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concentration gradient
element is in high concentration in one place, it tends to move to an area of lower concentration
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electrostatic pressure
when charge of one kind accumulates in one place it tends to move away to an area of different charge
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Sodium potassium pump
-helps maintain charge
-pushes 3 NA+ out, 2 K+ in
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3 main contributers of neural transmission
- Alan Lloyd Hodgkin
- Andrew Huxley
-John Eccles
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When a neuron becomes active it releases....
nuerotransmitters
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Neurotransmitters interact with...
receptors, that ultimately cause closed ion channels to open and permit flow of ions
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when channels open up and permit + ions to flow into the cell, cell becomes....
depolarized
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when channels open and permit - ions to flow into the cell becomes....
hyperpolarized
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EPSP, Excitatory post-synaptic potential
it is depolarization of the neuron
-Na flows in
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IPSP, inhibitory post-synaptic potential
hyperpolarization of the neuron
-Cl flows out
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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
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(PSP) info
-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
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How these PSPs interact ultimately determines whether that cell will fire...
an action potential
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spatial summation
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
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Temporal summation
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
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summation
a single neuron may receive tens to hundreds of synaptic contacts
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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
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Summation of ESPSPs and IPSPs sometimes leads to the generation of
action potential
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IF cell is depolarized past a certiain value then...
an action potential will be generated
-value closer to zero
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description of action potential
-all or none response
-action potential triggered by crossing of threshold is same size every time one is triggered.
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Ion channels that are always open and sodium potassium pump are critical for...
establishing the resting membrane potential of the cell (-70)
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Ligand-gated
ion channels that open in response to neurotransmitters
-these are critical for generating EPSP and IPSPs
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Voltage-gated ion channels
some ion channels will only open when neurons membrane potential has reached a certain value
-essential for generating action people
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when enough PSPs have summated to bring membrane to potential to threshold
-voltage-gated sodium channels open
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when voltage-gated na+ channels open...
Na+ floods into the cell because Na+ therefore has huge electrostatic pressure to move into the cell.
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Another reason When voltage-gated Na+ channels open...
Na+ moves into the cell because pf its concetration gradient
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As Na+ moves into the cell, the membrane potential....
- depolarizes further
- *goes near positive
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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`
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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
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3 stages of action potential
rising phase
repolarization
hyperpolarization
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(stages) Rising phse
Na floods into the cell
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(stages) Repolarization
Na closes and K comes out
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(Stages) Hyperpolarization
-K channels slow to close
- - sodium potassium pump going to work to bring K back in
- *3 Na out and 2 K in
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