Lecture Exam 3

Question 1

Myology

Answer 1

The scientific study of muscles

Question 2

Types of Muscular Tissue

Answer 2

Skeletal, cardiac, and smooth muscle tissue

Question 3

Muscular Tissue Difference in appearance, location, function and nerve innervations

Answer 3

Skeletal Muscle Tissue: Move the bones of the skeleton, striated, works in a voluntary manner.

Cardiac Muscle Tissue: Forms most of the heart wall, striated, action is involuntary, contraction and relaxation of the heart isn’t consciously controlled.

Smooth Muscle Tissue: Located in the walls of hollow internal structures like blood vessels and airways. Also found in the skin attached to hair follicles. Nonstriated. Involuntary action.

Question 4

Autorhythmicity

Answer 4

Built in rhythm. Found in cardiac and smooth muscle tissue.

Question 5

Functions Of Muscle Tissue

Answer 5

1) Producing body movements.
2) Stabilizing body positions.
3) Storing and moving substances within the body.
4) Generating heat.

Question 6

Properties Of Muscle Tissue

Answer 6

1) Electrical excitability.
2) Contractility.
3) Extensibility.
4) Elasticity.

Question 7

Level Of Organization Within A Skeletal Muscle

Answer 7

Skeletal Muscle: Organ made of fascicles that contain muscle fibers(cells), blood vessels, and nerves. Wrapped in epimysium.

Fascicle: Bundle of muscle fibers wrapped in perimysium.

Muscle fiber(cell): Long cylindrical cell covered by endomysium and sarcolemma. The fiber appears striated.

Myofibril: Threadlike contractile elements within sarcoplasm of muscle fiber that extend entire length of fiber, composed of filaments.

Filaments(myofilaments): Contractile proteins in myofibrils, 2 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.

Question 8

Connective Tissue Components(muscle fiber=muscle cell)

Answer 8

Fascia.
Three layers: Endomysium, perimysium, epimysium.
Tendon and aponeurosis.

Question 9

Fascia

Answer 9

Dense sheet or broad band of irregular connective tissue, lines the body wall and limbs and supports and surrounds muscles and other organs of the body. Holds muscles of similar function together, allows free movement of muscles, carries nerves, blood vessels, lymphatic vessels, and fills spaces between muscles.

Question 10

Three Layers

Answer 10

Endomysium: (Endo=within) Penetrates the interior of each fascicle and separates individual muscle fibers. Mostly reticular fibers.

Perimysium: Layer of dense irregular connective tissue, surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles.

Epimysium: (epi=upon) Outer layer, encircling the entire muscle, consists of dense irregular connective tissue.

Question 11

Tendon

Answer 11

Attaches a muscle to the periosteum of a bone.

Question 12

Aponeurosis

Answer 12

When the connective tissue elements extend as a broad, flat sheet.

Question 13

Nerve and Blood Supply

Answer 13

Rich supply. Somatic motor neurons provide the nerve impulses that stimulate skeletal muscle to contract.

Question 14

Sarcolemma

Answer 14

(sarc- flesh; -lemma sheath)The plasma membrane of a muscle cell

Question 15

Transverse Tubules

Answer 15

Thousands of tiny invaginations of the sarcolemma, they tunnel in from the surface toward the center of each muscle fiber.

Question 16

Sarcoplasm

Answer 16

Within the sarcolemma, the cytoplasm of a muscle fiber.

Question 17

Myoglobin

Answer 17

A red-colored protein, found only in muscle, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid. Myoglobin releases oxygen when it is needed by the mitochondria for ATP production.

Question 18

Myofibrils

Answer 18

(myo- muscle; -fibrilla little fiber)Little threads. the contractile organelles of skeletal muscle.

Question 19

Sarcoplasmic Reticulum(SR)

Answer 19

A fluid-filled system of membranous sacs, encircles each myofibril.

Question 20

Terminal Cisterns(SIS-terns reservoirs)

Answer 20

Dilated end sacs of the sarcoplasmic reticulum, butt against the T tubule from both sides.

Question 21

Triad(tri=three)

Answer 21

A transverse tubule and the two terminal cisterns on either side of it.

Question 22

Filaments

Answer 22

Within myofibrils, smaller protein structures. Thin filaments are 8 nm in diameter and 1–2 m long* and composed mostly of the protein actin, while thick filaments are 16 nm in diameter and 1–2 m long and composed mostly of the protein myosin. Both thin and thick filaments are directly involved in the contractile process.

Question 23

Sarcomere

Answer 23

Filaments inside a myofibril arranged in compartments. Basic functional units of a myofibril.

Question 24

A Band

Answer 24

Dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments.

