BIOLOGY II: Chapter 9: Muscular System
READING OUTLINE:
NAME_______________________
I. Structure of a Skeletal Muscle
A. Introduction
1. A___________________________is an organ of the skeletal system.
2. A skeletal muscle is composed of_______________________________________________________
B. Connective Tissue Coverings
1. Fascia is ________________________________
2. A tendon is ______________________________
3. Tendons connect a muscle to ________________
4. An aponeurosis is _________________________
5. Epimysium is ____________________________
6. Perimysium is____________________________
7. A fascicle is _____________________________
8. Endomysium is___________________________
9. Subcutaneous fascia is _____________________
C. Skeletal Muscle Fibers
1. A skeletal muscle fiber is a single _________________ 8. Thin myofilaments are composed of_______________
2. The sarcolemma is _____________________________ 9. Myofilaments create the________________________
3. The sarcoplasm is _____________________________ 10. Sarcoplasmic reticulum is ______________________
4. The sarcoplasm contains ________________________ 11. Transverse tubules are _________________________
5. Myofibrils are _________________ _______________ 12. Cisternae are _________________________________
6. Myofibrils play a role in ________________________ 13. A triad is formed by____________________________
7. Thick myofilaments are composed of ______________

A MUSCLE FIBER
D. The Sarcomere
10. A sarcomere is ____________________________________________________________________
11. Myofibrils may be thought of as ________________________________________ joined end to end.
12. I bands are composed of _____________________________________________________________
13. Z lines are ________________________________________________________________________
14. A bands are composed of ____________________________________________________________
15. The H zone is _____________________________________________________________________
16. The M line is _____________________________________________________________________
17. Titin connects _____________________________________________________________________
18. A sarcomere extends from one ________________________________________________________
19. Each myosin molecule consists of _____________________________________________________
20. Thin filaments consist of double ______________________________________________________
21. Actin has a binding site to which ______________________________________________ can attach.
22. Troponin and tropomyosin associate with _______________________________________________
THE SARCOMERE

II. Skeletal Muscle Contraction
A. Neuromuscular Junction
1. Each skeletal muscle is functionally connected to __________________________________________
2. A motor neuron passes outward from ____________________________________________________
3. Normally, a skeletal muscle fiber contracts only upon _______________________________________
4. A neuromuscular junction is ___________________________________________________________
5. A motor end plate is _________________________________________________________________
6. A motor unit is _____________________________________________________________________
7. A synaptic cleft separates _____________________________________________________________
8. Synaptic vesicles store _______________________________________________________________
B. Stimulus for Contraction
1. _______________________is the neurotrasnmitter that motor neurons use to control skeletal muscle.
2. ACh is synthesized in the cytoplasm of _____________________and is stored in _________________
3. When a nerve impulse_____________________, acetylcholine is released into the synaptic cleft.
4. ACh combines with__________________on the motor end plate, and stimulates __________________
5. A muscle impulse is _________________________________________________________________
6. A muscle impulse changes ____________________________________________________________
7. Ultimately the muscle impulse reaches __________________________________________________
C. Excitation Contraction Coupling
1. The sarcoplasmic reticulum has a high concentration of _____________________________________
2. In response to a muscle impulse, the membranes______________ and the calcium _______________
3. When a muscle fiber is at rest______________ block the binding sites on the actin molecules.
4. Calcium ions bind to ____________________, changing its______________and altering __________
5. The movement of the tropomyosin molecule exposes _______________, allowing ________________

THE SLIDING FILAMENT MODEL
D. The Sliding Filament Model of Muscle Contraction
1. The functional unit of skeletal muscles is_________________________________________________
2. According to the sliding filament model, when sarcomeres shorten, ____________________________
3. As contraction occurs, ________________ and __________________________________ get narrower
and move closer together.
