BMS Neuroanatomy Lecture 2 PDF

BMS Neuroanatomy Lecture 2 Meninges, Ventricular System, Brain Blood Supply (In-Person Class) Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus) Meninges The CNS is surrounded and protected by three membranes of connective tissue collec...

BMS Neuroanatomy Lecture 2 Meninges, Ventricular System, Brain Blood Supply (In-Person Class) Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus) Meninges The CNS is surrounded and protected by three membranes of connective tissue collectively known as meninges; the dura mater, arachnoid mater, and pia mater from outside to inside. Dura Mater The dura mater is a thick layer of dense connective tissue that attaches to the inner surface of the neurocranium in the skull but is separated from the walls of the vertebral canal by the epidural space. The dura mater surrounding the spinal cord ends at the level of vertebra S2. The dura mater within the skull comprises an outer periosteal layer and an inner meningeal layer. The periosteal layer is attached to the inner surface of the cranial cavities. The meningeal layer separates from the periosteal layer in several locations to form two distinct structures: 1. Dural reflections: form incomplete partitions to divide the cranial cavity into some compartments. These reflections include: a. Falx cerebri is a sagittal sickle shape reflection of the dura mater that occupies the longitudinal fissure of the cerebrum and partially separates the cerebral hemispheres. b. Tentorium cerebelli is a tent-like horizontal sheet that intervenes between the cerebellum and occipital lobe of the cerebral hemispheres. It is notched anteriorly to provide a passage for the midbrain. c. Falx cerebelli is a less prominent vertical reflection of the dura in the sagittal plane along the vermis that partially separates the cerebellar hemispheres. 2. Dural sinuses drain the venous blood of the brain to the circulatory system. Dura Sinuses The superficial veins of the brain are collected by the dural sinuses. The dural sinuses are venous channels between the two layers of the cranial dura mater. The dural sinuses are named based on their shape, location, or direction. The main dural sinuses include: a. The cavernous sinuses are a pair of sinuses located in the middle cranial fossa on either side of the hypophyseal fossa of the sphenoid bone and collect the venous blood of the orbital cavity contents. b. The superior and inferior sagittal sinuses are unpaired sinuses contained within the superior and inferior margins of the falx cerebri, respectively. c. The straight sinus is an unpaired short sinus that receives the posterior end of the inferior sagittal sinus and great cerebral vein and joins the posterior end of the superior sagittal sinus. d. The transverse sinuses are paired sinuses housed in the posterior margin of the tentorium cerebelli and receive the superior sagittal and straight sinuses. e. The sigmoid sinuses are paired sinuses located in a groove on the interior surface of the mastoid process of temporal bones. These sinuses receive all other dural sinuses (directly or indirectly) and empty into the internal jugular veins. The deep veins of the brain are mostly received by the great cerebral vein that, in turn, drains into the straight sinus. Protection of the CNS 1. Bone Skull Vertebral column 2. Connective tissues Meningeal layers Dura mater = tough outer layer Arachnoid mater = web-like middle layer Pia Mater = delicate/thin inner layer 3. Fluid Cerebrospinal fluid (CSF) 4 MENINGES OF BRAIN Skull Epidural space (only present pathologically) LAYER 1: Dura mater Two layers: 1. Periosteal (adhered to bone) 2. Meningeal (forms dural folds for venous sinuses) Subdural space (only present pathologically) LAYER 2: Arachnoid mater Named for its “web-like” appearance Arachnoid villus / arachnoid granulations Small protrusions of arachnoid through the dura mater SPACE 1: Subarachnoid space Where you find cerebrospinal fluid (CSF) LAYER 3: Pia mater Tightly adhered to neural tissue itself 5 MENINGES OF BRAIN Periosteal dura (outer layer) Meningeal dura (inner layer) Forms folds of tissue that separate cranial cavity into sections Separated by “venous sinuses” 6 Dural Reflections Meninges(Dura Mater) Spinal Cord Meninges, Epidural Space Dural Reflections Dura Sinuses Arachnoid Mater The arachnoid mater is a thin layer of loose connective tissue attached to the inner surface of the dura mater. The arachnoid mater is separated