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Psychologists study the brain using cadaver and lesion approaches, as well as through
neuroimaging techniques that include electroencephalography (EEG), functional magnetic
resonance imaging (fMRI), and transcranial magnetic stimulation (TMS).
Sensory (afferent) neurons carry information from the sensory receptors, whereas motor
(efferent) neurons transmit information to the muscles and glands. Interneurons, by far the most
common of neurons, are located primarily within the CNS and responsible for communicating
among the neurons.
The peripheral nervous system is itself divided into two subsystems, one controlling internal
responses (the autonomic nervous system, ANS) and one controlling external responses (the
somatic nervous system). The sympathetic division of the ANS is involved in preparing the body
for behavior by activating the organs and the glands in the endocrine system. The
parasympathetic division of the ANS tends to calm the body by slowing the heart and breathing
and by allowing the body to recover from the activities that the sympathetic system causes.
Glands in the endocrine system include the pituitary gland, the pancreas, the adrenal glands, and
the male and female sex glands. The male sex hormone testosterone and the female sex
hormones estrogen and progesterone play important roles in behavior and contribute to gender
differences.