7.7.1 Types of Muscles

There are three types of muscle tissues: smooth, cardiac and skeletal.

Smooth Muscles

• These are distributed widely throughout the body and are more variable in function than other muscle types.
• The smooth muscle cells are spindle shaped, with a single nucleus located in the middle of the cell.
• Myofilaments are not organised into sarcomeres.
• Consequently, smooth muscle does not have a striated appearance.
• Smooth muscle cells contain noncontractile intermediate filaments.
• Smooth muscles are involuntary in function.
• They are found in digestive, reproductive, urinary tract, blood vessels etc.

Cardiac Muscles

• These are found only in heart.
• They branch extensively.
• Cardiac muscles are striated like skeletal muscle, but each cell usually contains one nucleus located near the centre.
• Adjacent cells join together to form branching fibres by specialised cell-to-cell attachments called intercalated discs, which have gap like junctions that allow action potentials to pass from cell to cell.

Skeletal Muscles

- These muscles are attached to the bone and are responsible for movements of body parts and whole body movements (locomotion).

Summary Table of Muscle Types

Intermediate Level

Types of Muscles

Detailed Description of Each Muscle Type

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Muscles are specialized tissues.
• 2. They can contract and relax.
• 3. They provide movement.
• 4. They maintain posture.
• 5. They move body fluids.
• 6. They produce heat.
• 7. Study of muscles is myology.
• 8. Three types of muscles: smooth, cardiac, skeletal.
• 9. Smooth muscles are spindle-shaped.
• 10. Smooth muscles have one nucleus.
• 11. Smooth muscles are involuntary.
• 12. Smooth muscles are found in hollow organs.
• 13. Cardiac muscles are found only in the heart.
• 14. Cardiac muscles are branched.
• 15. Cardiac muscles have one nucleus.
• 16. Cardiac muscles have intercalated discs.
• 17. Skeletal muscles are attached to bones.
• 18. Skeletal muscles are striated.
• 19. Skeletal muscles are multinucleate.
• 20. Skeletal muscles are voluntary.

Remember

• - Muscles = specialized tissues for movement
• - Myology = study of muscles
• - Functions = movement, posture, movement of body fluids, heat production
• - Types = smooth, cardiac, skeletal
• - Smooth muscles = spindle-shaped; single nucleus; involuntary; in hollow organs
• - Cardiac muscles = branched; single nucleus; intercalated discs; in heart
• - Skeletal muscles = striated; multinucleate; voluntary; attached to bones

Common Mistakes

• 1. Confusing the three types of muscles — Smooth, cardiac, skeletal.
• 2. Mixing up the characteristics — Smooth: unstriated; cardiac: striated; skeletal: striated.
• 3. Forgetting the number of nuclei — Smooth: one; cardiac: one; skeletal: many.
• 4. Mixing up the locations — Smooth: hollow organs; cardiac: heart; skeletal: bones.
• 5. Confusing voluntary and involuntary — Skeletal: voluntary; smooth and cardiac: involuntary.
• 6. Forgetting the role of intercalated discs — Allow action potentials to pass from cell to cell.
• 7. Mixing up the speed of contraction — Smooth: slow; cardiac: intermediate; skeletal: slow to rapid.
• 8. Believing all muscles are voluntary — Only skeletal muscles are voluntary.
• 9. Mixing up the functions — Smooth: movement of substances; cardiac: pumps blood; skeletal: moves skeleton.
• 10. Forgetting the role of myology — Study of muscles.

Quick Revision

The specialized tissues that can undergo contraction and relaxation and provide movements of body parts or whole body are called muscles. The study of muscles is called myology. They also function to hold body parts in postural positions, movement of body fluids and heat production. There are three types of muscle tissues: smooth, cardiac and skeletal. Smooth muscles are distributed widely throughout the body and are more variable in function than other muscle types. The smooth muscle cells are spindle shaped, with a single nucleus located in the middle of the cell. Myofilaments are not organised into sarcomeres. Consequently, smooth muscle does not have a striated appearance. Smooth muscles are involuntary in function. They are found in digestive, reproductive, urinary tract, blood vessels etc. Cardiac muscles are found only in heart. They branch extensively. Cardiac muscles are striated like skeletal muscle, but each cell usually contains one nucleus located near the centre. Adjacent cells join together to form branching fibres by specialised cell-to-cell attachments called intercalated discs, which have gap like junctions that allow action potentials to pass from cell to cell. Skeletal muscles are attached to the bone and are responsible for movements of body parts and whole body movements (locomotion).

60-Second Revision

• Muscles = specialized tissues for movement
• Myology = study of muscles
• Functions = movement, posture, movement of body fluids, heat production
• Types = smooth, cardiac, skeletal
• Smooth muscles = spindle-shaped; single nucleus; involuntary; in hollow organs
• Cardiac muscles = branched; single nucleus; intercalated discs; in heart
• Skeletal muscles = striated; multinucleate; voluntary; attached to bones
• Warning: Skeletal muscles are voluntary; smooth and cardiac muscles are involuntary

NEXT TOPIC

• Chapter:
• 7. Support and Movement

• Topic:
• 7.8 STRUCTURE OF SKELETAL MUSCLES

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