Action Potential (HBF 102) - Helwan National University - 2024-2025 PDF

Faculty of Medicine Academic Year: 2024-2025 Year: 1 Semester: 1 Module: Human Body Function (HBF) 102  ACTION POTENTIAL By: ASHRAF ALGENDY PROFESSOR Department: MEDICAL PHYSIOLOGY 11/25/2024 22  prerequisites Be...

Faculty of Medicine Academic Year: 2024-2025 Year: 1 Semester: 1 Module: Human Body Function (HBF) 102  ACTION POTENTIAL By: ASHRAF ALGENDY PROFESSOR Department: MEDICAL PHYSIOLOGY 11/25/2024 22  prerequisites Before the lecture you must know:  Different types of channelS in plasma membrane.  Definition and mechanism of resting membrane potential.  Different types of transport across the cell membrane. 11/25/2024 HBF - 102 4  OBJECTIVES At the end of the lecture you will be able to:  understand essential terminology related to different electrical activities of excitable tissues.  Define different electrical activities of excitable tissues.  Clarify the importance of action potential. 11/25/2024 HBF - 102 5  OBJECTIVES At the end of the lecture you will be able to:  List and discriminate different types of action potential.  Draw and labels different phases of monophasic action potential. 11/25/2024 HBF - 102 6  OBJECTIVES At the end of the lecture you will be able to:  Explain the mechanism of different phases of monophasic action potential.  Recognize excitability changes that coincided with monophasic action potential. 11/25/2024 HBF - 102 7  Introduction The process of communication between the nerves and their target tissues was a big unknown for physiologists. With the development of electricity, electrophysiology and the discovery of electrical activity of neurons, it was proved that the transmission of signals from neurons to their target tissues is mediated by action potentials.  OBJECTIVES At the end of the lecture you will be able to:  understand essential terminology related to different electrical activities of excitable tissues.  Define different electrical activities of excitable tissues.  Clarify the importance of action potential. 11/25/2024 HBF - 102 10  polarization It is potential difference between outer surface and inner surface of excitable tissue during rest Value in medium sized nerve = - 70 11/25/2024 Helwan Special Medical Program 11 11/25/2024 Helwan Special Medical Program 12 11/25/2024 Helwan Special Medical Program 13  depolarization It is raising membrane potential toward positive value, i.e. decrease negativity inside the cell Value = - 69 up to -1 11/25/2024 Helwan Special Medical Program 14 11/25/2024 Helwan Special Medical Program 15  Loss of polarity No potential difference between outer surface and inner surface of excitable tissue Value = zero 11/25/2024 Helwan Special Medical Program 16  Reverse of polarity The inner surface of the membrane is positive in relation to outer surface Value = up to +35 11/25/2024 Helwan Special Medical Program 17  Repolarization Return membrane potential to normal state Value = - 70 11/25/2024 Helwan Special Medical Program 18 11/25/2024 Helwan Special Medical Program 19  Hyperpolarization The inner surface of the membrane is more negative than resting state Value = - 80 or more 11/25/2024 Helwan Special Medical Program 20 11/25/2024 Helwan Special Medical Program 21  OBJECTIVES At the end of the lecture you will be able to:  understand essential terminology related to different electrical activities of excitable tissues.  Define different electrical activities of excitable tissues.  Clarify the importance of action potential. 11/25/2024 HBF - 102 23 Electrical activities of excitable tissue Resting membrane potential. Electrotonus. Action potential. Electrical activities of excitable tissue Electrotonus. Local electrical changes that occur in excitable tissue when stimulated by subthreshold stimuli. Electrical activities of excitable tissue Action potential Series of brief, self propagated electrical changes that occur in excitable tissues when stimulated by adequate stimuli. 11/25/2024 Helwan Special Medical Program 28 11/25/2024 Helwan Special Medical Program 29  OBJECTIVES At the end of the lecture you will be able to:  understand essential terminology related to different electrical activities of excitable tissues.  Define different electrical activities of excitable tissues.  Clarify the importance of action potential. 11/25/2024 HBF - 102 30 Clinical significance of action potential ❖ Nerve Impulse Transmission Action potentials are the basis of nerve impulse transmission, allowing for. communication between neurons and other cells. Clinical significance of action potential ❖ Excitation contraction coupling. ❖ Excitation secretion coupling. ❖ Medical diagnosis : ECG ,EEG 3 Medical and EM Diagnosis  Clinical significance of action potential ❖ Research in neuroscience and AI field. List clinical significance of action potential? 11/25/2024 Helwan Special Medical Program 35  OBJECTIVES At the end of the lecture you will be able to:  List and discriminate different types of action potential.  