HHIS 221: MUSCLE TISSUES

Actin

Generate the forces necessary for the muscle contraction

Mesoderm

This is where all muscle cells originate

Skeletal Muscle

• Long

• Cylindrical (diameter of 10–100 μm)

• Multi-nucleated (found peripherally under the sarcolemma)

• Myoblasts; Satellite cells

• Cross-striated

Cardiac Muscle

• Elongated

• Branched

• Cross-striated

Smooth Muscle

Collection of fusiform (spindle-shaped) cells that don’t show striations

Sarcoplasm

Cytoplasm of muscle cells

Sarcoplasmic Reticulum

Smooth ER of muscle cells

Sarcolemma

Cell membrane and External lamina of muscle cells

Sarkos

means “flesh”

Plasma

means “thing formed”

Lemma

means “husk”

Voluntary

Under the control of Central Nervous System

Involuntary

Contract in response to stimulation of the autonomic nervous system

Striated

Presence of transverse or cross-striations known as dark and light bands

Smooth

No cross-striations but with longitudinal striations

Epimysium

Dense CT that surrounds the entire skeletal muscle

Fascicle

Bundle of skeletal muscle that is surrounded by perimysium

Perimysium

Dense CT that wraps fascicles

Muscle fiber

Multinuclear cells composed of several myofibrils

Endomysium

Delicate CT that surrounds muscle fibers

Myofibril

• Cylindrical filament bundles

• 1-2 μm in diameter

A bands

Dark bands on the myofibrils

Anisotropic or Birefringent

Other term for A bands

I bands

Light bands on the myofibrils

Isotropic

Other term for I bands

H zone

Lighter zone in the A band; because it only consists of myosin (no actin)

M line

Line that bisects H zone

Z line or Z disc

Dark transverse line that bisects I band

Thick Filaments

• Composed of myosin

• 1.6 μm long and 15 nm wide

• Bound to proteins of M line and to the Z disc

• Central portion of sarcomere

Titin

Binds thick filaments to Z disc

Thin Filaments

• Composed of

  • F-actin

  • Tropomyosin

  • Troponin

• 1.0 μm long and 8 nm wide

F-actin

• Contains 2 strands of G-actin

• Twisted around each other in a double-helical formation

• 5.6 nm in diameter
  

Tropomyosin

• Form a long polymer located in the groove between the twisted actin strands

Troponin

• Globular complex of three subunits

  • TnT- attaches to tropomyosin

  • TnC- binds calcium ions

  • TnI- inhibits the actin-myosin interaction

Type I Muscle Fibers

For slow, continuous contraction for prolonged periods

• Many mitochondria; abundant myoglobin

Slow, red oxidative fibers

Other term for Type I muscle fibers

Type IIa Muscle Fibers

For rapid contraction and short burst of activity

• Many mitochondria, myoglobin and glycogen

Fast, intermediate oxidative-glycolytic fibers

Other term for Type IIa muscle fibers

Type IIb Muscle Fibers

Specialized for rapid, short term contraction

• Few mitochondria or capillaries
  

Fast, glycolytic fibers

Other term for Type IIb muscle fibers

Purkinje Myocytes

Modified cardiac muscle fibers that are specialized for impulse

Visceral Smooth Muscle

Walls of hollow organs

Vascular Smooth Muscle

Walls of blood vessels

Smooth Muscle of the Iris

Sphincter and dilator of pupillae muscles