Chapter 10: Muscular Tissue

Question 1

Describe the 3 types of muscle tissue

Answer 1

1. Skeletal: striated and working in a voluntary manner
2. Cardiac: strates but works involuntary
3. Smooth muscle: non-striated and is involuntary

Question 2

built-in rhythm of the heart contolled by a natural pacemaker is known as ___________

Answer 2

autorhymicity

Question 3

What are the 4 key functions of muscular tissue?

Answer 3

Produce body movement
Stabolize body position
Store and move substances within body
Generating head

Question 4

What adaptive function does shivering achieve?

Answer 4

It is the involuntary contractions of skeletal muscles that increase rate of heat production (thermogenesis)

Question 5

What are the 4 special properties that allow muscular tissue to function and continue to homeostasis?

Answer 5

Electrical excitability – ability to response to stimuli by producing action potentials

Contractility – ability to contract forcefully when stimulated by action potentials

Extensibility – ability to stretch, within limits, without being damaged

Elasticity – ability to return to original length and shape after contraction or extension

Question 6

Which 3 layers of connective tissue extend from the fascia (lining of body wall that surrounds muscles/organs) to protect and strengthen skeletal muscles?

Answer 6

Epimusium: outer layer, encircles entire muscle

Permysium: surrounds groups of 10-100+ muscle fibers separating them into bundles called fascilcles

Endomysium: penetrates inferior of each fascicle and separates individual muscle fibers from one another

All layers form a role like tendon that attaches a muscle to the peristeirum of a bone

Question 7

When the connective tissue elements extend as a broad, flat sheet, it is called an _______

Answer 7

aponeurosis

Question 8

The neurons that simulate skeletal muscles to contract are ________ motor neurons

Answer 8

somatic

Question 9

Describe the following microscopic anatomic components of a skeletal muscle fibre:

Sarcolemma
Transverse tubules
Sarcoplasm

Answer 9

Sarcolemma: plasma membrane

Transverse tubules: tunnels into the centre of each muscle fibre where AP travel along

Sarcoplasm: cytoplasm of a muscle fibre that contains myoglobin that releases O2 needed for ATP production

Question 10

Describe the following microscopic anatomic components of a skeletal muscle fibre:

Myofibrils
Sacroplasmic reticulum

Answer 10

Myofibrils: contractile organelles that make muscles appear striated

Sacroplasmic reticulum: fluid-filled salts that encircles each myofibril that have terminal cisterns that attach to T tubules to release Ca2+ and trigger muscle contraction

Question 11

Define muscular hypertrophy

Answer 11

Muscle growth that occurs after birth by enlargement of existing muscle fibers due to increased production of myofibrils, mitochondria, SR, & organelles

occurs due to forceful muscular activity

Question 12

Define muscular atrophy

Answer 12

decrease in individual muscle fibers as a result of progressive loss of myofibrils

Question 13

Define fibrosis

Answer 13

replacement of fibers with scar

Question 14

Thin vs. thick filaments

Answer 14

Thin filaments (8nm) are composed mostly of protein actin 
Thick filaments (16nm) are composed mostly of protein myosin

There are 2 thin filaments for every thick filament in the regions of overlap - both involved in the contractile process

Question 15

The basic unit of a myofibril are filaments that are arranged in compartments called _____, which are separated from one another by _______

Answer 15

sarcomeres; z-discs (plate shaped proteins)

Question 16

Describe the arrangement of filaments within a sarcomere:

A band
I band
H zone
M Line

Answer 16

A band: darker middle part of the sarcomere which extends the entire length of a thick filament (H zone is the centre of each A band)

I band: lighter, less dense area that contains the rest of the thin filaments and has a z-disc in the middle

I IS THIN AND H IS THICK

M line: middle of the sacromere that holds thick filaments together

Question 17

What are the 3 types of proteins that constitute a myofibril?