Draw and labels different phases of monophasic action potential. 11/25/2024 HBF - 102 36 Types of action potential Monophasic Biphasic compound Types of action potential Monophasic Electrical activities of excitable tissue Monophasic Action potential of medium sized nerve 11/25/2024 Helwan Special Medical Program 40 Electrical activities of excitable tissue Monophasic Action potential of large sized nerve and skeletal muscle 11/25/2024 Helwan Special Medical Program 42 Electrical activities of excitable tissue Monophasic Action potential of non-nodal ventricular cardiac muscle 11/25/2024 Helwan Special Medical Program 44 Electrical activities of excitable tissue Monophasic Action potential of nodal cardiac muscle 11/25/2024 Helwan Special Medical Program 46 Types of action potential Biphasic 11/25/2024 Helwan Special Medical Program 48 Types of action potential Monophasic Biphasic compound 11/25/2024 Helwan Special Medical Program 50 11/25/2024 Helwan Special Medical Program 51  OBJECTIVES At the end of the lecture you will be able to:  List and discriminate different types of action potential.  Draw and labels different phases of monophasic action potential. 11/25/2024 HBF - 102 52 11/25/2024 Helwan Special Medical Program 53 11/25/2024 Helwan Special Medical Program 54 11/25/2024 Helwan Special Medical Program 55  OBJECTIVES At the end of the lecture you will be able to:  Explain the mechanism of different phases of monophasic action potential.  Recognize excitability changes that coincided with monophasic action potential. 11/25/2024 HBF - 102 56 57 11/25/2024 Helwan Special Medical Program 58  Rapid depolarization Loss of Firing level polarity Slow Reverse of depolarization polarity Rapid RMP repolarization Hyper Slow polarization repolarization 59  Selective permeability Na/K pump 11/25/2024 Helwan Special Medical Program 61  Caused by subthreshold stimulus 11/25/2024 Helwan Special Medical Program 62 11/25/2024 Helwan Special Medical Program 63 What ion enters a neuron causing depolarization of the cell membrane? A) phosphate. B) chloride C ) sodium D) potassium. E) calcium. Depolarization Stimulus A stimulus triggers depolarization, making the inside of the neuron more positive. Sodium Channels Open Sodium channels open, allowing sodium sodium ions to rush into the cell. Membrane Potential Rises The influx of sodium ions causes the membrane membrane potential to become more positive positive  Voltage –Gated Sodium channel The activation gate opens when the Activation Gate membrane potential reaches a certain certain threshold. The inactivation gate closes shortly after the activation Inactivation Gate gate opens, limiting the flow flow of sodium ions.  Rapid depolarization Sodium Influx The rapid influx of sodium ions causes a steep rise in the membrane potential. Positive Feedback As the membrane potential rises, more sodium channels channels open, accelerating the depolarization process. process. Peak Potential The membrane potential reaches a peak value, typically typically around +30 mV. 11/25/2024 Helwan Special Medical Program 70 Repolarization 1 Sodium Channels Close Sodium channels inactivate, stopping the influx of influx of sodium ions. 2 Potassium Channels Open Potassium channels open, allowing potassium ions to flow out of the cell. 11/25/2024 Helwan Special Medical Program 74 Hyperpolarization 3 Membrane Potential Falls The efflux of potassium ions causes the membrane potential to become more negative. Repolarization Na/K PUMP causes the membrane potential returning towards its resting value (RMP). 11/25/2024 Helwan Special Medical Program 78  OBJECTIVES At the end of the lecture you will be able to:  Explain the mechanism of different phases of monophasic action potential.  Recognize excitability changes that coincided with monophasic action potential. 11/25/2024 HBF - 102 79  Response of the excitable tissues when stimulated by threshold stimuli 1 ELECTRICAL CHANGES (AP) 1. EXCITABILITY CHANGES 1.. THERMAL CHANGES 1… METABOLIC CHANGES EXCITABILITY CHANGES 1 Absolute Refractory Period (ARP) 2 Relative Refractory Period (RRP) 3 Super Normal Phase (SNP) 4 Sub-Normal Phase (Sub NP)  Excitability = zero ARP Excitability more than zero but less than RRP normal Excitability more than normal but less than SNP normal Excitability more than zero but less than Sub NP normal  No response what ever the strength of ARP stimuli Only suprathreshold stimuli can produce RRP response SNP Subthreshold stimuli can produce response Only suprathreshold stimuli can produce Sub NP response  Coincide with rapid depolarization and early ARP part of rapid repolarization Coincide with late part rapid of rapid RRP repolarization. SNP Coincide with after depolarization. Sub NP Coincide with after hyperpolarization. 11/25/2024 Helwan Special Medical Program 86 Summary 88 88  References ❖ Linda S. Costanzo: physiology, six edition, ELSEVER. ❖ Linda S. Costanzo: BRS physiology, seventh edition, Lippincott Williams & Wilkins. ❖ Lecture notes. 11/25/2024 HBF - 102 89 89