Ch10: Muscular Tissue

Front 1

Describe the structural differences among the three types of muscular tissue.

Back 1

Skeletal muscle tissue
-striated (alternating light&dark bands) = voluntary

Cardiac muscle tissue
-striated
-autorhythmicity (heart has own pacemaker for contractions) = involuntary

Smooth muscle tissue
-nonstriated = involuntary

Front 2

Describe the functions and properties of muscular tissue

Back 2

FUNCTIONS
1 producing body movements
2 stabilizing body positions (postural muscles)
3 storing & moving substances within body (accomplished by sphincters)
4 producing heat (thermogenesis)

PROPERTIES
1 electrical excitability (=ability to produce action potentials, triggered by autorhythmic electrical signals or chemical signals)
2 contractility (=ability of musc tiss to stretch without being damaged)
3 extensibility
4 elasticity (=ability to return to original length and shape after contraction or extension)

Front 3

List and identify the connective tissue components, blood vessels, and nerves of skeletal muscles

Back 3

Muscle fibre/cell
Connective tissue components
-fascia
-superficial fascia / subcutaneous layer / hypodermis
-deep fascia
-epimysium
-perimysium
-fascicles
-endomysium
-tendon
-aponeurosis
Nerves & blood supply
-capillaries
-somatic motor neuron

Front 4

Describe the function and components of superficial fascia / subcutaneous layer / hypodermis (a ct component in skeletal muscles)

Back 4

-separates muscle from skin
-composed of areolar ct & adipose tissue

Front 5

Descibe the components and functions of Fascia (a ct component in skeletal muscles)

Back 5

=dense sheet or broad band of irregular ct
-lines body wall & limbs
-supports & surrounds musc & other organs
-holds muscles with similar functions together
-allows free movement of muscles
-carries nerves, blood vessels, and lymphatic vessels
-fills spaces between muscles

Front 6

Describe the components and functions of epimysium, perimysium, and endomysium (ct components in skeletal muscles)

Back 6

Epimysium = outermost layer, encircles entire muscle
Perimysium - surr groups of 10-100+ muscle fibers, separ them into fascicles
Endomysium = penetrates interior of each fascicle, separates individual muscle fibers from one another
*epi&peri = dense irreg ct
*endo = areolar ct

Front 7

Describe the components and functions of tendons in skeletal muscles

Back 7

= all 3 ct layers extend beyond muscle fibers
= cord of dense regular ct
-composed of parallel bundles of collagen fibers
-attach a muscle to periosteum of bone (ie.calcaneal/Achilles tendon)

Front 8

Describe what an aponeurosis is and its structure

Back 8

=tendon
-when ct elements extend as a broad, flat layer (ie. epicranial aponeurosis)

Front 9

Describe the function of Somatic motor neurons in skeletal muscles

Back 9

=stimulate skeletal muscle to contract
-each one has a threadlike axon that extends from brain or spinal cord to a group of skeletal muscle fibers
*axon of a somatic motor neuron typically branches many times, each branch extending to a different skeletal muscle fiber
*1 artery & 1or2 veins accompany each nerve

Front 10

Name the blood vessels in skeletal muscles and describe their functions

Back 10

Capillaries = Microscopic blood vessels, plentiful in muscular tissue
-bring in oxygen and nutrients
-remove heat and the waste products of muscle metabolism

Front 11

Define hypertrophy of skeletal muscle fibers and when does it occur?

Back 11

=An excessive enlargement or overgrowth of existing cells, in this case muscle cells, without cell division
-occus after birth & at puberty (from testosterone hormone)
*opposite of hyperplasia (=increase in number of cells)

Front 12

Define Sarcolemma

Back 12

= cell membrane of a muscle fiber (cell)
*action potentials travel along sarcolemma

Front 13

Describe the structure and location and function of Transverse (T) tubules

Back 13

-thousands of tiny invaginations in sarcolemma
-filled w interstitial fluid
*action potentials travel thru T tubules
-ensures an action potential excites all parts of the muscle fibers at essentially the same instant

Front 14

Define sarcoplasm and its components (glycogen, myoglobin, mitochondria, myofibrils, SR)

