Action Potentials and Synaptic Transmission Flashcards by Ashley Atkins

What is Ohm’s Law?

Rate of FLOW of charges across a membrane = current

I=V/R (current=voltage/resistance

charge, difference of charges across membrane, voltage, permeability

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When is Ohm’s law most useful?

UNEQUAL distribution of charges VERY close on either side of membrane

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Nernst potential

Membrane potential is which in/out movement of an ion is balanced/equal. EQUILIBRIUM

DIFFUSIONAL force/ energy gradient

NOT FLOW OR RESISTANCE

VOLTAGE across a membrane that is PERMEABLE to X given ratio of X in:out

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At rest, neurons typically have a membrane potential of _______ which is close to the Nernst potential for ______ which is ________.

-75mV, K+, -90mV

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At rest, which ion channels are the only ones open? What are they known as?

K+, leak channels

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What does the membrane potential of any cell depend on?

relative permeability of the membrane to each ion AND the concentration of the ion on either side of membrane

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What does it mean if the membrane potential is close to the Nernst potential of a particular ion?

That it is more permeable to that ion

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What is the modified form of the Nernst equation, considering more than 1 ion involved? More accurate.

The Goldman Field equation

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Why is the membrane potential of a neuron close to, but not the same, as the equilibrium (Nernst) potential for K+?

Because of the presence of other ions and the activity of ion pumps that contribute to the overall resting membrane potential.

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Membrane potential depends on 2 things for each ion. Name them.

1.) permeability
2.) concentration gradients

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Membranes are poorly permeable to what kind of particles? What does the membrane need for these particles?

charged, channels

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What is a channel?

pores in the membrane that allow movements of an ion

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Are channels selective to few ions which the same charge, or open to many ions with different charges?

few ions, same charge

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Can membrane permeability change very quickly?

yes

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What dictates how channels change their open/closed states?

What they are “built” to detect

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What are the different types of channels/their stimuli? (4)

1.) voltage-gated
2.) stretch/mechanical deformation- mechanoreceptors/osmoreceptors
3.) intracellular messengers
4.) extracellular messengers -ionotropic receptors (ligand binds to a receptor which is also a channel, binding opens channel and allows ion to cross membrane

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Which 3 parts of the neuron are involved in the action potential?

axon, axon hillocks, synaptic terminal

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What kind of channel does an action potential require?

sodium voltage-gated
SOMETIMES calcium voltage-gated

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What kind of feedback do action potentials rely on?

positive

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Action potentials always result in a membrane voltage change that is the same size or gradually increasing in size?

same size

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Action potentials occur very quickly/or relatively slowly? The membrane becomes more positive/negative?

Very quickly, positive (miliseconds!)

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What helps to quickly terminate the action potential?

K+ VGC

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For Na+/K+ ATPase channel, Na+ go in or out? How many? K+?

3 Na+ out, 2 K+ in

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K+ concentrations are high inside/outside, so it diffuses in/out? This is why we need the pump

out

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Step 1 is the _____ ________ _________

resting membrane potential

What is step 2?

depolarization

What does is depolarization activated by?

The inside of the membrane becoming more positive

What is the membrane potential that activates Na + VGC to open and Na+ to enter the cell?

~-55mV

What channels open in response to depolarization of the cell membrane?

Na+ VGC

How do Na+ initiate and propagate action potentials ?

By allowing rapid influx of sodium ions

When do K+ VGC open?

In response to depolarization but typically with slight delay

What is the role of K+ VGC?

contribute to REPOLARIZATION and RESTORATION of resting membrane potential by allowing efflux of potassium ions

What is the period called after an action potential has begun, when a second action potential cannot be triggered for about 1-2 msec, no matter how large the stimulus?

absolute refractory period- time required for the Na+ channel gates to reset to their resting positions

Why is absolute refractory period important?

so that action potentials moving from trigger zone to axon terminal cannon overlap and cannot travel backward

What's happening in the relative refractory period?

some but not all Na+ have reset and K+ channels are still open. Na+ that have not quite returned to their resting position CAN BE REOPENED by a stronger-than-normal graded potential.

What limits the rate at which signals can be transmitted down a neuron?

refractory periods

What are depolarizations or hyperpolarizations whose strength is directly proportional to the strength of triggering event. They lose strength through cell.

graded potential

_____________ made a neuron more likely to fire an action potential. ______________ make a neuron less likely to do so.

depolarizing graded potentials hyderpolarizing graded potentials

Which is faster, activation gate or inactivation gate?

activation

What initiates an action potential?

depolarization

Difference in fiber size/ speed of impulse?

