3 of tongue.

To the oropharynx below the palantine tonsil. There is also a small amount of cutaneous sensation carried by the nervous intermedius from the skin in and around the auricle.

• The lacrimal gland, the submandibular, and sublingual salivatory glands, increasing their production
• Also to the glands of the eyelids (tarsal glands) and inhibits the tarsal muscles.

Motor control of most of the muscles of facial expression. It also innervates the porsterior belly of the digastric muscle, the stylohyoid muscle, and stapedius muscle.

Inside the pons of the brain stem, close related to the superior salivatory nucleus.

Motor neurons

Parasympathetic preganglionic neurons (which are also efferent) and some afferent neurons related to the Glossopharyngeal nerve nucleus,

• At the Ponto-medullary junction, lateral to the Abducens nerve and medual to the 8th CN.
• Between these two, the axons from the salivatory nucleus is called the Nervous intermedius.

Preganglionic parasumpathetic fibers and some afferent fibers.

• Exits the interior of the pons, and enters the geniculate ganglion. After it leaves this ganglion, it contains the fibers of the nervous intermedias, and they travel together.
• Inside the skull, It enters the internal aucostic meatus of the petrous portion of the temporal bone, and gives several branches- the main one being the Greater Petrosal Nerve.
• The Greater Petrosal nerve exits the skull and enters into the Pterygopalantine ganglion.

The vidian nerve

The sphenopalatine ganglion and Meckel's ganglion

• Pre-ganglionic parasympathetic fibers from the superior salivatory nucleus. 
• These fibers synapse with neurons found in the Meckel's ganglion.
• The neurons then produce post-ganglionic parasympathetic fibers.

• The Sytlomastoid
• - Temporal, Zygomatic or Malar, Buccal, Mandibular, Cervical.