MUSCLES

Types of Muscles

1. Smooth muscle

2. Cardiac muscle

3. Skeletal muscle

Each type is unique in structure and function

Smooth Muscle

• Single, spindle-shaped cells

• No visible striations (hence the name)

• Found within the walls of “hollow” organs

• Involuntary

Examples: - Gastrointestinal tract

- Bladder

- Kidneys

- Uterus

- Respiratory tract

Cardiac Muscle

• The heart!

• Striated

• Involuntary

Skeletal Muscle

• Usually attached to the skeleton (hence the name)

• Striated

• Voluntary and Involuntary (reflexes)

SKELETAL MUSCLE ANATOMY

All muscles have an origin and insertion.

Origin: The part of the body where the muscle attaches (usually a bone) and does not move when a muscle contracts. (Proximal to the trunk)

Insertion: The other part of the body where the muscle attaches and DOES move when a muscle contracts. (Distal to the trunk)

How do muscles actually work???

Imagine that you reach out to pick up your AP biology textbook to leisurely

read and study for your AP test. Describe and draw pictures of what

you think is going on in your arm muscle when you do this.

Myofibrils: cylindrical organelles found within muscle cells.

Sarcomere: the basic unit of a muscle’s myofibril

Muscle fiber: a single cell of a muscle.

Myosin: the thick filament in a sarcomere

Actin: the thin filaments in a sarcomere

Sliding-filament model of muscle contraction (a.k.a. muscle twitch)

Z lines: border sarcomeres

I bands: contain only actin

A bands: actin and myosin overlap

H zone: contain only myosin (disappears during contraction)

http://upload.wikimedia.org/wikipedia/commons/c/c0/Skeletal_muscle.jpg

Troponin and tropomyosin are two proteins integral in muscle contraction. Troponin is the calcium binding site and tropomyosin

shifts to cover and uncover myosin binding sites.

Sequence of Sliding Filament Model

1. Action potential in motor neuron releases acetylcholine, depolarizing muscle fiber.

2. Transverse tubules depolarize the sarcoplasmic reticulum.

3. Calcium is released and binds to troponin.

4. Tropomyosin shifts and unblocks the actin cross-bridge binding sites

5. Thin filaments are ratcheted across thick filaments by myosin heads and ATP

animation

Dark

vs.

White

Meat

Red and White Fiber

Have more mitochondria

Metabolize ATP slowly, steadily….

For endurance & sustained contractions. Marathon runners have more red fibers

Have high amounts of “myoglobin”

Have less mitochondria

• Metabolize ATP more quickly

• Associated with strength—Weightlifters and sprinters have more white fibers

Red Fibers: “slow twitch”

White Fibers: “fast twitch”