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