The cerebral cortex is a sheet of neurons and their interconnections. About 1800 cm 2 (2 ft 2 ) in surface area, the cortex covers the corrugated surface of the cerebral hemispheres in a layer just a few millimeters thick. This…
Photoreceptors are sensitive but slow, and all animals with image-forming eyes have mechanisms to prevent images of interest from moving across the retina too quickly to be analyzed. (Our eyes behave in many respects like cameras with a shutter speed…
Cerebellum means “little brain,” and in a real sense, it is: it accounts for only about 10% of the mass of the brain, but the cerebellum contains as many neurons as all the rest of the central nervous system (CNS)…
In 1817 James Parkinson, an English country physician, published a brief monograph entitled “An Essay on the Shaking Palsy,” in which he described the symptoms of several individuals who had the disease that now bears his name. Patients with Parkinson's…
Each of us has fewer than a million motor neurons with which to control muscles. Without them, we would be completely unable to interact with the outside world. With them, however, we are capable of an enormous range of complex…
It is clear from everyday experience that humans are a visually oriented species. Although it is arguable which of our senses is most important, loss of vision certainly has a greater impact on humans than loss of, for example, olfaction…
The diencephalon, mostly hidden from view between the cerebral hemispheres ( Fig. 16.1A ), constitutes only about 2% of the central nervous system (CNS) by weight. Nevertheless, it has widespread and important connections, and the great majority of sensory, motor,…
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Hearing and balance are very different senses functionally, but they begin peripherally in very similar ways. The eighth cranial nerve carries two special sensory components, one in a cochlear division and one in a vestibular division. Both divisions innervate elaborate…
Dating back to their origins in some primordial sea, living cells have shared an ability to respond to chemicals, at a minimum detecting and absorbing nutrients. Neurons detect chemicals at synapses, but some cells in or closely associated with the…