E. Cross-bridge Cycling
1. The force that shortens the sarcomeres comes from _________________________________________
2. A myosin cross-bridge attaches to actin in order to _________________________________________
3. The cross-bridge can release, straighten, and combine with __________________________________
4. Myosin cross-bridges contain the enzyme ________________________________________________
5. ATPase catalyzes ___________________________________________________________________
6. The force for muscle contraction is provided by ___________________________________________
7. Breaking down of ATP puts the myosin cross-bridge in a _____________________________ position.
8. When a muscle is stimulated to contract, a_______attaches to_________ and pulls _______________ , shortening the ________________________________________________________________________
9. When another ATP binds, the________________is released,_____________then breaks down the
____________________to return to _________________________________________________
10. The cross-bridge cycle may repeat over and over as long as _________________________________
F. Relaxation
1. In order for a muscle fiber to relax, acetylcholine must be decomposed by an enzyme called ________
2. The action of acetycholinesterase prevents _______________________________________________
3. When acetylcholine is breaks down,______________ceases.
4. The calcium pump moves calcium________________________________________
5. When calcium is removed from the cytoplasm, the_____________break and rolls back into its groove, preventing ____________________________
6. ATP is necessary for both muscle________________________ and ___________________________
7. The trigger for contraction is __________________________________________________________
G. Energy Sources for Contraction
1. Creatine phosphate is ________________________________________________________________
2. Creatine phosphate includes ___________________________________________________________
3. As ATP is decomposed to ADP, the energy from________is transferred back to __________________
4. After creatine phosphate is used, a muscle cell must depend on_____________to synthesize ________
5. Typically a muscle stores glucose in the form of ___________________________________________

H. Oxygen Supply and Cellular Respiration
1. Glycolysis occurs _______________________ and is ______________________________________
2. Glycolysis releases a few _____________________________________________________________
3. The complete break down of glucose occurs in _________________and requires _________________
4. The citric acid cycle and electron transport chain produce____________________________________
5. Oxygen is carried in the blood stream bound to ____________________________________________
6. Myoglobin is ________________________________________________________________ in color.
7. Myoglobin stores ______________________________________________________ in muscle tissue.
I. Oxygen Debt
1. Lactic acid threshold is _______________________________________________________________
2. Under anaerobic conditions, glycolysis breaks down glucose into_______________________________
3. Lactic acid is carried by the blood to the _________________________________________________
4. Liver cells can convert lactic acid to ____________________________________________________
5. Oxygen debt reflects _________________________________________________________________
J. Muscle Fatigue
1. Fatigue is _________________________________________________________________________
2. Fatigue may result from ______________________________________________________________
3. A cramp is ________________________________________________________________________
4. The strenuous exercise of aerobic training ________________________________________________
K. Heat Production
1. Heat is a by-product of _______________________________________________________________
2. Blood transports heat____________________which helps ___________________________________
III. Muscle Responses
A. Introduction
1. One way to observe muscle contraction is t _______________________________________________
2. An _________________________________is usually used to produce muscle contraction.
B. Threshold Stimulus
1. Threshold stimulus is ________________________________________________________________
C. Recording a Muscle Contraction
1. A twitch is ________________________________________________________________________
2. A myogram is ______________________________________________________________________
3. Three periods of a muscle fiber contraction are ____________________________________________
4. During the period of contraction, a muscle fiber is _________________________________________
5. The latent period is __________________________________________________________________
6. The period of relaxation is ____________________________________________________________
7. The refractory period is ______________________________________________________________
8. An all-or-none response is ____________________________________________________________
9. The length to which a muscle is stretched before stimulation affects ___________________________
D. Summation
1. Twitches in a muscle can combine to become _____________________________________________
2. Summation is ______________________________________________________________________
3. Tetanic contractions are ______________________________________________________________
E. Recruitment of Motor Units
1. The _______________ in the motor units, __ ______ ____the movements can be produced in a muscle.
2. All muscle fibers in a motor unit are stimulated at ______________________________________ time.
3. Multiple motor unit summation is ______________________________________________________
4. Recruitment is _____________________________________________________________________
5. As the intensity of stimulation increases, recruitment continues until all motor units are activated in a muscle.
F. Sustained Contractions

