Lab 4-The Muscular System
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• Muscle cells are involved in every movement that
our bodies perform.
• When muscles are stimulated they can
– shorten to produce movement
– relax to allow the body part to return to its
original length
• Muscles must be pulled back to their original
length either by gravity or by opposing muscles,
called “antagonistic muscles”
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Lab 4-The Muscular System
• There are 3 types of muscles:
– Skeletal muscles
– Cardiac muscles
– Smooth muscles
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Lab 4-The Muscular System
• Skeletal muscles
– attach to the bones of our skeleton and provide
strength and mobility for our body
• Cardiac muscle
– found in the heart; this muscle pumps blood
throughout the body
• Smooth muscles
– found in most internal organs
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Lab 4-The Muscular System
• Muscles may also be classified as
– voluntary (muscles over which we have
conscious control)
– involuntary (muscles over which we have no
conscious control)
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Skeletal Muscle
• Is also called Striated or Voluntary muscle
– they have striations (or stripes) which are caused by
alternating dark and light “bands”
– bands are composed of tightly packed contractile
proteins called myofilaments
• Myofilaments composed of actin and myosin
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•
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are multinucleated
cells are arranged in a parallel fashion
are responsible for all locomotion and manipulation
they enable us to respond quickly to changes in the
external environment
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Skeletal Muscle Summary
• Key words to remember are striated, and
voluntary
• Muscle fibers are long, cylindrical and
multinucleated
• Fibers are structurally and functionally
independent of each other
• Muscle can contract rapidly but tires easily
and requires rest after short periods of
activity
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Cardiac Muscle
• Cells are striated
• BUT, (unlike skeletal muscle), the cells are short,
fat, branched and interconnected
• Have specialized areas called intercalated disks
where the cells connect with each other
• These connections allow cardiac muscle to work
as a single, coordinated unit
• usually contracts at a steady rate set by the heart’s
pacemaker, but neural controls allow for a faster
beat for brief periods (i.e. when you perform
intense activities)
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Cardiac Muscle Summary
• Key words to remember are involuntary
and intercalated disks
• Muscle is highly resistant to fatigue
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Smooth Muscle
• Cells are shorter than skeletal and cardiac muscle cells
• Cells do not have striations (thus they are called
smooth muscle)
– Cells have fewer contractile proteins (thus no striations)
• Cells are spindle shaped (thicker in the middle and
tapered at each end); each cell has a centrally
located nucleus
• Are found in the walls of hollow visceral organs
(i.e. stomach, intestines, bladder, blood vessels)
• role is to force fluids and other substances through
body channels
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Smooth Muscle Summary
• Key words to remember are visceral,
nonstriated, and involuntary
• Cells are short and spindle shaped
• muscle contractions are slow and sustained,
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Skeletal Muscle Contraction
• Contractile proteins or myofilaments,
called actin and myosin, slide past each
other using energy from ATP molecules.
• These myofilaments produce alternating
light and dark areas called striations
– The Z-line is a thin, dark line where sets
of actin myofilaments are woven together
– The space between 2 Z-lines is called a
sarcomere; a sarcomere is the smallest
contractile unit of a muscle fiber
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– The Z-line is a thin, dark line where sets
of actin myofilaments are woven together
– The space between 2 Z-lines is called a
sarcomere
• A sarcomere is the smallest contractile
unit of a muscle fiber
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Muscle Contraction
• In order for a muscle to contract, its cells
must be stimulated by a nerve
• The motor neuron secretes acetylcholine
(ACh) at the neuromuscular junction (the
space where the motor neuron and muscle
cell meet).
– ACh is a neurotransmitter--a chemical
which can either stimulate or inhibit
another “excitable” cell (either a nerve
cell or a muscle cell)
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Muscle Contraction
• The ACh diffuses across the space between the
neuron and the muscle cell (called the synaptic
cleft) and binds to receptor sites on the muscle cell
membrane.
• The ACh binding causes the muscle cell membrane
to generate an electrical impulse which travels
along the cell membrane and along the T-tubules
(cylindrical extensions of the cell membrane which
travel into the interior parts of the cell)
– the function of the T-tubules is to allow the
electrical impulse to quickly travel to all cell parts
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Muscle Contraction
• The T-tubules are in close contact with the
sarcoplasmic reticulum.
• The sarcoplasmic reticulum stores calcium.
• The electrical impulse triggers the release of
calcium from the sarcoplasmic reticulum so
the muscle can contract.
• Relaxation of a muscle cell occurs when
nerve cell stimulation stops.
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Energy Use by Muscle Cells
• Muscle contraction requires energy
• ATP is the muscle’s energy source
• Typically muscle cells store enough ATP
for only 30-40 seconds of heavy activity.
After this, muscles must rely on stored
glycogen.
• Glycogen is broken down (a process called
glycolysis).
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Energy Use by Muscle Cells
• Glucose molecules are removed from the
glycogen and the cell uses the glucose to
synthesize more ATP.
– Part of the glucose breakdown process
can be done anaerobically. This is a fast
process but only yields 2 ATP molecules
per glucose molecule.
– It also produces lactic acid as a waste
product which can make muscles sore.
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Energy Use by Muscle Cells
– The most efficient, but much slower,
process for energy production is aerobic
metabolism. This yields 36 ATP
molecules from 1 molecule of glucose.
Carbon dioxide is produced as a waste
product.
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Gross Anatomy of Skeletal Muscle
• Individual muscle fibers are wrapped and held
together by several different layers of connective
tissue
• The outermost layer is called the epimysium and
surrounds the whole muscle.
• The fibers within the muscle are grouped into
fascicles or bundles and resemble a bunch of sticks.
• The perimysium surrounds each fascicle.
• The individual muscle fibers are surrounded by
the endomysium.
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Gross Anatomy of Skeletal Muscle
• Each of the connective tissue coverings are
continuous with the other ones and also
with the tendons located at the end of the
muscle.
• Tendons attach muscle to bone.
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Movememt
• If the muscle spans a joint, one bone moves
while the other one remains stationary
– the muscle’s origin is on the bone which
does not move
– the insertion is on the bone which moves
• Terms used to describe movement are on
page 48 of your lab manual. You need to
know the bulleted terms.
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REMINDER
1. There are 4 slides to look at:
– Learn muscle tissues using the slides.
– Learn the motor nerve ending slide.
2. Learn the microstructure of muscles using models
and the diagrams.
3. Learn the location and function of selected
muscles in tables 7.1, 7.2 and 7.3.
4. Perform the muscle physiology experiments on
page 58.
5. Complete the chart on page 59.
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