1. Chapter 6
Muscular System

2. Muscle is a Contractile Organ
There are three types of muscular tissue
Skeletal muscle, cardiac muscle, smooth muscle
Skeletal muscle is part of the skeleto-muscular system
Functions to move bones
In general, each skeletal muscle has a
Belly – the middle portion of the muscle
Origin - an end that remains stationary when the organ shortens
Insertion - an end that moves during contraction
Knowing the origin and insertion of any skeletal muscle offers clues about its function
Skeletal muscle is composed of numerous elongated muscle cells
Spanning from origin to insertion, one nested inside another
Muscle cells also are called muscle fibers
Muscle cells must shorten, creating tension
Connective tissue structurally supports skeletal muscle

3. Skeletal Muscle Characteristics
Most are attached by tendons to bones
Cells are multinucleate
Striated—have visible banding
Voluntary—subject to conscious control

4. Skeletal Muscle Most skeletal muscles work in pairs Synergistic pairs
Work together to cause movement in the same direction
i.e., muscles of the quadriceps or muscles of the hamstrings
Antagonistic pairs
Cause movement in opposite directions, opposite to one another
i.e., biceps and triceps

5. Fascicle (wrapped by perimysium)
Muscle fiber (cell)
Blood vessel
Perimysium
Epimysium
(wraps entire
muscle)
Fascicle (wrapped by perimysium)
Endomysium (between fibers)
Tendon
Bone
Figure 6.1

6. Connective Tissue Wrappings of Skeletal Muscle
Endomysium—encloses a single muscle fiber
Perimysium—wraps around a fascicle (bundle) of muscle fibers
Epimysium—covers the entire skeletal muscle
Fascia—on the outside of the epimysium

7. Structure of Skeletal Muscle

8. Microscopic Anatomy Sarcolemma Myofibril Nucleus Light (I) band
Dark (A) band
(a) Segment of a muscle fiber (cell)

9. Microscopic Anatomy Sarcolemma—specialized plasma membrane
Myofibrils—long organelles inside muscle cell
Sarcoplasmic reticulum—specialized smooth endoplasmic reticulum
Myofibrils are aligned to give distinct bands
I band = light band
Contains only thin filaments
A band = dark band
Contains the entire length of the thick filaments

10. Sarcomere: contractile unit of Muscle
Thick filaments = myosin filaments
Composed of the protein myosin
Has ATPase enzymes
Myosin filaments have heads (extensions, or cross bridges)
Myosin and actin overlap somewhat
Thin filaments = actin filaments
Composed of the protein actin
Anchored to the Z disc

11. Neuromuscular Junctions
Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract
Motor unit—one motor neuron and all the skeletal muscle cells stimulated by that neuron
Neuromuscular junction
Association site of axon terminal of the motor neuron and muscle

12. Neuromuscular Junction- Initiation of Contraction
Neurotransmitter—chemical released by nerve upon arrival of nerve impulse in the axon terminal
The neurotransmitter for skeletal muscle is acetylcholine (ACh)

13. Muscle Contraction Cycle- sliding filament theory

14. Energy for Muscle Contraction
Initially, muscles use stored ATP for energy
ATP bonds are broken to release energy
Only 4–6 seconds worth of ATP is stored by muscles
After this initial time, other pathways must be utilized to produce ATP

15. Creatine Phosphate
Direct phosphorylation of ADP by creatine phosphate (CP)
Muscle cells store CP
CP is a high-energy molecule
CP transfers a phosphate group to ADP, to regenerate ATP
Produces: 1 ATP is created per CP molecule
Duration: 15 seconds
Oxygen use: none

16. Aerobic Respiration C6H12O6 + 6O2  6CO2 + 6H2O + 32 ATP
Products: 32 ATP, carbon dioxide, water
Occurs: in the mitochondria
Requires continuous oxygen
Slow

17. Anaerobic Glycolysis Pyruvic acid is converted to lactic acid
Oxygen Use: No
Produces: 2 ATP, lactic acid
Occurs: cytoplasm
Duration: 40 s
Not as efficient, but is fast
Huge amounts of glucose are needed
Lactic acid produces muscle fatigue

18. There are Three Types of Muscle Cells
Fast Twitch (or fast glycolytic)
Anaerobic, fatigue quickly
Provide a short burst of extreme energy and contraction power
Thicker, contain fewer mitochondria, usually contain larger glycogen
Responsible for hypertrophy
Because short bursts of power come from these fibers, exercises that continuously require bursts of power will enlarge them
Weight training puts demands on fast twitch fibers, resulting in the hypertrophy (muscle enlargement) we associate with body-building
Intermediate (or fast oxidative-glycolytic)

19. Three types of muscle cells
Slow Twitch (or slow oxidative)
Appear red, have a large blood supply, have many mitochondria within their sarcolemma, and store an oxygen-carrying protein called myoglobin
Are sometimes called nonfatiguing or aerobic cells
Distance running and other aerobic sports stimulate these cells
Efficiency and strength come not from increasing mass but from using oxygen more efficiently
Although training can alter the functioning of both red (slow twitch) and white (fast twitch) fibers, it does not change their proportions
The percentage of fast and slow twitch fibers is genetically determined