1. Lesson Overview
32.2 The Muscular System

2. Skeletal Muscle
Cardiac Muscle
Smooth Muscle
- Striations
Controlled by nervous system.
Cells are large with many nuclei.
- Similar to skeletal muscle in striated shape and similar to smooth muscle because is not under control of central nervous system.
Spindle-shaped cells with single nucleus.
Function without direct stimulation by nervous system
Attached to the bones
Found only in the heart
Walls of stomach, blood vessels, and digestive system

3. Muscle Contraction Muscle fiber myofibrills Sarcomere Actin & miosin
 During a muscle contraction, myosin filaments form cross-bridges with actin filaments. The cross-bridges then change shape, pulling the actin filaments toward the center of the sarcomere.
Muscle fiber
myofibrills
Sarcomere
Actin & miosin

4. Control of Muscle Contraction (skeletal muscle)
Motor neuron
Acetylcholine (neurotransmitter)
Activation of muscle fibers cell membranes
Release of Ca+ ions
Stimulation of myosin and actin interaction

5. How Muscles and Bones Interact
Skeletal muscles are joined to bones by the tendons.
Tendons pull on the bones and make them work like levers.

6. The joint (where two bones meet) functions as a fulcrum (the fixed point around which the lever moves)
The muscles provide the force to move the lever.

7. How Muscles and Bones Interact
Most skeletal muscles work in opposing pairs—when one muscle contracts, the other relaxes.

8. Types of Skeletal Muscle Fibers.
Present in all skeletal muscle and activated depending on need. Fibers type can be modified.
RED FIBERS (40%)
WHITE FIBERS (60%)
slow contraction velocity
fast contraction velocity
Very resistant to fatigue. Work for long periods of time
Fatigue easily. Generates more force
Postural muscles of the neck.
Activities that require great strength or quick bursts of speed, like sprinting, weight lifting

9. Exercise and Health RESTING MUSCLE TONE: state of partial contraction.
Muscle tone keep the back and legs straight and the head upright, even when we are relaxed.
Muscles that are exercised regularly stay firm and increase in size and strength.