1. Chapter 6 The Muscular System “The Basics”
Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 6 The Muscular System “The Basics”
While muscles have several functions, their essential function is contraction, or shortening.
Slides 6.1 – 6.17
Lecture Slides in PowerPoint by Jerry L. Cook
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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
We discussed these types of muscle tissues in chapter 4. We’ll visit them again in this chapter.
Slide 6.1
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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
Muscle cell is the same thing as muscle fiber. Fiber seems to be more accurate. When you look closely at skeletal muscle (MEAT) you can see the fibers running along the long axis.
In a cell, as we studied in chapter 3, there is the cytoplasm. This was the skeleton of the cell. In the muscle we find the same structure except we call it a Sarcoplasm.
Slide 6.2
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4. Connective Tissue Wrappings of Skeletal Muscle
Endomysium – around single muscle fiber
Perimysium – around a fascicle (bundle) of fibers
Figure 6.1
Slide 6.4a
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5. Connective Tissue Wrappings of Skeletal Muscle
Epimysium – covers the entire skeletal muscle
Fascia – on the outside of the epimysium
Figure 6.1
Slide 6.4b
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6. Skeletal Muscle Attachments
Epimysium blends into a connective tissue attachment
Tendon – cord-like structure
Aponeuroses – sheet-like structure
Sites of muscle attachment
Bones
Cartilages
Connective tissue coverings
The aponeuroses attaches the muscles indirectly to bone, cartilages, or connective tissue coverings of each other.
Slide 6.5
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7. Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Single nucleus
Involuntary – no conscious control
Found mainly in the walls of hollow organs
Smooth muscle contraction is slow and sustained. It is often rhythmic.
Most smooth muscles are laid together in layers. One runs circularly and the other longitudinally.
Figure 6.2a
Slide 6.6
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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
The cardiac fibers are cushioned by small amounts of soft connective tissue and arranged in spiral or figure 8-shaped bundles.
Cardiac muscle is ALWAYS rhythmic.
Figure 6.2b
Slide 6.7
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9. Function of Muscles Produce movement Maintain posture Stabilize joints
Generate heat
Slide 6.8
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15. Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are just beneath the sarcolemma
Remember…skeletal muscle cells are multinucleate.
In this next section we’ll take a closer look at the muscle fiber or cell.
This picture shows a single muscle fiber (cell).
The sarcolemma is yet another covering…a membrane.
Figure 6.3a
Slide 6.9a
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16. Microscopic Anatomy of Skeletal Muscle
Sarcolemma – specialized plasma membrane
Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum
Beneath a plasmic membrane, known as the sarcolemma, you can see these nuclei.
Like a cell which has endoplasmic reticulum, the muscle fiber also has sarcoplasmic reticulum. This reticulum is for storage of calcium. We’ll look again at this later.
Let’s look at the individual myofibril.
Figure 6.3a
Slide 6.9b
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17. Microscopic Anatomy of Skeletal Muscle
Myofibril
Bundles of myofilaments
Myofibrils are aligned to give distrinct bands
I band = light band
A band = dark band
One myofibril is yet again a bundle of other filaments…myofilaments.
These myofilaments are lined up in a way that gives a banding appearance. These are I and A bands.
Figure 6.3b
Slide 6.10a
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18. Microscopic Anatomy of Skeletal Muscle
Sarcomere
Contractile unit of a muscle fiber
The banding and the differences you see between what’s light and what’s dark is very important. When you take an even closer look, you’ll see more structures called myofilaments within sarcomeres
The arrangements are much like a train with its multiple boxcars.
Figure 6.3b
Slide 6.10b
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19. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thick filaments = myosin filaments
Composed of the protein myosin
Has ATPase enzymes
Figure 6.3c
Slide 6.11a
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20. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thin filaments = actin filaments
Composed of the protein actin
Figure 6.3c
Slide 6.11b
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21. Microscopic Anatomy of Skeletal Muscle
Myosin filaments have heads (extensions, or cross bridges)
Myosin and actin overlap somewhat
Figure 6.3d
Slide 6.12a
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22. Microscopic Anatomy of Skeletal Muscle
At rest, there is a bare zone that lacks actin filaments
Sarcoplasmic reticulum (SR) – for storage of calcium
Figure 6.3d
Slide 6.12b
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23. Chapter 6 The Muscular System (cont.) Stimulus and Muscular Activity
Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 6 The Muscular System (cont.) Stimulus and Muscular Activity
Slides 6.1 – 6.17
Lecture Slides in PowerPoint by Jerry L. Cook
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

