I want 20 multiple-choice questions that measure levels of memorization and understanding of the following: Lecture objectives
By the end of discussing “Membrane properties of excitable cells (neurons & muscle cells)”, student will be able to:
1. Describe Electrical activity (action potential), development, and, properties.
2. Interpret the impact of changing ionic conductance on AP.
3. Describe Excitability changes that occurs during the electrical activity of the membrane.
4. Define and list mechanisms of cellular propagation of electrical signals.
2Changes accompanying the
propagation of a nerve impulse:
1- Electrical change
RMP
AP
3Resting Membrane Potential
(RMP)
• Potential difference
across the cell
membrane in millivolts
(mV).
• It is established
by diffusion
potentials that
result from
concentration
differences of
permeant ions.
1
4Resting membrane
potential(RMP)
• In the nerve-70mvHow to ensure the negativity of
the membrane ?
• K+ Leak channels ( Selective permeability)plays
essential role in the development of RMP.
• Presence of proteins (-ve charged)inside the cells
ensure that the membrane tends to be negative.
• if any disturbance occurs the presence of Na+,K+
pump ,quickly corrects the changeThen comes the stimulus and….Thershold stimulusAction Potential
1
0Action Potential
• Definition:
• The action potential is the rapid changes in
membrane potential produced by application
of an effective (threshold or suprathreshold)
stimulus to the nerve.
• These changes transmitted along the nerve as
a self propagated disturbances known as the
nerve impulse.
1
1Recording of action potential:
• Action potential can be
recorded by cathode
ray
oscilloscope
through
2
microelectrodes, one is
inserted inside the
nerve and the other is
placed on its outer
surface.
1
2After the latent period, the successive stages of
the action potential are recorded, including:
Phases
1. Depolarization stage.
2.Repolarization stage.
3. The negative after-potential
4. The positive after-potential
10Action potential
1112The action potential consists of:
•Spike potential: It is large wave of a short duration
(0.5-1 m. sec) in myelinated nerve fibers ?). It
consists of:
1) Ascending limb: which represents the process of
depolarization. It is due to Na+ influx which occurs in
two stages:
•Slow until the threshold potential: gradual Na+
influx changes the membrane potential form the
resting potential (-70 m.v.) to the threshold
potential (-55 m.v.).
14•Rapid : at the threshold potential or the firing
level, the voltage sensitive Na+ channels open
suddenly leading to rapid Na+ influx and rapid
depolarization of the membrane
•With continuous Na+ influx, the membrane
potential becomes positive (+ 35 m.v.). This is
known as reversal of polarity or overshoot.
15Descending limb:
• Which represents the major part of the
process of
repolarization (about 70%).
Repolarization is caused by K+ efflux which
occurs at first rapid due to the sudden
opening of the voltage sensitive K+ channels
(open immediately after closure of Na+
channels). So, the descending limb is caused
by rapid K+ efflux.
16Ionic basis (mechanism) of
Depolarization
A. The stimulus increases the permeability of the cell membrane
(several hundred folds) to Na+ ions, which diffuse inside
causing gradual change in the membrane potential from the
resting potential (-70m.v) to the threshold potential or the
firing level (-55m.v).
B. At that level, the gates of the voltage activated sodium
channels open and Na+ ions flow into the cell (Na influx )
C. These inactivating gates close after a certain time. As a result
of sudden Na+ influx, the membrane potential quickly reaches
zero potential and then overshoots to about + 35 m.v, so that
there is a momentary reversal in polarity.
17Redistribution of ions inside and outside:
• Redistribution of Na+ and K+ ions to the normal resting condition is established by the Na–K pump which actively transports sodium out and potassium into the cell
• To Regain the Resting Membrane potential(RMP)