Physiology-CSF

Question 1

What are the different cisterns through which CSF flows in the subarachnoid space? Where do these end?

Answer 1

Cerebellomedullary (magna), pontine, superior (ambines), interpeduncular and chiasmatic cisterns. These all drain into the superior sagittal sinus via the arachnoid villi.

Question 2

Where does 70% of CSF secreted from?

Answer 2

Choroid epithelia in the lateral venticles, roofs of III & IV ventricles and the foramina of Luschka and Munro (IVF).

Question 3

What separates the CSF in the ventricle from the blood vessels in the choroid plexus?

Answer 3

Fenestrated endothelia of the capillaries is surrounded by choroid epithelium w/tight junctions.

Question 4

What processes contribute to CSF formation in the choroid plexus?

Answer 4

Filtration of CSF through the fenestrated endothelium in capillaries and active secretion of CSF by choroidal epithelium?

Question 5

Where does the other 30% of CSF come from?

Answer 5

Cerebral capillary walls

Question 6

How many times is your CSF replaced per day?

Answer 6

Total volume of CSF ~ 140mL (30 in the ventricles and 110 in SAS & spinal cord). You make about 500mL per day, so you replace it 3-4 per day.

Question 7

What are the three main functions of CSF?

Answer 7

1) Constant external environment for neurons & glia 2) Remove metabolites in unidirectional fashion to venous system 3) Protect CNS from trauma

Question 8

How is CSF different from normal blood plasma?

Answer 8

Lower [protein], [Glc], [Ca2+], [K+] and pH. Higher [Mg2+], [Cl-], [Lactate] and [H2O]. Same [Na+].

Question 9

What is the normal CSF pressure?

Answer 9

100-150 mm H2O

Question 10

A patient comes to see you in the ED with decreased blood pressure and a severe headache. Spinal tap reveals a bloody and yellow-colored CSF. What might this indicate?

Answer 10

Hemorrhage

Question 11

A patient comes to see you complaining of recurrent headaches. Spinal tap reveals a CSF with a protein content > 600 mg/dL. What might this indicate?

Answer 11

Tumor. This is likely due to a subarachnoid blockade that causes protein to accumulate.

Question 12

What might cause a patient to have a CSF protein level > 150 mg/dL?

Answer 12

Bilirubin bound to albumin has been brought to the CSF from the plasma.

Question 13

A patient comes to see you with > 4 lymphocytes/mL in his CSF. What microbe might be causing this?

Answer 13

Fungal meningitis.

Question 14

A patient comes to see you with > 4 neutrophils/mL in his CSF and decreased glucose concentration. What microbe might be causing this?

Answer 14

Bacterial meningitis.

Question 15

A patient comes to see you because he has a family history of multiple sclerosis. What might you look for in his CSF if you do a spinal tap?

Answer 15

Increased gamma-globulin content.

Question 16

What are three possible causes of the condition seen in the patient below?

Answer 16

This patient has hydrocephalus. This can be caused by oversecretion of CSF (choroid tumors), impaired reabsorption of CSF (tumors/scarring) or obstruction of CSF circulation in the ventricles or SAS.

Question 17

If a patient comes to see you with a noncommunicating hydrocephalus, where are the most likely locations of this blockade?

Answer 17

Cerebral aquaduct (pineal gland tumor) or the foramina of the 4th ventricle (Magendie or Luschka)

Question 18

An elderly gentleman comes to see you in clinic after having an MRI of his brain. You notice an enlargement of the ventricles and a thinning of the cortical tissue. Intrathecal catheterization reveals no increase in intracranial pressure. What is your diagnosis in this patient?

Answer 18

Hydroecphalus ex vacuo. This is due to cerebral atrophy, not imbalance between CSF formation and reabsorption.

Question 19

What are the three fluid barriers in the CNS?

Answer 19

Blood-brain, blood-CSF and the CSF-brain barrier

Question 20

What cells form the blood-CSF barrier? What nutrients pass through this barrier?

Answer 20

Choroid epithelial cells with tight junctions. Nutrients that are needed in small amounts over a long period of time pass through this barrier (vitamins, folates etc.)

Question 21

What cells form the CSF-brain barrier?

Answer 21

Ependymal cells. These do not have tight junctions and allow for bidirectional movement of molecules between the CSF and the extracellular space of the brain.

Question 22

What cells form the blood-brain barrier? What nutrients pass through this barrier?

Answer 22

Endothelial cells with tight junctions and surrounding astrocytes form this barrier. Metabolites that are consumed rapidly by the brain are transported across this barrier (glucose, amino acids, lactate and ribonucleosides)

Question 23

What 4 methods can drug companies employ in allowing their drug to be delivered across the blood-brain barrier?

Answer 23

If it’s lipid, no problem. Temporarily open the BBB w/a hypertonic solution. Piggyback on existing carriers. Implant a reservoir catheter or add membrane receptors to the BBB.

Question 24

What is a circumventricular organ? Why do we need these?

Answer 24

Specialized tissue that lacks a blood-brain barrier (Pineal body, subcommisural organ, subfornical organ, organum vasculosum of the lamina terminalis, median eminence, neurohypophysis and area postrema). We need these so that the CNS can respond quickly to systemic changes.

Question 25

What clinical scenarios may result in a breakdown of the blood-brain barrier? (5 things)

Answer 25

Brain tumors (leaky vessels), stroke, bacterial meningitis, multiple sclerosis (break down of BBB is what allows T cells to attack myelin in brain), inflammation.

Question 26

What is the difference between vasogenic edema and cytotoxic edema?

Answer 26

Vasogenic edema is due to increased permeability of the BBB and capillary walls. This will increase brain interstitial fluid and shrink the ventricles. This occurs in ischemia, head trauma and meningitis. Cytotoxic edema is due to a shift of ECF in the brain into the cells. This causes cell swelling, decreased interstitial fluid and reduced ventricle size. This can be a result of hyponatremia and toxicity.