Brain Electrophysiology I & II Flashcards
what were the results of the Hodgkin and Huxley (1939) model?
1) axons at rest are electrically polarized
2) -60mV inside v.s the outside
what were the methods of the Hodgkin and Huxley model?
voltage clamp experiments and by varying extracellular Na and K concentrations
what is an action potential?
when polarization of the membrane is removed (due to depolarization)
what is hyperpolarization?
a rapid swing in membrane potential to more negative values following depolarization
what is after-polarization?
a period of increased polarization
what forces determine the passive distribution of ions?
electrical and thermodynamic forces
how do ions move down their concentration gradients?
via ion channels or diffusion
what does the movement of ions result in?
redistribution of electrical charge (voltage gradient), which can cause either hyperpolarization or depolarization
what is the reversal potential?
the membrane potential at which the net current flips direction
what is the equilibrium potential?
the membrane potential at which there is not net movement of ions, which is basically a balance between voltage and concentration gradients
how can the equilibrium potential be calculated?
Nernst Equation
what are the ions that contribute to the resting membrane potential?
Na, K, Cl
the membrane is not at equivalent potentials for one ion (as they all contribute to the resting potential
what do ion pumps do?
maintain concentration gradients
how do ion pumps maintain the concentration gradient?
by actively transporting ions
what is one example of an ion pump?
the Na/K ATPase pump
how is the Na/K ATPase pump get stimulated?
by increased of intracellular Na
what does the Na/K ATPase pump move in and out?
Na out and K in
the Na/Ca2 exchanger is an example of an…
ion pump
a chloride-bicarbonate exchanger is an example of an…
ion pump
which ions increase in conductance during an action potential?
Na and K
Na and K conductance causes the membrane to become more positive or negative?
positive, in order to reach depolarization
what happens after an action potential?
the membrane potential re-polarizes (becomes more negative) than resting (hyperpolarization)
what is a transient inward current?
a more positive charge inside of the cell
what happens in the giant squid action when you increase the voltage from -60mV to 0mV?
produces a transient inward current and it is followed by a sustained outward current
what is a pharmacological blockade?
drugs or substances that inhibit or block specific physiological or biochemical processes in the body
what does tetradotoxin (TTX) block?
Na channels
when you increase the membrane potential in the presence of TTX, what ion current increases?
K only
what does tetraethylammonium (TEA) block?
K channels
when you increase the membrane potential in the presence of TEA, what ion current increase?
Na only
how do K channels open?
via their voltage sensitive gates and depolarization
how do K channels close?
via depolarization, which leads to deactivation
what are the different states that a Na channel can be in throughout an action potential?
activated, deactivated, and inactivated
what is the inactivation state of the Na channel?
when the channel is inactive despite maintained depolarization
what is “deinactivation”?
the removal of the inactivation state of the Na channel
what Na gate opens during depolarization?
activation gates
what Na gates close during depolarization?
inactivation gates
what Na gate closes during repolarization?
activation gates
what Na gates open during repolarization?
inactivation gates
what is the action potential threshold?
-55mV
how does the movement of Na ions depolarize the axon?
by moving more Na inside, this opens more Na channels
what are the two voltage-sensitive processes that Na channels display?
1) activation -> deactivation
2) inactivation -> deinactivation
what is propagation?
initiation
in what two places can action potentials start?
1) the axon initial segment
2) the axon hillock
where does the action potential move (2 directions)?
1) propagates down the axon
2) antidromically backwards to the dendrites
what is antiromically?
the propagation of an action potential in the opposite direction to the normal flow
what is the threshold for AP generation in the initial segment?
low threshold
what is the density of Na channels in the initial segment?
high density
how can the speed of action potentials be affected?
by myelination
how do unmyelinated axons move the action potential?
by depolarizing adjacent regions of the membrane
how do myelinated axons move the action potential?
by regenerating the action potential ate the nodes of ranvier
what does the axon look like at the nodes of ranvier?
exposed to the external medium
what are the five different firing patterns that can be performed by neurons?
- regular firing
- rhythmic bursts
- short duration
- spontaneous low frequency discharges
- steady-slow discharges
what is regular firing?
trains of action potentials (one spike at a time)
what is a feature of regular firing?
spike frequency adaptation
what is spike frequency adaptation?
the tendency to slow down in frequency with time
what is an example of regular firing?
cortical/hippocampal pyramidal cells
what are rhythmic bursts of action potentials?
when clusters of APs are generated through activation of Ca2+ currents
what is an example of rhythmic bursts of action potentials?
thalamic relay neurons (they can perform phasic bursts and slower discharges)
what are short duration action potentials?
action potentials that have high frequencies (>300 HZ)
what is an example of short duration action potentials?
fast spiking neurons like GABAergic interneurons
what cells display spontaneous low frequency discharges?
neuromodulatory neurons
what is an example of a neuromodulatory neuron?
dopaminergic neurons
what cells display steady-slow discharges?
medial hebanular neurons
what are the 3 main features by which ion currents are characterized by
1) the type of ions conducted by channels
2) the voltage and time dependence
3) their sensitivity to second messengers
what are the different types of Na currents?
1) I Na(t)
2) I Na(p)
what are the features of the I Na(t) current?
transient and can rapidly activate and deactivate action potentials
what are the features of the I Na(p) current?
persistent and non-inactivating
what does non-inactivating enhance?
depolarization and steady-state firing
what are the different types of Ca currents?
1) I (L)
2) I (T)
3) I (P)
what are the features of I (L) currents?
high threshold currents, long lasting, and slowly inactivate
what can display an I (L) current?
dendritic spikes
what are the features of an I (T) current?
low threshold, transient, and rapidly inactivating
what firing pattern displays an I (T) current?
rhythmic burst firing
what cells perform an I (P) current?
purkinje cells (their dendritic spikes)
what are the different types of K currents?
1) I (K)
2) I (C)
3) I (AHP)
4) I (A)
5) I (H)
how is the I (K) current activated?
by strong depolarization and repolarization of the action potential
how is the I (C) current activated?
by increasing calcium levels and acton potential repolarization
what part of the action potential displays I (AHP) current?
afterhypolarization (because of slow adaptation of action potential discharge)
what is the I (A) current?
transient inactivating current
how does the I (H) current occur?
via a depolarizing current activated by hyperpolarization
what are the two different patterns of activity that thalamic relay neurons display?
rhythmic bursts and tonic firing
when does the transition from rhythmic burst (phasic) to tonic firing occur in thalamic cells?
during sleep to waking
