Muscle Physiology Flashcards
Which type of skeletal muscle is red in color?
Slow aka Type 1
Which type of skeletal muscle is white?
Fast aka Type 2
True or false: Type 1 muscles are larger in diameter than Type 2 muscles.
False
Which skeletal muscle type contains large amounts of myoglobin and is powered largely by aerobic metabolism?
Slow aka Type 1 aka Red muscle
Which skeletal muscle type has an extensive SR?
Fast aka Type 2 aka White
What are the two types of smooth muscle? What are the differences between the two?
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.
Vascular smooth muscle has properties of both _________ and _________ smooth muscle.
unitary and multiunit
What initiates action potentials in cardiac muscle?
Spontaneous pacemaker potentials of the SA node.
Which zone of the sarcomere shortens during muscle contraction?
the H zone.
What three proteins make up thin filaments?
Actin, tropomyosin, and troponin.
What is the main purpose of tropomyosin?
To interfere with actin-myosin binding during muscle relaxation.
Name the trimeric components of troponin and state what they do.
TnT - binds to tropomyosin
TnC - binds Ca2+
TnI - binds actin (think I band - actin filaments only) and also Inhibits myosin-actin binding.
What does an increase in [Ca2+] do to troponin?
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.
Describe the five cross-bridge cycling steps.
- Rest - ATP is bound and hydrolyzed
- Influx of Ca2+, myosin-actin bind
- ADP + Pi released –> power stroke
- A new ATP binds to myosin, cross-bridge detaches
- Repeat
What is the TnC equivalent in smooth muscle?
Calmodulin
What happens after calmodulin binds Ca2+?
Calmodulin-Ca2+ phosphorylates myosin light chain kinase (MLCK), which activates ATPase activity so that ATP can bind and be hydrolyzed by the myosin head.
What are T-tubules?
Invaginations of the skeletal muscle sarcolemma that allow APs to penetrate deep into the cells.
One T-tubule makes contact with two terminal ______ at the triad.
cisternae
APs that come down the T-tubule membrane activate voltage gated ____ ____ channels in the T-tubule membrane.
L-type Ca2+ channels AKA DHP receptors
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.
Ca2+ release channels
What is a ryanodine receptor?
The same thing as the SR Ca2+ release channels
How are ryanodine receptors connected to the L-type Ca2+ channels?
Mechanically and chemically (ligand). Poorly understood.
What is malignant hyperthermia?
Mutant ryanodine receptor causes an increase in Ca2+ sensitivity while under (volatile) general anesthesia.
What are the three mechanisms of smooth muscle EC coupling?
- Ca2+ entry through L-type Ca2+ channels.
- SR release of Ca2+ (ryanodine receptors).
- IP3-induced Ca2+ release from SR (ligand-gated channels).
What is the most important Ca2+ reuptake mechanism responsible for restoring muscle relaxation?
SR Ca2+ pump
