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3/21/17
Outline
The Muscular System
Biol 105
Chapter 6
I.  Characteristics of muscles
II.  Three types of muscles
III.  Functions of muscles
IV.  Structure of skeletal muscles
V.  Mechanics of muscle contraction
VI.  Energy source for muscle contraction
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Muscular System
Types of Muscles
§  Remember there were different types of
muscles: cardiac, smooth and skeletal.
1.  Smooth muscle
§  All muscle cells are elongated and contain
many protein fibers and therefore are called
muscle fibers. (muscle cell = muscle fiber)
3.  Skeletal muscle
2.  Cardiac muscle
§  All muscle tissues contract.
§  Muscles contain muscle cells (called muscle
fibers), connective tissue, blood vessels, and
nerves
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Smooth Muscle
Cardiac Muscle
§  Smooth muscles are involuntary
muscles found in the walls of many
internal organs (digestive tract,
respiratory system, blood vessels).
§  Cardiac muscles are involuntary muscles
found only in the heart wall.
§  Function by contracting to force blood from
the heart into the arteries.
§  Aid in the function of other organs.
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Skeletal Muscle
§  Skeletal muscle are voluntary muscles
attached to the skeleton.
§  Usually work in pairs.
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Skeletal Muscles Work in Pairs
Skeletal Muscles Work in Pairs
§  Most skeletal muscles are found in
antagonistic pairs.
§  When one muscle contracts, the other relaxes.
§  The insertion is attached to the bone that
moves.
§  Muscles are attached to the bone by
tendons.
§  Skeletal Muscles are usually attached to two
bones on opposite sides of a joint.
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Functions of Skeletal Muscles
Origin of muscle:
attachment of muscle
to less moveable bone
The biceps contracts
and pulls the forearm
up, flexing the arm.
The relaxed triceps
is stretched.
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§  Bones act as levers in working with skeletal
muscles to produce movement.
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Skeletal Muscles Work in Pairs
(a) Flexion
§  The origin of the muscle is attached to the
bone that remains stationary during
movement.
Insertion of muscle:
attachment of muscle
to more moveable bone
Figure 6.1a
1.  Support the body – maintain our posture.
2.  Movement of bones and other tissues.
3.  Help maintain a constant body temperature
– generates heat.
4.  Helps move blood through the veins and
lymphatic fluid through the lymphatic
vessels.
5.  Help to protect vital organs.
6.  Stabilize joints.
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Smooth muscles are found in
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1.  The heart
2.  Digestive tract
3.  Attached to bones
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1.  The heart
2.  Digestive tract
3.  Attached to bones
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Smooth muscles are found in
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1.  Voluntary
2.  Involuntary
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1.  Voluntary
2.  Involuntary
Smooth muscles are under this kind of control
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Smooth muscles are under this kind of control
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Muscle Cells (Muscle Fibers)
Muscle Cells (Muscle Fibers)
§  Bundles of myofilaments are the contractile
portion of a muscle fiber.
§  Long, thin bundles of myofilaments are called
Myofibrils.
§  Myofilaments are made of actin and myosin
filaments.
§  Muscle cells are long cells packed with
myofibrils and are therefore called muscle
fibers.
§  When muscle fibers are stimulated to
contract, myofilaments slide past one
another, causing sarcomeres to shorten.
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Structure of Skeletal Muscles
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Structure of Skeletal Muscles
Skeletal muscle
consists of
many bundles
of muscle cells.
§  A muscle contains bundles of skeletal muscle
fibers (muscle cells), the bundles are called
fascicles. These bundles are covered by
connective tissue.
§  Blood vessels and nerves are between the
fascicles.
A muscle cell
consists of many
myofibrils.
A bundle of
muscle cells is
called a fascicle.
A myofibril
consists of many
myofilaments.
(a) A section of a
skeletal muscle
The striped (striated)
appearance of a skeletal
muscle cell is due to the
regular arrangement of
myofilaments.
§  Muscles are covered by connective tissue
called fascia.
(b) A light micrograph of a longitudinal view of skeletal muscle cells
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Figure 6.3a–b
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Sarcomeres
A bundle of muscle cells is called a:
The striped (striated)
appearance of a skeletal
muscle cell is due to the
regular arrangement of
myofilaments.
1.  Fascicle
2.  Fascia
3.  Muscle Fiber
(b) A light micrograph of a longitudinal view of skeletal muscle cells
Z line
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Figure 6.3b–c
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§  Muscle cells (muscle fibers) have many of the
same components as typical cells but some of
their components have different names.
