Action Potentials, Interneuronal Communication, Week 3 Lab Flashcards by Mia Sassano

Explain how a receptor potential in a sensory neuron can lead to the initiation of an action potential at the trigger zone of the sensory axon

Opening transduction channels in the membrane of sensory receptors from stimuli
Graded potentials generated to reach threshold.
Voltage gated Na+ channels open, Na+ flows inward, and depolarizes the membrane.
Na+ channels inactivate, Voltage gated K+ channels show their effect and repolarize the membrane.
K+ channels close once after hyperpolarizing the membrane
Return to RMP

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Transduction channels are located in

Sensory receptors

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What channel mediates sensory receptor potential (graded potentials)

Transduction channel

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The size and duration of the receptor potential in transduction channels is determined by

how long and how many channels are open

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Voltage gated Na and K channels are located…

in the trigger zone and throughout the length of the axons

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What channel mediates action potentials

Voltage gated Na and K channels

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The voltage gated Na and K channels open when

the membrane potential is depolarized to -55 mV from rest

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Voltage Na channels open __, then VG K channels open more __

first (faster), slowly

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Compare and contrast VG Na and K channels…

VG Na channels open and cause depolarization, and inactivate.
VG K channels open and cause repolarization and hyperpolarization (don’t inactivate)

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VG Na channels are what kind of feedback

positive

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VG K channels are what kind of feedback

negative

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VG Na channels stop because

inactivation stops depolarization

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How do VG K channels close

by repolarizing membrane potential and removing the stimulus that opens them

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all voltage gated channels are closed, membrane at resting membrane potential

resting state

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when membrane potential reaches threshold (graded potential), Na channel gates opens, Na ions flow in and cause a positive charge buildup (depolarization).

Depolarizing phase

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Repolarizing phase begins when

Na+ channel inactivation gates close and K channels open; membrane becomes repolarized once K+ ions leave the neuron and negative charges are left behind

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The hyperpolarizing phase begins when

as more K+ ions leave the neuron the more negative charges build up in the membrane and hyper-polarizes; K+ channels eventually close and resting membrane potential is restored

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During the resting membrane potential, what channels are active

only leak channels will then open and close.

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refers to the passive process, also known as graded potential–but is localized in that trigger zone, initiating the action potential

Local Current Flow

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Local current flow is decremental due to the

loss of ions across a membrane through leak channels

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The propagation of action potential is a __ process

active

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During the propagation of action potential, depolarization causes…

VG Na+ and K+ channels to open and local current flow to initiate more voltage gated channels to open at the next Node of Ranvier.

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In myelinated axons, leak channels are…

insulated by myelin–leads to loss of current flow and bette conduction

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In myelinated axons, Ion channels are only located at the

Nodes of Ranvier

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Myelinated axons have what conduction

saltatory

The conduction in myelinated axons moves way __ than unmyelinated axons because...

faster, due to insulation of myelin

In an unmyelinated axon, ion channels are...

placed all along the axon

Unmyelinated axons have what kind of conduction

continuous

Unmyelinated axons take a __ time sending signals down the axon

longer

Describe how stimulus intensity is encoded by neurons

The greater the stimulus strength above threshold, the greater the frequency of action potentials

Frequency refers to...

how many and how long

Explain how an increase in extracellular K+ concentration can have a dramatic effect on the Equilibrium potential for K, the resting membrane potential, and the neural status of a person.

- The equilibrium potential and resting membrane potential would depolarize - The neural status of a person would be less likely to repolarize and stuck in a depolarized state.

Define threshold

Minimum amount of stimulus required to initiate an action potential

The time during which a cell is absolutely unable to fire another action potential

Absolute refractory period

The time after an action potential when a larger stimulus is required to generate a second action potential, second stimulus can only evoke an action potential if this stimulus is relatively strong

relative refractory period

Describe chemical neurotransmission, listing in correct temporal sequence events beginning with the arrival of an action potential at the pre-synaptic axon terminal and ending with a graded potential generated at the postsynaptic membrane

- Action potential from VG Na+ and K+ channels arrive at axon terminal, causing a depolarization that opens up the VG Ca2+ channels. - Calcium in the ECF, enters the inside of the cell - Calcium acts with proteins in the axon terminals that help neurotransmitters dock/diffuse at the presynaptic membrane. - Vesicles of neurotransmitters fuse through exocytosis - Neurotransmitters are released into the synaptic cleft - Neurotransmitters diffuse across the gradient, and bind to ligand gated channels in post synaptic membrane - The ligand gated channels open and ions (Na) to come through - Na+ or ion moves in, and depolarize the membrane causing a graded postsynaptic potential in postsynaptic cell - Local current flow moves current through the cell body

Explain the mechanism by which the opening and closing of ligand-gated ion channels (i.e. ionotropic receptors) is regulated

Neurotransmitters binding to ligand gated ion channels, open the channel Neurotransmitters unbind= channel closes

What's an EPSP?

EPSP (Excitatory postsynaptic potential): neurotransmitters bind to the channel, channel opens, causing a depolarization

Example of EPSP

ligand gated cation channel, nic. acetylcholine receptor

What's an IPSP?

