A&P Ch9 Study question

24. Describe three ways ATP is regenerated during skeletal muscle contraction.

♥ ATP is the only source used directly for contractile activity ♥ As soon as available stores of ATP are hydrolyzed (4-6 Seconds), they are regenerated by: The interaction od ADP with creatine phosphate (CP) Anaerobic glycolysis Aerobic respiration

14. What is the function of calcium ions in regard to the shape of troponin?

♥ Bind to regulatory sites on troponin to remove contraction inhibition

19. What is a motor unit?

♥ Consists of one motor neuron and all the muscle fibers it innervates, or supplies

7. Describe the microscopic structure of skeletal muscle fibers.

♥ Each fiber is a long cylindrical cell with multiple nuclei just beneath the sarcolemma. ♥ Fibers are 10- 100micrometers in diameter, and up to hundreds of centimeters long. ♥ Each cell is a syncytium produced by fusion of embryonic cells ♥ Sarcoplasm has numerous glycosomes and a unique oxygen-binding protein called myoglobin (not same as blood) ♥ Fiberscontain the usual organelles, myofibrils, sarcoplasm reticulum, and Ttubules.

12. What is myosin? What is a thick filament?

♥ Thick filaments are composed of the protein myosin ♥ Each myosin molecules has a rod-like tail and two globular heads Tails: two interwoven, heavy polypeptide chains. Heads: two smaller, light polypeptide chains called cross bridges

11. What is actin? What is a thin filament?

♥ Thin filaments are chiefly composed of the protein actin. ♥ Each actin molecule is helical polymer of globular subunit called G Actin ♥ The subunit contain the active sites to which myosin heads attached during contraction ♥ tropomyosin and troponin are regulatory subunits bound to actin.

6. Describe the gross structure of a skeletal muscle, including the location and names of its connective tissue coverings and attachments.

♥ Each muscle is a discrete organ compose of muscle tissue, blood vessels nerve fibers and connective tissue. ♥ Three connective tissue sheaths are: Endomysium: fine sheath of connective tissue composed of reticular fiber surrounding each muscle fiber. Perimysium: fibrous connective tissue that surrounds groups of muscle fibers called fascicles. Epimysium: an overcoat of dense regular connective tissue that surrounds the entire muscle ♥ Skeletal Muscle- Nerve and blood supply Each muscle is serve by one nerve, an artery, and one or more veins, Each skeletal muscle fiber is supplied with a nerve ending that controls contraction. Contracting fibers require continuous deliver of oxygen and nutrients via arteries. Waste must be removed via vein. ♥ Attachments Muscle attach: ϖ Directly: epimysium od the muscle is fused to the periosteum of a bone. Indirectly: connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis(sheet like tendon)

5. Explain each of the 4 functional characteristics of muscle.

♥ Excitability or irritability: the ability to receive and respond to stimuli. (full of energy -Action potential) ♥ Contractility: the ability to shorten forcibly ♥ Extensibility: the ability to stretched or extended. ♥ Elasticity: the ability to recoil and resume the original resting length.

25. Compare and contrast the gross and microscopic anatomy of smooth muscle fibers to that of skeletal muscle fibers.

♥ Have endomysia; but generally lack: perimysia and epimysia ♥ No neuromuscular junction; have diffuse junction instead ♥ No myofibril; have myofibil-like bundles of: myofilaments ♥ No 2 lines; have corresponding dense bodies.

21. What is a muscle twitch?

♥ Is a motor unit's response to a single action potential of its motor neuron

22. What are the 3 phases of a muscle twitch and what happens during each phase?

♥ Latent period- first few msec after stimulus; EC coupling taking place. ♥ Period of contraction- cross bridges from; muscle shortens ♥ Period of relaxation- Ca2+ reabsorbed; muscle tension goes to zero.

8. What is the functional role of myofibrils?

♥ Myofibrils are densely packed, rodlike contractile elements ♥ They make up most of the muscle volume ♥ The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A band and light I band is evident.

17. Explain excitation/contraction coupling.

♥ Myosin cross bridges alternately attach and detach ♥ Thin filaments move toward the center of the sarcomere. ♥ Hydrolysis of ATP power this cycling process. ♥ Ca2+ is removed into the SR, tropomyosin blockage is restored, and the muscle fiber relaxes. ♥ Once generated, the action potential: Is propagated along the sarcolemma Travels down the T tubules Triggers Ca2+ release from terminal cisternae ♥ Ca2+ bind to troponin and causes: The blocking action of tropomyosin to cease Actin active binding sites to be exposed.

