Lecture 3-4 Action potential 1 and 2 Flashcards Preview

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Flashcards in Lecture 3-4 Action potential 1 and 2 Deck (29)
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1
Q

excitable cells

A

cells that produce electrical signals when stimulated

like nerves or muscles

2
Q

when a membrane is excited, what are the stages it does thru and what defines this change?

A

there is a charging time, maximum voltage time and then a decay.
Length constant defines how fast the signal decays over a certain length of a neuron- the larger the length constant the slower it decays

3
Q

active conduction

A
  • what is used to spread electric signal across a large distance like down the leg
  • there is no decay over the distance
4
Q

what is the structure of a voltage gated Na channel and how many states go along with it?

A
  • the voltage gated Na channel has two gates-an inactivation and activation gate.
  • There are three states: during the CLOSED state the inactivation gate is open and the activation gate is closed
  • in the OPEN state, both gates are open allowing Na thru
  • in the INACTIVATED state, the inactivation gate is closed and the activation gate is open
  • In order to let Na thru again, you must go thru the closed state and start over
5
Q

Voltage Gated K channels- how many states and how many gates?

A

-has one gate and two states- closed and open

6
Q

How are action potentials generated?

A
  • the membrane starts at a resting state with Na and K voltage gated ion channels being closed.
  • then, depolarization (make membrane less neg) opens the membrane up to A Na channel
  • the rising phase of the actin potential causes further depolarization and more Na voltage gated channels to open
  • falling phase- closes sodium influx and opens voltage gate K channels letting K out. (membrane repolarizes)
  • undershoot- K volt. gated channels remain open and then close causing all to go back to resting phase
7
Q

when the membrane potential goes up (gets less negative) what happens to Na and K channels?

A

-Na channels open, reach a max voltage and then close allowing K channels to open

8
Q

Local anesthetic

A

-Na channel blocker that blocks action potential and decreases pain sensation by binding on outside of Na channel, inside and in the bilayer

9
Q

what does tetrodotoxin do? where is it from? symptoms?

A

from a puffer fish, it’s a Na voltage gated channel blocker

causes weakness, dypnea, and oral paresthesias caused by a lack of being able to generate an action potential

10
Q

If ouabain is used, what occurs?

A
  • Ouabain is a Na/K ATPase pump inhibitor (poison)
  • it makes it stop pumping Na and K but the chemical concentration gradients take time to degrade and a large axon can fire thousands of action potentials via Na and K voltage gated channels before the Na and K concentrations are depleated
11
Q

AP threshold

A
  • action potential threshold
  • the lowest amount of depolarization or lowest voltage that allows Na channels to go into fast, positive feedback loop
  • once threshold is reached, action potential generation Is no longer dependent on stimulation
12
Q

what influences AP threshold?

A

k channels
na channels
ca2+ concentration

13
Q

how does Ca2+ influence AP threshold?

A
  • when calcium is low, it makes the AP threshold go to almost resting state
  • smaller amount of depolarization needed to reach threshold
14
Q

symptoms of low ca2+

A

neuropsych probs
neuromuscular irritability- chvostek’s sign, Trousseau sign
cardiovascular probs
autonomic probs

15
Q

Chvostek’s sign

A
  • tapping near ear where facial nerve is causeing contraction of eye, mouth or nose
  • sign of hypocalcemia 2/3 of pt but 10% of normal people have it
16
Q

Trousseau’s sign

A
  • MORE specific for hypocalcemia than chvostek’s sign
  • in 94% of hypocalcemic pt
  • if put a B.P cuff on pt and increase above systolic pressure, it triggers muscle spasm in hands
17
Q

Hypercalcemia

A
  • action potential threshold is increased and moves further away from resting membrane potential as external Ca++ conc increases
  • larger amount of depolarization needed to reach threshold
18
Q

how is the calcium concentration related to sodium channels and action potential?

A
  • as calcium concentration increases the threshold for action potential gets higher
  • the more the calcium, the less likely the Na channels are open for depolarization of the membrane
19
Q

Relative refractory period?

A
  • a second response (second action potential) from the membrane can be elicited but at a greater “cost” (ie strength or duration of stimulus is higher)
  • represented by the hyperpolarized state with the K channels open
20
Q

Absolute refractory period

A
  • a second membrane response impossible regardless of strength or duration of stimulus
  • represented by Na channel activation and inactivation
21
Q

how does action potential propagation work?

A

-via a sequential propagation down the neuron that extends to either side of the stimulus

22
Q

what prevents bidirectional flow of an action potential across neurons and prevents weirdo firing in our systems?

A
  • axons have an axon hillock
  • the hillock has the lowest membrane AP threshold so they generate the first AP
  • the structure of the hillock allows only unidirectional flow down the axon
  • the AP travels down the axon via propagation
23
Q

how is the axon width related to the velocity of the action potential across the axon

A

the bidder the diameter the faster the axon conducts action potentials

24
Q

what purpose does myelin serve and what is it made out of? Overall affect of myelination?

A
  • electrical insulation
  • proteins, lipids, cholesterol
  • it decreases axon membrane capacitance and increases membrane resistance to give insulation
25
Q

what cells do myelin cover in the peripheral nervous system? central?

A
  • peripheral = schwann

- central = oligodendrocytes

26
Q

node of ranvier

A
  • breaks in myelin sheath where current is propagated -straight down the node rather than in the internodal space.
  • since the current can only go thru via the nodes of ranvier, the rest of the current bounces off the membrane and forms a loop along the axon
27
Q

why is conduction so fast in myelinated axons?

A

-because the axon doesn’t waste time forming a AP on the myelin covered portion and because myelin causes capacitance to be lower

28
Q

multiple sclerosis

A
  • demyelination via autoimmune disease of the CNS
  • demyelination of oligodendrocytes responsible for not only myelination of CNS but nutritional (trophic) support to axons
29
Q

guillain barr syndrome

A
  • causes demyelination of PNS (schann cells)
  • cause muscle weakness and paralysis
  • usually follows infections like stomach bugs or respiratory infection
  • can recover because unlike CNS, PNS can remyelinate =IMPORTANT