1. The Muscular System Anatomy and Physiology: Chapter 6

2. Functions of Muscles Produce movement Maintain posture
Stabilize joints
Generate heat

3. The Muscular System Cells are elongated (muscle cell = muscle fiber)
Muscles are responsible for all types of body movement
Contraction of muscles is due to the movement of microfilaments
The Muscular System

4. The Muscular System
Cardiac Muscle Smooth Muscle Skeletal Muscle

5. 3 Basic Muscle Types Cardiac Muscle Smooth Muscle Skeletal Muscle
Has striations
Usually has a single nucleus
Joined to another muscle cell at an intercalated disc
Involuntary
Found only in the heart
Smooth Muscle
Has no striations
Spindle-shaped cells
Single nucleus
Involuntary – no conscious control
Found mainly in the walls of hollow organs
Skeletal Muscle
Most are attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by connective tissue

6. Connective Tissue Wrappings of Skeletal Muscle Endomysium
Around and between single muscle fibers
Perimysium
Around a fascicle (bundle) of fibers
Epimysium
Covers the entire skeletal muscle
Blends into a tendon to attach the muscle to bone

7. Microscopic Anatomy of Skeletal Muscle
Sarcolemma
Specialized plasma membrane
Several nuclei
Myofibrils
Long organelles within muscle
Composed of
Sarcomeres
Tiny contractile units
Myofilaments
Actin
Thin filaments
Myosin
Thick filaments

8. Microscopic Anatomy of Skeletal Muscle
Myofibrils are aligned to give distinct bands
I band = light band
A band = dark band
Myosin filaments have heads (extensions, or cross bridges)
Myosin and actin overlap somewhat
At rest, there is a bare zone that lacks actin filaments.

9. Sliding Filament Theory of Muscle Contraction
Activation by nerves causes myosin heads (crossbridges) to attach to binding sites on the thin filament.
Myosin heads then bind to the next site of the thin filament.
This continued action causes a sliding of the myosin along the actin.
The result is that the muscle is shortened (contracted).

10. The Sliding Filament Theory

11. Nerve Stimulus to Muscles
Synaptic cleft:
gap between nerve and muscle
Nerve and muscle do not make contact
Filled with interstitial fluid
Neuromuscular junctions:
association site of nerve and muscle
Motor unit:
one neuron and the muscle cells stimulated by that neuron
Skeletal muscles must be stimulated by a nerve to contract.

12. Transmission of Nerve Impulse to Muscle
Neurotransmitter
Chemical released by nerve upon arrival of nerve impulse
Acetylcholine
Neurotransmitter for skeletal muscle
Attaches to receptors on the sarcolemma stimulating muscle contraction.
Once started, muscle contraction cannot be stopped.

13. Contraction of a Skeletal Muscle
Muscle fiber contraction is “all or none”
Within a skeletal muscle, not all fibers may be stimulated during the same interval
Different combinations of muscle fiber contractions may give differing responses
Graded responses – different degrees of skeletal muscle shortening, rapid stimulus = constant contraction or tetanus

14. Muscle Response to Strong Stimuli
Muscle force depends upon the number of fibers stimulated
More fibers contracting results in greater muscle tension
Muscles can continue to contract unless they run out of energy

15. Energy for Muscle Contraction
Stored ATP provides energy for the first 4-6 seconds worth of activity.
Creatine phosphate (CP) can regenerate ATP for another 20 seconds worth of activity.
Cellular respiration
Aerobic respiration
Breaks down glucose which provides hours of energy
Requires constant oxygen so it can’t be used for intense activity
Glycolysis
Anaerobic respiration
Also breaks down glucose but only provides enough energy for seconds of activity
Fast process so it can be used for intense activity

16. Muscle Fatigue and Oxygen Debt
When a muscle is fatigued, it is unable to contract
The common reason for muscle fatigue is oxygen debt
Oxygen must be “repaid” to tissue to remove oxygen debt
Oxygen is required to get rid of accumulated lactic acid
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

17. Types of Muscle Contractions
Isotonic contractions
Myofilaments are able to slide past each other during contractions
The muscle shortens
Isometric contractions
Tension in the muscles increases
The muscle is unable to shorten

18. Muscle Tone Some fibers are contracted even in a relaxed muscle.
Different fibers contract at different times to provide muscle tone.
The process of stimulating various fibers is under involuntary control.

19. Effects of Exercise on Muscle
Results of increased muscle use
Increase in muscle size
More contractile filaments are produced
Increase in muscle strength
Increase in muscle efficiency
How they burn fuel for energy
Muscle becomes more fatigue resistant

20. Muscles and Body Movements
Movement is attained due to a muscle moving an attached bone
Muscles are attached to at least two points
Origin: attached to an immoveable or less movable bone
Insertion: attached to a movable bone
When the muscle contracts, the insertion moves toward the origin.

21. Types of Ordinary Body Movements
Flexion
Decreases angle of joint and brings two bones closer together
Extension
Opposite of flexion
Rotation
Movement of a bone in longitudinal axis, shaking head “no”
Abduction/Adduction (see slides)
Circumduction (see slides)

22. Types of Ordinary Body Movements

23. Abduction -Moving the leg away from the midline
Circumduction Cone-shaped movement, proximal end doesn’t move, while distal end moves in a circle.
Adduction -Moving toward the midline

24. Types of Muscles
Prime mover
Muscle with the major responsibility for a certain movement
Antagonist
Muscle that opposes or reverses a prime mover
Synergist
Muscle that aids a prime mover in a movement and helps prevent rotation
Fixator
Stabilizes the origin of a prime mover

25. Naming of Skeletal Muscles
Direction of muscle fibers
Example: rectus (straight)
Relative size of the muscle
Example: maximus (largest)
Location of the muscle
Example: many muscles are named for bones (e.g., temporalis)
Number of origins
Example: triceps (three heads)
Location of the muscles origin and insertion
Example: sterno (on the sternum)
Shape of the muscle
Example: deltoid (triangular)
Action of the muscle
Example: flexor and extensor (flexes or extends a bone)

26. Head and Neck Muscles

27. Trunk Muscles

28. Deep Trunk and Arm Muscles

29. Muscles of the Pelvis, Hip, and Thigh

30. Muscles of the Lower Leg

31. Superficial Muscles: Anterior

32. Superficial Muscles: Posterior

33. Disorders Relating to the Muscular System
Muscular Dystrophy: inherited, muscle enlarge due to increased fat and connective tissue, but fibers degenerate and atrophy
Duchenne MD: lacking a protein to maintain the sarcolemma
Myasthemia Gravis: progressive weakness due to a shortage of acetylcholine receptors