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Muscle Tissue
• Muscle tissue is highly specialized to
convert chemical energy into kinetic
energy
• Your movements occur through the
coordinated contracting and relaxing
of many muscles
• When muscles contract (shorten) it
causes a part of the body to move
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There are 3 types of muscle cells
Skeletal
Smooth
Cardiac
Food moves through the intestines due
to peristalsis of the smooth muscles
• Your heart beats because of cardiac
muscles
• And your body moves because skeletal
muscles pull on your bones
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Basic
Muscle
Types
• The cells of smooth muscle tissue
are long and tapered at each end and
have one nucleus
• They are arranged in parallel lines,
forming sheets
• Are found in the walls of blood
vessels, hollow internal organs, and
in the iris of the eye
• Contraction of these muscles is
involuntary (without your control)
• The smooth muscles contract slower
but can remained contracted for an
extended amount of time because
they don’t fatigue easily
• The cardiac muscle is unique to the
heart and forms the walls
• These cells are tubular and have
bands of light and dark (striated), and
have one nucleus
• The muscle cells are branched,
creating a netlike structure
• Like smooth muscles, cardiac
muscles contract involuntary
• Skeletal muscles are also tubular
and striated
• the “meat” of our bodies are
composed of these muscles
• The contraction of these muscles is
voluntary and is controlled by the
nervous system
• The bodies movements is due to over
600 skeletal muscles
• The skeletal muscles have the following
functions:
–Supports the body by opposing the force
of gravity allowing us to stand upright
–Makes our body move
–Helps maintain a constant body
temperature by releasing heat when
using energy
–Protects the internal organs and
stabilizes the joints
• Unlike smooth and cardiac muscle
cells, skeletal muscles are very long
and have many nuclei which maintain
the normal functions of these cells
• They are usually referred to as fibers
rather than cells because of their
structure
Cooperation
• When muscles contract, they shorten
• This means that muscles can only pull
• The work of a muscle is done when it
contracts and when it relaxes it is in a
passive state
• Muscles that allow motion come in pairs
• For the action of each muscle, there is
another muscle that does the opposite
action
Bundles of Fibers
• Each muscle in the body lies along the
length of a bone
• A tough, heavy band of tissue, called a
tendon, attaches each end of a muscle
to a different bone
• The long skeletal muscle fibers can be
up to 20 cm in length
• Muscle fibers are organized into many
larger bundles
• A muscle then consists of clusters of
these bundles of muscle fibers
• A layer of connective tissue wraps
around each fiber
• Another layer wraps around each
bundle and another around the whole
muscle itself
• Blood vessels and nerves run
between the bundles of muscle fibers
• The blood provides the fibers with
nutrients and oxygen required to power
the contractions as well as removes
cellular wastes
• The nerves trigger and control muscle
contractions
• Most of the volume of a muscle fiber
consists of many subunits called
myofibrils
• And each myofibril is made of even finer
myofilaments
Muscle Contractions
• Muscle contractions involve the
coordinated action of the two types of
myofilaments, actin and myosin
• A thin actin myofilament consists of two
strands of protein molecules that are
wrapped around each other
• A thick myosin myofilament also
consists of two strands of protein
molecules wound around each other
but is about 10 times longer
• When a myofilament contracts, the
heads of the myosin move first
• Like flexing your hand at the wrist, the
heads bend backward and inward
• This moves them closer to their rodlike “backbone” and a bit in the
direction of the flex
• Because the heads are attached at
this time to an actin myofilament, the
actin is pulled along with the myosin
heads
• As each myosin head flexes one after
the other, the myosin walks along the
actin
• Each step requires ATP to provide
energy that repositions the myosin
head before each flex
• The sliding of actin past the myosin is
part of the sliding filament model of
the muscle contraction
• The actin is anchored at one end of
each myofilament at a position in the
muscle tissue called the Z line
• Because the actin is anchored like
this, its movement pulls the Z line
along with it
• As the Z lines are pulled closer
together, the plasma membranes to
which they are attached to cause the
entire muscle fiber to contract
Aerobic Cellular Respiration
• Aerobic cellular respiration provides
most of a muscle’s ATP
• The muscle fibers use glucose from fats
and oxygen to produce ATP
• The other products are carbon dioxide,
water and heat
• CO2 leaves the body at the lungs, water
is absorbed, and the heat warms the
body
• About 2/3 of the heat that maintains a
constant body temperature comes
from the aerobic cellular respiration of
the skeletal muscles throughout the
body
Role of Calcium
• When a muscle is relaxed, its myosin
heads are raised and ready but not
attached to actin due to another
protein called tropomyosin blocking
the attachment site
• For a muscle to contract the
tropomyosin must be moved out of
the way
• Another protein called troponin binds
to the tropomyosin to form a complex
regulated by calcium concentration
• When calcium concentration is low,
tropomyosin prevents myosin from
binding to actin
• When calcium concentration is raised,
the complex forms and is shifted
away, allowing the binding of myosin
and actin
Muscles and Health
• During active use, some muscles are
contracting and others relaxing
• Even when muscles appear to be at
rest, their fibers are always contracting
• This continuous low-level activity results
in muscle tone
• Muscle tone is important for maintaining
posture
• If all our muscles were to completely
relax, our body would collapse
• In general, the skeletal muscles are
subject to fewer disorders compared
to other organ systems
• However they are vulnerable to
injuries that result from sudden and
intense stress placed on them and on
tendons
• Complete the description of the listed
muscular system disorders
• Muscles may also be impaired simply
from lack of use, this is referred to as
atrophy
• Atrophy is a reduction in size, tone,
and muscle power
• If extreme atrophy occurs, the loss of
muscle function is permanent
• Exercise is important to strengthen
muscles and allow them to use
energy more efficiently
• Create your own set of notes for slowtwitch fibers and fast-twitch fibers