what does the neuron do?
it recieves stimuli and conducts an electrical impluse
why is the membrane:cytoplasam ratio high in neurons?
it is high because the electrical impulses conducted by neurons happen through the ion channels found in the membrane
what does the neuron do to the electrical charge across the membrane ?
no matter what signal the neuron is sending, it changes the electrical charge across the neuron membrane
what are myelin sheath ?
myelin sheaths are basically when schwann cells wrap the plasma membrane around an axon
what are the areas that dont have shwann cells called?
their called nodes of ranvier
what do dendrites do?
dendrites branch out alot which allows the axon cell body to recieve 100,000 signals at once
what is the synaptic cleft ?
the synaptic cleft is the space between the synaptic terminal of one neuron and the dendrites of the other neuron
how do neurotransmitters use these clefts?
when their released from the pre-synpatic neuron , they travel through the cleft in order to conduct an electrical impulse in the post synaptic neuron
what is the method of measuring electrical charge difference across an axon ?
we can use electrodoes with wires in them
penetrate one side of the axon with an electrode , put another electrode into the extracellular fluid and attach both to the voltmeter to measure charge difference
what do we find in a resting cell ?
1) Na+/K+ pumps are working
2) the leak channels are open
3) no net flux of ions
4) gated channels are closed
the resting potential is -70mV
what is the first change in the membrane potential that is required by the action potential ?
it requires a stimuli
the ligand gated Na+ channels can trigger action potential in a post synaptic cell by introducing small inital depolarizations at the dendrites
what happens when the ligand gated channels introduce the small inital depolarizations ?
the neurotransmitters from the pre-synaptic cell traverse through the cleft and bind to the receptors on the post synaptic cell, doing so triggers the release of sodium into the cell
if this depolarization causes the membrane potential to reach the treshold of -55mV then action potential occurs , if not then the membrane potential goes back down to resting(all or none response)
where are the sums of the dendrites depolarizations and ligand gated channels found?
what happens if treshold is reached here
their found at the axon hillock , if the membrane treshold potential is reached here then sodium rushes into the cell passively
what happens next after the stimulus?
after NA+ rushes into the axon ,the membrane potential reaches 40+mv causing the membrane to become depolarized
what happens after depolarization?
when the membrane potential is at +40mv this causes the potassium channels to open and K+ rushes out of the cell down its steep gradient , this causes membrane potential to go back down to resting
what happens after repoalrization?
as the K+ channels begin to close around the membrane resting potential, the potential overshoots -70Mv and drops even further down , this is when the membrane becomes hyperpolarized and the K+ channels begin to close
what returns the cell back to the resting potential
the Na+/K+ pumps and leak channels return the cell to resting membrane potential
what is the refactory period
the length of time where there is absolutely no chance of AP occuring
what is relative refactory period ?
when there is a possibility of the action potential to occur but its unliekly because it would require an enchanced stimulus
what is AP propagation ?
basically nerve impulses are propagted along an axon because the action potential at one site affects the action potential at the next site
Local flow of current upon depolarization means the region just
ahead of the action potential readily reaches the threshold voltage of -55mV
can the direction of propagation go backwards?
no it cant because the Na+ channels are inactivated and membrane is hyperpolarized
what is the saltory conduction ?
the action potential of one node of ranvier triggers the depolarization at the next rode of ranvier and nerve impulses appear to jump from node to down the axon
what is found in neurons where there is a myelin sheath
1) no significant access to the extracellular fluid
2)sodium potassium channels are absent
3)saltory conductions occur, this allows the signal to propagate down the axon 20 times faster
what is the first step that happens when the action potential reaches the synapse?
Ca2+ is low in the cytoplasam but the arriving of AP in the cytoplasam causes the channels to open