Question 25

I Band

Answer 25

Lighter, less dense area of sarcomere that contains remainder of thin filaments but no thick filaments. A Z disc passes through center of each I band.

Question 26

H Zone

Answer 26

Narrow region in center of each A band that contains thick filaments but no thin filaments.

Question 27

M Line

Answer 27

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

Question 28

Z Discs

Answer 28

Narrow, plate-shaped regions of dense material that separate one sarcomere from the next.

Question 77

Contractile Proteins: Proteins that generate force during muscle contractions.

Answer 77

Myosin: Makes up thick filament; molecule consists of a tail and two myosin heads, which bind to myosinbinding sites on actin molecules of thin filament during muscle contraction. Actin: Main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction.

Question 78

Regulatory Proteins: Proteins that help switch muscle contraction process on and off.

Answer 78

Tropomyosin: A component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosinbinding sites on actin molecules, thereby preventing myosin from binding to actin. Troponin: 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.

Question 79

Structural proteins: Proteins that keep thick and thin filaments of myofibrils in proper alignment, give myofibrils elasticity and extensibility, and link myofibrils to sarcolemma and extracellular matrix.

Answer 79

Titin: Connects Z disc to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils. Nebulin: Wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development. Dystrophin: Links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons.

Question 80

The Sliding Filament Mechanism

Answer 80

During muscle contractions, thin filaments move toward the M line of each sarcomere.

Question 81

The Contraction Cycle

Answer 81

Sarcomeres exert force and shorten through repeated cycles during which the myosin heads attach to actin (cross-bridges), rotate, and detach. 1) Myosin heads hydrolyze ATP and become reoriented and energized 2) Myosin heads bind to actin, forming cross-bridges 3) Myosin cross-bridges rotate toward center of sarcomere (power stroke) 4) As myosin heads bind ATP, the cross-bridges detach from actin

Question 82

Excitation Coupling Mechanism

Answer 82

Connect excitation (a muscle action potential propagating along the sarcolemma and into the T tubules) to contraction (sliding of the filaments). An increase in the Ca2 level in the sarcoplasm starts the sliding of thin filaments. When the level of Ca2 in the sarcoplasm declines, sliding stops. The sarcoplasmic reticulum membrane also contains Ca2 active transport pumps that use ATP to move Ca2 constantly from the sarcoplasm into the SR. While muscle action potentials continue to propagate through the T tubules, the Ca2 release channels are open.

Question 83

Rigor Mortis

Answer 83

Muscles are in a state of rigidity (cannot contract or stretch).

Question 84

Length-Tension Relationship

Answer 84

Maximum tension during contraction occurs when the resting sarcomere length is 2.0–2.4 m. A muscle fiber develops its greatest tension when there is an optimal zone of overlap between thick and thin filaments.

Question 85

Neuromuscular Junction

Answer 85

Where muscle action potentials arise, the synapse between a somatic motor neuron and a skeletal muscle fiber.

Question 86

Synapse

Answer 86

A region where communication occurs between two neurons, or between a neuron and a target cell

Question 87

Synaptic Cleft

Answer 87

At most synapses a small gap, separates the two cells.

Question 88

Neurotransmitter

Answer 88

First cell communicates with the second by releasing a chemical messenger called a neurotransmitter.

Question 89

Motor End Plate

Answer 89

The region of the sarcolemma opposite the synaptic end bulbs.

Question 90

A Nerve Impulse Elicits A Muscle Action Potential

Answer 90

1) ACh is released from synaptic vesicle 2) ACh binds to ACh receptor 3) Muscle action potential is produced 4) ACh is broken down

Question 91

Events of Contraction and Relaxation in a Skeletal Muscle

Answer 91

1) Nerve impulse arrives at axon terminal of motor neuron and triggers release of acetylcholine (ACh). 2) ACh diffuses across synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle action potential (AP). 3) Acetylcholinesterase in synaptic cleft destroys ACh so another muscle action potential does not arise unless more ACh is released from motor neuron. 4) Muscle AP traveling along transverse tubule opens Ca2+ release channels in the sarcoplasmic reticulum (SR) membrane, which allows calcium ions to flood into the sarcoplasm. 5) Ca2+ binds to troponin on the thin filament, exposing the binding sites for myosin. 6) Contraction: power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere. 7) Ca2+ release channels in SR close and active transport pumps use ATP to restore low level of Ca2+ in sarcoplasm. 8) Troponin–tropomyosin complex slides back into position where it blocks the myosinbinding sites on actin. 9) Muscle relaxes.

