Week 1 quiz

Describe the sliding filament theory

1) CNS stimulates sarcolemma and Ca++ is released from the T-tubules of the SR 2) Ca++ binds to troponin causing tropomyosin to shift shape, exposing active binding sites on the actin 3) Myosin cross-bridges bind to active sites on actin 4) ATPase in cross-bridge head cleaves ATP resulting in the power stroke 5) ATP binds to cross-bridge head and calcium pump restores Ca++ to SR (It is the process of muscle contraction involving the sliding of actin & myosin myofilaments past each other to shorten the length of each sacromere.)

sarcoplasmic reticulum

A network of saccules and tubes surrounding myofibrils of a muscle fiber (cell), comparable to endoplasmic reticulum; functions to reabsorb calcium ions during relaxation and to release them to cause contraction.

Acetylcholine

A neurotransmitter that enables learning and memory and also triggers muscle contraction, released at the neuromuscular junction. - Acetylcholine is a small molecule that acts as a chemical messenger to propagate nerve impulses across the neuromuscular junction between a nerve and a muscle. When the nerve impulse from a motor neuron arrives at the tip of its axon, acetylcholine molecules stored there in vesicles are released into the synaptic gap.

Tendon

A white fibrous cord of dense regular connective tissue that attaches muscle to bone.

Calcium

At the onset of contraction, the sarcoplasmic reticulum releases calcium ions (Ca2+) into the sarcoplasm. There, they bind to troponin. Troponin then moves tropomyosin away from the myosin‐binding sites on actin. Once the binding sites are "free," the contraction cycle—the repeating sequence of events that causes the filaments to slide—begins. (Release of Ca2+ from the terminal cisterns of the sarcoplasmic reticulum triggers muscle contraction.)

Actin

Contractile protein that is the main component of thin filament; each actin molecule has a myosin‐binding site where myosin head of thick filament binds during muscle contraction.

filament

Contractile proteins within myofibrils that are of two types: thick filaments composed of myosin and thin filaments composed of actin, tropomyosin, and troponin; sliding of thin filaments past thick filaments produces muscle shortening.

ATP

Especially during contraction, a muscle fiber synthesizes and uses considerable ATP (adenosine triphosphate). - ATP is responsible for cocking (pulling back) the myosin head, ready for another cycle. When it binds to the myosin head, it causes the cross bridge between actin and myosin to detach. ATP then provides the energy to pull the myosin back (When calcium binds to troponin, the troponin changes shape, removing tropomyosin from the binding sites. The sarcoplasmic reticulum stores calcium ions, which it releases when a muscle cell is stimulated; the calcium ions then enable the cross-bridge muscle contraction cycle.)

muscle fiber (cell)

Long cylindrical cell covered by endomysium and sarcolemma; contains sarcoplasm, myofibrils, many peripherally located nuclei, mitochondria, transverse tubules, sarcoplasmic reticulum, and terminal cisterns. The fiber has a striated appearance.

Troponin

Regulatory protein that is a component of thin filament; when calcium ions (Ca2+) bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin‐binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.

Tropomyosin

Regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin‐binding sites on actin molecules, thereby preventing myosin from binding to actin.

endurance training vs strength training

Such anaerobic training (strength) activities stimulate synthesis of muscle proteins and result, over time, in increased muscle size (muscle hypertrophy). Athletes who engage in anaerobic training should have a diet that includes an adequate amount of proteins. This protein intake will allow the body to synthesize muscle proteins and to increase muscle mass. As a result, aerobic training (endurance) builds endurance for prolonged activities; in contrast, anaerobic training builds muscle strength for short‐term feats. Interval training is a workout regimen that incorporates both types of training—for example, alternating sprints with jogging.

Sarcolemma

The cell membrane of a muscle fiber (cell), especially of a skeletal muscle fiber.

Myofibrils

Threadlike contractile elements within sarcoplasm of muscle fiber that extend entire length of fiber; composed of filaments.

Structure of Actin and Myosin

actin- Contractile protein that is the main component of thin filament; each actin molecule has a myosin‐binding site where myosin head of thick filament binds during muscle contraction. myosin- Contractile protein that makes up thick filament; molecule consists of a tail and two myosin heads, which bind to myosin‐binding sites on actin molecules of thin filament during muscle contraction.

hyperplasia vs hypertrophy

hypertrophy: the enlargement of existing cells hyperplasia: an increase in the number of fibers.

