1. The Muscular System

2. The Muscular System Function of Muscles: Produce movement
Maintain posture
Stabilize joints
Generate heat
Three basic muscle types are found in the body
Skeletal muscle
Cardiac muscle
Smooth muscle

3. Characteristics of Muscles
Muscle cells are elongated, and are called muscle fibers (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
Multinucleate – more than 1 nucleus
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by connective tissue

5. Connective Tissue Wrappings of Skeletal Muscle
Endomysium – around single muscle fiber
Perimysium – around a fascicle (bundle) of fibers
Epimysium – covers the entire skeletal muscle
Fascia – on the outside of the epimysium
Figure 6.1

6. Skeletal Muscle Attachments
Muscles attach to bones by:
Tendons – 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
Figure 6.2a

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
Figure 6.2b

9. Microscopic Anatomy of Skeletal Muscle
Sarcolemma – specialized plasma membrane
Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum
Sarcomere – contractile unit of a muscle fiber
Figure 6.3a

10. Microscopic Anatomy of Skeletal Muscle
Myofibril
Bundles of myofilaments – actin & myosin
Myofibrils are aligned to give distinct bands
I band = light band
A band = dark band
Figure 6.3b

11. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thick filaments = myosin filaments
Made of the protein myosin
Thin filaments = actin filaments
Composed of the protein actin
Figure 6.3c

12. Microscopic Anatomy of Skeletal Muscle
Myosin filaments have heads (extensions, or cross bridges)
At rest, there is a bare zone that lacks actin filaments
Sarcoplasmic reticulum (SR) – stores calcium used in
contractions
- During contraction myosin & actin slide past eachother
Figure 6.3d

13. Nerve Stimulus to Muscles
Irritability –receive and respond to stimulus
Contractility – shorten when stimulated
Skeletal muscles must be stimulated by a nerve to contract
Motor unit
One neuron
Muscle cells stimulated by that neuron
Figure 6.4a

14. Nerve Stimulus to Muscles
Neuromuscular junctions – association site of nerve and muscle (where they meet)
Figure 6.5b

15. Nerve Stimulus to Muscles
Synaptic cleft – gap between nerve and muscle
Nerve and muscle do not touch
Area between nerve and muscle filled with interstitial fluid
Neurotransmitters travel across space
Figure 6.5b

16. Transmission of Nerve Impulse to Muscle
Neurotransmitter acetylcholine – chemical released by nerve upon arrival of impulse
Acetylcholine attaches to receptors on the sarcolemma of muscle
Sarcolemma becomes permeable to sodium (Na+)
Sodium rushes into the cell and generates an action potential (stimulus) for contraction
Once started, muscle contraction cannot be stopped

17. The Sliding Filament Theory of Muscle Contraction
Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on actin
Myosin heads then bind to the next site actin
This continued action slides myosin along actin
The result is that the muscle is shortened (contracted)
Figure 6.7

18. The Sliding Filament Theory
Figure 6.8

19. Contraction of a Skeletal Muscle
Skeletal Muscle Contraction:
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

20. Types of Graded Responses
Twitch
Single, brief contraction
Not a normal muscle function
Figure 6.9a–b

21. Types of Graded Responses
Tetanus (summing of contractions)
One contraction is immediately followed by another
Contraction is
smooth and
sustained
Figure 6.9a–b

22. 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

23. Energy for Muscle Contraction
First, muscles used stored ATP for energy
Bonds of ATP are broken to release energy (lasts only few seconds)
After this initial time, cells need to undergo aerobic or anaerobic respiration to produce energy for contraction

24. Energy for Muscle Contraction
Aerobic Respiration
Occurs in the mitochondria
Glucose is broken down to carbon dioxide, water and ATP (energy)
This is a slower reaction that requires continuous oxygen
Figure 6.10b

25. Energy for Muscle Contraction
Anaerobic glycolysis
Breaks down glucose without oxygen
Glucose is broken down to pyruvic acid, then lactic acid, to produce some ATP
Not as efficient as aerobic respiration
Build up of lactic acid
Produces muscle fatigue
Figure 6.10c

26. 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
Different fibers contract at different times to provide muscle tone

27. Muscles and Body Movements
Movement is attained due to a muscle moving an attached bone
Muscles are attached to at least two points
Origin – attachment to an immoveable bone
Insertion – attachment to a movable bone
Figure 6.12

28. Effects of Exercise on Muscle
Results of increased muscle use
Increase in muscle size
Increase in muscle strength
Increase in muscle efficiency
Muscle becomes more fatigue resistant

29. Types of Ordinary Body Movements
Types of body movements due to muscles
Flexion: brings bones closer together
Extension: opposite of flex, increases distance between bones
Rotation: movement around longitudinal axis (shaking head no)
Abduction: moving limb away from body
Adduction: opposite, move limb toward body
Circumduction: proximal end is stationary and distal end moves in a circle

30. Body Movements
Figure 6.13a–c

31. Body Movements
Figure 6.13d

32. Special Movements Dorsifelxion: toes up, walking on heels
Plantar flexion: toes down, walking on toes
Inversion: turn sole medially (in toward body)
Eversion: turn sole laterally (away from body)
Supination: turn palm up (facing anteriorly)
Pronation: turn palm down (facing posteriorly)
Opposition: ability to move thumb to touch other fingers

33. Types of Muscles
Prime mover (Agonist) – 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

34. Naming of Skeletal Muscles
Direction of muscle fibers:
Example: rectus (straight)
Relative size of the muscle:
Example: maximus (largest)
Location of the muscle:
Example: temporalis (temporal bone)
Number of origins:
Example: triceps (three heads)
Shape of the muscle
Example: deltoid (triangular)
Action of the muscle
Example: flexor and extensor

35. Head and Neck Muscles
Figure 6.15

36. Trunk Muscles
Figure 6.16

37. Deep Trunk and Arm Muscles
Figure 6.17

38. Muscles of the Pelvis, Hip, and Thigh
Figure 6.19c

39. Muscles of the Lower Leg
Figure 6.20

40. Superficial Muscles: Anterior
Figure 6.21

41. Superficial Muscles: Posterior
Figure 6.22