Chapter 9: Muscles Flashcards

Question

Z disc (line)

Answer 1

coin shaped sheet of proteins on midline of light I band that anchors thin filamnets and connects myofibrils to one another

Answer 2

line on midline of H zone

Answer 3

region between 2 successive Z discs

Answer 4

- Skeletal muscle fiber contracts, Myosin heads bind to actin; sliding begins - Cross bridges form and break several times, ratcheting thin filaments toward center of sarcomere - When this happens: 1. H bands & I bands get smaller 2. Zones of overlap get larger 3. Z lines move closer together 4. Width of A band remains constant shortening of myofibril during a contraction

Answer 5

- A skeletal muscle fiber contracts when stimulated by a motor neuron - Neuromuscular junction: site where motor neuron meets midpoint of muscle fiber - Each muscle fiber has only one NMJ - A single neuron may branch to control more than one muscle fiber

Answer 6

-Events that transmit AP along sarcolemma lead to sliding of myofilaments * Excitation – AP traveling * Coupling – actual contraction - AP brief; ends before contraction * Causes rise in intracellular Ca2+ which ->contraction -Latent period: Time between AP initiation and beginning of contraction

Answer 7

AP propagated along sarcomere to T tubules

Answer 8

1. The action potential (AP) propagates along the sarcolemma and down the T tubules. 2. Calcium ions are released. (The AP travels along sarcolemma and down into the T tubules, this impulse causes release of Ca from sarcoplasmic reticulum) 3. Calcium binds to troponin and removes the blocking action of tropomyosin. When Ca2+ binds, troponin changes shape, exposing binding sites for myosin (active sites) on the thin filaments. 4. Contraction begins: Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins. At this point, E-C coupling is over This Ca assists in exposing active binding sites on actin filaments

Answer 9

-Cross bridge detachment requires ATP 3–4 hours after death muscles begin to stiffen with weak rigidity at 12 hours post mortem * Dying cells take in calcium ->cross bridge formation * No ATP generated to break cross bridges

Answer 10

sodium ions

Answer 11

Calcium binds to troponin, changing its shape and removing the blocking action of tropomyosin.

Answer 12

- Contraction produces muscle tension, - Contraction may/may not shorten muscle -Isometric contraction: no shortening; muscle tension increases but does not exceed load -Isotonic contraction: muscle shortens because muscle tension exceeds load

Answer 13

no shortening; muscle tension increases but does not exceed load

Answer 14

muscle shortens because muscle tension exceeds load

Answer 15

- Each muscle served by at least one motor nerve * Motor nerve contains axons of up to hundreds of motor neurons - Motor unit = motor neuron and all (four to several hundred) muscle fibers it supplies * Smaller number = fine control Motor units in muscle usually contract asynchronously; helps prevent fatigue

Answer 16

motor neuron and all (four to several hundred) muscle fibers it supplies *Smaller number = fine control

Answer 17

Motor unit's response to single action potential of its motor neuron 3 phases: - Latent period - period of contraction - period of relaxation

Answer 18

Events of excitation-contraction coupling; no muscle tension

Answer 19

cross bridge formation;tension increases

Answer 20

calcium ions reentry into SR; tension declines to zero

Answer 21

Graded muscle responses: *Varying strength of contraction for different demands -Required for proper control of skeletal movement - Increased force graded by: 1. Changing frequency of stimulation 2. Changing strength of stimulation (recruitment)

Answer 22

a single stimulus is delivered. the muscle contracts and relaxes

Answer 23

if another stimulus is applied before the muscle relaxes completely, then more tension results. this is WAVE (or temporal) summation and results in unfused (or incomplete) tetanus low stimulation frequency-> unfused (incomplete) tetanus

Answer 24

at higher stimulus frequencies, there is no relaxation at all between stimuli. this is fused (complete) tetanus high stimulation frequency-> fused (complete) tetanus

Answer 25

- The smooth ↑ in muscular tension produced by the ↑ in the number of active motor units - Contraction starts w/ activation of the smallest motor units in a stimulated muscle - As movement continues, larger motor units are activated & tension production rises steeply

Answer 26

- Recruitment works on size principle: * Motor units with smallest muscle fibers recruited first * Motor units with larger and larger fibers recruited as stimulus intensity increases * Largest motor units activated only for most powerful contractions

Answer 27

- Muscle changes in length and moves load - Isotonic contractions either concentric or eccentric: * Concentric contractions—muscle shortens and does work - Eccentric contractions—muscle generates force as it lengthens

