The cerebellum is attached to the back of the brainstem and located just beneath the cerebral hemispheres. The lower brainstem flows into the spinal cord. The spinal cord is the point of exit for nerves on their way out to the muscles they control, and the point of entry for sensory fibers returning from the body's sensory organs. All the nerves outside the central nervous system are collectively called the peripheral nervous system.
The two cerebral hemispheres are built around a connecting system of hollow spaces called the ventricular system. The ventricles are filled with cerebrospinal fluid (CSF).

Physiology and biochemistry of cerebrospinal fluid

Cerebrospinal fluid (CSF) is a clear, colorless liquid formed within the cavities or ventricles of the brain by the choroid plexus and diffused blood plasma.
The ventricular system and subarachnoid space are filled with cerebrospinal fluid (CSF). The total volume of CSF in adults is about 150 ml, including 30 ml within the cerebral ventricles and 120 ml in the subarachnoid space (including its spinal segment). CSF is constantly produced and reabsorbed at a rate of approximately 500 ml/day (0.35 ml/min). This means that the total amount of CSF is replaced every 4 to 6 hours

CSF is produced in the ventricles by a specialized sponge like structure called the choroid plexus. Beginning in the lateral ventricles, where it is formed, it circulates into the third ventricle and then into the fourth ventricle. It leaves the fourth ventricle through three small openings or foramina, to circulate through the intracranial and spinal subarachnoid spaces. The circulation may be blocked in any of the ventricles or at the foramina between them, leading to an "obstructive" hydrocephalus (accumulation of fluid in the brain).

In 1921, Stern and Gautier used the term "blood-brain barrier" (BBB) to refer to a physiological barrier separating the brain and CSF from the blood-borne substances. BBB allows the brain and CSF composition to be maintained at the levels quite different from those of the blood with respect to proteins, ions, and other molecular elements. The BBB is extremely important in clinicall practice.

Functions of cerebrospinal fluid

  • CSF provides mechanical support to the brain, and a "floating brain" weighs less than if it were simply resting on the bony table of the skull.
  • CSF probably functions to help remove metabolic products or waste from the brain, a function that is poorly understood but probably important in both normal and diseased states.
  • There is some evidence that CSF transports biologically active compounds that may function as chemical messengers.
  • It plays an important role in maintaining the chemical environment of the brain.
  • Although its communication with the plasma compartment is tightly regulated, CSF seems to be in relatively free communication with the brain's extracellular fluid compartment, which aids brain cells themselves.

 

Pathologic conditions in the neurological diseases

Damage to discrete (focal) areas of the brain or spinal cord produces predictable circumscribed signs and symptoms (for example, paralysis of an arm, leg, or side of the body, loss of ability to speak or comprehend spoken language, incoordination, and so on).

Diffuse impairment of cerebral tissue, on the other hand, leads to its own characteristic clinical picture. Failure of various "intellectual" functions such as attention, concentration, judgment, memory, problem-solving ability, and insight are early findings in mild diffuse disease. Other symptoms include changes in alertness beginning with clouding of consciousness and proceeding to drowsiness, stupor, and coma. Seizures can accompany both diffuse and focal damage.
Various disease states tend to produce either focal or diffuse brain damage, so that the pattern of deficits is often helpful to the clinician in working backward toward a specific diagnosis. Some examples of conditions that cause focal damage are stroke caused by arterial occlusion or hemorrhage: trauma: cerebral abscess; and tumors. Many of these conditions also cause changes in the CSF by damaging the BBB (elevating protein) and stimulating inflammatory changes (with leukocytosis), tissue necrosis (elevating CSF protein and cell count), or shedding of tumor cells in cytologic specimens.

Examples of conditions associated with generalized cerebral dysfunction (encephalopathic states) are anoxia, generalized ischemia, hypoglycemia, sepsis, thyroid abnormalities, disseminated intravascular coagulation, and the entire group of toxic and metabolical disorders.

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