RBM2200 Workshop 8 Brain (1).pdf
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RBM2200 Functional Anatomy of the Head & Back WORKSHOP 8 BRAIN BLOOD SUPPLY ACTIVITY 1: Video & Diagram Watch “Circle of Willis” video (16.33) to complete the Circle of Willis diagram BRAIN BLOOD SUPPLY The brain receives its arterial...
RBM2200 Functional Anatomy of the Head & Back WORKSHOP 8 BRAIN BLOOD SUPPLY ACTIVITY 1: Video & Diagram Watch “Circle of Willis” video (16.33) to complete the Circle of Willis diagram BRAIN BLOOD SUPPLY The brain receives its arterial supply from two pairs of vessels, the vertebral arteries & internal carotid arteries These arteries are interconnected in the cranial cavity to produce a cerebral arterial Circle of Willis The two vertebral arteries enter the cranial cavity through the foramen magnum of the occipital bone & just inferior to the pons fuse to form the basilar artery The two carotid arteries enter the cranial cavity through the carotid canals on either side of the temporal bone Each vertebral artery arises from the first part of the subclavian artery Passes superiorly through the transverse foramina of the VERTEBRAL upper six cervical vertebrae On entering the cranial cavity through the foramen ARTERY magnum the vertebral artery gives off a small meningeal branch The vertebral artery gives to the following branches: Anterior spinal artery Posterior spinal artery Posterior inferior cerebellar artery IT THEN JOINS ITS COMPANION VESSEL TO FORM THE BASILAR ARTERY The basilar artery along the anterior aspect of the pons Its branches include the: Anterior inferior cerebellar arteries Several small pontine arteries Superior cerebellar arteries The basilar artery ends as a bifurcation, giving rise to two posterior cerebral arteries The vertebrobasilar arteries supply 20% of blood to the brain INTERNAL CAROTID ARTERIES The two internal carotid arteries arise as one of the two terminal branches of the common carotid arteries Entering the cranial cavity each internal carotid artery gives off the: Ophthalmic artery The posterior communicating artery The middle cerebral artery The anterior cerebral artery The internal carotid arteries supplies 80% of blood to the brain CEREBRAL ARTERIAL CIRCLE (OF WILLIS) The cerebral arterial circle (of Willis) is formed at the base of the brain by the interconnecting vertebrobasilar and internal carotid systems of vessels This anastomotic interconnection is accomplished by: An anterior communicating artery connecting the right and left cerebral arteries to each other Two posterior communicating arteries, one on each side, connecting the internal carotid with the posterior cerebral artery CLINICAL RELEVANCE STROKE A stroke or cerebrovascular accident (CVA), is defined as the interruption of blood flow to the brain or HAEMORRHAGIC ISCHAEMIC brainstem resulting in impaired neurological function lasting more than 24hrs. Caused by rupture of Thrombotic or embolic Based on their etiology, strokes are broadly classified as blood vessels Embolic (most common) either ischaemic or haemorrhagic. often caused by emboli Stroke is a neurological from atherosclerotic emergency plaques in carotid Early diagnosis and arteries that dislodge & treatment is critical travel & block smaller arteries Brain imaging & CT scan Blood thinning drugs can to identify haemorrhagic restore cerebral blood flow stroke as thrombolytic if given within 3-4hrs of therapy is contraindicated symptoms & to exclude malignancy CLINICAL RELEVANCE STROKE RISK FACTORS SYMPTOMS Diabetes Rapid-onset hemiparesis-one-sided Hypertension muscle weakness/partial paralysis Smoking Hemisensory loss-loss of sensation In younger patients: on one side of the body Underlying clotting Visual field defects disorders Dysarthria-slurred or slowed speech Use of oral that is difficult to understand contraceptives Ataxia-lack of voluntary Illicit substance coordination of muscle movements abuse such as walking or picking up objects Decreased level of consciousness MENINGES & DURAL PARTITIONS ACTIVITY 2: Video Watch “Meninges, Dural Partitions & Dural Venous Sinuses” video (0:00-4:49) MENINGES Meninges are