1-Action Potential

Question 1

excitable cells

Answer 1

nerve + muscle

Question 2

types of electrical signals

Answer 2

1. local/passive: receptor potential, synaptic potential
2. active: action potential (stim in brain)

main difference that active does not decay over distance like passive

Question 3

circuit of excitable membrane

Answer 3

bilayer acts as capacitor to slow the charge/time constant*

*amount of time for voltage to change by 63% of eventual new steady state value

Question 4

passive conduction

Answer 4

-signal at the site of stimulation

-will decay over distance

Question 5

voltage gated Na channels

Answer 5

2 gates: activation + inactivation
3 states: closed (resting), open (activated), inactivated
-always in that order

tetrodotoxin from puffer fish blocks Na channel

Question 6

voltage gated K channel

Answer 6

1 gate
2 states: closed (resting), open (slow activation)

Question 7

action potential steps

Answer 7

1. resting state- both Na and K channels closed
2. depolarization- Na channel opens, K stays closed
3. rising of action potential- Na open, K closed
4. action potential- peak of voltage, overshoot
5. falling phase- Na inactivates, K opens, repolarize
6. undershoot- K stay open prolonged

Na cycle fast regeneration, K cycle slower

Question 8

membrane permeability during AP

Answer 8

1. resting- K>Na
2. rising- Na inc
3. AP- Na>K
4. falling- Na dec

Question 9

shape of action potentials

Answer 9

1. cardiac- AP w/ Ca plateau, slower
2. skeletal muscle- no plateau, sharper peaks
3. neurons- vary based on type

Question 10

local anesthesia

Answer 10

blocks Na channels to inhibit action potentials and reduce pain

Question 11

voltage threshold

Answer 11

AP’s are all or nothing so indicates a threshold

lowest voltage/minimal depolarization required to drive Na channels into fast feedback loop

above threshold stimulation not needed

Question 12

factors affecting AP threshold

Answer 12

1. Na channel
2. K channel
3. external Ca- indirectly thru Na channels open probability, direct relation to threshold

Question 13

hypocalcemia symptoms

Answer 13

1. neuropsychiatric
2. neuromuscular irritability (Chvostek, Trousseau)
3. cardiovascular
4. autonomic

bc lower threshold required so more spasms/contractions

Question 14

Chvostek sign

Answer 14

contraction of muscles @ eye, nose, mouth but not very sensitive or specific

Question 15

Trousseau sign

Answer 15

muscle spasm of hand and forearm, more specific and sensitive

Question 16

hypercalcemia

Answer 16

increases threshold so larger amount of depolarization needed to reach threshold

fatigue, muscle weakness, diminished reflexes

Question 17

refractory periods

Answer 17

absolute: no response to second stimulus bc Na channels inactivate

relative: second response possible but greater cost, bc K channel prolonged open

set up upper limit of firing frequency and unidirectional propogation

Question 18

AP propagation

Answer 18

if axon stimulated in the middle the current flow in both directions so AP goes both directions theoretically

Question 19

unidirectional propagation

Answer 19

stimulus at initial segment of axon with lowest threshold to open Na channels then flows down axon

some will flow back upstream but since Na channels inactive nothing happens

Question 20

axon size

Answer 20

larger axon diameter = faster axon conducts potential
-electrical conductance inc faster than capacitance

velocity = square root of radius

Question 21

myelination

Answer 21

greatly dec axon capacitance (bc capacitors connected in series) and inc membrane resistance = effective insulator

inc action potential conduction speed (saltatory conduction)

Question 22

myelin sheath composition

Answer 22

cholesterol
lipids
proteins

Question 23

Nodes of Ranvier

Answer 23

where Na channels are located high density so where AP generated, unmyelinated segments

Question 24

saltatory conduction steps

Answer 24

1. AP at one node = current flow to next node
2. new node reaches threshold = new AP jump to next node

fast bc no time wasted generating nodes in myelin covered and capacitance is lower

energy efficient bc less membrane to generate AP so less Na flows into cell aka less work for pump

length not matter

Question 25

Schwann Cells

Answer 25

myelinate a single axon in PNS

Question 26

oligodendrocytes

Answer 26

myelinate multiple axons in CNS

Question 27

Multiple Sclerosis

Answer 27

demylelination disease of CNS that damages axons

autoimmune attack oligodendrocytes

Question 28

Guillain-Barre Syndrome

Answer 28

demyelination of PNS, autoimmune

muscle weakness and paralysis but can recover bc remyelinaton/regeneration

maybe after infection or stomach flu