Sensory and Motor Mechanisms – chpt 49-

Sensory and Motor Mechanisms – chpt 49-

I. Anatomy & physiology of Muscular systemI. Anatomy & physiology of Muscular system

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

3. cardiac muscle – heart muscle

– a. produces its own action potential (doesn’t need to be stimulated by a neuron)

B. Anatomy of a muscleB. Anatomy of a muscle 1. muscle built of muscle cells called muscle

fibers 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

3. muscle fiber loaded with myofibrils made of filaments

– a. actin - thin, light-stained, globular protein1) 2 strands in a double helix2) troponin & tropomyosin cover binding

sites

– b. myosin – thick, darker-stained, fibrous protein1) each filament has a protruding head at

one end2) an array of myosin filaments has

multiple heads at each end

sarcomeresarcomere

Video muscle actionVideo muscle action Contract/relax: antagonistic pairs

w/skeleton Muscles: bundle of…. Muscle fibers: single cell w/ many

nuclei consisting of…. Myofibrils: longitudinal bundles

composed of…. Myofilaments:

•Thin~ 2 strands of actin protein and a regulatory protein •Thick~ myosin protein

Sarcomere: repeating unit of muscle tissue, composed of….

Z lines~sarcomere border I band~only actin protein A band~actin & myosin protein overlap H zone~central sarcomere; only myosin

C. Micromuscular movement/contractionC. Micromuscular movement/contraction

1. Muscle cells contract only when stimulated by motor neuron

2. When not stimulated the binding sites on the actin are blocked by a protein call tropomyosin

3. A second protein – troponin- controls position of tropomyosin

4. For a muscle cell to contract the myosin binding sites on the actin must be exposed

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

c. membrane becomes permeable to Na+, so Na+ moves into cell

d. Na+ in cell triggers the SR to release Ca++

e. Ca++ bonds w/ troponin which changes the shape of tropomyosin THUS uncovering the myosin binding site on the actin

Muscle contraction regulationMuscle contraction regulation

1- Myosin head hydrolyzes ATP to ADP --splits ATP (into ADP & Pi inorganic phosphate) through the addition of a water molecule

2- Myosin head binds to actin; termed a “cross bridge”

3- This causes the release of ADP and Pi myosin relaxes into its “low E” state & this allows the actin to slide

4- Binding of new ATP releases myosin head

D. Actin-myosin interactionD. Actin-myosin interaction

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)