three membranes (the dura mater, arachnoid, and pia mater) that line the skull and vertebral canal and enclose the brain and spinal cord LAYER DETAILS EPIDURAL/EXTRADURAL Found between skull & SPACE dura mater DURA MATER Thickest & most external meningeal layer SUBDURAL SPACE Potential space between dura and arachnoid mater ARACHNOID MATER Middle membrane SUBARACHNOID SPACE Contains cerebrospinal fluid PIA MATER Thinnest, innermost membrane lining surface of brain & spinal cord CRANIAL DURA MATER The cranial dura mater is a thick, tough, outer covering of the brain Consists of an outer periosteal layer and an inner meningeal layer Outer periosteal layer: Firmly attached to the skull Is the periosteum of the cranial cavity Contains the meningeal arteries Is continuous with the periosteum on the outer surface of the skull at the foramen magnum & other intracranial foramina Inner meningeal layer: In close contact with the arachnoid mater Is continuous with the spinal dura mater through the foramen magnum The two layers of dura separate from each other at numerous locations to form two unique types of structures: Dural partitions which project inward and completely separate parts of the brain Intracranial venous structures DURAL PARTITIONS The dural partitions project into the cranial cavity & partially subdivide the cranial cavity They include the: Falx cerebri Tentorium cerebelli Falx cerebelli Diaphragma sella FALX CEREBRI The falx cerebri is a crescent-shaped downward projection of meningeal dura mater from the dura lining the calva that passes between the two cerebral hemispheres It is attached to the anteriorly to the crista galli of the ethmoid bone & frontal bones Posteriorly it is attached to & blends with another dural partition the tentorium cerebelli TENTORIUM CEREBELLI The tentorium cerebelli is a horizontal projection of the meningeal dura mater that covers & separates the cerebellum in the posterior cranial fossa from the posterior parts of the cerebral hemispheres The tentorium cerebelli is attached to the occipital bone posteriorly & the temporal bone laterally Its anterior & medial borders are free, forming an oval opening in the midline called the tentorial notch through which the midbrain passes FALX CEREBELLI The falx cerebelli is a small midline projection of meningeal dura mater in the posterior cranial fossa It is attached posteriorly to the occipital bone & superiorly to the tentorium cerebelli Its anterior edge is free & is between the two cerebellar hemispheres DIAPHRAGMA SELLAE The diaphragma sellae is a small horizontal shelf of meningeal dura mater that covers the hypophyseal fossa in the sella turcica of the sphenoid bone The hypophyseal fossa is the deepest part of the sella turcica which houses & helps to protect the pituitary gland The infundibulum is a hollow stork connecting the hypothalamus and the posterior pituitary gland There is an opening in the centre of the diaphragma sellae through which the infundibulum passes ARACHNOID MATER The arachnoid mater is a thin, avascular membrane that lines, but is not adherent to, the inner surface of the dura mater From its inner surface thin processes called trabeculae extend downward, across the subarachnoid space & become continuous with the pia mater Unlike the pia mater, the arachnoid does not enter the grooves or fissures of the brain, except for the longitudinal fissures between the two cerebral hemispheres PIA MATER The pia mater is a thin, delicate membrane that closely invests the surface of the brain It follows the contours of the brain, entering the grooves & fissures on its surface It is closely applied to the roots of the cranial nerves at their origins CLINICAL RELEVANCE BRAIN HEMORRHAGES EXTRADURAL/EPIDURAL SUBDURAL SUBARACHNOID An extradural haemorrhage is caused by Bleeding due to the tearing of a cerebral May occur in patients arterial damage & results from tearing of the vein as it crosses through the dura to who have undergone branches of the middle meningeal artery, enter a dural venous sinus can result in a significant cerebral which typically occurs in the region of the subdural haematoma trauma