General Neurophysiology Flashcards
Describe the Formation of CSF.
- Most of the CSF (50-70%) is made by the CHOROID PLEXUS
- Remaining CSF is made by the tissue that lines the ventricles and blood vessels 2 step Process:
- Passive filtration of the Serum
- HCO3, Cl, and K concentrations controlled by channels on epithelial cells. Aquaporins also exist
How much CSF is flowing at any moment? How much do you make a day?
~150 mL
~ 550 mL/day because the CSF is NOT recirculated
Differentiate between the composition of the CSF and the Plasma.
** Na+: Higher or the same in CSF
Cl- & HCO3: SAME in the two
Higher in CSF: Mg2+; CO2
Lower in CSF: K+; Ca2+; Protein; Glucose
Describe the Flow of the CSF.
- One way Flow and it is NOT re-circulated
- Major Absorption point is at the Arachnoid Villi into the Venous sinus (Primary way of absorption); Endothelium of SINUS and the membrane on the VILLI have fused
Describe the relationship between Intracranial pressure and Absorption of CSF. What is the normal intracranial pressure?
Absorption of CSF is PROPORTIONAL to Intracranial Pressure
- At pressure below 68 mm CSF, NO ABSORPTION
Normal Pressure: 112 mm CSF
- Increased Pressure changes can damage neurons
List the two MAIN components of the Blood-Brain Barrier.
- Tight Junctions between endothelial cells
- Glial endfeet come in close contact with blood vessel
What can pass through the Blood-Brain Barrier through Passive diffusion?
- H2O
- CO2
- O2
- Free steroid hormones
What is the major energy source for neurons?
GLUCOSE
Which Glucose transporter is going to be in the brain? Describe some of its properties
GLUT1
- Located on the Endothelial Cells (55K) and Astroglial End-Feet (45K)
- NOT insulin-dependent!
Describe the purpose of the Na/K/2Cl Transporter in the Blood-Brain Barrier.
Moves all ions FROM CSF TO blood
- Expression of the transporter is tied to Endothelin 1 and 3
- May be related to the [K+] in the CSF
What is the function of P-Glycoprotein (Multi-Drug Resistance 1) in teh Blood-Brain Barrier?
It will pump substances back out into the blood that should not have entered into the CSF!
** Protects the composition of the CSF
Define what is meant by “Circumventricular Organs.” Where are the four regions found that fall into this category?
Regions in the brain that lack TIGHT JUNCTIONS between the endothelium.
- Posterior Pituitary (Neurohypophysis)
- Area Postrema (Right @ the opening of the 4th ventricle); Strongly associated with VOMITTING (manages toxins that enter the blood stream)
3 & 4. Organum vasculosum of the lamina terminalis (OVLT) and Subfornical organ (Both involved in control of body water/thirst/blood volume control)
How much of the Cardiac Output will go to the Brain?
15-20%
Describe the Cerebral Circulation of the Brain (Circle of Willis).
Mainly supplied by the Internal Carotid Arteries and the Basilar Artery (Fusion of the two Vertebral Arteries)
Describe the Blood Flow in the Circle of Willis and what happens if there is a disruption of blood from one of the arteries.
- Little mixing of the blood from the different sources
- Disruption of one of the inputs will produce LOCALIZED areas of ischemia
Explain the relationship between Cerebral Blood Flow and Intracranial Pressure (Also relate it to Sympathetics and Mean Arterial Pressure).
As Intracranial pressure goes UP; Venous Outflow is Obstructed which will lead to a REDUCED arterial flow
- You will be doing damage to the Blood-Brain Barrier if you increase Mean Arterial Blood Pressure above 140 mmHg
- Sympathetics will INCREASE the range of blood pressure that the body can have before you do harm to the brain (They will VASOCONSTRICT the vasculature in the brain for protection)
