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Transcript
Learning objectives of Today’s Lecture Describe the physiological basis of Resting membrane potential of a neuron Enlist the sequence of events in synaptic transmission Differentiate between Excitatory Post Synaptic Potential EPSP and Inhibitory Post Synaptic Potential IPSP Synaptic transmission Dr Ghulam Mustafa Resting Membrane Potential of the Neuronal Soma. Resting Membrane Potential -65 millivolts. Less negative than the -90 millivolts Lower voltage is important: Allows both positive and negative control of the degree of excitability of the neuron. Decreasing the voltage - less negative value - neuron more excitable Increasing the voltage - more negative value - neuron less excitable. Resting Membrane Potential of the Neuronal Soma 40 nm vesicles formed in GA of cell body- Motor neuron Vesicles transported---axoplasmic streaming to nerve terminal Acetylcholine synthesized in terminal parts of nerve - stored Action potential opens calcium channels Calcium bind with protein molecules (Release sites) Exocytosis of Acetylcholine vesicle 2000 and 10,000 molecules of acetylcholine are present in each vesicle Enough vesicles in the Presynaptic terminal To transmit more than 10,000 action potentials. Acetylcholine. Acetyl cholinesterase reformation Acetate Choline Reabsorbed BACK Vesicles Coated pits - Clathrin New vesicles ACETYLCHOLINE (NT) IN SYNAPTIC CLEFT Transmitter substance activates Ion Channel Second Msgr System If transmitter substance activates an Ion Channel opens within a fraction of a millisecond Cation channel Sodium Ions Anion Channel Chloride ions Excitatory Transmitter Inhibitory Transmitter “Second Messenger” System in the Postsynaptic Neuron. G Protein activation Alpha Beta Alpha Gamma G Protein mediated actions 1. Opening specific ion channels 2. Activation of cAMP or cyclic cGMP in the neuronal cell. 3. Activation of one or more intracellular enzymes. Activation of gene transcription. Excitation Opening of Sodium Channels Depressed conduction through Chloride or Potassium channels, or both. Various changes in the internal metabolism of the postsynaptic neuron Effect of Synaptic Excitation on the Postsynaptic Membrane Increase the membrane’s permeability to Na+ Neutralizes part of the negativity of the RMP Positive increase in voltage above the RMP Excitatory Postsynaptic Potential (or EPSP) 20 millivolts more positive than RMP simultaneous discharge of many terminals — about 40 to 80 EPSP EPSP Inhibition Opening of Chloride ion channels through the postsynaptic neuronal membrane. Increase in conductance of potassium ions out of the neuron. Activation of receptor enzymes that Inhibit cellular metabolic functions the number of inhibitory synaptic receptors or Increase Decrease the number of excitatory receptors. Electrical Events During Neuronal Inhibition Open mainly Chloride channels Potassium efflux Increase the degree of intracellular negativityHyperpolarization Inhibitory Postsynaptic Potential (IPSP) More negative value of -70 millivolts IPSP of -5 millivolts IPSP Ensure impulse to pass in one direction Prevent damage of effectors due to over stimulation Act as junctions for dividing up and merging of neurons Resting Membrane Potential of the Neuronal Soma EPSP IPSP