neuro Flashcards
oligodendrocytes
glial cells that make myelin sheath
ependymal cells
glial cell, border areas next to ventricles in brain
microglia
glial cell, cells from immune system that help 2 clear up dead material, police these areas
astrocytes
glial cell found around synapses - help regulate potassium ion levels
neurons vs glial cells- who is post- mitotic- what does that mean?
only neurons. glial cells can indeed divide. leads to brain tumors
what are schwann cells in peripheral nervous sys? what do they do?
in peripheral nervous system (outside brain/spinal cord), schwanns wraps around axon many times, forming the myelin sheath
spaces between myeline sheath name
node of ranvier
what is myelin sheath and what does it do?
The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and that facilitates the transmission of nerve impulses, formed from the cell membrane of the Schwann cell in the peripheral nervous system and from oligodendroglia cells.
issues when myelin sheath malfunctions
multiple sclerosis. diabetics who have trouble with feet- myelin not properly layed down
concentration of potassium inside and outside of cell
120 mM inside, 4 mM outside
concentration sodium inside/outside cell
low inside, high outside 14, 140
concentration of Cl- inside , outside cell
low inside, high outside 4, 105 mM
permeability of potassium vs sodium
potassium has highest permeability
describe how electrical force and chemical diffusion interact with each other
as K diffuses out of cell, (diffuses down its gradient) inside of cell becomes negative. pos voltage builds up outside of cell. tends to push K + back into cell. chemical and electrical are roughly equal, but you do have positive leakage of K+ out of cell, and Na+ leakage into cell
how does the cell handle na,k leakage?
Na/K pump; pumps Na+ out of cell, K+ into cell
what happens to permeability when you stimulate a nerve?
leaves resting state, enters an active state in which cell’s membrane is more permeable to sodium than it is to potassium
Using the nernst equation, -87 mV inside the cell; why is this not the cell’s voltage?
that would be if cell was ONLY permeable to potassium. in reality it is closer to -80
Mechanism for sending electrical signal
i. The axon is normally + on outside and – on inside ii. Resting membrane potential is at -70mV (on inside of axon) iii. Our action potential begins at the axon hillock iv. Axon potential gets triggered in an “all or nothing” response in about 1msec (if we get the action potential we get it all v. Changes to +35mV on the inside of the axon and negative on the outside vi. As it increases this is depolarization and then as it drops back down it is repolarization
Resting membrane potential is ____
-70 mV inside cell. (Permeability for potassium is greater at rest and it will diffuse to outside of cell and bring + charges outside, leaving inside more negative)
what mechanism makes membrane selectively permeable to the ions?
The membrane of the cell is selectively permeable because ions have to move through special voltage gated ion channels (respond to potential difference across the membrane)
What is responsible for the ion distribution (three experiements)
- Axon at 4 celsius and the RMP is 0mV
* This suggests there is a metabolic event required - Take an axon at rest with no stimulation and put radioactive sodium 22 ion on the outside of axon. Sodium 22 ion will slowly show up on the inside of the cell
* This is the “sodium leak” which indicates the axon is not exactly impermeable to sodium at rest. This leak brings some positive charge inside the axon - Use oubain, a poison that attacks Na+/K+ pump. The resting membrane potential goes to 0mV
- Pump brings sodium outside and potassium inside to set up concentration gradient for ions. Pump is electrogenic because it puts more positive charges on the outside than inside so it helps create potential difference
- With oubain we kill the pump and we don’t have the gradient and we don’t have the potential difference in the axon
explain where you would see depolarization, repolarization and hyperpolarization on the resting membrane potential curve and what they mean
- During an action potential, permeability for sodium is greater and it diffuses into the cell and brings + charge inside, leaving the inside more positive. This is depolarization (increase conductance of sodium)
For repolarization, potassium channels open up again (even more than at rest) and let potassium leave again and take + charge outside and make – inside again
Refractory period:
a point where additional stimulus will not give u another action signal. (you already have one going on)
Its important because you only want an action potential going in ONE direction.
Refractory period has 2 parts; absolute (length of curve) and relative (outside of curve)
experimentally, if you can stimulate an axon in the middle, can you get action potentials going in both directions? can the body do this?
experiment: yes.
body: no
normally we start at axon hillock where we have only voltage gated Na channels; lets us only conduct one way. cell body does not have ion channels. only axon/axon terminal has them.
