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FoundSci Unit 6 > Muscle Tissue > Flashcards

Muscle Tissue Flashcards

1
Q

What is muscle tissue specialized for?

A

Specialized for contractions that produce movement

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2
Q

What type of movement occurs in muscle tissue?

A

Movement of body itself and its parts
Pumping of blood through heart/vessels
Force air into/out of the body
Moves food through gut

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3
Q

What are characteristics of muscle tissue? (cells, ECM, CT, innervation/vascularized, embryo origin)

A

cells > ECM

cells in direct contact with each other in most types of muscle tissue

Amount of ECM depends on muscle type - muscle cells have own external lamina

Some type of muscle tissue are compartmentalized by CT

Always innervated and well vascularized

From mesoderm

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4
Q

What are the 2 categories of muscle and the types of muscle tissue?

A
  1. Striated muscle - cells have striations; skeletal muscle and cardiac muscle
  2. Non-striated muscle - cells lack striations; smooth muscle
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5
Q

What is the orientation of striations in striated muscle?

A

Striations are perpendicular to the long axis of a muscle cell

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6
Q

What is a generic term for muscle cells?

A

Myocytes

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7
Q

What are skeletal and cardiac cells called?

A

Muscle Fibers

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8
Q

What is a muscle cell membrane?

A

Sarcolemma

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9
Q

What is the muscle cell cytoplasm?

A

Sarcoplasm

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10
Q

What is the smooth endoplasmic reticulum of the muscle cell?

A

Sacroplasmic reticulum

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11
Q

What are contractile cytoskeletal filaments of muscle cells?

A

Myofilaments - Actin (thin) filaments and myosin (thick) filaments

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12
Q

What is the function of skeletal muscle tissue?

A

Moves the skeleton as well as some soft tissue structures (eyeball, tongue, esophagus, and scrotum)

Has roles in stability, balance, breathing, speaking

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13
Q

Skeletal muscle tissue is under ______ control in response to _____ signals

A

Voluntary

In response to CNS signals (motor nerves)

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14
Q

Where is skeletal muscle located?

A

Most skeletal muscle tissue attaches to bone indirectly via tendons (dense regular CT)

Some skeletal muscle tissue is embedded within other structures

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15
Q

What are the 2 types of resident cells in skeletal muscle? What are their functions?

A

Skeletal muscle fibers - contraction (contractile cells)

Satellite cells - stem cells; help repair and regenerated injured skeletal muscle fibers

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16
Q

What 3 CT sheaths surround and subdivide a skeletal muscle at organ and tissue levels?

A

Endomysium

Perimysium

Epimysium

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17
Q

What is the composition of endomysium?

A

Reticular CT around 1 muscle fibers and its EL

Capillary rich

Good environment for calcium, potassium, and sodium exchange

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18
Q

What is the composition of perimysium?

A

Loose CT around each fascicle (fascicle = bundle of muscle fibers)

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19
Q

What is the composition of epimysium?

A

Dense irregular collagenous CT surrounding entire muscle

Binds all fascicles together

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20
Q

What are the benefits of sheaths around skeletal muscle?

A

Blood/Nerve supply and lymph drainage are very close to muscle fibers

Facilitates more powerful contractions

Helps connects a muscle to its tendons

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21
Q

What are key features of skeletal muscle fibers in LM?

A

Fibers are very long, cylindrical and parallel within a fascicle

Multinucleated - heterochromatic nuclei at periphery

Endomysium and capillaries between muscle fibers

Perimysium around fascicles

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22
Q

What is the sarcoplasm mainly made up of?

A

Most of sacroplasm/cell volume is myofibrils

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23
Q

What is each myofibril composed of?

A

Repeating sarcomeres that line up end to end down entire length of myofibril

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24
Q

What is the smallest functional contractile unit in skeletal muscle?

A

Sarcomeres

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25
Q

Where are the nuclei in the sarcoplasm?

A

Nuclei lie just inside sarcolemma, in the peripheral sarcoplasm

26
Q

What are the two myofilaments?

A

Myosin (thick) filaments

Actin (thin) filaments

27
Q

What is myosin made of and what does it do?

A

Mostly myosin II

Binding sites for ATP and actin

28
Q

What are actin filaments made of and what is the function of each part?

A

Mostly actin - binding sites for myosin and TnI

Tropomyosin

Troponin - 3 subunits
1. TnT - binds tropomyosin
2. TnC - binds calcium
3. TnI - binds actin; when TnI binds actin, it inhibits actin from interacting with myosin

29
Q

What myofilaments are in the sarcomere?

A

Actin (thin) and myosin (thick) myofilaments

30
Q

What is the Z disk in the sarcomere? What does it do?

