Synapse and Neural Integration Lecture Notes PDF

‫بسم الله الرحمن الرحيم‬ Synapse and Neural Integration Dr Nisreen Daffa Alla Omer M.B.B.S, Ph. D (Human Physiology), MSc medical education Assistant prof. Physiology Al Maarefa University& University of Khartoum  Object...

‫بسم الله الرحمن الرحيم‬ Synapse and Neural Integration Dr Nisreen Daffa Alla Omer M.B.B.S, Ph. D (Human Physiology), MSc medical education Assistant prof. Physiology Al Maarefa University& University of Khartoum  Objectives Define synaptic transmission List the types of synapses Describe the mechanism of action of chemical and electrical synapse. Explain the mechanisms of excitatory and inhibitory post-synaptic potentials. Compare EPSP &IPSP Describe the properties of synaptic transmission 2  SNAPSES AND NEURONAL INTEGRATION A Neuron may terminate on one of THREE structures: 1) MUSCLE 2) GLAND 3) ON ANOTHER NEURON – JUNCTION BETWEEN TWO NEURON IS CALLED SYNAPSE 3  Synapses Junction between two presynaptic and postsynaptic neurons There are two types of Synapse: 1. Electrical Synapses: Two neurons connected by gap junctions 2. Chemical Synapses: Chemical messenger is transmitted across the junction separating the two neurons 4 Synapses between neurons  ELECTRICAL SYNAPSES In electrical synapses, two neuron are connected by Gap Junction which allow ions (charged particles) to flow between the two cells. Therefore Action Potential travels from one cell to another. Electrical synapse are rare in Human Nervous System. 6  ELECTRICAL SYNAPSES [cont] Example of Electrical Synapses --- Pulp of tooth --- Retina of the Eye --- Cardiac Muscle --- Smooth Muscle 8  CHEMICAL SYNAPSES In human CNS , most of the synapses are Chemical, where chemical messenger transmits information from one neuron to another. WE WILL DISCUSS CHEMICAL SYNAPSE 9 Chemical synapse Chemical synapse 11 Transmission in chemical synapses 13  Neurotransmitters Vary from synapse Some common neurotransmitters to synapse – Acetylcholine – Dopamine Same – Norepinephrine neurotransmitter is – Epinephrine always released at a – Serotonin particular synapse – Histamine – Glycine – Glutamate Quickly removed – Aspartate from the synaptic – Gamma-aminobutyric cleft acid (GABA 14  ‘Important’ Glutamate – Most common excitatory neurotransmitter in the brain. It causes EPSP. GABA [Gamma amino butyric acid] – Most common inhibitory neurotransmitter in brain. It causes IPSP. 15 What is next after neurotransmitter binds to its receptor Signal at synapse either excites or inhibits the postsynaptic neuron Two types of synapses – Excitatory synapses – Inhibitory synapses 16  Post-Synaptic Potential Postsynaptic potentials are changes in the membrane potential of the postsynaptic terminal of a chemical synapse. Postsynaptic potentials are graded potentials and not action potentials. Two: 1. EPSP 2. IPSP 17  Excitatory postsynaptic potential- EPSP If the neurotransmitter stimulate opening of sodium channels or calcium channels, the postsynaptic cell membrane deperpolarize  Inhibitory postsynaptic potential- IPSP If the neurotransmitter stimulate opening of chloride channels or potassium channels, the postsynaptic cell membrane hyperpolarize  Types of summation of postsynaptic potential 1. Temporal Summation When single presynaptic neuron is stimulated many times after short intervals, to summate several EPSP, it is called ‘Temporal Summation’. Up to 50 EPSPs might be needed to bring post-synaptic membrane to threshold level. 20  2. Spatial Summation When two or more excitatory neurons are stimulated together at the same time, to get the action potential. It is called Spatial Summation. 21 22 Presynaptic inhibition or facilitation can selectively alter the effectiveness of a presynaptic input. 23  Convergence And Divergence  Convergence: On a given neuron, many other neurons come and synapse on it. It is called ‘Convergence’. Due to convergence input, a single neuron is influenced by thousands of other cells. 24  Convergence And Divergence [cont]  Divergence It refers to the branching of axon terminals so that single cell synapses with many other cells. 25 Convergence And Divergence 26  ‘Important Information’ There are about 100 billion neurons in the brain. A single neuron maybe connected to 5000 to 10,000 other neurons. Brain is responsible for different activities like sensations, movements of muscle, thought, emotion, memory – all these depend on electrical and chemical signaling between neurons along wired neural pathways. 27 Neurotransmitter Removal From The Synaptic Cleft Neurotransmitters are quickly removed from the synaptic cleft by various ways: 1. Inactivated by enzymes present on post synaptic membrane. 2. Diffuse away from synaptic cleft. 3. Actively taken back into axon terminal. 28 Inactivated by enzymes present on post synaptic membrane.  Classroom questions The most abundant type of synapse The Most common excitatory/inhibitory neurotransmitter in the brain Steps of transmission in chemical synapse Ion trigger neurotransmitter release Ionic basis of EPSP& EPSP Removal of neurotransmitter from the synapse  References Human physiology by Lauralee Sherwood, seventh edition Text book physiology by Guyton &Hall,11th edition Text book of physiology by Linda.s contanzo,third edition 31