Testicles lift and descend in response to the contraction and relaxation of the cremaster muscle. Testicles rest gently inside this thin, pouch-shaped muscle, which draws them toward or away from the body as a way of regulating their temperature. The Mayo Clinic lists several factors, apart from temperature, that can trigger the retraction of the testicles. These include stimulation of the genitofemoral nerve and extreme emotions such as anxiety.Know More
Sexual arousal is another condition that can affect the tension in the cremaster muscle. At high states of arousal, the muscle often contracts and brings the testicles close to the body. When this happens, the skin of the scrotum becomes wrinkled and the testicles' temperature, which is usually a degree or two cooler than the body's core temperature, rises. According to HowStuffWorks, these movements are perfectly normal and are part of the male body's system for maintaining the optimal temperature for the formation of sperm.
Pain experienced during retraction, or at any other time, is potentially a sign of a serious medical problem. The National Institutes of Health considers acute pain in one testicle to be a medical emergency. If pain is present, or if the testicles fail to return to their normal state after retraction, it is important to seek medical assistance as soon as possible.Learn more about Human Anatomy
Neurons transmit information through neurotransmitters, molecules that are released from one neuron and travel to another to produce a response. Several neurotransmitters, both inhibitory and excitatory, have been studied extensively. Neurotransmitters that are commonly discussed are GABA, seratonin, dopamine, norepinephrine and epinephrine.Full Answer >
Usually, the pupils of the eyes become small, or constrict, in response to a strong light source, such as sunlight. Certain medications, drugs or ailments also cause small pupil size.Full Answer >
The University of Western Australia explains that human bones are hollow because this structure makes them light enough to easily move but sturdy enough to avoid easy breakage or collapse. In addition, the hollow areas of bones store fat.Full Answer >
Plants can move when their cells grow as a response to either light or gravity, which they are able to detect even as seedlings. This type of movement is slow and permanent. Other kinds of plants are capable of quick, momentary bursts of movement, which is due to hydraulics.Full Answer >