CSF, BBB and intracranial pressure

Question 1

where is CSF found in the CNS?

Answer 1

-fills the subarachnoid space (between arachnoid and pia mater of brain and spinal cord)
-also fills the ventricles

Question 2

what are the functions of CSF?

Answer 2

-supports and provides mechanical cushioning
-maintains constant external environment for neuron’s & glia
-distributor of hormones
-major route for removing harmful brain metabolites

Question 3

what is CSF formed by?

Answer 3

-choroid plexus

Question 4

what are the characteristics of the wall of the choroid plexus?

Answer 4

-the choroid plexus capillaries are fenestrated and have no tight junctions
- the ependyma act as a continuous sheath of tissue covering and sealing the capillary wall

Question 5

what does the choroid plexus have low permeability to?

Answer 5

lipid insoluble solutes eg ions, glucose and amino acids
- ie these molecules have restricted movement and are tightly regulated

Question 6

what does the movement of lipid insoluble solutes through the choroid plexus depend on?

Answer 6

presence of transported in the walls of the ependyma eg glucose transporter GLUT1

Question 7

what do the choroid plexus have high permeability to?

Answer 7

-lipid soluble solutes eg fats, O2, CO2, lipid soluble drugs etc
-ie these molecules have unrestricted mvt and they can move freely

Question 8

what is the blood - CSF barrier?

Answer 8

-barrier by the choroid plexus and certain other brain capillaries and their associated transporters
- the transporters promote entry of some substances and restrict entry of others into CSF from blood

Question 9

how can a sample of CSF be obtained in a human?

Answer 9

• a needle is inserted between the 3rd and 4th or 4th and 5th lumbar vertebrae so that the tip lies in the subarachnoid space

Question 10

what effect does meningitis have on CSF composition?

Answer 10

-increased number of WBC in the CSF

Question 11

what can happen to the CSF after a subarachnoid haemorrhage?

Answer 11

CSF becomes discoloured and yellowish a few hours later

Question 12

how does the CSF flow through the ventricles?

Answer 12

-produced in the choroid plexus in lateral ventricle
-flows from lateral ventricle into the 3rd ventricle via the interventricular foramen
-flows from the 3rd ventricle to the 4th ventricle through the cerebral aqueduct
-flows from the 4th ventricle into the subarachnoid space via the lateral and medial aperture

Question 13

what is the pressure of CSF in mmHg normally?

Answer 13

10mmHg

Question 14

what is hydrocephalus?

Answer 14

excessive accumulation of CSF in the ventricles of the brain
-this can lead to brain damage

Question 15

what are examples of causes of hydrocephalus in infants vs adults?

Answer 15

infants:
-stenosis or inflammation of the aqueduct between 3rd and 4th ventricle

adults:
-obstruction of aqueduct between 3rd and 4th

Question 16

what is the blood brain barrier (BBB)?

Answer 16

• a highly specialised system of cells and blood vessels that serve as a protective barrier between the bloodstream and the brain

Question 17

how are the blood CSF and blood brain barrier similar?

Answer 17

-functionally the 2 barriers are the same but structurally they are different

Question 18

what is the function of the BBB?

Answer 18

-maintain a constant environment for the neurons of the CNS to function effectively
-exclusion of toxic substances
-protects brain from circulating neurotransmitters

Question 19

what is intracranial pressure?

Answer 19

Intracranial pressure (ICP) refers to the pressure exerted by the cerebrospinal fluid (CSF) within the skull and on the brain tissue.

Question 20

what are examples of things that could cause an increase in ICP?

Answer 20

-brain swelling due to injury or infection
-excess CSF eg hydrocephalus
-bleeding in the brain - eg aneurysm / traumatic head injury
-tumours - can cause increased in ICP by compressing the brain

Question 21

what can happen to the cerebral vessels and flow as a result of an increased ICP?

Answer 21

–increased ICP- cerebral vessels compression - reduction in cerebral flow and therefore can eventually lead to cerebral ischemia

Question 22

what are examples of symptoms associated with an increase in ICP initially and as the condition worsens?

Answer 22

-initially- headache, nausea and restlessness
-as condition worsens, there can be neural dysfunction eg confusion and drowsiness
-as ICP rises further, the cerebral pressure becomes very low and cushings reflex occurs

Question 23

what is cushings reflex?

Answer 23

a set of physiological responses that occur when the ICP rises

Question 24

what are the 3 components of cushings reflex?

Answer 24

-increase in ICP compresses the brain and can cause compression of the medulla oblongata - ie the cardioresp centre - causing bradycardia
-increase in ICP - causes compensatory mechs by the body to increase flow to the brain - therefore increased BP
- compression of brain can also lead to abnormal respiratory conditions eg cheyne stokes respiration

Question 25

in simple words , what are the 3 components / physical symptoms of a patient with a cushings reflex due to increased ICP? ie the cushings triad

Answer 25

-increased BP
-bradycardia
-decrease in respiration