IPSP (inhibitory postsynaptic potential): neurotransmitter (such as GABA) opens the channel, causing a hyperpolarization

Example of IPSP

If K+ channels are open, ligand gated Cl- channel, GABA

Explain why postsynaptic potentials are transient (i.e. short lived). In other words, what terminates the action of the neurotransmitter on the postsynaptic cell

They can be broken down, reused, or diffused from synaptic cleft

occurs when two subthreshold potentials arrive at trigger zone within short period of time, sum and initiate action potential (same synapse)

temporal summation

occurs when currents from nearby simultaneous graded potentials combine (separate synapses)

spatial summation

In temporal summation, fired from...

the same presynaptic neuron at different locations

In spatial summation, fired from...

different presynaptic neurons that sum potentials together to meet threshold

Allows for two subthreshold graded potentials from the same neuron to be summed up and -55 mV (Threshold required for action potential)

temporal summation

Explain two ways that activation of a G protein-coupled receptor (GPCR) can regulate opening and closing of ion channels on a postsynaptic membrane.

1. Direct= the receptor that binds a neurotransmitter (NTX) is the same protein that forms the channel. (or bind to protein that works on channel) 2. Indirect= the receptor for the neurotransmitter is a separated protein (have secondary messenger)

Example of a direct way GPCR can open and close channel

Acetylcholine binds to a receptor with a G protein, G protein interacts with K+ channel, K+ channel opens, K+ leaves cell causing an IPSP, acetylcholine releases (lets go) of K+ channel, the channel closes.

Example of a indirect way GPCR can open and close channel

Neurotransmitter binds to a GPCR, activates the G protein, G protein turns on enzyme, produce a second messenger, second messenger binds to ion channel and open up, ions will come in or come out.

4 attributes of a stimulus that the CNS can distinguish:

Modality, location, intensity, duration

type of stimulus in transduction channels

Modality

what determines modality

type of stimulus in transduction channels, structure within which the channels located, and location of receptor in the tissue

Types of modality

Vibration, Temperature, Pain

nociceptors have transduction channels that open when exposed to

extreme temperature, intense mechanical stimuli, and chemicals released from damaged cells

Vibration (pacinian corpuscle), temperture (thermoreceptors), and pain (chemical) are encapsulated or free nerve endings

Vibration= encap Temp and pain= free nerve endings

The location of a stimulus refers to

sensory neurons with separate receptive fields and sensory neurons with overlapping receptive fields

Two factors that encode stimulus intensity

1. Frequency of action potentials generated in response to the stimulus 2. Number of sensory receptors activated by a stimulus

Duration of a stimulus refers to

slow or quick to adapt to stimulus

What receptors are involved in duration of stimulus

tonic and phasic

rapidly adapt to stimulus, immediate strong receptor potential that returns to rest

Phasic receptors

adapt slowly to stimulus and informs about the presence and strength of stimulus (strength of stimulus doesn’t change, receptor adapting to stimulus–reduces the number of action potentials)

Tonic receptors

where a stimulus must fall into for an action potential to occur

receptive field

__ of receptive fields influence our spatial resolution

Size and density

enhances the difference between signal strength in neighboring secondary sensory neurons, and helps define edges (boundaries) of stimulus

Lateral inhibition

Lateral inhibition continues to __ the response of a stimuli in neighboring sensory neurons while __ the strength of a signal of the main sensory neuron to the cortex

weaken, maintaining

affects the release of neurotransmitters

Presynaptic inhibition

affects the events at the receptors

Post synaptic inhibition

Differentiate between sensory receptor activation and perception of a stimulus.

We are only aware of a stimulus if it reaches threshold

What happens when an excitatory postsynaptic potential occurs on a dendrite? A. positive ions move via local current flow from the postsynaptic site to more negative regions within the cell. B. ligand-gated K channels open to repolarize the membrane potential. C. the membrane potential is hyperpolarized and the neuron is less likely to generate an action potential.

What happens when two or more synapses on a single postsynaptic neuron are activated at the same time?

spatial summation

Why can't an action potential be generated, no matter how large the stimulus, during the absolute refractory period?

Because too few voltage-gated Na channels have recovered from inactivation.

Why is the conduction velocity of action potentials faster in myelinated axons than in unmyelinated axons? A. Because the distance between adjacent nodes of Ranvier is larger than the distance between adjacent clusters of voltage-gated Na and K channels on unmyelinated axons. B. Because voltage-gated Na channels open faster on myelinated axons than on unmyelinated axons C. Because myelinated axons have a smaller diameter than unmyelinated axons

myelinated axons have a __ diameter than unmyelinated axons

larger

In which one of the following ways do primary sensory neurons differ from multipolar neurons? A. Action potentials are initiated at the peripheral end of the axon in primary sensory neurons. B. Action potentials are initiated by the summation of postsynaptic potentials on the soma of primary sensory neurons. C. Action potentials are propagated along the axon by regeneration of action potentials at regular intervals in primary sensory neurons.

When an action potential arrives at the presynaptic axon terminal it triggers neurotransmitter release into the synaptic cleft. What causes neurotransmitter release to stop?

Ca2+ concentration in axon terminal is decreased