pterion The tear & resulting seepage of blood Typically results from a Blood collects between the periosteal layer separates the thin layer of dural border ruptured intracerebral of the dura & the calvaria and under cells from the rest of the dura as the aneurysm arising from pressure arterial pressure slowly expands haematoma develops the vessels supplying & The typical history is of a blow to the head The increased CSF space in patients with around the arterial circle that produces a minor loss of consciousness cerebral atrophy results in in a greater of Willis Following the injury the patient usually than normal stress on the cerebral veins regains consciousness & has a lucid interval entering the sagittal sinus for a period of hours The clinical history usually includes a After this rapid drowsiness & trivial injury followed by an insidious loss unconsciousness ensue, which may lead to of consciousness or alteration of death personality ACTIVITY 3: Blood Supply Revision Kahoot Open http://kahoot.com in a new browser on your phone or computer and enter the pin to play RBM2200 Functional Anatomy of the Head & Back WORKSHOP 9 BRAIN VENOUS DRAINAGE ACTIVITY 4: Video Watch “Meninges, Dural Partitions & Dural Venous Sinuses” video (4:49-13:29) VENOUS DRAINAGE The dural venous sinuses are endothelial- lined spaces between the outer periosteal layer & the inner meningeal layers of the dura mater The dural venous sinuses receive blood from the veins associated with the cerebrum, cerebellum and brainstem. They also receive contributions from the diploic and emissary veins (draining the cranium and the scalp, respectively). Venous blood then flows through the dural venous sinus system – which consists of a series of paired and unpaired sinuses. They eventually empty into the internal jugular vein, where deoxygenated blood is returned to the systemic circulation. VENOUS DRAINAGE The dural venous sinuses also receive contributions from the diploic and emissary veins (draining the cranium and the scalp, respectively). Diploic veins, which run between the internal & external tables of compact bone in the roof of the cranial cavity, drain the diploe. Emissary veins are valveless venous structures which pass from outside the cranial cavity to drain the extracranial vessels of the scalp into the dural venous sinuses. The emissary veins are important clinically because they can be a conduit through which infections can enter the cranial cavity because they have no valves. UNPAIRED DURAL VENOUS SINUSES UNPAIRED DETAILS SUPERIOR SAGITTAL SINUS Largest dural venous sinus. It receives venous blood from many tributaries of the cerebral hemispheres and superficial cortical veins Lies within the superior border of the falx cerebri. INFERIOR SAGITTAL SINUS The inferior sagittal sinus lies within the inferior margin of the falx cerebri. Posteriorly, it combines with the great cerebral vein to form the straight sinus. STRAIGHT SINUS The straight sinus forms from the convergence of the inferior sagittal sinus with the great cerebral vein. It is located where the falx cerebri meets the tentorium cerebelli. OCCIPITAL SINUS The occipital sinus is the smallest of the venous sinuses and is situated on the inner surface of the occipital bone within the falx cerebri. CONFLUENCE OF SINUSES It is the connecting point of the superior sagittal sinus, the straight sinus, the occipital sinus, and the two transverse sinuses. It drains blood from the brain to the transverse sinuses. BASILAR PLEXUS The basilar venous plexus is located on the internal surface of the skull floor, posterior to the sella turcica of the sphenoid bone. It interconnects the inferior petrosal sinuses PAIRED DURAL VENOUS SINUSES PAIRED DURAL VENOUS SINUSES PAIRED DETAILS TRANSVERSE SINUSES The right and left transverse sinuses (also known as lateral sinuses) are formed at the confluence of sinuses by the convergence of the superior sagittal, straight and occipital sinuses. As they approach the petrous part of the temporal bone, the transverse sinuses become the sigmoid sinuses. SIGMOID SINUSES The sigmoid sinuses are a continuation of the transverse sinuses