Absolute Refractory Period - ANS period associated with the opening of the Na+ channels until they begin to reset to their original resting state. (Neuron can NOT respond to another stimulus)
relative refractory period - ANS follows the absolute refractory period, most Na+ channe...
Absolute Refractory Period - ANS period associated with the opening of the Na+ channels
until they begin to reset to their original resting state. (Neuron can NOT respond to another
stimulus)
relative refractory period - ANS follows the absolute refractory period, most Na+ channels
have returned to their resting state, some K+ channels are still open, and repolarization is
occurring. (Requires exceptionally strong stimulus to open channels)
A neuron will not respond to a second stimulus of equal strength to the first stimulus to which it
has already responded because - ANS because the neuron is in the relative refractory
period.
Group A fibers - ANS Largest diameter, are mostly somatic and sensory fibers serving the
skin, skeletal muscles, and joints. Thicc myelin sheaths and conduct at speeds up to 150 m/s
Group B Fibers - ANS Intermediate diameter, lightly myelinated fibers
Transmit at 15 m/s
Group C Fibers - ANS Smallest diameter, unmyelinated ANS fibers
Transmit at 1 m/s
Excessive potassium efflux as a result of relatively slower closure of the potassium gates
corresponds to what part of an action potential curve? - ANS The hyperpolarization phase
of an action potential
Which of the following could cause a graded depolarization?
A. K+ leaving the cell through leakage (nongated) channels
B. Na+ entering the cell through chemically gated channels
C. K+ leaving the cell through voltage-gated channels
D. Na+ entering the cell through voltage-gated channels - ANS B. Na+ entering the cell
through chemically gated channels
FEEDBACK: Depolarizing graded potentials are small deviations in voltage across the
membrane that make the membrane potential more negative. The diffusion of Na+ into the cell
, through chemically gated channels would make the inside of the cell less negative. In other
words, the influx of Na+ causes a depolarizing graded potential.
The sodium-potassium ion pump will __________. - ANS pump three sodium (Na+) ions
out of the cell for every two ions of potassium (K+) it brings into the cell (3 Na+ in, 2 K+ out)
How would an increased extracellular K+ concentration affect K+ diffusion at leakage
(nongated) channels and the membrane potential? - ANS A decrease in the
electrochemical gradient would reduce K+ leak so cells would be less negative (more
depolarized).
FEEDBACK: Potassium ions normally diffuse out of the cell along their concentration gradient
from higher intracellular concentration to lower extracellular concentration. K+ flowing out of the
cell causes the cell to become more negative inside. If extracellular K+ is increased, the
concentration gradient across the membrane is decreased and therefore K+ is less likely to
leave the cell. The retention of positively charged ions within the cell would depolarize the
membrane.
What could have resulted from an increase in extracellular K+ - ANS Depolarizing graded
potential
The resting membrane potential of neurons is determined by __________. - ANS the
distribution, across the cell membrane, of large anionic cytoplasmic proteins, Na+, K+, and Cl-
Which of the following describes acetylcholine? - ANS Excites skeletal muscle
In a chemical synapse, which of the following best describes the role of calcium ions? - ANS
Calcium ions trigger exocytosis of neurotransmitter.
Which of the following represents a hyperpolarizing change in membrane potential called an
inhibitory postsynaptic potential (IPSP)? - ANS The postsynaptic membrane becomes
more permeable to potassium and chloride.
FEEDBACK: If K+ channels open, K+ moves out of the cell. If Cl− channels open, Cl− moves in.
In either case, the charge on the inner face of the membrane becomes more negative
(hyperpolarizing). As the membrane potential becomes more negative and is driven farther from
the axon's threshold, the postsynaptic neuron becomes less and less likely to "fire," and larger
depolarizing currents are required to induce an AP. Hyperpolarizing changes in potential are
called inhibitory postsynaptic potentials (IPSPs).
Spatial summation occurs when __________.
A. multiple local potentials occur at the same synapse on a cell
B. multiple local potentials occur at different places on the same cell at the same time
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