Problem 8 - Campbell Biology Concepts & Connections

Question

The diaphragm is a large sheet of muscle that helps move air in and out of your lungs. Breathing is automatically controlled by the brain, but you can choose to hold your breath or breathe deeper. What kind of muscle do you suppose makes up the diaphragm? (Explain your answer.)

Step-by-Step Solution

Answer

The diaphragm is made up of skeletal muscle because it is controlled both voluntarily and involuntarily.

Step 1: Identify Muscle Types

Begin by identifying the three main types of muscle tissues in the human body: skeletal muscle, smooth muscle, and cardiac muscle. Understand the primary functions and characteristics of each type.

Step 2: Determine Control Mechanism

Analyze how the diaphragm is controlled. It is largely automatic (involuntary) but can also be controlled voluntarily. Compare this with the control mechanisms of each muscle type.

Step 3: Understand Skeletal Muscle

Recall that skeletal muscles are typically under voluntary control by the somatic nervous system, but they can also operate involuntarily, as seen in reflex actions.

Step 4: Match Characteristics

Match these characteristics with those of the diaphragm. The diaphragm’s ability to be controlled both voluntarily and involuntarily suggests it is made of skeletal muscle.

Step 5: Conclusion

By matching control mechanisms and muscle characteristics, conclude that the diaphragm is made up of skeletal muscle due to its voluntary and involuntary control.

Key Concepts

Muscle Types

There are three main types of muscles in the human body: skeletal, smooth, and cardiac.
Each type has distinct functions and characteristics:

• Skeletal Muscle: These are attached to bones and help with voluntary movements.
• Smooth Muscle: Found in the walls of internal organs, these muscles are not under conscious control.
• Cardiac Muscle: This muscle makes up the heart and contracts involuntarily to pump blood.

Understanding these muscle types is key to figuring out which one the diaphragm belongs to.

Skeletal Muscle

Skeletal muscles are commonly associated with physical activities and movements we can control.
They are often attached to the skeleton by tendons. These muscles are known for the following:

• Voluntary Control: Most of the time, we can consciously control these muscles.
• Striated Appearance: Under a microscope, they have a striped look due to the organized pattern of muscle fibers.
• Reflex Actions: Though primarily under voluntary control, they can work involuntarily in certain situations like reflex responses.

The diaphragm is a type of skeletal muscle because it shares these characteristics.

Involuntary Control

Involuntary control means that certain muscles function automatically without conscious effort.
Examples include the heart beating or the intestines moving food along.

• Cardiac Muscle: This muscle contracts involuntarily to pump blood throughout the body.
• Smooth Muscle: These muscles in our digestive system work without us thinking about them.

Although skeletal muscles are often voluntary, they can be involuntarily controlled as seen in reflex actions. The diaphragm, similarly, works both unconsciously—when we breathe normally—and consciously—when we choose to hold our breath.

Voluntary Control

Voluntary control refers to actions that are consciously initiated by our brains.
When we walk, pick up objects, or talk, we are using skeletal muscles under voluntary control.

• Somatic Nervous System: This is the part of the nervous system that governs voluntary movements.
• Feedback Mechanisms: Our brains send signals to muscles to contract, and muscles send feedback to the brain regarding their position and force.

The diaphragm can also be controlled voluntarily when we decide to take deep breaths or hold our breath. This dual control is unique to skeletal muscles, confirming that the diaphragm is indeed a skeletal muscle.