Muscles
Muscles
- Unit 1: Cells
- Unit 2: Organisms
- Unit 3: Microorganisms
- Unit 4: Digestion and excretion
- Unit 5: Respiration
- Unit 6: Circulatory System
- Unit 7: Nervous System
- Unit 8: Senses
- Unit 9: Musculoskeletal
- Unit 10: Endocrine System
Muscles
The skeleton alone cannot produce movement. Movement is made possible by the connection and cooperation between muscles and the bones of the body.
Muscles attach to bones and use them as leverage points. By contracting and relaxing, they create movement.
Some body movements are voluntary, meaning we control them — these are carried out by skeletal muscles. Other movements are involuntary, such as the beating of the heart, controlled by cardiac muscle, or the motion of the digestive system, controlled by smooth muscles that open and close passageways automatically.
Quick Fact
There are three types of muscles in the human body: skeletal, cardiac, and smooth — each with a specific structure and function.
Important Concept
There are three main types of muscle: skeletal (voluntary), cardiac (involuntary), and smooth (involuntary). Each type performs distinct roles in body movement and internal function.
Common Mistake
Many people believe only skeletal muscles are important, but cardiac and smooth muscles are vital for involuntary actions like digestion and heartbeat, which are essential for survival.
Questions
| Skeletal | Smooth | Cardiac | |
|---|---|---|---|
| Shape |
|
|
 |
| Function | Involuntary | ||
| Color | Red | White – pink | Red |
| Location | Walls of digestive, respiratory systems |
Show Answer
| Skeletal | Smooth | Cardiac | |
|---|---|---|---|
| Shape |
|
|
|
| Function | Voluntary | Involuntary | Involuntary |
| Color | Red | White – pink | Red |
| Location | Attached to bones | Walls of digestive, respiratory systems | Heart |
Skeletal Muscle Tissue
Skeletal muscle tissues are long, thin fibers arranged in bundles running parallel along their length. These fibers are grouped together and surrounded by connective tissue. The connective tissue joins them together and attaches them to tendons, which then connect to bones to form a working muscle group.
There are connective tissues between muscle fibers and around the muscle as a whole. These tissues continue into the tendons (see Figure 10), which connect muscles to bones and help transmit force during movement.
When all the muscle fibers contract together, the muscle becomes thicker and shorter. The tendon connected to the muscle pulls the bone and causes it to move.
Muscles typically work in pairs, contracting and relaxing in opposition. When one muscle contracts and shortens, it pulls the bone in one direction. The opposing muscle relaxes. When the movement reverses, the roles switch. This is why skeletal muscles often act in antagonistic pairs — flexor and extensor muscles.
Quick Fact
Tendons are strong connective tissues that attach muscles to bones. Unlike ligaments, which connect bones to other bones, tendons transfer the force of muscle contraction to the skeleton.
Important Concept
Antagonistic muscle pairs consist of two muscles that work in opposition — when one contracts, the other relaxes. This system allows controlled movement in both directions, such as bending and straightening the arm.
Common Mistake
It’s a common misunderstanding to think that muscles can push bones. In fact, muscles can only pull. Movement in the opposite direction requires a second muscle pulling the bone back — this is why muscles must work in pairs.
Questions
Show Answer
Tendons connect skeletal muscles to bones and transmit the force of muscle contraction, enabling movement of the skeleton.
Show Answer
Because muscles can only contract (pull), they must work in pairs so one muscle moves a bone in one direction while the other moves it back — allowing controlled, reversible movement.
Did You Know?
Skeletal muscles in the body are categorized based on their shape, location, and function. Below, you can see some of the most important skeletal muscles labeled on the human body.