Dystrophin

links thin filaments of the sarcomere to integral membrane proteins of the sarcolemma, which are attached in turn to proteins in the connective tissue extracellular matrix that surrounds muscle fibers. Dystrophin and its associated proteins are thought to reinforce the sarcolemma and help transmit the tension generated by the sarcomeres to the tendons.

twitch contraction

the brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron

arrange in size: 1. fascicle 2. muscle fiber (cell) 3. skeletal muscle 4. filament 5. myofibrils

1. skeletal muscle 2. fascicle 3. muscle fiber (cell) 4. myofibril 5. filaments

Sarcomere

A contractile unit in a striated muscle fiber (cell) extending from one Z disc to the next Z disc.

Fascicle

Bundle of muscle fibers wrapped in perimysium.

list/describe the processes that individual muscle fibers employ to generate ATP (krebs cycle/gycolysis)

If sufficient oxygen is present, the pyruvic acid formed by glycolysis enters the mitochondria, where it undergoes aerobic respiration, a series of oxygen‐requiring reactions (the Krebs cycle and the electron transport chain) that produce ATP, carbon dioxide, water, and heat (Figure 10.11c). Thus, when oxygen is present, glycolysis, the Krebs cycle, and the electron transport chain occur. Although aerobic respiration is slower than anaerobic glycolysis, it yields much more ATP. Each molecule of glucose catabolized under aerobic conditions yields about 30 or 32 molecules of ATP. - Aerobic respiration supplies enough ATP for muscles during periods of rest or light to moderate exercise provided sufficient oxygen and nutrients are available. These nutrients include the pyruvic acid obtained from the glycolysis of glucose, fatty acids from the breakdown of triglycerides, and amino acids from the breakdown of proteins. In activities that last from several minutes to an hour or more, aerobic respiration provides nearly all of the needed ATP.

isotonic vs isometric

In an isotonic contraction, the tension (force of contraction) developed in the muscle remains almost constant while the muscle changes its length. Isotonic contractions are used for body movements and for moving objects. The two types of isotonic contractions are concentric and eccentric. In an isometric contraction, the tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length. (In an isotonic contraction, tension remains constant as muscle length decreases or increases; in an isometric contraction, tension increases greatly without a change in muscle length.) Comparison between isotonic (concentric and eccentric) and isometric contractions. (a and b) Isotonic contractions of the biceps brachii muscle in the arm. (c) Isometric contraction of shoulder and arm muscles.

neuromuscular junction

Muscle action potentials arise at the neuromuscular junction (NMJ), which is the synapse between a somatic motor neuron and a skeletal muscle fiber. structure: Synaptic end bulbs at the tips of axon terminals contain synaptic vesicles filled with acetylcholine (ACh). (Neuromuscular junction is a microstructure present at the junction of motor neurons and the skeletal muscle fibers. It acts as a bridge connecting the skeletal system and the nervous system. The neuromuscular junction is a chemical synapse. motor neuron containing synaptic vesicles.)

understand the relationship between actin and myosin

Muscle contraction thus results from an interaction between the actin and myosin filaments that generates their movement relative to one another. The molecular basis for this interaction is the binding of myosin to actin filaments, allowing myosin to function as a motor that drives filament sliding. (Contractile proteins (myosin and actin) generate force during contraction)

skeletal muscle

Organ made up of fascicles that contain muscle fibers (cells), blood vessels, and nerves; wrapped in epimysium.

M line

Region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere.

list all functions of skeletal muscles

Skeletal muscles maintain posture, stabilize bones and joints, control internal movement, and generate heat. Skeletal muscle fibers are long, multinucleated cells. 1. Produce skeletal movement- Contractions pull tendons, move bones 2. Maintain posture and body position- By tension in skeletal muscles 3. Support soft tissues- Support organs, shield internal tissues 4. Guard entrances and exits- Openings of digestive/urinary tracts 5. Maintain body temperature- Heat released by working muscles 6. Store nutrient reserves- Proteins in muscles can break down