In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: NCS included recording of sensory nerve action potentials ( SNAPs ) from median , radial , ulnar , and sural nerves .
### Output Text:
NCS included recording of sensory nerve action potentials ( SNAPs ) from median , radial , ulnar , and sural nerves . 