Page | 1 25 Aug 2010

D’ ANOTHERS

NEUROANATOMY: Ventricular System and Cerebrospinal Fluid

Dr. John Vincent Estrada

This trans belongs to: _____________________________________

VENTRICULAR SYSTEM

Four fluid-filled cavities located within the brain.

Lined throughout with ependyma and are filled with

cerebrospinal fluid.

Consists of the two lateral ventricles, third and fourth

ventricles.

Communications:

o Between lateral and third ventricles:

INTERVENTRICULAR FORAMINA OF MONRO

o Between the third and fourth ventricles:

CEREBRAL AQUEDUCT OF SYLVIUS

Diagrammatic Illustration:

LATERAL VENTRICLES

Roughly C-shaped cavity

Divided into:

o BODY= Occupies the parietal lobe.

o ANTERIOR HORN= Occupies the frontal lobe.

o INFERIOR HORN= Occupies the temporal lobe.

o POSTERIOR HORN= Occupies the occipital lobe.

The body divides into posterior and inferior horns at the

posterior end of the thalamus.

The anterior horn is continuous with the body at the

Interventricular foramen.

INTERVENTRICULAR FORAMEN OF MONRO

Boundaries:

o Anterior: Anterior column of the fornix

o Posterior: Anterior end of the thalamus

THIRD VENTRICLE

Slitlike cleft between the two thalami

Communicates anteriorly with the lateral ventricles

through the interventricular foramina and posteriorly with

the fourth ventricle through the cerebral aqueduct of

Sylvius.

CEREBRAL AQUEDUCT OF SYLVIUS

A narrow channel about ¾ of an inch (1.8 cm)

Connects the third and fourth ventricles

Surrounded by a layer of gray matter called the central

gray.

FOURTH VENTRICLE

Tent-shaped cavity

Situated anterior to the cerebellum and posterior to the

pons and the superior half of the medulla oblongata.

EMBRYOLOGY OF THE VENTRICULAR SYSTEM

Lateral Ventricle is derived from the central lumen of

cerebral vesicles

The Third and Fourth Ventricles are derived from the

central lumen of the neural tube.

Superior View

NEUROANATOMY | Ventricular System and Cerebrospinal Fluid

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SUMMARY: VENTRICULAR SYSTEM

VENTRICLE EMBRYOLOGY LOCATION COMMUNICATIONS

Lateral Ventricle Derived from the central lumen of cerebral vesicles

Body- occupies the parietal lobe.

Anterior horn- occupies the frontal lobe.

Posterior horn- occupies the occipital lobe.

Inferior horn- occupies the temporal lobe.

Interventricular Foramen of Monro

3rd Ventricle Derived from the central lumen of the neural tube.

Located between the two thalami.

Cerebral Aqueduct of Sylvius

4th ventricle Anterior to the cerebellum, posterior to the pons and medulla.

CEREBROSPINAL FLUID

Found in the ventricles of the brain and subarachnoid

space around the brain and spinal cord.

Volume = 150ml

Clear, colorless fluid.

Contents

o Trace amounts of protein.

o WBCs are absent or rare.

If there is a significant number of WBCs,

there’s an infection.

o Inorganic salts similar to those in the blood

plasma.

Higher sodium, chloride and

magnesium content

Lower potassium, calcium, and glucose

content

Glucose content is about half

that of the blood

Formation

1. Formed in the choroid plexuses (lateral, third

and fourth ventricles)

2. Some from the ependymal cells lining the

ventricles

3. From the brain substance through the

perivascular spaces

o Production is not pressure regulated and it continues

to be produced even if the reabsorption mechanisms

are obstructed

Choroid plexuses

o Much-folded surface

o Each fold consists of a core of vascular

connective tissue covered with cuboidal to

columnar epithelium (free surfaces covered with

microvilli) of the ependyma.

o Blood of the capillaries is separated from the

ventricular lumen by endothelium, a basement

membrane, and the surface epithelium

(fenestrated and permeable to large molecules)

o Actively secretes CSF (creates a small pressure

gradient)

o Actively transport nervous system metabolites

from the CSF into the blood (decrease

concentrations of potassium, calcium,

magnesium, bicarbonate and glucose in the CSF)

Physical Characteristics and Composition of the Cerebrospinal Fluid

Appearance Clear and colorless Volume c. 150 ml Rate of Production 0.35 – 0.4 ml/min (accdg. to Dr. Estrada);

0.5 ml/min (accdg. to Snell) Turnover Time 5 hours Pressure (spinal tap in recumbent position)

60-150 mm of water

Composition Protein 15-45 mg/100ml Glucose 50-85 mg/100ml Chloride 720-750 mg/100ml

Number of Cells 0-3 lymphocytes/mm3

FUNCTIONS OF CSF

1. Serves as a cushion between the central nervous system

and the surrounding bones

o Protecting it against mechanical trauma

2. Nourishment of the nervous tissue

o Cerebrospinal fluid is an ideal physiologic

substrate

3. Preserves homeostasis in the Nervous System

4. Assists in the removal of products of neuronal metabolism

Other functions:

1. Provides mechanical buoyancy and support for the brain

o Density of the brain is only slightly greater

than that of the cerebrospinal fluid

2. Serves as a reservoir and assist in the regulation of the

contents of the skull

o Close relationship of the fluid to the

nervous tissue and the blood

3. Serves as a pathway for pineal secretions to reach pituitary gland

NEUROANATOMY | Ventricular System and Cerebrospinal Fluid

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CIRCULATION

CSF not only bathes the ependymal and pial surfaces of the brain

and spinal cord but also penetrates the nervous tissue along the

blood vessels

ABSORPTION

Occurs when the CSF pressure exceeds the venous pressure in

the sinus

Some probably is absorbed directly into the veins in the

subarachnoid space

Some possibly escapes through the perineural lymph vessels of

the cranial and spinal nerves

Production of CSF is constant, the rate of absorption controls

CSF pressure

ARACHNOID VILLI (main sites for absorption)

Project into the dural venous sinuses, especially the superior

sagittal sinus

Grouped together to form elevations (Arachnoid granulations)

o Increase in number and size with age

o Become calcified with advanced age

Each villus is a diverticulum of the subarachnoid space, pierces

the dura mater

o It is capped by a thin cellular layer(covered by the

endothelium of the venous sinus)

Fine tubules lined with endothelium permit a direct flow of

fluid from the subarachnoid space into the lumen of the venous

sinuses

Compression of the tips of the villi, closes the tubules and

prevents the reflux of blood into the subarachnoid space

(serves as valves)

NEUROPHYSIOLOGY OF CSF

Normal Values of Cerebrospinal Fluid Pressure

In recumbent Position 100- 150 mmH2O (accdg to Dr. Es) 60- 150 mmH2O (accdg to Snell)

In sitting Position 200- 300 mmH2O

Clinical Application:

Hydrocephalus = abnormal increase in the volume of the CSF within

the skull

MORE THAN INCEPTION

Circulation is aided

by the arterial

pulsations of the

choroid plexuses

and by the cilia on

the ependymal cells

lining the ventricles

(Lateral-4th

Ventricle)

assisted by the

pulsations of the

cerebral arteries

(Lateral aspect

of each cerebral

hemisphere)

↑ brain

weight

↑ blood

volume

↑ CSF

production

↑ CSF

Pressure

↑ intracranial

pressure

Obstructions

in CSF flow

Pictures are in our book: Snell’s Clinical

Neuroanatomy. No handy atlas for this

topic.