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element is in high concentration in one place, it tends to move to an area of lower concentration
when charge of one kind accumulates in one place it tends to move away to an area of different charge
Sodium potassium pump
-helps maintain charge
-pushes 3 NA+ out, 2 K+ in
3 main contributers of neural transmission
- Alan Lloyd Hodgkin
- Andrew Huxley
When a neuron becomes active it releases....
Neurotransmitters interact with...
receptors, that ultimately cause closed ion channels to open and permit flow of ions
when channels open up and permit + ions to flow into the cell, cell becomes....
when channels open and permit - ions to flow into the cell becomes....
EPSP, Excitatory post-synaptic potential
it is depolarization of the neuron
-Na flows in
IPSP, inhibitory post-synaptic potential
hyperpolarization of the neuron
-Cl flows out
brief description of post-synaptic potentials
-begins at dendrites or cell bodies
- -moves passively along dendrites and cell body
- *moves rapidly
-magnitude of signal diminishes with distance
-many EPSP and IPSP in the post-synaptic neuron all the time
-how these PSPs interact ultimately determines whether that cell will fire an a
How these PSPs interact ultimately determines whether that cell will fire...
an action potential
occurs when excitatory potentials from many different presynaptic neurons cause the postsynaptic neuron to reach its threshold and fire.
ex) many shovels fill up a hole all at once
occurs when a single presynaptic neuron fires many times in succession, causing the postsynaptic neuron to reach its threshold and fire.
ex) one shovel trying to fill a hole
a single neuron may receive tens to hundreds of synaptic contacts
importance of position of summation
PSPs generated distal portions of dendrites will impact less than PSPs generated proximal (close) to cell body.
-PSPs diminish with distance
Summation of ESPSPs and IPSPs sometimes leads to the generation of
IF cell is depolarized past a certiain value then...
an action potential will be generated
-value closer to zero
description of action potential
-all or none response
-action potential triggered by crossing of threshold is same size every time one is triggered.
Ion channels that are always open and sodium potassium pump are critical for...
establishing the resting membrane potential of the cell (-70)
ion channels that open in response to neurotransmitters
-these are critical for generating EPSP and IPSPs
Voltage-gated ion channels
some ion channels will only open when neurons membrane potential has reached a certain value
-essential for generating action people
when enough PSPs have summated to bring membrane to potential to threshold
-voltage-gated sodium channels open
when voltage-gated na+ channels open...
Na+ floods into the cell because Na+ therefore has huge electrostatic pressure to move into the cell.
Another reason When voltage-gated Na+ channels open...
Na+ moves into the cell because pf its concetration gradient
As Na+ moves into the cell, the membrane potential....
- depolarizes further
- *goes near positive
when voltage-gated K+ channels open...
-Na+ still flows into the cell via their channels
but K+ flows out of the cell as well
-K moves out because of its concentration gradient and eletrcostaci pressure`
Summary of action potential
- 1. PSPs bring membrane to threshold
- 2. Na+ gates flood open
- 3. As Na+ floods in, membrane depolarizes
- 4. As membrane potential rises, voltage gated potassium channels open
- 5.At 50+, Na gates shut off(this point neuron is positive reltive to the outside of cell-causes K to come out more because of gradients)
- 6. As membrane potental begins to fall, K channels slowly begin to close
3 stages of action potential
(stages) Rising phse
Na floods into the cell
Na closes and K comes out
-K channels slow to close
- - sodium potassium pump going to work to bring K back in
- *3 Na out and 2 K in