Back 14

=muscle fiber cytoplasm
-contains LOTS of glycogen for synthesis of ATP
-contains myoglobin (red-coloured protein)
>>binds incoming oxygen molecules & releases it when needed by mitochondria for ATP production
-mitochondria lie in rows throughout sarcoplasm, strategically close to muscle proteins that use ATP during contraction (Figure 10-2c)
-contains myofibrils (contractile, little threads, make musc fibers striated)
-sarcoplasmic reticulum (encircles each myofibril, similar to smoothER, reabsorbs Ca2+ ions during relaxation & releases them to cause contraxn, terminal cisterns = dilated end sacs )

Front 15

Define muscular atrophy and name the two types

Back 15

=wasting away of muscles from fibers decreasing in size bc of loss of myofibrils
1 Disuse atrophy (reversible –ie. Casts)
2 Denervation atrophy (=nerve supply to muscle disrupted or cut >> irreversible, replaced by fibrous ct, reduced to ¼ of original size)

Front 16

Define muscular hypertrophy

Back 16

=increased diameters of musc fibers due to increased production of myofibrils, mitochondria, SR, and other organelles
*more myofibrils = more forceful contractions

Front 17

Compare the length, diameter, function, and ratio of Thick & thin filaments

Back 17

~same length
Thick filament diameter is ~double that of thin filament
Both directly involved w contractile process
Ratio of thin to thick filaments = 2:1

Front 18

Define sarcomere and what are its components? Fig10-3

Back 18

=basic functional unit of a myofibril
=compartments carrying filaments
-separ by Z discs
-A band = darker, middle part of sarcomere >> extends entire length of thick filament
-Zone of overlap – where thin and thick filaments lay side by side
-I band = lighter, less dense area >> contains rest of thin filaments but no thick filaments, Z band passes through center of it
-H Zone = narrow, center of each A band >> contains thick but no thin filaments
-M line = formed by supporting proteins holding thick filaments together, at center of H zone & middle of sarcomere

Front 19

What are the 3 proteins of myofibrils and their functions?

Back 19

(1) contractile proteins - generate force during contraction (myosin & actin)
(2) regulatory proteins - help switch the contraction process on and off (tropomyosin & troponin)
(3) structural proteins
- keep the thick and thin filaments in proper alignment
-give myofibril elasticity and extensibility
-link the myofibrils to the sarcolemma and extracellular matrix

Front 20

Describe the structure, function and components of myosin in myofibrils

Back 20

= motor protein in all 3 types of musc tissue
- push/pull various cell structures to achieve movement by converting chemical E in ATP to mechanical E of motion/produc’n of force
-Each myosin molecule is shaped like two golf clubs twisted together (Figure 10-5a)
-Myosin heads = 2projections off each myosin molecule, project away from M-line (golf club heads)

Front 21

Describe the structure, function of actin in myofibrils

Back 21

-main component of thin filament
- actin mlcls twist together into a helix to form actin filament
-contains myosin-binding site where myosin head attaches

Front 22

Describe Tropomysin and its function

Back 22

=regulatory protein & component of thin filament
-covers myosin-binding sites on actin tf blocks myosin
-held in place by troponin molecules (when Ca2+ions bind to troponin, troponin undergoes shape change >> moves tropomyosin away from myosin-binding sites >> myosin binds to actin >> musc contraxn begins

Front 23

Define contraction cycle and describe its 4 steps

Back 23

= repeating sequence of events that causes the filaments to slide
*Does not always shorten musc fibers or entire muscle
1 ATP hydrolysis:
myosin head (includes ATP-binding site, ATPase, phosphate group) Hydrolysis reorients and energizes the myosin head
Products (ADP & P group) still attached to the myosin head
2 Attachment of myosin to actin to form crossbridges: energized myosin head attaches to myosin-binding site on actin & releases previously hydrolyzed P group.
Crossbridges = When myosin heads attach to actin during contraction
3 Power stroke: the site on crossbridge where ADP is still bound opens >> crossbridge rotates & releases ADP. The crossbridge generates force as it rotates toward center of sarcomere, sliding thin filament past the thick filament toward the M line
4 Detachment of myosin from actin: After power stroke, crossbridge remains firmly attached to actin until it binds another molecule of ATP. As ATP binds to the ATP-binding site on the myosin head, the myosin head detaches from actin