1. During sustained contractions, _________________________________________ are recruited earlier.
2. The larger motor units respond _________________________________________________________
3. Muscle movements are smooth because __________________________________________________
4. Muscle tone is ______________________________________________________________________
5. Muscle tone is important for maintaining _________________________________________________
G. Types of Contractions
1. An isotonic contraction is _____________________________________________________________
2. A concentric contraction is ____________________________________________________________
3. An eccentric contraction is ____________________________________________________________
4. An isometric contraction is ____________________________________________________________
5. An example of an isometric contraction is ________________________________________________
6. An example of an isotonic contraction is _________________________________________________
H. Fast and Slow Twitch Muscle Fibers
1. Type I fibers are ____________________________________________________________________
2. Examples of type I fibers are __________________________________________________________
3. Type I fibers are _________________ in color because _____________________________________
4. Type I fibers are resistant to ___________________________________________________________
5. Type IIa fibers are __________________________________________________________________
6. Type IIa fibers are ________________ in color because _____________________________________
7. Type IIb fibers are __________________________________________________________________
8. All muscles include ______________________________________________________ of fiber types.
IV. Smooth Muscles
A. Smooth Muscle Fibers
1. Compared to skeletal muscle fibers, smooth muscle fibers ___________________________________
2. Two major types of smooth muscle are __________________________________________________
3. Multiunit smooth muscle is located _____________________________________________________
4. Visceral smooth muscle is located ______________________________________________________
5. Fibers of visceral smooth muscle are connected by _________________________________________
6. Rhythmicity is _____________________________________________________________________
7. Peristalsis is _______________________________________________________________________
8. Peristalsis helps force ________________________________________________________________
B. Smooth Muscle Contraction
1. Compared to skeletal muscle fibers, smooth muscle fibers lack_______________
2. Two neurotransmitters that affect smooth muscle are _______________________________________
3. Hormones affect smooth muscle by _____________________________________________________
4. Stretching of smooth muscle can trigger _________________________________________________
5. Smooth muscle is slower to_________________ and_______________________than skeletal muscle.
6. Unlike skeletal muscle, smooth muscle fibers can change length without changing __________________
V. Cardiac Muscle
A. Cardiac muscle appears only in _______________________________________________________________
B. Cardiac muscle is composed of______________cells, forming fibers that are ___________________________
C. Cardiac muscle fibers can contract________________________________________ then skeletal muscle fibers.
D. Intercalated discs are _______________________________________________________________________
E. Intercalated discs allow muscle impulses to ______________________________________________________
F. A syncytium is ____________________________________________________________________________
VI. Skeletal Muscle Actions
A. Introduction
1. Skeletal muscles generate ____________________________________________________________
2. The action of each muscle mostly depends upon ___________________________________________

