Action potential presenation.pptx

OFFICI AL ACTION POTENTIAL AND SYNAPSES OFFICI AL OBJECTIVES​ -Describe the resting membrane potential​ -Describe the generation of action potentials​ -Describe the phases of action potentials​ -Describe the propagation of an action potential​ -Describe signal transmission at a synapse​ identify com...

OFFICI AL ACTION POTENTIAL AND SYNAPSES OFFICI AL OBJECTIVES​ -Describe the resting membrane potential​ -Describe the generation of action potentials​ -Describe the phases of action potentials​ -Describe the propagation of an action potential​ -Describe signal transmission at a synapse​ identify common neurotransmitters​ OFFICI AL The Nervous System detects and responds to changes inside and outside the body  -  CNS:   Brain and spinal cord PNS:  All nerves outside of brain and spinal cord  Cranial nerves and sacral nerves  In the PNS, sensory nerves (afferent) and motor nerves (efferent)  Motor section:  Voluntary – somatic NS – controls movement of voluntary muscles  Involuntary – ANS – control of smooth and cardiac muscle and glands  2 branches – sympathetic and parasympathetic OFFICI AL OFFICI AL OFFICI AL A Neurone  Is a cell in the nervous system  Consists of:  Dendrites, A cell body, An axon and an axon terminal  Cannot divide and needs continuous supply of oxygen and glucose  A nerve impulse or action potential is the electrical charge that moves along the neurone  Some neurones initiate action potentials  Others act as ‘relay stations’ to pass the signal along OFFICI AL The Nerve Cell OFFICI AL OFFICI AL OFFICI AL The Nerve Impulse/ Action Potential  Impulse is initiated by stimulation of sensory nerve endings or by the passage of an impulse from one nerve to another.  Transmission of the impulse or action potential is due to movement of ions across the nerve cell membrane  In the resting state, the nerve cell membrane is polarised due to differences in concentration of ions across the plasma membrane OFFICI AL OFFICI AL The Nerve Impulse/ Action Potential  This means there is a different electric charge on each side of the membrane, this is called the resting membrane potential.  At rest the outside is positive and the inside is negative OFFICI AL Resting Membrane - The principal ions involved are: Na+ - the main extracellular cation K+ - the main intracellular cation - Nerves and muscles are excitable tissue, both use this potential by undergoing transient fluctuations in membrane potential OFFICI AL OFFICI AL Resting Membrane 2 kinds of potential: - action - graded OFFICI AL What Is Action Potential?  The momentary change in the voltage difference across the cell membrane of a neuron  Characterised by an influx of positively charged sodium ions (Na+)  This results in the propagation (spreading) of the impulse along the neuron  Resting potential of the neuron is approximately -70 millivolts (mV) OFFICI AL What Is Action Potential? (cont…)  High A concentration of Na+ outside the cell stimulus occurs (E.g. pressure at the finger)  Na+ rushes through cell membrane – changes the inner surface to +40 mV  This causes the inner cell membrane to be positively charged  This is known as the Depolarisation Stage OFFICI AL  What is the voltage during the resting stage?  What is the threshold voltage?  During the ‘resting’ stage, is there more Na+ on the inside or outside of the cell?  When Na+ due to the voltage sodium gates being opened, what is this phase called? OFFICI AL OFFICI AL What Is Action Potential? (cont…)  Membrane becomes more permeable to potassium ions (K+)  K+ gated ion channels open – K+ rushes through the cell membrane  Higher concentration of K+ outside of the cell compared to the intracellular  This causes the cell membrane to become negatively charged OFFICI AL  When threshold is reached, what happens to the Sodium channels?  What then happens to the Potassium channels?  In terms of charge, as a result of these changes what happens to the polarity of the inside of the cell?  Is the sodium channel closed or inactive?  