Download 8.2 Structure of skeletal muscle

Functions of the Muscular System
• Muscles are organs composed of
specialized cells that use chemical
energy stored in nutrients to contract
Functions of the Muscular System
• The main function of the muscular
system is movement
• Muscular action also:
• Propels body fluids and foods
• Generates heartbeat
Skeletal Muscle
- Composed of
- Muscle tissue
- Nervous tissue
- Blood
- Other Connective
Tissues
Connective Tissue
Coverings
- Fascia is a connective
tissue that separates
an individual skeletal
muscle from adjacent
muscles
- It also holds the muscle
in position
- Like plastic wrap
around muscles
Connective Tissue
Coverings
- Aponeuroses are
broad fibrous sheets
of connective tissue
- These can attach to
bone or to the
coverings of
adjacent muscles
Skeletal Muscle
Anatomy
- Tendons attach
muscle to bone
- The main part of the
muscle is called the
belly of the muscle
Skeletal Muscle Anatomy
- Muscles are made up of bundles of muscle
fibers which are called fascicles
- These fascicles are separated by connective
tissue
Skeletal Muscle Anatomy
- Fascicles are made of individual muscle
fibers, which are the muscle cells
Skeletal Muscle Anatomy
- Muscle cells are called fibers because they are
much longer than they are wide
- These cells are usually as long as the whole
muscle
Skeletal Muscle Fibers
- Skeletal muscle fiber is a
single cell that contracts
in response to a stimuli
- The cytoplasm of the
skeletal muscle fiber is
called sarcoplasm
Skeletal Muscle Fibers
- The muscle fiber has
many nuclei, because it is
so long
- The endoplasmic reticulum
of the muscle fiber is
called sarcoplasmic
reticulum
Skeletal Muscle Fibers
- The muscle cell contains
many myofibrils which
are composed of thick
and thin elements
- The thin filaments in
myofibrils are actin,
the thick ones are
called myosin
- The organization of
these filaments make
up the striations you
see in skeletal muscle
fibers
- The cytoplasm within
the muscle fiber is
called sarcoplasm
- The endoplasmic
reticulum inside the
muscle fiber is
called sarcoplasmic
reticulum
- The repeating units
on the myofibrils are
called sarcomeres
- Myofibrils can be
thought of a chain
of sarcomeres.
- Sarcomeres run from
Z-line to Z-line,
which the actin
filaments are
attached directly to
- I bands are the part
of the sarcomere
which is only actin
filaments
- A bands are
composed of thick
myosin filaments
- In parts of the A
band, the myosin
and actin overlap
- I bands are the
lighter colored
bands
- A bands are the
darker colored
bands
- The brain sends
signals to muscle
fibers to cause a
contraction
- Motor neurons are
the nerves that bring
the signal from the
brain to the muscle
- Skeletal muscle fibers
are functionally but
not physically
connected to the
neuron
- Think of how your
voice travels from
your mouth to your
cell phone
- This functional
connection is called
a synapse
- Neurons
communicate with
the cell through
neurotransmitters,
which are a
chemical signal
- A neuromuscular
junction is the entire
connection between
the motor neuron
and the muscle fiber
(what this picture is
showing)
- The brain sends a
signal through the
neuron
- When the signal
reaches the end of
the neuron,
neurotransmitters
are released from the
synaptic vesicles
- The neurotransmitter
travels through the
synaptic cleft and is
picked up by
receptors on the
muscle fiber
- When the receptors
sense the
neurotransmitter, they
cause calcium to
enter the muscle fiber
- This increase in
calcium is what
causes a muscle
contraction
- The functional unit
of a muscle
contraction is the
sarcomere
- Let’s start off when
the neurotransmitter
is picked by the
receptors on the
outside of the muscle
cell
- This causes a flood of
calcium into
sarcoplasm
Where did the calcium
come from?
- The sarcoplasmic
reticulum has a
storage of calcium
- When the cell senses
the neurotransmitter,
calcium is released
from the SR into the
sarcoplasm
- Calcium floods over
the myofibrils
- The calcium binds to
troponin
- This causes the
troponin to move
tropomyosin off of
the myosin binding
sites of the actin
- Now, the myosin cross
bridges can bind to
myosin to actin
- Cross bridge pulls the
actin filament, and then
releases
- If calcium is still present,
this happens again
- This is how the myosin
“walks” across the actin
- When the signal to the
muscle stops, myosin cross
bridges release
- The muscle contraction
stops