Sensory and Motor Mechanisms – chpt 49-

I. Anatomy & physiology of Muscular system n A. 3 types of muscle tissue –1. skeletal muscle aka striated muscle– < a. attached to bone < b. responsible for movement < c. looks “striped” through the microscope –2. smooth muscle tissue < a. lines walls of blood vessels & dig sys. < b. non-striated so muscle contraction is slower & more controlled

n 3. cardiac muscle – heart muscle –a. produces its own action potential (doesn’t need to be stimulated by a neuron)

B. Anatomy of a muscle n 1. muscle built of muscle cells called muscle fibers n 2. muscle fibers (myofibers) are not typical cells –a. long, thin, multinucleate –b. cell membrane = sarcolemma < 1) sarcolemma is highly invaginated with transverse tubules (t-tubules) –c. cytoplasm = sarcoplasm –d. ER = SR – sarcoplasmic reticulum

n 3. muscle fiber loaded with myofibrils made of filaments –a. actin - thin, light-stained, globular protein < 1) 2 strands in a double helix < 2) troponin & tropomyosin cover binding sites –b. myosin – thick, darker-stained, fibrous protein < 1) each filament has a protruding head at one end < 2) an array of myosin filaments has multiple heads at each end

sarcomere

Video muscle action n Contract/relax: antagonistic pairs w/skeleton n Muscles: bundle of…. n Muscle fibers: single cell w/ many nuclei consisting of…. n Myofibrils: longitudinal bundles composed of…. n Myofilaments: Thin~ 2 strands of actin protein and a regulatory protein Thick~ myosin protein n Sarcomere: repeating unit of muscle tissue, composed of…. n Z lines~ sarcomere border n I band~ only actin protein n A band~ actin & myosin protein overlap n H zone~ central sarcomere; only myosin

C. Micromuscular movement/contraction n 1. Muscle cells contract only when stimulated by motor neuron n 2. When not stimulated the binding sites on the actin are blocked by a protein call tropomyosin n 3. A second protein – troponin- controls position of tropomyosin n 4. For a muscle cell to contract the myosin binding sites on the actin must be exposed

n 5. Occurs in each muscle fiber after it’s been stimulated by a nerve –a. gap between neuron & muscle fiber – neuromuscular junction – is bridged by acetylcholine – a neurotransmitter –b. acetylcholine causes the electrical charge on muscle fiber membrane to change – change is due to ions on inside & outside of cell membrane (sarcolemma)

–1) before stimulated – membrane resting potential –2) after stimulation – membrane acting potential n c. membrane becomes permeable to Na+, so Na + moves into cell n d. Na + in cell triggers the SR to release Ca ++ n e. Ca++ bonds w/ troponin which changes the shape of tropomyosin THUS uncovering the myosin binding site on the actin

Muscle contraction regulation

n 1- Myosin head hydrolyzes ATP to ADP --splits ATP (into ADP & Pi inorganic phosphate) through the addition of a water molecule n 2- Myosin head binds to actin; termed a “cross bridge” n 3- This causes the release of ADP and Pi myosin relaxes into its “low E” state & this allows the actin to slide n 4- Binding of new ATP releases myosin head D. Actin-myosin interaction

n 5. Sliding-filament model-Process of muscle contraction –a. Sarcomere length reduced –b. Span from 1 Z-line to the next becomes shorter –c. Actin and myosin slide past each other (overlap increases)