Musculo-Skeletal System
Muscles + Bones = Locomotion
Muscles
• When you work out frequently, your
muscles get larger. What do you think is
happening at the cellular level to
increase muscle size?
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• Both men and women can increase
muscle mass by exercise. Why are men
able to increase their muscle mass more
than women?
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• Exercise that increases muscle mass is
a safe way to increase metabolism to
help control weight. Why does higher
muscle mass increase metabolism?
Why muscles?
• Muscle tissue is responsible for
movement and locomotion in animals.
• Muscles rely on contractile fibers to
create motion.
• In vertebrate animals and arthropods,
muscles attach to a skeletal system to
produce locomotion.
Locomotion
• Locomotion is
the result of
muscles pulling
on skeletal
systems, which
is why we often
study these
systems
together.
Types of muscle tissue
•These three types are
found in vertebrates:
•Skeletal: striated,
voluntary control
•Smooth: involuntary
control
•Cardiac: involuntary
control
Smooth muscle
• Have contractile
fibers, but lack
orderly striations of
skeletal muscle.
• Where would you
expect smooth
muscle (involuntary
control) to be
found?
Cardiac muscle
• Influenced by
nerves and
hormones, but has
“electrical” system
of its own to initiate
and coordinate
contractions.
• Where would you
expect cardiac
muscle to be
found?
Skeletal muscle
• Orderly striations
are due to
arrangement of
contractile fibers.
• Produces
locomotion.
• Where would you
expect skeletal
(voluntary control)
muscle to be
found?
Which kind of muscle constricts veins
when blood pressure drops suddenly?
76%
1. Smooth
2. Skeletal
3. Cardiac
21%
2%
1
2
3
Which kind of muscle contracts during
the knee-jerk reflex?
95%
1. Smooth
2. Skeletal
3. Cardiac
2%
1
2%
2
3
Muscle fibers
• A muscle cell is a
“fiber.”
• Fibers are
multinucleated and
contain myoglobin.
(Similar to
hemoglobin – what
is its function?)
• Myofibrils contain
the contractile
fibers.
Myofibril
• The myofibril is
composed of “thick”
and “thin” filaments.
• Each of these
filaments is made
up of strands of
protein.
• How might this
arrangement of
proteins create
motion?
Thick and thin filaments
• The thick filaments,
made mostly of
myosin, have small
“heads” that move.
• The thin filaments
have points to
which the myosin
heads temporarily
attach.
Muscle fiber action
All or nothing
• Fibers are either “on”
(contracted) or “off”
(relaxed).
• When lifting light
weights, only a few
fibers may be “on.”
For heavy weights,
many more may be
“on,” and may take
turns to prevent
fatigue.
Skeletal muscles contract when ___
“walk” along the ___.
1. Actin heads; myosin
fibers
2. Myosin heads, actin
fibers
3. Sarcomeres,
microtubules
4. Microtubles,
sarcomeres
69%
24%
7%
0%
1
2
3
4
What could happen if a person has
a severe calcium deficiency?
1. Cross bridges would
not release from
actin.
2. Muscles would not
contract as strongly
as they should.
3. Motor neurons would
not function properly.
4. ATP would be
depleted.
63%
16%
16%
5%
1
2
3
4
Slow Twitch, Fast Twitch
• Slow-twitch fibers: lots of myoglobin and
mitochondria. What activities would use these
fibers?.
• Fast-twitch: less myoglobin, but more able to
use glycolysis to quickly produce ATP. What
activities would use these fibers?
• Different people have different ratios of these
two fibers.
Fast-twitch fibers
• Fast-twitch fibers
are for bursts of
strength and speed.
• The tradeoff: Fasttwitch fibers fatigue
sooner.
Slow-twitch fibers
• Slow-twitch fibers
are for endurance.
• Trade-off: Slowtwitch fibers cannot
supply a lot of
power at once.
A person born with lots of slow-twitch
muscle fibers would be great at:
93%
1.
2.
3.
4.
High jump
Cross-country skiing
Power lifting
Gymnastics
5%
1
2%
2
3
0%
4
Working out
• Exercise can build
muscle mass.
However, because
muscle fibers (cells) are
large, they rarely
divide.
• If muscle cells rarely
divide, how do muscles
get bigger from
exercise?
Stretching
• Stretching exercises add
strength and flexibility by
increasing muscle length.
• Again, if muscle cells do
not divide, how does a cell
get longer from stretching?
• Caution: stretching
tendons can weaken
joints.
Try this:
• Hold your pen or pencil so that it casts a
shadow on your paper. Line up the tip of
the shadow with a point on your paper.
• How still can you hold your hand? Does
the point of the shadow move? Muscles
generally contract by continuous
“twitching” of muscle fibers. This makes
it hard to hold your hand completely
steady.
