The nervous system would be greatly limited in its ability to make realistic physiological decisions without
sensory information. Therefore, the senses set the stage for many physiological changes or responses to
changes. Sensory organs detect the amounts and types of certain types of energy or matter, for example
certain light wavelengths or pressure. The organs then either release or stop releasing a neurotransmitter,
this change in concentration then being detected by the associated sensory neurons. This chapter
investigates the general senses, chemoreception, sound, equilibrium, and vision.
Here are some concepts that students should have a better understanding of after reading this chapter:
receptors as transducers or energy converters;
types of information receptors transmit;
ways of classifying receptors: modalities, localization of receptors, and origins of stimuli;
structures, functions, and locations of general sense organs and the pathways of afferent neurons
associated with them;
the detection of pain and information route to the central nervous system as well as related topics
such as referred pain, chemical agents, neuromodulation, and anesthesia;
anatomy and physiology of gustation;
structure and function of olfaction including projection pathways and pheromones;
the qualities of sound, the morphology of the ear, the processes of hearing, projection routes, and
the methods by which we detect equilibrium and balance and then send the information on to the
the properties of light, accessory orbital structures, apparatus of the eye and optic nerve, visual
reflexes, light refraction, disorders of image formation, sensory transduction and photochemical
reactions, the mechanisms of color as compared to black and white vision; stereoscopic vision, and
the visual projection pathway;
the history of anesthesia and mechanisms for some anesthesias;
and numerous visual and auditory pathologies.
Topics for Discussion
Tinnitus, or ringing in the ears, is a common complaint. Assign a student to try to find more recent
ideas about its specific cause. The student can use the library and the Internet resources.
Vitamin A, modified by the body and then used as a visual pigment, is toxic taken in higher
concentrations. The liver does store vitamin A and, therefore, sequesters the chemical but excesses will
overwhelm that defense. There are many examples, both historical and modern, of vitamin A toxicity.
Students may be interested in pursuing this further.
The vomernasal organ houses olfactory cells that detect pheromones. It has been shown to be
operational in humans and probably detects pheromones.