Lecture 14: General Neurophysiology Flashcards
(31 cards)
Formation of CSF is a 2 stage process, what are the 2 stages?
- Passive filtration of serum
2. HCO3, Cl- and K concentrations controlled by channels on epithelial cells. Aquaporin 1 allows H2O to cross
What molecules end up in equal concentrations in both the plasma and the CSF?
Na+
HCO3
What molecules are found in greater concentration in CSF than in plasma?
Mg2+
Cl-
CO2
What substances are found in higher concentration in plasma than CSF?
K+
Ca2+
Protein
Glucose
Absorption of CSF is proportion to what?
Intracranial pressure
Absorption of CSF is proportional to intracranial pressure. At pressures below _______ mm CSF, no absorption occurs. Normal pressure is _______ mm CSF. Increased pressure causes damage to neurons
68; 112
What is the role of CSF?
Protect the brain
Capillaries in the brain have 2 components that limit exchange acrosss the BBB, what are they?
Tight junctions between endothelial cells
Glial endfeet come in close contact with blood vessel
The BBB allows passive diffusion of what substances?
H2O via Aquaporin 4
CO2
O2
Free steroid hormones (most are protein bound)
What is the major energy source for neurons
Glucose -> which doesnt readily cross the BBB
How is glucose transported across the BBB
GLUT 1 transporter -> not insulin dependent
2 forms: 55K on capillaries and 45K on astroglia
What glucose transporter do neurons use to move glucose in?
GLUT3
What is the role of the Na/K/2Cl transporter in the BBB?
Moves all of these ions from CSF to the blood
Expression tied to release endothelin 1 and 3 from capillary endothelial cells
Expression of Na/K/2Cl is tied to expression of endothelin 1 and 3 from capillary endotheial cells. What is the production of endothelin tied to?
A signal from the astrocytes, which may be related to [K+] in the CSF -> very important bc when you think you fire APs which then hyperpolarize causing K+ to leave the cell then in order to get this EC K+ out of the CSF you need the Na/K/2Cl channel on
Many drugs do move across the BBB, but are moved back to the blood via ________________
P-glycoprotein
What is the function of the BBB?
Protect chemical compositionof CSF from blood-borne agents
Maintain electrolyte composition of CSF (particularly K+)
Protection from toxins
Prevent escape of NTs
What are circumventricular organs?
Neural tissue that is outside or not as well protected by the BBB as other neural tissue -> the capillaries in these areas dont have the tight junctions between endothelial cells
Name the 4 circumventricular organs
Posterior pituitary
Area postrema
Organum vasculosum of the lamina terminalis (OVLT)
Subfornical organ
Why is the posterior pituitary a circumventricular organ?
Bc it needs to be in direct contact with blood in order to release hormones into the blood
**Post pituitary AKA neurohypophysis
What is the area postrema responsible for and why is it considered a circumventricular organ?
It triggers vomiting if there’s something in the blood that the body needs to get rid of, therefore this area needs to be in direct contact with the blood
Organum vasculosum of the lamina terminalis (OVLT) and subfornical organ are both circumventricular organs. What is their function and why are they circumventricular organs?
Both are involved in control of body water/thirst/blood volume control (angiotensin) -> responsible for sensing plasma osmolarity so needs to be in direct contact with blood
What are the NT’s and receptors for sympathetic innervation of the cerebral circulation?
NT’s = NE & NPY
Receptors = alpha-adrenergic
What is the effect of sympathetic innervation on cerebral innervation?
Leads to constriction when systemic cardiac output/BP increases
Where are parasympathetic fibers found on cerebral circulation and what is the effect of their stimulation?
Larger blood vessels -> cause vasodilation
