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DURAL VENOUS SINUSES Channels within meningal layer of dura mater Function: veins draining brain Components: Unpaired & paired sinuses Unpaired Sinuses: Superior saggital Inferior saggital Straight Confluence Occipital Venous Flow tends to be - anterior to posterior - posterior and downward - from midline outwards UNPAIRED SINUSES Superior saggital: lies in upper margin of falx cerebri Terminates in the internal occipital protuberance Drains into the confluence of sinuses Paired Sinuses: Cavernous Transverse Superior petrosal Inferior petrosal Sigmoid Inferior Saggital sinuses: lies lower margin of the falx cerebri Joined by the great cerebral vein to form the straight sinus. Straight sinus: located in the tentorial attachment of falx cerebri Terminates turning left at internal occipital protuberance & becomes the left transverse sinus Occipital sinus: runs superiorly in cranial attachment of falx cerebelli & ends in the confluence of sinuses. Confluence of sinuses: The superior & the straight sinus converge at the confluence of sinuses, from here blood flows laterally on either side in the transverse sinus. PAIRED SINUSES Transverse sinuses: lies in the attachment of tentorium cerebelli Each transverse sinus runs forwards to lateral part of petrous temporal bone where it turns inferomedially towards jugular foramen as sigmoid sinus Superior petrosal sinus: Located in the anterior attachment of tentorium cerebelli Connects posterior aspect of cavernous sinus with transverse & sigmoid sinuses 1 Inferior Petrosal sinus: overlies petro-occipital fissure of temporal bone Connects cavernous sinus with internal jugular vein Cavernous sinus: located on body of sphenoid bone Interconnected by anterior & posterior intercavernous sinuses Sigmoid sinus: Continuation of transverse sinus Drain into internal jugular vein NB: STUDENTS TO REVISE CRANIAL FOSSA TO REVIEW THE IMPRESSIONS FORMED BY THE SINSUES. 2 Ventricular system Cavities within the cerebrum Includes: Lateral (2); third & fourth ventricle - LATERAL VENTRICLE Parts: Central part, Anterior , posterior and inferior horn. Anterior to interventricular foramen. Its roof & anterior border are formed by corpus callosum, its vertical medial wall by septum pellucidum. Floor is formed by the head of caudate nucleus. Extends from splenium of the corpus callosum; medially, by posterior part of the septum pellucidum; & below, by parts of caudate nucleus, thalamus, choroid plexus and fornix. Extends into occipital lobe. Its roof is formed by fibers of corpus callosum. It traverses the temporal lobe. Its roof is formed by white substance of cerebral hemisphere. Along medial border is stria terminalis and the tail of caudate nucleus. Amygdaloid nucleus bulges into terminal part of inferior horn. Floor & medial wall are formed by fimbria, hippocampus and the collateral eminence. Third Ventricle Slit-like structure situated in the diencephalon Wedged between the thalami and hypothalami in each hemisphere Connected to the lateral ventricle via the interventricular foramen Connected to the 4th ventricle via the cerebral aqueduct Anterior wall formed by – lamina terminalis and anterior commissure Roof formed by – thin layer of ependyma (velum interpositum), that stretches between the medullary stria of the thalami and is lined by choroid plexus, which passes anteriorly through the interventricular foramen to become continuous with that of the lateral ventricle Posterior wall formed by - habenular commissure, the stalk/infundibulum of the pineal gland and the posterior commissure, from superior to inferior The floor is fashioned from anterior to posterior Optic chiasm, infundibulum of the hypophysis, tuber cinereum, mammillary bodies, tegmentum of the midbrain 3 The lateral wall is formed by - Columns of the fornix, thalamus, hypothalamic sulcus and the hypothalamus 70% of people present with an interthalamic adhesion (massa intermedia) where the 2 thalami touch each other, this is not a commissure and has no function whatsoever. Fourth Ventricle The fourth ventricle is a cavity which lies posterior to the pons and upper half of the medulla oblongata and anterior to the cerebellum. It is continuous with the cerebral aqueduct (mesencephalic or Sylvius) above and the central canal of the spinal cord in the lower half of the medulla. On each size, a narrow prolongation, the lateral recess, projects around the brainstem; its lateral aperture (foramen of Luschka) lies below the cerebellar flocculus. The fourth ventricle has lateral boundaries, a roof and a floor. The lateral boundaries: are formed on each side by the superior cerebellar peduncle, the inferior cerebellar peduncle and the cuneate and gracile tubercles. Roof of the fourth ventricle - Formed by thin laminae of white matter. The lower has a median aperture (foramen of Magendie); cerebrospinal fluid escapes through this opening and lateral apertures into the subarachnoid space. The floor of the fourth ventricle, also known as rhomboid fossa, is formed by the dorsal surfaces of the pons and medulla oblongata. The cerebral aqueduct is a narrow canal in the midline connecting the third and fourth ventricle. CEREBROSPINAL FLUID - CSF is a colourless , odourless fluid formed by choroid plexus Choroid plexus is composed of pia mater, ependyma & capillaries. Found in all ventricles of brain 4 Circulation of CSF Lateral ventricle Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle Medial & lateral foramen Subarachnoid space Central canal REABSORPTION OF CSF - Arachnoid granulations which project into superior sagittal sinus & small venous lacunae FUNCTION OF CSF - Supports & cushions CNS against trauma Provides buoyancy Removes waste products Controls microenvironment of neurons & glial cells. 