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Chapter 13
Lecture Outline
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Muscular System
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Points to ponder
• What are the three types of muscle tissue?
• What are the functions of the muscular system?
• How are muscles named and what are the muscles of
the human body?
• How are skeletal muscles and muscle fibers structured?
• How do skeletal muscles contract?
• How do skeletal muscle cells acquire ATP for
contraction?
• What is rigor mortis?
• What are some common muscular disorders?
• What are some serious muscle diseases?
• How do the skeletal and muscular system help maintain
homeostasis?
• How are these two systems related to other systems in
maintaining homeostasis?
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13.1 Overview of the Muscular System
Review: Types of muscle tissue
1. Smooth – involuntary muscle found in hollow
organs and vessels
2. Cardiac – involuntary muscle found in the
heart
3. Skeletal – voluntary muscle that is attached to
the skeleton
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13.1 Overview of the Muscular System
Review: Types of muscle tissue
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Skeletal muscle
• has striated cells
with multiple nuclei.
• occurs in muscles
attached to skeleton.
• functions in voluntary
movement of body.
Smooth muscle
• has spindle-shaped
cells, each with a
single nucleus.
• cells have no striations.
• functions In movement of
substances in lumens of body.
• is involuntary.
• is found in blood vessel walls and walls
of the digestive tract.
Cardiac muscle
• has branching,
striated cells, each
with a single nucleus.
• occurs in the wall of
the heart.
• functions in the pumping
of blood.
• is involuntary.
250X
striation
400X
nucleus
250X
Intercalated disk nucleus
Smooth muscle cell nucleus
a.
b.
c.
(smooth): © The McGraw-Hill Companies, Inc. Dennis Strete, photographer; (cardiac, skeletal): © Ed Reschke;
Figure 13.1 The three classes of muscles in humans.
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13.1 Overview of the Muscular System
What are the functions of
skeletal muscles?
1. Support the body by allowing us to stay
upright
2. Allow for movement by attaching to the
skeleton
3. Help maintain a constant body temperature
4. Assist in movement in the cardiovascular and
lymphatic vessels
5. Protect internal organs and stabilize joints
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13.1 Overview of the Muscular System
How are skeletal muscles attached?
• Tendon – connective
tissue that connects
muscle to bone
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muscle fiber
• Origin – attachment of
a muscle on a
stationary bone
• Insertion – attachment
of a muscle on a bone
that moves
fascicle
dense
connective
tissue
tendon
radius
Figure 13.2 Connecting muscle to bone.
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13.1 Overview of the Muscular System
How do skeletal muscles work?
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• Antagonistic –
muscles that work in
opposite pairs
tendon
origin
biceps brachii
(contracted)
triceps brachii
(relaxed)
radius
ulna
humerus
insertion
• Synergistic –
muscles working in
groups for a
common action
Figure 13.3 Skeletal muscles often work in pairs.
a.
biceps brachii
(relaxed)
triceps brachii
(contracted)
b.
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13.1 Overview of the Muscular System
Examples of how skeletal muscles
are named
• Size – the gluteus maximus is the largest
buttock muscle
• Shape – the deltoid is triangular (Greek letter
delta is Δ)
• Location – the frontalis overlies the frontal bone
• Direction of muscle fiber – the rectus abdominis
is longitudinal (rectus means straight)
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13.1 Overview of the Muscular System
Examples of how skeletal muscles
are named
• Attachment – the brachioradialis is attached to
the brachium and radius
• Number of attachments – the biceps brachii has
2 attachments
• Action – the extensor digitorum extends the
digits
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13.1 Overview of the Muscular System
Muscles of the human body
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Orbicularis oculi:
blinking, winking,
responsible for
crow’s feet
Orbicularisor is:
“kissing” muscle
Pectoralis major:
brings arm
forward and
across chest
Serratus
anterior:
pulls the scapula
(shoulder blade)
forward, as in
pushing or
punching
External
oblique:
compresses
abdomen;
rotation of
trunk
Quadriceps femoris:
straightens leg at
knee; raises thigh
Tibialis anterior:
turns foot upward, as
when walking on heels
Extensor digitorum
longus:
raises toes; raises foot
a.
