GRADE 6 - SCIENCE WEEK 6
MUSCULAR SYSTEM
Muscles
• 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?
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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?
1. Smooth 2. Skeletal 3. Cardiac
Which kind of muscle contracts during the knee-jerk reflex?
1. Smooth 2. Skeletal 3. Cardiac
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
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.
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: Fast-twitch fibers fatigue sooner.
Slow-twitch fibers
• Slow-twitch fibers are for endurance.
• Trade-off:
Slow-twitch fibers cannot supply a lot of power at once.
A person born with lots of slow-twitch muscle fibers would be great at:
1. High jump
2. Cross-country skiing
3. Power lifting 4. Gymnastics
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?
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 may made up of:
• Compact bone tissue.
• Spongy bone (location of red marrow)
• Marrow cavity
(location of yellow marrow)
Bones
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.
GOOD JOB!
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