Unit II (4-8) - Membrane Physiology, Nerve and Muscle

Question 1

The resting membrane potential is

Answer 1

-90mv

Question 2

During the depolarization stage there is increased permeability to what electrolyte

Answer 2

Na+

Question 3

During the depolarization stage ____ channels close and ___ channels open

Answer 3

Na+

K+

Question 4

_____ is responsible for establishing the action potential gradient

Answer 4

Na/K ATPase pump

Question 5

The plateau in some action potentials is caused by

Answer 5

opening of slow Ca channels

Question 6

What is the difference between an absolute and a relative refractory period?

Answer 6

Absolute - no action potential can occur when with strong stimulus
Relative - follows an absolute refractory period, action potential can be generated with a large enough stimulus

Question 7

What is the difference between the I bend and the A band?

Answer 7

I band - light band - contains actin only

A band - dark band - contains actin and myosin

Question 8

The ___ band in skeletal muscle decreases in length with muscle contraction

Answer 8

I band

Question 9

The troponin complex is composed of what 3 subunits? and what does each subunit have strong affinity for

Answer 9

Troponin I (inhibitory) - strong affinity for actin
Troponin T - strong affinity for Tropomyosin
Troponin C - strong affinity for Calcium ions

Question 10

Describe the general mechanism of skeletal muscle contraction

Answer 10

1. AP travels along nerve cell to muscle fiber
2. ACh secreted and opens ACh gated channels
3. Na goes into muscle fiber
4. AP travels along muscle fiber causing release of Ca from sarcoplasmic reticulum
5. Ca binds troponin complex and allows for interaction between actin and myosin = contraction
6. Ca goes back into sarcoplasmic reticulum and out of the cell = relaxation

Question 11

What is the difference between Type I and Type II muscle fibers?

Answer 11

Type I - red muscle, smaller fibers with large amounts of myoglobin because it needs to store O2, fibers react slowly but with prolonged contraction
Type II - white muscle, larger fibers with no myoglobin, react rapidly

Question 12

Why does rigor mortis occur?

Answer 12

Muscles become rigid due to loss of ATP (ATP is required to cause separation of cross bridges)

Question 13

What is responsible for initiation of contraction of smooth muscle?

Answer 13

Ca -Calmodulin complex

Question 14

What is responsible for relaxation of smooth muscle?

Answer 14

Decrease in the intracellular Ca concentration and myosin phosphatase removes phosphate from the myosin light chain, causing detachment of myosin from actin therefore relaxation

Question 15

By what mechanisms can hormone or local tissue factors mediate smooth muscle excitation

Answer 15

Opening of Na or Ca channels = depolarization of membrane
Stimulation of action potential
Depolarization w/o AP - promoting Ca entry into the cell
Stimulation of Ca release from SR

Question 16

By what mechanism can hormones or local tissue factors mediate smooth muscle relaxation

Answer 16

Close Na and Ca channels = prevent influx of ions
Opening K channels which = allowing efflux
Through second messengers = cAMP, cGMP - activates Ca pumps making it go into SR or out of muscle fiber

Question 17

What is the source of energy in primary active transport?

Answer 17

ATP

Question 18

What is the source of energy in secondary active transport?

Answer 18

ionic concentration gradient

Question 19

Examples of primary active transport include

Answer 19

Na-K ATPase pump
Calcium pump
Hydrogen pump

Question 20

What are the functions of the Na-K ATPase pump?

Answer 20

1. maintain the electrical gradient in the cell
2. controls cell volume
3. makes ATP (only when working in reverse)

Question 21

Examples of secondary active transport include

Answer 21

Co transport (Na-Glu and Na-aa)
Counter transport (Na-Ca and Na-H) - Na into cell, Ca and H out of cell