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Lecture 6

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Human Biology

Lecture 6 Membrane potential govern the ability to be able to move signals across the body: you can move them in a more public way like endocrine way or nervous system which is more private! We will start from the synapse onwards then leads to the autonomic nervous system 1) Synapse 2) Neurotransmitter 3) Receptor types 4) Autonomic nervous system Signal transmission, electrical and chemical synapses: Action potential comes down from the axon and reaches the electrical synapse where you have gap junctions. This is less common in animals but it is important for communication. You will find these in certain areas in nervous system in the brain Presyanptic neuron depolarized and been propagated down the action potential and has ions flux or pass through the gap junction with electrical signal and goes through the postsynaptic neuron Now fine, we get why we have electrical synapse, then why bother with the electrical synapse? Chemical synapse has the ability to amplilify or diminishes a chemical signal  the chemical that are released from presyanptic cam amplify or diminish to the post synaptic Electrical synapse Chemical synapse - Direct flow of electric current from one cell - Secrete neurotransmitter molecules that activate - to another through gap junctions: receptors: - Fast - Slower - Bi-directional - Unidirectional - Postsynaptic signal is similar to presynaptic - Pre and postsynaptic signals can differ signal - Excitatory or inhibitory (either ions will change or it - excitatory ( always gonna be like that, will be inhibited) always there will be a change in ions) Chemical synapsing: Action potential bringing down an electrical current all the way down the presyanptic cell. What happens? Voltage gated calcium ions, what is the key for synapse to release the neurotransmitter? 1) The voltage gated calcium channels 2) The presence of vesicles with important neurotransmitter released in the presyanptic cleft. Synaptic vesicles come down the axon and transported down the axon terminal. They are independent from the action potential!!! They weren’t there at first, they appear after. Invasion of calcium because of the change in the membrane potential at the axon bud and this invasion signals to the synaptic vesicles and bind to the docking protein which fuses with cell membrane then exocytose to the synaptic cleft and after there are ligand gated channels that bind with neurotransmitter and induces a response. That’s why calcium is involved. (REMEMBER, CHEMICAL SINGNAL ALWAYS HAS A LIGAND) Transmission of signal at the chemical synapse: - Postsynaptic cells have specific receptors for neurotransmitter! SPECIFIC! - Neurotransmitter will alter the membrane potential of the postsynaptic cell and this changes the membrane channel of this postsynaptic Response of postsynaptic cell dependent on: - Density of receptors on postsynaptic cell (how they are there) - Amount of neurotransmitter released which is determined by the frequency of action potential ( how much neurotransmitter are released) - The rate of removal (how long it takes) - Low frequency AP, low neurotransmitter, high then high neurotransmitter Neurotransmitter removal mechanisms: - Passive diffusion out of synapse - Degradation by synaptic enzyme
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