Upper Arm Muscle - Bicep Muscle Anatomy. There are three major muscle groups in the arm. The biceps brachii is a two headed muscle with point of origin under the deltoid and point of insertion just below the elbow. The basic function of your biceps is to lift and curl the arm, and to also pronate (twist downward) the wrist.
Testosterone is primarily responsible for the development of male secondary sexual characteristics, e.g., beard growth, pubic hair growth, deepening of voice, etc. Testosteron â¦ e.
Because the transcription factor produced by Sox9 affects a gene that plays a major role in sex determination, the expression of this gene changes when temperature (and therefore Sox9 expression) changes, thus resulting in a specific phenotype of maleness or femaleness.