BIPN 145 Neurophysiology Lab NAME:_________________________________
QUIZ 1
Answer each of the questions below in the space
provided.
1. (20 points) What limits the frequency at which action potentials can be generated ? Explain your answer.
The absolute and relative refractory periods limit AP freq. Because the Na channels are closed during the absolute refractory period no new Aps can be generated so this represents the maximum freq. At which AP can be produced. The relative refractory period would extend this off period for a given stimulus strength because the open K channels would short circuit any new depolarizing input.
2. (20 points) The Nernst model for membrane potential is given as: Vm = RT/zF ln( [ion] out / [ion] in). You make a mistake when you make up your frog ringers and use KCl instead of NaCL. If the correct concentration of ions is NaCl (150mM), KCl (20 mM), CaCl2 (3 mM) and the intracellular concentrations of these ions are NaCl (30mM), KCl (80 mM), CaCl2 (0.01 mM), what effect will your incorrectly made up solution have on the resting membrane potential of your cells?
(R= 8.3 J /mol oK, T= 293oK, F = 96,480 J/V mol) SHOW ALL YOUR WORK!
If the only change is to increase the extracellular [K]
and assuming that the resting membrane permeability for K is much greater than
for Na we can calculate the new resting membrane potential using the Nernst
equation (you can also use the Goldman equation and info from class that the K
permeability is 100 xs grater than the Na permeability at rest).
Vm = RT/zF ln (170 mM / 80 mM) = 19 mV
The membrane potential would rise to +19 mV meaning the cell would most likely be depolarized!
3. (10 points)Which of the parameters in the Goldman/Katz/Hodgkin modification of the Nernst equation
(Vm = RT/F ln( p[ion1]1/z out + p[ion2]1/z out .. / [ion1] 1/z in + [ion2] 1/z in .)
changes when neurotransmitter molecules bind to post synaptic receptors and open ligand-gated channels? Explain your answer.
The binding of neurotransmitter opens ligand gated ion channels. This allows various ions to cross the dendritic membrane. Thus the membrane permeability (p) has changed for the ions that can diffuse thru the open channel.
BIPN 145 Neurophysiology Lab NAME:_________________________________
QUIZ 1
4. (20 points) Based on the data presented, what is the conduction velocity for the nerve prep shown below? Explain how your got your answer and show your work!
Velocity is distance per time. The distance between C and D is 1.2 cm/ 5 ms or 120 mm / 5ms = 2.4 m/s
5 a) (10 points) Identify the biological phenomenon is shown in the frog muscle action potential traces below?
This is a compound muscle action potential which is the combined electrical activity of many fibers in the muscle bundle.
b) (10 points) Why does the second peak in the red 30 ms interstimulus interval trace occur sooner than in the black 50 ms interstimulus interval trace?
The two peaks occur at different times because the length of time between the two stimuli in successive trains is different.
c) (10 points) What is the postulated ionic basis for this phenomenon?
The muscle action potential is due to a Na+ influx into
muscles cells causing a depolarization that results in the release of stored calcium
from the sarcoplasmic reticulum. (It is
the increase in intracellular calcium that allows actin and myosin to
interact.)
BIPN 145 Neurophysiology Lab NAME:_________________________________
QUIZ 1
Bonus questions (5pts. Each):
B1. What was the effect of Barium on facilitation of the frog muscle action potentials?
Barium is reported to facilitate facilitation. Several groups observed a broadening of the muscle action potentials but an increase in amplitude is also possible.
B2. Explain your results.
Barium blocks the K channels, which should delay the repolarizing phase of the action potentials in the sciatic nerve. This means that the terminals will remain depolarized longer resulting in an increase in the amount of neurotransmitter released at the NMJ. The result would be a longer (or stronger) contraction of the postsynaptic muscle fiber.