Front 24

Define and Describe excitation-contraction coupling

Back 24

=the steps that connect excitation (a muscle action potential propagating along the sarcolemma and into the T tubules) to contraction (sliding of the filaments)
As a muscle action potential propagates along the sarcolemma and into the T tubules, it causes Ca2+ release channels in SR membrane to open >> Ca2+ flows into the cytosol around thick & thin filaments >> Ca2+ concentration rises 10x or more
Released Ca2+ combine w troponin, causing it to change shape
>> tropomyosin away from myosin-binding sites on actin
>> myosin heads bind to sites to form crossbridges
Then contraction cycle begins
*Ca2+ concentration must be sufficiently high. If conc in sarcoplasm decreases, sliding of thin filaments stops
*Ca2+ conc in SR is 10 000x higher than in cytosol

Front 25

Define and describe length–tension relationship

Back 25

=how forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins
* The more optimal the zone of overlap is, the greater the tension of the muscle fiber
* If zone of overlap is far greater or far less than optimal, tension is minimal
Optimal zone of overlap = when a sarcomere length is ~2.0–2.4 μm (very close to the resting length in most muscles)
Figure 10-9 >> maximum tension (100%) occurs when zone of overlap between a thick and thin filament extends from the edge of the H zone to one end of a thick filament

Front 26

Describe the events that occur at a neuromuscular junction (NMJ = the synapse between the synaptic end bulb of the motor somatic neuron and the motor end plate of the muscle fiber)

Back 26

1 ACh Release: Arrival of nerve impulse at synaptic end bulbs causes many synap vesicles to undergo exocytosis >> synap vesicles fuse w motor neuron's plasma membrane >> frees ACh into synaptic cleft >> ACh diffuses across syn cleft towards motor end plate

2 Activan of ACh receptors: 2Ach mlcls bind to receptor on motor end plate, opens an ion channel in ACh receptor >> small cations (Na+) flow across membrane

3 Production of musc axn potential: inflow of Na+ (down electrochem gradient) makes inside of muscle fiber more +chrgd >> chg in memb potential triggers a musc axn potential (*1 action potential = 1 nerve impulse)
Musc axn potential propagates along sarcolemma into T tubule system >> causes SR to release stored Ca2+ into sarcoplasm >> musc fiber subsequently contracts

4 Termination of ACh activity: effect of ACh binding = brief bc ACh rapidly broken down by enzyme AChE (attached to collagen fibers in EC matrix of synaptic cleft >> acetyl & choline=products, cannot activate ACh receptor)

Front 27

Identify and describe the 3 sources from where ATP used during muscle contraction is produced

Back 27

Muscle fibers= 3 ways to produce ATP:
(1) from creatine phosphate (unique to musc fibers): formed from ATP while muscle is relaxed; transfers a high-energy P group to ADP to form ATP during musc contraction (w enzyme CK creatine kinase) *lasts ~15sec
(2) by anaerobic cellular respiration: Breakdown of muscle glycogen into glucose, then glycolysis = production of pyruvic acid from glucose, produce both ATP & lactic acid ***no oxygen needed *lasts ~30-40sec
(3) by aerobic cellular respiration (Figure 10-12) Within mitochondria- pyruvic acid, fatty acids, amino acids used to produce ATP (requires oxygen) *lasts ~10min+

Front 28

Describe the factors that contribute to muscle fatigue

Back 28

-results mainly from changes within muscle fibers
-central fatigue (before actual musc fatigue occurs): caused by changes in central ns (brain & spinal cord) *its exact mechanism is unknown but may be a protective mechanism to stop a person from exercising before muscles become damaged

-Inadequate release of ca2+ ions from SR = lower Ca2+ conc in sarcoplasm
-Depletion of creatine phosphate *BUT ATP levels in fatigued muscle often are not much lower than those in resting muscle
-insufficient oxygen
-depletion of glycogen and other nutrients
-buildup of lactic acid and ADP
-failure of action potentials in motor neuron to release enough Ach

Front 29

Define a motor unit and explain what the total strength of a contraction depends on

Back 29

Motor unit = A somatic motor neuron plus all the muscle fibers (cells) it stimulates (1:150)
Because all 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.

