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Microanatomy > Muscle Tissue > Flashcards

Muscle Tissue Flashcards

1
Q

4 basic tissues of the body:

A

Epithelium, connective tissue, muscle tissue, nervous tissue

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2
Q

Muscle cells contract to produce movement needed for:

A

Locomotion, propulsion, and pressure regulation

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3
Q

Other names for muscle cells

A

Myocytes and myofibers (cell and fiber are used interchangeably)

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4
Q

What shape are muscle cells and where do they originate?

A

Spindle-shaped and originate from the mesoderm (myoblasts)

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5
Q

Myotubes

A

Multinucleated tubes of mesenchymal cells that have aligned and fused together

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6
Q

Myofilaments

A

Differentiated myotubes; the nuclei are displaced against the plasma membrane

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7
Q

Satellite cells

A

Undifferentiated mesenchymal cells that function in muscle repair

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8
Q

Sarcoplasm

A

Cytoplasm of muscle cells, contains glycogen and myoglobin

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9
Q

Sarcolemma

A

Plasma membrane of the muscle cell

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10
Q

Sarcoplasmic reticulum

A

The highly specialized smooth ER of a muscle cell (regulates calcium flow)

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11
Q

How much of the body weight is made up of skeletal muscle?

A

50%

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12
Q

T/F: Skeletal muscles are involuntary muscles.

A

False - voluntary

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13
Q

Epimysium

A

The dense irregular connective tissue layer that surrounds muscles

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14
Q

Fascicles

A

Many smaller bundles that make up a whole muscle; composed of myocytes and myofibers

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15
Q

Perimysium

A

Surrounds fascicles; dense connective tissue

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16
Q

Myofibrils

A

Cylindrical bundles contained in myofibers

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17
Q

Myofilaments

A

Smaller bundles found in myofibrils; composed of actin and myosin - contractile proteins and tropomyosin - regulatory proteins

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18
Q

Endomysium

A

Reticular fibers surrounding individual myocytes

19
Q

Describe the components of the I and A bands.

A

I band - actin only A band - actin and myosin overlap

20
Q

Sarcomere

A

Contractile or functional unit of the myocyte; includes all elements from Z line to Z line; at full contraction, Z lines (discs) will be drawn closer to each other

21
Q

Z-line

A

A protein disc that bisects the I band; actin filaments are anchored here

22
Q

Sliding filament model

A

Each sarcomere shortens –> myofilament length is constant –> I band shortens, almost disappears –>thin filaments slide past thick filaments

Summation of all sarcomere shortening produces contraction of the muscle cell

23
Q

Steps in muscle contraction

A
  1. Binding of calcium to troponin C
  2. Conformational change in tropomyosin, exposing the myosin-binding site on actin
  3. Myosin head binds to actin; ATP –> ADP moving myosin head
  4. Bound thin filaments slide over thick filaments
  5. Shortening of entire muscle fiber
24
Q

T-tubules (transverse tubules)

A

A deep invagination of the sarcolemma (plasma membrane) only found in skeletal and cardiac muscle cells; these invaginations allow depolarizaton of the membrane to quickly penetrate to the interior of the cell allowing calcium release from the sarcoplasmic reticulum

25
Q

Sarcoplasmic reticulum

A

Equivalent to the endoplasmic reticulum but seen in smooth and striated muscle; stores and releases calcium ions to initiate contractions

26
Q

Identify and describe each numbered structure

A

1) Myofibrils, made of myosin and thin actin myofilaments
2) Sarcoplasmic reticulum, stores and releases calcium
3) Terminal cisterna, expanded ends of sarcoplasmic reticulum

T) Transverse T-tubule, deep tubular finger-like invaginations of sarcolemma (plasma membrane) of skeletal muscle cell create anastomosing network of tubules

27
Q

Describe Type 1 skeletal muscle fibers

A
  • “red muscle”
  • slow twitch
  • dark color - rich in myoglobin which accounts for dark color
  • aerobic metabolism –> fatigue resistant
    • high fat, low glycogen content
    • many mitochondria
    • myoglobin - to help transfer oxygen
28
Q

