Skeletal, Smooth (and Cardiac) Muscle 1-3 Flashcards
Describe the structure and ultrastructure of skeletal muscle.
Each skeletal muscle consists of thousands of muscle fibers wrapped together by connective tissue sheaths. The individual bundles of muscle fibers in a skeletal muscle are known as fasciculi. The outermost connective tissue sheath surrounding the entire muscle is known as epimysium.
Explain the process of excitation-contraction coupling.
First coined by Alexander Sandow in 1952, the term excitation–contraction coupling (ECC) describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction. Excitation-contraction (E-C) coupling is the process by which the action potential of the motor neuron leads to the synchronous contraction of the myofibrils, of which there may be between hundreds to thousands within a given muscle fiber.
Explain the mechanics of skeletal muscle contraction.
An action potential (AP) travels along a motor nerve to its endings on muscle fibers. At each motor nerve ending, the nerve secretes acetylcholine (ACh). ACh acts locally on the muscle fiber membrane to open ACh-gated cation channels.
Define ‘isometric’ and ‘isotonic’ twitches.
Isotonic muscle contraction produces limb movement without a change in muscle tension, whereas isometric muscle contraction produces muscle tension without a change in limb movement.
Explain the sliding-filament theory of muscle contraction and its relationship to the
length-tension properties of muscle.
The sliding filament model describes the process used by muscles to contract. It is a cycle of repetitive events that causes actin and myosin myofilaments to slide over each other, contracting the sarcomere and generating tension in the muscle. According to the sliding filament theory, a muscle fiber contracts when myosin filaments pull actin filaments closer together and thus shorten sarcomeres within a fiber. When all the sarcomeres in a muscle fiber shorten, the fiber contracts.
Describe the generation of controlled force by recruitment of motor units.
Activation of motor units in a random order produces a roughly linear force increase with progressive recruitment, whereas recruitment of motor units in order of increasing force produces an approximately exponential force increase as the number of active motor units increases. Because more motor units are activated, the muscle produces more force. Finally, with the highest rates of descending activity, the largest alpha motor neurons are recruited, producing maximal muscle force.
Explain tetanus and fatigue.
Tetanus is a serious disease of the nervous system caused by a toxin-producing bacterium. The disease causes muscle contractions, particularly of your jaw and neck muscles. Tetanus is commonly known as lockjaw. Severe complications of tetanus can be life-threatening. There’s no cure for tetanus. You can get tetanus infection when the spores enter your body through an injury or wound. The spores become active bacteria that spread in the body and make a poison called tetanus toxin (also known as tetanospasmin). This poison blocks nerve signals from your spinal cord to your muscles, causing severe muscle spasms.
Describe the aerobic and anaerobic properties of muscle.
Aerobic System: This system provides long-term energy through the breakdown of oxygen, effectively supporting sustained activities lasting several minutes to hours. [2] The anaerobic energy system, particularly the lactic acid system, is the body’s method of rapidly creating energy in the form of ATP.
Describe the structure and function of smooth muscle.
Smooth muscle consists of thick and thin filaments that are not arranged into sarcomeres giving it a non-striated pattern. On microscopic examination, it will appear homogenous. Smooth muscle cytoplasm contains a large amount of actin and myosin. Actin and myosin act as the main proteins involved in muscle contraction.
Explain contraction and relaxation in smooth muscle.
Active myosin cross-bridges slide along actin and create muscle tension. Smooth muscle relaxation occurs as free Ca in the cytosol decreases when Ca is pumped out of the cell or back into the SR. Ca unbinds from calmodulin.
Explain how differences in elastic properties of muscles contribute to force production
NB: Cardiac muscle will be dealt with in the cardiovascular system course
Skeletal muscles are organized multinucleated myofibers, whose function is to generate length and velocity dependent forces for movement or stability.
The peak force and power output of a muscle depends upon numerous factors to include: (1) muscle and fiber size and length: (2) architecture, such as the angle and physical properties of the fiber-tendon attachment, and the fiber to muscle length ratio: (3) fiber type: (4) number of cross-bridges in parallel: (5) force per cross-bridge: (6) peak
: (7) force-velocity relationship: (8) fiber Vmax: (9) force-pCa2+ relationship: and (10) the force-frequency (action potential Hz) relationship.
