Which of the following muscles act involuntarily? (a) Striated muscles (b) Smooth muscles © Cardiac muscles (d) Skeletal muscles

Options

A. (a) and (b)
B. (b) and (c)
C. (c) and (d)
D. (a) and (d)

Explanation

To determine which muscles act involuntarily, we need to analyze the different types of muscles mentioned in the question: striated muscles, smooth muscles, cardiac muscles, and skeletal muscles.

### Step-by-Step Solution:

1. **Identify Muscle Types**:
- Striated muscles (also known as skeletal muscles)
- Smooth muscles
- Cardiac muscles

2. **Understand Striated Muscles**:
- Striated muscles are primarily skeletal muscles.
- They are attached to bones and are responsible for voluntary movements such as walking, running, and other physical activities.
- Since these movements are under conscious control, striated muscles do not act involuntarily.

3. **Examine Smooth Muscles**:
- Smooth muscles are found in various organs such as the urinary bladder, uterus, and respiratory tract.
- The actions of smooth muscles are not under conscious control; they function automatically.
- Therefore, smooth muscles act involuntarily.

4. **Analyze Cardiac Muscles**:
- Cardiac muscles are specialized muscles found in the heart.
- They are responsible for the rhythmic contraction and relaxation of the heart, which is essential for pumping blood.
- Similar to smooth muscles, cardiac muscles operate involuntarily, meaning they function without conscious control.

5. **Summarize Findings**:
- Striated muscles (skeletal muscles) are voluntary.
- Smooth muscles are involuntary.
- Cardiac muscles are involuntary.
- Therefore, the correct options for muscles that act involuntarily are smooth muscles (B) and cardiac muscles (C).

### Final Answer:
The muscles that act involuntarily are (b) Smooth muscles and (c) Cardiac muscles.

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