ELECTRICAL OUTPUT OF THE BRAIN
Have you ever wondered what goes on in the brain when you hear a sound? Suppose a firecracker blasts off nearby; you hear the noise, you jump, and you may become frightened.
By now you should have a good general idea of what must transpire in such a situation: that sound jars the eardrum, jiggles the cells in the inner ear, and thus sets off nerve impulses that spread through the brain in some orderly way. Biophysical studies have been a great help in defining where the nerve impulses go, how long they take to get there, and what they do upon arrival.
Fig. 21 shows one major path along which the impulses proceed. From anatomical studies we know that this nervous pathway, the auditory pathway, extends from the cochlea (where nerve excitation begins) forward through the brain to its highest level, the cortex. In several well-defined places along this route nerve cells end and other nerve cells begin. These regions, called brain nuclei, prove to be relay stations for the nerve messages. At the synapse here incoming cells provoke EPSPs and IPSPs from cells that will carry the message