TAILIEUCHUNG - Lecture Biology 25 (Human Biology): Chapter 12 - Prof. Gonsalves

Chapter 12 provides knowledge of muscular system. The following will be discussed in this chapter: Skeletal muscles, mechanism of muscle fiber contraction, whole muscle contraction, energy for muscle contraction, homeostasis. | Chapter 12 Biology 25: Human Biology Prof. Gonsalves Los Angeles City College Loosely Based on Mader’s Human Biology,7th edition Muscular System Components: Skeletal muscles. Functions: Skeletal muscle contraction allows for voluntary movement: Movement and locomotion. Mechanical work: Lifting, pulling, pushing objects. Communication: Body language and facial expression. Homeostatic Role: Allows animals to respond to and control their environment. Muscular System: Skeletal Muscle Allows Voluntary Movement Skeletal Muscle Composed of individual muscle fibers. Contract when stimulated by motor neuron. Motor neuron innervates # of muscle fibers. Activation of varying # of muscle fibers causes gradations of strength of contraction. Structure and Actions Skeletal muscle attached to bone on each end by tendons. Tension on tendons by muscles cause movement of the bones. Insertion: More movable attachment. Origin: Less movable attachment. Structure of Skeletal Muscle Epimysium: Fibrous sheath. Fascicles: Columns of muscle fibers. Contain same organelles as other cells. Types of Muscle Contractions Twitch: Muscle is stimulated with a single electrical shock (above threshold). Quickly contracts and then relaxes. Increasing stimulus increases the strength of the twitch (up to maximum). Types of Muscle Contractions Summation: If second electrical shock is administered before complete relaxation of muscle. Types of Muscle Contractions Incomplete tetanus: Stimulator delivers an increasing frequency of electrical shocks. Relaxation period shortens between twitches. Strength of contraction increases. Complete tetanus: Fusion frequency of stimulation. No visible relaxation between twitches. Smooth sustained contraction. Types of Muscle Contractions Treppe: Staircase effect. Electrical shocks are delivered at maximal voltage. Each shock produces a separate, stronger twitch (up to maximum). Due to an increase in intracellular Ca++. Types of Muscle Contractions In order for a muscle .

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