Download Structure of Skeletal Muscle

Unit: Muscular System
Please, help me out!
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If there are things throughout this unit you do
not like, please write it down and explain why.
If you feel I could have done something
differently that would have been more
effective for you, please record it.
At the end of the unit I will ask you to answer
these questions on sheet of paper. Thanks for
your help!!
What you will learn:
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Review Muscle types
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I can label the major parts of skeletal muscle
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I can describe how skeletal muscle contracts (sliding filament model)
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I can identify the origin and insertion points of major muscles within the
human body.
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I can describe the functions of skeletal muscle
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I can identify the parts of a motor unit
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I can describe a muscle stimulus (all-or-none)
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I can identify the types of skeletal muscle contractions (tonic, twitch,
tetanic, isotonic, isometric)
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I can explain why a muscle fatigues
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Learn the name, location, function, insertion and origin points of the
major muscles in the body (cat dissection, Yeah!)
Lets get started: Review
Take five minutes to recall and record in your
journal:
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The three types of muscle tissue
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Identify two distinguishing characteristics for
each.
Muscle Tissues
Smooth
 Cardiac
 Skeletal
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Smooth Muscle
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Cells are tapered at each
end
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Have a single nucleus
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Lack cross striations
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Involuntary
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Important in blood
vessel walls and in many
hollow internal organs
(such as gut, urethra, and
ureter)
Cardiac Muscle
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Composes the heart
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Cross striations
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Involuntary
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Intercalated disks - where
the membranes of adjacent
cardiac fibers come in contact
with each other.
Skeletal Muscle
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Voluntary
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Many cross striations
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Multi-nucleated
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Attached to bone and
when contracted allow
for movement.
Skeletal Muscle
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Voluntary
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Many cross striations
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Multi-nucleated
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Attached to bone and
when contracted allow
for movement.
Do you know:
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Do you know why the muscular system is
classified as a system?
- What makes it a system?
- Take a moment to describe why it is classified as
system in your electronic journal.
Do you know (cont.):
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The muscular system is an organ system
consisting of skeletal, smooth and cardiac
muscles. It permits movement of the body,
maintains posture, and aids in blood circulation.
-Multiple muscles interact with each other to
produce body movements.
- Synergists: (Muscles of the truck External oblique,
Internal oblique, Transverse abdominis compress
abdomen)
- Antagonist: (Triceps brachii vs. Biceps brachii aides
in extension and flexion)
Function of Skeletal Muscle:
1. Movement – as skeletal muscle becomes
shorter as fibers contract, the bones to which
the muscle/s attach move closer together
causing movement.
- Voluntary muscular movement is smooth and free
of jerks because skeletal muscles generally work
in teams.
- Several muscles contract, while others relax
- Prime mover: of all the muscles contracting
simultaneously, the one that is mainly responsible
for producing the movement is the PM.
Function of Skeletal Muscle:
2. Posture or muscle tone – we are able to
maintain our body position because of a
specialized type of skeletal contraction called
tonic.
- Tonic contraction: do not move any body parts but
hold muscles in position (muscle tone maintains
posture through constant tension).
Function of Skeletal Muscle:
3. Heat Production – contraction of
muscle fibers produces most of the heat
required to maintain a constant body
temperature.
- the energy for muscle contractions
comes form ATP (powerhouse of the
cell) and is used to shorten the muscle
fibers.
- hypothermia: any decrease below normal
(below 98.6 ◦F)
- Why is this significant?
Structure of Skeletal Muscle:
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Skeletal muscle is an organ composed mainly
of striated muscle cells and connective tissue.
Skeletal muscles attach to two bones that have
a moveable joint between them.
- recall the three classifications of joints,
synarthroses, amphiarthroses, diarthroses
- example: deltoid muscle
Structure of Skeletal Muscle:
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One bone is more stationary in a given
movement than the other.
The muscles attachment to this more stationary
bone is called its origin point.
The attachment to the more movable bone is
called the muscles insertion point.
- Think Biceps brachii - origin: scapula (supraglenoid
tubercle & coracoid process, insertion: radius)
Structure of Skeletal Muscle:
Movements Produced by Skeletal
Muscle Contractions:
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Muscles acting on some joints produce
movement in several directions, whereas only
limited movement is possible at other joints.
1) Flexion - is a movement that makes the angel
between two bones at their joint smaller than it
was at the beginning of the movement.
