GENERATION OF ELECTRICAL POTENTIALS BY AN ARTIFICAL MEMBRANE
RMP – arises because the cell membrane is more permeable to some ions than others.
K+ more inside (diffuse out). Na+ more outside (restricted) – can’t pass as easily.
= positive charge on outside of cell (RMP).
AP/GP – disturb charge difference (reduce, increase, reverse) – send sensory info to s-cord, brain to send signals to
muscles and organs.
USSING CHAMBER – membrane ONLY permeable to Na/K (CATIONS) not anions (Cl/I). Cations diffuse down their
concentration gradient = difference in charge. Poured some solution in, rinsed the chamber with it. Drained. 60ml then
of each solution into each chamber. Important to fill them at the same time so minimum pressure is applied to the
membrane. Measuring chamber 2 with respect to chamber 1, voltage should read negative (black in chamber 1); these
electrodes will always go into the same chambers.
Aeration – ensure good mixing of solutions, prevent unstirred layers of solution next to membrThe membrane itself
is inert, and does not require oxygenation.
Asymmetry potential – the last trial (average reading) was the value for if the readings were too positive or negative.
Subtracted its value from each average reading.
Activity Values – use the log a1/a2 values for each of the trials.
Concentration Factor – each trial: the higher concentration was divided by the lower concentration
We compared the potentials we measured here, to those calculated by the Nerst Equation.
NERST: E = RT/Fz (ln - Iout/Iin)
V = 0.199 x T x log a1/a2
V = mV, T = room temp in Kelvin (298)
A1 or 2 = multiply solution concentration by activity coefficient
ACTIVITY COEFFICIENT – measure of how independently solute molecules or ions behave when they are dissolved.
Ideal = act completely separately. Reality? They interact. BECOMES MORE SIGNIFICANT THE HIGHER THE
CONCENTRATION IS. Interaction causes solutions to behave as if they hold fewer dissolved particles than they actually
C 1 1 C 2 2
Concentration and Volumes used
1 2 3 4 5 6 7
Concentration 10 100 500 500 100 10 1
Avg reading 0.8
Corrected -0.8 -0.8 -0.8 -0.8 -0.8 -0.8 -0.8
Calculated -59.3 -118.6 -160.1 160.05 118.6 59.3
BASICALLY, THE CONCENTRATION FACTOR AND WHICH SUBCHAMBER EACH SOLUTION WAS IN
DETERMINED THE VALUE, AND IT SWITCHED WHEN THEY WERE PLACED IN OPPOSITE CONTAINERS.
NEGATIVE READINGS OBSERVED WHEN HIGHER CONCENTRATION WAS IN CHAMBER 1.
POSITIVE READINGS OBSERVED WHEN HIGHER CONCENTRATION WAS IN CHAMBER 2.
How is the generation of a potential in this experiment similar to the way in which a resting membrane potential
is generated in a living neuron?
In the "classical" case (vertebrate nerve and skeletal muscle), the resting membrane potential and the membrane potential
difference (graded potential) arises primarily from a K+ - diffusion potential. The concentration gradient of K+ across the
membrane is such that K+ tends to diffuse out of the cell without a concomitant inward flow of positive charge
(permeability is high for K). Thus, there develops a slight excess of positive charge outside the cell which, at equilibrium,
opposes the further outward. Like a living neuron, the membrane in the experiment is permeable only to cations,
leading to a graded potential generated by a cation induced diffusion potential. The experiment facilitates a
concentration gradient much like a living neuron membrane would. How is the generation of a potential in this experiment different from the way in which a resting membrane
potential is generated in a living neuron?
The ions are in subchambers rather than inside and outside a cell. There is no Na/K ATPase pump that can facilitate
passive leakage - In a living cell, this system is in a dynamic equilibrium due to the sodium/potassium exchange pump
that constantly restores the Na+ and K+ gradients that maintain the resting potential. The difference between the living cell
and the experiment is that the resting potential is impossible to maintain without the pump and because it is anion-
impermeable, therefore, a permanent electric potential will always persist between the solutions.
Why were the membrane potentials we calculated for two trials with opposite concentration factors the same (but
with different polarities)?
