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Myelin again

Myelin again . Myelin speeds up the nerve impulse because nerve fibers have Schwann cells around them Schwann cells restrict ion movement So impulse “jumps” between the nodes of Ranvier This jumping is called saltatory transmission . Synaptic Transmission .

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Myelin again

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  1. Myelin again • Myelin speeds up the nerve impulse because nerve fibers have Schwann cells around them • Schwann cells restrict ion movement • So impulse “jumps” between the nodes of Ranvier • This jumping is called saltatory transmission

  2. Synaptic Transmission • Saltatory transmission impulse along a neuron • Synaptic transmission impulse between neurons • Happens at the end of an axon • No actual connection between the terminus and the membrane of the next cell • Space between is called a synapse or synaptic gap/cleft

  3. Synaptic membranes • Axon membrane is called the pre-synaptic membrane • Has Ca2+ gate • Has synaptic vesicles with neurotransmitters inside • Membrane on the other side of synaptic cleft is the post-synaptic membrane • Has protein receptor sites

  4. Steps • Impulse arrives at end of axon • depolarization of pre-synaptic membrane • Ca2+ gates open - Ca2+ in the synaptic cleft moves into the axon • Vesicles with neurotransmitters inside fuse with the pre-synaptic membrane • Neurotransmitters are released (exocytosis) into the synaptic cleft and diffuse across to the post synaptic membrane

  5. 1. After an action potential arrives at an axon terminal, Ca2+ enters, and synaptic vesicles fuse with the presynaptic membrane. axon terminal Ca2+ synaptic vesicles enclose neurotransmitters synaptic cleft

  6. 2. Neuro- transmitters are released and bind to receptors on the postsynaptic membrane. axon terminal NT Ca2+ synaptic vesicles enclose neuro- transmitters synaptic cleft

  7. 6) Neurotransmitters bond to receptor sites on the post-synaptic membrane 7) Step (6) causes the Na+ gates to open on post synaptic membrane which starts the nerve impulse along that cell 8) Synaptic cleft is returned to normal - enzymes that destroy specific neurotransmitters - Ca2+ returned to the synaptic cleft (active transport)

  8. axon terminal 3. When an excitatory neurotransmitter binds to a receptor, Na+diffuses into the postsynaptic neuron, and an action potential begins. Ca2+ NT receptor Na+ postsynaptic neuron synaptic cleft

  9. Synaptic Transmission in General • Energy for synaptic transmission comes from mitochondria in the axon • Synaptic transmission only occurs in one direction due to nature of the membranes on either side of the synaptic cleft • 2 types of neurotransmitters • Inhibitory NT – makes it harder for depolarization of the next membrane • Excitatory NT – promotes depolarization of the next membrane

  10. ANIMATION • Transmission across a synapse

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