- ex. Hamstring group
2) Extension – makes the angle between two
bones at their joint larger.
- ex. Quadriceps group
Movements Produced by Skeletal
Muscle Contractions:
3) Abduction - means moving a part away from the
midline of the body.
- ex. Moving arm out to the side
4) Adduction – means moving a part toward the
midline.
- ex. Bring your arm down to your side, toward midline
5) Rotation – movement around a longitudinal axis.
- ex. Head rotates on cervical axis.
Movements Produced by Skeletal
Muscle Contractions:
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Refers to hand positions that result from
rotation of the forearm.
6) Supination – hand position with the palm
turned to the anterior position (as in the
anatomical position)
- Supine: means lying face up
7) Pronation – hand position with the palm facing
posteriorly.
- Prone: means lying face down
Movements Produced by Skeletal
Muscle Contractions:
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Refers to ankle movements.
8) Dorsiflexion – the dorsum or top of the foot is
elevated with the toes pointing upward.
9) Plantar Flexion – bottom of foot is directed
downward, as if standing on toes.
Structure of Skeletal Muscle:
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Body – all the muscle, except the two ends
Tendons – anchor muscles firmly to bones.
Made of dense fibrous connective tissue in the
shape of heavy cords, have great strength but
less mobility.
Bursae – are small flexible sacs that lie between
tendons and bone and are lined with synovial
membrane. Aides in tendon movement over bone
when it the tendon shortens (contracts).
Synovial Membrane - secretes a slippery
lubricating fluid that fills the bursa.
Structure of Skeletal Muscle:
Note: Microscopic Structure of Muscle
Microscopic Structure of Muscle (see
handout):
http://www.youtube.com/watch?v=WVuW560nRII
Microscopic Structure of Muscle:
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Muscle Fibers – specialized contractile cells
that are grouped together and arranged in a
highly organized way.
- Each muscle fiber contains multiple myofibrils that
house sarcomeres (the basic functional contractile
unit of skeletal muscle) arranged end to end within
the myofibril.
- Each sarcomere is filled with two kinds of very fine
and threadlike structures: thick and thin
myofilaments.
Microscopic Structure of Muscle:
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Muscle Fibers – specialized contractile cells
that are grouped together and arranged in a
highly organized way.
- Each muscle fiber contains multiple myofibrils that
house sarcomeres (the basic functional contractile
unit of skeletal muscle) arranged end to end within
the myofibril.
- Each sarcomere is filled with two kinds of very fine
and threadlike structures: thick and thin
myofilaments.
Microscopic Structure of Muscle:
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Thick myofilaments – are formed from a
protein called myosin.
Thin myofilaments – are composed mostly of
protein called actin. (Note: Z-lines denote new sarcomere)
Sliding Filament Model:
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The Sliding filament model describes a
process used by muscles to contract. It is a
cycle of repetitive events that cause a thin
filament to slide over a thick filament and
generate tension in the muscle thus shortening
the sarcomere and the muscle.
- Note: That even in a relaxed state, the thick and
thin filaments still over lap.
Sliding Filament Model:
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During a contraction the thick and thin
myofilaments in a muscle fiber first attach to one
another by forming cross-bridges.
- This acts as levers to ratchet or pull the myofilaments
past each other.
- Form properly only when calcium is present.
- Calcium is stored in the endoplasmic reticulum in the
muscle cell.
- Is released into the cytoplasm, only when the cell is
simulated by a nerve impulse.
- Energy (ATP) also needs to be present in order to
shorten the muscle.
Microscopic Structure of Muscle:
Microscopic Structure of Muscle (see
handout):
Muscle Fatigue:
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Occurs when muscle cells are stimulated repeatedly
with inadequate periods of rest.
-During exercise ATP is depleted through cellular
respiration.
- The body tries to replenish the oxygen debt, through
increased oxygen intake (increased inhalation; aerobic
respiration).
- However, when that is not enough the body produces
lactic acid through lactic acid fermentation (anaerobic).
-This is only temporary, and the build up of lactic acid can
cause muscle soreness after exercise.
Muscle Fatigue:
- Therefore, the strength of muscle contractions
decreases which results in muscle fatigue.
- Eventually muscle contraction will no longer occur
(cease).
- After exercise, labored breathing will persist in order
to “pay the debt” for the metabolic effort. This is an
example of your body trying to maintain
homeostasis (bringing your body back into a stable
internal environment).