Synapses

Synapses - Synapse and synaptic transmission of neurons...

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Synapse and synaptic transmission of neurons PHSI 0441, Spring 2012 1
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Synapse Specialized apposition between cells that mediate signals 2
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Synapse Neurons come very close together at chemical synapses , but their membranes and cytoplasm remain distinct . At electrical synapses , ions and other small solutes can diffuse through the gap junctions 3
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Types of synapse – electrical and chemical Electrical synapse Gap junction; proteins in membranes that form pores between cells Cells are electrically coupled Flow of ions from cytoplasm to cytoplasm Very fast transmission Postsynaptic potentials – integrate to form an action potential 4
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Gap junction 5
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Functions Rapid signaling Synchronize electrical activity Eg. brainstem neurons that synchronize breathing pattern Hormone secreting neuron surge Found in retina CNS, axons Cardiac muscle Smooth muscle Receptor cells 6
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Electrical and chemical synapse 7
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Why chemical synapse rather than electrical? Amplification Inhibition Broad time domain Plasticity 8
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Chemical synapse Most common cell-cell communication Found in Neurons NMJ Neuron glandular epithelium 9
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Neuromuscular junction Neuromuscular junction - Chemical synapse between a motor neuron and a skeletal muscle cell Neurotransmitter of skeletal neuromuscular junction is always acetyl choline The receptor is nicotinic Ach receptors 10
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11 Chemical neurotransmitter substance is acetylcholine .
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12 Synaptic vesicles are lined in rows along the inner surface of the terminal membrane. The presynaptic membrane region associated with each double row of vesicles is called an active zone where synaptic vesicles will release acetylcholine into the synaptic cleft. The presynaptic terminal also contain mitochondria. Some mitochondrial products (e.g., acetyl-CoA, ATP) play a role in the local synthesis of acetylcholine and in its movement into the synaptic vesicles
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Postsynaptic membrane Postsynaptic muscle cell membrane contains receptors for acetylcholine The membrane has a series of invaginations, called junctional folds The acetylcholine receptors are most densely packed at the mouth of these junctional folds, and these mouths are aligned with the active zones of the presynaptic terminals Transmission of signal is from neuron to muscle, not in the reverse direction . A motor neuron gives off several presynaptic terminals to an individual muscle fiber which is localized to a restricted region of the muscle fiber 13
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Neuronal synapses Neuronal synapses use many transmitters like glutamate, aspartate (excite), g amino butyric acid and glycine (inhibit) Simple amines- Ach, norepinephrine, serotonin, histamine and peptides Receptors are ionotropic or metabotropic 14
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Synapses - Synapse and synaptic transmission of neurons...

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