1. The Human Body in Health and Illness, 4th edition
Barbara Herlihy
Chapter 9:
Muscular System

2. Lesson 9-1 Objectives Identify three types of muscle tissue.
Describe the sliding filament mechanism of muscle contraction.
Describe the motor unit and recruitment.
Explain the role of calcium and ATP in muscle contraction.
Describe the events at the neuromuscular junction.
Trace events from nerve stimulation to muscle contraction.
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3. Types and Functions of Muscles
Cardiac muscle
-Intercalated discs – where the branching cells fit together
-intercalated discs promote rapid conduction of electrical signals
Skeletal muscle cells are striated and voluntary. They cause movement of the skeleton.
Smooth muscle cells (visceral muscle) are nonstriated and involuntary. The contraction of smooth muscle enables the viscera or organs to perform their functions.
Cardiac muscle is found only in the heart. It is striated and involuntary. Cardiac cells fit tightly together to conduct the heart’s electrical signals better.
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4. Whole Muscle Structure
Fascia
Epimysium-outer
Perimysium-bundles of muscle fibers
Endomysium-around a muscle fiber
Fascicles (bundles)
Tendon
Belly – enlarged fleshy body
Figure 9-2 from top to bottom shows a muscle’s parts from largest to smallest; the next three slides examine this figure.
This slide refers to part A of figure, the view of the muscle as a whole.
This cross section of the triceps brachii illustrates the layers of fascia and the fascicles, or bundles of muscle cells. The fascia tapers into the tendon, which attaches the muscle to the bone.
The fascia separates the muscle into compartments. Injury can cause compartment syndrome.
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5. Muscle Attachments Tendon attaches the muscle to bone
Muscles attach directly (without a tendon) to a bone or to soft tissue
A flat sheetlike fascia called aponeurosis connects muscle to muscle or bone
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6. Muscle Fiber: Cell Group of myofibrils
Series of sarcomeres
Sarcoplasmic reticulum-specialized ER
Sarcolemma-cell membrane
T-tubule system-transverse tubules
This slide refers to part B of Figure 9-2, which illustrates a muscle fiber (cell).
The muscle fiber is a group of myofibrils surrounded by the SR. The cell membrane is the sarcolemma. The T tubules are part of the sarcolemma and penetrate to the interior of the muscle.
Later slides will discuss how the T tubules transmit electrical signals to the interior of the muscle.
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7. Sarcomeres: Inside the Myofibril
From Z line to Z line
Thin filaments
Actin-contains binding sites for myosin
Troponin-tropomyosin
Thick filaments
Myosin
This slide refers to part C of Figure 9-2, which illustrates the structure of a single myofibril.
A myofibril is a series of sarcomeres.
A sarcomere extends from Z line to Z line and is composed of thick and thin filaments. These proteins are involved in the sliding filament mechanism, which is responsible for muscle contraction.
The arrangement of the thick and thin filaments accounts for the striated pattern on skeletal and cardiac muscle.
Ask students to point out on the slide differences in length of the relaxed and contracted sarcomeres.
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8. Two Aspects of Muscle Contraction
Electrical
Involves motor neuron and NMJ
Results in calcium release from SR
Happens first
Contractile
Involves actin and myosin
Sliding filaments
Happens second
Muscle contraction can be described in terms of two events, electrical and contractile. This slide gives a preview of the two events, which will then be described in detail in LATER slides.
This slide points out that the electrical function happens before the contractile function; however, the contractile function will be discussed first.
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9. Contractile Function: Sliding Filament Mechanism
Myosin heads make contact with actin.
Myosin heads rotate.
Actin is pulled to the center of the sarcomere.
Sarcomere shortensmuscle contraction
Muscles must contract or shorten to be able to pull. Muscles can only pull, not push.
The slide shows the time order of the contractile events and how the contractile proteins (actin and myosin) interact to produce a contraction.
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10. Contracting Muscles Need Calcium
Calcium is stored away from thin and thick filaments in the sarcoplasmic reticulum (SR).
When stimulated, the SR releases calcium.
Calcium allows actin, myosin, and ATP to interact, causing muscle contraction.
Why does muscle relax? Calcium returns to the SR.
Muscle contraction requires calcium.
Calcium is stored in the sarcoplasmic reticulum (SR).
When a muscle is called into action, SR releases calcium.
The calcium floods the sarcomere and permits the interaction among actin, myosin, and ATP. This causes contraction.
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11. Whole Muscle Contraction
A single muscle fiber has an “all or nothing” response, but a whole muscle can vary its force of contraction.
