10.24.11+-+Meninges+and+Blood+Supply+to+the+Brain

Meninges


 * 1a. Describe the 3 layers of the meninges and state which layer is deepest and which is most superficial.**

Superficial: Dura Mater - Thick fibrous layer Intermediate: Arachnoid Mater - Divided into two portions: membranous and trabecular. Membranous is on surface of dura mater. Trabecular is extensions that cross the subarachnoid space to the pia mater. Projections of arachnoid mater, villi or granulations, pierce dura mater and serve as valves allowing passage of CSF back into venous blood. Deep: Pia Mater - Simple squamous sheet enveloping brain


 * 1b. Describe the spaces (or "potential spaces") that exist between the meningeal layers.**

Between the pia mater and the arachnoid mater is the real subarachnoid space filled with CSF and the superficial veins that lead to the dural sinuses. The potential space between the arachnoid mater and the dura mater is the subdural space. Divided into anterior, middle, and posterior. The potential space between the dura mater and the cranium is the epidural space.


 * 1c. Name the branches of the trigeminal nerve that innervate the dura mater of the anterior cranial fossa, the middle cranial fossa, and the posterior cranial fossa.**

Anterior cranial fossa: anterior and posterior ethmoidal branches + meningeal branches of maxillary and mandibular Middle cranial fossa: meningeal branches of maxillary and mandibular + tentorial nerve Posterior cranial fossa: tentorial fossa + cervical branches from C2 and C3


 * 2. Describe the 4 projections of dura mater, and what parts of the nervous system are separated by each of these projections.**

Falx Cerebri - divide two hemispheres of cerebrum, crista galli to tentorium cerebelli. Superior and inferior borders are superior and inferior sagittal sinuses Falx Cereblli - divide two hemispheres of cerebellum, tentorium cerebelli and inferior. Base splits to form occipital sinus. Tentorium Cerebelli - divide cerebrum from cerebelli/brain stem. Supports occipital lobe. Cranial attachments splits to form transverse sinuses. Anterior borders split to contain superior petrosal sinuses. Internal edge open, called the incisure; a swollen brain can press the oculomotor nerve against the incisure causing oculomotor nerve palsy. Diaphragma Sella - much smaller roof above the hypophyseal fossa of sella turcica. Hypophysial stalk pierces it. Connects pituitary gland to rest of brain.


 * 3. Describe the major venous sinuses within the dura mater. Explain how venous drainage from the area of the face around the nose can result in infections of the cavernous sinus.**

ISS - Inferior Sagittal Sinus - Unpaired Great Cerebral Vein - Unpaired Straight Sinus - Unpaired Superior Sagittal Sinus - Unpaired Occipital Sinus - Unpaired Confluence of Sinuses - Unpaired Cavernous Sinuses - Paired Superior Petrosal Sinus - Paired (Depending on the angle of the body, the SPS, which also receives blood from internal carotid venous plexus, can drain backwards into the CS) Inferior Petrosal Sinus - Paired Transverse Sinus - Paired Sigmoid SInus - Paired Inferior Jugular Vein - Paired


 * 4a. State which major arteries subserve the anterior and posterior circulations.**

Anterior circulation: internal carotid artery Posterior circulation: basilar artery from the vertebral arteries


 * 4b. Describe the Circle of Willis and how the anterior and posterior circulations join to form this structure.**

The terminal branches of the basilar artery (posterior circulation) are the paired cerebral arteries. They each give off branches called the posterior communicating arteries that intersect with the internal carotid artery (anterior circulation) as it gives off the anterior cerebral artery. The two anterior cerebral arteries are connected by the anterior communicating artery.