The Musculoskeletal System Support, Protection, Movement and Locomotion

Characteristics of muscle tissue Excitability – receive and respond to stimuli Contractility – shorten and thicken Extensibility – stretch and extend Elasticity – return to original shape after contraction or extension

Functions Motion Maintenance of posture Heat production Protection of internal organs

Origin of muscle tissue Forms from the mesoderm germ layer Triploblasts simplest: flatworms Segmentation  annelids, arthropods, vertebrates

Types of muscle tissue Striated Smooth Invertebrate muscles Skeletal Attached to bones Striated and voluntary Cardiac Heart wall Highly branched Striated and involuntary Smooth Walls of hollow internal structures Nonstriated and involuntary Striated Voluntary movements Longitudinal or circular in shape Smooth Involuntary movements Invertebrate muscles Vertebrate muscles

Muscle action Motion produced by action of muscles on bones  levers Tendons  attach muscles to bones (e.g. Achilles tendon) 1 fixed point of attachment (origin) and 1 moving point of attachment (insertion) Fascia  sheets that cover muscles Muscles work in antagonistic or opposing pairs

Muscle movement Adduction Abduction Flexion Extension Rotation Sphincters Levators Depressors Supination Pronation

Human skeletal muscle groups

Anatomy of skeletal muscles epimysium tendon perimysium Muscle Fascicle Surrounded by perimysium endomysium Skeletal muscle Skeletal muscle fiber (cell) Surrounded by epimysium Surrounded by endomysium

Organization of skeletal muscles

Overview of the Sliding Filament Theory The muscle fiber is stimulated. Ca2+ ions are released. Thin filaments move to middle of sarcomere. Muscle fiber contracts. Muscle tension increases.

Muscle twitch Cycle of contraction and relaxation generated from one stimulus All or none response of muscle fibers Force Summation Increasing # and size of fibers contracting Increasing frequency at which action potentials are sent to muscle fibers

Slow and Fast Twitch Fibers Slow Twitch More ATP from aerobic respiration Continuous extended contractions over time More myoglobin Fast Twitch Anaerobic metabolism (creatine phosphate and lactic acid fermentation) Short bursts of speed Fatigue quickly

Muscle and exercise

Cramps Painful sensations caused by contraction/ overshortening of muscles Causes Hyperflexion Inadequate oxygenation Changes in temperature Dehydration Low amount of electrolytes in blood Treatment Correct breathing Increasing intake of water and electrolytes