A ction p otential

1. Action potential Under supervision of : Dr. Randa Salah Group 3 Zagazig university Faculty of medicine Sub group 3 6 – SHEHATA WAGEH SHEHATA 1 - SAMAR MAHMOUD OSAMA 7 – SHROUK EHAB ABDELAZIZ 2 – SAMIR KAMAL FATHY 8 – SHERIF ELSAYD MOHAMED 3 – SONDOS SAMI MOHAMED 9 – SHERIF SOBHY IBRAHIM 4 – SAHAR ABDELHAMID MOHAMED 10 – SHERIF MOHAMED SEF 5 – SHADY MOHAMED AWNY

2. definition an electric impulse consisting of a self-propagating series of polarizations and depolarizations, transmitted across the cell membranes of a nerve fiber during the transmission of a nerve impulse and across the cell membranes of a muscle cell during contraction. n 2. the electrical potential developed in a muscle or nerve during activity.

3. :Types of action potential : muscular cardiac neural

4. Neural action potential overview A typical action potential is initiated at the axon hillock when the membrane is depolarized As the membrane potential is increased, sodium ion channels open, allowing the entry of sodium ions into the cell. This is followed by the opening of potassium ion channels that permit the exit of potassium ions from the cell. This is followed by the opening of potassium ion channels that permit the exit of potassium ions from the cell. The inward flow of sodium ions causes depolarization The sodium channels close at the peak of the action potential , while potassium continues to leave the cell The efflux of potassium ions cause repolarization then hyperpolarization Then the membrane return to it’s normal resting value

5. Neural action potential overshoot repolarization depolarization RMP hyperpolarization

6. Neural action potential initiation propagation termination

7. Neural action potential Initiation The basic requirement is that the membrane voltage at the hillock be raised above the threshold for firing Action potential result from external stimulus as in neurotransmission and sensory neuron however some excitable cells spontaneously depolarize their axon hillock and fire action potentials (as pacemaker )

8. Neural action potential Neurotransmission Action potentials are most commonly initiated by excitatory postsynaptic potentials from a presynaptic neuron. an external signal such as pressure, temperature, light, or sound is coupled with the opening and closing of ion channels Sensory neurons excitatory inhibitory By depolarization Byhyperpolarization

9. Neural action potential propagation • The action potential propagates as a wave along the axon • This basic mechanism was demonstrated by Alan Lloyd Hodgkin in 1937.

10. Neural action potential Un myelinated N fibers Myelinated N fibers • The impulse propagate along the axon • The impulse jump from node to node • So it’s called jumping (saltatory) conduction • This mechanism was suggested by Ralph Lillie in 1925

11. Myelin has 2 important advantages 1 – fast conduction 2 – energy efficiency

12. Neural action potential termination Chemical synapse Electrical synapse Neuromuscular junction

13. Synapse types :

14. Cardiac action potential : definition : Is a specialized action potential in the heart with unique properties necessary for functions of the electrical conduction system of the heart Phases Phase 3 Phase 4 Phase 2 Phase 0 Phase 1

15. Cardiac action potential Phase 4 : is the rest membrane potential Phase 0: is the rapid depolarization phase Phase 1 : is the rapid small repolarization phase Phase 2 : is the plateau phase Phase 3 : is the rapid large repolarization phase

16. Cardiac action potential : Phase 4 : during which the cell remains until it is stimulated ….it associate with diastole Phase 0 : is due to opening of fast Na+ channels that increase Na+ permeability Phase 1 : due to inactivation of the fast Na+channels transient influx of Cl- and out flow of K+ Phase 2 : due to balance between Ca+2 influx & K+efflux through slow K+channels Phase 3 : due to closure of Ca+2 channels (L-type) , while slow K+are still open

17. MUSCULAR ACTION POTENTIAL The action potential in a normal skeletal muscle cell is similar to the action potential in neurons. Action potentials result from the depolarization of the cell membrane (the sarcolemma), which opens voltage-sensitive sodium channels; these become inactivated and the membrane is repolarized through the outward current of potassium ions. The resting potential prior to the action potential is typically −90mV, somewhat more negative than typical neurons. The muscle action potential lasts roughly 2–4 ms, the absolute refractory period is roughly 1–3 ms, and the conduction velocity along the muscle is roughly 5 m/s. The action potential releases calcium ions that free up the tropomyosin and allow the muscle to contract. Muscle action potentials are provoked by the arrival of a pre-synaptic neuronal action potential at the neuromuscular junction , which is a common target for neurotoxins.

18. All Or None The all-or-none law is the principle that the strength by which a nerve or muscle fiber responds to a stimulus is not dependent on the strength of the stimulus. If the stimulus is any strength above threshold, the nerve or muscle fiber will give a complete response or otherwise no response at all. It was first established by the American physiologist Henry Pickering Bowditch in 1871 for the contraction of heart muscle

19. Action potential 2010 By : Shady