Bicep(Flexor)/Tricep(Extensor)

    Skeletal muscles are attached to the skeleton in pairs. one muscle pulls in one

direction and the other pulls in the opposit direction. In the limbs each opposing muscle incleudes a flexor and an extensor.\

A flexor causes a joint to bend while the extensor causes a joint to straighten. A Tricep is an extensor. A Bicep is a flexor.      

Images  

http://www.criticalbench.com/muscular-system.htm

http://www.criticalbench.com/triceps-muscles.htm