5 Diencephalon Area of the brain wedged between 2 cerebral hemispheres, above the midbrain of the brainstem Main components include: Thalamus Epithalamus Metathalamus Hypothalamus Subthalamus Thalamus Inner chamber or bedroom - 2 grey collections of nuclei in the lateral walls of the 3rd ventricle Comprises approximately 80% of the diencephalon Surfaces include: superior, inferior, medial and lateral Anterior and posterior extremities Anterior extremity - bordered by the interventricular foramen and the columns of the fornix Posterior extremity - Ends in the pulvinar The medial surface - forms the postero-superior part of the lateral wall of the 3rd ventricle covered by ependyma At the superomedial border of the thalamus, where the ependyma is reflected medially to form the roof of the third ventricle, it forms a fold in which a fibre bundle – the stria medullaris thalami, is embedded The superior surface – lies in relation to the central part of the lateral ventricle , the fornix and the caudate nucleus The striae terminalis and the thalamostriate vein are located in the interval between the thalamus and caudate nucleus The lateral surface – is covered by the posterior limp of the internal capsule and the hypothalamus abuts against the inferior surface from below The hypothalamic sulcus depicts the line of separation between the thalamus and hypothalamus 6 The thalamus - largest relay station for afferent impulses to the cortex - involved in the integration of motor activity for impulses between the basal nuclei, cerebellum and the cerebral cortex The 4 basic roles of the thalamus include - All sensory tracts, except olfactory nerves, have direct projections to the thalamus. In turn the thalamic nuclei project to the sensory cortex. The conscious awareness of the crude aspects of pain, touch, pressure and temperature are realized in the thalamus - The thalamus has vital motor connections that relay critical influences from the basal nuclei and cerebellum to the motor and premotor areas of the cortex - Essential in processing cerebral cortical rhythms (EEG) and phases of the sleepwake cycle. - Involved in aspects of emotion and behavior through connections with the limbic system and prefrontal cortex. This contains structures essential to cortical activity such as though, symbols of communication and creativity The internal medullary laminae divide the thalamic nuclei into 4 groups. i.e. anterior, medial lateral and intralaminar nuclei Epithalamus Above the thalamus Consists of the pineal gland, habenular nucleus, medullary stria of the thalamus Metathalamus Composed of the medial and lateral geniculate nuclei auditory pathway optic tract and relay Subthalamus Below the thalamus and lateral to the hypothalamus Continuous with the tegmentum of the midbrain Hypothalamus Situated beneath or ventral to the thalamus and forms the base of the diencephalon 7 The antero-inferior part of the lateral wall of the 3rd ventricle forms its medial relation - the subthalamus and internal capsule lies lateral to it The anterior border is formed by the lamina terminalis, and the anterior commissure and hypothalamic sulcus lies superior to it The structures forming its floor or base have been described with the 3rd ventricle. The nuclei of the hypothalamus are: Controls parasympathetic nuclei Preoptic nucleus Synthesis & secretion of Supraoptic nucleus vasopressin. Lesions of this nucleus can cause diabetes insipidus. Receives retinal input & projects Suprachiasmatic nucleus to pineal gland. This controls circadian rhythms. Involved in response to Anterior nuclei temperature & sexual preference. Synthesis & secretion of oxytocin Paraventricular nucleus (milk ejection reflex and uterine contractions). It also regulates food intake. Dorsomedial nucleus Ventromedial nucleus Arcuate nucleus Both of these may be involved with paraventricular nucleus in inhibiting eating and drinking (satiety centre). Lesions of these nuclei can cause eating disorders. Function is unknown. The hypothalamus occupies a strategic area between the cerebrum and brainstem It has vast connections with visceral (sympathetic and parasympathetic) and somatic systems. It plays an important role in the following activities - Regulation of body temp Emotional behavior Hunger and thirst 8 - Sexual activity and procreation Autonomic activities Endocrine activities and Biorhythms REFERENCES: - Crossman, AR and Neary D, Neuroanatomy, An illustrated colour text Snell,R. Clinical Neuroanatomy, 6th ed. 9