Notes on Cerebrospinal Fluid

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Flow of Cerebrospinal Fluid:

• Produced by choroid plexuses of the lateral, third and forth ventricles.

• Production of CSF is an energy-consuming process.

• Choriod plexus epithelium cells have large nuclei, abundant cytoplasm and numerous mitochondria.

• Some components of blood plasma used in CSF production.

• Osmotic equilibrium between blood and CSF is maintained by active transport of certain ions.

• CSF flows: lateral ventricles > interventricular foramen > third ventricles > cerebral aqueduct > fourth ventricles > median and lateral apertures of fourth ventricles > absorption into venous blood through arachnoid villi.

• Hydrostatic pressure of CSF is greater than that of blood in dural sinuses.

• Total volume maintained at 80 ~ 150 mL.

VENTRICULAR SYSTEM

(= CSF - filled cavities within the brain)

1. Lateral ventricles within (cerebral hemispheres): C-shaped, consists of anterior horn, body, posterior and inferior horn. Cavities within each cerebral hemisphere.

2. Third ventricle (diencephalon). Cleft-like cavity sited between the thalami.

3. Fourth ventricle (communicates with spinal cord). Linked to the cisterna magna of the subarachnoid space by the median foramen of Magendie and two lateral foramina of Luschka.

Lateral Relations of Third Ventricle:

Thalamus, pineal body, posterior perforated substance, hypothalamus, pituitary gland, anterior and posterior commissure.

Structures in Floor of Fourth Ventricle:

This diamond-shaped area is also referred to as the rhomboid fossa. Facial nerve (facial colliculus), abducent nucleus, vestibular nuclei, locus caeruleus (part of reticular formation), hypoglossal trigone (12th nerve) and vagal trigone (for 10th cranial nerve).

Secretion of CSF:

Origin: Choroid plexus (largest in the lateral ventricles): Secrete 300-500 ml/24 hours. The choroid plexus is composed of capillaries, pia and ependyma. These secrete CSF. There is a constant circulation and reabsorption. About 150 ml of CSF fills the entire system (23 ml in the ventricles and the remaining 127 ml fills the subarachnoid space). Other features include a pressure of 50 - 150 mm of water, SG of 1.007, cell free with a leukocyte count less than 5 cells, low protein, glucose, potassium and calcium, but high sodium, magnesium and chloride. Osmolality of 289 MOSM/L which is lower than that of serum. Active ATP-dependent pump mechanism in function to regulate sodium and potassium content. Clear, colorless liquid.

Interventricular Communications:

1. Between lateral and 3rd: interventricular foramen of Monro.

2. Between 3rd and 4th: aqueduct.

CSF Circulation:

Secreted by choroid plexus sited in the lateral, third and fourth ventricles.

CSF flows from the lateral ventricles through the interventricular foramen into the third ventricle. From the 3rd ventricle passes through the aqueduct into the 4th ventricle. Gains the subarachnoid space through the median and lateral apertures. Bathes spinal cord (lumbar cistern) and cerebral hemispheres. CSF is re-circulated to the blood through the arachnoid granulations which project into major venous sinuses (i.e. superior sagittal sinus and small venous lacunae). An important blood-brain barrier exists that provides a protective internal milieu for the delicate neurons in the CNS. Also protects the brain from harmful endogenous and exogenous toxins in the blood. Barrier develops in the early years of life and controls entry of metabolic substrates (glucose), ionic movements (sodium, potassium).

Functions of CSF:

1. Supports and cushions the CNS against trauma ("protective buffer").

2. Provides buoyancy; reduces momentum and acceleration.

3. Removes waste products of metabolism and drugs/toxins ("blood/CSF barrier").

4. Integrates brain endocrine function i.e. hypothalamic releasing factors are secreted directly into the CSF!

5. Controls microenvironment of neurons and glial cells.

Pathology of CSF Circulation:

Blockage at the arachnoid granulation level results in communicating hydrocephalus and at the fourth ventricle or cerebral aqueduct in non-communicating hydrocephalus. Tuberculous meningitis is an important cause of hydrocephalus.

Additional Reading:

Basic Neurology

1. Peripheral Nervous System
2. Central Nervous System
3. The Ventricular System
4. The Spinal Cord
5. The Brain Stem
6. The Cerebellum
7. Visual Pathways
8. Diencephalon
9. Basal Ganglia
10. Cerebral Cortex
11. Sleep Disorders
12. Autonomic Nervous System
13. Cranial Nerves and Parasympathetic Ganglia
14. Cells of the Nervous System
15. Cerebrospinal fluid
16. Additional short notes on Cerebrum
17. Functions and Diseases of Cerebrum
18. Subcortical Grey Matter
19. Notes on The Spinal Cord
20. Regulation of Heart Rate by Autonomic Nervous System
21. Action Potentials, Axon Conduction, and Neuromuscular Junction
22. Types of Seizures
23. What is a Cough Reflex?
24. Notes on Congenital Prosopagnosia
25. Findings in Parkinson's Disease
26. Types of Heat Strokes
27. Types of Strokes
28. What is Benign Intracranial Hypertension?
29. What is Cauda Equina Syndrome?
30. Cranial Nerve Locations in Brain Stem

Neurology Videos

1. Video of Neurology Examination in a Clinical Setting

Medical Images

Useful Medical Images & Diagrams (link opens in a new window)

Related Topics

1. Nervous System Disorders
2. Histology of Nervous Tissue
3. Cranial Nerve Reflexes
4. Motor System Examination

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