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Histology Final > Muscle tissue > Flashcards

Muscle tissue Flashcards

1
Q

Four types of contracting cells

A
  1. Myoepithelial cells: expels secretion from Gland
  2. Pericytes: around small blood vessels
  3. Myofibroblasts: secrete Collagen
  4. Myoid cells: outside basal lamina of seminiferous tubules in testes
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2
Q

Types of muscles

A

> Skeletal muscle
Cardiac muscle
Smooth muscle

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3
Q

Skeletal muscle

A
  • cross striations
  • contraction is quick and vigorous
  • contraction is voluntary
  • LOCOMOTION; MASTICATION; PHONATION
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4
Q

structure of skeletal muscle

A
  • muscle composed of fibers
  • each Fiber: multinucleate structure–> symplast
  • cells: myoblasts (somites)

layers

  • Epimysium (dense irregular with blood vessels and nerves)
  • Perimysium (surrounds fascicles)
  • Endomysium (surrounds fibers)
  • Sacrolemma (surrounds fibers)
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5
Q

Skeletal muscle fiber

A
  • nuclei are in the periphery
  • MYOFIBRIL fill 80% of the Fiber
  • myofibrils surrounded by sacroplasm with mitochondria, sER, glycogen
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6
Q

Cross striation of skeletal muscle

A
  • Alternation of I and A bands –> Arrangement of myofilaments
  • I bands: light, thin, bisected by Z lines (Actin)
  • A bands: dark, thick, bisected by H lines and further bisected by M lines (actin and Myosin)
  • H bands: thick Filaments only (Myosin)

Z lines divide each myofibril in sacromeres

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7
Q

Thin (actin) filament

A

three proteins:

  1. Actin (Kügelchen)
  2. Tropomyosin (Bänder)
  3. Troponin
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8
Q

Actin

A
  • globular proteins
  • globules are called G-ACTIN
  • Many g-actin globules from a strand of F-ACTIN
  • two f-actin make a double helix
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9
Q

Tropomyesin

A
  • coil protein
  • 7 globules of g-actin Long
  • in regulating interactions between actin and Myosin –> “hides” the active Myosin binding sites on actin filaments
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10
Q

Troponin

A

three regulatory proteins:
1- Troponin C: binds to Calcium
2- Troponin T: binds to tropomyosin
3- Troponin I: binds to actin –> inhibits Myosin-actin binding

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11
Q

Thick (Myosin) filament

A
  • composed of Myosin
  • each Myosin molecule has tail –> fixed to M line
  • has two heads
  • heads hydrolyze ATP, bind to active sites on actin and form cross bridges
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12
Q

Structural proteins in a sacromere apart from Myosin and actin

A

Titin (Myosin associated)
Nebulin (actin associated)
Myomesin (inside M line)
Alpha actinin (inside Z line)

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13
Q

The sliding Filament theory

A
  • thick and thin Filaments slide over each other
  • all Filaments stay constant in length
  • amout of overlap: contraction and Relaxation
  • A bands: constant in width
  • I & H bands: narrow during contraction
  • Z lines move Closer togehter –> contraction
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14
Q

Conduction System for contractile Stimuli

A
  1. T tubules of sacrolemma

2. Terminal cisternae

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15
Q

T (transverse) tubules

A
  • extensions of the Plasma membrane (sacrolemma)

- run perpendicular to myofibrils

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16
Q

Terminal cisternae

A
  • flattened cisternal arranement in sER around each myofibril
17
Q

Triad

A
  • one tubules and two cisternae

function: Propagation of Signal to sER to release Ca

18
Q

Motor unit

A
  • motor Neuron and all muscle fibers it supplies

- Action potentials from axons are transmitted across NEUROMUSCULAR JUNCTIONS

19
Q

Neuromuscular Junction /motor end plate

A
  • Presynaptic part: has vesicles with acetylcholine
  • Synaptic cleft
  • Postsynaptic part (sacrolemma): contains receptors

depolarization is passed on by T tubules to the sacroplasmic reticulum
–> release of Ca initiates contraction

20
Q

Contraction cycle

A
  • Ca binds to Troponin
  • -> Change in tropomyosin
  • -> active sites on actin are revealed
  • -> Myosin binds to actin
  • -> Myosin pulls actin to M line
  • -> ATP binds to Myosin head
  • -> Myosin detaches from actin
21
Q

Types of skeletal muscle

A

> Type I: (Aerobic/ red): mitochondria, Myoglobin
—> “slow-twitch” fibers: can contract continuously

> Type II: (anaerobic/ White): few mitoch. and Myoglobin
—> “fast-twitch” fibers: can contract intensely and sporadic

22
Q

Cardiac muscle

A
  • in myocardium in heart
  • in proximal portions of great blood vessels
  • striated but involuntary
23
Q

Cardiac muscle Fiber/ cardiomyocyte

A
  • Long cylindrical cells
  • split longitudinally in branches
  • interconnected by intercalated Discs
  • 1 or 2 centrally located nuclei
  • contains: myofibrils, mitochondria, glycogen, sER
24
Q

T-tubules in cardiac muscle

A

2x larger in Diameter than in skeletal muscle

25
Q

Sacroplasmic reticulum in cardiac muscle

A

One t tubule and one terminal cisterna of sER –> DIAD

26
Q

Intercalated Disc and the three types of contact

A
  1. Zonulae adherentes: actin Filaments insert for MECHANICHAL COUPLING
  2. Maculae adherentes (desmosomes): intermediate Filaments insert for MECHANICAL COUPLING
  3. Gap Junction: in longitudinal Portion, ELECTRICAL COUPLING

–> FOR SIMULTANEOUS CONTRACTION

27
Q

Smooth muscle

A
  • in blood vessels and inner organ walls
  • involuntary
  • mediated by autonomic nervous System and Hormones
  • in inner Organs: inner circular layer and outer longitudinal –> for peristaltic contractions
  • in blood vessels: circular arrangements
28
Q

Smooth muscle cell/ myocyte

A
  • fusiform
  • non-striated
  • centrally located, elongated nucleus
  • intercellular spaces filled with loose CT
  • Interconnected by gap junctions
29
Q

Ultrastructure of smooth muscle

A
  • MYOFILAMENTS criss cross the cytoplasm
  • INTERMEDIATE FILAMENTS(Desmin)
  • DENSE BODIES: spots when fibers cross
  • Thin (actin) Filaments: only associated with tropomyosin
  • CAVEOLAE: invaginations in Plasma membrane, analogue to T tubules, in contact with sER
30
Q

Smooth muscle contraction

A
  • contraction: shortening of cells and Twist of nucleus
  • -> globular shape of myocyte

MECHANISM

  • -> depolarization vie calveolae and sER
  • -> release of Ca
  • -> Ca binds to calmodulin
  • ->Activates Myosin
  • -> Myosin binds actin
31
Q

Important difference between smooth muscle cells and cardiac muscle cells

A

Smooth muscle cells can divide, while cardiac myocytes cannot

Histology Final (18 decks)

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