BI SC 004
Human Body:
Form and Function
STUDY GUIDE
The Muscular System
Dr. Martha Aynardi
aynardi@psu.edu
The Muscular System
Chapter Learning Objectives
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Upon completion of this chapter, you should be able to:
◦ Recall definitions of the following terms: neuromuscular junction,
acetylcholine, motor unit, and motor end plate.
◦ Compare the general characteristics of smooth, cardiac, and skeletal
muscle.
◦ Describe the functions of skeletal muscle.
◦ Describe the organization (both gross anatomy and microanatomy) of
skeletal muscle. Key terms to be familiar with: skeletal muscle, muscle
fiber, sarcolemma, sarcoplasmic reticulum, T-tubule, myofibril,
sarcomere, myosin, actin, thin filaments, thick filaments, Z-line,
troponin, and tropomyosin.
◦ Recall the sequence of events that bring about skeletal muscle
contraction from beginning to end.
◦ Define and recall the cause of the following diseases and conditions of
the muscular system: hernia, cramp, muscular dystrophy, tetanus, rigor
mortis.
The Muscular System
`
Recall definitions of the following terms: neuromuscular junction,
acetylcholine, motor unit, and motor endplate (pg. 190 & 197).
◦ Neuromuscular junction is the point of synapse between a motor
neuron and a muscle fiber.
◦ Acetylcholine (ACh) is a neurotransmitter released by some motor
neurons to communicate with other cells.
◦ Motor unit is a single motor neuron and all the muscle fibers it
innervates (controls).
◦ Motor endplate is the region of the sarcolemma of the muscle fiber that
lies beneath the synaptic knob of the motor neuron & contains
receptors for neurotransmitter.
`
Compare the general characteristics of smooth, cardiac, and skeletal
muscle (pg. 107-109).
Cells are long, cyndrical, striated, and multinucleate. Locations: Combined with connective tissues and neural tissue in skeletal muscles. Functions: Moves or stabilizes the position of the skeleton; guards entrances and exits to the digestive, respiratory, and urinary tracts; generates heat; protects internal organs. Cells are short, branched, and striated, usually with a single nucleus; cells are interconnected by intercalated discs. Location: Heart Functions: Circulates blood; maintains blood (hydrostatic) pressure. Cells are short, spindle‐shaped, and nonstriated, with a single, central nucleus. Locations: Found in the walls of blood vessels and in digestive, respiratory, urinary, and reproductive organs. Functions: Moves food, urine, and reproductive tract secretions; controls diameter of respiratory passageways, regulates diameter of blood vessels. `
Describe the functions of skeletal muscle (pg. 186).
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Produce movement of the skeleton.
•
Support soft issues.
•
Guard entrances and exits.
•
•
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Maintain posture and body position.
Maintain body temperature.
Describe the organization (both gross anatomy and microanatomy) of
skeletal muscle. Key terms to be familiar with: skeletal muscle, muscle
fiber, sarcolemma, sarcoplasmic reticulum, T-tubule, myofibrils,
sarcomere, myosin, actin, thin filaments, thick filaments, Z-line, troponin,
and tropomyosin (pg. 187).
FIGURE 7-1 The Organization of a Skeletal Muscle.
`
Recall the sequence of events that bring about skeletal muscle contraction
from beginning to end (pg. 190-194).
Steps That Start a Contraction
1. At the neuromuscular junction,
Acetylcholine (ACh), released by the
synaptic terminal, binds to receptors on the
sarcolemma.
2. The resulting change in the membrane
potential of the muscle fiber leads to the
production of an action potential that
spreads across the entire surface of the
muscle fiber and along the T tubules.
3. The sarcoplasmic reticulum (SR) releases
stored calcium ions, increasing the calcium
concentration of the sarcoplasm in and
around the sarcomeres.
4. Calcium ions bind to troponin, resulting in
the movement of tropomyosin and the
exposure of active sites on the thin (actin)
filaments. Cross-bridges form when
myosin heads bind to active sites.
5. The contraction begins as repeated cycles
of cross-bridge binding, pivoting, and
detachment occurs, powered by the
breakdown of ATP. These events produce
filament sliding, and the muscle fiber
shortens.
Steps That End a Contraction
6. Action potential generation ceases as Ach is
broken down by acetylcholinesterase
(AChE).
7. The SR reabsorbs calcium ions, and the
concentration of calcium ions in the
sarcoplasm declines.
8. When calcium ion concentrations approach
normal resting levels, the troponin and
tropomyosin molecules return to their
normal positions. This change re-covers
the active sites and prevents further
cross-bridge interaction.
9. Without cross-bridge interactions, further
sliding cannot take place and the
contraction will end.
10. Muscle relaxation occurs, and the muscle
returns passively to its resting length.
`
Define and recall the cause of the following diseases and conditions of the
muscular system: hernia, cramp, muscular dystrophy, tetanus, rigor mortis
(pg. 229).
◦
Hernia is a condition that results from weakness in abdominal muscles
that leads to protrusion of an abdominal organ through an opening in
the abdominal wall.
◦
A cramp is a prolonged, involuntary, painful muscular contraction(s).
◦
Muscular dystrophy is an inherited disease that produces progressive
muscle weakness and deterioration.
◦
Tetanus is a disease caused by a bacterial toxin that results in
sustained, powerful contractions of skeletal muscles throughout the
body.
◦
Rigor mortis is a state following death during which muscles are locked
in the contracted position, making the body extremely stiff.
Key Terms
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Neuromuscular junction
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Acetylcholine
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Motor unit
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Motor end plate
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Skeletal muscle
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Skeletal muscle
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Muscle fiber
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Sarcolemma
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Sarcoplasmic reticulum
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T-tubule
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Myofibrils
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Sarcomere
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Myosin
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Actin
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Thin filaments
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Thick filaments
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Z-line
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Troponin
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Tropomyosin
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Hernia
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Cramp
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Muscular dystrophy
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Tetanus
Rigor mortis
Chapter Review Questions
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Can you answer the following questions?
◦
Can you define following terms? Neuromuscular junction,
acetylcholine, motor unit, and motor end plate.
◦
What are the general characteristics of smooth, cardiac, and skeletal
muscles?
◦
What are the functions of skeletal muscle?
◦
Can you describe the organization (both gross anatomy and
microanatomy) of skeletal muscle?
x
Are you familiar with the following terms? Skeletal muscle, muscle
fiber, sarcolemma, sarcoplasmic reticulum, T-tubule, myofibrils,
sarcomere, myosin, actin, thin filaments, thick filaments, Z-line,
troponin, and tropomyosin.
◦
What is the sequence of events that bring about skeletal muscle
contraction from beginning to end?
◦
Can you define and recall the causes of the following diseases and
conditions of the muscular system? Hernia, cramp, muscular
dystrophy, tetanus, rigor mortis.
Questions to consider when studying for the exam
` How does structure relate to function?
` Are you able to recognize examples and apply knowledge?
` Do you know the sequential steps of any mechanisms discussed?