1. Chapter 6 The Muscular System O.K. Everybody flex!

2. How many muscles are there? 656 (more or less) Comprise about half your body weight 3 main functions…

3. 3 major functions 1.Body movement 2.Body form and shape, posture 3.Body heat: maintain body temperature 1.Skeletal muscle, a.k.a. voluntary or striated muscle 2.Smooth muscle, a.k.a. involuntary 3.Cardiac muscle (found only in the heart) also Involuntary. 3 types of muscle

4. Skeletal muscle, a.k.a. voluntary or striated muscle –Attached to the skeleton, moves the limbs –Contracts quickly, tires easily, can’t stay contracted for long periods of time. –Multinuclear –May be long: ex thigh 12-16”

5. Smooth muscle, a.k.a. involuntary –Unattached to bone. –Walls of the internal organs esp digestive tract, but uterus and blood vessels as well. –Single nucleus, long spindle shape. –Act slowly, do not tire easily, can stay contracted for long periods of time

6. Cardiac muscle- found only in the heart. –Involuntary. –Membranes fused together at intercalated discs to form a continuous network. –No independent cell contraction

7. Muscles are hundreds to thousands of muscle cells, called fibers. Each fiber is in turn made up of myofibrils Muscle cells are long cylinders- each cell may have 100 or more nuclei located just underneath membrane Striated Muscle

8. 4 characteristics of muscle 1. Contractibility. -No other body tissue has this quality -Muscles only contract or relax - they do not push 2. Excitability -Both muscle and nerve cells respond to stimuli by producing electrical signals called action potentials 3. Extendibility - The ability to be stretched 4. Elasticity - The ability to return to the original length when relaxed These four qualities; contractibility, excitability, extendibility and elasticity create a mechanical mechanism capable of complex, intricate movement

9. Muscles need to be attached to something to exert a pulling force Muscles only pull, never push. Attached to bones by non elastic cords of connective tissue called tendons. Muscles bridge the joints of bones

10. Muscles are attached at both ends; bones, tendons, skin or other muscles. Muscles arranged in antagonistic pairs- one works in one direction while a second muscle works in the opposite direction. Biceps/Triceps and movement of arm One is prime mover, the other is antagonist

11. Muscles are made up of muscle fibers (muscle cells), which in turn are made up of myofibrils. Myofibrils have two main components –Actin (thin) –Myosin (thick) We will discuss later how muscles move (sliding filament theory)

12. A review of terminology When discussing muscles and what they move, you use the terms origin and insertion The point of origin moves the least. The insertion is attached to a moveable part. Ex- flex your arm. Origin of biceps is the humerus; it’s insertion is the radius Atrophy- shrink from disuse Hypertrophy- increase in size. ( Note: an increase in the size of a muscle is caused by an increase in cytoplasm, not by an increase in muscle fibers)