The vestibular bulbs are believed to relate closely to the clitoris. During arousal, the vestibular bulbs fill with blood. This cuffs the opening of the vagina, which makes the vulva swell up to two or three times its usual thickness. This also puts pressure on the internal clitoris, creating pleasure upon arousal. The spasm of orgasm releases the blood from the bulbs. If orgasm doesn't occur, blood leaves the area over a matter of hours.
The muscles that lay over the top of the vestibular bulbs contract during orgasm. These contractions might feel like they occur in the vagina or even the G-spot. However, they always occur near the vestibular bulbs.
Unlike the bulb of the penis, the vestibular bulbs do not need time to recover between orgasm. Multiple orgasms can be experienced with prolonged stimulation.