section 1, chapter 9 muscular system
DESCRIPTION
Muscular system chapter for anatomy & physiologyTRANSCRIPT
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Chapter 9, Section 1
Muscular System
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Muscle is derived from Musculus, for “Mouse”
Imagine a mouse running beneath the skin.
Functions of Muscles:
1. Body movement
2. Maintain posture
3. Produces heat
4. Propel substances
through body
5. Heartbeat
Types of muscles:
1. Smooth muscle
2. Cardiac muscle
3. Skeletal muscle
Imagine a mouse running beneath the skin.
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Smooth Muscle Fibers
Characteristics of smooth muscles
• Involuntary control
• Tapered cells with a single, central nucleus
• Lack striations
• Visceral Smooth Muscle
• Form sheets of muscle
• Cells are connected by gap junctions
• Multi-unit Smooth Muscle
• unorganized cells that
contract as individual cells • Cells are connected by gap junctions
• Muscle fibers contract as a group
• Rhythmic contractions
• Within walls of most hollow organs
(viscera)
contract as individual cells
•Located within the iris of eye
and the walls of blood vessels
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Cardiac Muscle
•Located only in the heart•Located only in the heart
•Striated cells
•Intercalated discs
• Muscle fibers branch
•Muscle fibers contract
as a unit
• Self-exciting and rhythmic
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Skeletal Muscle
• Usually attached to bone
• Voluntary control
• Striated (light & dark bands)
• Muscle fibers form bundles
• Several peripheral nuclei
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Coverings of Skeletal Muscle
Fascia
• Dense connective tissue surrounding
skeletal muscles
Tendons
• Dense connective tissue that
attaches muscle to bones
• Continuation of muscle facia and • Continuation of muscle facia and
bone periosteum
Aponeurosis
• Broad sheet of connective tissue
attaching muscles to bone, or to
other muscles.
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Coverings of Skeletal Muscle
Epimysium
• Connective tissue closely
surrounding a muscle
• Lies deep to fascia
PerimysiumPerimysium
• Surrounds organized bundles of
muscle fibers, called fascicles
Endomysium
• Connective tissue that surrounds
individual muscle fibers (cells)
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Figure 9.3 Scanning electron micrograph of a
fascicle surrounded by its perimysium. Muscle
fibers within the fascicle are surrounded by
endomysium.
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Organization of Skeletal Muscle
Fascicle
• Organized bundle of muscle fibers
Muscle Fiber
• Single muscle cell
• Collection of myofibrils
MyofibrilsMyofibrils
• Collection of myofilaments
Myofilaments
• Actin filament
• Myosin filament
Figure 9.2
Skeletal muscle
organization
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Sarcolemma
• Cell membrane of muscle fibers
Sarcoplasm
• Cytoplasm of muscle fibers
Sarcoplasmic Reticulum
• Modified Endoplasmic Reticulum
Skeletal Muscle Fibers
• Modified Endoplasmic Reticulum
• Store large deposits of Calicium
sarcolemma
Figure 9.2 c. A single muscle fiber
composed of several myofibrils. A
sarcolemma (membrane) surrounds the
cell, and an extensive sarcoplasmic
reticulum runs along the cell.
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Skeletal Muscle Fibers
(Transverse)T-tubules:
• invaginations of sarcolemma,
extending into the sarcoplasm.
Cisternae:
• Enlarged region of sarcoplasmic
reticulum, adjacent to t-tubules
Openings into t-tubules
reticulum, adjacent to t-tubules
Triad
• T-tubule + adjacent cisternae
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Myofibrils
Myofibrils
• Actin – thin filaments
• Myosin – thick filaments
Striations
Figure 9.4 Organization of actin and myosin filaments
Striations
• appear from the
organization of actin and
myosin
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Sarcomere
Sarcomere
• Functional unit of
skeletal muscle
•Area between
adjacent Z-lines
•During contraction
Z-lines approach together
and sarcomeres shorten
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• I Bands (light): actin filaments
• Z Line = attaches to actin
filaments (center of I bands)
• A Band (dark) : Myosin
filaments and overlapping actin
filaments
Striation Pattern of Skeletal Muscle
Figure 9.5 thin and thick filaments in a
sarcomere.
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• Thick myofilaments
• Myosin proteins
• Cross-bridges (heads) on myosin
• Cross-bridge attaches to actin
during contraction
• Thin myofilaments
• Actin proteins
• Associated with troponin
and tropomyosin proteins
MyofilamentsMyofilaments
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Cross-BridgesCross-Bridges• Myosin cross-bridges are extended when muscles are at rest “cocked”
position.
•During a contraction, cross-bridges bind to actin and “spring” forward. (Power Stroke)
• Cross-bridges pull on actin as they spring forward.
• ATP is required to “recock” the cross-bridges. (Recovery stroke)
Myosin cross-bridge
In the “cocked” position
Myosin cross-bridge
In the “sprung” position
Actin binding site
Power stroke