Answer 17

Contractile
Regulatory
Structural

Question 18

The two types of contractile proteins in muscles are:

Answer 18

Myosin (thick)

• myosin tail points toward M line and the tails of neighbouring myosin molecules run parallel
• myosin heads - 2 projections of each myosin molecule

Actin (thin): joint to form an actin filament that is twisted int a helix
- Each actin is a myosin-binding site where a myosin head can attach

Question 19

Describe the 2 regulatory proteins

Answer 19

Tropomyosin: cover myoson-bdingin sites when muscle is relaxed

Tyoponin: binds with Ca2+ to move the topomyospin away from binding site

Question 20

Describe tintin (structural protein)

Answer 20

Spands half a sarcomere in a relaxed muscle - stabilizes thick filaments; can stretch without harm; accounts for elasticity and extensibility

Question 21

Describe the 4 steps of the contraction cycle

Answer 21

1. Myosin heads hydroyze ATP and become reoriented and energized
2. Myosin heads bind to actin, forming cross-bridges
3. Myosin cross-bridges rotate toward centre of sarcomere (power stroke)
4. As myosin heads bind to ATP, cross-bridges detach from actin

Question 22

Describe exitaiton-contraction coupling

Answer 22

Ca2+ is stored in SR - as an AP propagates along the sarcolemma and into the T tubules, it causes Ca2+ release

Ca2+ combines with troponin, causing conformation change which moves tropmyposin away from myosin-bdinign sites on acting

Myosin heads bind to form cross-bridges and the contraction cycle begins

Question 23

What is the length-tension relationship of muscle contraction?

Answer 23

The forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins

Maximum tensions occurs when the zone of overlap extends from edge of Hzone to one end of a thick filaments (too much or too little overlap decreases tension)

Question 24

What are the steps of a muscle action potential?

Answer 24

1. Release of ACh - Ca2+ flows inward stimulating ACh vesicles to undergo exocytosis and are released into the cleft
2. Activation of ACh receptors: binds to motor end plate causing influx of cations
3. Production of muscle action potential: increases membrane potential (makes it more positively changed) and triggers AP which travels along T tubules triggering Ca2+ release in the SR
4. Termination of ACh: acetylcholinesterase (AChE) breaks fawn ACh

Question 25

How do muscle fiebers produce ATP? Creatine prophase Anaerobic glycolysis Aerobic respiration

Answer 25

Creatine phosphate: formed from ATP while muscle is relaxes, transfers a high-energy P group to ADP forming ATP during muscle contraction Anaerobic glycolysis (no oxygen): breakdown of glycogen then glycolysis forms ATP and pyrutic acid Aerobic respiration (oxygen): within mitochondria pyretic acid, faty acids, and amino acids, + oxygen produces ATP

Question 26

Define muscle fatigue and central fatigue

Answer 26

Inability to maintain force of muscle contraction after prolonged activity Central fatigue: the feeling of tiredness and desire to cease activity prior to muscle fatigue (CNS response)

Question 27

Define oxygen debt/recovery oxygen uptake

Answer 27

added oxygen, over and above the resting oxygen consumption that is taken into the body after exercise used to 'payback' metabolic conditions

Question 28

Define motor unit

Answer 28

a somatic motor neuron plus all the skeletal fibers it simulates (150) Whole muscles that control precise movements consists of many small motor neurons

Question 29

What is a twitch contraction? What are the stages (as seen in myogram)?

Answer 29

the brief contraction of all muscle fibers in a motor unit in response to a single AP in its motor neuon Latent period - ~2ms delay in which the AP sweeps over the sarcolemma and Ca2+ released from the SR Contraction period - ~10-100ms in which Ca2+ binds to troponin, myosin-binding sites exposed, cross-bridges are formed and peak tension develops Relaxation period – ~10-100ms, Ca2+ actively transported back into SR, myosin-binding sites covered, tension decreases Refractory period: lost excitability The length of the twitch contraction depends on the type of muscle fiber – some are fast-twitch and others are slow-twitch fibers

Question 30

Describe how frequency of stimulation affects muscle tension

Answer 30

When a second stimulus occurs after the refractory period but before the muscle fiber is relazed, the second contraction will be stronger, a phenomenon called wave summation Unfused (incomplete) tetanus: sustained but wavering contraction 20-30x/sex Fused (complete) tetanus: contact contraction - twitches undetectable 80-100x/sec The combination of the tautness of the elastic components and the partially contracted state of the filaments enables the force of another contraction to be greater than the one before

Question 31

Define motor unit recruitment

Answer 31

process in which the number of active motor units increases They have a staggered activity to delay muscle fatigue (weak ones are recruited first)

Question 32

Muscle tone vs. flaccidity

Answer 32

Muscle tone: small amount of tautness or tension doe to weak, involuntary contractions, even at rest - this keeps muscles firm but is not strong enough to produce movement Flaccidity: when motor neurons become damaged/cut, they become flaccid

