L1 Physiology Synaptic Transmission PDF

Central Nervous System Synaptic transmission By Abeer El-Emam Prof. of Medical Physiology Alexandria Faculty of Medicine  ILOs By the end of this lecture, the student should be able to: 1. Define synapse and list their types 2. Ex...

Central Nervous System Synaptic transmission By Abeer El-Emam Prof. of Medical Physiology Alexandria Faculty of Medicine  ILOs By the end of this lecture, the student should be able to: 1. Define synapse and list their types 2. Explain the types of synaptic transmission 3. Explain types of post synaptic potentials 4. Differentiate different mechanisms of synaptic inhibition 5. Describe the properties of synaptic transmission  How can you transfer information to another person, place, or group?? The brain uses precise and specific pathways to communicate. Synaptic Transmission  SYNAPTIC TRANSMISSION Synapses are highly specialized contacts between nerve cells that transmit signals from the presynaptic neuron to the postsynaptic cell. between the axon or other portion of the presynaptic cell to the dendrites, cell body or axon of another neuron (postsynaptic), or in some cases a muscle or gland cell along which transmission of electrical messages takes place. Electrical & Chemical synapse Synaptic transmission  Each presynaptic neuron typically releases only one neurotransmitter Recent evidence suggests, however, that in some cases two different neurotransmitters can be released simultaneously from a single axon terminal. On binding with their subsynaptic receptor-channels, different neurotransmitters cause different ion permeability changes. excitatory synapses and inhibitory synapses.  How can NT produce their action By binding to specific receptors binding of a neurotransmitter with its appropriate subsynaptic receptor-channels always leads to change in permeability and resultant change in potential of the postsynaptic membrane. Excitatory postsynaptic potential Inhibitory postsynaptic potential  Types of NT INHIBITORY NT EXCITATORY NT Acetylcholine GABA Glutamate Glycine Norepinephrine Dopamine Serotonin Histamine SUMMATION OF POSTSYNAPTIC POTENTIAL  DIRECT & INDIRECT INHIBITION Inhibition in the CNS can be postsynaptic or presynaptic. Postsynaptic inhibition during the course of an IPSP is called direct inhibition. There are various forms of indirect inhibition, which is inhibition due to the effects of previous postsynaptic neuron discharge.  Presynaptic inhibition Mechanisms that suppress release of neurotransmitters from axon terminals or varicosities. Involves axo-axonal transmission where release of a neurotransmitter from one axon acts at receptors on another axon to suppress release of transmitter from the second axon. The increase in Cl- conductance or K efflux reduces transmitter release by inactivation of voltage- gated Na+ and Ca2+ channels Figure 4  lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction. This creates a contrast in stimulation that allows increased sensory perception. Figure 5  The vast majority of drugs that influence the nervous system function by altering synaptic mechanisms. Synaptic drugs may block an undesirable effect or enhance a desirable effect Properties of synaptic transmission Effect of alkalosis or acidosis Effect of drugs Stimulants: caffeine, theophylline (found in coffee-tea) Inhibitory: anaesthetics  Synaptic plasticity Synaptic plasticity is the ability of the synapse, between two neurons to change in strength in response to either use or disuse of transmission over synaptic pathway, i.e., synaptic conduction can be strengthened or weakened on the basis of past experience.  Post- tetanic facilitation increase in neurotransmitter release after a brief, high-frequency train of action potentials The successive stimulation causes Ca++ to accumulate in the presynaptic neuron; the elevated Ca++ level causes more and more vesicle to release their transmitter producing a greater response of the postsynaptic neuron. may last for minutes and sometimes hours THANK YOU