Physiology of CSF
Cerebrospinal fluid is secreted into each ventricle of the brain by choroid plexuses. These are vascular areas where there is a proliferation of blood vessels surrounded by ependymal cells in the lining of ventricles walls. Cerebrospinal fluid (CSF)passes back into the blood through into diverticula of arachnoid mater, called arachnoid villi, which project into the venous sinuses.the movement of CSF movement from the subarachnoid space to venous sinuses depends upon the difference in pressure on each side of the wall of the arachnoid villi which act as one-way valves. When CSF pressure is higher than venous pressure, CSF is pushed into the blood and when the venous pressure is higher the arachnoid villi collapse, preventing the passage of blood constituents into the CSF. There may also be some reabsorption of CSF by cells in the wall of the ventricles.
Cerebrospinal Fluid (CSF) from the roof of the fourth CSF flows through foramina into the subarachnoid space and completely surrounds the brain and spinal cord. There is no intrinsic system of CSF circulation but its movement is aided by pulsating blood vessels, respiration and changes of posture.
CSF is secreted continuously at a rate of about 0.5 ml per minutes, i.e. 720 ml per day. The volume remains fairly constant at about 150 ml, as absorption keeps pace with secretion. CSF pressure may be measured using a ventricle tube attached to a lumber puncture needle inserted into the subarachnoid space above or below the 4th lumber vertebrae . The pressure remains fairly constant at about 10 cm H2O when lying on one side and about 30 cm H2O when sitting up. If the brain is enlarged by, e.g. haemorrhage or tumour, some compensation is made by a reduction in the amount of CSF. When the volume of brain tissue is reduced, such as in degeneration or atrophy, the volume of CSF is increased. CSF is a clear, slightly alkaline fluid with a specific gravity of 1.005.
It consisting of following material
Water
Mineral salt
Glucose
Plasma protein : small amount of Albumin and globulin
A few leukocytes
Creatinine and Urea (small amount)
Functions of cerebrospinal fluid (CSF)
1- CSF supports and protects the brain and spinal cord by maintaining a uniform pressure around these vital structures and acting as a cushion or shock absorber between the brain and skull
2- It keeps the brain and spinal cord moist .
3- there may be exchange of nutrients and waste products between CSF and the interstitial fluid of the brain.
4- CSF is thought to be involved in regulation of breathing as it bathes the surface of the medulla where the central respiratory chemoreceptors are located.
Meninges physiology
The brain and spinal cord are completely surrounded by three layers of tissue, the meninges, lying between the skull and the brain, and between the vertebral foramina and the spinal cord.
Meaninges consists of the three layers-
1- Dura mater
2- Arachnoid mater
3- Pia mater
The cerebral dura mater consists of two layers of dense fibrous tissue. The outer layer takes the place of the periphery on the inner surface of the skull bones and the inner layer provides a protective covering for the brain. There is only a potential space between two layers except where the inner layer sweeps inwards between the cerebral hemisphere to form the falx cerebri ; between the cerebral hemisphere to from the fall cerebelli ; and between the cerebrum and cerebellum to from the tentorium cerebelli.
Venous blood from the brain drains into venous sinuses between the two layers of dura mater. The superior sagittal sinus is formed by the falx cerebri and the tentorium cerebelli forms the straight and transverse sinuses .
This is a layer of fibrous tissue that lies between the dura and Pia mater. It is separated from the dura mater by the subdural space that contains a small amount of serous fluid and from the Pia mater by the subarachnoid space, which contain cerebrospinal fluid (CSF). The arachnoid mater passes over the convolutions of the brain and accompanies the inner layer of dura mater in the formation of the falx cerebri , tentorium cerebelli and falx cerebelli. It Continues downwards to envelop the spinal cord and ends by merging with the dura mater at the level of the 2nd sacral vertebra
This is delicate layer of connective tissue containing many minute blood vessels. It adhere to the brain, completely covering the convolutions and dipping into each fissure. It continues downwards surrounding the spinal cord. Beyond the end of the cord it continues as the filum terminal, pierces the arachnoid tube and goes on, with the dura mater, to fuse with the periosteum of the coccyx.
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