Transcript[]
Text reads: The Mysteries of Life with Tim and Moby
Tim is lifting a weight, while Moby stands beside him.
TIM: One, two, three. Whew, what a workout!
MOBY:Beep.
Moby hands Tim a towel.
TIM: Thanks.
Tim wipes sweat off his face and reads from a typed letter.
TIM: Dear Tim and Moby, If the heart is a muscle, how come I can’t flex it? From Dorothy. You can’t flex your heart because it’s an involuntary muscle.
An animated heart pumps a steady heartbeat.
MOBY:Beep?
TIM:Well, that’s one of the two basic types of muscle. The other kind is voluntary.
An animation shows the muscular system of a human figure.
TIM:Voluntary muscles are the ones that let you move the different parts of your body.
The human figure shrugs its shoulders.
TIM:Whenever you smile, lift weights, or walk around, your voluntary muscles are at work.
A split screen shows images of a face smiling, an arm lifting a weight, and a leg walking. The images then reveal the network of muscles in each body part underneath the skin.
MOBY:Beep?
TIM:They’re called voluntary because they’re under your conscious control.
An animation shows nerve signals travelling from the brain, down the spine, across the ribs, and down each arm and leg of the human figure.
TIM:When you decide to move a part of your body, a nerve signal travels from your brain to the right muscle, making it move.
A fly buzzes and lands on the arm muscles of the figure. An impulse flares in the nerve of the arm. The figure swats the fly.
TIM:Of course, not all movement of voluntary muscle is consciously done—there are also reflexes, like when you automatically move your hand away from a hot object. Anyway, voluntary muscles are also called skeletal muscles because their job is to move bones.
MOBY:Beep?
TIM:Skeletal muscles work in teams at your joints, where two or more bones meet.
An image appears of elbow muscles and bones joined together.
TIM:To move the elbow joint, one set of muscles shrinks, or contracts, while the other one relaxes and gets longer.
An animation shows the elbow muscles moving up and down. The muscle on top reads “contracts.” The muscle on the bottom reads “relaxes.” An inset image of an arm with skin covering the muscles and joints mimics the same up and down motion.
TIM:The contracting muscle pulls on the bone.
An arrow points up toward the contracting muscle. . TIM:When the muscles switch jobs, your arm bends the other way.
The arms bend in the opposite directions; now, the upper muscle reads “relaxes” and the lower muscle read “contracts.”
TIM:Skeletal muscles are attached to bones by thick bands of tough tissue called tendons.
An image of a face appears. Only the muscles are visible, without the layer of skin. Muscles surround the lips and eyes, and form bands over the cheeks, forehead, scalp, and down the neck.
TIM:Some of your face muscles are a little different—they’re attached directly to the skin and other tissues, letting you make different expressions.
The face smiles and then frowns.
MOBY:Beep?
TIM:Involuntary muscles are totally different.
A silhouette of a human appears with a beating heart in the chest.
TIM:For one thing, you don’t have any control over them—they work all day long, whether you want them to or not. These muscles line the walls of digestive organs, like the esophagus, stomach, and intestines. They contract slowly and rhythmically to move food through. The heart inside the human silhouette is replaced with an image of the digestive system, from the mouth to the stomach to the intestines.
TIM:Involuntary muscles in your veins and arteries control the flow of blood.
An animation shows blood cells moving through a blood vessel.
TIM:Under the microscope, voluntary and involuntary muscles look different.
An image shows striated muscle fibers in voluntary muscle tissue.
TIM:The voluntary tissue is striated, or striped. They're arranged in bundles of cells called muscle fibers. Most involuntary tissue is made of smooth muscle. It appears smooth because its cells are arranged in sheets.
An image shows the arrangement of cells in smooth muscle tissue.
TIM: The heart is a kind of in-between case called cardiac muscle. It's striated, like skeletal muscles, but involuntary- it just keeps beating and beating.
The human silhouette with the beating heart reappears.
TIM:Like the rest of your body, muscles are powered by a sugar called glucose.
A split screen shows an image of the muscles, bones, and tendons of the elbow next to an image of glucose molecules. The elbow lifts up and down as the glucose molecules pop and disappear.
TIM:Without a constant supply of glucose, muscles start to get tired.
The elbow slows its motion, and all of the glucose is gone. Small oxygen molecules appear in their place.
TIM:They also need plenty of oxygen, or they cramp up.
A buzzer of alarm sounds, and the arm muscle shoots out pain signals.
TIM:You’ve probably felt that when you exercise too hard.
An image shows an arm lifting a weight.
TIM:Exercising your skeletal muscles helps them get bigger and stronger. It also strengthens your heart muscle by making it beat harder and faster.
TIM:Which is why I’m so huge.
Tim lifts a small weight.
TIM:Errr…
Moby grabs Tim and lifts him above his head.
TIM:Whoa! Moby! Whoa! Put me down!
Moby presses Tim overhead, up and down.
TIM:Aaaaah! I’m getting sick!