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Muscle PhysiologyChapter 1
Objectives
Describe the micro and macrostructure of muscle
Describe the sliding filament theory Differentiate types of muscle
actions Discuss factors that affect force
production
Huxley?
KEY POINT The muscular system is the
organ system responsible for movement. Muscles develop tension, causing bones to act as levers and rotate around an axis.
Neuromuscular ComponentsNeuromuscular junction- the point
where a motor neuron joins muscle fibers, the motor end plate
Motor unit- a motor neuron and all the muscle fibers it innervates
All or none law- all the muscle fibers in a motor unit contract, or none contract
Structure of a Muscle Cell
Sarcoplasm- the cytoplasm of a muscle fiber, contains mitochondria, sarcoplasmic reticulum
Sarcomere- smallest contractile unit of muscle tissue
Sarcoplasmic Reticulum – contains calcium.
Structure of a Muscle Cell Myofibrils- long fibers in the sarcoplasm of muscle cells•Actin (thin)•Myosin (thick)
•Crossbridges- globular heads on the myosin molecules
Structure of Skeletal Muscle Contractile proteins- actin and
myosin Myofibril- muscle fiber, one muscle
cell Regulatory proteins- troponin and
tropomyosin Sarcomere- Z-line to Z-line Sarcoplasmic reticulum/T-tubules-
“communications” system in the muscle cell
Sliding Filament Theory of Muscle Contraction 1. Resting phase- calcium is
segregated in the sarcoplasmic reticulum (SR), few crossbridges are attached, the muscle cell is “at rest”
Sliding Filament Theory of Muscle Contraction 2. Excitation phase-
contraction coupling phase- calcium ions are released from the SR, troponin and tropomyosin undergo a conformational change, allowing actin to bind to myosin, causing flexion of the myosin head
Sliding Filament Theory of Muscle Contraction 3. Contraction phase- ATP
causes myosin heads to detach from actin, ATP is hydrolized which “cocks” the myosin head, the myosin head attaches to the next active site
Sliding Filament Theory of Muscle Contraction 4. Recharge phase- as long
as ATP is present to break the attraction of actin to myosin, and calcium is present, the cycle continues causing tension to develop in the muscle
Sliding Filament Theory of Muscle Contraction
5. Relaxation phase- stimulation from the motor nerve stops, calcium is re-segregated into the sarcoplasmic reticulum, troponin and tropomyosin return to their original shape and block the attraction of actin and myosin, the muscle returns to the resting unbound state
Cycle Time
Sliding Filament Animation
http://www.sci.sdsu.edu/movies/actin_myosin_gif.html
Summary of Muscle Contraction Acetylcholine (ACH) released from
terminal portion of motor neuron ACH crosses the gap at the
neuromuscular junction Muscle fiber membrane depolarizesdepolarizes
through transverse tubulestransverse tubules to the sarcoplasmic reticulum
Next Class
Finish Chapter 1