Chapter 49 ~ Sensory and Motor Mechanisms

Vertebrate Skeletal Muscle

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

Sliding-filament model

Theory of muscle contraction

Sarcomere length reduced

Z line length becomes shorter

Actin and myosin slide past each other (overlap increases)

Actin-myosin interaction

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

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

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

4- Binding of new ATP releases myosin head

Creatine phosphate~ supplier of phosphate to ADP

Muscle contraction regulation, I

Relaxation : tropomyosin blocks myosin binding sites on actin

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

Muscle contraction regulation, II

Calcium (Ca+)~ concentration regulated by the….

Sarcoplasmic reticulum~ a specialized endoplasmic reticulum

Stimulated by action potential in a motor neuron

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

Ca+ then binds to troponin

Muscle contraction