Neurophysiology Flashcards
Neuronal communication occurs through…
Electrical signaling (action potentials)
Chemical signaling (release of neurotransmitters)
What is an action potential?
A propagated electrical message of a neuron that travels along the axon to the presynaptic axon terminal
All living cells possess an electrical charge which means…
It is more negative inside the cell than outside
What is polarization?
The reversal of the electrical charges inside/outside of the cell
By inducing a change in polarization…
an action potential is initiated and propagated
Changes caused by the action potential help …
initiate release of neurotransmitters
What causes a change in polarization?
Movement of specific ions into or out of the neuron
What is a neuron’s resting state?
State in which the neuron is inactive - not receiving or sending information
What is a neuron’s resting membrane potential?
The difference in voltage between the inside and outside of a neuron.
What is the range for a neuron’s resting membrane potential?
-50 to -90 mV
A neuron’s resting state is dependent on..?
- Distribution of different ions (what is the concentration of ions in and out of the neuron?)
- Membrane selectivity (how easily can ions cross the membrane?)
Ion channels are selectively permeable to…
Potassium (K+)
Other ions cannot easily travel across the membrane
What forces act on ions to maintain a resting state?
-Forces that drive K+ ions in or out of the neuron
(Diffusion and electrostatic pressure)
-Ion transporters
(Sodium-potassium pump)
What is diffusion?
Ions want to travel from an area of high concentration to an area of low concentration
Where do K+ molecules want to go based on diffusion?
Inside the cell
less ions inside the cell than outside
Where do K+ molecules want to go based on electrostatic forces?
Inside the cell
Potassium is positive and the inside of the cell is more negative
What are the key components of ion transporters?
- Actively move ions against concentration gradient
- Create ion concentration gradients
What are the steps involved in ion transporters?
- Ion binds
2. Ion transported across membrane
What are the key characteristics of ion channels?
- Allow ions to diffuse down concentration gradients
- Cause selective permeability to certain ions
Is the sodium-potassium pump an ion transporter or an ion channel?
Ion transporter
Active transport - requires energy (ATP!)
What ions are pumped into and out of the neuron in a sodium-potassium pump?
3,2,1 NOKIA
- 3 Na+ ions pumped out of neuron
- 2 K+ ions pumped into neuron
What maintains the resting membrane potential in a sodium-potassium pump?
- Sodium-potassium pump brings K+ into the neuron
- K+ leaves the neuron through ion channels (diffusion)
- As negative charge builds up in neuron, electrostatic pressure pulls K+ ions back inside neuron
What is equilibrium?
The point at which movement of ions across the cell membrane is balanced
Corresponds to the resting membrane potential (-50 to -90 mV)
What forces act on ions to initiate an AP?
EPSPs and IPSPs
What is an excitatory postsynaptic potential (EPSPs)?
Message from neuron causes the membrane potential to become less negative (depolarization)
What is an example of an EPSP?
Opens Na+ ion channels
Where do Na+ molecules want to go based on electrostatic forces?
Inside the cell
Sodium is positive and the inside of the cell is more negative
Where do Na+ molecules want to go based on diffusion?
Inside the cell
There are less molecules inside the cell than outside
What are inhibitory postsynaptic potentials (IPSPs)?
Message from neuron causes the membrane potential to become more negative (hyper polarization)
What is an example of an IPSP?
Opens Cl- ion channels
If combination of inputs drives membrane potential to ______ mV, an action potential is triggered.
-40 mV
True or False:
An action potential is an all-or-none property
True.
What is special about -40 mV?
Na+ voltage-gated ion channels open when the membrane potential depolarizes to -40 mV (threshold)
What are voltage-gated ion channels?
Ion channels that open when a specific membrane potential is reached
True or False:
Many voltage-gated Na+ channels in the membrane are present in the membrane of the soma or the dendrites which is why many APs start here.
False
There are many voltage-gated Na+ channels at the axon hillock which is why APs start here
Based on diffusion and electrostatic pressure…
Na+ rushes through voltage-gated channels
When Na+ rushes through the voltage-gated channels, this opens additional channels, and Na+ continues to enter until the membrane potential of the neuron is _____ mV.
+ 40
What is change in polarization that is characteristic of an AP?
The change from a membrane potential of -40 mV to +40 mV
What happens after the membrane potential reaches +40 mV?
- Na+ channels close
- Voltage-gated K+ channels open, further increasing the permeability of the membrane to K+
- Neuron becomes hyperpolarized
- Resting membrane potential is restored
What are the 5 steps of an AP?
- Resting state
- Depolarization
- Rising phase of the action potential
- Falling phase of the action potential
- Undershoot
What is a refractory period?
A period where it is unlikely or impossible for another AP to be initiated
What are the two forms of refractory periods?
- Absolute refractory period
- Relative refractory period
What is an absolute refractory period?
No AP can happen because voltage-gated Na+ channels are either open or unresponsive
What is a relative refractory period?
AP is unlikely because K+ is still rushing out of the neuron and the neuron is hyperpolarized
Why is a refractory period important?
Refractory periods help ensure that the axon potential is propagated in one direction down the axon
How does the AP travel?
-AP is regenerated down the axon by an impulse within a neuron
(Voltage-gated channels are crucial for this process)
- Depolarization of the far end of the axon leads to the opening of nearby voltage-gated Na+ channels
- Entire process repeats itself down the axon
Propagation speed of the AP is dependent on…
- Diameter of the axon
- Whether the axon is myelinated
Why do AP travel faster on a myelinated axon?
Because myelin prevents K+ leakage
Depolarization is maintained and spreads
Where do voltage-gated Na+ channels open at?
Nodes of Ranvier
What is saltatory conduction?
AP jumps from node to node
What occurs at the end of the axon in the presynaptic terminal?
Depolarization
True or False:
Most electrical messages (APs) cannot be sent between neurons.
True
Neurons are structurally independent
AP causes release of neurotransmitters into the ______.
synaptic cleft
A higher frequency of APs is related to a…
A higher amount of Ca2+ in the axon terminal
True or False:
All neurotransmitters bind on the postsynaptic neuron dendrites.
False.
(Some bind to auto receptors on the presynaptic neuron to tell the neuron the concentration of the transmitter in the synaptic cleft)
What determines the postsynaptic reaction?
Postsynaptic receptors
The same neurotransmitter may produce an EPSP or IPSP, depending on what type of receptor it binds to
What is a ligand?
A substance that binds to receptor molecules
Ex: Acetylcholine
What are the 2 different types of receptors?
- Ionotropic
- Metabotropic
What are the key characteristics of ionotropic receptors?
- Directly control ion channel
- ‘Ligand-gated ion channels’
- Fast synapse
What are key characteristics of metabotropic receptors?
- Indirectly control ion channel
- Neurotransmitter binds to a G protein-coupled receptor
- Slow synapse
What does the binding of the neurotransmitter to the G protein coupled receptor activate?
Alpha subunit of G protein
What does the alpha subunit open?
The ion channel
True or False:
The alpha subunit may activate a second messenger.
True
What is degradation?
Enzymes break down the neurotransmitter
Specific enzymes for specific neurotransmitters
What is reuptake?
Transporters (receptors for the transmitter) bring transmitter back into the presynaptic neuron
