electrochemical physiology (4b) Flashcards
what is irritability
the ability to respond to a stimulus and convert it to a nerve impulse
what is conductivity
ability to transmit the impulse to other neurons, muscles or glands
what is an action potential
electrochemical signal involving sodium and potassium ions that cross the cell membrane through ion channels
what is the resting membrane potential
when the neuron is not conducting an impulse
as long as the inside of the membrane is more negative than the outside the cell is inactive
characteristics of the resting membrane potential
the inner surface of the membrane is more negative than the outer surface
more sodium ions outside the membrane than inside
more potassium ions inside than outside
more calcium ions outside than inside
more chlorine ions outside than inside
what maintains the resting membrane potential state
sodium potassium pump
how is the action potential started
neuron has to receive enough electrical stimuli to depolarize (sodium gates open) the cell membrane potential to the threshold
enough sodium of calcium must enter the neuron from the dendrites and cell body to push the membrane potential to the threshold for firing to occur
what is the all or nothing law
neuron either fires or doesnt
action potential always reaches the same amplitude of depolarization (no in between states)
what are the steps of the action potential
depolarization and repolarization
what is depolarization
sodium ion channels open and sodium enters the axon (following gradient so no energy needed)
membrane potential becomes less negative
what is repolarization
potassium ion channels open and potassium leaves the axon (following gradient so no energy needed)
membrane potential becomes negative
neuron becomes impermeable to sodium
does the sodium potassium pump continue to work during the action potential
yes but is unsuccessful
what is the refractory period
following the action potential, the neuron cant fire again for a period
sodium channels are closed and cant be reopened
what are the subcategories of refractory period and what are they
absolute refractory period: no amount of stimulus can force the neuron to fire again
relative refractory period: large (greater than threshold) stimulus can force neuron to refire
what makes it so that the impulse always goes from the hillock to the terminals
due to refractory period of sodium channels
what is the graded potential
stimuli causing the membrane potential to be more positive, initiates impulse
sodium and calcium ions entering neuron
what is the last step of a neuron firing
the sodium potassium pump restoring the initial ionic concentrations across the membrane (not the same as repolarization)
what is synaptic transmission
communication between neuron and adjacent cell that occurs by neurotransmitters
what are neurotransmitters
chemical messengers (water-based) that are stored and released by axon terminals
responsible for transmitting the impulse to the next cell
are neurotransmitters specific
yes they change based on the neuron and the receiving cell has specific receptors for each neurotransmitter
characteristics of synaptic transmission
occurs at the synaptic cleft (20nm wide)
neurotransmitters diffuse across the gap from presynaptic neuron to postsynaptic neuron (when its two neurons)
what is the synaptic knob
swelling at the end of the axon terminal of the presynaptic neuron
what are the steps of neurotransmitter release
nerve impulse reaches synaptic knob of presynaptic neuron
impulse causes calcium to move into the synaptic knob from the outside
calcium causes the neurotransmitter-containing vesicles to bind to the presynaptic membrane and release the neurotransmitter into the synaptic cleft
neurotransmitter diffuses across the cleft and binds to receptors on the postsynaptic neuron
causes ion channel on postsynaptic membrane to open
how are neurotransmitters removed
can be deactivated by enzymes or pumped back into knob of the presynaptic axon
how fast are neurotransmitters removed from synaptic cleft
hundred microseconds
very bad for them to stay there
