Neural Physiology Flashcards
Nervous System Organization
Receptor > Sensory NS > CNS > Motor NS > Effector
action potential
a neural impulse; a brief electrical charge that travels down an axon
- produce electrical signal from ion mvmnt
- strong enough signals get action potentials
- (-50-55mmVol gets an action potential)
electrical signals
changes in a cell’s membrane potential
- when produced by cells called action potential
- transfer info to diff parts of body
- due to ion conc differences across PM and membrane permeability
resting potential of the membrane
the difference btwn the charges of the inside (-) and outside (+) of the membrane = -90mmVol
- change in this causes action potential (at -50mVol)
- lots of Na and Cl outside = (+)
- lots of K inside = (-)
depolarization
The process during the action potential when Na is rushing into the cell causing the interior to become more positive
- charge is less (-) and more (+) (closer to being equal)
- caused by hypopolarization (“less polar”)
repolarization
Return of the cell to resting state, caused closing of Na gates and opening of K gates
- more negative
Na/K exchange pump
- 3 Na ( moves inside) and 2 K (moves outside) move in opposite directions via antiport
- this movement starts repolarization since more Na leaks out than K leaks in
-Na/K pump fires up to push Na back outside and K inside to prevent repolarization (done w active transport (ATP payment))
membrane permeability
- K is attracted to the inside’s (-) and wants to move in to be with the neg. charged protein colloids
- Na also likes being inside with the (-)
- K moves in due to non-gated channels and Brownian mvmnt
- Na has a gated channel normally closed
- proteins do not leave cell as often too big to diffuse (also are (-) charged)
Non gated (leakage) channels
always open
- proteins repel the also (-) Cl out of the cell
- K moves out and follows conc gradient (more inside than outside) (despite attracted to the colloids)
- more K and Cl leakage channels than Na because leaks more often and causes depolarization
Gated ion channels
ion channels that open or close in response to stimuli
- voltage gated
- ligand gated
Ligand gated ion channel
Open/close in response to ligand/neurotransmitter binding to receptor protein (usually glycoprotein)
voltage gated ion channel
- open/close in response to voltage changes in cell membrane
- at rest more (-) inside > outside
- Ca (+) loves the (-) of proteins and will cover the gates; need slight depolarization to remove Ca
-ex: Na and K both have voltage gated channels
Touch receptors
respond to mechanical stimulation of the skin
Temperature receptors
respond to temperature changes in the skin
potential difference
unequal charge distributes btwn immediate inside and immediate outside of PM
-70 to -90mVol
establishing membrane potential
- at equilibrium there is little mvmnt of ions across PM
- K can leak out if Na leaks in (K’s job is to counteract Na)
- If K does not leak inside it leads to action potential since the inside is more (-)
- Cl, Ca and Na not important as they have few leakage channels
- if just rely on leakage channels then Na and K would be equal; instead we use Na/K pump
- 3 Na out and 2 K in per ATP used (outside (+))
K: change resting potential
- too much K outside = depolarization/hypopolarization
- too little K outside = hyperpolarization (steeper conc gradient)
- non gated K channels: help with maintaining membrane potential
- gated K channels: initiate repolarization after action potential
Na: change resting potential
- Na’s job is to get inside membrane and depolarize ASAP
- Initiates Action Potential
- Na has strong conc gradient
- Na has few leakage channels
Ca: change resting potential
- Ca2+ is attracted to voltage-gated channels and can block those gates
- lifts off when depolarization has occurred
- Decrease Ca2+ = Na gates open and depolarization
- Increase Ca2+ = Na gates closed, membrane repolarized/hyperpolarized
Local Potentials
changes in membrane potential of a neuron (not enough for the while membrane action potential)
- caused by: ligands binding to receptors, charge change in PM, mechanical stimulation, temp change, spontaneous change.
- must be strong and/or frequent stimulus to make action potential (can add on to each other)
all-or-none principle
the law that the neuron action potentials either fires at 100% or not at all
5 action potential steps
1: resting membrane potential - voltage gated Na and K channels are closed
2: depolarization - Na gates open as activation gates open. All Na gates open and diffuse in, causing K to diffuse out at a slower rate than Na
3: repolarization - Na gates close because inactivation gates open. Now K keeps diffusing out to repolarize cell
4: after potential - Na gates close, activation gates close, inactivation gates open; Na gates return to rest
5: resting membrane potential is reestablished once K gates close
refractory period
a period of inactivity after a neuron has fired; incapable of repeating action potential
-absolute: no size of stimulus can produce another action potential
- relative: if stimulus is stronger than the threshold an action potential may occur
threshold stimulus
cause strong local potential to make action potential