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BIOL131 - Skeletal Muscle Tissue > Muscle Tissues Part 1 > Flashcards

Muscle Tissues Part 1 Flashcards

1
Q

What are muscle tissues?

A

Tissues that are specialized to actively shorten
- contraction provides means of mobility

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2
Q

What are the three types of muscle?

A
  1. Skeletal Muscle: moves and positions the body
  2. Smooth Muscle: pushes fluids and solids along digestive tract; and regulates artery diameters
  3. Cardiac Muscle: pushes blood through circulatory system
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3
Q

How can you distinguish each type of muscle?

A
  1. Skeletal Muscle:
    - striated, multinucleated
  2. Smooth Muscle:
    - non-striated, mononucleated
  3. Cardiac Muscle:
    - striated, mononucleated, branching fibres
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4
Q

What are the functions of skeletal muscle? (6)

A
  1. Skeletal Movement: pulls tendons to move bones
  2. Maintains posture and body positions
  3. Supports soft tissues: e.g. muscles of the abdominal wall and pelvic cavity
  4. Guard entrances and exits: e.g. openings of the digestive and urinary tracts (sphincters)
  5. Maintain body temperature
  6. Store nutrients: glucose, lipids, and even muscle proteins used during fasting
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5
Q

What is the meaning of the word roots myo, mys?

A

Muscle

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6
Q

What is sarco?

A

Flesh (Gk)

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7
Q

What is the sarcolemma?

A

Cell membrane of a muscle cell

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8
Q

What is the sarcoplasm?

A

Cytoplasm of a muscle cell

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9
Q

What is the sarcoplasmic reticulum?

A

Modified endoplasmic reticulum of a muscle cell (smooth, no ribosomes, stores Ca++)

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10
Q

What does myofibre/fibre refer to?

A

A singular skeletal muscle cell

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11
Q

How are skeletal muscles organized? (3; general)

A

3 layers of connective tissue

  1. Muscle fibre (cell surrounded by endomysium)
  2. Muscle fascicle (bundle of cells surrounded by perimysium)
  3. Skeletal muscle (organ that is surrounded by epimysium)
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12
Q

Explain the organization of a skeletal muscle?

A

A muscle consists of muscle fibres (myofibres) wrapped in a connective tissue called the endomysium. A number of fibres are wrapped together in perimysium to form a fascicle, while fascicles are bundled together to form a muscle, which is wrapped in epimysium or fascia. The three CT layers come togehter to form a tendon. Individual fibres are literally full of contractile organelles called myofibrils, which fill the cell and displace the nuclei to one side

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13
Q

What are myofibrils?

A

Bundle of myofilaments; a systematic arrangement of proteins which form the contractile unit of the muscle called a sarcomere, which gives muscle its striated appearance

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14
Q

What creates striations in a muscle?

A

Sarcomeres

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15
Q

What is the connective tissue around cells (myofibres)?

A

Endomysium

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16
Q

What is the connective tissue around fascicles?

A

Perimysium

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17
Q

What is the connective tissue around whole muscle?

A

Epimysium

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18
Q

What are the attachments of skeletal muscles?

A

Collagen fibers of the 3 different connective tissue layers come together at the ends of the muscle to form tendons (bundles) or aponeuroses (sheets)

structure: tendons in turn are continuous with matrix of the bone that they are attached to

Aponeuroses: layers of flat broad tendons with fewer vessels and nerves
structure: typically both tendons and aponeuroses attach muscle to bone

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19
Q

Nerve and blood supply of skeletal muscles?

A

Nerves and blood vessels penetrate epimysium together and branch through perimysium and endomysium

each cell is:
- adjacent to capillaries
- innervated by nerve fibre axons

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20
Q

What are characteristics of skeletal muscle cells?

A

Striated, lots of mitochondria, lots of capillaries, multi-nucleated

long and thin

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21
Q

What are myofibrils?

A

Rod like structures that come in bundles to form skeletal muscle cells; made up of even smaller structures/proteins called microfilaments

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22
Q

What does the sarcoplasmic reticulum contain an abundance of?

A

Ca++ store; 10000x more than outside the cell

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23
Q

Explain the development of a skeletal muscle fibre from myoblast to maturity

A

Myoblasts: immature muscle fibers
- muscle fibers develop through the fusion of embryonic mesodermal cells called myoblasts

Overtime, most of the myoblasts fuse together to form larger multinucleated cells. However, a few myoblasts remain within the tissue as myosatellite cells, even in adults

The multinucleate cells begin differentiating into skeletal muscle fibers as they enlarge and begin producing the proteins involved in muscle contraction

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24
Q

What are T-tubules (Transverse Tubules)?

