A Tiny Look at Muscle

A Tiny Look at Muscle

Skeletal Muscle Characteristics

Skeletal Muscle Structures- Actin and Myosin Myofilaments

• Makes up 40% of body weight
• Named because attached to bones (skeleton)
• Many nuclei per cell (near periphery)
• Striated
• Longest of muscle types

• Actin: thin myofilament
• Resemble 2 strands of pearls
• Myosin: thick myofilament
• Resemble golf clubs
• Troponin: attachment site on actin for Ca2+
• Tropomyosin: filament on grooves of actin
• Attachment site on actin for myosin

Skeletal Muscle Structures-Connective Tissue Coverings

Abilities of Skeletal Muscles

• Contractility: ability to shorten
• Excitability: respond to stimulus
• Extensibility: can stretch
• Elasticity: recoil

• Epimysium: connective tissue that surrounds entire skeletal muscle (outside)
• Muscle fasciculus: bundle of muscle fibers
• Perimysium: connective tissue around each muscle fasciculus
• Muscle fiber: skeletal muscle cells
• many nuclei
• Endomysium: connective tissue that surrounds each muscle fiber

Functions

Skeletal Muscle Structures-Sarcomeres

• Movement
• Maintain posture
• Respiration
• Production of body heat
• Communication
• Heart beat
• Contraction of organs and vessels

• Sarcomere: contractile unit
• Contains actin and myosin
• Z disk: protein fibers that form attachment site for actin
• H zone: center of sarcomere
• Contains only myosin
• I band: contains only actin
• A band: where actin and myosin overlap
• M line: where myosin are anchored

Skeletal Muscle Structures-Muscle Fiber Structure

• Myofibril: thread-like proteins that make up muscle fibers
• Myofilament: proteins that make up myofibrils
• Ex. actin and myosin
• Sarcoplasm: cytoplasm of muscle fiber (cell)
• Sarcolemma: cell membrane
• Contains T-tubules
• T-tubules (transverse): wrap around sarcomeres at A band
• Associated with sarcoplasmic reticulum
• Sarcoplasmic reticulum: surrounds myosin
• Stores and releases Ca2+