BRAIN VENTRICULAR SYSTEM CSF THE BRAIN BRAIN The brain - - PowerPoint PPT Presentation

BRAIN VENTRICULAR SYSTEM CSF

THE 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.

BRAIN

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.

The rhombencephalon is subdivided into:

• myelencephalon or medulla oblongata,
• metencephalon or pons,
• cerebellum.

BRAIN

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.

The pons lies rostral to the medulla and is distinguished by a mass of transverse nerve fibres that connect it to the cerebellum.

BRAIN

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.

The diencephalon comprises mostly the thalamus and hypothalamus but also includes the smaller epithalamus and subthalamus.

BRAIN

The telencephalon is composed mainly of the two cerebral hemispheres or cerebrum. 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.

The cerebrum consists of two cerebral hemispheres.

BRAIN

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.

Several large nuclei of grey matter, usually referred to as the basal ganglia, are partly embedded in the subcortical white matter.

BRAIN

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

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).

VENTRICULAR SYSTEM

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.

CEREBRAL VENTRICULAR SYSTEM The cerebrospinal fluid (CSF) leaves the fourth ventricle through three apertures to reach the subarachnoid space surrounding the brain.

VENTRICULAR SYSTEM

The cerebrospinal fluid (CSF) flows from the lateral to the third ventricle, through the cerebral aqueduct and into the fourth ventricle. The cerebral ventricular system consists of a series of interconnecting spaces and channels within the brain

Within each cerebral hemisphere lies a large C-shaped lateral ventricle.

VENTRICULAR SYSTEM

CEREBRAL VENTRICULAR SYSTEM 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.

The fourth ventricle, a wide, tent-shaped cavity lying between the brain stem and cerebellum.

VENTRICULAR SYSTEM

CEREBRAL VENTRICULAR SYSTEM Caudally, the fourth ventricle is continuous with the central canal of the spinal cord.

The two ventricles are located within the cerebral hemispheres.

VENTRICULAR SYSTEM

LATERAL VENTRICLES The two ventricles communicate with the third ventricle via the interventricular foramina (of Monro).

• FRONTAL (ANTERIOR) HORN
• BODY
• TEMPORAL (INFERIOR) HORN
• OCCIPITAL (POSTERIOR) HORN
• TRIGONE (ATRIUM)

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.

VENTRICULAR SYSTEM

LATERAL VENTRICLES – 5 PARTS: 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.

OCCIPITAL (POSTERIOR) HORN

• located in the parietal and occipital lobes.
• lacks choroid plexus.

VENTRICULAR SYSTEM

LATERAL VENTRICLES – 5 PARTS: TRIGONE (ATRIUM)

• found at the junction of the body, occipital horn, and temporal horn
• f 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).

THIRD VENTRICLE

• a slit-like vertical midline cavity of the diencephalon.

VENTRICULAR SYSTEM

THIRD VENTRICLE

• communicates with the lateral ventricles via the interventricular

foramina and with the fourth ventricle via the cerebral aqueduct.

• contains choroid plexus in its roof.

The cerebral aqueduct lies in the midbrain and connects the third ventricle with the fourth ventricle. CEREBRAL AQUEDUCT (AQUEDUCT OF SYLVIUS) The cerebral aqueduct lacks choroid plexus. Blockage leads to hydrocephalus (aqueductal stenosis).

The fourth ventricle lies between the cerebellum and the brainstem.

VENTRICULAR SYSTEM

FOURTH VENTRICLE 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.

It is a clear, colorless, acellular fluid found in the subarachnoid space and ventricles.

VENTRICULAR SYSTEM

CEREBROSPINAL FLUID 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

Choroid plexus secretes CSF into all ventricles. Arachnoid granulations are sites of CSF resorption.

VENTRICULAR SYSTEM

CEREBROSPINAL FLUID 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.

From the third ventricle, CSF flows through the aqueduct of Sylvius into the fourth ventricle.

VENTRICULAR SYSTEM

CEREBROSPINAL FLUID 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.

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

CEREBROSPINAL FLUID

NONCOMMUNICATING HYDROCEPHALUS results from obstruction within the ventricles, most commonly occurs at narrow points, i.e., congenital aqueductal stenosis.

VENTRICULAR SYSTEM

HYDROCEPHALUS - CEREBROSPINAL FLUID 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).

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.

VENTRICULAR SYSTEM

HYDROCEPHALUS - CEREBROSPINAL FLUID 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.

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.

VENTRICULAR SYSTEM

HYDROCEPHALUS - CEREBROSPINAL FLUID

The CONCENTRATION OF PROTEIN (including all immunoglobulins) is much lower in the CSF as compared with serum. Normal CSF contains 0 to 4 LYMPHOCYTES or MONONUCLEAR CELLS per cubic millimeter. Although the presence of a few monocytes or lymphocytes is normal, the presence of polymorphonuclear leukocytes is always abnormal, as in bacterial meningitis.

VENTRICULAR SYSTEM

CEREBROSPINAL FLUID – CLINICAL CORRELATE

RED BLOOD CELLS (RBCs) are NOT normally found in the CSF but may be present after traumatic spinal tap or subarachnoid hemorrhage. Increased PROTEIN LEVELS may indicate a CNS tumor. TUMOR CELLS may be present in the CSF in cases with meningeal involvement.

VENTRICULAR SYSTEM

CEREBROSPINAL FLUID – CLINICAL CORRELATE