1. The Muscular System

2. The Muscular System
Muscles are responsible for all types of body movement
Three basic muscle types are found in the body
Skeletal muscle
Cardiac muscle
Smooth muscle

3. Characteristics of Muscles
Muscle cells are elongated (muscle cell = muscle fiber)
Contraction of muscles is due to the movement of microfilaments
All muscles share some terminology
Prefix myo refers to muscle
Prefix mys refers to muscle
Prefix sarco refers to flesh

4. Skeletal Muscle Characteristics
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. Skeletal Muscle Attachments
Connective tissue attachment
Tendon – cord-like structure
Aponeuroses – sheet-like structure
Sites of muscle attachment
Bones
Cartilages
Connective tissue coverings

7. Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Single nucleus
Involuntary – no conscious control
Found mainly in the walls of hollow organs

8. Cardiac Muscle Characteristics
Has striations
Usually has a single nucleus
Joined to another muscle cell at an intercalated disc
Involuntary
Found only in the heart

9. Function of Muscles Produce movement Maintain posture Stabilize joints
Generate heat

10. Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are just beneath the sarcolemma
Figure 6.3a

11. Microscopic Anatomy of Skeletal Muscle
Sarcolemma – specialized plasma membrane
Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum

12. Microscopic Anatomy of Skeletal Muscle
Myofibril
Bundles of myofilaments
Myofibrils are aligned to give distinct bands
I band = light band
A band = dark band

13. Microscopic Anatomy of Skeletal Muscle
Sarcomere
Contractile unit of a muscle fiber

14. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thick filaments = myosin filaments
Composed of the protein myosin
Has ATPase enzymes

15. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thin filaments = actin filaments
Composed of the protein actin

16. Microscopic Anatomy of Skeletal Muscle
Myosin filaments have heads (extensions, or cross bridges)
Myosin and actin overlap somewhat

17. Microscopic Anatomy of Skeletal Muscle
At rest, there is a bare zone that lacks actin filaments
Sarcoplasmic reticulum (SR) – for storage of calcium

18. Properties of Skeletal Muscle Activity
Irritability – ability to receive and respond to a stimulus
Contractility – ability to shorten when an adequate stimulus is received

19. Nerve Stimulus to Muscles
Skeletal muscles must be stimulated by a nerve to contract
Motor unit
One neuron
Muscle cells stimulated by that neuron
Figure 6.4a

20. Nerve Stimulus to Muscles
Neuromuscular junctions – association site of nerve and muscle

21. Nerve Stimulus to Muscles
Synaptic cleft – gap between nerve and muscle
Nerve and muscle do not make contact
Area between nerve and muscle is filled with interstitial fluid

22. Transmission of Nerve Impulse to Muscle
Neurotransmitter – chemical released by nerve upon arrival of nerve impulse
The neurotransmitter for skeletal muscle is acetylcholine
Neurotransmitter attaches to receptors on the sarcolemma
Sarcolemma becomes permeable to sodium (Na+)

23. Transmission of Nerve Impulse to Muscle
Sodium rushing into the cell generates an action potential
Once started, muscle contraction cannot be stopped

24. The Sliding Filament Theory of Muscle Contraction
Activation by nerve 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

25. The Sliding Filament Theory of Muscle Contraction
This continued action causes a sliding of the myosin along the actin
The result is that the muscle is shortened (contracted)

26. The Sliding Filament Theory

27. 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

28. Types of Graded Responses
Twitch
Single, brief contraction
Not a normal muscle function

29. Types of Graded Responses
Tetanus (summing of contractions)
One contraction is immediately followed by another
The muscle does not completely return to a resting state
The effects are added

30. Types of Graded Responses
Unfused (incomplete) tetanus
Some relaxation occurs between contractions
The results are summed
Figure 6.9a, b

31. Types of Graded Responses
Fused (complete) tetanus
No evidence of relaxation before the following contractions
The result is a sustained muscle contraction
Figure 6.9a, b

32. 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

33. Muscles and Body Movements
Movement is attained due to a muscle moving an attached bone

34. Muscles and Body Movements
Muscles are attached to at least two points
Insertion– attachment to a moveable bone
Origin – attachment to an immovable bone

35. Types of Ordinary Body Movements
Flexion- the angle at a joint decreased.
Extension- the angle at a joint is increased.

36. Rotation- a bone turns on its long axis.
Abduction- movement away from the midline of the body.
Adduction- movement toward the midline of the body.
Circumduction- movement in a circle.

37. Special Movements Dorsifelxion - sole of foot elevates
Plantar flexion - extension of the foot

38. Special Movements Inversion - sole of foot turns inward
Eversion - sole of foot twists outward

39. Special Movements Supination - turns palm toward anterior
Pronation - turns palm toward posterior
Opposition - move thumb to touch fingers

40. 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

41. Naming of Skeletal Muscles
Direction of muscle fibers
Example: rectus (straight)
Relative size of the muscle
Example: maximus (largest)

42. Naming of Skeletal Muscles
Location of the muscle
Example: many muscles are named for bones (e.g., temporalis)
Number of origins
Example: triceps (three heads)

43. Naming of Skeletal Muscles
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)

44. TRICEPS BRACHII BICEPS BRACHII DELTOID STERNOCLEIDOMASTOID
© 2001 Brooks/Cole . Thomson
©2005 Brooks/Cole . Thomson n
TRICEPS BRACHII
BICEPS BRACHII
DELTOID
STERNOCLEIDOMASTOID
PECTORALIS MAJOR
TRAPIZIUS
EXTERNAL OBLIQUE
LATISSIMUS DORSI
RECTUS ABDOMINUS
GLUTEUS MAXIMUS
ADDUCTOR LONGUS
SARTORIUS
BICEPS FEMORIS
Figure 6.2: Some of the major muscles of the muscular system.
QUADRICEPS FEMORIS
GASTROCNEMIUS
TIBIALIS ANTERIOR