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Propagation of Action Potential
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Deploration Na+
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Nervous Tissue II
Nervous Tissue II_Chp 12
| Question | Answer |
|---|---|
| Propagation of Action Potential | spreads over the surface of the axon membrane |
| Deploration Na+ | fows into the cell; affects voltage of adjacent areas; voltage-gated Na+ channels open; |
| Action Potentional | self propagated along membrane; can be progagated via continuous or saltatory conduction, depending on myelin |
| Continuous Conduction | occurs in unmyelinated axons; AP is propagated b step-by-step depolarization of each portion of the length of the axon membrane "domino effect" |
| Saltatory Conduction | occurs in myelinated axons; deplorization occurs only at nodes of ranvier (where ion channels are); current is carried through ECF and "jumps" from node to node |
| myelinated axons (saltatory conduction) | ions only have to diffuse at nodes not across the entire membrane; this allows for more rapid conduction of action potentials |
| factors that affect speed of Impulse Conduction | fibers myelinated or not; diameter of fiber (thick fibers transmit AP's faster; presece/absence of calcium ions |
| Calcium ions | are needed to close Na+ channels |
| If Na+ keeps diffusing in | impulses are transmitted repeatedly (muscle spasms); fetus may take up to much calcium and cause mother to cramp a lot. |
| Electrical Synapses 1 | AP's conduct directly between adjacent cells through gap junctions; AP spreads from cell to cell via cytosol |
| Electrical Synapses 2 | common in visceral smooth muscle, cardiac muscle, and developing embryo; conduction is faster than chemical synapse; allows synchronization-a large number of neurons can produce AP's in unison-coordinated contraction |
| Gap Junctions | in cardiac and visceral smooth muscle allow the action potential itself to spread from cell to cell, enabling coordinated contraction of muscle fibers |
| Chemical synapse 1 | AP is transferred from teh presynaptic ("sending") neuron to the postsynaptic ("receiving") neuron across a synaptic cleft |
| Chemical synapse 2 | current generates AP, then AP is transmitted; requires neurotransmitters; takes longer than electrical synapse |
| Excitatory (effects of neurotransmitters) | if the neurotransmitter causes opening of Na+ channels; Na+ diffuses in - membrane depolarizes; if enough Na+ channels open to reach threshold nerve impulse will be generated |
| Inhibitory (effects of neurotransmitters) | if the neurotransmitter causes opening of other channels (Cl- or K+, hyperpolarizing membrane; Cl- can diffuse in, or K+ will leave neuron; inside of neuron will be even more negatice and will be less likely to reach threshold |
| Summation | each neuron in brain and spinal cord may receive neurotransmitters from hundreds of nerve fibers; some neurotransmitters may be excitatory or inhibitory; sum of excitatory+inhibitory messages determines whether AP will be generated in postsynaptic neuron |
| Removal of Neurotransmitter | after AP is generated in postsynaptic neuron, the neurotransmitter must be removed |
| Diffusion (Removal of Neurotransmitter) | NT simply diffuses out of synaptic cleft, losing contact with postsynaptic neuron and NT receptors |
| Enzymatic degradation (Removal of Neurotransmitter) | enzyme from postsynaptic neuron breaks down NT after AP has been generated; Acetycholine & acetylcholinesterase; epinephrine and monoamine oxidase |
| Uptake into cells (Removal of Neurotransmitter) | NT may be actively transported into neighboring neuroglial cells (uptake) or into presynaptic neuron (re-uptake) |
| drug effects on re-uptake (cocaine) | re-uptake of blocks dopamine (produces continued stimulation pleasure |
| drug effects on re-uptake (SSRI's-selective serotonin re-uptake inhibitors) | keeps deficient serotonin in cleft as long as possible (elevates mood, relieves depression) |
| drug effects on re-uptake (MAO-monamine oxidase inhibitors) | prevent MAO from breaking down epinephrine and norepinphrine; EPI and NE do a lot of stuff, including elevating mood; preventing breakdown may help treat depression |
| Acetylcholine (ACh) (representative neurotransmitters) | released by many PNS neurons & some CNS; excitatory in skeletal muscle; inhibitory in cardiac muscle |
| Amino Acid (representative neurotransmitters) | Glutomate=released by most excitatory neurons in the brain; inactivated by re-uptake; GABA=inhibitory NT for 1/3 of all brain synapses, & 1/2 of inhibitory synapses in spinal cord |
| Amino Acid (representative neurotransmitters) | Glycine is inhibitory NT for other 1/2; |
| Valium | enhances binding GABA=increasing inhibition=decreases anxiety |
| Huntington's disease | causes progressive GABA deficiency=thrashing, dementia |
| Strychnine | blocks glycine receptors on skeletal muscles=no inhibition of excessive contraction=can't relax muscles, including diaphragm=can't breathe |
| Norepinephrine (representative neurotransmitters) | affects mood, dreaming, awakening from a deep sleep |
| Dopamine (representative neurotransmitters) | affects skeletal muscle tone, emotion, pleasure, addictive behavior (Parkinson's disease=tremors) |
| Serotonin (representative neurotransmitters) | involved in control of mood, appetie, temp regulation, induces sleep |
| Endorphins and enkephalins (representative neurotransmitters) | pain reliever, may be released in response to stress; morphine, heroin, opium fit same receptors; blocked endorphins acupunture don't work |
| Substance P (representative neurotransmitters) | when released in sensory nerves, transmits pain related info to CNS; endorphins and enkephalins suppress release; 200x stronger than morphine |
| chemical synapse (AP process step 1) | AP reaches synaptic end bulb and depolarizes membrane causing voltage-gated calcium channels to pen in the synaptic end bulb |
| chemical synapse (AP process step 2) | calcium ions in ECF diffuse into the presynaptic neuron |
| chemical synapse (AP process step 3) | calcium ions trigger exoctosis of vesicles containing neurotransmitters (NT) |
| chemical synapse (AP process step 4) | NT is released into the synaptic cleft and diffuses across to the postsynaptic neuron; receptors in the membrane of the postsynaptic neuron bind NT |
| chemical synapse (AP process step 5) | Ligand-gated ion channels open, ionsdiffuse in and membrane depolarizes |
| chemical synapse (AP process step 6-7) | if membrane potentional reaches threshold, AP in the postsynaptic neuron and AP/nerve impulse is sent on. |
Created by:
sweetlatrece
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