Muscle Physiology

Question 1

Which type of skeletal muscle is red in color?

Answer 1

Slow aka Type 1

Question 2

Which type of skeletal muscle is white?

Answer 2

Fast aka Type 2

Question 3

True or false: Type 1 muscles are larger in diameter than Type 2 muscles.

Answer 3

False

Question 4

Which skeletal muscle type contains large amounts of myoglobin and is powered largely by aerobic metabolism?

Answer 4

Slow aka Type 1 aka Red muscle

Question 5

Which skeletal muscle type has an extensive SR?

Answer 5

Fast aka Type 2 aka White

Question 6

What are the two types of smooth muscle? What are the differences between the two?

Answer 6

Multiunit - each cell is innervated by one or more autonomic nerve terminals so contraction can happen independently of other muscle cells. Few gap junctions.

Unitary - Extensive gap junctions allow for coordinated contractions. AKA visceral smooth muscle.

Question 7

Vascular smooth muscle has properties of both _________ and _________ smooth muscle.

Answer 7

unitary and multiunit

Question 8

What initiates action potentials in cardiac muscle?

Answer 8

Spontaneous pacemaker potentials of the SA node.

Question 9

Which zone of the sarcomere shortens during muscle contraction?

Answer 9

the H zone.

Question 10

What three proteins make up thin filaments?

Answer 10

Actin, tropomyosin, and troponin.

Question 11

What is the main purpose of tropomyosin?

Answer 11

To interfere with actin-myosin binding during muscle relaxation.

Question 12

Name the trimeric components of troponin and state what they do.

Answer 12

TnT - binds to tropomyosin
TnC - binds Ca2+
TnI - binds actin (think I band - actin filaments only) and also Inhibits myosin-actin binding.

Question 13

What does an increase in [Ca2+] do to troponin?

Answer 13

Ca2+ binds to the low affinity binding sites on TnC, causing a conformational change that moves the Troponin and Tropomyosin complexes out of the way so that the myosin head can bind to actin.

Question 14

Describe the five cross-bridge cycling steps.

Answer 14

1. Rest - ATP is bound and hydrolyzed
2. Influx of Ca2+, myosin-actin bind
3. ADP + Pi released –> power stroke
4. A new ATP binds to myosin, cross-bridge detaches
5. Repeat

Question 15

What is the TnC equivalent in smooth muscle?

Answer 15

Calmodulin

Question 16

What happens after calmodulin binds Ca2+?

Answer 16

Calmodulin-Ca2+ phosphorylates myosin light chain kinase (MLCK), which activates ATPase activity so that ATP can bind and be hydrolyzed by the myosin head.

Question 17

What are T-tubules?

Answer 17

Invaginations of the skeletal muscle sarcolemma that allow APs to penetrate deep into the cells.

Question 18

One T-tubule makes contact with two terminal ______ at the triad.

Answer 18

cisternae

Question 19

APs that come down the T-tubule membrane activate voltage gated ____ ____ channels in the T-tubule membrane.

Answer 19

L-type Ca2+ channels AKA DHP receptors

Question 20

Through the conformational change and influx of Ca2+ through L-type Ca2+ channels, ______ ______ _______ in the SR membrane opens to allow for Ca2+ ion flow into the sarcoplasm.

Answer 20

Ca2+ release channels

Question 21

What is a ryanodine receptor?

Answer 21

The same thing as the SR Ca2+ release channels

Question 22

How are ryanodine receptors connected to the L-type Ca2+ channels?

Answer 22

Mechanically and chemically (ligand). Poorly understood.

Question 23

What is malignant hyperthermia?

Answer 23

Mutant ryanodine receptor causes an increase in Ca2+ sensitivity while under (volatile) general anesthesia.

Question 24

What are the three mechanisms of smooth muscle EC coupling?

Answer 24

1. Ca2+ entry through L-type Ca2+ channels.
2. SR release of Ca2+ (ryanodine receptors).
3. IP3-induced Ca2+ release from SR (ligand-gated channels).

Question 25

What is the most important Ca2+ reuptake mechanism responsible for restoring muscle relaxation?

Answer 25

SR Ca2+ pump

Question 26

Fast fiber will

Answer 26

fatigue faster because they contain less mitochondria

Question 27

muscle tension increases with

Answer 27

increasing frequency of motor stimulation

Question 28

dantrolene

Answer 28

muscle relaxant that lower the affinity of the ryandone receptor to calcium