Action potentials Flashcards
(28 cards)
what is a presynaptic neuron
what is a post synaptic neuron
how does a chemical signal get converted into a electrical signal
- a chemical signal (neurotransmitter) binds to and opens chemically gated ion channels
- ions flow in or out, changing the voltage at a localized area of membrane
- if the membrane voltage reaches -60mV at the axon hillock an electrical signal (action potential) begins
what are the 3 types of gated ion channels
- chemically
- voltage
- mechanically
explain how a chemically gated ion channel works
- stimulus - chemical neurotransmitter binds to ion channel
- channel changes shape - opens
- ion cross the membrane driven by the electrochemical gradient
- the neurotransmitter unbinds, causing the channel to close
explain how a voltage gated ion channel works
- stimulus - membrane depolarizes to threshold voltage (-60mV)
- channel changes shape - opens
- ion cross the membrane driven by the electrochemical gradient
- membrane potential changes will cause the channel to inactivate or close
explain how a mechanically gated ion channel works
- stimulus - deformation of membrane (eg stretch or squish)
- channel changes shape - opens
- ion cross the membrane driven by the electrochemical gradient
- when the membrane returns to original shape the channel closes
what type of ion gate is found in the dendrites and cell body
chemically gated Na and Cl (and others) channels
(mechanically gated ion channels are found on dendrite some sensory neurons)
what type of ion gate is found in the axon hillock
voltage gated Na and K channels
what type of ion gate is found in the axon
voltage gated Na and K channels k
what type of gate is found in the axon terminals
Voltage gated Ca channels
how is an electrical gradient created
at rest, the intracellular space has more negative charge than the extracellular space
what is the resting membrane potential
-70mV
what is a local potential
an excitatory or inhibitory change in voltage in a small location (localized area) somewhere on the dendritic/cell body membrane of a post-synaptic cell
why can local potentials also be called post-synaptic potentials (PSP)
because they occur on the membrane of the post-synaptic cell
why can local potentials also be called graded potentials
because they vary in size depending on how many ions enter or exit
how do excitatory local potentials or excitatory post-synaptic potential (EPSP) form
- a presynaptic neuron releases excitatory neurotransmitter
- when neurotransmitter binds, it opens chemically-gated Na channels
- Na enters post-synaptic cell, causing depolarization (membrane becomes more positive)
how do inhibitory local potentials or inhibitor post-synaptic potential (IPSP) form
- a presynaptic neuron releases inhibitory neurotransmitter
- when neurotransmitter binds, it open chemically gated K or Cl channels
- K exits or Cl enters postsynaptic cell, causing hyperpolarization (membrane becomes more negative)
what is summation
the summation of local potentials is the combination of excitatory and inhibitory potentials
local potentials are summed in what 2 ways
- spatial summation
- temporal summation
what is spatial summation
local potentials are a summed input from multiple presynaptic neurons
what is temporal summation
local potentials are a summed input from repeated firing from one presynaptic neuron
why are presynaptic inputs summed at the axon hillock
- the axon hillock has a high density of voltage gated channels
- threshold potential is the key that opens voltage gated channels
- if summation occurs at or above -60mV, voltage gated Na channels open at the axon hillock
what is the 1st step of an action potential
voltage gated Na channels open when a membrane depolarizes to -60mV
(voltage gated K channels are triggered to open at -60mV but open more slowly that voltage gated Na channels)