Masseter:
a chewing muscle;
clenches teeth
Deltoid:
brings arm away
from the side of
body; moves arm
up and down in
front
Trapezius:
Raises scapula, as
When shrugging
shoulders; pulls head backward
Latissimus dorsi:
brings arm down
and backward
behind the body
Biceps brachii:
bends forearm at
elbow
Rectus abdominis:
Bends vertebral
column;
compresses
abdomen
Flexor carpi
group:
bends wrist
and hand
Triceps brachii:
straightens
forearm at elbow
Extensor carpi
group:
straightens wrist
and hand
Extensor
digitorum:
straightens
fingers and wrist
Adductor longus:
moves thigh toward
midline; raises
Gluteus maximus:
extends thigh back
Sartorius:
raises and laterally rotates
thigh; raises and rotates leg
close to body; these
combined actions occur
when “crossing legs” or
kicking across, as in soccer
Limbs
Arm: above the elbow
Forearm: below the
elbow
Thigh: above the knee
Leg: below the knee
Figure 13.5 The major skeletal muscles of the human body.
Biceps femoris:
bends leg at knee;
extends thigh back
Gastrocnemius:
turns foot downward,
as when standing on toes;
bends leg at knee
Achilles tendon
b.
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13.2 Skeletal Muscle Fiber Contraction
Muscle fibers/cells
• Terminology for cell structure
– The plasma membrane is called the sarcolemma.
– The cytoplasm is called the sarcoplasm.
– The SER of a muscle cell is called the
sarcoplasmic reticulum and stores calcium.
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13.2 Skeletal Muscle Fiber Contraction
Muscle fibers/cells
• Terminology for structure within a whole muscle
– Muscle fibers are arranged in bundles called
fascicles.
– Myofibrils are bundles of myofilaments that run the
length of a fiber.
– Myofilaments are proteins (actin and myosin) that
are arranged in repeating units.
– Sarcomeres are the repeating units of actin and
myosin found along a myofibril.
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13.2 Skeletal Muscle Fiber Contraction
Visualizing muscle structure
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A muscle contains
bundles of muscle
fibers, and a muscle
fiber has many
myofibrils.
bundle of
muscle cells
(fibers)
myofibril
sarcolemma
mitochondrion
one myofibril
sarcoplasm
skeletal
muscle
cell
(fiber)
myofilament
Z line
T tubule sarcoplasmic
reticulum
one sarcomere
Z line
nucleus
A myofibril has many sarcomeres.
6,000×
(myofi bril): © Biology Media/Photo Researchers, Inc.
Figure 13.6 The structure of a skeletal muscle fiber.
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13.2 Skeletal Muscle Fiber Contraction
The sarcomere
• Made of 2 protein myofilaments
– A thick filament is composed of several
hundred molecules of the protein myosin.
Each myosin molecule is shaped like a golf
club.
– Primarily, a thin filament consists of two
intertwining strands of the protein actin.
– These filaments slide over one another
during muscle contraction.
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13.2 Skeletal Muscle Fiber Contraction
The sarcomere
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crossbridge
myosin
actin
H band
Sarcomeres are relaxed.
Z line
A band
I band
Sarcomeres are contracted.
Figure 13.6 The structure of a skeletal muscle fiber.
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13.2 Skeletal Muscle Fiber Contraction
The beginning of muscle contraction:
The sliding filament model
1. Nerve impulses travel down a motor neuron to
a neuromuscular junction.
2. Acetylcholine (ACh) is released from the
neuron and binds to the muscle fiber.
3. This binding stimulates the fiber causing
calcium to be released from the sarcoplasmic
reticulum.
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13.2 Skeletal Muscle Fiber Contraction
The beginning of muscle contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
skeletal muscle
fiber
axon branch
axon terminal
(photo):© Victor B. Eichler
synaptic
vesicle
a. One motor axon goes to
Several muscle fibers.
synaptic
cleft
acetylcholine
(ACh)
axon terminal
synaptic vesicle
folded
sarcolemma
synaptic cleft
sarcolemma
Ach receptor
b. Asynaptic cleft exists between an axon
terminal and a muscle fiber.
c.Neurotransmitter (ACh) diffuses across synaptic cleft and
binds to receptors in sarcolemma.
Figure 13.7 Motor neurons and skeletal muscle fibers join neuromuscular junctions.
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13.2 Skeletal Muscle Fiber Contraction
Muscle contraction continued…
4. Released calcium combines with troponin, a
molecule associated with actin.
