synapse and n eural integration
DESCRIPTION
بسم الله الرحمن الرحيم. Synapse and N eural Integration . Dr.Mohammed Sharique Ahmed Quadri Assistant prof. Physiology Al Maarefa College. Objectives . Define synaptic transmission List the types of synapses Describe the mechanism of action of chemical and electrical synapse. - PowerPoint PPT PresentationTRANSCRIPT
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Synapse and Neural Integration
بسم الله الرحمن الرحيم
Dr.Mohammed Sharique Ahmed QuadriAssistant prof. Physiology
Al Maarefa College
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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
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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
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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
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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 signals are rare in Human Nervous System.
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ELECTRICAL SYNAPSES [cont]
• Example of Electrical Synapses --- Pulp of tooth --- Retina of the Eye --- Cardiac Muscle --- Smooth Muscle
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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
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synapse
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Synapse
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Synaptic Delay
• Transmission of electrical impulse [AP] by chemical means from presynaptic neuron to post-synaptic neuron takes time. It is called ‘Synaptic Delay’. It is 0.5 to 1 millisecond.
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SynapsesSignal at synapse either
excites or inhibits the postsynaptic neuron
• Two types of synapses– Excitatory synapses– Inhibitory synapses
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Neurotransmitters
• Vary from synapse to synapse
• Same neurotransmitter is always released at a particular synapse
• Quickly removed from the synaptic cleft
• Some common neurotransmitters– Acetylcholine– Dopamine– Norepinephrine– Epinephrine– Serotonin– Histamine– Glycine– Glutamate– Aspartate– Gamma-aminobutyric acid
(GABA
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‘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.
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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.
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Neuropeptides
• Large molecules consisting of from 2 to 40 amino acids
• Synthesized in neuronal cell body in the endoplasmic reticulum and Golgi complex
• Packaged in large, dense-core vesicles present in axon terminal
• Neuropeptides are considered neuromodulators don’t cause the formation of EPSP or IPSP, but bring about long term changes that subtly modulate, depress or enhance the action of the synapse
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Comparison of Classical Neurotransmitters and Neuropeptides
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Post-Synaptic Potential
• EPSPs and IPSPs are graded potential [local]. They can be summated [added].
• Types of Summation 1. Temporal Summation 2. Spatial Summation
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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.
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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.
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Presynaptic inhibition or facilitation can selectively alter the effectiveness of a presynaptic input.
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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.
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Convergence And Divergence [cont]
Divergence It refers to the branching of axon
terminals so that single cell synapses with many other cells.
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Convergence And Divergence
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‘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. 25
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Synaptic Drug Interactions
• Possible drug actions
1. Altering the synthesis, axonal transport, storage, or release of a neurotransmitter
2. Modifying neurotransmitter interaction with the postsynaptic receptor
3. Influencing neurotransmitter reuptake or destruction4. Replacing a deficient neurotransmitter with a
substitute transmitter
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Assignment
• Drugs and diseases that modifies the synaptic transmission
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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