B. Body Movement
1. Bones and muscles interact as _________________________________________________________
2. The four basic components of a lever system are ___________________________________________
C. Origin and Insertion
1. The origin of a muscle is _____________________________________________________________
2. The insertion of a muscle is ___________________________________________________________
3. When a muscle contracts, its ___________________________________________ is pulled toward its
4. The head of a muscle is ______________________________________________________________
5. The origins of the biceps brachii are ____________________________________________________
6. The insertion of the bicep brachii is _____________________________________________________
7. When the biceps brachii contracts, the ______________________________________________ bends.
D. Interaction of Skeletal Muscles
1. A prime mover is ___________________________________________________________________
2. A synergist is ______________________________________________________________________
3. An antagonist is ____________________________________________________________________
VII. Major Skeletal Muscles
A. Introduction
1. The name of a muscle may reflect ______________________________________________________
2. An example of a muscle named for it size is ______________________________________________
3. An example of a muscle named for its shape is ____________________________________________
4. An example of a muscle named for its function is __________________________________________
5. An example of a muscle named for its number of origins is __________________________________
6. An example of a muscle named for its attachments site is ____________________________________
7. An example of a muscle named of the direction of its muscle fibers is __________________________
B. Muscles of Facial Expression
1. As a group, muscles of facial expression connect __________________________________________
2. Identify the following muscles.
Frontalis
Orbicularis oculi
Orbicularis oris
Buccinator
Zygomaticus
Platysma
C. Muscles of Mastication
1. Muscles of mastication produce_______________________movements.
2. Identify the following muscles.
Masseter Temporalis

D. Muscles That Move the Head, Vertebral Column and Pectoral Girdle
1. Identify the following muscles.
Sternocleidomastoid
Erector spinae
Trapezius
Rhomboideus major
Serratus anterior
Pectoralis major
E. Muscles That Move the Arm
1. Identify the following muscles.
Pectoralis major
Teres major
F. Muscles of the Abdominal Wall
1. Identify the following muscles.
External oblique
Internal oblique
Latissimus dorsi
Deltoid
Transversus abdominis
Rectus abdominis
G. Muscles That Move the Forearm
1. Identify the following muscles.
Biceps brachii
Brachialis
Triceps brachii
Supinator
Brachioradialis Pronator teres
H. Muscles That Move the Hand* (you should recognize these, but not identify location)
1. Identify the following muscles.
Flexor carpi radialis longus
Flexor carpi ulnaris
Palmaris longus
Extensor carpi radialis brevic
Extensor carpi ulnaris
Extensor digitorum

I. Muscles That Move the Thigh
1. Identify the following muscles.
Psoas major
Gluteus maximus
J. Muscles That Move the Leg
1. Identify the following muscles.
Biceps femoris
Semitendinosus
Adductor magnus
Gracilis
Sartorius
Quadriceps femoris group
K. Muscle That Move the Foot
1. Identify the following muscles.
Tibialis anterior
VIII. Life-Span Changes
Fibularis longus
Extensor digitorum
Gastrocnemius
A. Signs of aging of the muscular system begin to appear _____________________________________________
B. At a microscopic level, ________________________________________________________________ decline.
C. being to replace some muscle tissue.
D. can help maintain a healthy muscular system
E. According to the National Institute on Aging, exercise should include _________________________________

ANSWER KEY Chapter 9: Muscular System
I. Structure of a Skeletal Muscle
A. Introduction
1. A skeletal muscle is an organ of the muscular system.
2. A skeletal muscle is composed of skeletal muscle tissue, nervous tissue, blood, and connective tissues.
B. Connective Tissue Coverings
1. Fascia is dense connective tissue that separates individual skeletal muscles.
2. A tendon is a cordlike structure that consists of dense connective tissue.
3. Tendons connect a muscle to a bone.
4. An aponeurosis is a sheetlike structure composed of dense connective tissue.
5. Epimysium is a layer of connective tissue that closely surrounds a skeletal muscle.
6. Perimysium is connective tissue that separates muscles into fascicles.
7. A fascicle is a section of a muscle.
8. Endomysium is connective tissue that surrounds individual muscle cells.
9. Deep fascia is fascia that surrounds or penetrates muscles.
10. Subcutaneous fascia is fascia just beneath the skin.
11. Subserous fascia is connective tissue layer of the serous membranes covering organs in various body cavities and lining those cavities.
C. Skeletal Muscle Fibers
1. A skeletal muscle fiber is a single muscle cell.
2. The sarcolemma is the cell membrane of a muscle cell.
3. The sarcoplasm is the cytoplasm of a muscle cell.
4. The sarcoplasm contains many small nuclei, mitochondria and myofibrils.
5. Myofibrils are threadlike structures and are located in the sarcoplasm.
6. Myofibrils play a fundamental role in the muscle contraction mechanism.
7. Thick myofilaments are composed of myosin.
8. Thin myofilaments are composed of actin.
9. The organization of myofilaments produces the alternating light and dark striation characteristic of skeletal muscles.
10. A sarcomere is a repeating pattern of a myofibril.
11. Myofibrils may be thought of as sarcomeres joined end to end.
12. I bands are composed of thin actin filaments.
13. Z lines are structures that connect that anchor I bands.
14. A bands are composed of thick myosin filaments overlapping thin actin filaments.
15. The H zone is a central region of an A band that only contains thick filaments.
16. The M line is a region of an A band which consists of proteins that help hold the thick filaments in place.
17. Titin connects proteins that connect myosin filaments to Z lines.
18. A sarcomere extends from one Z line to another Z line.
19. Each myosin molecule consists of two twisted protein strands with globular parts called crossbridges that project outward along their lengths.
