Presentation on theme: "GRADED POTENTIAL & ACTION POTENTIAL Dr.Mohammed Sharique Ahmed Quadri Assistant prof. Physiology Al Maarefa College."— Presentation transcript:
GRADED POTENTIAL & ACTION POTENTIAL Dr.Mohammed Sharique Ahmed Quadri Assistant prof. Physiology Al Maarefa College
Objectives Define graded potential and action potential. Describe characteristics of graded potential Compare between the different phases of excitability during a nerve action potential( relative refractory period, absolute refractory period) step-by-step, explain how an action potential is produced Describe the characteristics of action potential.
Two major regulatory systems of the body: that ensure survival of the body: The Nervous System: Neural Communication Accomplished by Nerve Cells( signals) The Endocrine System: Hormonal Communication Accomplished by Hormones
Neural Communication Nerve and muscle are excitable tissues Can undergo rapid changes in their membrane potentials. Can change their resting potentials into electrical signals –Electrical signals are critical to the function of the nervous system and all muscles
Neural Communication Electrical Signals are produced due to changes in ions movement across the membrane. Two kinds of potential change( electrical signals) –Graded potentials Serve as short-distance signals –Action potentials Serve as long-distance signals
GRADED POTENTIAL Graded Potential is local change in the membrane potential. E.g. RMP changes from -70 mv to -60 mv (a 10mv change). Graded Potential is due to Na + entry at the small specialized region of plasma membrane. Graded Potential can be summated by giving stronger stimulus.
Graded Potentials The Stronger a triggering event is, The larger the resultant graded Potential Graded Potential spread by passive Current flow. Graded potentials die over short distances
Graded Potential Occurs in small, specialized region of excitable cell membranes Magnitude of graded potential varies directly with the magnitude of the triggering event
GRADED POTENTIAL ‘Important Points’ It is localized. It can be summated. Longer the stimulus – longer the duration of graded potential. Graded Potential die down over short distance. Example of Graded Potential: - Receptor Potential, Pace-maker Potential, end plate potential
Action Potentials Brief, rapid, large (100mV) changes in membrane potential during which potential actually reverses Involves only a small portion of the total excitable cell membrane Do not decrease in strength as they travel from their site of initiation throughout remainder of cell membrane
Changes in Membrane Potential During an Action Potential
ACTION POTENTIAL (cont) AP is referred as Spike potential because it appearance looks like spike. When excitable membrane produces AP, it is said it is Firing. Therefore Action potential, Spike, Firing all refer to same thing.
Channels & Local Potentials The ionic basis of the action potential membrane permeability ion channels Voltage gated Na+ and K+ Channels
Action Potentials Permeability Changes and Ion Fluxes During an Action Potential
Action Potentials The Na + /K + pump gradually restores the concentration gradients disrupted by action potentials. –Sodium is pumped into the ECF –Potassium is pumped into the ICF
Action Potentials Additional characteristics –As the action potential develops at one point in the plasma membrane, it regenerates an identical action potential at the next point in the membrane. –Therefore, it travels along the plasma membrane undiminished.
ACTION POTENTIAL (cont) Action Potential follows All or None Law. It means excitable membrane either responds to a stimulus with a maximal action potential or it does not respond with an action potential at all.
Refractory period during AP Refractory period is that period,during which no new action potential can be initiated. Refractory Period – Two Types: 1– Absolute Refractory period 2– Relative Refractory
Refractory Period Absolute Refractory Period It is that period of action potential during which no new action potential can be initiated even by strong stimulus. Relative Refractory period It is that period during which second action potential can be produced by very strong stimulus.
The action potential (AP) An action potential is: A regenerating depolarization of membrane potential that propagates along an excitable membrane. Action potentials: are all-or-none events need to reach threshold have constant amplitude do not summate are initiated by depolarization involve changes in permeability rely on voltage-gated ion channels
Comparison of Graded Potentials and Action Potentials Graded Potential Action Potential 1.Stimulus does not reach threshold level. 2.Stimulus causes local change in membrane potential e.g. -70 to -60mv 3.It dies down over short distance. 4.Can be summated. 5.Does not obey all or none law. 1.Stimulus reaches threshold level therefore causes AP. 2.Stimulus causes depolarization to threshold level. 3.It is propagated. 4.Can not be summated. 5.Obeys all or none law.