A

Tiny tubules that penetrate the sarcolemma and travel deep into the cell surrounding the myofibrils

The T-tubule can conduct waves of electrical activity through pores from the sarcolemma deep into the cell, providing the signal for the cell to contract

25
Q

What is the structure of myofibrils?

A

Muscle cell = Bundles of thick and thin filaments (protein strands)

26
Q

Where is the Z-line?

A

Line in the middle of thin filaments, act as the boundaries of a sarcomere (singular repeating unit), in the middle of the I-band

  • When muscle fibers contract, the Z-lines move closer together, shortening the sarcomere and leading to muscle contraction.
  • The Z-line anchors the thin filaments (made of actin), which extend toward the center of the sarcomere.
27
Q

Where is the M-line?

A

Line in the middle of thick filaments, located at the center of the A-band (the dark band of the sarcomere) and runs vertically through the middle of the sarcomere.

It is made up of proteins that help anchor and stabilize the thick filaments (myosin) during muscle contraction.

28
Q

What is the range of a sarcomere?

A

From 1 Z-line/disc to the next Z-line

29
Q

What is a sacromere?

A

A sarcomere is the smallest functional unit of a muscle. It is the repeating structure within a muscle fiber (myofibril) that is responsible for muscle contraction. Contain:

Z-disc (Z-line): The boundary of the sarcomere. (middle of i-band)
A-band: The dark band, which contains the entire length of the thick filaments (myosin).
I-band: The light band, which contains only thin filaments (actin) and is bisected by the Z-disc.
H-zone: The region in the A-band where there are only thick filaments, with no thin filaments overlapping.
M-line: The line in the center of the A-band, where thick filaments (myosin) are anchored.

30
Q

What is the zone of overlap?

A

region where the thin filaments (actin) and the thick filaments (myosin) overlap with each other. This overlap occurs in the A-band (ends, area before A band meets I band), specifically in the area where the thin actin filaments overlap with the thick myosin filaments.

31
Q

What is the function of the z-line?

A
  • When muscle fibers contract, the Z-lines move closer together, shortening the sarcomere and leading to muscle contraction.
  • The Z-line anchors the thin filaments (made of actin), which extend toward the center of the sarcomere.
32
Q

What is the a-band vs i-band?

A

A-band: The dark band, which contains the entire length of the thick filaments (myosin).
I-band: The light band, which contains only thin filaments (actin) and is bisected by the Z-disc.

33
Q

What is the function of the m-line?

A

Line of proteins that connect the thick filaments
- serves as an anchor for the thick filaments (myosin).
- ensuring that the sarcomere retains its correct shape during muscle contraction and relaxation

During muscle contraction, the thin filaments (actin) slide over the thick filaments (myosin). While this sliding happens along the length of the sarcomere, the M-line helps keep the thick filaments in the center of the sarcomere, providing a stable point for the thin filaments to interact with them

34
Q

What is the H-zone?

A

In the A-band, thick myosin filaments a lighter region that contains no overlap

35
Q

What creates striations in muscles?

A

The myofibril arrangement of A-bands (dark bands) and I-bands (light bands)

36
Q

What is the sarcolemma?

A

The plasma membrane of a muscle fiber

  • has an intricate system of penetrating t-tubules that connect to sarcoplasmic reticulum (specialized smooth ER)
37
Q

What is the sarcoplasmic reticulum?

A

Specialized smooth ER in muscle fibers

  • functions to store and release calcium ions, which are important for muscle contraction
  • most SR Ca2+ are bound to calsequestrin protein
  • forms a tubular network around each myofibril
  • portions form enlarged sacs adjacent to the T-tubules
    = terminal cisternae
  • contains some Ca++ ions (some free) and some bound to calsequestirin
    The cell contracts when stored Ca++ ions are released into the sarcoplasm
38
Q

What is the protein titin?

A

Anchors thick filaments to Z lines and provides elasticity for resting muscle

Titin stabilizes the myosin thick filaments within the sarcomere, preventing them from drifting or misaligning during muscle contractions. This is crucial for maintaining the proper function of muscle fibers.

z-line to m-line

39
Q

What type of filaments can be found in each section of the sarcomere?

A

Z-line: Actin filaments (thin), attachment of titin (protein)
I-band: titin filament
M-line Myosin filament (thick)
H-zone: Myosin filament (thick)
Zone of Overlap: thick and thin filament

40
Q

What is the effect of sliding filament mechanism of contraction on H zone?

A

Becomes more narrow

41
Q

What is the effect of sliding filament mechanism of contraction on I band?

A

Becomes more narrow

42
Q

What is the effect of sliding filament mechanism of contraction on A band?

A

Stays the same

43
Q

What is the effect of sliding filament mechanism of contraction on zone of overlap?

