University of Galway Physiology Lecture 3 on Action Potentials 2024-2025 PDF

Physiology School of Medicine Founded in 1845 Course: MD137 2024-2025 Introduction to Physiology Lecturer: Lecture 3:...

Physiology School of Medicine Founded in 1845 Course: MD137 2024-2025 Introduction to Physiology Lecturer: Lecture 3: Leo Quinlan Action potentials [email protected] Action potentials Neural Signalling Learning Outcomes 3 What is an action potential (AP). Describe the main ion movements in formation of AP. Explain the role of ion channels, what is threshold ? Describe the kinetics of an AP. Love action potentials !! Polarisation states of the membrane 4 Passive properties 5 H&H found that membrane potential changing in response to the stimulation but decreased as you measure further from the stimulation electrode. Describes as passive properties of the neuron.  Active properties 6 + 40 - A small depolarizing stimulus (-65 mV) + 10 - Voltage (mV) 0 - - 10 - - 40 - - 80 - time Stim REC 1 REC 2 REC 3 Elec ++++ +++ ++ +  Active properties 7 + 40 - Increase depolarizing stimulus (-60 mV) + 10 - Voltage (mV) 0 - - 10 - - 40 - - 80 - time Stim REC 1 REC 2 REC 3 Elec +++++ ++++ +++ ++  Active properties 8 + 40 - Increase depolarizing stimulus further (-55 mV) + 10 - Voltage (mV) 0 - - 10 - - 40 - - 80 - time Stim REC 1 REC 2 REC 3 Elec ++++++ +++++++++ +++++++++ +++++++++  Active properties 9 + 40 - Increase depolarizing stimulus further (-40 mV) Action + 10 - Voltage (mV) potentials 0 - - 10 - Local potentials - 40 - - 80 - time Stim REC 1 REC 2 REC 3 Elec ++++++ +++++++++ +++++++++ +++++++++ ++ Generating action 10 potentials Phases of AP 11 Deplorarisation MP Δ110mV -70mV up to +40mV Replorarisation MP Δ110mV +40mV down to -70mV Hyperplorarisation Overshoot and recovery to RMP Phases of AP 12 Deplorarisation Na+ entry Facilitated by Voltage gated Na+ channels Replorarisation K+ exit Facilitated by Voltage gated K+ channels Generating action potentials 13  Potentials in real cells 14 Dendrites Graded or Local Axon Terminal Potentials Axon Trigger Zone Action Potentials Integrating center of Neuron (Axon Hillock, Initial Segment) Generating action potentials 15  16 Properties of action potentials 1. Na+ entry triggers AP 17 2. Threshold 18 –55mV represents the threshold potential Beyond this membrane potential we get a full action potential Threshold is a voltage below which voltage gated channels do not open. Threshold is a voltage above which voltage gated channels open. 2. Threshold 19 Membrane Potential +30mV 0mV Threshold -90mV + Stimulus Strength Threshold 0 - Subthreshold Suprathreshold 3. All or nothing 20 Membrane Potential +30mV 0mV Threshold -90mV + Stimulus Strength Threshold 0 - Subthreshold Suprathreshold 3. All or nothing 21 All action potentials for a given nerve look the same, there are not big ones and little ones. This is the all-or-nothing law. How do we code for two stimuli when both are above threshold ???? 3. All or nothing 22 4. Regeneration 23 5. Membrane Potential reverses 24 Intracellular Vs Extracellular Recording 6. Refractory Period 25 6. Refractory Period 26 Generating action potentials 27 Mr. Sykes 28 Local/Graded Vs Action Potentials 29 Local Potentials Action Potentials Generally re ect shape, Do not re ect the shape, size of voltage stimulus size of the stimulus, rather Bigger stimuli give bigger they are uniform in size, depolarizations. shape; always identical They “die out” as they move They do not diminish in size from site of stimulation and regenerate anew at each point along the axon fl fl Learning Outcomes 30 What is an action potential (AP). Describe the main ion movements in formation of AP. Explain the role of ion channels, what is threshold ? Describe the kinetics of an AP. Love action potentials