Muscle Tissue (overview diagram) (muscle cell diagram)

I. Skeletal Musclediagram)

A. General Features

• Called Somatic (body) Musculature
• Rapid Contractions
• Voluntary Innervation
• Striations Visible with light microscope

B. Skeletal Muscle Cell Morphology (see diagram)

• Fibers = Cell
• Cylindrical with tapered ends
• Relatively long, typically at least 20mm (i.e. 2cm), but often many centimeters
• Relatively thick, about 10-100 microns in diameter
• Multinucleated - nuclei located along cell edge
• Striations - alternating light and dark bands - visible with light microscope

C. Skeletal Muscle Ultrastructural Features

• Myofibrils - tubular arrangement within cells
• Thick myofilaments = Myosin - contractile protein
• Thin myofilaments = Actin - contractile protein
• Intermediate filaments = Z line - structural proteins
• Myofilaments align in overlapping arrangement
• Cytoplasm = Sarcoplasm

D. Skeletal Muscle Striation Ultrastructure

• Dark = A band, area with of overlap myosin and actin
• H zone = in the middle of A band with no actin overlap
• Light = I band, primarily actin
• Sarcomere = area between two Z lines, forms the contractile unit
• Z line = structural protein holding actin at I band

 

E. Skeletal Muscle and Connective Tissue

Three basic layers (muscle cover diagram)

• endomysium - surrounds each cell(fiber)
• perimysium - surrounds a group of cells forms a fascicle
• epimysium - surrounds entire gross muscle

Endomysium

• thin delicate connective tissue
• blends with muscle cell membrane

Perimysium

• ordinary loose connective tissue
• divides groups of muscle cells into bundles within the gross muscle

Epimysium

• capsule = dense irregular connective tissue

All three layers merge together at end of a gross muscle to form a tendon.

 

II. Cardiac Muscle

A. General Features

• Wall of heart
• Contracts rapidly
• Autonomic (involuntary) innervation

 

B. Cardiac Muscle Morphology (see diagram)

• Cells = Fibers
• Fibers branch and anastomose
• Moderate length, about 100 microns
• Moderate diameter, 10-50 microns
• Striations present and visible with light microscope but not distinct
• Single nucleus - centrally placed
• Intercalated disks join ends of cells together
  • desmosomes
  • gap junctions

 

III. Smooth Muscle

A. General Features

• Walls of hollow viscera
• Contracts slowly
• often prolonged sustained contractions
• Autonomic (involuntary) innervation

 

B. Smooth Muscle Morphology (see diagram)

• Fibers = Cell
• Spindle shape cells - elongated and tapered
• Moderate length - about 100-200 microns
• Thin diameter - about 5-10 microns
• Single nucleus - centrally placed
• NO Striations
• Typically arranged in bundles or sheets (may look like dense regular CT)