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Muscle Cell Components
A bundle of muscle cells is called a:
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(c) A diagram and electron micrograph of a myofibril
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1.  Fascicle
2.  Fascia
3.  Muscle Fiber
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Fa
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One sarcomere
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Muscle Cell Components
§  Sarcolemma – plasma membrane (cell
membrane).
§  Sarcoplasm – similar to cytoplasm, contains
large amount of stored glycogen and myoglobin.
§  Sarcoplasmic Reticulum – similar to
endoplasmic reticulum, one of its functions is to
store Ca2+.
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Muscle Cell Components
§  Muscle cells (muscle fibers) also have
unique features:
§  Multiple nuclei.
§  Transverse tubules (T tubules) – extensions of the
sarcolemma that come into contact with the
sarcoplasmic reticulum.
§  Myoglobin - an oxygen binding protein similar to
hemoglobin, but found only in muscles.
§  Sarcomeres – the contractile units of a muscle
fiber.
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c. myofibril
b. Sarcoplasmic reticulum
a. T tubule
Muscle Contraction
§  The small myofibrils that make up the muscle
fiber (muscle cell) contain two types of
myofilaments: actin and myosin filaments.
§  Sarcomere is the name for the structural unit
of these myofilaments.
§  The sarcomere stretches between two dark
lines called Z lines. The Z lines are protein
sheets where the actin filaments attach.
d. Z line
e. sarcomere
f. sarcolemma
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Sarcomeres
Myofilaments – Actin and Myosin
Z line
§  The two myofilaments are:
§  Actin filaments: thin filaments that form by
two intertwining strands of the protein actin.
One sarcomere
§  Myosin filaments: Thick filaments of the
protein myosin shaped like a golf club, with a
round “head”.
(c) A diagram and
electron micrograph
of a myofibril
Z line
One sarcomere
Z line
Actin
Myosin
(d) A sarcomere, the contractile unit of a skeletal muscle, contains actin and
myosin myofilaments.
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Figure 6.3c–d
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Myofilaments – Actin and Myosin
Muscle Contraction cont…
§  The myosin heads can bind and detach
from the thin actin filament. When bound
they create cross-bridges.
§  A neuron signals the muscle to contract.
§  When the muscle is stimulated, these
filaments slide past each other, causing the
sarcomere to shorten. This action is called a
power stroke.
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§  Then the myosin heads detach.
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Sarcomeres
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§  The myosin heads attach to the actin
(cross bridge formation) then pull the actin
toward the center of the sarcomere (power
stroke).
Neuromuscular Junction
Figure 6.4
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Figure 6.7 (1 of 2)
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Steps of Muscle Contraction
1.  Action potentials are transmitted through the
neurons.
2.  At the end of the neurons the
neurotransmitter Acetylcholine is released.
3.  Acetylcholine binds to its receptor on the
sarcolemma.
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Steps of Muscle Contraction
Steps of Muscle Contraction
4.  The receptors are ion channels that open and
allow Na+ to enter the cell triggering an action
potential.
8.  The calcium binds to the troponin on the actin
filament, causing tropomyosin to move.
5.  The action potential travels down the Ttubules.
6.  The action potential reaches the sarcoplasmic
reticulum.
9.  This opens up binding site for the myosin to
attach.
10. Now the myosin binds to the actin.
11. ATP is needed for the myosin to slide past
the actin.
7.  The sarcoplasmic reticulum releases Ca2+.
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Troponin-Tropomyosin Complex
Sarcomeres
§  The tropomyosin-troponin complex is
attached to the actin filament.
§  Calcium binds to the troponin, causing a
shift in the complex, opening the sites for
myosin to attach.
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Figure 6.6 (1 of 2)
Sarcomeres
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Figure 6.6 (2 of 2)
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ATP is needed for the myofilaments to slide past each other
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Myosin
Actin
Hemoglobin
Myoglobin
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1. 
2. 
3. 
4. 
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Myosin
Actin
Hemoglobin
Myoglobin
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1. 
2. 
3. 
4. 
What is the an oxygen binding protein found only in
muscles?
A
What is the an oxygen binding protein found only in
muscles?
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di
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Where is the calcium stored?
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1.  Nucleus
2.  Sarcolemma
3.  Sarcoplasmic
reticulum
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1.  Nucleus
2.  Sarcolemma
3.  Sarcoplasmic
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Where is the calcium stored?
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Potassium
Calcium
Chloride
Sodium
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2. 
3. 
4. 
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Potassium
Calcium
Chloride
Sodium
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1. 
2. 
3. 
4. 
What ion is required for the myofilaments to bind
to each other?
C
What ion is required for the myofilaments to bind
to each other?
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ATP
§  ATP is the currency. Like money in your
pocket.