at the internal surface of the petrous part of the temporal bone. When they pass through the jugular foramen to leave the cranial cavity, the right and left sigmoid sinuses become the internal jugular veins. CAVERNOUS SINUSES The cavernous sinuses are interconnected by the intercavernous sinuses and drained by the superior and inferior petrosal sinuses. SUPERIOR PETROSAL SINUSES The superior petrosal sinuses drain the cavernous sinuses into the transverse sinuses. INFERIOR PETROSAL SINUSES The inferior petrosal sinuses assist in the drainage of the cavernous sinuses. SPHENOPARIETAL SINUSES The sphenoparietal sinus is situated along the posterior edge of the lesser wing of the sphenoid bone. It drains into the cavernous sinus PAIRED DURAL VENOUS SINUSES ACTIVITY 5: Vascular Systems “Survivor” Part A: Select an anatomical structure label Part B: Determine whether you belong in the BLOOD SUPPLY or VENOUS DRAINAGE ‘tribes’ Part C: First tribe to collect all the correct vessels of their vascular system wins! BRAIN VENTRICULAR SYSTEM ACTIVITY 6: Video Watch “The Ventricular System” video (8:44) VENTRICULAR SYSTEM The ventricular system of the brain is 4 interconnected cavities in the brain consisting of the right and left ventricles-one in each hemisphere, third ventricle and fourth ventricle. The ventricular system is continuous with the central canal of the spinal cord. In each of the ventricles there is a region of choroid plexus producing cerebrospinal fluid (CSF) to transport around the cranial cavity. CSF is a clear, colourless, cell-free fluid that provides cushioning and protection of the CNS, buoyancy for the brain as well as nutrient delivery and waste removal from the brain CSF is produced at a rate of 500ml/day with ~125-150ml in the body at any given time VENTRICLES OF THE BRAIN The left and right lateral ventricles are located within their respective hemispheres of the cerebrum. The lateral ventricles are connected to the third ventricle by the interventricular foramen. The third ventricle is situated in between the right and the left thalamus. The fourth ventricle is the last in the system – it receives CSF from the third ventricle via the cerebral aqueduct. Cerebrospinal fluid (CSF) is produced by the choroid plexus, located in the lining of the ventricles. CSF produced in the ventricles flows from lateral ventricles à interventricular foramenà third ventricle à cerebral aqueduct à fourth ventricle à central canal of spinal cord SPOTLIGHT ON… SUBARACHNOID SPACE Deep to the arachnoid mater is the only normally occurring fluid-filled space associated with the meninges, the subarachnoid space The subarachnoid space surrounds the brain & spinal cord and in certain locations it enlarges into expanded areas called subarachnoid cisterns It contains cerebrospinal fluid (CSF) & blood vessels CSF is produced by the choroid plexus, primarily in the ventricles of the brain CSF is a clear, colourless, cell-free fluid that circulates through the subarachnoid space surrounding the brain & spinal cord The CSF returns to the venous system through arachnoid villi These project as clumps called arachnoid granulations into the superior sagittal sinus, which is a dural venous sinus ACTIVITY 7: Worksheet Open up the document: ‘Session 8: Ear & Blood Supply to the Brain Worksheet’ You will be allocated a question/s to answer from this worksheet with your group/table. Using reputable resources and lecture material answer the questions. Come back together as a class at the end and your educator will get you to contribute your answers to share with the rest of the class. ACTIVITY 8: Worksheet Open up the document: ‘Session 9: Dural Partitions & Venous Sinuses Worksheet’ You will be allocated a question/s to answer from this worksheet with your group/table. Using reputable resources and lecture material answer the questions. Come back together as a class at the end and your educator will get you to contribute your answers to share with the rest of the class. ACTIVITY 9: Venous Sinuses & Dural Partitions Revision Kahoot Open http://kahoot.com in a new browser on your phone or computer and enter the pin to play
