Chapter 4 Key Terms and Definitions
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| 314897260 | rising phase | The first part of an action potential, characterized by a rapid depolarization of the membrane. | |
| 314897261 | overshoot | The part of an action potential when the membrane potential is more positive than 0 mV. | |
| 314897262 | falling phase | The part of an action potential characterized by a rapid fall of membrane potential from positive to negative. | |
| 314897263 | undershoot | The part of an action potential when the membrane potential is more negative than at rest; also called after-hyperpolarization. | |
| 314897264 | after-hyperpolarization | The hyperpolarization that follows strong depolarization of the membrane; the last part of an action potential, also called undershoot. | |
| 314897265 | threshold | A level of depolarization sufficient to trigger an action potential. | |
| 314897266 | absolute refractory period | The period of time, measured from the onset of an action potential, during which another action potential cannot be triggered. | |
| 314897267 | relative refractory period | The period of time following an action potential during which more depolarizing current than usual is required to achieve threshold. | |
| 314897268 | voltage clamp | A device that enables an investigator to hold the membrane potential constant while transmembrane currents are measured. | |
| 314897269 | voltage-gated sodium channel | A membrane protein forming a pore that is permeable to Na+ ions and gated by depolarization of the membrane. | |
| 314897270 | patch clamp | A method that enables an investigator to hold constant the membrane potential of a patch of membrane while current through a small number of membrane channels is measured. | |
| 314897271 | channelopathy | A human genetic disease caused by alterations in the structure and function of ion channels. | |
| 314897272 | tetrodotoxin (TTX) | A toxin that blocks Na+ permeation through voltage-gated sodium channels, thereby blocking action potentials. | |
| 314897273 | voltage-gated potassium channel | A membrane protein forming a pore that is permeable to K+ ions and gated by depolarization of the membrane. | |
| 314897274 | saltatory conduction | The propagation of an action potential down a myelinated axon. | |
| 314897275 | spike-initiation zone | A region of the neuronal membrane where action potentials are normally initiated, characterized by a high density of voltage-gated sodium channels. |