Why is this important? OFFICI AL What Is Action Potential? (cont…)  K+ release causes the membrane potential to fall below -70 mv (approx. -90 mV)   This is known as the Repolarisation Stage This impulse occurs from the axon hillock at a speed of 0.1 to 10 meters per second OFFICI AL What Is Action Potential? (cont…)  Too much K+ released from the cell  This  This causes a -90 mV impulse is known as the Hyperpolarisation Phase OFFICI AL  Why does hyper-repolarisation occur? OFFICI AL What Is Action Potential? (cont…)  Refractory Stage of the action potential occurs with assistance of the Na+ /K+ pump 3 Na+ ions are received through the membrane and 2 K+ ions are released  This mV returns the resting membrane to -70 OFFICI AL Action Potential Graph  https://www.youtube.com/watch?v =plFOiU7sTO4 OFFICI AL Action Potential OFFICI AL OFFICI AL OFFICI AL Propagation Of Action Potential  How does the signal move from one place to another?  Action potential occurs at a very small area of the membrane  Positive charge exist on the outside of the membrane  Negative charge exists inside of the membrane OFFICI AL OFFICI AL OFFICI AL Propagation Of Action Potential Stimulus occurs – leading to the phases of the action potential This causes a “domino” type effect through the cells/neuron until it reaches the end terminal https://www.youtube.com/watch?v=Sa1wM75 0Rvs OFFICI AL OFFICI AL Myelinated V Non Myelinated Sheath Axon Myelinated Non Myelinated  Myelinated sheath around a nerve  Without a myelinated sheath  Impulses move more quickly   This increases the information processing speed Comprise the smaller axons of the CNS  Slower conduction time  Found in the peripheral nervous system  Found in the visceral nervous system (internal organs)  Decreases reaction time to stimuli  Faster communication from brain to organs  Utilises a significant amount of metabolic energy to produce the many layers of the sheath  Found in both the central and peripheral nervous system OFFICI AL  High concentration of Na+ outside the cell  A stimulus occurs (E.g. pressure at the finger)  Na+ rushes through cell membrane – changes the inner surface to +40 mV  This causes the inner cell membrane to be positively charged  This is known as the Depolarisation Stage  Membrane becomes more permeable to potassium ions (K +)  K+ gated ion channels open – K+ rushes through the cell membrane  Higher concentration of K+ outside of the cell compared to the intracellular  This causes the cell membrane to become negatively charged  K+ release causes the membrane potential to fall below -70 mv (approx. 90 mV)  This is known as the Repolarisation Stage  Too much K+ released from the cell  This causes a -90 mV impulse  This is known as the Hyperpolarisation Phase  Refractory Stage of the action potential occurs with assistance of the Na+ /K+ pump  3 Na+ ions are received through the membrane and 2 K + ions are released  This returns the resting membrane to -70 mV OFFICI AL OFFICI AL OFFICI AL OFFICI AL SYNAPSE OFFICI AL OFFICI AL OFFICI AL Presynapse The neurotransmitter is released into a space called the synapse Chemicals released from neurons communicate wit no a g Or Postsynapse e, l c s Mu uron Ne r OFFICI AL Neurotransmitter= The ‘Key’ Receptor= The ‘Lock’ OFFICI AL OFFICI AL  Acetylcholine  Catecholamines:  Dopamine, Norepinephrine, epinephrine  Serotonin  Histamine  GABA (Gamma-Aminobutyric Acid)  Glutamate NEUROTRANSMITTERS​ OFFICI AL Acetylcholine  Can be found in the neuromuscular junction  The neurotransmitter that signals voluntary muscle movement is Acetylcholine OFFICI AL Parasympathetic Neuron Organ, Heart, Lung, Pupils Parasympathetic response: Decrease heart rate (To normal) Constrict pupils (To normal) Acetylcholine Constrict bronchioles (To normal) OFFICI AL Catecholamines- Dopamine, Norepinephrine, Epinephrine  Family of neurotransmitters  They ‘speed up’ heart rate, dilate airways, dilate pupils  They are the neurotransmitters that signal a sympathetic response  The receptor type is alpha and beta OFFICI AL Ways to remove excess neurotransmitters 1. 2. 3. 4. Diffusion Enzymes Reuptake pumps Astrocyte endfeet OFFICI AL  Acetylcholine  Catecholamines:  Dopamine, Norepinephrine, epinephrine  Serotonin  Histamine  GABA (Gamma-Aminobutyric Acid)  Glutamate NEUROTRANSMITTERS​ OFFICI AL -Under normal conditions Serotonin would be pumped out of the synapse by the reuptake pumps -If we block these pumps we end up with more Serotonin OFFICI AL Ways to remove excess neurotransmitters 1. 2. 3. 4. Diffusion Enzymes Reuptake pumps Astrocyte endfeet OFFICI AL OBJECTIVES​ -Describe the resting membrane potential​ -Describe the generation of action potentials​ -Describe the phases of action potentials​ -Describe the propagation of an action potential​ -Describe signal transmission at a synapse​ identify common neurotransmitters​ OFFICI AL ANY QUESTIONS