Weight and WorkSkeletal Muscle

Definitions• Motor Unit: a motor neuron and all muscle fibers it

innervates.• Twitch: single contraction in response to a single

stimulus/AP.• Isotonic: muscular contraction where constant

tension continues while the length of the muscle changes. – Concentric– Eccentric

• Isometric: muscular contraction against resistance in which the length of the muscle remains the same.

Isotonic Contraction

Isometric Contraction

Work• Work is accomplished only when an object is moved.• Work = Force X Distance• Force = muscle tension required to overcome the

load (weight of the object).• In an isometric contraction where no object is

moved (muscles do not change length) the work done = zero.

Load/Velocity relationship

• Load is an important determinant of shortening velocity. Load = velocity

Load/Velocity Relationship

3 Muscle Fiber TypesSlow Oxidative

Fast Oxidative Fast Glycolytic

Postural muscles

Bird flight muscles

Mammal breast muscles

Lithobates pipiens• Referred to as Rana pipiens

also.• Opportunistic feeders• Occurs through much of US

and Canada (cosmopolitan)• Status is controversial:

widespread, but most populations throughout range are decreasing rapidly.

• Commonly used in research.

HOMEWORK!!!!• Write an entire lab report, again. • Include answers to ALL labscribe

questions WITHIN the body of the paper.

• Follow my formatting instructions!!!!!!

• Due on November 28/29.

Next Week…• Have a GREAT Thanksgiving!!!