This document provides an overview of how animals move through the skeletal and muscular systems. It discusses the three types of skeletons (hydrostatic, exoskeleton, endoskeleton), focusing on the human skeletal system. It also describes the structure and function of bones, skeletal joints, and skeletal muscle. The key points are the sliding filament model of muscle contraction using actin and myosin, and how muscles interact with bones through tendons to generate movement.

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HOW ANIMALS MOVE
Chapter Outline
IMPACTS/ISSUES: BULKING UP MUSCLES Getting Energy for Contraction
THE SKELETAL SYSTEM PROPERTIES OF WHOLE MUSCLES
Types of Skeletons Muscle Tension
The Human Skeleton Diseases and Disorders Affecting Muscle
Bone Structure and Function Contraction
Where Bones Meet—Skeletal Joints IMPACTS/ISSUES REVISITED
HOW BONES AND MUSCLES INTERACT SUMMARY
SKELETAL MUSCLE STRUCTURE AND SELF-QUIZ
FUNCTION CRITICAL THINKING
Sliding-Filament Model for Contraction
Objectives
• Explain the process by which muscles become larger and stronger.
• Name the hormones that affect muscle mass.
• Describe how a lack of myostatin affects muscle mass.
• Name the three types of skeletons, and describe how they work.
• List a representative organism for each skeleton type.
• List the component bones that comprise the following areas:
o Skull
o Pectoral girdle
o Vertebral column
o Upper limb bones
o Pelvic girdle
o Lower limb bones
• Compare and contrast the structure and function of compact bone and spongy bone.
• Know the location and function of red marrow and yellow marrow.
• Describe the matrix arrangement of compact bone.
• Understand the mineral deposition and removal of calcium with respect to the bones.
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2. • List functions of calcium other than providing a substrate for bones.
• Define osteoporosis.
• Compare and contrast the structure and function of cartilaginous joints, fibrous joints, and
synovial joints.
• Name the most common joint injury in humans.
• Explain how osteoarthritis and rheumatoid arthritis are different.
• Explain how bones and muscles are attached to each other.
• Explain how muscles can pull but not push bones.
• Be able to make a simple diagram of a muscle fiber, a myofibril, and a sarcomere.
• Make a simple drawing showing the arrangement of myosin and actin in a myofibril.
• Understand the sliding-filament model of muscle contraction.
• Describe the specific action of myosin in muscle contraction.
• Describe the specific action of actin in muscle contraction.
• Explain the role of ATP in muscle contraction.
• Define motor unit and name approximate numbers of muscle fibers for sample motor units.
• Define muscle tension.
• Define muscle fatigue.
• Explain the disease process called muscular dystrophy.
• Describe the effects of Clostridium tetani on skeletal muscle.
Key Terms
endoskeleton joint sarcomere
exoskeleton ligament tendon
hydrostatic skeleton red marrow muscle fatigue
intervertebral disk sprain motor unit
vertebrae spongy bone muscle tension
arthritis synovial joint muscle twitch
cartilaginous joint yellow marrow sarcoplasmic reticulum
compact bone actin sliding-filament model
dislocation myofibrils muscle fatigue
fibrous joint myosin
Lecture Outline
20.1 Impacts/Issues: Bulking up Muscles
A. Muscles become larger by adding more protein to existing cells.
1. Muscle cells in adults do not divide (like neurons).
2. Exercise favors synthesis of more proteins in muscles.
3. The regulatory protein myostatin slows production of muscle protein.
4. Muscles become excessively large and bulky in individuals lacking myostatin.
5. Myostatin blockers may be useful in treating muscle wasting diseases.
6. Myostatin-blockers are being sold in nutritional supplements to body builders and
athletes.
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3. 20.2 The Skeletal System
A. Types of skeletons
1. Hydrostatic skeletons
a. fluid-filled, internal chambers
b. found in soft bodied organisms such as earthworms
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4. 2. Exoskeletons
a. shell, cuticle, or other hard external body part
b. insects such as flies exert internal muscles against inside of exoskeleton
3. Endoskeleton
a. internal framework of hardened elements to which muscles attach
b. seen in all vertebrates including humans
B. The human skeleton
1. The skull consists of flattened cranial bones and facial bones.
2. The vertebral column consists of 23 vertebrae and intervertebral disks made of
cartilage.
3. The rib cage attaches to the vertebral column and wraps around in front to connect to
the sternum (forms a protective cage around the heart and lungs).
4. The pectoral girdle consists of the scapula and clavicle.
5. The upper limb bones are the humerus, radius, ulna, and hand and finger bones.
6. The pelvic girdle consists of six fused bones, three on each side.
7. The lower limb bones are the femur, fibula, tibia, and ankle foot and toe bones.
C. Bone structure and function
1. Bones maintain posture and change the orientation of the body and parts.
2. They surround and protect vital organs.
3. They are sites for blood cell formation.
4. They are reservoirs for calcium and phosphorus ions.
5. Compact bone
a. Weight bearing parts of bones are compact.
b. Thin, concentric layers of calcium matrix surround canals for blood and nerves.
