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Copyright © 2015 Wolters Kluwer Health | Lippincott Williams & Wilkins
Chapter 8
The Muscular System

Copyright © 2015 Wolters Kluwer • All Rights Reserved
Overview

Key Terms
acetylcholine membrane potential synapse
actin motor unit synergist
action potential myalgia tendon
agonist myoglobin tonus
antagonist myosin tropomyosin
atrophy neuromuscular junction troponin
contractility neurotransmitter
excitability origin
fascicle prime mover
glycogen sarcomere
insertion spasm

Types of Muscle
Learning Objective
1. Compare the three types of
muscle tissue.

The Muscular System
Learning Objectives
2. Describe three functions of
skeletal muscle.
3. Describe the structure of a skeletal
muscle to the level of individual
cells.
4. Outline the steps in skeletal
muscle contraction.

The Muscular System (cont.)
Learning Objectives
5. List compounds stored in muscle
cells that are used to generate
energy.
6. Explain what happens in muscle
cells contracting anaerobically.
7. Cite the effects of exercise on
muscles.
8. Compare isotonic and isometric
contractions.

The Mechanics of Muscle Movement
Learning Objectives
9.Explain how muscles work together
to produce movement.
10.Compare the workings of muscles
and bones to lever systems.

Skeletal Muscle Groups
Learning Objectives
11. Explain how muscles are named.
12. Name some of the major muscles
in each muscle group, and
describe the locations and
functions of each.

Effects of Aging on Muscles
Learning Objective
13. Describe how muscles change
with age.

Muscular Disorders
Learning Objective
14. List the major disorders of
muscles and their associated
structures.

Case Study
Learning Objective
15. Describe some of the
diagnostic signs of
muscular dystrophy
based on the case study.

Word Anatomy
Learning Objective
16. Show how word parts are used to build words related
to the muscular system.

Types of Muscle

Types of Muscle (cont.)
✓
Checkpoint
8-1 What are the three types of muscle?

?
Pop Quiz
8.1 Which type of muscle tissue is striated and
involuntary?
A)Cardiac
B)Intercalated
C)Smooth
D)Skeletal

?
Pop Quiz Answer
8.1 Which type of muscle tissue is striated and
involuntary?
A)Cardiac
B)Intercalated
C)Smooth
D)Skeletal

The Muscular System
Learning Objectives
2. Describe three functions of
skeletal muscle.
3. Describe the structure of a skeletal
muscle to the level of individual
cells.
4. Outline the steps in skeletal
muscle contraction

Skeletal Muscle Has Three Primary Functions:
•Skeletal movement
•Posture maintenance
•Heat generation

Muscle Structure
•Fascicles
– Bundles of muscle cells (fibers) that make up a whole
muscle
•Connective tissue
– Holds fascicles and whole muscle together
– Three layers
• Endomysium
• Perimysium
• Epimysium
•Tendons

Figure 8-1 Structure of a skeletal muscle.
What is the innermost layer of connective tissue in a
muscle? What layer of connective tissue surrounds a
fascicle of muscle fibers?

Muscle Cells in Action
•Motor unit: A single neuron and all the muscle fibers it
stimulates
– Small motor units used for fine movements
– Large motor units used for broad movements

Muscle Cells in Action (cont.)
•Neuromuscular junction (NMJ): The point at which a
nerve fiber contacts a muscle fiber
– A type of synapse
– NMJ anatomy
• Motor neuron
• Neurotransmitter (acetylcholine; ACh)
• Motor end plate (on muscle fiber)
 Contains acetylcholine receptors

•The NMJ allows motor neuron to stimulate the muscle
fiber to become electrically excited (action potential).
•Action potential stimulates muscle contraction.
•Events at the NMJ:
– ACh is released from motor neuron into synaptic cleft.
– ACh diffuses across synaptic cleft toward motor end
plate.
– ACh binds to receptors on motor end plate and
stimulates action potential.

Figure 8-2 The neuromuscular junction (NMJ).

•The sarcomere is the functional unit of contraction in the
skeletal muscle fiber.
•Sarcomere anatomy:
– Thick filaments (myosin)
– Thin filaments (actin)
– Regulatory proteins
• Troponin
• Tropomyosin

Figure 8-3 Detailed structure
of a skeletal muscle cell.

•Sarcomeres contract via the sliding filament mechanism:
– Myosin heads bind to actin, forming cross-bridges.
– Using stored energy, myosin heads pull actin
filaments together within the sarcomeres, and the cell
shortens.
– New ATP is used to detach myosin heads and move
them back into position for another “power stroke.”

