Biomedical Engineering Reference
In-Depth Information
senses. Sensory receptors are distributed throughout the body. Sensory information
is interpreted on the basis of the frequency of arriving action potentials. Every
receptor has a distinctive sensitivity. i.e., a touch receptor is sensitive to pressure
but comparatively insensitive to chemical stimuli, while a taste receptor is sen-
sitive to dissolved chemicals but insensitive to pressure. Various classifications of
human sensory system and its associated stimuli are shown in Table 3.1 .
The purpose of transduction is to convert a pattern of information distributed
over space and time to a pattern of neural activity which is also appropriately
distributed across space (different neurons) and time. The process through which a
specific pattern of information (energy) in the environment (e.g., light, vibrations,
dissolved chemicals or airborne chemicals) is converted to a pattern of electrical
activity in the nervous system is called transduction. (Conversion of a chemical
signal (odor binding) to an electrical signal [change in neuron's V m )].
In human olfactory process when odorant molecules reach the olfactory mucosa
and bind to the olfactory receptor proteins on the cilia of the olfactory receptor
neurons olfactory transduction occurs. Each olfactory receptor neuron has multiple
types of receptor sites for different molecules [ 5 ]. The various types of receptor
sites are distributed in different proportions on different olfactory receptor neurons.
Binding of odorants to receptor sites associated with ion channels causes a receptor
potential at the dendrites, and action potentials at the cell body and axon. The
axons of olfactory receptor cells project directly to the brain via the olfactory
nerve.
Table 3.1 Classification of human sensory system
Type of sensory
system
Modality
Adequate stimuli
Mechanical
Touch
Contact with body surface
Hearing
Sound vibrations in air or water
Vestibular
Head movement and orientation
Joint
Position and movement
Muscle
Tension
Photic
Seeing
Visible radiant energy
Thermal
Cold
Skin temperature decrease
Warmth
Increase in skin temperature
Chemical
Smell
Odorous substances dissolved in air or water in
the nasal cavity
Taste
Substances in contact with the tongue or other
taste receptor
Common chemical
vomeronasal
Changes in CO 2 , pH, osmotic pressure
Electrical
Electroreception
Differences in density of electrical currents
Search WWH ::




Custom Search