chapter-12.4- 12.5 Membrane Potential

Question 1

Extracellular fluid contains—-concentrations of —and——

Answer 1

high
Na+
Cl-

Question 2

Cytosol contains————–and ———–

Answer 2

high concentration of K+
negatively charged proteins

Question 3

What are the passive processes acting across cell membranes

Answer 3

• Chemical gradients
• Concentration gradients of ions (Na+, K+)
• Electrical gradients
• Charges are separated by cell membrane
• Cytosol is negative relative to extracellular fluid
• Electrochemical gradient
• Sum of chemical and electrical forces acting on an ion across the
  membrane
• A form of potential energy

Question 4

What is the function of the sodium-potassium pump?

Answer 4

• Powered by ATP
• Ejects 3 Na+ for every 2 K+ brought in
• Balances passive forces of diffusion
• Stabilizes resting membrane potential (–70 mV)
• When ratio of Na+ entry to K+ loss through passive channels is
  3:2

Question 5

Describe the passive ion channel

Answer 5

These are also called leak channels and are always open and permeability changes with conditions.

Question 6

Describe active ion channels

Answer 6

These are also called gated ion channels which open and close in response to stimuli. Most are closed at resting membrane potential.

Question 7

What are the types of active channels

Answer 7

• Chemically gated ion channels
• Voltage-gated ion channels
• Mechanically gated ion channels

Question 8

Describe the chemically gated ion channels

Answer 8

the chemically gated ion channels are also called ligand-gated ion channels which open when they bind to specific chemicals. These are found on cell bodies and dendrites of neurons.

Question 9

Describe the voltage-gated ion channel

Answer 9

They are found in the axons of neurons and sarcolemma of skeletal and cardiac muscle cells which respond to changes in membrane potential

Question 10

Describe the mechanically gated ion channels

Answer 10

these respond to membrane distortion and found in sensory receptors that respond to touch, pressure or vibration

Question 11

Explain hyperpolarization

Answer 11

Results from opening potassium ion channels
* Positive ions move out, not into cell
* Opposite effect of opening sodium ion channels
* Increases the negativity of the resting potential

Question 12

What is the threshold for an axon

Answer 12

-60 to -55

Question 13

At which mv do sodium channels closed and what also open at the same time

Answer 13

sodium channels close and potassium channels open.
potassium moves out of cytosol and repolarization begins

Question 14

What is value for hyperpolarization

Answer 14

-90

Question 15

what is absolute refractory period

Answer 15

all voltage-gated sodium channels are open or inactivated
the membrane cannot respond to further stimulation

Question 16

What is a relative refractory period

Answer 16

This begins when sodium channels regain resting condition and continues until membrane potential stabilizes.
only a strong stimulus can initiate another action potential.

Question 17

What is propogation

Answer 17

moves an action potential along an axon in a series of steps

Question 18

what are the two types of propagation

Answer 18

continuous propagation
saltatory propagation

Question 19

Describe continuous propagation

Answer 19

It occurs in unmyelinated axons and it happens in each segment. Therefore as one segment is repolarizing the other segment is depolarizing

Question 20

Describe saltatory propagation

Answer 20

this occurs in myelinated axons
it is faster that continuous propagation and requires less energy

Question 21

What are the types of fibers

Answer 21

• Type A fibers
• Type B fibers
• Type C fibers

Question 22

Describe the types of fibers

Answer 22

Type A fibers
* Myelinated
* Large diameter
▪ Type B fibers
* Myelinated
* Medium diameter
* Transmit information at intermediate speeds (18 m/sec)
▪ Type C fibers
* Unmyelinated
* Small diameter
* Transmit information slowly (1 m/sec)
* Example: most sensory information