BRAIN VENTRICULAR SYSTEM CSF
THE BRAIN
BRAIN The brain (encephalon) lies within the cranium. It receives information from, and controls the activities of, the trunk and limbs, mainly through rich connections with the spinal cord. The brain possesses 12 pairs of cranial nerves through which it communicates mostly with structures of the head and neck. Ascending in sequence from the spinal cord, the principal divisions are • the rhombencephalon or hindbrain, • the mesencephalon or midbrain, • the prosencephalon or forebrain.
BRAIN The rhombencephalon is subdivided into: • myelencephalon or medulla oblongata, • metencephalon or pons, • cerebellum. The medulla oblongata, pons and midbrain are collectively referred to as the brain stem , which lies on the basal portions of the occipital and sphenoid bones (clivus). The medulla oblongata is the most caudal part of the brain stem and is continuous with the spinal cord below the level of the foramen magnum.
BRAIN The pons lies rostral to the medulla and is distinguished by a mass of transverse nerve fibres that connect it to the cerebellum. The midbrain is a short segment of brain stem, rostral to the pons. The cerebellum consists of paired hemispheres united by a median vermis; it lies within the posterior cranial fossa, dorsal to the pons, medulla and caudal midbrain, areas with which it has rich fibre connections. The prosencephalon may be subdivided into the diencephalon and the telencephalon.
BRAIN The telencephalon is composed mainly of the two cerebral hemispheres or cerebrum. The diencephalon comprises mostly the thalamus and hypothalamus but also includes the smaller epithalamus and subthalamus. The diencephalon is almost completely embedded in the cerebrum and is therefore largely hidden. The cerebrum constitutes the major portion of the volume of the human brain. It occupies the anterior and middle cranial fossae and is directly related to the cranial vault.
BRAIN The cerebrum consists of two cerebral hemispheres. The surface of each hemisphere is convoluted in a complex pattern of ridges (gyri) and furrows ( sulci ). Internally, each hemisphere has an external layer of grey matter , called the cerebral cortex , beneath which lies a dense mass of white matter . One of the most important components of the cerebral white matter is the internal capsule , which contains nerve fibres that pass to and from the cerebral cortex.
BRAIN Several large nuclei of grey matter, usually referred to as the basal ganglia , are partly embedded in the subcortical white matter. Connections between corresponding areas of the two sides of the brain cross the midline within commissures . By far the largest commissure is the corpus callosum , which links the two cerebral hemispheres.
VENTRICULAR SYSTEM AND CEREBROSPINAL FLUID
VENTRICULAR SYSTEM CEREBRAL VENTRICULAR SYSTEM The ventricular system is a set of communicating cavities within the brain. These structures are responsible for the production, transport and removal of cerebrospinal fluid (CSF). The ventricular system contains cerebrospinal fluid (CSF) , which is secreted mostly by the choroid plexuses located within the lateral, third and fourth ventricles. Tight junctions of the choroid plexus cells form the blood-CSF barrier .
VENTRICULAR SYSTEM CEREBRAL VENTRICULAR SYSTEM The cerebrospinal fluid (CSF) flows from the lateral to the third ventricle, through the cerebral aqueduct and into the fourth ventricle. The cerebrospinal fluid (CSF) leaves the fourth ventricle through three apertures to reach the subarachnoid space surrounding the brain. The cerebral ventricular system consists of a series of interconnecting spaces and channels within the brain
VENTRICULAR SYSTEM CEREBRAL VENTRICULAR SYSTEM Within each cerebral hemisphere lies a large C-shaped lateral ventricle . Near its rostral end the lateral ventricle communicates through the interventricular foramen (foramen of Monro) with the third ventricle. The third ventricle , which is a midline, slit-like cavity lying between the right and left halves of the thalamus and hypothalamus . Caudally, the third ventricle is continuous with the cerebral aqueduct , a narrow tube that passes the length of the midbrain.
VENTRICULAR SYSTEM CEREBRAL VENTRICULAR SYSTEM The fourth ventricle , a wide, tent-shaped cavity lying between the brain stem and cerebellum . Caudally, the fourth ventricle is continuous with the central canal of the spinal cord.
VENTRICULAR SYSTEM LATERAL VENTRICLES The two ventricles are located within the cerebral hemispheres. The two ventricles communicate with the third ventricle via the interventricular foramina (of Monro). LATERAL VENTRICLES – 5 PARTS: • FRONTAL (ANTERIOR) HORN • BODY • TEMPORAL (INFERIOR) HORN • OCCIPITAL (POSTERIOR) HORN • TRIGONE (ATRIUM)
VENTRICULAR SYSTEM LATERAL VENTRICLES – 5 PARTS: FRONTAL (ANTERIOR) HORN - located in the frontal lobe; its lateral wall is formed by the head of the caudate nucleus. - lacks choroid plexus. BODY - located in the medial portion of the frontal and parietal lobes. - contains choroid plexus. - communicates with the third ventricle via the interventricular foramina. TEMPORAL (INFERIOR) HORN - located in the medial part of the temporal lobe. - contains choroid plexus.