Front 30

Define Twitch contraction

Back 30

=brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron
-Twitches of skeletal muscle fibers last anywhere from 20 to 200 msec. This is very long compared to the brief 1–2 msec* that a muscle action potential lasts.

Front 31

Describe the phases in a twitch contraction

Back 31

1 Latent period= brief delay between application of stimulus and beginning of contraction
-muscle action potential sweeps over sarcolemma
-calcium ions released from SR
2 Contraction period
-Ca2+ binds to troponin, myosin-binding sites on actin are exposed, and crossbridges form
-Peak tension develops in muscle fiber
3 Relaxation period
-Ca2+ actively transported back into SR
-myosin-binding sites are covered by tropomyosin / myosin heads detach from actin
-tension in the muscle fiber decreases
*actual duration of these periods depends on the type of skeletal muscle fiber

Front 32

Describe the refractory period

Back 32

When a muscle fiber temporarily loses its excitability and cannot respond for a time after it’s received enough stimulation to contract
*If two stimuli are applied, one immediately after the other, the muscle will respond to 1st stimulus but not to 2nd
*characteristic of all muscle and nerve cells
*duration varies with the muscle involved (Skeletal muscle has a short refractory period ~5ms; cardiac muscle is longer ~ 300ms)

Front 33

Define motor unit recruitment

Back 33

=The process in which the number of active motor units increases (weakest motor units are recruited first, with progressively stronger motor units added if the task requires more force)
*Typically, different motor units of an entire muscle are not stimulated to contract in unison (While some motor units are contracting, others are relaxed)
-delays muscle fatigue
-allows contraction of a whole muscle to be sustained for long periods
*is 1 factor responsible for producing smooth movements rather than a series of jerks

Front 34

Describe how frequency of stimulation affects muscle tension

Back 34

*Increased frequency of stimulation produces a greater and more sustained contraction force / myogram line
*When a 2nd stimulus occurs after the refractory period of the 1st stimulus is over, but before the skeletal muscle fiber has relaxed, the 2nd contraction will actually be stronger than the 1st
Define Wave summation, Unfused tetanus, and Fused tetanus
Wave summation = when stimuli arriving at different times cause larger contractions
Unfused (incomplete) tetanus = sustained but wavering contraction caused by a skeletal muscle fiber that can only partially relax between stimuli (Figure 10-15c)
Fused (completed) tetanus = a sustained contraction in which individual twitches cannot be detected, caused by a skeletal muscle fiber that does not relax at all (bc it’s stimulated at a higher rate of 80-100x/s (Figure 10-15d)

Front 35

Define and Describe how muscle tone is produced

Back 35

=a small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units >> small groups of motor units are alternatively active and inactive in a constantly shifting pattern
-muscle tone is established by neurons in brain & spinal cord that excite the muscle's motor neurons
*if motor neurons serving a skeletal muscle are damaged or cut, muscle >> flaccid
*Muscle tone keeps skeletal muscles firm, but it does not result in a force strong enough to produce movement

Front 36

Define isotonic muscle contractions and its 2 types

Back 36

isotonic contraction = the tension (force of contraction) developed by muscle remains almost constant while the muscle changes its length
-used for body movements and for moving objects.
1 concentric isotonic contraction = if tension generated is great enough to overcome the resistance of the object to be moved
2 eccentric isotonic contraction = When the length of a muscle increases during a contraction
-tension exerted by the myosin crossbridges resists movement of a load (ie. a book) and slows the lengthening process
***repeated eccentric isotonic contractions (ie. walking downhill) produces more muscle damage and more delayed-onset muscle soreness than do concentric isotonic contractions

