Download Chapter 6

Human Biology Concepts and Current Issues
Seventh Edition
Michael D. Johnson
6
The Muscular
System
© 2014 Pearson Education, Inc.
Lecture Presentations by
Robert J. Sullivan
Marist College
Introduction to Muscles
 Muscle tissue is found in every organ
 Muscles participate in every activity that requires
movement
 Large proportion of body weight is muscle
– 40% of body weight in males
– 32% of body weight in females
 Skeletal muscle: attaches to skeleton and provides
strength and mobility
 Cardiac muscle: exclusively in the heart
 Smooth muscle: walls of digestive tract, blood
vessels, uterus, ureters
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Muscles Produce Movement or Generate Tension
 Muscles may produce movement
– Voluntary: conscious control over movement (picking
up a pen)
– Involuntary: unconscious control over movement
(beating of heart, movement of intestines)
 Muscles generate heat
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The Fundamental Activity of Muscle Is Contraction
 Excitable: contract in response to electrical or
chemical stimuli
 All muscle cells have one mechanism of action:
– They contract (shorten), then relax (lengthen)
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Pectoralis major
•Draws arm forward
Trapezius
Serratus anterior
•Contributes to pushes
•Draws shoulder blade forward
•Lifts shoulder blade
•Braces shoulder
Deltoid
Biceps brachii
•Bends forearm at elbow
Rectus abdominus
•Compresses abdomen
•Raises arm
Triceps brachi
•Straightens forearm
at elbow
Latissimus dorsi
•Draws arm backward
External oblique
•Compresses abdomen
Gluteus maximus
Adductor longus
•Extends thigh
•Draws thigh toward body
Hamstring group
•Bends knee
Sartorius
•Bends thigh at hip
Gastrocnemius
•Bends foot away from
knee
Quadriceps group
•striaghtens leg at knee
Achilles tendon
Tibialis anterior
•Flexes foot toward knee
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•Connects
gastrocnemius
muscle to heel
Skeletal Muscles Cause Bones to Move
 600 skeletal muscles
 Synergistic muscles: work together to created the
same movement
 Antagonistic muscles: muscles that oppose each
other
 Many muscles attach to bones via tendons
 Origin: end of muscle that attaches to relatively
immovable bone
 Insertion: end of muscle attached to relatively
movable bone, action pulls insertion toward origin
© 2014 Pearson Education, Inc.
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A Muscle Is Composed of Many Muscle Cells
 Muscles
– Group of muscle fibers with same origin, insertion, and
function
 Fasicles
– Bundles of muscle fibers (cells) wrapped with
connective tissue (fascia)
 Muscle fibers (muscle cells)
–
–
–
–
Long, tube shaped
Vary in length from few mm to 30 cm
Multinucleate (many nuclei)
Packed with myofibrils, which are long cylindrical
structures which contain proteins actin and myosin
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Figure 6.3
Muscle bundle (fascicle)
surrounded by connective
tissue (fascia)
Whole muscle
Single muscle
cell (fiber)
Tendon
Bone
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Figure 6.4
Muscle
Cell (muscle fiber)
Myofibril
A single muscle cell contains
many myofibrils
Nuclei
and has more than one
nucleus.
Muscle
cell
A photograph of portions of several skeletal muscle cells.
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The Muscle Contractile Unit Is the Sarcomere
 A myofibril is made of end to end sarcomeres:
 A sarcomere: contractile unit made of:
– Myosin: forms thick filaments
– Actin: forms thin filaments
 Z Lines: attachment points for sarcomeres
 A sarcomere is a segment of myofibril extending
from one Z line to the next
 Arrangement of filaments gives rise to striated
appearance of skeletal muscle
© 2014 Pearson Education, Inc.
Figure 6.5
Myofibril
Z-line
Z-line
Sarcomere
A closer view of a section of a myofibril
showing that it is composed of
sarcomeres joined end to end at the
Z-line.
Thin filament
(actin)
Thick filament
(myosin)
Sarcomeres contain thin filaments of
actin that attach to the Z-lines and
thicker filaments of myosin
a sarcomere.
.
© 2014 Pearson Education, Inc.
Myosin
Actin
An electron micrograph
cross section of a sarcomere
in a region that contains both
actin and myosin.
Calcium Initiates the Sliding Filament Mechanism
 Thick filaments: myosin
 Thin filaments: actin
 When skeletal muscle is stimulated by nerve, it will
contract
 Contraction: when thin filaments slide over thick
filaments
 Calcium must be present for contraction
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Cardiac and Smooth Muscles Have Special Features
 Involuntary
 Able to contract entirely on their own in absence of
nerve stimulation
 Cardiac muscle cells
– Have gap junctions allowing cells to electrically
stimulate the next one
 Smooth muscle cells joined by gap junctions allowing
cells to activate each other
 Cardiac and smooth muscle cells respond to
stimulation from autonomic nervous system, which
can modify the degree of contraction
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Figure 6.12
Cardiac muscle cell
Intercalated disc
A view of several adjacent
cardiac muscle cells showing
their blunt shape and the
intercalated discs that join
them together.
Adhesion junction
Protein channel
Gap junction
Cell membranes
of adjacent cells
A closer view showing that intercalated discs are
bridged by gap junctions that permit direct electrical
connections between cells.
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Speed and Sustainability of Contraction
 Skeletal muscle: fastest
 Cardiac muscle: moderate
 Smooth muscle:
– Very slow
– Partially contracted all of the time
– Almost never fatigues
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Arrangement of Myosin and Actin Filaments
 Cardiac muscle
– Sarcomere arrangement of thick and thin filaments
– Striated appearance
 Smooth muscle
– Filaments not arranged in sarcomeres
– No striations
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Cardiac muscle
striated
© 2014 Pearson Education, Inc.
Smooth muscle
Not striated
Diseases and Disorders of the Muscular System
 Tetanus
– Infection of deep wound by bacteria, Clostridium tetani
– Bacteria produce tetanus toxin which causes muscles
to contract forcefully
– Death due to respiratory failure
– Preventable by tetanus vaccine
 Muscle cramps: often caused by dehydration and ion
imbalances
 Pulled muscles: result from overstretching of a
muscle, fibers tear apart
© 2014 Pearson Education, Inc.