Cerebrospinal Fluid Production and Flow Flashcards
Name the protective Membranes Surrounding the Brain and the Spinal Cord
Dura Mater-Tough
Arachnoid Mater-Spidery
Pia Mater-Vascular
Dura Mater
A double membrane:
The outer layer lines the skull.
The inner layer separates in certain parts from the outer layer to form the venous sinuses into which most of the venous blood of the brain circulation drains.
Pia Mater
The pia mater is a highly vascular, fragile membrane, covering all the convolutions of the surface of the brain.
Subarachnoid Space
(Between the pia and Arachnoid membrane) stretches to the sacral region and contains cerebrospinal fluid.
From the arachnoid, projections bulge into the venous sinuses (the arachnoid villi), which act as valves
for the return of CSF to the circulation
List the Ventricles of the Brain
Two lateral ventricles in each cerebral hemisphere.
The third ventricle in the midline between the two thalami.
The fourth ventricle is located on the medial dorsal aspect of the pons and medulla oblongata, which extends down into the central canal of the spinal cord.
The four ventricles are interconnected through canals and connected to the subarachnoid space through three openings from the fourth ventricle.
The ventricles and channels are filled with CSF.
The flow of the CSF occurs from the ventricles to the subarachnoid space via the foramina.
What is Cerebrospinal Fluid(CSF)
CSF is an ultra filtrate of plasma that circulates freely throughout the cerebral ventricles and central
canal of the spinal cord.
Normal volume of CSF
150 ml
Formation of CSF
Formed from the blood capillaries (brain tissue), pia
capillaries, capillaries of choroid plexus. It is formed (and absorbed in arachnoid granulations) at a rate
of about 500 ml/day.
Where is CSF Normally Found
It is found in the ventricles of the brain, the cisterns on the outside of the brain and the subarachnoid space around the brain and the spinal cord.
Composition of CSF
Chloride greater than plasma. Potassium less. Glucose less.
Normally the CSF protein content is very low compared to plasma (.02 vs. six
g/100ml), and increased protein in the CSF is of concern.
Describe the Flow of CSF
CSF flows from the Lateral Ventricles to the Third Ventricle via the Interventricular Foramen to the Fourth Ventricle via the Cerebral Aquaduct
How does CSF enter the Subarachnoid Space
CSF enters the Subarachnoid Space via the Lateral Foramina of Luschka as well as the Midline Foramen of Magendie which are located In the walls of the 4th Ventricle
Where is CSF resorbed back into the blood circulation?
Subarachnoid Space has Arachnoid villi where CSF is reabsorbed back into the blood circulation
The Villi act as 1-way valves whereby the CSF is reabsorbed into Superior Sagittal Sinus
What is the function of the cerebral spinal fluid?
The cerebral spinal fluid allows the brain to float, and allows the brain to move simultaneously with
the skull during minor acceleration preventing brain contortion.
Mechanical Protection
Removes excessive fluid “lymphatic system of CNS.”
Circulates chemicals to certain brain centers involving in adjusting vital functions (respiratory center)
Cerebrospinal Fluid Pressure
The normal pressure in the cerebral spinal fluid system when a patient is lying in a horizontal position average 130millimeters of water (10mmHg).
The cerebrospinal fluid pressure is typically regulated
almost entirely by absorption of the fluid through the arachnoid villi.
The villi function as “valves” that allow the fluid and its contents to flow readily into the blood of the venous sinuses while not allowing blood to flow backward in the opposite direction.
Papilledema
Anatomically the dura of the brain extends as a sheath around the optic nerve and then connects with
the sclera of the eye. When the pressure rises in the cerebrospinal system, it also rises inside the optic
nerve sheath. High pressure in the sheath pushes fluid along the spaces between the optic nerve fibers
to the interior of the eye. The swelling of the optic disc results, which can be observed with an
ophthalmoscope, is called papilledema.
Hydrocephalus
“Hydrocephalus” means excess water in the cranial vault. This condition is frequently divided
into communicating hydrocephalus and non-communicating hydrocephalus. .
Communicating Hydroccephalus
In communicating hydrocephalus, fluid flows readily from the ventricular system into the subarachnoid space.
Excess CSF formation or decreased arachnoid villi drainage. (A subarachnoid haemorrage may block the return of CSF into the circulation. If CSF accumulates in the subarachnoidalspace, the condition is called communicating hydrocephalus)
Non-Communicating Hydrocephalus
In non-communicating hydrocephalus, fluid flow out of one or more of the ventricles is blocked
It prevents the Ventricles from “Communicating” with Subarachnoid space (caused by a block in the aqueduct of Sylvius , resulting from atresia (closure) before birth in many babies or from blockage by a brain tumor at any age
Name causes for an increase in CSF pressure.
Tumor of choroid plexus
Occlusion of arachnoid villi
Occlusion of aqueduct
Infection/edema
Haemorrhage
Treatment of Hydrocephalus
Treatment of hydrocephalus includes the surgical institution of a silicone shunt from one of the
ventricles to the abdominal cavity (so-called VP shunt).
Cushing’s reflex / CNS ischemic reflex
An acute increase in CSF pressure also may elicit vascular responses. Cushing’s reflex, or the CNS
ischemic reflex, is triggered by such an increase in CSF pressure. Peripheral arterioles constrict,
resulting in elevated arterial pressure, which causes increased cerebral blood flow. The increased
pressure activates the baroreceptor reflex, and resulting increased vagal tone caused bradycardia.
Thus, in patients with head injuries who have elevated arterial pressure and bradycardia, increased
CSF pressure should be considered.
