Lecture 5-Chp. 4

Question 1

Excitable tissues

Answer 1

• Nerve and muscle cells produce electrical signals when excited
• Neurons use these electrical signals to receive, process, initiate, and transmit messages
• Muscles use these electrical signals to stimulate cytoskeletal movement
• Some endocrine tissues release hormones as response to excitation

Question 2

3-19. Membrane Potential (Vm)

Answer 2

• Separation of opposite charges across the plasma membrane
• Results from differences in the concentration and permeability of key ions
• Expressed as inside relative to outside

Question 3

Resting membrane potential

Answer 3

• Characteristic of all cells, used for purpose by some cells
• Balance of passive leaks and active pumping (ATP powered)
• Neither K+ or Na+ at equilibrium, Cl- not influential
• In most cells, Vm is < 0 (anions dominate in the cytosol)

Question 4

Neural Communication

Answer 4

• Signals are produced by changes in ion movement across the plasma membrane
• An event triggers a change in membrane potential
• Alters the membrane permeability and consequently alters ion flow across the membrane

Question 5

Gated ion channels

Answer 5

• Voltage
• Ligand
• Mechano-gated (stomach)

Question 6

Graded Potentials

Answer 6

• Local changes in membrane potential
• Occur in varying degrees of magnitude
• The stronger a triggering event, the larger the resultant graded potential
• Spread by passive current flow
• Current: any flow of electrical charges
• Die out over short distance

Question 7

Depolarization

Answer 7

More positive

Question 8

Repolarization

Answer 8

return to resting membrane potential

Question 9

Hyperpolarization

Answer 9

more negative, overshoot resting potential

Question 10

Action potential

Answer 10

• Brief, rapid, large (100mV) changes in Vm
• Inside of cell transiently becomes more positive than outside
• Marked changes in ion movement
• Voltage gated Na+ and K+ channels
• Positive feedback: Change in Vm causes more channels to open
• Once Vm hits “threshold” level, many channels open, many ions move, large change in Vm

Question 11

Pion

Answer 11

membrane permeability to ion (channel/pumps open or closed?)

Question 12

Activation gate

Answer 12

mid-protein portion of ion channel which blocks ion movement unless rapidly opened when channel changes conformation (voltage gated)

Question 13

Inactivation gate

Answer 13

cytosolic portion of Na+ channel that blocks the channel 0.5 msec after opening and has a time release; contributes to refractory period.

Question 14

Detailed steps of Action potential

Answer 14

1. Resting: channels closed
2. 5 Some voltage gated Na+ channels open (activation gates open), Na+ influx
3. Vm rises to -50mV (threshold). Many Na+ activation gates open, large Na+ influx, large depolarization.
4. Steep rising phase-Na+ influx.
5. At peak of AP, Na+ inactivation gates close, P Na+ falls, K+ activation gates open.
6. Falling phase-K+ efflux repolarization
7. At resting Vm Na+ channels reset (activation gate closed, inactivation gate open)
8. Continued K+ efflux hyperpolarizes membrane
9. K+ activation gate closes, membrane returns to resting Vm, (partly action of Na+/K+ ATPase).

Question 15

Resting Vm

Answer 15

(-70mV)

• Large net diffusion of K+ outward establishes an Ek+ of -90mV
• There is no diffusion of A- across membrane
• Relatively small net diffusion of Na+ inward neutralizes some of the potential created by K+ alone