Review these questions:
• When you work out frequently, your muscles
get larger. What do you think is happening at
the cellular level to increase muscle size?
• Both men and women can increase muscle
mass by exercise. Why are men able to
increase their muscle mass more than
women?
• Exercise that increases muscle mass is a safe
way to increase metabolism to help control
weight. Why does higher muscle mass
increase metabolism?
Skeletal Systems
W
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K
• Is bone living tissue? Why or why not?
• Why do broken bones take so much
longer to heal than cuts in the skin?
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Types of systems
• Three basic types of skeletal systems in
the animal kingdom:
• Hydrostatic
• Exoskeleton
• Endoskeleton
Hydrostatic skeleton
• Earthworms and sea
anemones have a
hydrostatic skeleton.
• Circular muscles
squeeze the body.
Longitudinal muscles
shorten the body. How
do these actions
produce motion in the
earthworm?
Exoskeleton
• Arthropods (insects,
spiders, etc) have an
external skeleton made of
chitin (a carbohydrate).
• Muscles attach to the
exoskeleton, which is
flexible at the joints.
• What are some
advantages and
disadvantages of an
exoskeleton?
Endoskeleton
• Vertebrates have
an endoskeleton
made of cartilage or
bone.
• Bone and cartilage
are living tissue
(connective tissue).
• What are some
advantages and
disadvantages of an
endoskeleton?
What is an advantage of an
exoskeleton over an endoskeleton?
25%
25%
25%
25%
1. Protection for
internal organs.
2. Must be shed for
growth.
3. Becomes heavy if it
is too large.
4. Storage of minerals.
1
2
3
4
What is an advantage of an
endoskeleton over an exoskeleton?
1. Provides external
protection.
2. Grows as the
organism grows.
3. Provides a point of
attachment for
muscles.
4. Made of protein.
25%
1
25%
2
25%
3
25%
4
Functions of the endoskeleton
• Support and protection for the body.
• Locomotion (in concert with muscles).
• Produce blood cells in bone marrow.
• Store calcium and phosphorous.
• Store energy in yellow marrow.
Cartilage
• Cartilage tissue
consists of
chondrocytes
(cartilage cells) in a
matrix of collagen
protein.
• Cartilage is tough,
flexible material that
pads joints and is
found in the nose and
ears.
Bone tissue
• Bone is made up of
bone cells in a matrix
of collagen and
minerals.
• Three types of bone
cells: osteocytes,
osteoblasts, and
osteoclasts.
• Looking at this
arrangement, can you
see why bone and
cartilage take a long
time to heal?
Bones
• Bones may made up
of:
• Compact bone tissue.
• Spongy bone (location
of red marrow)
• Marrow cavity
(location of yellow
marrow)
Healing fractures
Osteoporosis
• Osteoporosis is loss
of bone mass, leading
to brittle bones.
• Age, lack of calcium
and Vitamin D,
sedentary lifestyle,
multiple pregnancies,
menopause, alcohol,
and smoking
contribute to
osteoporosis.
Review these questions:
• Is bone living tissue? Why or why not?
• Why do broken bones take so much longer to
heal than cuts in the skin?
Locomotion
Motion in Vertebrates
• Motion and locomotion are produced by muscles
pulling on bones.
• Joints in the skeleton allow for parts of the body
to flex and extend, allowing for motion.
Ligaments attach bones to bones at the joints.
• Muscles attach to bones by tendons. Origin is on
a bone that remains stationary. Insertion is on a
bone that moves.
Hinge joint
• A hinge joint allows
flexing and
extending along
one plane.
• Pairs of muscles
work opposite one
another to create
motion.
Ball and socket joint
• A ball and socket
arrangement allows
rotational
movement.
• Multiple pairs of
muscles allow
movement in a
range of directions.
Gliding joints
• In gliding joints,
bones slide past
one another.
• Gliding joints allow
twisting motion.
Movement
• Flexion: decreases angle of a joint.
• Extension: increases angle of a joint.
• Abduction: movement away from
midline.
• Adduction: movement toward midline.
• Rotation: turning around an axis.
• The knee is a hinge joint. Find another
hinge joint in the body. What muscles
move it?
• The hip is a ball and socket joint. Find
another ball and socket joint in the body.
What muscles move it?
• The wrist is a gliding joint. Find another
gliding joint in the body. What muscles
move it?
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• Give examples of joints and movements
that demonstrate:
• Flexion
• Extension
• Abduction
• Adduction
• Rotation
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Name that muscle!
• For each of the following slides:
• Name the muscle or muscle group, if you
can.
• State what kind of movement it produces.
• Locate the bone (or bones) that it moves.
• Which muscles produce the opposite
movement?
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One last question:
• In what ways do muscles and the
skeletal system help maintain
homeostasis? Discuss and list as many
ways as you can think of.