lecture 4

Question 1

excitability

Answer 1

ability to produce an electrical signal that can transmit information between different regions of the membrane
their membrane is called an excitable mebrane

Question 2

graded potentials

Answer 2

a small, local change in membrane potential

occur in depolarizing or hyperpolarizing direction

• are graded
• are decremental (lose strength with distance)
• can be summed

Question 3

action potentials

Answer 3

• large alterations in the membrane potential
• are rapid and have high frequency

-all-or-none

-need voltage gated channels to occur

duration : 1-2 ms

-sustained nerve signaling over longer distances

3 phases : rising, falling, after hyperpolarization

-happen at axon hillock

Question 4

Na + and K+ voltage gated channels

Answer 4

• activated by a change in electrical membrane potential
• important for AP
• sodium has activation and inactivation gate (very rapid open/close)
• potassium on activation gate (very slow open/close)

Question 5

ligand gated channels

Answer 5

• open in response to the binding of a chemical messenger
• important for graded potentials

opens at 55mV

Question 6

mechanically gated channels

Answer 6

• open in response to a physical deformation (pressure on membrane)
• important for graded potentials

Question 7

rising phase

Answer 7

• voltage-gated (activation gate) Na+ channels open at -55mV
• potassium activation gates start to open as well (slowly)
• peaks at around +30 where inactivation gate for sodium closes
• potassium activation gate finally open here and begins to repolarize cell

Question 8

falling phase

Answer 8

• potassium leaving the cell
• Resetting: Na + activation gate is closed now, inactivation gate is open

Question 9

after hyperpolarization

Answer 9

voltage gated K+ channels slow to close which leads to hyperpolarization

-finally close which leads to resting membrane potential once again

Question 10

lodocaine and tetroxin

Answer 10

• prevent AP’s by blocking voltage-gated Na+
• poison produced by puffer fish that blocks Na+ voltage gated channels

Question 11

threshold stimulus

Answer 11

just strong enough to depolarize the membrane to threshold, usually 15mV less negative than resting membrane potential (-55mV)

Question 12

relative refractory period

Answer 12

larger than normal stimulus is required to trigger another AP

Question 13

absolute refractory period

Answer 13

second AP cannot be triggered

-wont fire because sodium channels already open during rising, and falling there in an inactivation gate inhibiting from firing

(absolutely not)

Question 14

will one AP affect the concentration gradients???!!!!!!

Answer 14

NO!

Question 15

can AP propagatte backwards????!!??!?!!

Answer 15

NO!!!

-refractory period prevents firing of another AP

Question 16

Na channels during depolarization

Answer 16

entry of Na+ into the membrane causes additional Na+ channels to open in adjacent segment (positive feedback loops)

Question 17

saltatory conduction

Answer 17

how an electrical impulse skips for node to node down the full length of an axon

• myelinated setions : current flows quick because of insolation and no leak
• nodes of ranvier : unmyelinated sections. depolarization opens Na+ channels and AP is replenished

Question 18

2 factors that affect the speed of conduction

Answer 18

• greater diameter
• myelination