A fibers=largest/fastest/myelinated (touch, pressure, position, heat, cold) final common pathway (12-130 m/sec) B fibers=medium/medium speed/Non-myelinated15m/sec) viscera to brain/SC, autonomic efferents to auto. ganglia C fibers= smallest, non-myelinated (.5-2m/sec) pain, touch, pressure, heat, cold from skin, pain impulses from viscera, efferents to heart/smooth muscle/glands

In a chemical synapse, which neuron releases a neurotransmitter?

presynaptic

In a chemical synapse, where are the receptors?

post-synaptic cell membrane

What transport mechanism is used in chemical synapses for NT to cross the synaptic cleft from pre-synaptic to post-synaptic membrane?

diffusion

Where is synapse located? What expresses the receptor for NT?

between a dendritic spine or an axon terminal dendritic spine

NT vesicles are synthesized and packaged where? Transported down the axon via what? What is this called??

rER and Golgi microtubules fast axonal transport

Where are NT synthesized?

cytosol of presynaptic terminal

How are the NTs transported into the viscle?

proton pump

In the presynaptic terminal cytoskeleton, vesicles bind to ______ and are transported to release sites aka _________ close to synapse

actin, active zone

Which type of channels are used in NT release?

calcium VGC which leads to release and diffusion across synaptic cleft

What does the entry of calcium trigger?

exocytosis of synaptic vesicle contents

5 steps of neurotransmitter release

1.) AP depolarizes axon terminal 2.) depolarization opens Ca2+ VGC and Ca2+ enters the cell. 3.) Ca2+ triggers exocytosis of synaptic vesicle contents 4.) NT diffuses across syn. cleft and binds with receptors of the postsyn. cell. 5.) NT binding initiates response in the postsyn. cell.

Key players in vesicle release?

v-SNARES, t-SNARES, complexin, synaptotagmin

v-SNARES are attached to what? What do they do?

vesicles, they "force" the vesicles to fuse with the presynaptic membrane and dock with t-SNARES

What type of protein is synaptobrevin?

v-SNARE

What protein complex is attached to the pre-synaptic membrane and "grabs" the v-SNARE?

t-SNARE (target)

What are 2 t-SNARES?

syntaxin and SNAP-25

Which molecule prevents premature release after v-SNARE and t-SNARES engage?

complexin

Name the calcium-binding protein that "knocks" complexin off the v-SNARE/t-SNARE complex

synaptotagmin

What does the toxin released by Clostridium botulinum do?

impairs assembly and function of v-SNARES and t-SNARES

What does Botox A bind to?

SNAP-25 (v-SNARE)

Which enzymes degrades acetylcholine to acetate and choline?

acetylcholinesterase

Once NTs are degraded, what reabsorbs them? Where are they then diffused out?

astrocytes and presynaptic terminal. Out of cleft and carried by blood

What is the result of NTs causing cation channels to open?

depolarization for sodium and calcium hyperpolarization for potasium

What is the result of NTs causing anion channels opening?

hyperpolarization

Many NTs cause what kind of effect? (ex. G-protein)

intracellular cascade of second messengers. Can open/close for longer periods of time. Change kinase activity, and gene expression

What do ionotropic receptors do?

open an ion channel when they bind to their ligand

Which type of receptor binds to the NT glutamate which causes Na+ and Ca2+ channel to open

NMDA receptor

Which receptor binds to acetylcholine, causing Na+ channels to open?

Nicotinic acetylcholine receptor

Which receptors bind to GABA and glycine causing Cl- channels to open?

GABA(a) and glycine receptors

Most ____________ receptors are linked to G-protein signaling.

metabotropic receptors

What is the NT of the neuromuscular junction and expressed through the brain?

acetylcholine

What is the most important inhibitory NT of the "intracranial" CNS?

GABA

What is the most important inhibitory NT of the spinal cord?

glycine

What is are the most common excitatory NT of the CNS?

glutamate

NMDA receptors are very important for what?

learning and memory

Which NT has autonomic NS functions, cortical and limbic system roles

norepinephrine

If NT binds to an inhibitory receptor what happens? excitatory?

hyperpolarization (membrane becomes more negative) depolarization (membrane becomes more positive)

What brings about graded potentials in the dendrites and cell bodies?

graded potentials

Graded potential is any change in membrane potential that DOES NOT result in what?

action potential Include changes in membrane potential that are below the threshold for an action potential or occur in areas of the cell that do not have Na+ VGCs

Which lasts longer, graded or action potential?

graded

If multiple graded potentials add up in a "staircase" fashion over time, this is called what?

temporal summation

What does it take for graded potentials to initiate an action potential in a Na+ VGC?

The net result of all EPSPs and IPSPs are integrated and the axon hillock and if it brings the hillock to threshold, an AP (or string of APs) will fire

What kind of receptors can have very long-lasting effects including protein synthesis and long-lasting intracellular signals?

metabotropic