3.2. CELL MEMBRANE PHYSIOLOGY - Part 2 (1).pdf

CHAPTER 3 CELL MEMBRANE PHYSIOLOGY - ACTION POTENTIAL 3.1. Cell Membrane Structure 3.2. Membrane Transport 3.3. Membrane Potential 3.4. Action Potential Human Anatomy and Physiology I HUAP 210 Objectives You will be able to: 1. Describe the structure and function of the cell membrane, incl...

CHAPTER 3 CELL MEMBRANE PHYSIOLOGY - ACTION POTENTIAL 3.1. Cell Membrane Structure 3.2. Membrane Transport 3.3. Membrane Potential 3.4. Action Potential Human Anatomy and Physiology I HUAP 210 Objectives You will be able to: 1. Describe the structure and function of the cell membrane, including its regulation of materials into and out of the cell 2. Recognize the significant of membrane potential. 3. Describe the function of ion channels and sodium/potassium pump in maintaining membrane potential. 4. Describe the stages of action potential and explain the threshold potential. 5. Identify the characteristics of action potential. 6. Describe the conduction of action potential along nerve fibers. Human Anatomy and Physiology I HUAP 210 Membrane Potential Section 3.3 Membrane Potential Membrane potential is the difference created by the unequal distribution of ions across the membrane, with positively charged ions being more concentrated outside the cell and negatively charged ions being more concentrated inside the cell. All plasma membranes have a membrane potential. Membrane potential is measured in mV. Human Anatomy and Physiology I HUAP 210 Differences in the concentration of ionic composition across the membrane Human Anatomy and Physiology I HUAP 210 All plasma membrane have membrane potential but Excitable cells - Nerves and Muscles - have the ability toAll change it and generate electrical signals. Resting Membrane Potential (RMP) Resting membrane potential (RMP)- the constant membrane potential present when the excitable cells is electrically at rest (not producing electrical signals “Action Potential”). RMP for neuron cell = - 70 mV. Human Anatomy and Physiology I HUAP 210  Neuron Cell Neuron cell is the functional unit of the nervous system. consist of: Soma: Cell body. Dendrites: Carry nerve impulses from surrounding cells to the soma. Axon Hillock: The neural action potential is created here. Axon: conduct impulses from soma to the axon terminal. Axon Terminal: Pass the impulses to another cell. Human Anatomy and Physiology I HUAP 210 Action Potential Section 3.4 Action Potential An action potential in neurons, the rapid rise in membrane potential, depolarization, is an all-or-nothing event that is initiated by the opening of sodium ion channels within the plasma membrane. The subsequent return to resting potential, repolarization, is mediated by the opening of potassium ion channels. Ionic movement is triggered by an electrical, chemical, thermal or mechanical stimulus. The stimulus causes the opening of the gates of ion channels leading to the ionic movement. Human Anatomy and Physiology I HUAP 210 Action Potential Depolarization : The membrane becomes less polarized that is inside becomes less negative or more positive compared to RMP. Repolarization: The membrane returns to the RMP. Hyperpolarization: The membrane potential becomes more polarized: The inside becomes more negative than RMP. Human Anatomy and Physiology I HUAP 210 Ionic Channels The role of Sodium and Potassium gates (channels) during action potential Human Anatomy and Physiology I HUAP 210 Ionic Channels The role of Sodium and Potassium gates (channels) during action potential Human Anatomy and Physiology I HUAP 210 Generation and Propagation of Action Potentials (All-or- Nothing Rule) For an action potential to fire (be generated), the stimulus has to be strong enough bring the membrane potential to the threshold potential (about -55 mV) and move towards the 0 (depolarization) Human Anatomy and Physiology I HUAP 210 Threshold Potential The threshold potential is the critical level to which a membrane potential must be depolarized to initiate an action potential At threshold potential explosive depolarization takes place because of opening large number of voltage gated ion (sodium) channels. Human Anatomy and Physiology I HUAP 210 1. At rest (RMP = -70 mV) At resting potential all Na+ and K+ voltage- gated channels are closed Human Anatomy and Physiology I HUAP 210  2. Threshold potential (-55mV) A triggering event depolarizes the membrane toward threshold potential Opens some voltage- gated channels Human Anatomy and Physiology I HUAP 210  3. Action Potential - Depolarization (-55 _ +30 mV) All voltage-gated Sodium channels open Explosive Na+ influx (moving inside the cells) Depolarization Human Anatomy and Physiology I HUAP 210  4. Action Potential - Peak of Action Potential (+30 mV) Na+ influx continues moving the membrane towards Na+ equilibrium potential At the peak of action potential, Na+ inactivation gates close and K+ voltage- gated channels open. Entry of Na+ stop K+ starts to leave the cell Human Anatomy and Physiology I HUAP 210  5. Action Potential - Repolarization (+30 _ -70 mV) Outward movement of K+ makes the inside of the cell progressively less positive and the outside less negative Repolarization Human Anatomy and Physiology I HUAP 210  6. Hyperpolarization (-70 _ -90 mV) Continuous outward movement of K+ (K+ efflux) restores the resting membrane potential Further outward movement of K+ through the still-open K+ voltage-gated channels transiently hyperpolarize the membrane Human Anatomy and Physiology I HUAP 210  Sodium/Potassium Pump The Na+/K+ pump is a major contributor to the resting state or equilibrium of the cell. It is responsible for maintaining the large excess of Na+ outside the cell and the large excess of K+ ions on the inside. It is an active transport process which makes use of the ATP energy currency of the cell. Human Anatomy and Physiology I HUAP 210 Action Potential Transmission The original action potential does not travel along the membrane. Instead it triggers an identical new action potential in the nearby area of the membrane. Human Anatomy and Physiology I HUAP 210 Frequency of Action Potential A stronger stimulus does not produce a larger action potential since almost all the sodium channels are opened when threshold is reached, but it does trigger greater number of action potentials/ sec. (frequency). Strength of a stimulus is coded by the frequency of action potentials. Human Anatomy and Physiology I HUAP 210 Wrap up and Questions