2. Functions of Muscular System
Slide 6.8
1. Produce movement and manipulate the
environment
2. Maintain posture
3. Stabilize joints
4. Generate heat
3. The Muscular System
Muscles are responsible for all types of
body movement
Three basic muscle types are found in
the body
Skeletal muscle
Cardiac muscle
Smooth muscle
4. Similarities of all Types of Muscles
Slide 6.2
Muscle cells are elongated
(muscle cell = muscle fiber)
Contraction of muscles is due to the
movement of microfilaments
All muscles share some terminology
Prefix myo refers to muscle
Prefix mys refers to muscle
Prefix sarco refers to flesh
7. Skeletal Muscle Characteristics
Most are attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by
connective tissue
Skeletal, striated, voluntary
9. Cardiac Muscle Characteristics
Has striations
Usually has a
single nucleus
Joined to another
muscle cell at an
intercalated disc
Involuntary; the
heart has a
pacemaker
Found only in the
heart
Figure 6.2b
Cardiac, striated, involuntary
10. Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Single nucleus
Involuntary – no
conscious control
Found mainly in the
walls of hollow
organs
Arranged in layers
2 layers Figure 6.2a
Smooth, no striations, involuntary
11. Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are just beneath the sarcolemma
Sarcolemma (organelle) – specialized
plasma membrane
Figure 6.3a
12. Microscopic Anatomy of Skeletal Muscle
Sarcoplasmic reticulum (organelle)
Specialized smooth ER that surrounds all
myofibrils
Stores Ca ions to be able to release them
on demand
Figure 6.3a
13. Microscopic Anatomy of Skeletal Muscle
Myofibril (organelle)
Bundles of myofilaments
Myofibrils are aligned to give distrinct bands
I band =
light band
A band =
dark band
Figure 6.3b
14. Microscopic Anatomy of Skeletal Muscle
Sarcomere
Chains of contractile units in myofibrils
Two types of myofilaments
Thick = myosin
Thin = actin
Figure 6.3b
15. Microscopic Anatomy of Skeletal Muscle
Thick filaments = myosin filaments
Composed of the protein myosin
Figure 6.3c
16. Microscopic Anatomy of Skeletal Muscle
Thin filaments = actin filaments
Anchored to the Z disc
Composed of the protein actin
Figure 6.3c
17. Microscopic Anatomy of Skeletal Muscle
Myosin filaments have heads
(extensions, or cross bridges)
Myosin heads link the thick and thin
during contraction
Myosin and
actin overlap
somewhat
Figure 6.3d
18. Microscopic Anatomy of Skeletal Muscle
Thick (myosin) and thin (actin) filaments
produce the striations in skeletal muscle
Figure 6.3d
19. Organizational levels of Skeletal Muscle
Organ – the muscle (biceps)
Fiber – a muscle cell
Myofibril – organelle composed of sarcomeres
and myofilaments
Sarcomeres – unit of myofibril
Myofilament – actin and myosin
20. Skeletal Muscle Cell
Nucleus – control center
Sarcolemma – plasma membrane
Sarcoplasm – cytoplasm
21. Skeletal Muscle Cell
Sarcoplasmic reticulum – storage of
calcium ions to be released when
stimulated by an impulse
T-tubules – surround the myofibrils and
assist in delivering ions
22. Skeletal Muscle Cell
Mitochondria (lots) – provide energy and
ATP
Myofibril – composed of thick and thin
filaments and many sarcomeres
24. Nerve Stimulus to Muscles
1. Skeletal muscles
must be stimulated
by a nerve to
contract
Motor unit is
composed of:
One neuron
All muscle cells
stimulated by
that neuron
One nerve cell
branches into
axonal terminals
Figure 6.4a
25. Nerve Stimulus to Muscles
Axonal terminals form
junctions with
sarcoplasm called
neuromuscular junctions
Nerve and muscle do
not make contact there
is a gap
Synaptic cleft – gap
between nerve and
muscle
Gap is filled with
interstitial fluid
Figure 6.5b
26. Nerve Stimulus to Muscles
2. Action potentials are
sent down the neuron in
response to a stimuli
Because the two cells
do not touch, the action
potential cannot ‘jump
the gap’
Figure 6.5b
27. Nerve Stimulus to Muscles
3. The neuron
communicates indirectly
with the muscle cell by
releasing a neurotransmitter
The neurotransmitter for
skeletal muscle is
acetylcholine (ACh) and it is
stored in the axonal terminal
4. Sarcolemma has
receptors for Ach and
causes an action potential in
muscle cell
28. Transmission of Nerve Impulse Wrap-up
1. How does the neurotransmitter
produced by the motor neuron cause
the skeletal muscle to contract?
2. What is the neurotransmitter in muscle
cells?
3. What is the synaptic cleft?
4. What makes up a motor unit?
5. List the steps of transmission of a
nerve impulse.
29. The Sliding Filament Theory of Muscle Contraction
Slide 6.17a
Put your right palm on
the back of your left
hand.
Now slide your right
palm toward your left
elbow
What happened to the
distance between your
elbows?
This is how muscle
contraction works!
Figure 6.7
30. The Sliding Filament Theory of Muscle Contraction
Slide 6.17a
Activation by nerve causes
calcium to be released by
the sarcoplasm reticulum
Calcium binds to actin and
exposes myosin binding
sites where the myosin
heads attach and form a
crossbridge
ATP is used as the energy
source
Figure 6.7
31. The Sliding Filament Theory of Muscle Contraction
Slide 6.17b
The thin filament slides
past the thick filament
towards the center as
each myosin head
attaches and detaches
Distance between Z
discs shortens as actin
moves toward the center
The result is that the
entire muscle is
shortened (contracted)
Figure 6.7
32. The Sliding Filament Theory of Muscle Contraction
Slide 6.17b
Length of the A band
(myosin and actin) stays
the same
Length of the H zone (only
thick filaments) shortens
Length of the I band (thin
filaments) shortens
http://highered.mcgraw-
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udent_view0/chapter42/anim
ations.html#
Figure 6.7
33. The Sliding Filament Theory
Go to figure 6.8 in your book and summarize the steps
for the sliding filament theory and explain how a muscle
contracts
34. Transmission of Nerve Impulse to Muscle
Contraction
1. Nerve impulse sent and received by axonal terminal
2. Neurotransmitter (acetylcholine) is released upon arrival
of nerve impulse
3. Diffuses across synaptic cleft and attaches to receptors
on the sarcolemma
4. Triggers an action potential of the muscle cell
5. The action potential causes the SR to release calcium
ions
6. The calcium ions bind with the actin filaments to open
the binding site for myosin
7. Myosin heads bind to them with the help of ATP
8. The cell contracts