Action Potentials Flashcards
membrane potential
potential to do work
polarized
difference in charge on either side of membrane
voltage
measurement of AP
excitable cells
cells that can rapidly change MP
is the membrane more permeable to K+ or Na+?
K+, 100x more
hyperpolarization
become more negative inside cell; MP decrease below RP -> inhibitory
inhibitory
lowers the ability to generate a signal
depolarization
becomes less negative inside cell (may become positive); still negative, but less positive; MP increases above RP -> excitatory
excitatory
increases ability to generate a signal
action potential
electrical signal w/in a neuron
- all or none
- either happens or doesn’t
- always the same voltage change
within action potentials, what does the intensity of the message depend on
- # neurons stimulated
- frequency of stimulus
- NOT strength of AP
voltage-gated (VG) ion channels
- aka “gates”
- ONLY open at certain voltages/MPs
- opened by a stimulus (facilitated diffusion of that ion down concentration gradient)
magnitude of depolarization (small stimulus)
- FEW Na+ gates open
- weak depolarization
- MP does NOT reach -55 mV
- no AP
magnitude of depolarization (strong stimulus)
- MANY VG Na+ channels open
- Strong depolarization
- if MP reaches -55 mV -> AP
conductions of AP
- signal propagates as series of APs along axon
- axon hillock -> synaptic terminal
- voltage shift in one region -> opens Na+ gates further down
- area behind now in refractory period (Na+ gates resetting)
- unidirectional signal
continuous conduction
- occurs in unmyelinated axons
- every spot on axon depolarizes and repolarizes
saltatory conduction
- occurs in myelinated axons
- insulation surrounding vertebrate axons, made by olgiodendrocytes (CNS) and Schwann Cells (PNS)
internodes
regions covered myelin - no depolarization
nodes of ranvier
no myelin - lots of Na+, K+ VG channels; depolarization only occurs at nodes
-“saltatory” - signal “jumps” from node to node
which is better: saltatory or continuous?
saltatory. its >50 x faster and more E efficient
multiple sclerosis
- immune system attacks myelin sheath and oligodendrocytes in the CNS
- slows AP conduction, exposes nerve fibers to damage
- weakness, impaired vision, numbness … depending on sites of damage