24. Properties of Skeletal Muscle Activity
Irritability – ability to receive and respond to a stimulus
Contractility – ability to shorten when an adequate stimulus is received
Remember both of these definitions.
Slide 6.13
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25. Nerve Stimulus to Muscles
Skeletal muscles must be stimulated by a nerve to contract
Motor unit
One neuron
Muscle cells stimulated by that neuron
One motor neuron may stimulate a few muscle cells or hundreds of them, depending on what that muscle does.
On the slide, a motor unit is the ONE neuron and all of the muscle cells (fibers) it comes into contact with.
Figure 6.4a
Slide 6.14
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26. Nerve Stimulus to Muscles
Neuromuscular junctions – association site of nerve and muscle
As a nerve branches onto a muscle, it branches into a number of axonal terminals, each of which forms junctions with the sarcolemma of a different muscle cell.
Figure 6.5b
Slide 6.15a
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27. 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
It’s important to remember that nerve endings and the muscle cells’ membranes NEVER touch.
The gap between the two is what is called the synaptic cleft.
At the neuromuscular, the muscle fiber membrane (or sarcolemma) is actually folded inward to form a motor end plate.
Figure 6.5b
Slide 6.15b
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28. 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+)
Remember that the axonal terminals and the sarcolemma don’t touch.
The neurotransmitter is released by the axonal terminal through the synaptic cleft and is received by receptors on the sarcolemma.
The neurotransmitters are stored within the motor neuron endings
Binding of acetylcholine to its receptor opens the sodium channel.
Slide 6.16a
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29. Transmission of Nerve Impulse to Muscle
Sodium rushing into the cell generates an action potential
Once started, muscle contraction cannot be stopped
The sodium rushing into the cell is like a disturbance and forms an electrical current. This is the action potential.
As the slide says, once this is started, muscle contraction cannot be stopped.
The result is contraction or shortening of the muscle cell.
We’ll look more closely at this series of events in the nervous system chapter when we talk about nerve physiology.
Slide 6.16b
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30. 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
Figure 6.7
Slide 6.17a
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31. 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)
Figure 6.7
Slide 6.17b
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32. The Sliding Filament Theory
When an action potential sweeps along its sarcolemma and a muscle cell is excited, calcium ions are released from intracellular storage areas.
The flood of calcium acts as the final trigger for contraction. Calcium binds to the regulatory proteins of the actin filaments and change their shape and their position on the thin filaments.
When the action potential ends and calcium ions are reabsorbed into the SR storage areas, the regulatory proteins resume their original shape and position.
Figure 6.8
Slide 6.18
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37. 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
In general, there are two ways to produce these graded contractions: (1) by changing the frequency of muscle stimulation, and (2) by changing the number of muscle cells being stimulated.
Slide 6.19
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38. Types of Graded Responses
Twitch
Single, brief contraction
Not a normal muscle function
In a twitch, the muscle does relax after the contraction.
Figure 6.9a, b
Slide 6.20a
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39. 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
Figure 6.9a, b
Slide 6.20b
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40. Types of Graded Responses
Unfused (incomplete) tetanus
Some relaxation occurs between contractions
The results are summed
Figure 6.9a, b
Figure 6.9c,d
Slide 6.21a
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41. Types of Graded Responses
Fused (complete) tetanus
No evidence of relaxation before the following contractions
The result is a sustained muscle contraction
This is also known as a tetanic contraction.
Figure 6.9a, b
Figure 6.9c,d
Slide 6.21b
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42. 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
Slide 6.22
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43. 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
Slide 6.27
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44. 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
Most of what we do results in isotonic contractions.
Isometric contractions is partly isotonic contractions, but without relaxation.
A good example of isometric contractions is when you push against a wall with bent elbows, the wall doesn’t move, and the triceps muscles, which cannot shorten to straighten the elbows, are contracting isometrically.
Slide 6.28
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45. 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
Slide 6.29
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46. 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
Slide 6.31
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47. 5 Golden Rules of Skeletal Muscle Activity
All muscles cross at least one joint.
Bulk of the muscle lies proximal to the joint crossed.
Muscles have at least two attachments (origin and insertion).
Muscles can only pull.
During contraction, the muscle insertion moves toward the origin.
This is not in your notes, but you will need to remember theses.

48. Muscles and Body Movements

49. Muscles and Body Movements
Movement is attained due to a muscle moving an attached bone
Figure 6.12
Slide 6.30a
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50. Muscles and Body Movements
Muscles are attached to at least two points
Insertion – attachment to a moveable bone
Origin – attachment to an immovable bone
REMEMBER: The insertion is attached to the movable bone, and when the muscle contracts, the insertion moves toward the origin.
Figure 6.12
Slide 6.30b
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51. Types of Ordinary Body Movements
Flexion
Extension
Rotation
Abduction
Circumduction
You’ll need to know these movements.
Slide 6.32
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52. Body Movements Figure 6.13 Slide 6.33
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53. Special Movements Dorsiflexion Plantar flexion Inversion Eversion
Supination
Pronation
Opposition
Slide 6.34
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54. 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
Need to remember these. You’ll see them again.
Slide 6.35
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55. Naming of Skeletal Muscles
Direction of muscle fibers
Example: rectus (straight)
Relative size of the muscle
Example: maximus (largest)
Slide 6.36a
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56. 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)
Slide 6.36b
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57. 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)
Slide 6.37
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58. Questions?

59. Head and Neck Muscles Figure 6.14 Slide 6.38
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60. Trunk Muscles Figure 6.15 Slide 6.39
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61. Deep Trunk and Arm Muscles
Figure 6.16
Slide 6.40
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62. Muscles of the Pelvis, Hip, and Thigh
Figure 6.18c
Slide 6.41
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63. Muscles of the Lower Leg
Figure 6.19
Slide 6.42
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64. Superficial Muscles: Anterior
Figure 6.20
Slide 6.43
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65. Superficial Muscles: Posterior
Figure 6.21
Slide 6.44
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