A

Z line

Ends of a sarcomere
Proteins (alpha-actinin) that anchor thin filaments
Bisects I band

31
Q

What is the I band made of and where is it located?

A

Thin filaments only

Straddles adjacent sarcomeres

32
Q

What is the A band made of?

A

Thin and thick filaments

33
Q

What is the H band made of and where is it?

A

Thick filaments only

Bisects A band

34
Q

What is the M line made of and where is it?

A

Proteins that bind thick filaments

Middle of sarcomere

Bisects H band

35
Q

What does the sarcolemma have a lot of and what is that?

A

Sarcolemma has many T tubules which are tubular invaginations that extend deep into the cell

T tubule lumens are continuous with extracellular space and are important for initiating contraction

36
Q

What is the function and structure of the sarcoplasmic reticulum?

A

Sarcoplasmic reticulum is extensive and elaborate

Regulates contraction

Sequesters calcium in its terminal cisterns (when cell is relaxed) and released calcium into cytosol to initiate contraction

37
Q

What is a triad in reference to the sarcoplasmic reticulum?

A

Group of 2 sarcoplasmic reticulum terminal cisterns flanking a T tubule

38
Q

What is the short version of skeletal muscle contraction? 8 steps

A
  1. Motor neurons trigger depolarization of sarcolemma
  2. T tubules carry depolarization deep into sarcoplasm
  3. Depolarization reaches triad -> large amounts of calcium released from SR terminal cisterns into cytosol
  4. Calcium in cytosol binds troponin in actin filaments
  5. Actin filaments slide along thick filaments toward M line and thick filaments do not move
  6. Z discs pulled along - shortens length of sarcomere
  7. Actin filament sliding and sarcomere shortening happens simultaneously in all sacromere in 1 myofibril and all myofibrils in fiber contract so muscle fiber shorten
  8. Calcium returns to SR - actin filaments slide back into resting position
39
Q

Does the sarcoplasm have a lot of mitochondria?

A

yes! Many mitochondria

40
Q

What does the myoglobin in the sarcoplasm do?

A

Oxygen binding

41
Q

How does skeletal muscle fibers get fuel for glycolysis?

A

Skeletal muscle fibers contain varying amounts of glycogen

42
Q

What is type I skeletal muscle fibers? What is the myoglobin content, mitochondria, contractions, and primary method of ATP generation of type I?

A

Red, slow twitch

High myoglobin

Many mitochondria

Slow and repetitive contractions, not easily fatigued

Slow aerobic respiration

43
Q

What is type IIa skeletal muscle fibers? What is the myoglobin content, mitochondria, contractions, and primary method of ATP generation of type IIa?

A

Intermediate

Intermediate myoglobin content

Intermediate number of mitochondria

Fast and not easily fatigued contractions

Aerobic respiration but can switch to anaerobic glycolysis

44
Q

What is type IIb skeletal muscle fibers? What is the myoglobin content, mitochondria, contractions, and primary method of ATP generation of type IIb?

A

White, fast twitch

Low myoglobin

Few mitochondria

Fast and easily fatigued

Anaerobic glycolysis

45
Q

What is the sarcolemma dual anchored by?

A

Sarcolemma is surrounded by external lamina and endomysium - satellite cells lie between sarcolemma and EL

Costamere (dystrophin-associated protein complex) - link cytoskeleton, sarcolemma, EL, and endomysium

Dystrophin - large intracellular linker protein that binds sarcolemma and actin filaments in peripheral myofibrils

46
Q

What is the purpose of the sarcolemma being dual anchored?

A

Anchoring cells to the CT layer that extends throughout the muscle strengthens the force of contraction

Balancing/distributing forces on both sides of sarcolemma protects it from being torn by strong tensile forces during muscle contraction

47
Q

What is skeletal myogenesis?

A

Initial formation of muscle tissue in embryos

Mesenchymal cells in somites or paraxial mesoderm differentiates to myoblasts

Myoblasts fuse end to end and form syncytia called myotubules

Some myoblasts remain unfused and do not differentiate into satellite cells

Myotubules make myofilaments which organize into sarcomeres

48
Q

What is the function of cardiac muscle tissue? How does it accomplish this?

A

Contracts the heart wall and moves blood from chamber to chamber and into arteries

Rigorous and rhythmic contractions in response to electrical signals generated by heart itself

Contraction rate modulated by ANS nerves and hormones, but they do not initiate contraction

49
Q

What is the control and location of cardiac muscle tissue?

A

Involuntary control

Located in heart wall and forms the myocardium of atria and ventricles

50
Q

What are the 4 main types of cardiac muscle tissue?