Question 92

Production of ATP in muscle fibers

Answer 92

(a) (15 seconds) Creatine phosphate, formed from ATP while the muscle is relaxed, transfers a high-energy phosphate group to ADP, forming ATP during muscle contraction. (b) (2 minutes) Breakdown of muscle glycogen into glucose and production of pyruvic acid from glucose via glycolysis produce both ATP and lactic acid. Because no oxygen is needed, this is an anaerobic pathway. (c) (Several minutes to hours) Within mitochondria, pyruvic acid, fatty acids, and amino acids are used to produce ATP via aerobic respiration, an oxygen-requiring set of reactions.

Question 93

Muscle Fatigue

Answer 93

The inability of a muscle to maintain force of contraction after prolonged activity. Even before actual muscle fatigue occurs, a person may have feelings of tiredness and the desire to cease activity; this response, called central fatigue, is caused by changes in the central nervous system (brain and spinal cord).

Question 94

Factors Thought To Contribute To Muscle Fatigue

Answer 94

Inadequate release of calcium ions from the SR, resulting in a decline of Ca2 concentration in the sarcoplasm. Depletion of creatine phosphate also is associated with fatigue. Other factors that contribute to muscle fatigue include insufficient oxygen, depletion of glycogen and other nutrients, buildup of lactic acid and ADP, and failure of action potentials in the motor neuron to release enough acetylcholine.

Question 95

Oxygen Consumption After Exercise

Answer 95

Oxygen Debt: The added oxygen, over and above the resting oxygen consumption, that is taken into the body after exercise. Recovery Oxygen Uptake: A better term than oxygen debt for the elevated use of oxygen after exercise.

Question 96

Motor Unit

Answer 96

Consists of a somatic motor neuron plus all of the skeletal muscle fibers it stimulates. Whole muscles that control precise movements consist of many small motor units. Because all of the muscle fibers of a motor unit contract and relax together, the total strength of a contraction depends, in part, on the size of the motor units and the number that are activated at a given time.

Question 97

Twitch Contraction

Answer 97

1) Latent Period: The muscle action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum. 2) Contraction Period: Ca2 binds to troponin, myosin-binding sites on actin are exposed, and cross-bridges form. Peak tension develops in the muscle fiber. 3) Relaxation Period: Ca2 is actively transported back into the sarcoplasmic reticulum, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, and tension in the muscle fiber decreases. The actual duration of these periods depends on the type of skeletal muscle fiber. Refractory Period: The period of lost excitability, cardiac muscle has a longer refractory period than skeletal muscle.

Question 98

Frequency Of Stimulation

Answer 98

Wave Summation: Stimuli arriving at different times cause larger contractions. Unfused Tetanus: A sustained but wavering contraction. Fused Tetanus: A sustained contraction in which individual twitches cannot be detected Wave summation and both kinds of tetanus occur when additional Ca2 is released from the sarcoplasmic reticulum by subsequent stimuli while the levels of Ca2 in the sarcoplasm are still elevated from the first stimulus.

Question 99

Motor Unit Recruitment

Answer 99

The process in which the number of active motor units increases. Typically, the different motor units of an entire muscle are not stimulated to contract in unison. While some motor units are contracting, others are relaxed.

Question 100

Muscle Tone

Answer 100

A small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units. To sustain muscle tone, small groups of motor units are alternatively active and inactive in a constantly shifting pattern.

Question 101

Isotonic and Isometric Contractions

Answer 101

If the tension generated in a concentric isotonic contraction is great enough to overcome the resistance of the object to be moved, the muscle shortens and pulls on another structure, such as a tendon, to produce movement and to reduce the angle at a joint. Eccentric isotonic contraction: When the length of a muscle increases during a contraction. Isometric Contractions: the tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length. An example would be holding a book steady using an outstretched arm.

Question 102

Skeletal Muscle Fiber Types

Answer 102

1) SLOW OXIDATIVE (SO) FIBERS 2) FAST OXIDATIVE–GLYCOLYTIC (FOG) FIBERS 3) FAST GLYCOLYTIC (FG) FIBERS (Pg 316)Table 10.4

Question 103

Distribution and Recruitment of Different Types of Fibers

Answer 103

Most skeletal muscles are a mixture of all three types of skeletal muscle fibers; about half of the fibers in a typical skeletal muscle are SO fibers. However, the proportions vary somewhat, depending on the action of the muscle, the person’s training regimen, and genetic factors.

Question 104

Exercises And Skeletal Muscle Tissue

Answer 104

The relative ratio of fast glycolytic (FG) and slow oxidative (SO) fibers in each muscle is genetically determined and helps account for individual differences in physical performance. For example, people with a higher proportion of FG fibers often excel in activities that require periods of intense activity, such as weight lifting or sprinting. People with higher percentages of SO fibers are better at activities that require endurance, such as long-distance running. Endurancetype (aerobic) exercises, such as running or swimming, cause a gradual transformation of some FG fibers into fast oxidative–glycolytic (FOG) fibers. By contrast, exercises that require great strength for short periods produce an increase in the size and strength of FG fibers.

