Regional Anatomy II_Week 10_SU22.pdf

Week 10 Brain circulation Arterial Supply of the Brain ● ● Provided by vertebral and internal carotid arteries Vertebral artery: ○ ○ ○ ○ Enters cranial cavity via foramen magnum Right and left vertebral arteries join each other at pontomedullary junction to form basilar artery Basilar artery run...

Week 10 Brain circulation Arterial Supply of the Brain ● ● Provided by vertebral and internal carotid arteries Vertebral artery: ○ ○ ○ ○ Enters cranial cavity via foramen magnum Right and left vertebral arteries join each other at pontomedullary junction to form basilar artery Basilar artery runs along midline of anterior surface of pons and ends at upper end of pons by dividing into 2 posterior cerebral arteries Vertebral and basilar arteries give branches that supply spinal cord, brainstem, cerebellum and posterior parts of cerebral hemispheres Arterial Supply of the Brain ● Internal carotid artery: ○ ○ begins at bifurcation of common carotid artery (at level of upper border of thyroid cartilage) Components: ■ Cervical (from origin to base of the skull) ■ Petrous (within carotid canal in petrous part of temporal bone) ■ Cavernous (within cavernous sinus the dural venous sinus located in middle cranial fossa, just lateral to sella turcica) ■ Cerebral (from the point it exits cavernous sinus to its termination, where it divides into anterior and middle cerebral arteries) Arterial Supply of the Brain ● Internal carotid artery (cont.): ○ Main branches: ■ Ophthalmic artery enters orbit via optic canal together with optic nerve ■ Posterior communicating artery joins posterior cerebral artery ■ Two terminal branches: anterior and middle cerebral arteries (right and left anterior cerebral arteries are connected by anterior communicating artery) Circle of Willis ● ● Formed by large cerebral arteries and their interconnections on ventral surface of the brain Components: ○ ○ ○ ○ ○ ● Anterior communicating a. Anterior cerebral a. Internal carotid a. Posterior communicating a. Posterior cerebral a. Serves as a potential vascular shunt, assisting in development of collateral circulation if one of the proximal vessels is occluded Dura Mater of the Brain ● ● ● Endosteal (outer layer) - equivalent to periosteum covering inner surface of skull bones Meningeal (inner layer) - dura mater proper, faces the brain The two layers are closely united, except where they separate to form dural venous sinuses Dural Venous Sinuses ● ● ● Located between inner and outer layers of dura mater Receive blood from brain (via superficial and deep cerebral veins) as well as cerebrospinal fluid from subarachnoid space (via arachnoid granulations) Blood collected by dural venous sinuses drains ultimately into internal jugular veins Dura Mater of the Brain ● ● ● Meningeal layer forms 4 septa - divides cranial cavity into freely communicating compartments Cerebral falx (falx cerebri) - sickle-shaped fold that lies in the midline between two cerebral hemispheres Cerebellar tentorium (tentorium cerebelli) - crescent-shaped fold that roofs over posterior cranial fossa (separates cerebellum from occipital lobes of cerebral hemispheres) ○ ● ● Tentorial notch - space between anterior, free border of tentorium cerebelli and dorsum sellae; filled mostly by midbrain Cerebellar falx (falx cerebelli) - small sickle-shaped fold in posterior cranial fossa that projects between two cerebellar hemispheres Sellar diaphragm (diaphragma sellae) - small circular fold that roofs over sella turcica (turkish seat) and has small opening for pituitary stalk. Dural Venous Sinuses ● ● ● ● Superior sagittal sinus - runs along upper border of falx cerebri and terminates posteriorly in confluence of the sinuses (over internal occipital protuberance) Inferior sagittal sinus - runs along lower, free border of falx cerebri, joins great cerebral vein (largest of the deep cerebral veins) to form straight sinus Straight sinus - runs in midline, along junction of falx cerebri and tentorium cerebelli and terminates posteriorly in confluence of the sinuses Transverse sinus - begins in confluence of the sinuses and runs along posterior border of tentorium cerebelli and when it reaches petrous part of temporal bone, it turns down to become continuous with sigmoid sinus Dural Venous Sinuses ● ● Sigmoid sinus - direct continuation of transverse sinus and terminates in jugular foramen, where it becomes continuous with internal jugular vein Occipital sinus - small sinus that runs along posterior border of falx cerebelli and ends superiorly in confluence of the sinuses and inferiorly communicates with internal vertebral venous plexus (within vertebral canal) Dural Venous Sinuses ● Cavernous sinus: ○ ○ ○ ○ Located in middle cranial fossa, one on each side of sella turcica Drains contents of orbit, parts of cerebral hemisphere, pituitary gland and sphenoparietal sinus Internal carotid artery and abducens nerve are located inside cavernous sinus Cranial nerves III and IV and V1 and V2 divisions of trigeminal nerve are embedded in lateral wall of sinus