Muscular System
Organization
Muscle Contraction
Energy for Movement
Functions of the Muscular System
• Supports the body
• Makes the bones move
• Helps maintain constant body
temperature
• Assists movement in
cardiovascular and lymphatic
vessels
• Helps protect internal organs
and stabilize joints
Structure of Skeletal Muscle
Each fascicle is
a bundle of
muscle fibers
Whole muscle
is a bundle of
many fasicles
The fascia
surrounds the
muscle
Each sarcomere
is made of actin
and myosin fibers
Each muscle
fiber is a bundle
of myofibrils
Each myofibril is
made of many
sarcomeres
Skeletal Muscles Work in Pairs
• Muscles contract (shorten)
or relax
• Muscle contraction
pulls on an attached
bone
• Prime mover = muscle
doing the most work
• Synergists = muscles
assisting prime mover
• Antagonist = muscle with
action opposite to prime
mover
on
stationary
bone
on bone
that moves
Ways to Name Muscles
by location
by attachment
by direction of
muscle fibers
by shape
by number of
attachments
by action
by size
Structure of a Skeletal Muscle Cell
cytoplasm,
contains
organelles and
myofibrils
plasma
membrane
bundle of muscle
cells (fibers)
sarcolemma
myofibril
sarcoplasm
one myofibril
Skeletal
muscle cell
(fiber)
Z line
T tubule
nucleus
sarcoplasmic
reticulum
extensions of
sarcolemma,
contact sarcoplasmic
reticulum
one sarcomere
contractile
unit
Smooth ER,
stores calcium
Z line
Contains actin
and myosin
filaments for
contraction
Applying Your Knowledge
1.
2.
3.
4.
5.
Synergist
Sarcomere
Myofibril
Antagonist
Muscle Fiber
A. A fascicle is a bundle of ________.
B. Which one assists the primer mover?
C. Which one is the contractile unit?
Structure of the Sarcomere
Muscle has light and dark bands (striations) corresponding
to the placement of myofilaments in the sarcomere.
Sliding Filament Theory of Muscle Contraction
Sarcomere shortens when actin filaments slide
past myosin filaments and approach one another.
Events at the Neuromuscular Junction
Neurotransmitter
is released into
synaptic cleft
between neuron
and muscle cell
Neurotransmitter
binds to receptors
on sarcolemma,
impulse spreads
down T tubules
Sarcoplasmic reticulum
releases calcium
to stimulate contraction
Events at the Sarcomere
Attached to
tropomyosin at
regular intervals
Calcium binds to
troponin
Arranged over
myosin binding
sites on actin
filaments
Events at the Sarcomere
ATPase Enzyme
Energy from ATPADP + P causes myosin heads to
form cross-bridges that pull actin filaments toward
the center of the sarcomere.
Applying Your Knowledge
1.
2.
3.
4.
5.
Troponin
Actin
Tropomyosin
Myosin
Calcium
A. Which is released by the sarcoplasmic
reticulum to stimulate contraction?
B. Which one has ATPase activity?
C. Which one binds to calcium?
D. Which one slides past another fiber to
shorten the sarcomere?
Whole Muscle Contraction
• Strength of Contraction
depends on
– number of muscle fibers
contracting
– number of motor units
responding
– number of muscle fibers
within a motor unit
Energy for
Muscle Contraction
built up in
resting
muscle
anaerobic
aerobic
anaerobic
Slow-and-Fast Twitch Muscle Fibers
Motor units with
many fibers