Two characteristics of a whole muscle allow this
Motor unit
Recruitment
This slide shifts the focus from the individual muscle cell to the whole muscle, which is comprised of muscle fibers.
When an individual muscle cell contracts, it must contract maximally, but a whole muscle can vary its strength of contraction.
Motor unit and recruitment are mechanisms that allow the force of contraction in the whole muscle to vary. Each concept is treated in more detail in future slides.
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12. Motor Unit and Recruitment
Motor unit: The nerve and innervated muscle fibers
Recruitment: The more motor units activated, the greater the force of contraction.
Motor unit: A single motor nerve emerges from the spinal cord. It splits into branches. Each branch innervates a group of muscle cells. The motor unit is the nerve and the muscle fibers it innervates. Each whole muscle has many motor units.
Recruitment: In recruitment, various numbers of motor units are activated. The more motor units that are active—or recruited—the stronger the contraction.
For example, when a person lifts a pencil, far fewer motor units are activated than when a table is lifted.
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13. Side Note Difference between white meat and dark meat.
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14. Two Aspects of Muscle Contraction
Electrical
Involves motor neuron and NMJ(neuromuscular junction)
Results in calcium release from SR
Happens first
Contractile
Involves actin and myosin
Sliding filaments
Happens second
This slide repeats slide 7. Use it to emphasize to students that the discussion is now moving away from the mechanics of the contractile event to the underlying electrical events that control the contraction.
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15. Neuromuscular Junction (NMJ)
Space between motor neuron and muscle
Site of ACh action and activation of muscle membrane
Ach is a neurotransmitter
As the term neuromuscular junction suggests, the NMJ is the space the between the neuron and the muscle, where innervations occurs.
The action of ACh as a neurotransmitter occurs here.
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16. Electrical Events
Electrical signal travels to axon terminal, releasing ACh.
ACh diffuses across NMJ and activates muscle receptors.
Activated receptors send electrical signal along muscle membranes and T tubules.
Electrical signal stimulates the SR to release calcium, initiating the sliding filament.
Ach is destroyed by enzyme acetylcholinesterase
This slide provides a close-up of the chemical and electrical events that occur at the NMJ.
ACh activates receptors and allows the electrical signal to be transmitted along the T tubules. In this way, the electrical signal moves deep into the cell.
Calcium links the electrical and contractile events.
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17. Impairment at the NMJ
Myasthenia gravis – receptor sites cannot effectively bind Ach. Weakened muscle contraction.
Curare – a drug that works by blocking the receptor sites. Often used during surgery.
Neurotoxins
Clostridium tetani (tetanus) – causes excessive firing of the motor nerves
Clostridium botulinum (botulism and Botox) – prevents the release of Ach
The NMJ is not only a site for physiological activity. It is also a site for pharmaceutical activity and disease.
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18. Muscle Paralysis Spastic paralysis – caused by excess of ACh
Flaccid paralysis – caused by deficiency of ACh
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19. Lesson 9-2 Objectives Define twitch and tetanus.
Identify the sources of energy for muscle contraction.
State the basis for naming muscles.
List the actions of the major muscles.
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20. Responses of a Whole Muscle
Twitch: Single muscle response in which muscle contracts and then fully relaxes
Tetanus: Sustained muscle contraction caused by repeated stimulation
Tonus: Normal, continuous state of partial muscle contraction. One group of muscle fibers contracts first. As these relax, a second group contracts.
Twitch is unimportant physiologically.
Tetanus, not to be confused with the disease, is essential to maintain posture or any other activity that involves a sustained muscle contraction.
In tonus, different groups of muscle fibers within a muscle take turns contracting while others relax.
Smooth muscle tonus in the blood vessels maintains blood pressure.
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21. Sources of Energy (ATP)
Metabolism of creatine phosphate
Creatine phosphate is stored energy that can replenish ATP
Anaerobic metabolism: glycolysis
Aerobic metabolism
Review with students aerobic and anaerobic metabolism from Chapter 4.
Aerobic metabolism occurs in the presence of oxygen. This process facilitates the breakdown of fats, glycogen, and glucose to produce more ATP.
Anaerobic metabolism is a normal process that occurs when oxygen is not available. This process also causes lactic acid to build up in the muscle.
Creatine phosphate is metabolized for a quick ATP boost during muscle contraction. This molecule acts as “energy storage.”
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22. Muscle Terms Origin:to stationary bone Insertion:tomoveable bone
Prime mover
Synergist: assists prime mover
Antagonist: opposes prime mover
Origin attaches to the more stationary bone whereas insertion refers to the more moveable bone.