5. This causes the tropomyosin threads around
actin to shift and expose myosin binding sites.
6. Myosin heads bind to these sites forming crossbridges.
7. ATP binds to the myosin heads and is used for
energy to pull the actin filaments towards the
center of the sarcomere – contraction now
occurs.
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13.2 Skeletal Muscle Fiber Contraction
Visualizing the roles of calcium and
myosin in muscle contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
actin filament
troponin
myosin-binding sites
Ca2+
Ca2+
tropomyosin
Troponin—Ca+ complex pulls tropomyosin
away, exposing myosin-binding sites.
Function of Ca2+
actin filament
P
ADP
myosin
filament
cross-bridge myosin head
1.ATP is split when myosin
head is unattached.
ATP
2. ADP+ P are bound to
myosin asmyos in head
attaches to actin.
4.Binding of fresh ATP causes myosin
Head to return to resting position.
myosin
heads
actin
3.Upon ADP + P releases,
power stroke occurs:
head bends and pulls actin.
b. Function of myosin
Figure 13.8 The role of calcium ions and ATP during muscular contraction.
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13.2 Skeletal Muscle Fiber Contraction
What role does ATP play in muscle
contraction and rigor mortis?
•
ATP is needed to attach and detach the myosin
heads from actin.
•
After death, muscle cells continue to produce ATP
through fermentation and muscle cells can continue
to contract.
•
When ATP runs out, some myosin heads are still
attached and cannot detach, causing rigor mortis.
•
Rigor mortis and body temperature may be used to
estimate time of death.
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13.3 Whole Muscle Contraction
Terms to describe whole muscle
contraction
•
Motor unit – a nerve fiber and all of the muscle
fibers it stimulates
•
Muscle twitch – a single contraction lasting a
fraction of a second
•
Summation – an increase in muscle
contraction until the maximal sustained
contraction is reached
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13.3 Whole Muscle Contraction
Terms to describe whole muscle
contraction
•
Tetanus – maximal sustained contraction
•
Muscle tone – a continuous, partial contraction
of alternate muscle fibers causing the muscle
to look firm
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13.3 Whole Muscle Contraction
Physiology of skeletal muscle contraction
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contraction
period
Force
relaxation
period
latent
period
Stimulus
Time
a.
tetanus
summation
Force
fatigue
Stimuli
Time
b.
Figure 13.9 The three phases of a single muscle twitch and how summation and tetanus increase the force of contraction.
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13.3 Whole Muscle Contraction
Where are the fuel sources for
muscle contraction?
Stored in the
muscle
– Glycogen
– Fat
•
In the blood
– Glucose
– Fatty acids
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Percentage of energy expenditure
•
muscle triglycerides
plasma fatty acids
blood glucose
muscle glycogen
50
40
30
20
10
0
0
1
2
Exercise time (hr)
3
4
Figure 13.10 The sources of energy for muscle contraction.
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13.3 Whole Muscle Contraction
What are the sources of ATP for
muscle contraction?
•
Limited amounts of ATP are stored in muscle fibers.
•
Creatine phosphate pathway (CP) – fastest way to
acquire ATP but only sustains a cell for seconds;
builds up when a muscle is resting
•
Fermentation – fast-acting but results in lactate
build up
•
Cellular respiration (aerobic) – not an immediate
source of ATP but the best long term source
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13.3 Whole Muscle Contraction
Acquiring ATP for muscle contraction
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Anaerobic
Anaerobic
Aerobic
creatine
glycogen or
glycogen
phosphate
fatty acids
O2
fermentation
creatine
lactate
+
+
+
ATP
a.
CO2 + H2O
ATP
b.
ATP
c.
Figure 13.11 The three pathways by which muscle cells produce the ATP energy needed for contraction.
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13.3 Whole Muscle Contraction
Muscle fibers come in 2 forms
Fast-twitch fibers
•
•
•
•
•
•
Rely on CP and fermentation (anaerobic)
Adapted for strength
Light in color
Few mitochondria
Little or no myoglobin
Fewer blood vessels than slow-twitch
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13.3 Whole Muscle Contraction
Muscle fibers come in 2 forms
Slow-twitch fibers
•
•
•
•
•
•
Rely on aerobic respiration
Adapted for endurance
Dark in color
Many mitochondria
Myoglobin
Many blood vessels
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13.3 Whole Muscle Contraction
Types of muscle fibers
Figure 13.12 Fast-twitch and slow-twitch muscle fibers differ in structure.