Figure 8-4 Sliding filament mechanism of skeletal muscle
contraction.
Do the actin or myosin filaments change in length as
contraction proceeds?

•Calcium regulates sarcomeric contraction within the
muscle cell:
– Action potential from the NMJ travels to the
sarcoplasmic reticulum (SR).
– The SR releases calcium into cytoplasm.
– Calcium shifts troponin and tropomyosin off of thin
filament so that binding sites on actin are exposed.
– Sliding filament mechanism now able to proceed.
– Muscle relaxes when stimulation ends and calcium is
pumped back into the SR.

Figure 8-5 Role of calcium
in muscle contraction.

Summary of Events in a Muscle Contraction
•ACh is released from neuron ending into synaptic cleft at
the NMJ.
•ACh binds to motor end plate and produces an action
potential.
•The action potential travels to the SR.
•SR releases calcium into cytoplasm.
1.Calcium shifts troponin and tropomyosin off of thin
filaments so that binding sites on actin are exposed.

Summary of Events in a Muscle Contraction (cont.)
6.Myosin heads bind to actin, forming cross-bridges.
7.Using stored energy, myosin heads pull actin filaments
together within sarcomeres, and cell shortens.
8.New ATP is used to detach myosin heads and move
them back to position for another “power stroke.”
9.Muscle relaxes when stimulation ends and calcium is
pumped back into SR.

✓
Checkpoints
8-2 What are the three main functions of skeletal muscle?
8-3 What are bundles of muscle fibers called?
8-4 What is the term for the difference in electrical charge
on the two sides of a plasma membrane?
8-5 What is the name of the special synapse where a nerve
cell makes contact with a muscle cell?
8-6 What neurotransmitter is involved in the stimulation of
skeletal muscle cells?
8-7 What filaments interact to produce muscle contraction?
8-8 What mineral is needed for interaction of the
contractile filaments?

?
Pop Quiz
8.2 A single neuron and all the muscle fibers it
stimulates comprise a:
A)Motor end plate
B)Motor unit
C)Neuromuscular junction
D)Synapse

?
Pop Quiz Answer
8.2 A single neuron and all the muscle fibers it
stimulates comprise a:
A)Motor end plate
B)Motor unit
C)Neuromuscular junction
D)Synapse

?
Pop Quiz
8.3 The two filaments that form cross-bridges are:
A)Actin and troponin
B)Tropomyosin and myosin
C)Actin and myosin
D)Troponin and tropomyosin

?
Pop Quiz Answer
8.3 The two filaments that form cross-bridges are:
A)Actin and troponin
B)Tropomyosin and myosin
C)Actin and myosin
D)Troponin and tropomyosin

Energy Sources
•Muscle contraction requires ATP.
•Skeletal muscle prefers to produce ATP via aerobic
metabolism, which requires:
– Oxygen
– Glucose
•Storage compounds ensure an adequate supply of
oxygen and glucose for aerobic ATP metabolism.
– Myoglobin
– Glycogen

Energy Sources (cont.)
•Storage compounds: Myoglobin, glycogen, fatty acids
•During strenuous activity, muscle cells use anaerobic ATP
metabolism, which does not require ATP.
– Breakdown of creatine phosphate
– Anaerobic glycolysis
• Lactic acid accumulation and oxygen debt
• Excess postexercise oxygen consumption:
– After strenuous exercise, the person takes in extra
oxygen (via rapid breathing) to remove lactic acid
and replenish energy stores.

Effects of Exercise
•Improved balance, joint flexibility
•Increased muscle size (hypertrophy)
•Improved muscle tissue
•Vasodilation
•Strengthened heart muscle
•Improved breathing and respiratory efficiency
•Weight control
•Stronger bones

Types of Muscle Contractions
•Partial (muscle tone or tonus)
•Isotonic
– No change in tension
– Muscle length shortens
– Movement
•Isometric
– Great increase in tension
– Muscle length unchanged
– No movement

✓
Checkpoints
8-9 What compound is formed in oxidation of nutrients
that supplies the energy for muscle contraction?
8-10 What compound stores reserves of oxygen in
muscle cells?
8-11 What are the two main types of muscle
contraction?

?
Pop Quiz
8.4 Which muscle cell compound stores oxygen?
A)Creatine phosphate
B)Glycogen
C)Hemoglobin
D)Myoglobin

?
Pop Quiz Answer
8.4 Which muscle cell compound stores oxygen?
A)Creatine phosphate
B)Glycogen
C)Hemoglobin
D)Myoglobin

The Mechanics of Muscle Movement
Learning Objectives
9. Explain how muscles work
together to produce movement.
10. Compare the workings of muscles
and bones to lever systems.