§  The bonds between the phosphate groups
are high energy bonds.
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The Energy Source
§  Muscle contractions use a lot of energy in
the form of ATP.
§  Muscles get their ATP from three sources:
§  1. The breakdown of Creatine Phosphate
§  2. Anaerobic Fermentation
§  3. Cellular Respiration
1. Creatine Phosphate
§  Creatine phosphate regenerates ADP to
make ATP.
§  This gives quick energy for a few seconds
(up to ~10 sec).
§  Only 1 ATP is produced per creatine
phosphate.
§  Oxygen is not needed.
§  When a muscle is resting, the ATP in turn
regenerates creatine phosphate.
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2. Anaerobic Fermentation
3. Aerobic Cellular Respiration
§  This is when the cell only uses glycolysis,
and glucose is broken down to lactic acid.
§  In the mitochondria, glucose is broken down to
produce ATP.
§  Remember that oxygen is needed at the
electron transport chain to produce the ATP.
§  Carbon dioxide is produced as a waste product
during the Citric Acid Cycle and Transition Rxn
steps in cellular respiration.
§  Can provide energy for hours.
§  Produces 36 ATP per glucose molecule.
§  Can use glucose as well as fatty acids and
amino acids for energy source.
§  Since the Krebs cycle and the electron
transport chain is skipped, no oxygen is
required.
§  No CO2 is produced as a waste produce but
lactic acid is produced.
§  Can provide energy for 30 – 60 sec.
§  2 ATP produced per glucose molecule.
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ATP Comes from Many Sources
ATP Comes from Many Sources
6 seconds
ATP stored
in muscles
10 seconds
30–40 seconds
ATP formed from
creatine phosphate
and ADP
ATP generated from
glycogen stored in muscles
and broken down to form
glucose
Oxygen limited
• Glucose oxidized
to lactic acid
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Figure 6.10
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Figure 6.10 (1 of 2)
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ATP Comes from Many Sources
Fermentation
Requires O2
No
Yes
No
Produces
CO2
# ATP
produced
No
Yes
No
1
36
2
Duration
30 sec
Hours
30-60 sec
Breathe heavily to deliver oxygen
• Lactic acid used to produce ATP
• Creatine phosphate restored
• Oxygen restored to myoglobin
• Glycogen reserves restored
Which energy source would a long distance runner
mainly use on a run that lasted for hours?
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Ph
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1.  Fermentation
2.  Aerobic Cellular
Respiration
3.  Creatine
Phosphate
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C
1.  Fermentation
2.  Aerobic Cellular
Respiration
3.  Creatine
Phosphate
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pi
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Which energy source would a long distance runner
mainly use on a run that lasted for hours?
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Figure 6.10 (2 of 2)
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Oxygen present
• Heart beats faster to deliver
oxygen more quickly
• Myoglobin releases oxygen
After prolonged exercise
Oxygen debt paid back
Cellular
Respiration
la
r
End of exercise
ATP generated from glycogen
stored in muscles and broken
down to form glucose
CP
breakdown
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Which energy source would a sprinter use in the
first 5 seconds of the race?
Which energy source would a sprinter use in the
first 5 seconds of the race?
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§  What are the three types of muscles, where are
they found, are they under vol. or invol control
§  What stimulates a muscle to contract
§  What is the structure and the components of a
muscle, and of a muscle cell (muscle fiber) and the
functions of the muscle cell components.
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Important Concepts
§  What is the function of tendons?
§  How do skeletal muscles work in pairs?
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§  Read Chapter 10 for next lecture
§  What are the functions of skeletal, cardiac and
smooth muscles
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Important Concepts
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tio
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1.  Fermentation
2.  Cellular respiration
3.  Creatine
Phosphate
tio
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1.  Fermentation
2.  Cellular respiration
3.  Creatine
Phosphate
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§  Be able to describe the steps of how the message
is transmitted from the neuron to the myofilaments
§  What is the role of Ca2+.
§  What happens when the message is received by
the myofilaments?
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Important Concepts
§  What are the components of the muscle fibers,
their functions, be able to identify them in an
illustration, including: myofibrils, sarcomeres, Z
lines, the myofilaments - actin and myosin
filaments, cross-bridges, sarcolemma,
sarcoplasm, sarcoplasmic reticulum, T-tubules
Important Concepts
§  What are the three energy sources for muscle
contraction, which require oxygen, which produce
carbon dioxide, how many ATP are produced,
how long can it provide energy
§  What are the components and the function of the
tropomyosin-troponin complex
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Definitions
§  muscle fibers, Myoglobin, fascia, fascicles,
myofibrils, sarcomere, involuntary, voluntary,
origin, insertion
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