20. Thin filaments consist of double strands of actin twisted into a helix.
21. Actin has a binding site to which the cross-bridges of a myosin molecule can attach.
22. Troponin and tropomyosin associate with actin filaments.
23. Sarcoplasmic reticulum is endoplasmic reticulum of a muscle fiber.
24. Transverse tubules are membranous channels that extend into the sarcoplasm as invaginations continuous with the sarcolemma and contain extracellular fluid.
25. Cisternae are enlarged portions of sarcoplasmic reticulum.
26. A triad is formed by one transverse tubule and two cisternae.
II. Skeletal Muscle Contraction
A. Neuromuscular Junction
1. Each skeletal muscle is functionally connected to an axon of a motor neuron.
2. A motor neuron passes outward from brain or spinal cord.
3. Normally, a skeletal muscle fiber contracts only upon stimulation by a motor neuron.
4. A neuromuscular junction is the site where an axon and muscle fiber meet.
5. A motor end plate is a specialized portion of the muscle cell membrane that is extensively folded.
6. A motor unit is a motor neuron and the muscle fibers it controls.
7. A synaptic cleft separates the membranes of the neuron and the membrane of the muscle fiber.

8. Synaptic vesicles store neurotransmitters.
B. Stimulus for Contraction
1. Acetylcholine is the neurotrasnmitter that motor neurons use to control skeletal muscle.
2. ACh is synthesized in the cytoplasm of the motor neuron and is stored in synaptic vesicles in axons.
3. When a nerve impulse reaches the end of an axon, acetylcholine is released into the synaptic cleft.
4. ACh combines with ACh receptors on the motor end plate, and stimulates the muscle fiber.
5. A muscle impulse is an electrical signal that is like a nerve impulse.
6. A muscle impulse changes the muscle cell membrane in a way that transmits the impulse in all directions along and around the muscle cell.
7. Ultimately the muscle impulse reaches the sarcoplasmic reticulum and cisternae.
C. Excitation Contraction Coupling
1. The sarcoplasmic reticulum has a high concentration of calcium.
2. In response to a muscle impulse, the membranes become more permeable to calcium, and the calcium diffuses out of the cisternae into the cytosol of the muscle fiber.
3. When a muscle fiber is at rest, the troponin-tropomyosin complexes block the binding sites on the actin molecules.
4. Calcium ions bind to troponin, changing its shape and altering the position of the tropomyosin.
5. The movement of the tropomyosin molecule exposes the binding sites of the actin filaments, allowing linkages to form between myosin cross-bridges and actin.
D. The Sliding Filament Model of Muscle Contraction
1. The functional unit of skeletal muscles is the sarcomere.
2. According to the sliding filament model, when sarcomeres shorten, the thick and thin filaments slide past one another.
3. As contraction occurs, the H zones and the I bands get narrower and the Z lines move closer together.
E. Cross-bridge Cycling
1. The force that shortens the sarcomeres comes from cross-bridges pulling on the actin filaments.
2. A myosin cross-bridge attaches to actin in order to pull on the actin filament.
3. The cross-bridge can release, straighten, and combine with another binding site further down the actin filament, and pull again.
4. Myosin cross-bridges contain the enzyme ATPase.
5. ATPase catalyzes the breakdown of ATP to ADP.
6. The force for muscle contraction is provided by the breakdown of ATP into ADP.
7. Breaking down of ATP puts the myosin cross-bridge in a “cocked” position.
8. When a muscle is stimulated to contract, a cocked cross-bridge attaches to actin and pulls the actin filament toward the center of the sarcomere, shortening the muscle.
