Contraction of Skeletal Muscles

MUSCLE TWITCH AND SUMMATION Electric shocks were used to stimulate a frog muscle, and then the movements of the muscle were changed into an electrical current, displayed on the right. These studies showed: 1) a single electric shock results in a twitch. An action potential is produced, leading to a contraction. 2) If a second electric shock is delivered prior to the muscle relaxing, the second twitch will “ride piggyback” on the first. This is called summation. This leads to a stronger contraction

INCOMPLETE AND COMPLETE TETANUS

FORCE-VELOCITY CURVE This graph shows the inverse relationship between the force opposing a muscle contraction (load) and the velocity of muscle shortening. In other words, this lighter the load, the faster the muscle will shorten (duh). For very heavy loads (bottom of the curve) the muscle will reach a point where the contraction is isometric (the muscle does not actually move). Muscle contraction resulting in shortening is called isotonic.

TYPES OF ISOTONIC CONTRACTION: Concentric contraction: A muscle fiber shortens when force is greater than load. Eccentric contraction: A muscle may actually lengthen, despite contraction, if the load is too great. Allows you to lower a weight gently after a full concentric contraction

Series Elastic Component the series-elastic component refers to the elastic composition of the muscle (PARALLEL) and its associated structures (SEC), which must be stretched tight before the tension exerted by the muscle can cause movement.

THE LENGTH-TENSION RELATIONSHIP IN SKELETAL MUSCLE CELLS