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: Serotonergic drugs , benzodiazepines and baclofen block muscimol - induced myoclonic jerks in a strain of mice .
### Output Text:
Serotonergic drugs , <span class="chemical">benzodiazepines</span> and <span class="chemical">baclofen</span> block <span class="chemical">muscimol</span> - induced myoclonic jerks in a strain of mice . 