At the synapse, or the motor end plate, acetylcholine opens sodium channels causing sodium influx into the muscle fiber causing depolarization. This depoâ¦larization causes calcium released from the sarcoplasmic reticulum that initiates muscle contraction by activating sarcomeres.
On average, girls begin puberty around ages 10â11; boys around ages 11â12. Girls usually complete puberty around ages 15â17, while boys usually complete puberty around ages 16â17. The major landmark of puberty for females is menarche, the onset of menstruation, which occurs on average between ages 12â13; for males, it is the first ejaculation, which occurs on average at age 13.
Male normally start puberty at the age of 12 and end donât end puberty until the age of 25. It must be noted that there are different times when different parts/systems stop its own âpuberty.â For example, the typical male is skeletally matured at the age of 20, which is why a typical maleâs height growth stops at the latter half of the 19th year, anywhere from 19.5 to 20.