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: Studies of synergy between morphine and a novel sodium channel blocker , CNSB002 , in rat models of inflammatory and neuropathic pain .
### Output Text:
Studies of synergy between <span class="chemical">morphine</span> and a novel <span class="chemical">sodium</span> channel blocker , <span class="chemical">CNSB002</span> , in rat models of inflammatory and neuropathic pain . 