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: We suggest that the observed effects are dose - dependent and derive primarily from muscle atrophy and derive less from changes in acetylcholine receptor expression .
### Output Text:
We suggest that the observed effects are dose - dependent and derive primarily from muscle atrophy and derive less from changes in <span class="chemical">acetylcholine</span> receptor expression . 