Ion Channels--Fitz - Sheet1

Question 1

An ______ is triggered by a graded potential

Answer 1

action potential

Question 2

A graded potential causes the membrane to depolarize until it ….

Answer 2

reaches the threshold for activation of voltage-gated Na+ channels

Question 3

When the __________ channels _____ and ________ channels _____, the action potential ____ (between 0 and +40 mV).

Answer 3

voltage-gated Na+ channels; inactivate; voltage-gated K+ channels open; peaks

Question 4

delayed rectifier K+ channels

Answer 4

A group of slow opening and closing voltage-gated potassium channels.

Because of their delayed activation kinetics they play an important role in controlling ACTION POTENTIAL duration.

Question 5

After an action potential, Vm then repolarizes, overshoots the resting membrane potential (causing the _______)

Answer 5

afterhyperpolarization

Question 6

GABA channel

Answer 6

is a chloride channel, ligand gated.

Can’t really do too much in regard to the cell Vm.

Open GABA receptors decreases membrane resistance. Affects membrane stabilization.

Question 7

AP amplitude and Ca++ influx

Answer 7

Ca++ influx happens when Ca++ channels open.

So increase in intracellular Ca++ conc. cauese the AP waveform to elongate.

Question 8

synaptic integration: spacial vs. temproal

Answer 8

spacial: more presynaptic neurons will cause increase in EPSP in axon hillock.

temporal: if the presynaptic neuron produces signalling with a high enough frequency, the MP can go from -70 to -40mV.

Question 9

Graded Potential

Answer 9

Amplitude is proportional to the strength of the stimulus. Amplitude is generally small (a few mV to tens of mV). No refractory period.

Occur due to external stimuli (in sensory neurons) or by neurotransmitters released in synapses, where they cause graded potentials in the post-synaptic cell.

Question 10

Action Potential

Answer 10

Always lead to depolarization of membrane and reversal of the membrane potential.

Voltage-gated Na+ and voltage-gated K+ channels.

Absolute and relative refractory periods are important.

Triggered by membrane depolarization to threshold

Question 11

What two ion channels are primarily responsible for the action potential?

Answer 11

Voltage-gated Na+ and voltage-gated K+ channels are responsible for the neuronal action potential.

Question 12

What ion channels are primarily responsible for graded potentials?

Answer 12

ligand-gated (extracellular ligands such as neurotransmitters), mechanosensitive, or temperature sensitive channels, or may be channels that are gated by cytoplasmic signaling molecules.

Question 13

Opening of _______ channels cause a rapid depolarization resulting in an action potential.

Answer 13

Voltage-gated Na+ channels

Question 14

afterhyperpolarization is caused by…

Answer 14

voltage-gated K+ channels remaining open.

Question 15

Absolute refractory period

Answer 15

The period of time when the majority of voltage-gated Na+ channels are inactivated.

No amount of depolarizing current can cause an action potential

Question 16

Describe voltage gated Na+ channels.

Answer 16

Nerve and Muscle cells. Inactivated and closed state. Inactivation follows AP and is a period until the closed state is achieved–only then can an action potential be produced again.

Question 17

Relative refractory period

Answer 17

Period during which a stronger than normal stimulus is needed in order to elicit an action potential.

Question 18

opening of the Na+ channels, spontaneously and rapidly leads to…

Answer 18

innactivation = absolute refractory period

Question 19

graded potentials, action potential, unidirectional, bidirectional

Answer 19

AP = unidirectional

Question 20

Saltatory conduction

Answer 20

Occurs in myelinated axons and is a lot faster because only the nodes of Ranvier are involved in action potential conduction.

The action potential jumps down the axon from node to node.

Myelinated sections have Schwann cells that wrap VERY tight (no extracellular space for ions)

Question 21

conduction velocity is determined by two things…

Answer 21

diameter and myelination

Question 22

2 types of synapses: electrical and chemical

Answer 22

Electrical synapses feature extremely rapid, passive, bidirectional signals.

3 steps in chemical neurotransmission: 1) neurotransmitter release, 2) receptor activation and 3) neurotransmitter inactivation.

Question 23

Neurotransmitter release from the presynaptic terminal (5 steps)

Answer 23

1) depolarization of the terminal membrane, 2) activation of voltage-gated Ca2+ channels, 3) Ca2+ entry, 4) a change in the conformation of docking proteins, 5) fusion of the vesicle to the plasma membrane, with subsequent release of neurotransmitter into the synaptic cleft.

Question 24

Receptor mechanism: Slow = _______ and Fast = _____

Answer 24

Slow = Metabotropic; Fast = Ionotropic

Question 25

Receptor mechanism: Inhibitory = _______ and Excitory = _____

Answer 25

Inhibitory = producing EPSP; Excitory = producing IPSP

Question 26

EPSP

Answer 26

caused chemically by release of neurotransmitters from pre-synaptic cell.

Are graded potentials (i.e. additive).

Large EPSPs increase probabiliy of achieving treshold for AP.

Question 27

IPSP

Answer 27

a kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential.

Question 28

3 mechanisms for termination of the actions of neurotransmitters

Answer 28

diffusion (e.g. amino acid neurotransmitters like glutamate and GABA),

enzymatic degradation (e.g. ACh) and

reuptake (e.g., monoamines)

Question 29

Neuron drug targets relating to neurotransmitters

Answer 29

Block degredation = acetylcholinesterase inhibitors.

Block reuptake = monamine neurotransmitters (dopamine, norepinephrine and serotonin).

Question 30

Botulinum toxin

Answer 30

blocks neuromuscular conduction by inhibiting synaptic vessicle release of acetylcholine from peripheral motor nerve endings