Cremasteric reflex

[1] The normal response is an immediate contraction of the cremaster muscle that pulls up the testicle ipsilaterally (on the same side of the body).

These activate the motor fibers of the genital branch of the genitofemoral nerve which causes the cremaster muscle to contract and elevate the testis.

[2]: 262 In some males this reflex may be exaggerated which can occasionally lead to a misdiagnosis of cryptorchidism.

[3] The cremasteric reflex may be absent with testicular torsion, upper and lower motor neuron disorders, as well as a spine injury of L1-L2.

In any event, if testicular torsion cannot be definitively eliminated in an expeditious manner, a testicular Doppler ultrasound or exploratory surgical intervention is usually implemented to prevent possible loss of the testicle to necrosis.

Area A (in orange) represents the area of sensory fibers controlled by the genitofemoral nerve; area B (in green) represents that controlled by the ilioinguinal nerve; arrow C (in red with blue outline) shows the location where the skin must be stroked to elicit this reflex.
Cremasteric reflex