Nerve impulse/action potential Flashcards
What are the two types of channels for ions to cross a membrane
Ungated and gated channels
What are ungated channels
open all the time
What are gated channels
triggered by some stimulus to open
About positive and negative ions
they are located inside and outside a cell, potassium (K+) is high within the cell and sodium (Na+) is high outside the cell. the main negative outside the cell is chlorine (Cl-)
What is the resting state
Not transmitting an action potential/impulse. resting neurons are said to be polarized, in other words there is a charge different between the inside and outside of the neuron. this electric potential called the resting potential is approximately 70mv (may range from 50mv to 100mv). resting potential occurs because of 2 main factors
a: first the membrane is 50 times more permable to potassium (K+) than to sodium (Na+), therefore more potassium diffuses out of the cell than sodium diffusing in, this occurs through ungated channels
b: second, the special sodium/potassium pumps active transport (use energy) 3 sodium out of the cell for ever 2 potassium into the cell, these two events cause an excess of positively charged ions on the outside making the outside positive and the inside negative at resting.
note- gated channels for both sodium and potassium are closed at this point
What is depolarization
when a neuron is sufficiently stimulated by a neurotransmitter or a stimulus the permeability of the membrane changes in the region of stimulation, gated channels for sodium open causing an influx of sodium ions into the cell while the gated channels for potassium remain closed, this changes the polarity in that region of the neuron making it positive inside and negative outside. this in turn stimulates the adjacent region of the neuron to do the same thing and a wave of depolarization continues down the neuron like a chain reaction. this impulse or action potential as it is called finally reaches the synaptic knobs and neurotransmitters get released
What is re-polarization
as impulses travel down the axon but the sodium gates close potassium gates open. potassium starts to flow out of the cell restoring the neuron to positive outside and negative inside the cell.
once concentration of potassium reaches a certain amount gates will begin to close slowly, because the potassium gates close so slow, the membrane potential sometimes gets hyperpolarized (too much potassium outside) this is why you can see an undershoot on the graph. during this time no further impulse can be transmitted. this is called the refractory period
What is the refractory period
time during which no more impulses can occur, the resting state must be restored before any more impulses can occur. sodium/potassium pumps and the outward flow of potassium ions are critical to restoring this resting state. like a gun that must be reloaded before it can be fired again
What is the all or none principal/threshold
a neuron is governed by the all or none principle. this means that in order for an impulse to be started, a stimulus must have a certain min strength called the threshold. if the threshold is not reached then an impulse wont be started. in addition any stimulus above the threshold will start exactly the same impulse (pulling a guns trigger harder wont make it fire faster)
What are neurotransmitters
chemicals produced in tiny synaptic vesicles (membrane sacs) at the end of the axon synaptic knobs. when a nerve impulse reaches the synaptic knobs neutransmitters are released and diffuse across the synapse. the synapse is the space between neurons. the neurotransmitters are picked up by receptor molecules on the dendrites of an adjacent neuron. sometimes when the terminal branches of an axon ends at a muscle fibre, the neurotransmitter moves across the neuromuscular junction and is picked up by the muscle where it can initiate contraction of that muscle. (can affect many different types of cells, not only neurons)
