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The Muscular System.

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Presentation on theme: "The Muscular System."— Presentation transcript:

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)


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