Muscle and Muscle Tissue

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1

Three types of muscle tissue

  • Skeletal
  • Cardiac
  • Smooth
2

Skeletal muscle

  • organs attached to bones and skin
  • Elongated cells called muscle fibers
  • striated (striped)
  • voluntary
  • contract rapidly with required nervous system stimulation
3

Cardiac muscle

  • only in heart-bulk of heart walls
  • striated
  • involuntary, without nervousness system stimuli
4

Smooth muscle

  • in walls of hollow organs ie stomach, bladder airways
  • not striated
  • involuntary, without nervous system stimuli
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Excitability

(responsiveness or irritability)

ability to respond and receive to stimuli

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Contractility

Ability to shorten forcibly when stimulated

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Extensibility

Ability to be stretched

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Elasticity

ability to recoil to resting length

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Four Important muscle functions

  1. Movement of bones or fluids (e.g..blood)
  2. Maintains posture and body position
  3. Stabilizing joints
  4. Heat generation (especially in skeletal muscle)
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Each muscle served by one artery, one nerve, and one or more veins

Skeletal Muscle

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Connective tissie sheaths of skeletal muscle, supports cells and external to internal

Skeletal Muscle

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Epimysium

dense irregular connective tissue surrounding entire muscle; may blend with fascia

13

Perimysium

fibrous connective tissue surrounding fascicles (groups of muscle fibers)

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Endomysium

Fine areolar connective tissue surrounding each muscle fiber

15

Skeletal muscle attachments in at least two places

Insertion- movable bone

Origin- immovable (less movable) bone

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Direct attachments

epimysium fused to periosteum of bone or perichondrium of cartilage

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Indirect attachment

Connective tissue wrappings extend beyond muscle as ropelike tendon or sheetlike aponeurosis

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Skeletal muscle fiber

Long cylindrical cell- 10 to 100um in diameter, up to 30cm long

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Sarcolemma

Plasma membrane

20

Sacroplasm

Cytopplasm
-Glysomes for glycogen storage and myoglobin in O2 storage

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Modified structures

Myofibrils, sacroplasmic reticulum and T tubules

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Sarcomere

  • smallest contract unit of muscle fiber
  • align like boxcars on myofibril
  • Contains A band and 1/2 I band at each end
  • think and thin myofilaments made of contractile proteins
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Myofibril Banding Pattern

Orderly arrangement of actin and myosin myofilaments with sarcomere

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Myofibrils

  • Densely packed, rodlike elements
  • `80% of cell volume
  • contain sacromes,contractile units
  • exhibit striations-perfectly aligned repeating series of dark A bands and light I bands
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Actin Myofilaments

Thin filaments

  • extended across I band and partway in A band, anchored in Z discs
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Myosin myofilaments

Thick filaments

  • extended length of A band, connected at M line
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Sacroplasmic Reticulum (SR)

  • Network of smooth endoplasmic reticulum surrounding each myofibril
  • pairs of terminal cisternae
  • functions in regulation of intracellular Ca2+ levels (stores & releases Ca2+)
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T Tubules

  • continuations of sarcolemma
  • increase muscle fibers surface area
  • penetrate cells interior at each A and I-band junction
  • associated with paired terminal cisterns to form triads encircling sarcomere
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Sliding filament model of contraction

  • Generation of force
  • shortening occurs when tension generated by cross bridges on thin filaments exceeds force opposing shortening
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For skeletal muscle to contract

-Activation at neuromuscular junction

  • MUST BE nervous system stimulation
  • must generate action potential in sarcolemma

-Exciation-contraction coupling

  • action potential propagated along sarcolemma
  • intercellur Ca2+ levels rise briefly
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Phases leading to muscle fiber contraction Phase 1

Phase 1

  1. action potential (AP) arrives at axon terminal at neuromuscular junction
  2. ACH released; binds to receptors on sarcolemma
  3. ion permeability of sarcolemma changes
  4. local chance in membrance voltage occurs
  5. local depolarization ignites AP in sarcolemma
32

Phases leading to muscle fiber contraction Phase 2

  • AP traveks across entire sarcolemma
  • AP travels along T tubules
  • SR releases CA2+' Ca2+ binds to troppin' myosin-binding sites an actin exposed
  • Myosin heads bind to actin; contraction begins