<ul>
 <li>Cerebral blood flow represent 15% of cardiac output</li>
 <li>
 Cerebral hemispheres and diencephalon (the posterior aspect of the forebrain containing the
 thalamus and hypothalamus) are supplied by branches of the internal carotid artery and vertebral
 arteries
 </li>
 <li>
 The two systems meet in the circle of Willis
 </li>
</ul>

## Features of the Circle of Willis
<ul>
 <li>The posterior cerebral arteries are terminal branches of the basilar artery</li>
 <ul>
 <li>They supply the inferior aspects of the cerebral hemispheres and the occipital lobe</li>
 <li>
 They produce the posterior communicating arteries which meet the internal carotid artery
 </li>
 </ul>
 <li>
 The anterior communicating artery arises from and links the two anterior cerebral arteries
 </li>
 <li>The middle cerebral artery is the largest and a direct branch of the internal carotid</li>
 <ul>
 <li>
 It supplies the cortical areas for motor and sensory innervation to the contralateral half of
 the body
 </li>
 </ul>
 <li>Anterior cerebral arteries supply</li>
 <ul>
 <li>Medial surfaces of the hemispheres</li>
 <li>Superior frontal gyrus</li>
 <li>Area on adjacent parietal lobe</li>
 </ul>
 <li>The internal capsule is supplied by</li>
 <ul>
 <li>Anterior cerebral</li>
 <li>Middle cerebral</li>
 <li>Anterior choroidal arteries</li>
 <li>
 Note: the fibres of the optic radiations run amongst the most posterior fibres of the internal
 capsule and those from the frontal eye fields pass within the anterior limb
 </li>
 </ul>
</ul>

## Vertebral artery
<ul>
 <li>Branch from the subclavians</li>
 <li>Travel through the foramen transversarium of cervical vertebrae</li>
 <li>Enter foramen magnum</li>
 <li>Travels anterior to spinal accessory nerve</li>
 <li>Carries postganglionic sympathetic fibres from the stellate ganglion</li>
 <li>Give rise to the posterior inferior cerebellar artery</li>
</ul>

## Carotid arteries
<ul>
 <li>Right and left common carotids derive from</li>
 <ul>
 <li>The brachiocephalic artery</li>
 <li>The aortic arch</li>
 </ul>
 <li>The common carotids bifurcate at the level of C3</li>
 <ul>
 <li>There is a dilation here called the carotid sinus</li>
 </ul>
</ul>
<HotTopic>
 The internal carotid has no branches within the neck, but a number of branches in the head
</HotTopic>
<ul>
 <li>Ophthalmic</li>
 <li>
 Vidian (artery to the pterygoid canal): serves as an anastomosis with the external carotid
 </li>
 <li>Inferior hypophyseal</li>
 <li>Middle cerebral</li>
</ul>
External carotid branches (numbers in order of branching from bottom)
<ul>
 <li>Medial aspect</li>
 <ul>
 <li>Ascending pharyngeal (2)</li>
 </ul>
 <li>Anterior aspect</li>
 <ul>
 <li>Superior thyroid (1)</li>
 <li>Facial (4)</li>
 <li>Lingual (3)</li>
 </ul>
 <li>Posterior aspect</li>
 <ul>
 <li>Posterior auricular (6)</li>
 <li>Occipital (5)&nbsp;</li>
 </ul>
 <li>After entering parotid (terminal branches)</li>
 <ul>
 <li>Superficial temporal (8)</li>
 <li>Maxillary (7)</li>
 </ul>
</ul>

 Quick tip! Mnemonic: Some Anatomists Like Freaking Out Poor Medical Students

Carotid body chemoreceptor
<ul>
 <li>Stimulated by</li>
 <ul>
 <li>Increase in PCO2</li>
 <li>Decrease in PO2</li>
 <li>Decrease in pH</li>
 </ul>
 <li>Causes reflex peripheral vasoconstriction</li>
</ul>

## Temporal artery
<ul>
 <li>Last branch of external carotid as above</li>
</ul>
<ClinicalCorrelate>
 For Temporal Artery Biopsy:
 <ul>
 <li>
 Surgical landmarks: the artery runs deep to the skin and subcutaneous tissues but on the
 surface of the temporalis fascia
 </li>
 </ul>
</ClinicalCorrelate>
<ul>
 <li>
 Some people have anastomoses between the internal and external carotid circulations via the
 temporal artery and in this case the temporal can provide significant intracranial/cerebral
 blood flow: hence ligation can lead to stroke
 </li>
</ul>

## Maxillary artery (second last branch of external carotid)
<ul>
 <li>Main branches arise within the infratemporal fossa</li>
 <ul>
 <li>Middle meningeal artery</li>
 <li>Inferior alveolar artery: supplies mandibular gingiva</li>
 </ul>
 <li>Enters and ends in the pterygopalatine fossa</li>
 <ul>
 <li>Small branches accompanying the maxillary nerve</li>
 <li>Infraorbital artery supplies the maxillary incisor teeth</li>
 </ul>
 <li>Supplies muscles of mastication and the lateral wall of the nose</li>
 <li>Lies between the sphenomandibular ligament and mandible</li>
</ul>

## Facial artery
<ul>
 <li>Travels obliquely beneath digastric and stylohyoid</li>
 <li>Enters a groove on the posterior surface of the submandibular gland</li>
 <li>Travels over the mandible and ends at the medial commissure of the eye</li>
 <li>Becomes the angular artery, which supplies</li>
 <ul>
 <li>Orbicularis oculi</li>
 <li>Lacrimal sac</li>
 </ul>
 <li>Anastomoses with the dorsal nasal branch of the ophthalmic artery</li>
</ul>

Neuroanatomy

Cerebral Blood Supply

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Venous Sinuses

Cerebral Ventricles

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance