Lecture 3 - Neuronal Excitability Flashcards
what are the two types of cells in the CNS?
neurons and glia
true or false: there are 10-50x more glia cells than neurons in the CNS but both cell types take up to 50% of the space
true
cells that provide structure/support, isolating neurons from one another
oligodendrocytes/satellite cells
cells that produce myelin
oligodendrocytes (CNS) and Schwann cells (PNS)
cells that guide migrating neurons and direct axonal outgrowth during development
radial glia
cells that form the blood brain barrier, and play a role in neurotransmitter clean up after synaptic transmission
astrocytes
cells which act as scavengers, removing debris after injury or cell death
microglia
the word “glia” means:
glue
what are the three main categories of neurons?
- afferent neurons
- efferent neurons
- interneurons
neurons that carry information from the periphery to the CNS and are excitatory
afferent neurons
neurons that carry information from the CNS to the periphery and are excitatory
efferent neurons
neurons that carry information between neurons within the CNS and can be excitatory or inhibitory
interneurons
the anatomy of a neuron is determined by its:
function
what are the three main shapes of neurons?
biopolar, pseudo-unipolar, and multipolar
what is the purpose of protein pumps and channels in the cell membrane? (in the context of membrane potential)
controls movement of ions through the membrane
pumps in the cell membrane are _____, and help generate _____
active transporters, resting membrane potential
ion channels in the cell membrane can be ______ or ______, and they disrupt the membrane potential to ______
passive, gated, trigger action potentials
a measure of the electrical potential difference between the intracellular environment and extracellular environment
resting membrane potential (Em)
what is the resting membrane potential of a cell?
-70mV (negative inside)
which ions are primarily involved in setting resting membrane potential?
K+ and Na+
which pumps/channels are involved in setting resting membrane potential?
Na+/K+ exchanger, Na+ leak channels, and K+ leak channels
at rest, the concentration of K+ inside the cell is _____ than the concentration of K+ outside the cell
greater
at rest, the concentration of Na+ inside the cell is _____ than the concentration of Na+ outside the cell
less
at rest, the concentration of Cl- inside the cell is _____ than the concentration of Cl- ouside the cell
less
why doesn’t Cl- affect the resting membrane potential (Em)?
the equilibrium potential of Cl- is -70mV
the Na+/K+ pump is _______ as it moves charges across the membrane
electrogenic
where does the Na+/K+ pump get its energy from?
the hydrolysis of ATP to ADP and Pi
how many Na+ and K+ molecules are moved across the cell membrane by the Na+/K+ pump per molecule of ATP?
3Na+, 2K+
the Na+/K+ pump creates:
an electrochemical gradient
what are the chemical gradients created by the Na+/K+ pump?
- [K+]in > [K+]out (K+ wants to diffuse out of the cell)
- [Na+]in < [Na+]out (Na+ wants to diffuse into the cell)
what is the electrical gradient created by the Na+/K+ pump?
the intracellular environment is negative (and wants to become more positive)
Em is set by the:
relative number of leak channels
true or false: leak channels are always open
true
what is the function of leak channels?
they allow passive flow of ions into/out of the neuron
are leak channels selective?
yes - each ion has its own leak channels through which only they can pass
the membrane potential at which the chemical concentration gradient is balanced
equilibrium potential
what is the equilibrium potential for K+?
-90mV (alone, K+ would force Em to -90mV)
what is the equilibrium potential for Na+?
+60mV (alone, Na+ would force Em to +60mV)
the more permeable the membrane is to a given ion, the closer Em is to:
the equilibrium potential for that ion
is the bilayer more permeable to K+ or Na+?
K+ (why the equilibrium potential for K+ is closer to the equilibrium potential for Na+)
what is the effect of increasing the number of K+ leak channels on Em?
Em is decreased
what is the effect of increasing the number of Na+ leak channels on Em?
Em is increased
why is the resting membrane potential -70mV?
due to Na+/K+ pump and leak channels
what is the Nerst equation?
Eion = (RT/ZF)(ln([ion]out/[ion]in))
at 20C, (RT/ZF) =
25mV
go review slide 38
ewwwww Nerst equation calculations
how are afferents activated?
stimuli results in opening of specialized, physically-gated Na+ receptors, Na+ enters afferent terminals, and depolarization occurs
if Na+ entry into the afferent terminals is sufficient to depolarize the neuron to its threshold, the result is:
the opening of voltage gated Na+ channels and an action potential
what is the threshold potential of a neuron?
~-50mV
what are the 6 major stages of an action potential?
1) rest
2) depolarizing input
3) start of action potential (depolarization)
4) repolarization
5) end of action potential (hyperpolarization)
6) return to rest
what is the reason for the change in membrane permeability during depolarization?
the voltage gated Na+ channels open
what is the reason for the change in membrane permeability during repolarization?
voltage gated K+ channels open and Na+ channels inactivate
what is the reason for the change in membrane permeability during hyperpolarization?
voltage gated Na+ channels are at rest and voltage gated K+ channels are still open
what is the relative membrane permeability to K+ and Na+ at rest?
K+ > Na+
what is the relative membrane permeability to K+ and Na+ at the start of an action potential?
slight increase in Na+ permeability, but still more permeable to K+
what is the relative membrane permeability to K+ and Na+ during depolarization?
Na+ > K+
what is the relative membrane permeability to K+ and Na+ during repolarization?
K+ > Na+
what is the relative membrane permeability to K+ and Na+ during hyperpolarization?
K+ > Na+
dictates the phases of the action potential
relative membrane permeability