from the pia mater by subarachnoid space, mainly containing the CSF. The subarachnoid space surrounding the spinal cord continues inferiorly and ends at the level of vertebra S2. This space between the endpoint of the spinal cord (vertebrae L1/L2) and vertebra S2 is called the lumbar cistern and contains the roots of the spinal nerves and CSF. The arachnoid granulations (villi) are small finger-like projections of the arachnoid mater, mainly on the superior part of the brain, that drain the CSF into the dural sinuses. Pia Mater The pia mater is a delicate, thin layer of connective tissue that is intimately in touch with the surface of the brain and spinal cord. This layer follows the contours of the brain and spinal cord and carries the blood vessels to the depth of the nervous tissue of the CNS. The denticulate ligaments are lateral triangular extensions of the pia mater that anchor the spinal cord to the deep surface of the arachnoid and dura mater. The filum terminale is an extension of the pia mater arising from the conus medullaris that extends inferiorly and fuses with the arachnoid and dura mater to anchor the spinal cord to the coccyx. MENINGES OF SPINAL CORD Vertebral column SPACE 1: Epidural space Filled with fat for additional protection! LAYER 1: Dura mater 1 layer only: meningeal layer Thicker than other meninges – “tough mother” Subdural space (only present pathologically) LAYER 2: Arachnoid mater Named for its “web-like” appearance SPACE 2: Subarachnoid space Where you find cerebrospinal fluid (CSF) LAYER 3: Pia mater Tightly adhered to neural tissue itself AXIAL VIEW 14 MENINGES OF SPINAL CORD Dura Mater Sac that covers the spinal cord with bony attachments at foramen magnum, C1-C2 and at the level of S2 “dural sleeve” Surrounding this layer is the epidural space which contains fat, CT and blood vessels Arachnoid Middle layer of avascular CT with collagen and elastic fibers Deep to the arachnoid layer is the subarachnoid space containing CSF 15 MENINGES OF SPINAL CORD Pia Mater Denticulate ligaments are thickenings of the pia mater that suspend the spinal cord in the middle of its dural sheath. Located between ventral and dorsal nerve roots Protect the spinal cord against shock and sudden displacement/trauma 16 MENINGES OF SPINAL CORD CORONAL VIEW The end of the spinal cord L1/2 in adults L4 in children The remaining spinal nerves “horses tail” 17 Cerebral Ventricles The nervous system is developed from the embryonic neural tube. The caudal part of the neural tube forms the spinal cord, whereas the cephalic part forms the cerebral vesicles. The lumen of the neural tube in the brain is larger and develops into cerebral ventricles. This lumen in the spinal cord remains narrow and forms the central canal. The cerebral ventricles house a specialized vascular plexus known as the choroid plexus. This plexus is responsible for secretion of the cerebrospinal fluid (CSF) that circulates in all cerebral ventricles, the central canal of the spinal cord, and subarachnoid space. There are four ventricles within the brain. 1. Lateral ventricles: In each cerebral hemisphere, there is an amorphous space known as the lateral ventricle. Each lateral ventricle is connected to the third ventricle through the interventricular foramen (of Monro). 2. Third ventricle: The third ventricle is an irregular and narrow space within the diencephalon between the left and right thalami. This ventricle is connected to the fourth ventricle through the cerebral aqueduct that passes through the midbrain. 3. Fourth ventricle: This ventricle is a diamond-shaped space that is bounded by the pons and upper part of the medulla anteriorly and the cerebellum posteriorly. The fourth ventricle is connected to the central canal of the spinal cord (inferiorly), to the third ventricle (superiorly), and through two lateral apertures (foramina of Luschka) and a median aperture (foramen of Magendi) to the subarachnoid space. CSF Circulation Blood Supply of the Brain 1) Vertebro-basilar System: a) Vertebral Arteries b) Basilar A. c) Posterior Cerebral A. (PCA) (occipital lobecortical blindness) d) Posterior communicating Arteries e) Posterior Anterior Inferior Cerebellar Artery (PICA, also covers brainstem) f) Superior cerebellar (also covers brainstem) 2) Carotid System: a)Middle Cerebral A. (MCA) b)Anterior Cerebral A. (ACA) c)Anterior communicating A. ❑Circle of Willis is made by? 20 Circle of Willis in situ Blood Supply of the Cerebral Hemispheres