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| Corona radiata | |
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 Humanovum examined fresh in thefollicular fluid. Thezona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granulardeutoplasmic area and a peripheral clear layer, and encloses thegerminal vesicle, in which is seen the germinal spot. | |
| Anatomical terminology |
Thecorona radiata is the innermost layer of the cells of thecumulus oophorus and is directly adjacent to thezona pellucida, the inner protective glycoprotein layer of theovum.[1] Cumulus oophorus are the cells surrounding corona radiata, and are the cells between corona radiata and follicular antrum. Its main purpose in many animals is to supply vital proteins to the cell.[citation needed] It is formed by follicle cells adhering to theoocyte before it leaves theovarian follicle, and originates from the squamousgranulosa cells present at the primordial stage of follicular development. The corona radiata is formed when the granulosa cells enlarge and become cuboidal, which occurs during the transition from theprimordial to primary stage. These cuboidal granulosa cells, also known as the granulosa radiata, form more layers throughout the maturation process, and remain attached to the zona pellucida after theovulation of theGraafian follicle. Forfertilization to occur,sperm cells rely onhyaluronidase (an enzyme found in theacrosome of spermatozoa) to disperse the corona radiata from the zona pellucida of the secondary (ovulated) oocyte, thus permitting entry into theperivitelline space and allowing contact between the sperm cell and the nucleus of the oocyte.
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