A&P Chapter 10: Muscle Tissue
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What are the 6 functions of muscle tissue?
- 1. Produce skeletal movement (contract)
- 2. Maintain posture and body position
- 3. Support soft tissues
- 4. Guard entrances and exits (sphincters)
- 5. Maintain body temperature
- 6. Store nutrient reserves (glycogen)
Compare/contrast the characteristics of skeletal, cardiac and smooth muscle
- 1. Skeletal: Striated, multinucleate, voluntary
- 2. Cardiac: Striated, intercalated discs, branched, involuntary
- 3. Smooth: Non striated, involuntary
ALL: Help to maintain body temperature
What are the components found in a muscle fiber?
- 1. Sarcolemma: cell membrane of muscle fiber, change in transmembrane potential begins contractions
- 2. Sarcoplasm: cytoplasm of muscle fiber
- 3. T Tubules: transmit action potentials through cell, allows entire muscle fiber to contract simultaneously
- 4. Myofibrils: made up of bundles of myofilaments (actin/myosin) that are responsible for contractions
- 5. Sarcoplasmic Reticulum (SR): stores calcium, helps transmit action potentials, forms chambers attached to T tubules
- 6. Sarcomeres: The contractile unit of the muscle fiber, form striated appearance with overlap of thick and thing filaments
Excitation-Contraction coupling involves excitation of the muscle fiber and contraction. What are the 6 steps of excitation?
- 1. At neuromuscular junction, the cytoplasm of neuron contains ACh
- 2. AP arrives in the syn+aptic terminal
- 3. AP causes the release of ACh into the synaptic cleft
- 4. ACh binds to receptors on the sarcolemma of the muscle fiber depolarizing the membrane to threshold
- 5. Sudden rush of Na+ into the muscle fiber results in an AP
- 6. AP travels down T tubules into the SR causing the release of Ca2+ into the sarcomere
Excitation-Contraction coupling involves excitation of the muscle fiber and contraction. What are the 5 steps of contraction?
- 1. Ca2+ binds to troponin causing it to change shape and roll away tropomyosin, exposing the myosin binding sites on actin
- 2. Myosin heads get energy by breaking ATP into ADP+P, energized myosin heads bind to actin forming a cross bridge
- 3. Energy stored in myosin is released as myosin head pivots towards the M line, called power stroke
- 4. When another ATP binds to the myosin head, it releases from actin and the attachment site is exposed so it can bind with another myosin head
- 5. The myosin is reactivated when it breaks ATP into ADP+P again, energy released is used to re-cock the myosin head to be ready for another cross bridge formation and power stroke
What are the different types of contractions produced by a muscle?
- 1. Treppe: stair-step increase in twitch tension, repeated stimulations after relaxation phase, causes series of contractions with increasing tension
- 2. Wave summation: increasing tension, summation of twitches, repeated stimulation before the end of relaxation phase, causes increasing tension (summation of twitches)
- 3. Incomplete tetanus: twitches reach maximum tension, continuous, rapid stimulation prevents muscles from relaxing, twitches reach maximum level of tension
- 4. Complete tetanus: if stimulation frequency is high enough, muscle never begins to relax, remains in continuous contraction, happens when load exceeds capability
What is a motor unit?
- A motor unit is a skeletal muscle and the neuron that controls it:
- 1. Contains hundreds of muscle fibers
- 2. Contract at the same time
- 3. Controlled by a single motor neuron
What is motor recruitment?
- 1. multiple motor unit summation
- 2. in a whole group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated
- 3. Maximum tension: when all motor units reach tetanus, only sustained for a short time
What happens as the muscle relaxes?
- 1. Ca2+ concentrations fall, Ca2+ detaches from troponin, active sites on actin are re-covered by tropomyosin
- 2. Pull of elastic tendons and ligaments return sarcomeres to resting length
- 3. Opposing muscle contraction reverses the direction of original motion (opposing skeletal muscle pairs)
- 4. Gravity can return muscle to its original state
How do muscles create the energy they need to work?
- 1. ATP: muscles store enough ATP to start a contraction, the rest comes from glycolysis and aerobic respiration in the mitochondria
- 2. CP: Creatine phosphate stores excess ATP in resting muscles
- 3. Stored ATP lasts for 2 sec to initiate contraction --> muscle makes ATP from CP --> anaerobic glycolysis breaks down glucose for ATP --> aerobic metabolism breaks down fatty acids for ATP
What are the 2 different types of muscle fibers?
- 1. Slow: resistant to fatigue, thin, red, many mitochondria
- 2. Fast: fatigue quickly, large, white, few mitochondria
What structures to cardiac muscle cells have that enable them to communicate with each other?
- 1. Intercalated discs: Gap junctions at branches of cardiac muscle allow muscle cells to communicate quickly
- 2. Discs link heart cells mechanically, chemically, and electrically allowing heart to function as a single, fused mass of cells
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