Action Potentials, Interneuronal Communication, Week 3 Lab Flashcards
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
Transduction channels are located in
Sensory receptors
What channel mediates sensory receptor potential (graded potentials)
Transduction channel
The size and duration of the receptor potential in transduction channels is determined by
how long and how many channels are open
Voltage gated Na and K channels are located…
in the trigger zone and throughout the length of the axons
What channel mediates action potentials
Voltage gated Na and K channels
The voltage gated Na and K channels open when
the membrane potential is depolarized to -55 mV from rest
Voltage Na channels open __, then VG K channels open more __
first (faster), slowly
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)
VG Na channels are what kind of feedback
positive
VG K channels are what kind of feedback
negative
VG Na channels stop because
inactivation stops depolarization
How do VG K channels close
by repolarizing membrane potential and removing the stimulus that opens them
all voltage gated channels are closed, membrane at resting membrane potential
resting state
when membrane potential reaches threshold (graded potential), Na channel gates opens, Na ions flow in and cause a positive charge buildup (depolarization).
Depolarizing phase
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
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
During the resting membrane potential, what channels are active
only leak channels will then open and close.
refers to the passive process, also known as graded potential–but is localized in that trigger zone, initiating the action potential
Local Current Flow
Local current flow is decremental due to the
loss of ions across a membrane through leak channels
The propagation of action potential is a __ process
active
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.
In myelinated axons, leak channels are…
insulated by myelin–leads to loss of current flow and bette conduction
In myelinated axons, Ion channels are only located at the
Nodes of Ranvier
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.
- Direct= the receptor that binds a neurotransmitter (NTX) is the same protein that forms the channel. (or bind to protein that works on channel)
- 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
- Frequency of action potentials generated in response to the stimulus
- 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.
A
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
A
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.
A
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
