What are nodes of Ranvier?

Explanation

### Step-by-Step Solution:

1. **Definition of Nodes of Ranvier**:
- Nodes of Ranvier are defined as points of discontinuity along the axon of a neuron where the myelin sheath is absent.

2. **Structure of Neurons**:
- Neurons have a structure that includes dendrites, a cell body, and an axon. The axon can be covered by a myelin sheath, which is an insulating layer.

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