9-4 Action Potentials

1865 Julius Bernstein

when and who discovered the action potential recorded from frog nerves and called it the “negative variation”? this was before neuron staining and before Na/K pump identified (first action potential recorded in squid)

yes

are all cells polarized?

polarized

what does it mean to have a positive or negative charge?

negative

neuron membranes have a relatively what charge at rest?

when ions pass through the cell

when do charges change?

action potential

what is it called when neurons can alter polarization for a brief period of time?

stimulus, depolarization, action potential, repolarization, refractory period, resting state

process of action potential

refractory period

what happens at the end of an action potential to get back to baseline?

sodium

what does depolarization involve?

potassium

what does repolarization involve?

40

at what mV do the voltage gates close?

1. stimulus (something happens)

2. depolarization of cell membrane (voltage gets closer to 0mV)

3. if -55mV threshold is reached, voltage gated sodium channels open and an action potential will happen

4. In the rising (depolarization phase), Na+ floods into the cell through voltage gated Na+ channels

5. at +40mV, the voltage gated Na+ channels close

6. voltage gated K+ channels open, and K+ flows out of the cell (repolarization)

7. Because K+ ion channels are sluggish, the neuron is briefly hyperpolarized (refractory period)

8. to return back to resting potential, neuron uses sodium/potassium pumps (3 Na+ out/K+ in)

steps of action potential

myelinated, larger

action potentials move faster when axons are ___ and ____

saltatory conduction

what does myelin help with?

Na+ channels

myelinated axons don’t have _____ between nodes of ranvier

at exposed nodes of ranvier

where are Na+ channels located on axon?

unmyelinated axon

what axon takes a lot longer to reach axon terminal?

the action potential cannot travel continuously along axon, it jumps from one node to the next, which increases signal speed and consrves energy.

how does myeline help with saltatory conduction?

from axon hillock to axon to axon terminal

how does action potential travel?

multiple sclerosis

disorder where immune system attacks and damages myelin sheath, and without myelination, electrical signals slow down, scramble or stop completely leading to trouble walking, balance issues, muscle weakness. damaged issues develop scar like tissues called sclerosis, over time the nerve fibers can be injured or destroyed.

1. influx of Na+ ions

2. cell membrane depolarizes

3. voltage gated Ca2+ channels activate

4. Ca2+ flows into terminal

5. intracellular Ca2+ activates process that leads to neurotransmitter release

6. neurotransmitter molecules float in synaptic cleft (some bind to ligand channels, some bind to other receptors)

7. ligand channels allow ions to flow in/out of post synaptic cell (will change membrane potential of post synaptic

what happens at axon terminal?

synaptic cleft

microscopic space between two neurons

action potential reaches axon terminal, neurotransmitter is released from vesicles, neurotransmitter molecules diffuse into synaptic cleft

what happens during synaptic transmission?

key

in synaptic transmission, neurotransmitters become the ___ to open ligand gated ion channels which allow ions to flow into the post synaptic neuron

excitatory, inhibitory

synaptic transmission can be ____ or _____

excitatory synaptic transmission

action potentials from neuron A cause more action potentials in neuron B

inhibitory synaptic transmission

action potentials from neuron A suppress action potentials in neuron B

the neurotransmitter

what tells the transmission to be excitatory or inhibitory?

acetylcholine

neurotransmitter with excitatory actions that helps the brain encode new info, form memories, and maintain working memory (helps with attention, arousal, and filtering background noise)

donepezil, botox

drugs that affect acetylcholine (used to treat alzheimer’s disease - more excitation) and (release of Ach from presynaptic motor neurons (less excitation)

more

more excitation = ____ possibilities for memories or new information

GABA

neurotransmitter with inhibitory actions

reduces nerve cell hyperactivity (controls fear, stress, anxiety)

what does GABA do?

valium (anxiety - increases inhibition), klonopin (treats seizures, panic disorder, anxiety - increases inhibition)

drugs that act on GABA receptors