Nervous System 1 PDF

PH2130 Integrated Physiology Stuart Cruickshank  Series of Presentations. 1. Action Potential 2. Neurotransmitters 3. The Autonomic Nervous System Why the emphasis on the ANS? Example: Vasovagal syncope…… https://www.youtube.com/watch?v=Jl4W2AiZr2E An archetypal neuron Cell body (so...

PH2130 Integrated Physiology Stuart Cruickshank  Series of Presentations. 1. Action Potential 2. Neurotransmitters 3. The Autonomic Nervous System Why the emphasis on the ANS? Example: Vasovagal syncope…… https://www.youtube.com/watch?v=Jl4W2AiZr2E An archetypal neuron Cell body (soma) Axon Dendrite Myelin sheath Axon hillock (= initial Node of Ranvier segment) Presynaptic terminals  Axonal Conduction The resting membrane potential Ion channels generating the action potential Speeding up action potentials Compound action potentials The resting membrane potential is generated by the selective K+ permeability of the membrane Na+ K+ Na+ Na+ K+ K+ K+ Na+ K+ Na+ Na+ K+ The resting membrane potential is generated by the selective K+ permeability of the membrane K+ K+ K+ K+ K+ K+ Na + Na+ Na+ Na+ Na+ Na+ The resting membrane potential is generated by the selective K+ permeability of the membrane K+ K+ K+ K+ K+ K+ Na + Na+ Na+ Na+ Na+ Na+ The resting membrane potential is generated by the selective K+ permeability of the membrane K+ K+ K+ -ve K+ K+ K+ Na+ Na + Na+ Na+ Na+ Na+ The Nernst equation predicts the equilibrium potential for a single ion species RT [ion]o E= ln zF [ion]i R = gas constant z = valence of the ion T = absolute temp F = Faraday constant A short cut to understanding all electrophysiology Na+ Ca2+ Cl- K+ -70mV Permeability changes during the AP  The action potential resting membrane potential Na+ +40 0 K+ -40 Threshold potential -80 -70mV -120  The action potential depolarisation Na+ +40 0 K+ -40 -80 +40mV -120  The action potential repolarisation Na+ +40 0 K+ K+ -40 -80 -90mV -120  The action potential resting membrane potential again Na+ +40 0 K+ K+ -40 -80 -70mV -120  Absolute Refractory Period During the time interval between the opening of the Na+ channel activation gate and the opening of the inactivation gate, a Na+ channel CANNOT be stimulated. – This is the ABSOLUTE REFRACTOR Y PERIOD. – A Na+ channel cannot be involved in another AP until the inactivation gate has been reset.  Relative Refractory Period Could an AP be generated during the undershoot? Yes! But it would take an initial stimulus that is much, much stronger than usual. This situation is known as the relative refractory period. Imagine, a toilet (the bog, dunny…..). When you pull the handle, water floods the bowl. This event takes a couple of seconds and you cannot stop it in the middle. Once the bowl empties, the flush is complete. Now the cistern is empty. If you try pulling the handle at this point, nothing happens (absolute refractory). Wait for the cistern to begin refilling. You can now flush again, but the intensity of the flushes increases as the cistern refills (relative refractory)  Self-propagation of APs ----- ----- ----- ----- ----- -----  Self-propagation of APs ++--- ----- ----- ----- ----- -----  Self-propagation of APs Na+ +++++ ++--- ----- ----- ----- -----  Self-propagation of APs Na+ ---++ +++++ ++--- ----- ----- -----  Self-propagation of APs Na+ ----- ---++ +++++ ++--- ----- -----  Self-propagation of APs Na+ ----- ----- ---++ +++++ ++--- -----  Self-propagation of APs Na+ ----- ----- ----- ---++ +++++ ++---  Self-propagation of APs Na+ ----- ----- ----- ----- ---++ +++++  Properties of action potentials Are mediated by voltage-gated channels Are all-or-none Can only signal stimulus strength in frequency, and not amplitude Have a refractory period Are self-propagating - therefore good at signalling over long distances Travel slowly – conduction velocity improved by big axons, or myelination ……………..  Types of Nerve Fibers class mylination Dia. (µm) Conduction Functions velocity A heavy 12-20 70-120 Motor and proprioception A Moderate 5-12 30-70 Touch and pressure Aγ Moderately 3-6 15-30 Motor to muscle spindle A lightly 2-5 12-30 Pain, temperature, touch B lightly 1-3 3-15 Preganglionic autonomic C None 0.4-1.2 0.3-1.3 0.7-1.3 0.7-1.3 Pain & reflex response Postganglionic sympathetic Myelination speeds up AP transmission APs are only evoked at the node of Ranvier Myelination increases membrane resistance Myelination decreases membrane capacitance Produces saltatory conduction Velocity up to 120m/s  Effect of myelination ----- ----- ----- ----- ----- -----  Effect of myelination ++--- ----- ----- ----- ----- -----  Effect of myelination Na+ +++++ +++++ ++++- +++-- +++-- ++---  Effect of myelination Na+ ---++ --+++ --+++ -++++ +++++ +++++  Effect of myelination ----- ----- ----- ----- ----- ---++  Effect of myelination ----- ----- ----- ----- ----- -----  Effect of de-myelination ----- ----- ----- ----- ----- -----  Effect of de-myelination Na+ +++++ ++++- +++-- ++--- +---- -----  Effect of de-myelination ---++ ----- ----- ----- ----- -----  Effect of de-myelination ----- ----- ----- ----- ----- -----  What you should know Basis of the resting membrane potential, role of voltage-gated Na+ and K+ channels in the action potential Significance of threshold potential, refractory period Self-propagation, factors affecting velocity of conduction, myelination and saltatory conduction, compound action potentials.