The Mechanics of Muscle Movement (cont.)
• Tendons attach muscles to bones.
– Origin: Attached to more fixed part of skeleton
– Insertion: Attached to more movable part of
skeleton

Figure 8-6 Muscle attachments to bones.
Does contraction of the brachialis produce flexion or
extension at the elbow?

Muscles Work Together
•Many muscles function in pairs.
– Prime movers
– Antagonists
– Synergists

Levers and Body Mechanics
•Musculoskeletal system as a lever system
– Lever—bone
– Fulcrum—joint
– Force—applied by muscle
•Three classes of levers
– First class
– Second class
– Third class—most body systems

Figure 8-7 Levers.
In a third-class lever system, where is the fulcrum with
regard to the effort and the resistance?
The Mechanics of Muscle Movement(cont.)

✓
Checkpoints
8-12 What are the names of the two attachment points
of a muscle, and how do they function?
8-13 What is the name of the muscle that produces a
movement as compared with the muscle that produces an
opposite movement?
8-14 Of the three classes of levers, which one
represents the action of most muscles?

The Mechanics of Muscle Movement cont.)
?
Pop Quiz
8.5 In anatomic lever systems, the fulcrum is the:
A)Bone
B)Bursa
C)Insertion
D)Joint

?
Pop Quiz Answer
8.5 In anatomic lever systems, the fulcrum is the:
A)Bone
B)Bursa
C)Insertion
D)Joint

Skeletal Muscle Groups (cont.)
Characteristics for Naming Muscles

Figure 8-8 Superficial
muscles, anterior view.

Figure 8-9 Superficial
muscles, posterior view.

Muscles of the Head and Neck

Figure 8-10 Muscles of the head.
Which of the muscles in this illustration are named for a
nearby bone?

Muscles of the Upper Extremities

Muscles of the Upper Extremities (cont.)

Figure 8-11 Muscles that move the forearm and hand.
What does carpi refer to in the names of muscles? Digitorum?

Muscles of the Trunk

Figure 8-12 Muscles of respiration.

What does rectus mean? Oblique?
Figure 8-13 Muscles of
the abdominal wall.

Figure 8-14 Muscles of the female perineum (pelvic floor).

Muscles That Move the Leg and Thigh

Muscles That Move the Leg and Thigh (cont.)

Figure 8-15 Muscles of the thigh.
How many muscles make up the quadriceps femoris?

Muscles That Move the Foot

Figure 8-16 Muscles that move the foot.
On what bone does the Achilles tendon insert?

✓
Checkpoints
8-15 What muscle is most important in breathing?
8-16 What structural feature gives strength to the
muscles of the abdominal wall?

?
Pop Quiz
8.6 An antagonist to the gastrocnemius is the:
A)Gracilis
B)Sartorius
C)Soleus
D)Tibialis anterior

?
Pop Quiz Answer
8.6 An antagonist to the gastrocnemius is the:
A)Gracilis
B)Sartorius
C)Soleus
D)Tibialis anterior

Effects of Aging on Muscles
Learning Objectives
13. Describe how muscles change
with age.

Effects of Aging on Muscles (cont.)
• Beginning at about age 40
• Gradual loss of muscle cells
• Loss of power
• Tendency to flex hips and knees
• Decrease in height

Muscular Disorders
Learning Objectives
14. List the major disorders of
muscles and their associated
structures.

Muscular Disorders (cont.)
Common Terms Used When Describing Muscular
Disorders
•Spasms
– Colic
– Seizure
– Convulsion
•Cramps
•Atrophy

Muscle Injuries
•Strains
•Delayed-onset muscle soreness (DOMS)
•Rhabdomyolysis

Diseases of Muscle
•Muscular dystrophy
•Myasthenia gravis
•Myalgia
– Myositis
– Fibrositis
– Fibromyositis
•Fibromyalgia syndrome (FMS)

Disorders of Associated Structures
•Tendinitis
•Plantar fasciitis
•Tenosynovitis
•Shin-splints

Figure 8-17 Muscular disorders.

Case Study (cont.)
Diagnostic signs:
•Pseudohypertrophic calf muscles and thin thighs
•Weak thigh muscles
•Gower sign—using the arms to “walk” up the body
•Low levels of dystrophin determined from a muscle
biopsy

Word Anatomy
Learning Objective
16. Show how word parts are used to build words related
to the integumentary system.

Word Anatomy (cont.)

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