VENTRICULAR SYSTEM LATERAL VENTRICLES – 5 PARTS: OCCIPITAL (POSTERIOR) HORN - located in the parietal and occipital lobes. - lacks choroid plexus. TRIGONE (ATRIUM) - found at the junction of the body, occipital horn, and temporal horn of the lateral ventricle. - contains the glomus, a large tuft of choroid plexus, which is calcified in adults and is visible on x-ray film and computed tomography (CT).
VENTRICULAR SYSTEM THIRD VENTRICLE THIRD VENTRICLE - a slit-like vertical midline cavity of the diencephalon. - communicates with the lateral ventricles via the interventricular foramina and with the fourth ventricle via the cerebral aqueduct . - contains choroid plexus in its roof. CEREBRAL AQUEDUCT (AQUEDUCT OF SYLVIUS) The cerebral aqueduct lies in the midbrain and connects the third ventricle with the fourth ventricle. The cerebral aqueduct lacks choroid plexus. Blockage leads to hydrocephalus (aqueductal stenosis).
VENTRICULAR SYSTEM FOURTH VENTRICLE The fourth ventricle lies between the cerebellum and the brainstem . The fourth ventricle contains choroid plexus in the caudal aspect of its roof. The fourth ventricle expresses CSF into the subarachnoid space via the two lateral foramina and the single medial foramen.
VENTRICULAR SYSTEM CEREBROSPINAL FLUID It is a clear, colorless, acellular fluid found in the subarachnoid space and ventricles. produced by the choroid plexus at a rate of 500 to 700 ml/day. The total CSF volume is approximately 140 ml So all of CSF is turned over 2–3 times per day COMPOSITION: - contains not more than 5 lymphocytes/μl and is usually sterile. - other normal values are: pH: 7.35 Specific gravity: 1.007 Glucose: 66% of plasma glucose Total protein: <45 mg/dl in the lumbar cistern
VENTRICULAR SYSTEM CEREBROSPINAL FLUID Choroid plexus secretes CSF into all ventricles. Arachnoid granulations are sites of CSF resorption. CSF is absorbed into the venous system through arachnoid villi associated with the major dural venous sinuses, predominantly the superior sagittal sinus. CSF from the lateral ventricles passes through the interventricular foramina of Monro into the third ventricle .
VENTRICULAR SYSTEM CEREBROSPINAL FLUID From the third ventricle , CSF flows through the aqueduct of Sylvius into the fourth ventricle . The only sites where CSF can leave the ventricles and enter the subarachnoid space outside the CNS are through 3 openings in the fourth ventricle: • 2 lateral foramina of Luschka • 1 median foramen of Magendie.
VENTRICULAR SYSTEM CEREBROSPINAL FLUID HYDROCEPHALUS is dilation of the cerebral ventricles caused by blockage of the CSF pathways. It is characterized by excessive accumulation of CSF in the cerebral ventricles or subarachnoid space. Obstruction of the circulation of CSF leads to the accumulation of fluid (hydrocephalus), which causes compression of the brain
VENTRICULAR SYSTEM HYDROCEPHALUS - CEREBROSPINAL FLUID NONCOMMUNICATING HYDROCEPHALUS results from obstruction within the ventricles, most commonly occurs at narrow points, i.e., congenital aqueductal stenosis. COMMUNICATING HYDROCEPHALUS results from blockage within the subarachnoid space - impaired CSF reabsorption in arachnoid granulations or obstruction of flow in subarachnoid space (i.e., adhesions after meningitis).
VENTRICULAR SYSTEM HYDROCEPHALUS - CEREBROSPINAL FLUID NORMAL-PRESSURE HYDROCEPHALUS CSF is not absorbed by arachnoid villi (a form of communicating hydrocephalus). CSF pressure is usually normal. Ventricles chronically dilated. Produces triad of dementia, apraxic (magnetic) gait, and urinary incontinence (wacky, wobbly, and wet). Peritoneal shunt. HYDROCEPHALUS EX VACUO descriptive term referring to excess CSF in regions where brain tissue is lost due to atrophy, stroke, surgery, trauma, etc. Results in dilated ventricles but normal CSF pressure.
VENTRICULAR SYSTEM HYDROCEPHALUS - CEREBROSPINAL FLUID PSEUDOTUMOR CEREBRI (benign intracranial hypertension) - results from increased resistance to CSF outflow at the arachnoid villi. - characterized by papilledema without mass, elevated CSF pressure, and deteriorating vision. The ventricles may be slit-like. - typically occurs in obese young women.
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