Most movement is accomplished through the cooperation of groups of muscles. However, one “chief muscle,” or prime mover, is generally responsible for most of the movement.
A synergist is a muscle that helps the prime mover.
Antagonists help return the body parts moved by synergists and prime movers back to their original positions.
In this figure, the biceps brachii contracts to flex the forearm. To extend the forearm, the triceps contracts while the biceps brachii relaxes.
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23. Muscle Overuse and Underuse
Hypertrophy: Growth in response to overuse
Atrophy: Wasting
Disuse atrophy
Denervation atrophy
Senile atrophy: part of aging process
Contracture: Abnormal fibrous formation in muscle that “freezes” in flexed position, result of prolonged immobilization of a muscle
Skeletal muscle hypertrophy—bulking up—is the desired result of body building (and, to a lesser extent, general weight training).
Cardiac hypertrophy, however, is usually undesirable. The heart increases in size when it is chronically overworked, such as when a person has hypertension.
Atrophy occurs for a variety of reasons, such as disuse and poor innervation. It may also occur in older adults.
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24. How Skeletal Muscles Are Named
Size: Gluteus maximus
Shape: Trapezius
Direction of fibers: Rectus abdominis
Location: Pectoralis
Number of origins: Biceps
Origin and insertion: Sternocleidomastoid
Muscle action: Adductors
Students may refer to Figure 9-7 to find additional examples of muscle names to analyze.
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25. Muscles from Head to Toe
This is an overview of the muscles, anterior and posterior, that will be discussed in detail on the following slides.
Refer students to Table 9-1 for a description of individual muscles and their functions.
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26. Facial Muscles Frontalis Orbicularis oculi
Levator palpebrae superioris
Orbicularis oris
Buccinator
Zygomaticus
Platysma
Many facial muscles are inserted in soft tissue rather than bone. What physiological significance does this have?
Expressions such as smiling and frowning result from the contractions of the facial muscles.
The frontalis raises the eyebrows and wrinkles the forehead.
The orbicularis oculi encircles and closes the eye and assists in winking, blinking, and squinting.
The levator palpebrae superioris lifts the eyelid.
The orbicularis oris closes the mouth, helps form words, and purses the lips.
The buccinator flattens the cheek and helps position the food between the teeth.
The zygomaticus is the smiling muscle; it extends from the corner to the cheek or zygomatic bone.
The platysma allows you to pout and open your mouth wide.
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27. Facial Muscles: Chewing
Masseter
Temporalis
The chewing muscles are also called the muscles of mastication. They all insert into the mandible. Both of the chewing muscles contract to close the jaw.
Some people incorrectly consider the buccinators a chewing muscle. Why might they think this?
Although the buccinator does not attach to the mandible and close the jaw, it does compress the cheek to position the food for chewing.
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28. Muscles of the Neck Sternocleidomastoid Scalene muscles (three)
Trapezius
The muscles of the neck are involved in the movement of the head and shoulders and participate in movements within the throat.
The sternocleidomastoid contracts to cause flexion and rotation of the head and rotation of the head. The scalene muscles act synergistically with the sternocleidomastoid.
The trapezius helps with the extension and hyperextension of the head at the neck.
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29. Muscles of the Trunk: Breathing
Intercostal muscles
Internal
External
Diaphragm
Contraction and relaxation of the intercostal muscles and of the diaphragm change thoracic volume. Therefore, these muscles are primarily responsible for breathing or ventilation.
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30. More Muscles of the Trunk
Abdominal wall
Internal oblique
External oblique
Transversus abdominis
Rectus abdominis
Vertebral column
Erector spinae
Sternocleidomastoid
Trapezius
Abdominal muscles
Iliopsoas
The muscles of the abdominal wall are layered to provide strength to contain, support, and protect the abdominal organs. They cause flexion and rotation of the vertebral column, and they compress the abdominal organs for various functions.
The muscles that move the vertebral column attach to the vertebrae. These movements include flexion, extension, hyperextension, lateral flexion, and rotation. Asks students to demonstrate each of these movements, referring to
With aging, the erector spinae muscle loses contractile strength. How might that change the appearance of an older person?
One might observe stooped posture.
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31. Muscles of the Shoulder and Arm
Trapezius
Serratus anterior
Pectoralis major
Latissimus dorsi
Deltoid
Teres major
Rotator cuff muscles
The trapezius shrugs the shoulders and rotates the pectoral girdle.
The serratus anterior lowers the shoulders and allows the upper arm to move as if pushing a cart.
The pectoralis major moves the upper arm across the front of the chest.