Answer 28

muscle shortens and does work

Answer 29

muscle generates force as it lengthens

Answer 30

- Load greater than tension muscle can develop - Tension increases to muscle's capacity, but muscle neither shortens nor lengthens * Cross bridges generate force but do not move actin filaments

Answer 31

Anaerobic and Aerobic pathway

Answer 32

- Glycolysis – does not require oxygen * Small amount of ATP produced - At 70% of maximum contractile activity: * Bulging muscles compress blood vessels; oxygen delivery impaired *Lactic acid is produced which changes pH Results in MM fatigue

Answer 33

- Requires oxygen | - Produces 95% of ATP during rest and light to moderate exercise

Answer 34

To return muscle to resting state: *Oxygen reserves replenished * Lactic acid converted to pyruvic acid * Glycogen stores replaced * ATP and creatine phosphate reserves replenished - All require extra oxygen; occur post exercise ***Paying back the Oxygen Debt

Answer 35

Force of contraction depends on number of cross bridges attached, which is affected by: *Number of muscle fibers stimulated (recruitment) * Relative size of fibers—hypertrophy of cells increases strength * Frequency of stimulation *Degree of muscle stretch (Length-tension relationship – muscle fibers at 80–120% normal resting length ->more force

Answer 36

Influenced by: - Muscle fiber type * Slow and fast fiber type - Load * Greater the load, slower the contraction - Recruitment * More motor units contracting, the faster and more prolonged the contraction.

Answer 37

3 types: -Slow oxidative fibers (long distance) - Fast oxidative fibers - Fast glycolytic fibers (short sprints) - Most muscles contain mixture of fiber types * All fibers in one motor unit same type * Genetics dictate individual's percentage of each

Answer 38

- Large diameters, densely packed myofibrils, large glycogen reserves & few mitochondria - Produce powerful contractions - Use massive amounts of ATP & fatigue quickly - Use anaerobic glycolysis Classified according to two characteristics: speed of contraction and metabolic pathway

Answer 39

- Half the diameter as fast fibers - Specialized for long periods of contraction - Large capillary network supports oxygen demand - Myoglobin: red pigment that binds oxygen - Oxidative fibers (slow) use aerobic pathways Classified according to two characteristics: speed of contraction and metabolic pathway

Answer 40

Muscles contract fastest when no load added increase load -> increased latent period, slower contraction, and decreased duration of contraction If load exceeds muscle maximal tension speed of contraction is 0. (isometric

Answer 41

Leads to increased: * Muscle capillaries * Number of mitochondria * Myoglobin synthesis - Results in greater endurance, strength, and resistance to fatigue - May convert fast glycolytic fibers into fast oxidative fibers

Answer 42

typically anaerobic Muscle hypertrophy: *Due primarily to increase in fiber size -Increased myofilaments, glycogen stores, and connective tissue leads to Increased muscle strength and size

Answer 43

- Disuse atrophy * Result of immobilization * Muscle strength declines 5% per day - Neurogenic atrophy * Without neural stimulation muscles atrophy to ¼ initial size -Fibrous connective tissue replaces lost muscle tissue leads to rehabilitation impossible

Answer 44

- Found in walls of most hollow organs (except heart) - Usually in two layers (longitudinal and circular) Allows peristalsis - Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through lumen of hollow organs

Answer 45

- Spindle-shaped fibers - only one nucleus; no striations - Lacks connective tissue sheaths; endomysium only SR - less developed than in skeletal muscle Pouchlike infoldings (caveolae) of sarcolemma store Ca2+ - most calcium influx from outside cell; rapid No sarcomeres, myofibrils, or T tubules

Answer 46

No NMJ as in skeletal muscle Autonomic nerve fibers innervate smooth muscle at diffuse junctions Varicosities (bulbous swellings) of nerve fibers store and release neurotransmitters into diffuse junctions Slow synchronized contractions May be initiated by pacemaker cells, hormones or local chemicals

Answer 47

- Unitary (visceral) smooth muscle: * In all hollow organs except heart * Electrically coupled by gap junctions * Contract synchronously - Multi unit smooth muscle: * Located in large airways, large arteries, arrector pili muscles, and iris of eye *Contractions are rarely synchronously

Answer 48

In all hollow organs except heart * Electrically coupled by gap junctions * Contract synchronously

Answer 49

Located in large airways, large arteries, arrector pili muscles, and iris of eye *Contractions are rarely synchronously

Answer 50

With age, connective tissue increases and muscle fibers decrease - By age 30, loss of muscle mass (sarcopenia) begins - Regular exercise reverses sarcopenia - Atherosclerosis may block distal arteries, leading to intermittent claudication and severe pain in leg muscles

Chapter 9: Muscles Flashcards

(74 cards)