Front 37

Define isometric contraction

Back 37

=the tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length
-ie. holding a book steady using an outstretched arm
-important for maintaining posture and for supporting objects in a fixed position
*most activities involve both isotonic and isometric contractions

Front 38

List the 3 different types of skeletal muscle fibers

Back 38

Slow oxidative fibers (SO fibers)
Fast oxidative-glycolytic fibers
Fast glycolytic fibers

Front 39

Describe the structure and function of Slow oxidative (SO) fibers

Back 39

=smallest in diameter >> least powerful type of muscle fibers
-appear dark red (bc contains large amounts of myoglobin and many blood capillaries)
-many large mitochondria >> generate ATP mainly by aerobic cellular respiration, hence oxidative fibers
-“slow” bc ATPase in myosin heads hydrolyzes ATP slowly tf contraction slower and take longer to reach peak tension
- very resistant to fatigue
-capable of prolonged, sustained contractions for many hours
*adapted for maintaining posture and for aerobic, endurance-type activities such as running a marathon

Front 40

Describe the structure and function of fast oxidative–glycolytic (FOG) fibers

Back 40

= contain large amounts of myoglobin and many blood capillaries (like SO fibers) >> also dark red appearance
-generate considerable ATP by aerobic cellular respiration >> moderately high resistance to fatigue
-generate ATP by anaerobic glycolysis bc intracellular glycogen level is high
-“fast” bc ATPase in their myosin heads hydrolyzes ATP faster than SO fibers’ >> contraction faster >> twitches reach peak tension more quickly but are briefer in duration
*walking and sprinting

Front 41

Describe the structure and function of Fast glycolytic (FG) fibers

Back 41

=largest in diameter
-low myoglobin content, relatively few blood capillaries, few mitochondria, and appear white in color
-contain large amounts of glycogen
-generate ATP mainly by glycolysis
-contract strongly & quickly (Due to containing the most myofibrils, large size and ability to hydrolyze ATP rapidly
-adapted for intense anaerobic movements of short duration (ie. weight lifting, throwing a ball)
-fatigue quickly
*increase in muscle size (hypertrophy of FG fibers) due to increased synthesis of muscle proteins

Front 42

Describe the distribution and recruitment of different types of fibers

Back 42

-Most skeletal muscles =mix of all 3 types of skeletal muscle fibers
*in skeletal musc ~half are SO fibers
-proportions vary depending on action of the muscle, person's training regimen, and genetic factors
-ie. continually active postural muscles of the neck, back, and legs have a high proportion of SO fibers
-ie. Muscles of shoulders & arms (not constantly active, used briefly to produce large amounts of tension in lifting & throwing) >> high proportion of FG fibers
ie. Leg muscles (support body & for walking & running), have large #’s of both SO&FOG fibers
-W/in a particular motor unit, all of skeletal musc fibers =same type
-different motor units in a muscle are recruited in a specific order, depending on need (ie. if weak contraxns suffice to perform a task, only SO motor units are activated. If more force is needed, motor units of FOG fibers are also recruited. If maximal force required, motor units of FG fibers also called into action. Activation of various motor units is controlled by brain & spina

Front 43

Describe the major structural characteristics of cardiac muscle tissue

Back 43

-cardiac muscle fibers have the same arrangement of actin and myosin and the same bands, zones, and Z discs as skeletal muscle fibers BUT have intercalated discs (irregular transverse thickenings of sarcolemma, connect ends of cardiac muscle fibers to one another, discs contain desmosomes and gap junctions
-endomysium and perimysium (NO epimysium)

Front 44

Describe the major functional characteristics of cardiac muscle tissue

Back 44

-In response to a single action potential, cardiac muscle tissue remains contracted 10-15x longer than skeletal muscle tissue
>>long contraction is due to prolonged delivery of Ca2+ into sarcoplasm since Ca2+ enters sarcoplasm from both SR and interstitial fluid (channels that allow inflow of Ca2+ from interstitial fluid stay open for a long time)
-cardiac muscle tissue contracts when stimulated by own autorhythmic muscle fibers
-mitochondria in cardiac muscle fibers are larger and more numerous than in skeletal muscle fibers >> cardiac musc depends largely on aerobic cellular respiration to generate ATP tf requires a constant supply of oxygen
>>can also use lactic acid produced by skeletal muscle fibers to make ATP, a benefit during exercise

