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.
Primary & Secondary Sexual Characteristics. Primary and secondary sexual characteristics refer to specific physical traits that differentiate males and females in sexually dimorphic species; that is, species in which males and females look different. Primary sexual characteristics are there from birth (for example, penises vs. vaginas).