Notes: Skeletal Muscle Anatomy

(1) Levels of Organization

• Muscle (whole organ)• Fascicle (portion of muscle)• Muscle Fiber (single muscle cell)• Myofibril (muscle cell organelle)• Sarcomere (portion of myofibril)• Myofilament (part of sarcomere)

Macroscopic

Microscopic

Muscle (organ)Fascicle

Muscle Fiber (cell)

Muscle Fiber (with many nuclei)

Myofibril

Sarcomere

Thin Filament (actin)

Thick Filament (myosin)

(2) Muscle

• Organ of muscular system

• Contains:– Muscle Cells– Connective Tissue– Blood Vessels & Nerves– Contractile Units

• Covered By:– Epimysium (outer tissue-membrane)

(3) Fascicle

• Portion of muscle-organ

• One step down from whole muscle

• Relationships:– Bunch of Fascicles = Muscle– Fascicle = Bunch of Muscle Fibers

(4) Muscle Fiber

• Actual Muscle Cell

• Contains:– Multiple nuclei– Striations– Complex organelles called myofibrils

• Relationships:– Bunch of Muscle Fibers = Fascicle– Muscle Fiber = Bunch of Myofibrils & Nuclei

(5) Myofibril

• Organelle in a muscle cell

• Contains:– Contractile Units (Sarcomere)

• Relationships:– Bunch of Myofibrils = Muscle Fiber– Myofibril = Bunch of Sarcomere

(6) Sarcomere

• Portion of myofibril

• Contains:– Contractile proteins– Thin filaments with actin– Thick filaments with myosin

• Relationships:– Bunch of Sarcomeres = Myofibril– Sarcomere = Bunch of Myofilaments (Actin + Myosin)

(7) Myofilaments

• Contractile portions of sarcomere

• Types:– Thin filaments w/actin (type of protein)– Thick filaments w/myosin (type of protein)

• Relationships:– Bunch of Myofilaments = Sarcomere– Myofilaments = DO THE CONTRACTIONS