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.
girls usually complete puberty by ages 15 17 while boys usually complete puberty by ages 16 17 the major landmark of puberty for females is menarche the onset of menstruation which occurs on average between ages 12 13 for males it is the first ejaculation which occurs on average at age 13irls usually complete puberty by ages 15 17 while boys usually complete puberty by ages 16 17 the major landmark of puberty for females is menarche the onset of menstruation which occurs on average between ages 12 13 for males it is the first ejaculation which occurs on average at age 13