9. What is the functional role of sarcoplasmic reticula?

♥ SR is an elaborate, smooth endoplasmic reticulum that mostly runs longitudinally and surrounds each myfibril ♥ Paired terminal cisternae form perpendicular cross channels ♥ function in the regulation of intracellular calcium levels. ♥ Elongated tubes called T tubules penetrate into the call's interior at each A band-I band junction ♥ T tubules associate with the paired terminal cisternae to form triads.

What are the 3 basic types of muscle tissue?

♥ Skeletal Muscle: attached to the skeleton, is striated, and can be controlled voluntary. ♥ Cardiac Muscle: forms the heart, is striated, and we don't have any controlled involuntary. ♥ Smooth Muscle: located chiefly in the walls of hollow organs, is controlled involuntary. Its fiber are not striated

How is all muscle tissue alike?

♥ Skeletal and smooth muscle cells are elongated and are called muscle fiber. ♥ Muscle contraction depends on two kinds of myofilaments- actin and myosin ♥ Muscle terminology is similar Sarcolemma: muscle plasma membrane Sarcoplasm: cytoplasm of muscle cell Prefixes: myo, mys, and sarco all refer to muscle.

4. What are 4 important functions of muscle tissue?

♥ Skeletal muscle is responsible of all locomotion. ♥ Cardiac muscle is responsible for coursing the blood through the body ♥ Smooth muscle helps maintain blood pressure, and squeezes or propels substances (food and feces) through organs. ♥ Muscles also maintain posture, stabilize joints, and generate heat.

20. How are muscle fibers stimulated to contract?

♥ Stimulation of the sarcolemma by the somatic nervous system. ♥ Excitation- contraction coupling contraction occurs. ♥ Calcium ions are released from the sarcoplasmic reticulum. ♥ Sliding of the filaments. ♥ Muscle fiber contraction. ♥ Gross muscle contraction.

10. What is the functional role of T tubules?

♥ T tubules are with the sarcolemma ♥ They conduct impulses to the deepest regions of the muscle -These impulses signal for the release of Ca2+ from adjacent terminals cisternae

16. Describe the structure and function of the neuromuscular junction.

♥ The neuromuscular junction is formed from: Axonal endings, which have small membranous sacs( synaptic vesicles) that contain the neurotransmitter acetycholine (ACh) The motor end plate of a muscle, which is a specific part of the sarcolemma that contains ACh receptors and helps form the neuromuscular junction. ♥ Though exceedingly close, axonal ends and muscle fibers are always separated by a space called the synaptic cleft. ♥ When a nerve impulse reaches the end of an axon at the neuromuscular junction Voltage- regulated calcium channels open and allow Ca2+ to enter the axon. Ca2+ inside the axon terminal causes axonal vesicles to fuse with the axonal membrane. This fusion releases ACh into the synaptic cleft via exocytosis ACh diffuses across the synaptic cleft to ACh receptors on the sarcolemma. Binding of ACh to its receptors initiates an action potential in the muscle.

23. Explain how smooth graded contractions of a skeletal muscle are produced.

♥ They are control in two ways by changing the frequency of stimulation and by changing the strength of stimulation.

3. How are the 3 types different from one another?

♥ They differ in structure, location, and function and how they activate.

15. Explain the sliding filament theory of muscle contraction.

♥ Thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree. ♥ In the relaxed state, thin and thick filaments overlap only slightly. ♥ Upon stimulation, myosin heads bind to actin and sliding begins. ♥ Each myosin head binds and detaches several times during contraction, acting like a ratchet to generate tension and propel the thin filaments to the center of the sarcomere. ♥ As this event occurs throughout the sarcomeres, the muscle shortens.

13. What are troponin and tropomyosin? What do they do?

♥ Troponin: the other major protein in thin filaments, is a globular three- polypeptide complex. One of its polypeptide (TnI) is an inhibitory subunit that binds to actin. Second (TnT) binds to tropomyosin and helps position it on actin. Third (TnC) binds calcium ions. ♥ Tropomyosin: a rod- shape protein, spiral about the actin core and helps stiffen and stabilize it. Successive tropomyosin molecules are arranged end to end along the actin filaments, and in arelaxed muscle fiber, they bind to the thin filaments. ♥ Both troponin and tropomyosin help control the myosin-actin interactions involved in contraction. Several other proteins help form the structure of the myofibril.

18. Describe the all-or-none principle as it relates to muscle fiber contraction.

♥ a myocyte contracts Maximally, or Not at all