Chapter 49Chapter 49

Sensory and Motor MechanismsSensory and Motor Mechanisms

Muscle FunctionMuscle Function

Vertebrate Skeletal MuscleVertebrate Skeletal MuscleContract/relax: Contract/relax: antagonistic pairs antagonistic pairs w/skeletonw/skeleton

Muscles: Muscles: bundle of….bundle of….

Muscle fibers: Muscle fibers: single cell w/ many single cell w/ many nuclei consisting of….nuclei consisting of….

Myofibrils: Myofibrils: longitudinal bundles longitudinal bundles composed of….composed of….

Myofilaments:Myofilaments: •Thin~ •Thin~ 2 strands of actin protein and a 2 strands of actin protein and a

regulatory proteinregulatory protein •Thick~ •Thick~ myosin proteinmyosin protein

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

Z lines~Z lines~sarcomere bordersarcomere border

I band~I band~only actin proteinonly actin protein

A band~A band~actin & myosin protein overlapactin & myosin protein overlap

H zone~H zone~central sarcomere; only myosincentral sarcomere; only myosin

Sliding-filament modelSliding-filament modelTheory of muscle contractionTheory of muscle contraction

Sarcomere length reducedSarcomere length reduced

Z line length becomes shorterZ line length becomes shorter

Actin and myosin slide past each other Actin and myosin slide past each other (overlap increases)(overlap increases)

Actin-myosin interactionActin-myosin interaction1- Myosin head hydrolyzes ATP to ADP and inorganic phosphate (Pi); 1- Myosin head hydrolyzes ATP to ADP and inorganic phosphate (Pi); termed the “high energy configuration”termed the “high energy configuration”

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

3- Releasing ADP and (Pi), myosin relaxes sliding actin; “low energy 3- Releasing ADP and (Pi), myosin relaxes sliding actin; “low energy configuration”configuration”

4- Binding of new ATP releases myosin head4- Binding of new ATP releases myosin head

Creatine phosphate~ supplier of phosphate to ADPCreatine phosphate~ supplier of phosphate to ADP

Muscle contraction regulation, IMuscle contraction regulation, I

RelaxationRelaxation: : tropomyosin tropomyosin blocks myosin binding sites on blocks myosin binding sites on actinactin

ContractionContraction: : calcium calcium binds to toponin complex; binds to toponin complex; tropomyosin changes shape, tropomyosin changes shape, exposing myosin binding sites exposing myosin binding sites

Muscle contraction regulation, IIMuscle contraction regulation, IICalcium (Ca+)~ Calcium (Ca+)~ concentration concentration regulated by the….regulated by the….

Sarcoplasmic reticulum~ Sarcoplasmic reticulum~ a a specialized endoplasmic reticulumspecialized endoplasmic reticulum

Stimulated by action Stimulated by action potential in a motor neuronpotential in a motor neuron

T (transverse) tubules~ T (transverse) tubules~ travel travel channels in plasma membrane for channels in plasma membrane for action potentialaction potential

Ca+ then binds to troponinCa+ then binds to troponin