9. When another ATP binds, the cross-bridge is released, and then breaks down the ATP to return to the cocked position.
10. The cross-bridge cycle may repeat over and over as long as ATP is present and nerve impulses cause
ACh release at the neuromuscular junction.
F. Relaxation
1. In order for a muscle fiber to relax, acetylcholine must be decomposed by an enzyme called acetylcholinesterase.
2. The action of acetycholinesterase prevents a single nerve impulse from continuously stimulating a muscle fiber.
3. When acetylcholine breaks down, the stimulus to the sarcolemma and the membranes within the muscle fiber ceases.
4. The calcium pump moves calcium back into the sarcoplasmic reticulum.
5. When calcium is removed from the cytoplasm, the cross-bridge linkages break and tropomyosin rolls back into its groove, preventing any cross-bridge attachment.
6. ATP is necessary for both muscle contraction and relaxation.
7. The trigger for contraction is the increase in cytosolic calcium in response to stimulation by ACh from a motor neuron.
G. Energy Sources for Contraction
1. Creatine phosphate is an energy source available to generate ATP from ADP.
2. Creatine phosphate includes a high energy phosphate bond.
3. As ATP is decomposed to ADP, the energy from creatine phosphate is transferred back to ADP to produce ATP.

4. After creatine phosphate is used, a muscle cell must depend on cellular respiration of glucose to synthesize ATP.
5. Typically a muscle stores glucose in the form of glycogen.
H. Oxygen Supply and Cellular Respiration
1. Glycolysis occurs in the cytoplasm and is anaerobic.
2. Glycolysis releases a few ATP molecules.
3. The complete break down of glucose occurs in mitochondria and requires oxygen.
4. The citric acid cycle and electron transport chain produce water, carbon dioxide and a large amount of
ATP.
5. Oxygen is carried in the blood stream bound to hemoglobin.
6. Myoglobin is red in color.
7. Myoglobin stores oxygen in muscle tissue.
I. Oxygen Debt
1. Lactic acid threshold is the shift in cellular metabolism from breaking down pyruvic acid into carbon dioxide to pyruvic acid breakdown leading to lactic acid formation.
2. Under anaerobic conditions, glycolysis breaks down glucose into pyruvic acid and converts it to lactic acid.
3. Lactic acid is carried by the blood to the liver.
4. Liver cells can convert lactic acid to glucose.
5. Oxygen debt reflects the amount of oxygen liver cells require to use the accumulated lactic acid to produce glucose, plus the amount the muscle cells require to resynthesized ATP and creatine phosphate, and restore their original concentrations.
J. Muscle Fatigue
1. Fatigue is the condition in which a muscle fiber cannot contract.
2. Fatigue may result from decreased blood flow, ion imbalances across the sarcolemma, and the psychological loss of the desire to continue to exercise.
3. A cramp is a sustained, painful, involuntary muscle contraction.
4. The strenuous exercise of aerobic training stimulated new capillaries to grow within the muscles, supplying more oxygen and nutrients.
K. Heat Production
1. Heat is a by-product of cellular respiration.
2. Blood transports heat throughout the body, which helps to maintain body temperature.
III. Muscle Responses
A. Introduction
1. One way to observe muscle contraction is to remove a single muscle fiber from a skeletal muscle and connect it to a device that measures contraction.
2. An electrical impulse is usually used to produce muscle contraction.
B. Threshold Stimulus
1. Threshold stimulus is the minimal stimulus needed to start a muscle contraction.
2. An impulse in a motor neuron normally releases enough ACh to bring the muscle fibers in its motor unit to threshold.
C. Recording a Muscle Contraction
1. A twitch is the response of a single muscle fiber to the ACh released by a single action potential.
2. A myogram is a recording of the events of a muscle twitch.
3. Three periods of a muscle fiber contraction are latent, contraction, and relaxation.
4. During the period of contraction, a muscle fiber is generating force or contracting.
5. The latent period is the period before contraction.
6. The period of relaxation is the period in which a muscle fiber is decreasing tension.
7. The refractory period is the brief moment when a muscle fiber remains unresponsive to stimulation.
8. An all-or-none response is one in which a muscle fiber contracts completely or not at all.
9. The length to which a muscle is stretched before stimulation affects the force it will develop when stimulated.
10. If a muscle is stretched well beyond its normal resting length, the force will decrease.
11. At very short muscle lengths, the sarcomere becomes compressed and shortening is not possible.
12. In the whole muscle, the degree of tension reflects the frequency at which individual fibers are stimulated and how many fibers take part in the overall contraction of the muscle.
