The Brain gets its Primary Blood Supply from the Two Internal Carotid Arteries and the Two Vertebral Arteries.
The Vascular connections at the Base of the Brain form the Circle Of Willis, which is composed of a Vascular loop consisting of the Two Anterior Cerebral Arteries and the Anterior Communicating Artery in front and the Posterior Communicating Artery and the Posterior Cerebral Arteries behind.
There are numerous variations and congenital abnormalities associated with the Circle Of Willis.
The Internal Carotid Artery divides IntraCranially into two main branches. One is the Anterior Cerebral Artery, which passes forward and immediately above the Optic Chiasm to enter the Longitudinal Fissure of the Cerebrum.
It furnishes blood to the major part of the Medial Aspect of the Cerebral Hemisphere and gives off several vital Perforating branches at the base of the Brain that supply blood to the head of the Caudate, the Anterior part of the Lentiform Nucleus, the Internal Capsule, the Anterior Columns of the Fornix, and the Anterior Commissures.
The loss of these important Perforators leads to deep Coma.
The Middle Cerebral Artery is the larger of the two terminal branches of the Internal Carotid Artery and passes laterally through the Sylvian Fissure to the surface of the Insula, where it divides into numerous Parietal and Temporal Cortical branches.
During its course through the Sylvian Fissure it gives off important Perforating Arteries called Medial and Lateral Striate Arteries, which pass upwards through the Putamen of the Lentiform Nucleus, and also supplies blood to the Globus Pallidus and the Internal Capsule.
These arteries that frequently rupture in cases of spontaneous Cerebral hemorrhage are known as the Arteries Of Charcot.
The Vertebral Arteries enter the IntraCranial cavity and transverse the base of the Medulla, giving off two PosteroInferiore Cerebellar Arteries, which supply blood to the BrainStem and the PosteroInferior surface of the Cerebellum.
The Vertebral Arteries then join to become the Basilar Artery. The Perforating branches from the Basilar Artery to the remainder of the BrainStem are vital to many life functions.
The AnteroInferior Cerebellar Artery arises from the Basilar Artery at the Ponto-Medullary junction and gives blood to the AnteroInferior surface of the Cerebellum.
There is frequently an important loop that passes into the internal Auditory Canal from the AnteroInferior Cerebellar Artery and returns to the BrainStem to supply blood to the Pons.
Close to the Basilar summit arises the Superior Cerebellar Artery, which has perforating branches to the BrainStem and to the superior surface of the Cerebellum.
The Posterior Cerebral Arteries are the terminal branches of the Basilar System. They also have extremely important Perforating Central Arteries, which supply blood to the Cerebral Peduncle, the Posterior Perforated Substance, the Posterior part of the Thalamus, and the Mammillary Bodies during their course around the BrainStem.
The Posterior Choroidal branches pass through the upper part of the Choroid Fissure, then to the Posterior part of the Tela Choroidea of the Third Ventricle, and then to the Choroid Plexus.
The Posterior Cerebral supplies Blood to the Uncus, Hippocampal Gyrus, Medial Temporal Lobe, Occipital Lobe and to a small portion of the Posterior Parietal Lobe.
The Olfactory Nerve, or First Cranial Nerve, is the pathway taken by Olfactory impulses from the nasal mucosa to the Brain. The Olfactory Tract connects the Olfactory Bulb with the Olfactory Tubercle, where it divides into a Medial and Lateral Olfactory Tract.
The Optic Nerve, or Second Cranial Nerve, lies just Posterior and Inferior to the Medial Olfactory Tract. It carries information from the Eye for Vision and Ocular Reflexes.
The Third Cranial Nerve, or Oculomotor Nerve arises at the Ventral aspect of the MesenCephalon and transverses through the Cavernous Sinus to the Orbit.
It supplies all the Intrinsic Ocular muscles and all Extrinsic Ocular muscles except for the Lateral Rectus and Superior Oblque. The ParaSympathetic Fibers from this Nerve innervate the Ciliary Muscle of the Lens and the Sphincter Muscle of the Pupil.
The Fourth Cranial Nerve, or Trochlear Nerve, supplies only the Superior Oblique Muscle of the Eye, and it arises just below the Inferior Quadrigeminal Bodies of the BrainStem.
It emerges from the Posterior Aspect of the BrainStem and passes around the Lateral Side of the Cerebellar Peduncle into the Margin of the Tentorium and into the Cavernous Sinus, where it goes to the Orbit.
The Fifth Cranial Nerve, or Trigeminal Nerve, is the Largest Cranial Nerve, and it carries fibers that give sensation to the Face and Motor Fibers to the Muscles of Mastication. It exits from the BrainStem through the AnteroLateral Surface of the Pons.
The Sixth Cranial Nerve, or Abducent Nerve, supplies the Lateral Rectus Muscle of the Eyeball and issues from the Brain at the Inferior Border of the Pons, just above the Pyramid of the Medulla Oblongata.
The Seventh Cranial, or Facial Nerve, consists of two parts: the Motor Root, which supplies the Superficial Muscles of the Scalp, Face, and Neck; and a smaller Sensory Root, which contains the Afferent Taste Fibers for the Anterior two thirds of the Tongue and the Afferent ParaSympathetic Fibers for supply of the Lacrimal and Salivary Glands.
The Facial Nerve arises from the Lateral Aspect of the PontoMedullary Junction.
The Auditory Nerve, or Eighth Cranial Nerve, is Entirely Sensory, and consists of Vestibular and Cochlear Divisions.
The GlossoPharyngeal, or Ninth Cranial Nerve is a Mixed nerve consisting of an Afferent Part, which supplies the Pharynx and Tongue and the Carotid Sinus and Body.
The Efferent Part supplies the StyloPharyngeus Muscle. It arises from the Medulla by five or six Rootlets attached to the side of the Medulla Oblongata, close to the Facial Nerve.
The Vagus, or Tenth Cranial Nerve is also a Mixed Nerve, which contains a large number of ParaSympathetic Fibers and passes through the Neck and Thorax into the Abdomen (Viscera).
It supplies Afferent Fibers chiefly to the Pharynx, Esophagus, Stomach, Larynx, Trachea, and Lungs.
It's attached by numerous Rootlets to the side of the Medulla, in series with the Accessory Nerve below and the GlossoPharyngeal Nerve above. The Rootlets unite to form a single Tract, which exits from the Cranial Cavity through the Jugular Foramen.
The Accessory Nerve, or Eleventh Cranial Nerve, consists of Bulbar and Spinal Portions. It arises in series with the Vagus and GlossoPharyngeal Nerve and controls Motor Function of the SternoMastoid and the Trapezius Muscles.
The Twelfth Cranial Nerve, or Hypoglossal Nerve, is a predominantly Efferent Nerve that supplies all the Muscles of the Tongue, both Intrinsic and Extrinsic, except the Palatoglossus Muscle.
It arises from numerous Rootlets from the Anterior Portion of the Medulla Oblongata. The Rootlets are arranged in double bundles and unite in the Anterior Condylar Canal, where they emerge from the Cranial Cavity.