Front 45

Describe the major structural characteristics of smooth muscle tissue

Back 45

2 types
VISCERAL (single-unit) smooth muscle tissue (more common)
-form part of the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus, and urinary bladder
-autorhythmic
-fibers connect to one another by gap junctions >> if 1 fiber stimulated, neighboring fibers contract in unison, as a single unit
MULTIUNIT smooth muscle tissue
-3 autonomic motor neurons synapse with individual multiunit smooth muscle fibers >> Stimulation of 1 multiunit fiber causes contraction of that fiber only
-few gap junctions
-contract separately
-in walls of large arteries, airways to lungs, arrector pili muscles (attach to hair follicles), muscles of the iris that adjust pupil diameter, and ciliary body (adjusts focus of lens in eye)

Front 46

Describe the micorscopic anatomy of smooth musc tiss

Back 46

-thickest in the middle and tapers at each end
-thick and thin filaments present (ratios between 1:10 and 1;15) >> not arranged in orderly sarcomeres as in striated muscle
-intermediate filaments present
-non-striated
-lack transverse tubules
-only small amount of SR for Ca2+ storage of Ca2+
-caveolae = small pouchlike invaginations of plasma membrane called caveolae >> contain extracellular Ca2+
-thin filaments attach to dense bodies >> functionally similar to Z discs in striated muscle fibers >> Some dense bodies dispersed through sarcoplasm others attached to sarcolemma
-Bundles of intermediate filaments attach to dense bodies and stretch from one dense body to another

Front 47

Describe physiology of smooth muscle

Back 47

-Contraction in a smooth muscle fiber starts more slowly and lasts much longer than skeletal muscle fiber contraction
-can both shorten and stretch to a greater extent than the other muscle types

-little SR to store Ca2+ >> Ca2+ ions flow in from both interstitial fluid & SR
-no transverse tubules >> caveolae instead >> takes longer for Ca2+ to reach the filaments in fiber’s center & trigger contractile process >> slow onset of contraction of smooth musc
-calmodulin = regulatory protein binds to Ca2+ in cytosol to activate enzyme myosin light chain kinase (uses ATP to add a P group to myosin head so it can bind to actin for contraction to occur)
*Ca2+ leaving fiber & myosin light chain kinase = slow tf contraction slow
-prolonged presence of Ca2+ in the cytosol provides for smooth muscle tone
-can stretch considerably and still maintain contractile function

Front 48

Describe the stress-relaxation response in smooth muscle tissue

Back 48

=allows smooth muscle to undergo great changes in length while retaining the ability to contract effectively
*even though smooth musc in walls of blood vessels and hollow organs can stretch, the pressure on the contents within them changes very little. After the organ empties, the smooth muscle in the wall rebounds, and the wall retains its firmness.

Front 49

Describe myasthenia gravis

Back 49

=an autoimmune neuromuscular disease
>>fluctuating muscle weakness & fatiguability
-weakness caused by circulating antibodies that block acetylcholine receptors at the postsynaptic NMJ >> inhibits stimulative effect of Ach

Front 50

Describe muscular dystrophy

Back 50

= a group of hereditary muscle diseases >> weakens muscles that move human body
-characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue

Front 51

Describe spasm

Back 51

A sudden, involuntary contraction of large groups of muscles.

Front 52

Describe tremor

Back 52

Rhythmic, involuntary, purposeless contraction of opposing muscle groups

Front 53

Descibe tic

Back 53

= a sudden, repetitive, nonrhythmic, stereotyped motor movement or vocalization involving discrete muscle groups
-can be invisible to the observer, such as abdominal tensing or toe crunching. Common motor and phonic tics are, respectively, eye blinking and throat clearing.[

Front 54

Describe cramp

Back 54

A spasmodic, usually painful contraction of a muscle.

Front 55

Describe myalgia

Back 55

Pain in or associated w muscles