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Pema Lama
Nerve Signaling
| Term | Definition |
|---|---|
| Membrane potential | slight excess of positively charged ions on the outside of the membrane and slight deficiency of positively charged ions on the inside of the membrane |
| Polarized membrane | a membrane that exhibits a membrane potential |
| Resting membrane potential (RMP) | Membrane potential maintained by a nonconducting neuron’s plasma membrane; typically ⫺70 mV |
| Sodium-potassium pump | Active transport mechanism in plasma membrane that transports Na⫹ and K⫹ in opposite directions and at different rates Maintains an imbalance in the distribution of positive ions, resulting in the inside surface becoming slightly negative |
| Local potentials | slight shift away from the resting membrane in a specific region of the plasma membrane |
| Excitation | when a stimulus triggers the opening of additional Na⫹ channels, allowing the membrane potential to move toward zero (depolarization) |
| Inhibition | when a stimulus triggers the opening of additional K⫹ channels, increasing the membrane potential (hyperpolarization) |
| Action potential | the membrane potential of a neuron that is conducting an impulse; also known as a nerve impulse |
| Absolute refractory period | brief period (lasting approximately 0.5 ms) during which a local area of a neuron’s membrane resists restimulation and will not respond to a stimulus, no matter how strong |
| Relative refractory period | —time during which the membrane is repolarized and restoring the resting membrane potential; the few milliseconds after the absolute refractory period; will respond only to a very strong stimulus |
| Two types of synapses (junctions) | Electrical synapses and Chemical synapses |
| Electrical synapses | occur where cells joined by gap junctions allow an action potential to simply continue along postsynaptic membrane |
| Chemical synapses | occur where presynaptic cells release chemical transmitters (neurotransmitters) across a tiny gap to the postsynaptic cell, possibly inducing an action potential there |
| Synaptic knob | tiny bulge at the end of a terminal branch of a presynaptic neuron’s axon that contains vesicles housing neurotransmitters |
| Synaptic cleft | space between a synaptic knob and the plasma membrane of a postsynaptic neuron |
| Axodendritic | axon signals postsynaptic dendrite |
| Axosomatic | axon signals postsynaptic soma |
| Axoaxonic | axon signals postsynaptic axon; may regulate action potential of postsynaptic axon |
| Plasma membrane of a postsynaptic neuron | has protein molecules that serve as receptors for the neurotransmitters |
| Spatial summation | adding together the effects of several knobs being activated simultaneously and stimulating different locations on the post-synaptic membrane, producing an action potential |
| Temporal summation | when synaptic knobs stimulate a postsynaptic neuron in rapid succession, their effects can summate over a brief period to produce an action potential |
| Short-term memories | (seconds or minutes) may result from axoaxonic facilitation or inhibition of the presynaptic axon terminal |
| Intermediate long-term memory | (minutes to weeks) happens when sero-tonin blocks potassium channels in the presynaptic terminal—thus prolonging the action potential and increasing the amount of neurotrans-mitter released |
| Long-term memories | (months or years) require structural changes at the synapse—for example, more vesicles, more vesicle release sites, more presynaptic terminals, more sensitive postsynaptic membranes |
| Neurotransmitters | —means by which neurons communicate with one another; there are more than 50 compounds known to be neurotransmitters, and dozens of others are suspected |
| Chemical structure of Neurotransmitters | a. functions of specific neurotransmitters vary by location, they are often classified according to chemical structure b. Small-molecule neurotransmitters comprise four main class c. Large-molecule neurotransmitters are polypeptides called neuropeptides |
| Acetylcholine | a. Unique chemical structure b. It is deactivated by acetylcholinesterase, with the choline molecules being released and transported back to the presynaptic neuron to combine with acetate c. Present at various locations |
| Amines | a. Synthesized from amino acid molecules b. Two categories: monoamines and catecholamines c. Found in various regions of the brain, affecting learning, emotions, motor control, and so on |
| Amino acids | a. Believed to be among the most common neurotransmitters of the central nervous system b. In the peripheral nervous system, amino acids are stored in synaptic vesicles and used as neurotransmitters |
| Other small-molecule transmitters | a. Nitric oxide (NO) derived from the amino acid arginine b. NO from a postsynaptic cell signals the presynaptic neuron, providing feedback in a neural pathway |
| Neuropeptides | —large-molecule neurotransmitters Neuropeptides are short strands of amino acids called polypeptides or peptides |
| Convergence | more than one presynaptic axon synapses with a single postsynaptic neuron |
| Divergence | a single presynaptic axon synapses with many different postsynaptic neurons |
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Pemalama