week 3 Flashcards
diff bw GPs and APs in terms of…
a) location
b) channel types involved
c) ions involved
d) duration
GPs vs APs:
a) dendrites/soma/sensory receptors vs axon
b) ligand and mechanically-gated vs voltage-gated
c) Na+, Cl-, or K+ vs Na+ and K+
d) few msec to seconds vs 1-2 msec
phases of an AP (3)
- depolarization
- repolarization
- after-hyperpolarization
when do Na+ channels open?
once threshold is reached (~-55mV)
do VGSCs operate in a positive or negative feedback system?
positive
why does the peak depolarization of an AP only reach +30mV? why not reach the EP of Na+ (+60mV)?
because soon after the VGSCs open, they inactivate
what causes repolarization? (2)
- at rest, K+ leaks out of cell, so cell becomes more negative.
- VGPCs open (recall: EC of K+ = out).
which are faster: VGSC or VGPC?
- VGSCs are faster.
- this is why the repolarization phase (which depends on VGPCs) takes longer and overshoots (after-hyperpolarization).
do VGPCs operate in a positive or negative feedback system?
negative
review: at rest, is Na+ or K+ more permeable?
K+
what brings the membrane to threshold?
sum of the graded potentials
what restores resting membrane potential?
Na+/K+ pump
are the activation and inactivation gates open or closed at…
a) rest
b) depolarization
c) repolarization
a) rest: activation = closed, inactivation = open
b) depolarization: activation = open, inactivation = open
c) repolarization: activation = open, inactivation = closed
why are threshold and suprathreshold stimuli equal in size?
bc all-or-none principle
what is a refractory period? whats the diff bw absolute and relative refractory periods?
refractory period: decreased excitability following an AP because VGSCs are inactive until membrane potential is at rest.
absolute: ALL VGSCs are inactive. spans all of de and most of repolarization. second AP cannot occur.
relative: SOME VGSCs are inactive. last part of re and after-hyperpolarization. second AP may occur with stronger stimulus.
what is most common local anesthetic dentists use to “freeze” you and how does it work?
- lidocaine
- works as VGSC blocker, preventing APs (pain)
can you completely block membrane from generating AP?
- yes
- keep membrane depolarized above threshold to stop influx of sodium.
- inject KCl to destroy concentration gradient for K+ (will keep inside of cell positive, keeping VGSC inactive).
if APs are all-or-none, how do we differentiate strong vs weak stimuli?
- frequency coding
- strong stimuli encoded in higher frequency of APs
what are the cons of an unmyelinated axon? (2)
- leakage of ions
- decreased conduction velocity
how does the propagation of APs work in unmyelinated axons?
- A = depolarized
- positive charge of A attracted to negative charge of B
- B = depolarized
- cycle continues
what makes the propagation of APs unidirectional?
absolute refractory period
what are the factors affecting propagation? (3)
- refractory period (makes it unidirectional)
- axon diameter (larger = faster)
- myelination (saltatory conduction = faster)
how does the propagation of APs work in myelinated axons?
- high density of VGSC at nodes of ranvier
- AP jumps from node-to-node
in electrical synapses, neurons are linked together by ___. what do these contain?
- gap junctions
- contain connexins that allow ions to cross
functions of electrical synapses in the nervous system? (5)
- rapid communication
- ions or second messengers
- usually bidirectional communication
- excitation and inhibition at same synapse
- identified in retina, cortex, brainstem (breathing), and hypothalamus (neuroendocrine neurons).