A

Contractile cardiomyocytes - contraction

Myoendocrine cells - secrete peptide hormones

Nodal cells (in SA or AV nodes) - generate electrical impulses and coordinate the contraction of cells in atria and ventricle

Purkinje fibers - very rapid conduction of electrical impulses

51
Q

What are the key features of cardiac muscle fibers?

A

Shorter than skeletal muscle fibers

Y-shaped cells

1-2 large euchromatic nuclei in center of cell

Striation present but weak

Cells directly contact each other end to end at intercalated discs

52
Q

What are the characteristics of the sarcolemma and intercalated discs in cardiac muscle?

A

Sarcolemma surrounded by an EL and capillary rich endomysium - no satellite cells

Cardiac muscle has a dystrophin complex

Cardiac muscle fibers are in direct contact with each other

Intercalated discs are specialized regions of sarcolemma where 2 cells meet - lots of cell junctions

53
Q

What are the sarcoplasm contents of cardiac muscle fibers?

A

Most of sarcoplasm is myofibrils

Sarcomeres have thin and thick filaments

Dyads instead of triads in SR

Abundant myoglobin

More glycogen granules and more lipid droplets

Rows of very large mitochondria

54
Q

What is the heart’s conduction system? What is the system modulated by?

A

System generates and transmits electrical impulses to contractile cardiomyocytes

System is modulated by ANS nerves and hormones - can influence changes in contraction rates, but nerves don’t contact cells or initiate contractions

55
Q

What is the mechanism of contraction for cardiac muscle?

A
  1. Depolarization transferred from conducting cells (purkinje fibers) to contractile cardiomyocytes
  2. Depolarization travels down T tubules into sarcoplasm - triggers calcium release from SR and binds to TnC
  3. Thin filaments slide across thick filaments, pulling Z discs towards M line
  4. Contraction simultaneous in all sarcomeres in cardiac muscle fiber
  5. After contraction, calcium return to SR, binds to calsequestrin in SR terminal cisterns
56
Q

What is the function of smooth muscle tissue? How does it accomplish these tasks?

A

Functions:
- peristalsis in GI, repro, and urinary tracts - moves lumen contents
- blood vessel constriction and dilation - regulates blood flow (volume, rate)
- airway constriction and dilation

Slow and sustained contraction in response to variety of signals/stimuli

57
Q

What is the control and locations of smooth muscle tissue? What are the resident cells of smooth muscle tissue?

A

Involuntary control

Located in walls of blood vessels and tract (resp, GI, GU)

Resident cells - smooth muscle cells - contractile cells that can undergo mitosis and also synthesize and secrete EL and endomysium components

58
Q

What is contraction of smooth muscle cells triggered by?

A

Contraction may be triggered by ANS nerves, hormones, chemical stimuli

Mechanical stretching cells or electrical signals traveling between adjacent smooth muscle cells.

Contraction can depend on location - unitary (visceral) smooth muscle in wall of GI and GU has poor innervation and multiunit smooth muscle in iris of eye is richly innervated

59
Q

What are the characteristics of smooth muscle tissue?

A

Hard to see boundaries between adjacent smooth muscle cells

1 nucleus located in the cell center and is euchromatic

Look like inchworms - no striations or intercalated discs or branches

60
Q

What are characteristics of smooth muscle - sarcolemma and sarcoplasm?

A

Smooth muscle cells in extensive contact

Abundant gap junctions - rapid ion transmission from cell to cell and allows smooth muscle cells to coordinate and contract as a unit

Focal adhesions anchors smooth muscle cells to neighboring cells

Has dystrophin complex

Numerous calcium channels - bring extracellular calcium into cell and release it into cytosol to initiate smooth muscle cell contraction

Numerous caveolae (lipid rafts) form caveolin-dependent endocytotic vesicles and pinocytotic vesicles

61
Q

What are the contents of smooth muscle cell sarcoplasm?

A

No t tubules and SR not as well developed

Numerous mitochondria, some glycogen granules

Numerous intermediate filaments

No sarcomeres, no myofibrils, and no striations

Dense plaques - where thin filaments attach to sarcolemma

Dense bodies - attachment pints between thin filaments and intermediate filaments

62
Q

What are the steps of smooth muscle cell contraction?

A
  1. Stimulus triggers depolarization of smooth muscle cell sarcolemma
  2. Voltage gated calcium channels bring in extracellular calcium - triggers release of calcium stored in SR
  3. Calcium binds to smooth muscle cell specific version of myosin
  4. Thin filaments slide across myosin, drawing dense plaques closer to cell center

FoundSci Unit 6 (14 decks)

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