6. Spongy bone
a. Internal shaft and bone ends are spongy (have internal spaces).
b. Red marrow in spongy bone is site of blood cell formation.
c. Yellow marrow is mostly fat cells, but can convert to red marrow (located in
hollow cavity in large bones).
7. Calcium and phosphorus deposition and removal
a. Calcium and phosphorus ions are continually being removed from and deposited
into bones.
b. Calcium ions participate in nerve and muscle cell actions.
c. Until about age 24, more bone is deposited than removed.
d. After age 24, deposition slows.
e. Osteoporosis is a condition in which bone loss outpaces bone formation.
f. Dietary intake of vitamin D and calcium are important in maintaining bone
density.
D. Where bones meet – skeletal joints
1. Fibrous joints – connective tissue holds bones tightly in place.
a. cranial and facial bones
2. Cartilaginous joints – disks or pads provide a flexible connection.
a. vertebrae
b. ribs
3. Synovial joints – fluid filled space contains bone ends that are coated in connective
tissue.
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5. a. hip, knee, shoulder, elbow, wrist
4. Joint injuries
a. Sprains occur when ligaments overstretch or tear.
b. Torn ligaments (such as cruciate) may require surgery.
c. Dislocations occur when bone ends move out of place.
d. Arthritis is the chronic inflammation of a joint.
e. Osteoarthritis results from the wearing down of joints.
f. Rheumatoid arthritis occurs because the immune system attacks the joints.
20.3 How Bones and Muscles Interact
A. Bones and skeletal muscles interact to provide movement.
1. Tendons that attach muscles to bones are extensions of the fibrous connective tissue
that envelopes entire muscles.
2. Muscles connect to bones near a fixed point.
3. The bicep and tricep muscles pull the forearm in opposite directions, relative to the
humerus.
4. Muscles work in opposing pairs to move a bone or joint.
5. Cardiac muscle is present only in the heart, and smooth muscle in internal organs.
20.4 Skeletal Muscles Structure and Function
A. Skeletal muscles consist of many muscle fibers (muscle cells).
B. Muscle fibers consist of many myofibrils.
C. Myofibrils consist of sarcomeres.
1. Sarcomeres are basic units of contraction.
a. Actin (thin filament) and myosin (thick filament) are arranged in sections that allow
movement and shortening.
2. Muscle bundles, muscle fibers, myofibrils, and thin and thick filaments are all
arranged in the same parallel orientation.
D. How a muscle contracts
1. Actin and myosin filaments are close, but not interacting in the resting state.
2. ATP binds to a myosin head and allows it to bend and bind to a neighboring actin
filament.
3. Once actin and myosin are bound together, the myosin head tilts toward the center of
the sarcomere, and causes the actin to slide toward the center.
4. ADP and phosphate are now released.
5. New ATP is formed, and the myosin head releases from the actin and attaches to a
new binding site.
6. The process repeats itself.
E. Getting energy for contraction
1. ATP is the first energy source muscles use; it lasts only a few seconds.
2. Creatine phosphate store allows more ATP production that lasts another 5 to 10
seconds.
3. Aerobic respiration now kicks in and produces ATP which produces the needed
energy for about another five to ten minutes of activity.
4. Next, glucose and fatty acids break down to provide energy.
5. Lastly, fatty acids provide the needed energy.
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6. 6. Lactate production increases with exercise but does not yield much ATP.
20.5 Properties of Whole Muscles
A. Muscle tension
1. A motor neuron and the muscle fiber it controls is called a motor unit.
2. Brief stimulation causes contraction and relaxation called a twitch.
3. Continuous stimulation causes a sustained contraction.
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7. 4. The number of muscle fibers controlled by a neuron varies.
a. Small, fine movements require a small ratio of neurons to muscle fibers (1:5 in the
eye).
b. Larger muscles have as many as 700 muscle fibers per motor unit.
5. Muscle tension is the mechanical force exerted by a muscle on an object.
6. When muscle tension exceeds an opposing force, a stimulated muscle shortens.
7. Isometrically contracting muscles develop tension but cannot shorten.
8. Isotonically contracting muscles shorten and move a load.
9. Muscle fatigue is a decrease in the muscle’s ability to generate force.
10. Muscles begin to shrink with age.
a. The number of muscle fibers declines.
b. Existing muscle fibers respond more slowly to exercise.
B. Impaired muscle contraction
1. Muscular dystrophies are genetic diseases in which skeletal muscles progressively
weaken.
a. Duchenne’s muscular dystrophy is a sex-linked trait and is expressed more often in
males.
2. Some muscle disorders occur because neurons cannot signal muscles to contract.
a. Poliovirus infects and kills motor neurons.
b. Poliovirus has been essentially eradicated in the United States.
3. Clostridium tetani is a common soil bacteria that causes motor neurons to continuously
contract, producing tetanus.
a. Afflicted individuals die when breathing muscles become locked.
4. Amyotrophic lateral sclerosis (ALS) kills motor neurons.
20.6 Impacts/Issues Revisited: Bulking Up Muscles
A. Drugs that inhibit myostatin may help with muscle disorders.
B. Research on mice has been encouraging.
C. A drawback to the research has been a finding of very small, stiff, and easily torn tendons.
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