Question 105

Effective Stretching

Answer 105

Stretching cold muscles does not increase flexibility and may cause injury. Tissues stretch best when slow, gentle force is applied at elevated tissue temperatures.

Question 106

Strength Training

Answer 106

The process of exercising with progressively heavier resistance for the purpose of strengthening the musculoskeletal system. Helps to increase bone strength by increasing the deposition of bone minerals in young adults and helping to prevent, or at least slow, their loss in later life. By increasing muscle mass, strength training raises resting metabolic rate, the amount of energy expended at rest, so a person can eat more food without gaining weight. Strength training helps to prevent back injury and other injuries from participation in sports and other physical activities. Psychological benefits include reductions in feelings of stress and fatigue. As repeated training builds exercise tolerance, it takes increasingly longer before lactic acid is produced in the muscle, resulting in a reduced probability of muscle spasms.

Question 107

Cardiac Muscle Tissue

Answer 107

Cardiac muscle fibers have the same arrangement of actin and myosin and the same bands, zones, and Z discs as skeletal muscle fibers. However, intercalated discs (in-TERka-laˉt-ed; intercal- to insert between) are unique to cardiac muscle fibers. These microscopic structures are irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to one another. The discs contain desmosomes, which hold the fibers together, and gap junctions, which allow muscle action potentials to spread from one cardiac muscle fiber to another (see Figure 4.2e). Cardiac muscle tissue has an endomysium and perimysium, but lacks an epimysium. In response to a single action potential, cardiac muscle tissue remains contracted 10 to 15 times longer than skeletal muscle tissue (see Figure 20.11). The long contraction is due to prolonged delivery of Ca2 into the sarcoplasm. In cardiac muscle fibers, Ca2 enters the sarcoplasm both from the sarcoplasmic reticulum (as in skeletal muscle fibers) and from the interstitial fluid that bathes the fibers. Because the channels that allow inflow of Ca2 from interstitial fluid stay open for a relatively long time, a cardiac muscle contraction lasts much longer than a skeletal muscle twitch. Cardiac muscle depends largely on aerobic respiration to generate ATP, and thus requires a constant supply of oxygen. Cardiac muscle fibers can also use lactic acid produced by skeletal muscle fibers to make ATP, a benefit during exercise.

Question 108

Smooth Muscle Tissue

Answer 108

Visceral smooth muscle tissue. It is found in the skin and in tubular arrangements that form part of the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus, and urinary bladder. Multiunit smooth muscle tissue, found in the walls of large arteries, in airways to the lungs, in the arrector pili muscles that attach to hair follicles, in the muscles of the iris that adjust pupil diameter, and in the ciliary body that adjusts focus of the lens in the eye.

Question 109

Microscopic Anatomy of Smooth Muscle

Answer 109

The sarcoplasm of smooth muscle fibers contains both thick filaments and thin filaments, in ratios between 1:10 and 1:15, but they are not arranged in orderly sarcomeres as in striated muscle. Smooth muscle fibers also contain intermediate filaments. In smooth muscle fibers, the thin filaments attach to structures called dense bodies, which are functionally similar to Z discs in striated muscle fibers.

Question 110

Physiology of Smooth Muscle

Answer 110

Contraction in a smooth muscle fiber starts more slowly and lasts much longer than skeletal muscle fiber contraction. Another difference is that smooth muscle can both shorten and stretch to a greater extent than the other muscle types. An increase in the concentration of Ca2 in the cytosol of a smooth muscle fiber initiates contraction, just as in striated muscle. Several mechanisms regulate contraction and relaxation of smooth muscle cells. In one such mechanism, a regulatory protein called calmodulin binds to Ca2 in the cytosol. After binding to Ca2, calmodulin activates an enzyme called myosin light chain kinase. This enzyme uses ATP to add a phosphate group to a portion of the myosin head. Once the phosphate group is attached, the myosin head can bind to actin, and contraction can occur. on blood. Most smooth muscle fibers contract or relax in response to action potentials from the autonomic nervous system.

Question 111

Stress-Relaxation Response

Answer 111

When smooth muscle fibers are stretched, they initially contract, developing increased tension. Within a minute or so, the tension decreases. Allows smooth muscle to undergo great changes in length while retaining the ability to contract effectively.

Question 112

Regeneration of Muscular Tissue

Answer 112

(Table 10.5) pg 321

Question 113

Muscle Attachment Sites

Answer 113

Origin: The attachment of a muscle’s tendon to the stationary bone. Insertion: The attachment of the muscle’s other tendon to the movable bone Action: The main movements that occur when the muscle contracts.