Physiology: Cerebrospinal Fluid

Question 1

Where is the CSF produced?

Answer 1

Secretory epithelium of the choroid plexus

Question 2

What is cerebrospinal fluid?

Answer 2

Clear, watery fluid that surrounds the brain and the spinal cord

Question 3

What is idiopathic cranial hypertension/pseudotumor cerebri?

Answer 3

Increased CSF pressure but no imaging features of hydrocephalus

Question 4

Where is the choroid plexus found?

Answer 4

Two lateral ventricles, and in the roof of the third and fourth ventricles

Question 5

What is hydrocephalus?

Answer 5

Accumulation of CSF in the ventricular system or around the brain (either due to obstruction of drainage or overproduction), causing ventricular enlargement and increased CSF pressure

Question 6

Describe the flow of CSF from the lateral ventricles to the spinal cord

Answer 6

1. CSF originally formed in choroid plexus of lateral ventricles
2. Flows into third ventricle which adds more CSF
3. Flows through aqueduct of midbrain into the fourth ventricle which adds more CSF
4. Enters subarachnoid space through 3 openings in the roof of the fourth ventricle
5. Circulates in the central canal of spinal cord

Question 7

Describe the mechanical function of CSF

Answer 7

CSF acts as a shock-absorbing medium that protects brain tissue; brain ‘floats’ inside the cranial cavity

Question 8

How does CSF return to venous blood?

Answer 8

Through arachnoid granulations into the superior sagittal sinus (SSS)

Question 9

How does the blood-brain barrier form a selectively permeable barrier?

Answer 9

Tight junctions between brain endothelial cells prevent paracellular movement of undesirable molecules, while multiple cellular transport channels allow the movement of desired molecules

Question 10

Describe the appearance of normal CSF

Answer 10

Clear and colourless, contains little protein, little immunoglobulins and only 1-5 cells/ml

Question 11

How can CSF be obtained for clinical analysis?

Answer 11

Lumbar puncture

Question 12

What is the blood-brain barrier?

Answer 12

The blood-brain barrier is a highly selective barrier between the systemic circulation and the brain’s extracellular fluid formed by endothelial cells

Question 13

What is papilloedema?

Answer 13

Optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve

Question 14

What is the main function of the blood-brain barrier?

Answer 14

Protect the brain from potentially harmful neurotoxins and helps prevent infection from spreading to the brain

Question 15

Describe the circulatory function of CSF

Answer 15

Medium for minor exchange of nutrients and waste products between blood and brain tissue

Question 16

The interstitial fluid of the brain drains into the CSF through the ________ _______

Answer 16

Perivascular space

Question 17

How is CSF produced?

Answer 17

Ultra-filtrate of blood plasma involving the transport of ions (Na+, Cl- and HCO3-) across the epithelium from blood to CSF

Na+ transport across the cells produces an electrical gradient which pulls along Cl-, and both ions drag water by osmosis

Question 18

Any condition that causes CSF accumulation (overproduction or obstruction) causes serious ______ deficits

Answer 18

Neurological

Question 19

Describe the homeostatic function of CSF

Answer 19

pH of CSF affects pulmonary ventilation and cerebral blood flow, transports hormones