A

Becomes wider

44
Q

What is the effect of sliding filament mechanism of contraction on sarcomeres?

A

The sarcomere shortens during muscle contraction as the thin actin filaments slide over the thick myosin filaments.

  • As this sliding occurs, the Z-lines move closer together, which shortens the length of the sarcomere.
  • As all sarcomeres shorten during contraction, the myofibrils shorten
45
Q

What happens as all myofibrils in a muscle cell shorten?

A

The entire muscle fiber (cell shortens and pulls on tendon)

46
Q

Overview of skeletal muscle contraction: what happens?

A
  1. A skeletal muscle cell contracts only when activated by a neuron
  2. Electrical activity passes over the sarcolemma, and down the T-tubules, triggering the release of calcium from the sarcoplasmic reticulum
  3. Ca++ triggers interactions between the thick and thin filaments, causing them to contract muscle fiber
  4. As the cell shortens, it generates active tension
47
Q

What is active tension?

A

Active tension refers to the force generated by a muscle during contraction. It is the result of the interaction between the thick myosin filaments and the thin actin filaments within the sarcomeres, according to the sliding filament theory of muscle contraction.

48
Q

What is the structure of myosin molecule?

A

2 tails wrapped into 1 and two heads that can swivel

each myosin head has binding sites for actin and ATP

49
Q

What proteins make up thin filaments? (4)

A

Actin: globular, strung together like beads on a string, each molecule has an active binding site for myosin

Nebulin: long threadlike protein holding actin in place

Tropomyosin: strand-like protein, at rest lies over the active sites on actin molecules

Troponin: globular protein, holds tropomyosin in place, each troponin has a binding site for calcium

50
Q

What happens with Ca++ is present in the cytoplasm?

A

It binds to troponin. This changes the shape of troponin, causing it to allow tropomyosin to slide off the myosin binding sites of actin

the actin and myosin are now free to interact: cross bridge cycling

51
Q

What are the contractile proteins?

A

Myosin: the largest contractile proteins and are double stranded molecules that produces two heads at one end. Myosin is capable of using ATP to generate force, and is therefore called a molecule motor

Actin: molecules from thinner of the contractile filaments and serve as an anchoring strand for myosin. Each actin molecule has a binding site for the myosin heads. In order for contraction to occur, the myosin head must bind to an actin molecule

  • the binding site on each actin molecule is protected by a long tropomyosin strand. Interspersed along the tropomyosin strand are molecules called troponin. When calcium binds to troponin, the tropomyosin strand is pulled aside to reveal the myosin binding site on actin
52
Q

What is the role of calcium troponin, and tropomyosin?

A

When calcium binds to the troponin complex, tropomyosin is moved from its actin-blocking position. Once the myosin binding site is revealed on the actin molecule, the myosin head can bind and initiate the cross-bridge cycle

53
Q

What is the cross-bridge cycle?

A

Term used to describe the process of the myosin heads binding to actin and the generation force to contract the muscle fiber.

The cycle begins when myosin is bound to actin and the myosin head is “energized” from a molecule of ATP

The myosin head now changes shape, pulling on the actin filament and releasing ADP. This results in shortening of the sarcomere

The myosin head remains bound to the actin filament until another ATP binds to it, allowing myosin to release actin

Once released, the myosin head is “energized” when ATP is broken down, into ADP and Pi which provides the energy for subsequent binding and pulling

54
Q

What are the 4 steps of the cross bridge cycle?

A

Starting off in resting sarcomere:
1. myosin cross bridge attaches to the actin myofilament; myosin acts as an ATPase binding ATP and hydrolyzing it into ADP and P, transforming myosin to a crooked position (high energy configuration) ready to bind actin

  1. Working stroke - the myosin head pivots and bends as it pulls on the actin filament, sliding it towards the M line; myosin binds actin to form cross bridge
  2. As new ATP attaches to the myosin head, the cross bridge detaches; myosin released ADP and P, while power stroking
  3. As ATP is split into ADP and P, cocking of the myosin head occurs; myosin binds ATP and releases actin; cycle repeats
55
Q

The sarcomere and the cross bridge

A

When Ca++ is released into the cytosol, actin and myosin are allowed to interact, resulting in the myosin heads pulling the actin fibers, generating tension: if sufficient this force shortens the sarcomere and the muscle fiber

56
Q

Where does the Ca++ come from to bind troponin and initiate the contraction?

A

The cisternae of the sarcoplasmic reticulum

57
Q

What is the signal that causes the release of Ca++?

A

Wave of electric activity = action potential passing over the cell and down the T-tubules

58
Q

Where does the Ca++ go to end the contraction ?

A

Back to the sarcoplasmic reticulum; most of it is bound to calsequestrin

BIOL131 - Skeletal Muscle Tissue (3 decks)

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