The latissimus dorsi lowers the shoulders and brings the arm back behind the body. This is called the swimmer’s muscle because the movement mimics that of free-style swimming.
The deltoid abducts the arm to a horizontal position. It also flexes, extends, and rotates the arm at the shoulder joint. It is a common site for an intramuscular injection.
The teres major extends the arm at the shoulder joint.
The rotator cuff muscles stabilize the joint capsule and rotate the arm at the shoulder joint. Rotator cuff injury is common in athletes who use repetitive overhead motions. Add the names of the rotator cuff muscles.
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32. Muscles of the Forearm Biceps brachii Triceps brachii Brachialis
Brachioradialis
Supinators and pronators
The triceps brachii supports the weight of the body during push-ups. Strengthening the triceps is very important for crutch walking.
The biceps brachii acts synergistically with the brachialis and brachioradialis to flex the forearm.
Pronator and supinator muscles have their origin on the humerus and insert on the radius or ulna.
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33. Muscles of the Wrist and Hand
Flexor carpi group
Extensor carpi group
Flexor digitorum
Extensor digitorum
The flexor and extensor carpi groups and flexor and extensor digitorum groups are responsible for the movements of the hand and fingers.
These muscles are located in the forearm; the tendons extend into the hand and fingers, acting as “puppet strings.” This arrangement means that the hands and fingers are small enough to be dexterous.
In a relaxed hand, the flexors of the fingers are stronger than the extensors. What is likely to happen to the hand position of a person who is unconscious for a substantial amount of time?
The hand will form a contracture in the flexed position.
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34. Carpal Tunnel Syndrome
Repetitive motion of the hand and fingers can cause the tissues in the carpal tunnel to swell and become inflamed. This puts pressure on the median nerve and results in tingling, weakness, and pain in the hand.
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35. Muscles of the Thigh Gluteus maximus, medius, and minimus Iliopsoas
Tensor fasciae latae
Adductor group
Pectineus
Quadriceps femoris
Sartorius
Hamstrings
Contractions of the muscles that move the thigh result in movements of the hip joint. The gluteal muscles extend, rotate, and abduct the thigh at the hip.
The iliopsoas, the sartorius, and the pectineus flex the thigh at the hip.
The adductor group muscles are the adductor longus, adductor brevis, adductor magnus, and gracilis. During horseback riding, these muscles allow a person to stay in the saddle.
Quadriceps femoris and hamstrings move both the hip and the leg.
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36. Muscles: Leg/Foot, Anterior View
Quadriceps femoris
Rectus femoris
Vastus lateralis
Vastus medialis
Vastus intermedius
Sartorius
Tibialis anterior
Peroneus longus
This slide gives an anterior view of the muscles that move the leg and the foot.
The quadriceps femoris is made up of four smaller partsthe rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. They all insert on the leg, extending the leg at the knee.
The rectus femur has its origin on both the hip and thigh, allowing flexion of the thigh and extension of the leg.
The quadriceps femoris, as its name indicates, has four points of attachment. These muscles extend the leg at the knee.
The sartorius allows the legs to rotate into position so a person can sit cross-legged.
The tibialis anterior causes dorsiflexion and inversion of the foot.
The peroneus longus everts the foot, supports the arch, and assists in plantar flexion.
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37. Muscles: Leg and Foot, Posterior View
Hamstrings
Biceps femoris
Semitendinosus
Semimembranosus
Gastrocnemius
Soleus
Tibialis posterior
Calcaneal or Achilles tendon
The hamstrings allow for leg flexion and thigh extension.
The strong tendons of these muscles can be felt behind the knee. Ask students to find these on their own bodies and to put their fingers in the popliteal fossa.
The gastrocnemius and soleus form the calf of the leg. Both attach to the Achilles tendon. Contraction causes plantar flexion.
The tibialis posterior also assists in plantar flexion and inverts the foot.
Like the fingers, the toes are tugged on by tendons whose muscles (flexors and extensors) lie in the leg.
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38. Muscles with Colorful Names
Have students explain the origin of (1) hamstring muscle, (2) Achilles tendon, (3) sartorious.
(1) Butchers used the tendon of a hog to hang hams for smoking and curing, hence the name hamstring muscle. (2) In Greek mythology, Achilles’ mother held him by the heal and dipped him into the sacred Styx river to make him immortal; later he was killed by an arrow wound in the heal. Today the term is used both to name the muscle and to refer to a strong person’s vulnerable spot. (3) The Latin word for tailor is “sartor,” and tailors used to sit in the cross-legged position made possible by the sartorius muscle. Today it’s more likely to see someone in yoga class exercising the sartorius muscle.
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