Muscle Part 2

Question 1

Membrane potential exists across the membrane of what?

Answer 1

All cells

Question 2

How is membrane potential generated?

Answer 2

By the ionic differences between ICF and ECF

Question 3

Ionic differences are consequences of:

Answer 3

Differential permeability of the membrane to the ions

Operation of the membrane pump

Question 4

What cells generate rapidly changing electrochemical impulses at their membranes?

Answer 4

Muscle & nerve

Question 5

How are impulses used?

Answer 5

To transmit signals along the nerve or muscle fibers

Question 6

Skeletal muscle cells or fibers are controlled by what?

Answer 6

A motor neuron

Question 7

The ______ ______ is the origin of the nerve, with its location in the CNS (it looks like a spider web)

Answer 7

Motor neuron

Question 8

Motor neurons that synapse on skeletal muscles have their cell bodies located where?

Answer 8

Within the CNS (brain stem or spinal cord)

Question 9

Where do axons travel?

Answer 9

Within peripheral nerves out to the muscle

Question 10

Each nerve ending makes a _______________ __________

Answer 10

Neuromuscular junction

Question 11

How many NMJs per skeletal muscle cell?

Answer 11

ONE

Question 12

What 3 things cause diffusion of molecules and ions through cell membranes?

Answer 12

Chemical forces
Electrical forces
Pressure difference

Question 13

The rate of net diffusion into the cell is _________ to the concentration difference across a membrane

Answer 13

Proportional

Question 14

What is Nernst Potential?

Answer 14

When an electrical potential is applied across the membrane, the electrical charges of the ions cause them to move, even without concentration difference, until they come to equilibrium - there is NO NET OVERALL FLOW!!!!!

Question 15

Example of Nernst Potential

Answer 15

Positive charge attracts negative ions, while negative charges repel positive ions

Question 16

Pressure Difference is when what?

Answer 16

A higher pressure is applied to one side of membrane, so more molecules diffuse to other side

Question 17

Example of pressure difference in action:

Answer 17

Capillary exchange

Question 18

Explain how ions are distributed across cell membrane

Answer 18

Cytosol contains abundance of negatively charged proteins and K+
Proteins cant cross plasma membrane
Na+ is more concentrated outside of cell

Question 19

Resting potential of nerve fibers when not transmitting nerve signals is around what?

Answer 19

-70mV!

The potential inside the fiber is 70 mV MORE NEGATIVE than outside!!!!!!

Question 20

What 3 factors determine resting potential?

Answer 20

Diffusion of K+ thru nerve cell membrane
Diffusion of Na+ thru nerve cell membrane
Contribution of Na/K pump

Question 21

Potassium leak channels:

Answer 21

Allow K+ ions to diffuse out of cell
100 more Xs selective for K than Na
Protein anions remain in cell (think a/b orange anions in pic)
K also moves into cell bc attracted to - charge

Question 22

Sodium leak channels allow:

Answer 22

Na+ to leak INTO cell
NO diffusion of protein anions again :(
Relatively large net diffusion of K+! Bc membrane is more permeable to K+

Question 23

Na/K pump!

Answer 23

Continually transports Na+ OUT and K+ IN !!!!!!!!!
(Think Naout and Kin)
2 K+ ions bind on outside of pump, 3 Na+ ions on inside of pump
ATPase becomes activated AFTER binding

Question 24

Na/K pump…

Answer 24

Is an important way to control volume
Additionally contributes to negative resting potential
ATP is cleaved into ADP

Question 25

Cytosol contains what charge of proteins?

Answer 25

NEGATIVE

Question 26

What is an action potential?

Answer 26

Rapid changes in membrane potential that spread rapidly along the nerve fiber membrane

Question 27

Action potential moves along nerve fiber until…

Answer 27

It comes to fiber’s end

Question 28

5 steps in action potential:

Answer 28

1. Resting stage
2. Depolarization stage
3. Repolarization stage
4. Propagation of action potential
5. Refractory Period

Question 29

Resting Stage:

Answer 29

This is the moment before the AP begins; membrane is polarized because of the negative membrane potential
THE CELL IS NEGATIVE INSIDE

Question 30

Depolarization Stage:

Answer 30

-rise in membrane potential of 15-30 mV
-after mechanical, chemical or electrical disturbances
-a threshold for the INITIATION of the action potential is achieved!!!!
Now, the membrane SUDDENLY becomes permeable to sodium ions
—-this is a massive movement of + charged Na ions into the interior of axon

Question 31

Membrane Potential rising in the positive direction is called what?

Answer 31

Depolarization

Question 32

In the depolarization stage, the massive influx of Na ions occurs through what?

Answer 32

Voltage-gated Na+ channels

Question 33

Voltage-gated Na+ channels are activated when…

Answer 33

Membrane potential starts to change

–its a + feedback cycle

Question 34

Repolarization state

Answer 34

After the membrane becomes highly permeable to Na ions, Na channels begin to close
Voltage gated K channels open to a greater degree than normal (rapid diffusion of K out of cell)
Re-establishment of normal NEGATIVE resting potential, called repolarization

Question 35

Propagation (the wide spreading of) AP

Answer 35

AP elicited at any one point on an excitable membrane usually excites adjacent portions of the membrane

Question 36

The AP

Answer 36

Travels in all directions always from the stimulus until entire membrane has become depolarized

Question 37

Refractory period

Answer 37

A new action potential cannot occur in an excitable fiber as long as the membrane is still depolarizing from the preceding AP

Question 38

During the refractory period, the only condition that will allow channels to reopen is?

Answer 38

The returning of the original resting potential

Question 39

The period in which a second AP cannot be elected is called

Answer 39

ABSOLUTE refractory period