D. Summation
1. Twitches in a muscle can combine to become sustained.

2. Summation is the combination of the force of individual twitches.
3. Tetanic contractions are contractions that lack relaxation.
E. Recruitment of Motor Units
1. The fewer muscle fibers in the motor units, the more precise the movements can be produced in a particular muscle.
2. All muscle fibers in a motor unit are stimulated at the same time.
3. Multiple motor unit summation is recruitment.
4. Recruitment is an increase in the number of activated motor units.
5. As the intensity of stimulation increases, recruitment continues until all possible motor units are activated in a muscle.
F. Sustained Contractions
1. During sustained contractions, smaller motor units are recruited earlier.
2. The larger motor units respond later and more forcefully.
3. Muscle movements are smooth because the spinal cord stimulates contraction in different sets of motor units at different times.
4. Muscle tone is the amount of sustained contractions in a muscle.
5. Muscle tone is important for maintaining posture.
G. Types of Contractions
1. An isotonic contraction is a type of contraction that produces movement of a body part.
2. A concentric contraction is an isotonic contraction in which shortening of the muscle occurs.
3. An eccentric contraction is an isotonic contraction in which lengthening of the muscle occurs.
4. An isometric contraction is a contraction in which muscle tension increases but no movements of body parts are produced.
5. An example of an isometric contraction is standing.
6. An example of an isotonic contraction is walking.
H. Fast and Slow Twitch Muscle Fibers
1. Type I fibers are slow-twitch fibers.
2. Examples of type I fibers are those in the long muscles of the back.
3. Type I fibers are red in color because they contain a relatively large amount of myoglobin.
4. Type I fibers are resistant to fatigue.
5. Type IIa fibers are fast twitch glycolytic fibers.
6. Type IIa fibers are white in color because they contain relatively small amounts of myoglobin.
7. Type IIb fibers are fast twitch oxidative fibers.
8. All muscles include a combination of fiber types.
IV. Smooth Muscles
A. Smooth Muscle Fibers
1. Compared to skeletal muscle fibers, smooth muscle fibers are shorter and they have single nuclei.
2. Two major types of smooth muscle are visceral and multiunit.
3. Multiunit smooth muscle is located in the irises and the walls of blood vessels.
4. Visceral smooth muscle is located in the walls of hollow organs except for the heart.
5. Fibers of visceral smooth muscle are connected by gap junctions.
6. Rhythmicity is a pattern of spontaneous repeated contractions.
7. Peristalsis is a wavelike motion produced by smooth muscle contraction.
8. Peristalsis helps force the contents of a tube along its length.
B. Smooth Muscle Contraction
1. Compared to skeletal muscle fibers, smooth muscle fibers lack troponin and use calmodulin to bind calcium instead.
2. Two neurotransmitters that affect smooth muscle are acetylcholine and norepinephrine.
3. Hormones affect smooth muscle by stimulating or inhibiting contraction in some cases and lettering the degree of response to neurotransmitters in other cases.
4. Stretching of smooth muscle can trigger contractions.
5. Smooth muscle is slower to contract and relax than skeletal muscle.
6. Unlike skeletal muscle, smooth muscle fibers can change length without changing tautness.
V. Cardiac Muscle
A. Cardiac muscle appears only in the heart.
B. Cardiac muscle is composed of striated cells, forming fibers that are interconnected in branching, threedimensional networks.
