Chapter 10 review
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- When contraction occurs:
- H and I bands get smaller, Z lines move closer together, width of the A band remains constant.
- An action potential can travel quickly from one cardiac muscle cell to another because of the presence of
- Gap junctions and intercalated discs
- Describe what happens to muscles that are not used on a regular basis. What can be doen to offset this effect?
- They will atrophy. Even a temporary reduction in muscle use, such as wearing a cast, can cause some degree of atrophy. Physical therapy can offset this effect in cases of temporary inactivity.
- In the sarcomere, the I band is composed of
- Thin filaments and titin
- Describe the graphic events seen on a myogram as tension is developed in a stimulated calf muscle fiber during a twitch.
- In an initial latent period (after the stimulus arrives and before the tensions begins to increase), the action potential in the mustcle is generate and triggers the release of calcium ions from the SR. In the contraction phase, the calcium binds to troponin (cross bridges form) and the tension begins to increase. In the relaxation phase, tension drops because calcium levels have fallen, the active sites are once again covered by the troponin/tropomyosin complex.
- Describe the relationship between lactic acid and fatigue
- Fatigue at the level of the individual muscle fiber is defined as the period when it can no longer contract despite continued neural stimulation. It may result from the drap in pH that accompanies a build up of lactic acid.
- The timeof a murder victim's death may be estimated by the flexibility of the body. Explain why.
- In rigor mortis, the membranes of the dead cells are no longer selectively permeable, the SR is no longer able to retain calcium ions. As calcium ions enter the sarcoplasm, a sustained contraction develops. The muscles lock in the contracted position, making the body extremely stiff. Contraction persists because the dead muscle cells can no longer make ATP, which is necessary for cross-bridge detachment from the active sites. Rigor mortis begins a few hours after death and lasts 15-25 hours, until the lysosomal enzymes released by autolysis break down the myofilaments.
- How does cardiac muscle tissue contract without neural stimulation?
- Cardiac muscle tissue has the property of automaticity. The concentrations are timed by pacemaker cells, specialized in cardiac muscle fibers.
- What five interlocking steps are involved in the contraction process?
- Exposure of active sites, attachment of cross bridges, pivoting of myosin head (power stroke), detachment of cross-bridges, activation of myosin heads (cocking)
- The amount of tension produced during a contraction is not affected by:
- The amound of ATP available to the muscle. (IS affected by the degree of overlap between thick and thin filaments, interaction of troponin and tropomyosin, and the number of cross-bridge interactions in a muscle fiber)
- A motor unit in the skeletal muscle contains 1500 muscle fibers. What this muscle be involved in fine delicate movements, or powerful, gross movements?
- Powerful, gross movements; each time the motor unit is actvated, all the fibers will contract maximally. More powerful contractions result from the activity of large motor units that from the activity of small motor units. Fine movements require numerous small motor units that can be individually activated.
- What is the calcium-binding protein in smooth muscle tissue?
- Calmodulin
- The contraction of a muscle exerts a pull on a bone because
- Muscles are attached to bones by tendons
- Large-diameter, densely packed myofibrils, large glycogen reserves, and few mitochondria are characteristics of
- Fast fibers
- A muscle producing peak tension during rapid cycles of contraction and relaxation is said to be in
- Complete tetanus
- What is a motor unit?
- All the muscle fibers controlled by a single motor neuron
- What are the five functions of skeletal muscle?
- Producing skeletal movement, maintaining posture and body position, supporting soft tissue, guarding entrances and exits, maintaining body temperature
- What two factors affect the amount of tension produced when a skeletal muscle contracts?
- The frequency of motor unit stimulation, and the number of motor units involved
- The detachment of myosin cross-bridges is directly triggered by
- The attachment of ATP to myosin heads
- Areas of the body where you would not expect to find slow fibers include the:
- Eye and hand
- Define hypertrophy.
- An increase in the size of the tissue without an increase in the number of cells
- What forms of energy reserves do resting skeletal muscle fibers contain?
- ATP, creatine phosphate, glycogen
- Describe the basic sequence of events that occurs at a neuromuscular junction
- Acetylcholine released by the motor neuron at the neuromuscular junction changes the permeability of the cell membrane at the motor end plate. The permeability change allows the influx of positive charge, which triggers an action potential. The action potential spreads across the entire surface of the muscle fiber and into the interior via T tubules. The cytoplasmic concentration of calcium ions (released from the sarcoplasmic reticulum) increases, triggering the start of a contraction. The contraction ends when AChE removes the ACh from the synaptic cleft and motor end plate.
- List the three types of muscle tissue in the body.
- Skeletal, cardiac, smooth
- What neurotransmitter is responsible for muscle contraction? What enzyme breaks down this neurotransmitter?
- Acetylcholine. Acetylcholinesterase
- An activity that would require anaerobic endurance is
- 50-meter dash, pole vault, and weight lifting all require it.
- Many visceral smooth muscle cells lack motor neuron innervation. How are their contractions coordinated and controlled?
- Visceral smooth muscle fibers are interconnected by gap junctions. When one fiber fires an action potential, it is conducted quicklyto neighboring cells. The action potential in uninnervated smooth muscle fibers may be the result of exposure to chemicals, hormones, oxygen, carbon dioxide, stretching or irritation
- What two mechanisms are used to generate ATP from glucose in muscle cells.
- Aerobic metabolism, glycolysis
- What three layers of connective tissue are part of each muscle? What functional role does each layer play?
- Epimysium surrounds entire muscle. Perimysium surrounds muscle bundles (fascicles), Endomysium surrounds skeletal muscle fibers.
- Atracurium is a drug that blocks the binding of ACh to receptors. Give an example of a site where such binding normally occurs and predict the physical affect of the drug.
- At the motor end plates of neuromuscular junctions, the blocking of the binding process by atracurium would inhibit the ability of the muscle to contract. Thus the muscle would remain relaxed. Atracurium could be useful if administered before surgery.
- Under resting conditions, what two proteins prevent interactions between cross-bridges and active sites?
- Tropomyosin and troponin
- What structural feature of a skeletal muscle fiber is responsible for conducting action potentials into the interior of the cell?
- Transverse (t) tubules
- The type of contraction in which the tension rises, but the resistance does not change is
- An isometric contraction
- Why is cardiac muscle an example of a functional syncytium?
- Cardiac muscle fibers are mechanically, chemically, and electrically connected to one another, causing the entire tissue to resemble a single, enormous muscle fiber that performs as a functional syncytium
- The connective tissue coverings of a skeletal muscle, listed from superficial to deep, are:
- Epimysium, perimysium, endomysium
- What three processes are involved in repaying the oxygen debt during a muscle's recovery period.
- 1) Oxygen for aerobic respiration is consumed by liver cells, which need to make a great deal of ATP to convert lactic acid to glucose. 2) Oxygen for aerobic respiration is consumed by skeletal muscle fibers as they restore ATP, creatine phosphate, and glycogen concentrations to their former levels. 3) The normal oxygen concentration in blood and peripheral tissues is replenished.