These cell balls are separated by fibrovascular stroma and surrounded by sustentacular cells. The olfactory epithelium consists of olfactory sensory cells, sustentacular cells and basal cells. The carotid body is a small cluster of chemoreceptor cells, and supporting sustentacular cells. It includes two populations of cells; glomus (type I) cells and sustentacular (type II) cells. The sustentacular cells function as metabolic and physical support for the olfactory epithelium. The sustentacular cells are S-100 positive and focally positive for glial fibrillary acidic protein. Glomus type II cells are sustentacular cells having a similar supportive function to glial cells.