Neurological System V

Question 1

***In what areas is CSF located?

Answer 1

• Cerebral ventricles
• Cisterns
• Subarachnoid space surrounding the brain and spinal cord

Question 2

What are the major functions of CSF?

Answer 2

• Provides support
• Regulates ionic composition
• Removes metabolites
• Protects brain and spinal cord against trauma

Question 3

The cranial vault is a rigid structure with a fixed total volume, what the percentages of volume contained in each component of the central nervous system?

Answer 3

• Brain (80%)
• Blood (12%)
• CSF (8%)
• An increase in one compartment must be offset by an equivalent decrease in another
• Due to its’ rigid structure, the brain cannot tolerate an increase in pressure after age 2.

Question 4

What are the characteristics of CSF and what can this tell us about the state of the brain?

Answer 4

• Clear
• Colorless
• Odorless
• Alterations in composition present in various disorders

Question 5

What are the two parts in the system that comprises CSF?

Answer 5

• Internal portion

- External portion

Question 6

Communication of the internal and external portions occur through what 2 apertures?

Answer 6

• Foramen of Luschka

- Foramen of Magendie

Question 7

***What is the normal amount of CSF in adults?

Answer 7

• About 150mL combined in all spaces

Question 8

***How much CSF is produced and absorbed daily?

Answer 8

• 400-500 mL

- 21 mL per hour

Question 9

***What is the normal mean CSF pressure?

Answer 9

• 70-180 mmH20

- Memorization tool: The numbers are just about 10 higher than the CPP range of autoregulation (60-160). Likely not

Question 10

The pressure of the CSF rises if what factors occur?

Answer 10

• Intracranial volume
• Blood volume
• CSF volume
• All increases in the cranial vault

Question 11

***CSF production is formed primarily where?

Answer 11

• Choroid plexuses of the cerebral ventricles

Question 12

Small amounts of CSF is also formed directly by what other neurological structures?

Answer 12

• Ependymal cell lining

- And even smaller amounts from perivascular spaces surrounding cerebral vessels

Question 13

How is CSF secreted?

Answer 13

• Active transport of sodium ions through ependymal cells

- The resulting fluid is isotonic with plasma despite lower potassium, bicarbonate, and glucose concentrations

Question 14

***What are the factors that decrease CSF production?

Answer 14

• Carbonic anhydrase inhibitors (Glaucoma medication)
• Corticosteroids
• Spironolactone (diuretic)
• Furosemide (diuretic)
• Isoflurane
• Vasoconstrictors

Question 15

***What is the pathway of CSF circulation?

Answer 15

• Lateral ventricles
• Interventricular foramina (of Monro)
• Third Ventricle- Cerebral aqueduct (of Sylvius)
• Fourth ventricle
• Median aperture (foramen of magendie) and lateral apertures (foramina of Luschka)
• Cisterna magna
• Subarachnoid space
• Brain and spinal cord
• Absorbed in arachnoid granulations over cerebral hemispheres

Question 16

How does CSF absorption occur?

Answer 16

• It involves translocation of fluid from arachnoid granulations into cerebral venous sinuses in the superior sagittal sinus.
• Endothelial cellsof villi contain opening that permits the free flow of CSF, protein, and RBCs into venous circulation

Question 17

***What is the relationship between CSF absorption and ICP and cerebral venous pressure?

Answer 17

• Directly proportionate to ICP (Increase in CSF, increase in absorption)
• Inversely proportionate to cerebral venous pressure (Decrease in cerebral venous pressure, increase in CSF absorption)
• **Entire CSF volume replaced every 3-4 hours

Question 18

***What are the factors that affect the absorption of CSF?

Answer 18

• Blockage of villi by cell debris or fibrosis
• Tumors or hemorrhage which increase ICP
• Specific volatile anesthetic agents (Halothane)

Question 19

***What does restriction of the circulatory pathway of CSF lead to?

Answer 19

• Dilation of the ventricles upstream (hydrocephalus)
• CSF production continues despite obstruction
• Ventricles expand
• Gyri flatten
• If skull is still pliable, the head may enlarge

Question 20

In communicating hydrocephalus, where is the obstruction?

Answer 20

• In the subarachnoid space due to thickening of the arachnoid with a resultant block of return block of return-flow channels
• This can be the result of prior bleeding or meningitis
• If ICP increases as a result of excess CSF, the central canal of the spinal cord may dilate

Question 21

How do you treat noncommunicating hydrocephalus or improve absorption in general?

Answer 21

• Various procedures have been developed to bypass the obstruction
• V/P Shunt