Biomedical Engineering Reference
In-Depth Information
Extroreceptors-external-Chemoreceptors, Electroreceptors, Magnetoreceptors,
mechanorecptors, Photoreceptors, Thermoreceptors
Proprioceptors—internal-vestibular, muscular etc.
Interoreceptors—internal without conscious perception-Interoreceptors detect
stimuli originating inside the body blood pressure, oxygen tension etc.
Table 5.3 summarizes the receptor family and their detection of sensations.
Different forms of energy detected by sensory receptors are beginning of the
sensations. This energy is transformed to action potentials that travel to suitable
regions of the brain. Once the brain is sensitive of sensations, it interprets them,
giving the perception of stimuli. Perceptions such as colors, smells, sounds, and
tastes are creation formed in the brain and do not exist outside of it. We do
perceive objects using our sense of smell, but the objects of these experiences are
not the same as when we sense objects through touch, sight, or audition. The
objects of vision have sharply delineated spatial characteristics and the objects of
audition have clear temporal boundaries. Smells, however, seem to be neither
spatially nor temporally bound objects. The object of olfactory perception is unlike
our common sense conception of ordinary three-dimensional objects, identified
visually. Smells are not ordinary objects, but the chemical structure of simple
molecules or mixtures within odor plumes. Our olfactory perceptions are of the
material objects of chemistry. We smell the chemical structure of matter. Chem-
icals compounds, which could lead to smells, constantly surround us. Nonetheless
of us are able to separate out different smells from the environment.
The olfactory system consists of a sensory organ (the olfactory epithelium) and
specific olfactory brain regions and the olfactory bulb. The perception of odors
causes interesting and different problems for the nervous system. Primary one is
that there is no single dimension that relates stimulus to sensation. Vision and
hearing are stimulated by predictable variations in frequencies of light and sound;
touch by variations in frequencies of pressure on the skin. Specialized olfactory
receptor cells are located in a small patch of mucous membrane lining the roof of
the nose. Axons of these sensory cells pass through perforations in the overlying
bone and enter two elongated olfactory bulbs lying on top of the bone. The portion
of the sensory cell that is exposed to odors possesses hair like cilia which contain
the receptor sites that are stimulated by airborne odor molecules. These molecules
dissolve in the mucous lining in order to stimulate receptor proteins in the cilia to
start the smell response. An odorant acts on many receptors to different degrees.
Table 5.3 Receptor family (extroreceptors)
Receptor family
Sensations that are detected
Chemoreceptor
Taste, smell
Electroreceptor
Electro-location, impedance changes, conductivity changes
Magnetoreceptor
Flight navigation
Mechanoreceptor
Vibration, pressure, strain, force, muscle, hearing
Photoreceptor
Vision
Thermoreceptor
Heat, cold
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