Yes, the membrane potentials calculated were of the same magnitude – 118.6, regardless of polarity. The artificial
membrane was permeable to the K cations and impermeable to Cl anions, therefore, in either trial, these cations were
passing through the membrane down their concentration gradient. Given that in either trial the concentrations were
comparable, the cations were passing through the membrane, down their concentration gradient in the same magnitude,
resulting in the same membrane potential. There was no ATPase pump to possibly manipulate or alter the experimental
conditions in either trial. The polar differences resulted from the relative readings from the electrodes which did not
move, rather, the switching of the solutions between chambers simply resulted in the direction of the downward
movement of the gradient to switch directions (changing the fake-inside and outside of the cell, and the sign of
Which passes more easily through the membrane of the resting nerve cell: K+ or Na+ ions? What would you
expect to happen to the resting membrane potential if K+ ions could no longer leak across the membrane, but
the Na+/K+ ATPase pump continued to function?
Potassium is able to diffuse through the resting membrane of a nerve cell because all sodium gates are closed (some
potassium are open); sodium remains outside the membrane, while potassium can still mildly diffuse out. If K+ can no
longer leak out of the cell and the pump will keep working to bring them in, then an excess of K+ will accumulate in the
cell, depolarizing it, and making its resting potential less negative. RECORDING ACHILLES REFLEXES
Proprioceptors (muscle spindles) – activate when stretched or acted upon. Send info to CNS when stretched. Aligned
parallel. These lead to stretch reflexes..
Maintain muscle tone
Coordinate smooth movements
Maintain body posture
Proprioceptors (muscle spindles) – innervated by gamma motor neuron, intrafusal fiber, excites afferent nerve (bend)
Muscles – innervated by alpha motor neuron, extrafusal fiber, fosters tension in the muscle
Stretch Reflex (Myotatic reflex) – reflex arc, afferent nerves synapse onto motor neurons of the same muscle, limit
range of movement, prevent damage, keeps balance.
Achilles (Deep Tendon reflex) – achilles tendon stretched, tapped, afferent neuron (cell body in dorsal root ganglion),
efferent neuron (located in L5 / S1 of cord). Behind ankle, contract calf muscle, and plantar flexion of ankle.
Knee Jerk – one will contract (excitatory), the other relaxes (inhibitory)
Use EMG (electromyograms) to read activity.
Motor Nerve Conduction Velocity – path length of conduction from muscle to s-cord, and avg time it takes for travel
NOT THERE? DISEASE OF MUSCLE< NERVE< DORSAL ROOT GANGLION Calcium floods in at the axon terminal membrane, releases Ach, at the motor end plate. Chemically gated ion
channels here influx NA and efflux K, causing depolarization of the motor end plate: moves along the sarcolemma down
the t-tubules (leads to calcium in the muscle cell which cause the power stroke).
What role does phosphocreatine have in the functioning of skeletal muscle? ATP used for muscle energy, one phosphate molecule breaks off into the muscles for energy. Leaves ADP (just 2
phosphate molecules). Phosphocreatine works with ADP to recreate ATP (3 phosphate). If none of this? Can’t engage in
anaerobic activity. REPLENISHES ATP.
What causes fatigue in living human skeletal muscle?
1) Limitations of the nerve’s ability to generate sustained signal
2) Reduced ability of calcium (ca2) to stimulate contraction
3) Depleted ATP reserves
4) Not enough oxygen CARDIOVASCULAR PHYSIOLOGY
LUB – closure of the AV valves when ventricles pump blood out (systole)
DUB – closure of the semi-lunar (pulmonary/aortic) valves after ventricles pump blood out (systole)
1. HEART SOUNDS - Hearing the heart sound using a STETHOSCOPE – second right, second left, fifth left.
Lub is lower pitch, dub is higher pitch. Longer pause between dub and lub, not lub and dub.
WRIST PULSE – lub, dub, then pulse
CAROTID PULSE – lub, dub + pulse are simultaneous.
Loud and clear in second right.
2. BLOOD PRESSURE - Auscultatory Method (10% values within direct measurement of arteries):
First Korotkoff sound: constrict blood with sphygmomanometer, when released, blood will squirt in artery
with each systole. Pressure in the cuff when this sound is heard is SYSTOLIC PRESSURE.
Second Korotkoff sound: cessation of dull muff sound (laminar flow returns) is the DIASTOLIC
Line the brachial artery, place the stethoscope on it to look for sounds when pumped to 140 mmHg.
Systolic pressure = work done by left ventricle to overcome resistance of circulatory system.
HIGH BLOOD PRESSURE IS THREE READINGS > 160/95 separated by hours or days.
Females are typically 10 points lower than men. BP should be lower when lying down at rest than sitting up.
Pulse Pressure: pressure dif b/w systolic and diastolic pressure. 120/80? Pulse pressure is 40.
3. EXERCISE AND CARDIAC OUTPUT –
Q = HR x SV
SV = EDV – ESV
End diastolic volume is the amount of blood that fills the left ventricle at the end of