lecture 8 Flashcards
What are the characteristics of skeletal muscle?
Elongated cells, visible striations, multi-nuclear (peripheral), voluntary, no gap junctions, Ca2+ and troponin, fastest to contract.
What are the characteristics of cardiac muscle?
Branching cells, visible striations, single central nucleus, involuntary, stimulated by pacemaker, regulated by ANS, gap junctions, Ca2+ and troponin, medium rate of contraction.
What are the characteristics of smooth muscle?
Spindle-shaped, no visible striations, single central nucleus, involuntary, stimulated by hormones, pacemaker cells, ANS, stretch, gap junctions, Ca2+ and calmodulin, slowest to contract.
What are the three connective tissues of skeletal muscle?
- Epimysium
- Perimysium
- Endomysium
What is the function of epimysium?
Fibrous CT that envelopes the whole skeletal muscle and protects it from friction.
What is the role of perimysium in skeletal muscle?
Connective tissue that creates groups of muscle fibers called fascicles.
What does endomysium surround?
Each muscle fiber and electrically insulates them from each other.
What is the neuromuscular junction?
The junction between the nerve and the muscle fiber.
What is a sarcomere?
The smallest contractile unit of a muscle fiber, measured from Z-disk to Z-disk.
What gives rise to the striated pattern in muscle fibers?
The regular organization of contractile proteins within the entire fiber.
What are the components of the actin filament complex?
- F-actin
- Tropomyosin
- Troponin
What is the role of tropomyosin in muscle contraction?
Covers active sites on actin to prevent interaction with myosin in the resting state.
What is the function of troponin in muscle contraction?
Regulates binding of myosin to actin; sensitive to Ca2+.
What happens during the power stroke of myosin?
The myosin cross-bridge slides the actin filament into the middle of the sarcomere.
What is excitation-contraction coupling?
The process where nerve excitation leads to muscle contraction.
What triggers the release of calcium in muscle cells?
Excitation of the muscle cell.
What are the mechanisms of calcium removal from the muscle cell?
- Na+-Ca2+ exchanger
- Ca2+-ATPase
- Sequestration by calreticulin and calsequesterin
What is the difference between isotonic and isometric contractions?
- Isotonic: creates force and moves a load
- Isometric: creates force without moving a load
What does the length-tension relationship describe?
The overlap of thick and thin filaments and the potential for cross-bridge interaction.
How does load affect the velocity of muscle contraction?
Shortening velocity decreases as load increases.
What is the definition of twitch in muscle physiology?
The force generated following a single electrical pulse.
What occurs during a tetanic contraction?
Repetitive stimulation leads to summation of forces from individual pulses.
What is a motor unit?
A single alpha motor neuron and all the muscle fibers it innervates.
What are the characteristics of Type I muscle fibers?
- Dark red
- Slow shortening velocity
- Low myosin ATPase activity
- High mitochondrial density
What are the characteristics of Type IIB muscle fibers?
- White
- Fastest shortening velocity
- High myosin ATPase activity
- Lowest mitochondrial density
What are the characteristics of Type IIA muscle fibers?
- Red
- Fast shortening velocity
- Intermediate/high myosin ATPase activity
- High mitochondrial density
What principle explains motor unit recruitment?
Henneman’s Size Principle - smaller alpha motor neurons are more excitable than larger ones.