C. Cardiac muscle fibers can contract longer than skeletal muscle fibers.

D. Intercalated discs are membrane junctions that join cardiac muscle fibers together.
E. Intercalated discs allow muscle impulses to travel rapidly from cell to cell.
F. A syncytium is a group of muscle fibers that contract as a unit.
VI. Skeletal Muscle Actions
A. Introduction
1. Skeletal muscles generate a great variety of body movements.
2. The action of each muscle mostly depends upon the kind of joint it is associated with and the way the muscle is attached on either side of that joint.
B. Body Movement
1. Bones and muscles interact as levers.
2. The four basic components of a lever system are rigid bar, fulcrum, object that is moved against resistance, and a force.
3. In scissors, the handle and blades form a rigid bar.
4. The fulcrum of scissors is the screw.
5. The resistance of scissors is the material to be cut.
6. The force of scissors is supplied by the person on the handles.
7. In a first-class lever system, the parts are arranged resistance, fulcrum, force.
8. Besides scissors, other examples of first class lever systems are seesaws and hemostats.
9. In a second-class lever system, the parts are arranged fulcrum, resistance, force.
10. An example of a second-class lever system is a wheelbarrow.
11. In a third class lever system, the parts are arranged resistance, force, and fulcrum.
12. An example of a third-class lever system is a pair of tweezers.
13. In the action of bending the upper limb at the elbow, the rigid bar is the forearm bones, the fulcrum is the elbow joint, the resistance is the hand, and the force is applied by muscles on the anterior side of the arm.
14. Bending the arm at the elbow is an example of a third-class lever system.
15. When the upper limb straightens at the elbow, the rigid bar is forearm bones, the pivot is the elbow, the resistance is the hand, and the force is applied by the triceps brachii muscle located on the posterior surface of the arm.
16. Straightening the arm at the elbow is a first class lever system because the parts of the lever are arranged resistance, fulcrum, force.
17. An example of a second-class lever system in the body is a movement produced at the temporomandibular joint (opening of the mouth)
C. Origin and Insertion
1. The origin of a muscle is the immovable end of the muscle.
2. The insertion of a muscle is the movable end of a muscle.
3. When a muscle contracts, its insertion is pulled toward its origin.
4. The head of a muscle is the part nearest its origin.
5. The origins of the biceps brachii are the attachment to the coracoid process of the scapula, and the attachment to a tubercle above the glenoid cavity of the scapula.
6. The insertion of the bicep brachii is the radial tuberosity of the radius.
7. When the biceps brachii contracts, the elbow bends.
D. Interaction of Skeletal Muscles
1. A prime mover is the muscle primarily responsible for producing an action.
2. A synergist is a muscle that assists the prime mover.
3. An antagonist is a muscle that resists the action of a prime mover.
VII. Major Skeletal Muscles
A. Introduction
1. The name of a muscle may reflect its size, shape, function, number of origins, attachment sites, or direction of its muscle fibers.
2. An example of a muscle named for it size is pectoralis major.
3. An example of a muscle named for its shape is deltoid.
4. An example of a muscle named for its function is extensor digitorum.
5. An example of a muscle named for its number of origins is biceps brachii.
6. An example of a muscle named for it attachments sites is sternocleidomastoid.
7. An example of a muscle named of the direction of its muscle fibers is external oblique.

B. Muscles of Facial Expression
1. As a group, muscles of facial expression connect the bones of the skull to connective tissue in region of the overlying skin.
C. Muscles of Mastication
1. Muscles of mastication produce chewing movements.
D. Muscles That Move the Head and Vertebral Column
E. Muscles That Move the Pectoral Girdle
F. Muscles That Move the Arm
G. Muscles That Move the Forearm
H. Muscles That Move the Hand
I. Muscles of the Abdominal Wall
K. Muscles That Move the Thigh
L. Muscles That Move the Leg
M. Muscle That Move the Foot
VIII. Life-Span Changes
A. Signs of aging of the muscular system begin to appear one’s forties.
B. At a microscopic level, myoglobin, ATP, and creatine phosphate decline.
C. Connective tissue and adipose tissue begin to replace some muscle tissue.
D. Exercise can help maintain a healthy muscular system
E. According to the National Institute on Aging, exercise should include strength training, aerobics, and stretching.