Muscular System Chp. 6

The Muscular System is very complex: Figure 6.2

Muscle Function: Produce Movement or Generate Tension Principle function - produce movement or generate tension Contraction: shorten distances between bones Skeletal muscles function to move bones Two major types muscle groups: Synergistic muscles: groups work together Antagonistic muscles: groups oppose each other

Muscle Structure: Fascicles = bundles of muscle cells surrounded by sheath (connective tissue) Muscle fibers = few doz.- 1,000’s muscle cells Connective tissue surrounding entire muscle, collectively, these connective tissues form tendons. Figure 6.3

Skeletal Muscle Contractile Unit: Single muscle cell contains many myofibrils: ea myofibril is composed of sacromeres actin filaments myosin filaments z-lines

Skeletal Muscle Contractile Unit: Sarcomere - segment of single myofibril from one Z-line to the next Z-line Actin - protein w/tropomyosin binding sites Myosin - thick filament w/ myosin heads Z Lines - attachment points for sarcomeres Actin filaments linked with z-line Myosin filaments located w/in scaromeres

Skeletal Muscle Contractile Unit (cont.) Figure 6.5

Nerve Activation of Individual Muscle Cells: Acetylcholine released from motor neuron at neuromuscular junction Electrical impulse transmitted along T tubules Calcium released from sarcoplasmic reticulum

Nerve Activation of Individual Muscle Cells (cont.) Figure 6.6

Calcium Initiates the Sliding Filament Mechanism Thick filaments: myosin Thin filaments: strands of actin molecules Contraction = formation of cross bridges between thin & thick filaments

Calcium Initiates the Sliding Filament Mechanism (cont.) Figure 6.7

Mechanism of Muscle Contraction: Calcium released from sarcoplasmic reticulum Calcium binds to troponin Troponin-tropomysin complex shifts position Myosin binding site exposed Myosin heads form cross-bridges with actin Actin filaments pulled toward center of sarcomere

Mechanism of Muscle Contraction (cont.) Figure 6.8

Muscle Relaxation Nerve activation ends, contraction ends Calcium pumped back into sarcoplasmic reticulum Calcium removed from troponin Myosin-binding site covered No calcium = no cross-bridges

Energy Required for Muscle Activity Principle source of energy: ATP ATP replenished by variety of means Creatine phosphate Stored glycogen Aerobic metabolism of glucose, fatty acids, and other high-energy molecules

Activity of Muscles Can Vary Isotonic contractions: muscle shortens, movement occurs Isometric contractions: muscle doesn’t shorten, no movement Degree of nerve activation influences force Terms to know: Motor unit Muscle tension All-or-none principle Muscle tone

Muscle Contraction: Myogram Latent period Contraction Relaxation Summation vs. tetanus Figure 6.10

Slow Twitch vs. Fast Twitch Fibers Muscle Activity: Slow Twitch vs. Fast Twitch Fibers Slow twitch muscles: endurance, long duration contraction, contains myoglobin E.g. Jogging, swimming, biking Fast twitch: strength, white muscle, short duration contraction E.g. Sprinting, weight lifting, tennis

Exercise Training: Strength training Aerobic training Resistance training Short, intense Builds more fast-twitch myofibrils Aerobic training Builds endurance Increases blood supply to muscle cells Target heart rate at least 20 minutes, three times a week

Features of Cardiac & Smooth Muscles: Activation of cardiac and smooth muscles Involuntary Specialized adaptations in each Speed and sustainability of contractions 3. Arrangement of myosin and actin filaments

Diseases and Disorders of the Muscular System Muscular dystrophy Tetanus Muscle cramps Pulled muscles Fasciitis