2.2 The Nerve Impulse Flashcards
Concentration gradient
The difference in distribution for various ions between the inside and outside of the membrane
Selective permeability
The ability of some molecules to pass much more freely through the membrane than others do
Sodium-potassium pump
A protein complex which transports three sodium ions out of the cell while simultaneous drawing two potassium ions into the cell
Electrical gradient
The difference in positive and negative charges across the membrane
Hyperpolarization
Increased polarization
Depolarization
Reduction of its polarization
Threshold of excitation
Any stimulation beyond a certain level; produces a sudden, massive depolarization of the membrane
Action potential
A rapid depolarization and slight reversal of the usual polarization
Voltage-activated channels
Membrane channels whose permeability to sodium or some other ion depends on the voltage difference across the membrane
Local anesthetic drugs
Attached to the sodium channels of the membrane, preventing sodium ions from entering; i.e. Novocain and Xylocaine
General anesthetics
Decrease brain activity by opening stern potassium channels wider than usual; i.e. ether and chloroform
All-or-none law
The size, amplitude, and velocity of an action potential are independent of the intensity of the stimulus that initiated it
Refractory period
During which the cell resist the production of further action potentials
Absolutely refractory period
The sodium gates are firmly closed and the membrane cannot produce an action potential, regardless of the stimulation; ~1 ms
Relative refractory period
The sodium gates are reverting to the usual state, but potassium gates remain open. Because of the free flow of potassium, a stronger than usual stimulus is necessary to initiate an action potential. ~2-4 ms
Where does an action potential begin?
On the axon hillock
Axon hillock
A swelling where the axon exits the soma
The propagation of the action potential
Describe does the transmission of an action potential down an axon
Myelinated axon
Found only in vertebrates; covered with myelin sheath, a coating composed mostly of facts
Nodes of Ranvier
Short unmyelinated sections of axon; each node is only about one micrometer wide
Saltatory conduction
The jumping of action potentials from node to node
Plural of soma
Somata
Graded potentials
Membrane potential is that vary in magnitude and do not follow the all-or-none law
Polarization
The neuron inside the membrane has a slightly negative electrical potential with respect to the outside