Question 33

Distinguish between isotonic and isometric contractions

Answer 33

Isotonic: tension developed in the muscle remains almost constant - 2 types: 1. Concentric: when tension is great enough to overcome resistance of an object, the muscle shortens (picking up a book) 2. Eccentric: length of the muscle increases (lowering book) Isometric: tension generated is not great enough to exeed the resistance of the object to be moved and the muscle does not change in length (holding a book steady with outstretched arm)

Question 34

Contrast between the 3 totes of skeletal muscle fibers: ``` Slow oxidative (SO) Fast oxidative (FO) Fast glycolytic (FG) ```

Answer 34

Slow oxidative (SO): ATPase in the myosin head hydrozyxes ATP slowly- important for maintaining posture and aerobic endurance (aerobic respiration) Fast oxidative (FO) ATPase in the myosin head hydrozyxes ATP quickly - importing for walking & sprinting (aerobic respiration and anaeronbic glycolysis) Fast glycolytic (FG): hydrolyzes ATP rapidly, Fg fibers contract strongly and quickly (white) - important for intense movement of short duriaiton (anaerobic glycolysis)

Question 35

How are cardiac muscle tissues different from skeletal muscles?

Answer 35

They have the same arrangement of actin and myosin and same bands but also have intercalated discs - thickenings of the sarcolemma that connects each ends of cardiac muscle fibre They contain desmosomes which hold fibers together and gap junctions with allow APs to spread from one cardiac muscle to another They have prolonged Ca2+ delivery and stay contacted longer

Question 36

Describe the 2 types of smooth muscle tissue Visceral Multiunit

Answer 36

Visceral: most common and in tubular arrangements (auto-rhythmic, fibers connect via gap functions) Multiunit: consist of individual diners, which with their own motor neurone terminal and a few gap functions (found in airways, arrestor pills muscles, eye)

Question 37

What are the microscopic appearance & feature differences between skeletal, cardiac, and smooth muscles?

Answer 37

Skeletal: long cyndrical fibre with many peripherally located nuclei; unbranched; striated Cardiac: branches cyndrical fibre with one centrally located nucleus, intercalated discs join neighbouring fibers Smooth: fiber thickest in the middle, tapered at each end, and with one centrally positioned nucleus, not striated

Question 38

Describe the microscopic anatomy of smooth muscles (filaments, dense bodies)

Answer 38

They are comprised of thin, thick, and intermediate filaments but are not arranged orderly as in striated muscles They have no T-tubules but cave small invaginations called caveolae that contain Ca2+ for contraction The thin filaments attach to dense bodies (similar to z-discs) and during contraction, sliding of thin and thick filaments generates tension

Question 39

Describe the physiological features of smooth muscles calmodulin smooth muscle tone stress relaxation response

Answer 39

calmodulin (regulatory proteins) bind to Ca2+ in cytosol and activated an enzyme myosin which allows for binding to actin for contraction smooth muscle tone: prolonged ca2+ in cytosol provides muscle tone, a state of continued partial contraction Stress relaxation response: smooth muscles initially contract when stretched developing increased tension which decreases in ~1 min which allow smooth muscles to undergo great changes will retaining ability to contract

Question 40

Hypertrophy vs. hyperplasia

Answer 40

Hypertrophy: enlargement of texting cells (most common growth after birth) Hyperplasia: increase in number of fibers

Question 41

Define myasthenia gravis

Answer 41

An autoimmune disease that causes chronic, progressive damage of the NMJ - body binds and blocks ACh receptors, decreaseing the number of functional receptors at the motor end plates of sketal muscles

Question 42

Define muscular dystrophy

Answer 42

a group of inherited muscle-destorying diseases that cuase progressive degermation of skeletal muscle fibers

Question 43

# Define abnormal muscle contractions: ``` Spasm Cramp Tic Tremor Fasciculation Fibrilation ```

Answer 43

Spasm: involuntary contraction of a single muscle in a large group of muscle Cramp: painful spasmodic contraction Tic: spasmodic twitching made involuntary by muscles that are ordinarily under voluntary control (eye twitch) Tremor: rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement Fasciculation – involuntary, brief twitch of an entire motor unit that is visible under the skin Fibrillation – spontaneous contraction of a single muscle fiber that is not visible under the skin but can be recorded by an EMG

Question 44

Smooth muscle fibers use troponin and tropomyosin for contraction True or False

Answer 44

False - they use calmodulin and myosin light chain kinase (enzyme)