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13.3 Whole Muscle Contraction
Exercise, exercise, exercise
• Exercise increases muscle strength, endurance,
and flexibility.
• It increases cardiorespiratory endurance.
• HDL increases thus improving cardiovascular
health.
• The proportion of protein to fat increases
favorably.
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13.3 Whole Muscle Contraction
Exercise, exercise, exercise
• Exercise may prevent certain cancers: colon,
breast, cervical, uterine, and ovarian.
• It improves density of bones thus decreasing the
likelihood of osteoporosis.
• Exercise enhances mood and may relieve
depression.
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13.4 Whole Muscle Contraction
Anabolic steroids
•
Anabolic steroids are a group of steroids that usually
increase protein production.
•
The most common side effects are high blood
pressure, jaundice, acne, and greatly increased risk
of cancer.
•
Abuse of these drugs may also cause impotence and
shrinking of the testicles.
•
Anabolic steroid use may lead to increased
aggressiveness and violent mood swings.
•
Are they worth the risk? Should they be legal to use
in athletics?
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13.4 Muscle Disorders
Common muscle disorders
•
Spasms – sudden, involuntary muscle
contractions that are usually painful
•
Convulsions (seizures) – multiple spasms of
skeletal muscles
•
Cramps – strong, painful spasms often of the
leg and foot
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13.4 Muscle Disorders
Common muscle disorders
•
Strain – stretching or tearing of a muscle
•
Sprain – twisting of a joint involving muscles,
ligaments, tendons, blood vessels, and nerves
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13.4 Muscle Disorders
Muscular diseases
•
Myalgia – achy muscles due to injury or
infection
•
Fibromyalgia – chronic achy muscles; not
well understood
•
Muscular dystrophy – group of genetic
disorders in which muscles progressively
degenerate and weaken
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13.4 Muscle Disorders
Muscular diseases
•
Myasthenia gravis – autoimmune disorder
that attacks the ACh receptor and weakens
muscles of the face, neck, and extremities
•
Amyotrophic lateral sclerosis (ALS) –
commonly known as Lou Gehrig’s disease;
motor neurons degenerate and die leading to
loss of voluntary muscle movement
•
Sarcomas – cancers that originate in muscle,
or the connective tissue associated with
muscle
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13.5 Homeostasis
Homeostasis: The skeletal and
muscular systems
•
Both systems are involved with movement that
allows us to respond to stimuli, digestion of food,
return of blood to the heart, and moving air in and
out of the lungs.
•
Both systems protect body parts.
•
Bones store and release calcium needed for
muscle contraction and nerve impulse conduction.
•
Blood cells are produced in the bone.
•
Muscles help maintain body temperature.
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13.5 Homeostasis
How the skeletal and muscular systems
interact with other body systems
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The muscular and skeletal systems work
together to maintain homeostasis. The
systems listed here in particular also
work with these two systems.
Nervous System
The nervous system coordinates the activity
of muscles. Muscle contraction moves eyes,
permits speech, and creates facial
expressions.
Muscular Systems
The muscular system works with the skeletal
system to allow movement and support and
protection for internal organs. Muscle
contraction provides heat to warm the body;
bones play a role in Ca2+ balance. These
systems specifically help the other systems
as mentioned below.
Endocrine System
Growth and sex hormones regulate muscle
development. Parathyroid hormone and
calcitonin regulate Ca2+ content of bones.
Cardiovascular System
Respiratory System
Muscle contraction keeps blood moving in the
heart and blood vessels, particularly the veins.
Respiration provides the oxygen needed for
ATP production so muscles can contract.
Muscles assists in breathing
Urinary System
Muscle contraction moves the fluid within
ureters, bladder, and urethra. Kidneys
activate vitamin D needed for Ca2+ absorption
and help maintain the blood level of Ca2+ for
muscle contraction.
Reproductive System
Muscle contraction moves gametes in
oviducts, and uterine contraction occurs
during childbirth. Androgens promote
muscle growth.
Digestive System
Muscle contraction accounts for chewing
of food and peristaltic movement. The
digestive system absorbs ions needed for
muscle contraction.
Figure 13.13 The muscular system’s
contributions to homeostasis.
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