Describe Type 2 skeletal muscle fibers

A
  • “white muscle”
  • fast twitch
  • anaerobic metabolism –> more prone to fatigue
    • low fat, high glycogen content
    • less myoglobin and a few mitochondria
29
Q

Describe cardiac muscle

A
  • cardiomyocyte = myocardiocyte = cardiac myocyte
  • single cell with one central nucleus
  • cross striated
  • has intercalated discs
    • gap junctions
    • desmosomes
  • has sarcoplasmic reticulum
  • has many mitochondria (up to 20% cell volume) - requires a lot of O2
30
Q

Intercalated discs

A

Attach cardiac muscle cells to each other, providing strength and the ability to function as a syncytium

  • a true syncytium is a multinucleated cell (i.e. skeletal muscle cell)
  • consist of
    • transverse element
      • anchor
      • desmosome - fascia adherens and/or macula adherens
      • serve for strong attachment
    • longitudinal element
      • communication
      • gap junction (nexus) with ion channels
      • propagate electric impulse
31
Q

Identify the components of the intercalated disc

A
  1. macula adherens
  2. gap junction
  3. fascia adherens
32
Q

Atrial myocardium

A

Atrial muscle cells contain membrane bound granules that are especially numerous at the right atrium; atrial granules have an endocrine function due to the presence of ANF/ANP

33
Q

Name and describe the two types of cardiomyocytes

A
  1. contractile - red
  2. conductile - pale pink
34
Q

Purkinje fibers

A

Modified cardiac muscle cells with 1-2 nuclei, myofibrils are sparse and restricted to periphery of cell; arranged in groups, cells are bigger and paler than contractile cardiac muslce cells

35
Q

Describe smooth muscle cells

A
  • single centrally located nucleus
  • no striations
    • no myofibrils!
    • actin and myosin myofilaments are present but are not ordered
  • cytoplasmic dense bodies represent anchors for myofilaments (like Z bodies)
  • desmosomes and gap junctions
  • no T-tubules and sarcoplasmic reticulum is poorly developed
  • spindle shaped (fusiform) cells surrounded by a basal lamina and reticular fibers
  • parasympathetic and sympathetic innervations
  • contraction involuntary
36
Q

Single unit (unitary) smooth muscle

A
  • found in visceral organs
  • cells behave like syncytium contracting in a network
  • sparse nerve innervation but cells communicate via multiple gap junctions
37
Q

Multi-unit smooth muscle

A
  • found in iris of eye
  • precise contraction
  • individual innervation of each myocyte
  • lack of gap junctions, function individually
38
Q

Functions of smooth muscle

A
  • peristalsis - wave-like contractions
  • vascular dynamics - contraction alters blood flow and important in blood pressure
  • propulsion
  • secretion (minor role)
39
Q

Dense bodies

A

The smooth muscle equivalent of Z discs of skeletal and cardiac muscle; note cigar-shaped nucleus

40
Q

Innervation of smooth muscle

A
  • Innvervated by ANS (sympathetic and parasympathetic system)
  • allows stimulation (fast & slow) and inhibition of muscle cells
  • acetylcholine, norepinephrine, epinephrine are common neurotransmitters
41
Q

Myoepithelial cells

A
  • contractile non-muscle cells
  • ectodermal origin
  • contain actin/myosin
  • similar to smooth muscle
  • can also be stimulated by hormones (mammary gland)
  • basket-like shape –> known as basket cells
  • location: salivary/mammary/lacrimal (crying) glands
42
Q

Satellite cells

A

Skeletal muscle has limited regeneration capacity, and these cells retain mitotic potential and thus can accomplish some repair; positioned between basal lamina and sarcolemma of muscle cell; fibroblasts also form connective tissue (scar) as part of the repair process

43
Q

Muscle regeneration

A
  • cardiac muscle cells lack the ability to regenerate
  • smooth muscle regeneration is limited; in addition to some mitotic activity, new smooth muscle cells may be derived from pericapillary mesenchymal cells
  • in all muscle types, repair is completed by scar tissue formation

Microanatomy (4 decks)

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