Term
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Definition
Neuron in neuronal circuits talk to each other and other cell types (muscle, glandular epithelium) across special junctions between them called synapses.
Synapses transmit impulses in one direction from the presynaptic (transmitting) neuron to the postsynaptic (receiving) neuron |
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Term
| Synaptic end bulbs, presynaptic terminals |
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Definition
| bulblike structures at the end of neurons |
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Term
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Definition
| At a synaptic junction, the membranes of the pre- and postsynaptic neurons are separated by a little gap called the synaptic cleft. |
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Term
| Six known neurotransmitters |
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Definition
1) acetylcholine
2) norepinephrine (= noradrenalin)
3) dopamine
4) serotonin
5) glutamic acid
6) gamma-amino butyric acid (GABA)
7) neuropeptides (the endorphins, dynorphin, enkephalin, substance P, and somatostatin) |
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Term
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Definition
| If the neurotransmitter is acetylcholine, the transmitting neuron is said to be cholinergic. If the neurotransmitter is norepinephrine (noradrenalin), the neuron is said to be adrenergic. |
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Term
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Definition
| The presynaptic terminals enclose numerous synaptic vesicles, essentially little balloons of membrane that contain neurotransmitters |
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Term
| Release of neurotransmitters when an action potential arrives |
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Definition
| When a nerve impulse arrives at the presynaptic terminal, the presynaptic membrane depolarizes and this opens voltage-gatted calcium channels. Calcium therefore enters the presynaptic terminal and this of calcium concentration triggers fusion of synaptic vesicles with presynaptic membrane. The contents of the synaptic vesicles are then discharged by exocytosis into the synaptic cleft. |
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Term
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Definition
| After the release of neurotransmitter into the synaptic cleft, the combine with specialized receptors on the postsynaptic membrane. The time needed for them to be released, carry the message across the synaptic cleft, bind to is postsynaptic membrane receptor and cause a response is called synaptic delay (0.5 msec) |
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Term
| Action of Neurotransmitters |
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Definition
| Neurotransmitters act by opening ion channels in the plasma membrane of the postsynaptic (receiving) cell in two major ways |
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Term
| Excitatory neurotransmitters (example: glutamate) |
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Definition
| depolarize the plasma membrane of the receiving neuron. That is, they make the postsynaptic membrane permeable to sodium ions. They may do this directly by acting on transmitter-gated sodium channels. Alternatively, the neurotransmitter may act indirectly by activating an enzyme that generates a second messenger called cyclic AMP, which then goes on to activate enzymes that open up the sodium channels. |
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Term
| Excitatory postsynaptic potentials (EPSPs) |
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Definition
| generally, the release of a neurotransmitter by a single presynaptic terminal is not enough to make the postsynaptic neuron fire, develop an action potential in the postsynaptic membrane. there is usually a transient sub-threshold depolarization |
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Term
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Definition
| they last for about 15 msec. While a single EPSP may be insufficient to cause the postsynaptic neuron to fire, EPSPs can sum together, so that their combined depolarizations reach threshold, and therefore trigger an action potential at the axon hillock of the postsynaptic neuron. |
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Term
| Temporal summation of EPSPs |
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Definition
| when summation is the result of a train of impulses arriving one after the at a single synapse |
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Term
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Definition
| when the EPSPs are generated by impulses traveling down several axons arriving at several different synapses on one postsynaptic neuron, they may also sum together and cause the postsynaptic neuron to fire. In this way, the postsynaptic neuron is able to integrate inputs from a number of neurons that synapse with it. |
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Term
| Inhibitory Neurotransmission |
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Definition
| Some of the synapses on the surface of a neuron are excitatory but others may be inhibitory. That is, they make it more difficult to excite the neuron, or they damp down its activity. Like excitatory neurotransmitters, inhibitory neurotransmitters are removed by reuptake mechanisms or enzymatically. |
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Term
| Inhibitory neurotransmitters (example: gamma-amino butyric acid, GABA) |
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Definition
| are released at inhibitory synapses, and inhibit the effect of excitatory neurotransmitters on a postsynaptic neuron. |
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Term
| Inhibitory postsynaptic potential (IPSP) |
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Definition
| The Nernst potential for chloride is about -90 mV. If the resing membrane potential is less than this, say 85mV, the result will be a transient hyper-polarization. This transient hyper-polarization is called an inhibiroty postsynaptic potential (IPSP) |
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Term
| Acetylcholinesterase (or just cholinesterase) |
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Definition
| enzyme that removes Acetylcholine, present in the postsynaptic membrane |
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Term
Monoamine oxidase
Reuptake |
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Definition
| Norepinephrine (noradrenalin) can be destroyed by the enzyme monoamine oxidase, but is removed mainly by reuptake into the PREsynaptic terminal, where it may be recycled. The neurotransmitters serotonin and dopamine are also treated the same way. |
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Term
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Definition
| act by blocking the reuptake process (serotonin in the of Prozac, norepinephrine, serotonin, and dopamine in the case cocaine), so increasing the concentration of neurotransmitter in the synaptic cleft. |
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Term
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Definition
| (derived from L-gutamic acid) is also removed by an uptake mechanism, partly by reuptake at the presynaptic terminal, partly by astrocytes. The astrocytes convert glutmate into glutamine, which is then returned to the neuron for resynthensis of glutamate. |
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Term
| If the excitatory input is greater than the inhibitory input, then the result is either |
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Definition
1. a sub-threshold depolarization which facilitates the neuron; makes it excitable
2. a threshold or suprathreshold depolarization, exciting the neuron. The neuron generates an action potential or a train of action potentials if the depolarization is substantial |
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Definition
| is an important property of certain synapses in parts of the nervous system. Continued use of these synapses strengthens them, and it is thought that the process may be involved in memory formation. |
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Term
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Definition
| The neurotransmitter at the neuromuscular junction and other synapses in the nervous system. ITs action is terminated by the enzyme cholinesterase |
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Term
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Definition
| norepinephrine (NE), dopamine, serotonin. Dopamine is sometimes inhibitory, while NE and serotonin appear to be excitatory. The action of these neurotransmitters is often terminated by reuptake mechanisms involving special molecules in the plasma membrane called neurotransmitter transporters. |
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Term
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Definition
| Norepinephrine, epinephrine (also known as adrenaline) and dopamine are referred to as the catecholamines |
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Term
| Amino acids - gamma-amino butyric acid (GABA) |
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Definition
| is the most common inhibitory neurotransmitter in the brain. |
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Term
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Definition
is the most common excitatory neurotransmitter in the brain.
Terminated by reuptake methods |
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Term
| Neuropeptides - small peptides that include somatostatin, enkephalins, endorphins, substance P, dynorphin |
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Definition
| Endorphins, dynorphin, and enkephalins have morphine-like qualities, and appear to suppress transmission in pain pathways of the brain and spinal cord. Substance P, on the other hand, appears to be a neurotransmitter in the pain pathways |
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Term
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Definition
| modulate the response of neurons to other neurotransmitters. Neuromodulators may alter the responsiveness of a neuron by exciting or inhibiting the opening of ion channels, or by changing the properties of the neuron in the other ways. |
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