The heavy meromyosin (HMM) component, i.e the head and short arm projects outwards at regular distance and angle from each other from the surface of a polymerised myosin filament and is known as 

Options

A. Neuromuscular Junction
B. Motor unit
C. Cross bridge
D. Cross arm

Explanation

To solve the question regarding the heavy meromyosin (HMM) component and its projections from the surface of a polymerized myosin filament, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Components**: Start by identifying what heavy meromyosin (HMM) is. HMM is a part of the myosin molecule that consists of the head and the short arm.

2. **Analyze the Structure**: Recognize that the head and short arm of HMM project outward from the myosin filament. This projection occurs at a regular distance and angle, which is crucial for the function of myosin in muscle contraction.

3. **Review the Options**: The question provides four options:
- A) Neuromuscular junction
- B) Motor unit
- C) Cross-bridge
- D) Cross arm

4. **Evaluate Each Option**:
- **Option A (Neuromuscular junction)**: This is incorrect because it refers to the connection between a motor neuron and a muscle fiber, not related to myosin structure.
- **Option B (Motor unit)**: This is also incorrect as it describes the functional unit of a motor neuron and the muscle fibers it innervates, not the structure of myosin.
- **Option C (Cross-bridge)**: This option is incorrect as well; the cross-bridge refers to the interaction between actin and myosin during muscle contraction, not the projections of HMM.
- **Option D (Cross arm)**: This is the correct answer. The term "cross arm" refers to the specific projections of the heavy meromyosin component from the myosin filament.

5. **Conclusion**: Based on the analysis of the options, the correct answer to the question is **Option D: Cross arm**.