Chapter 5 Notes - Part Ten

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18 Dec 2010
When a molecule of an odorous substance fits a receptor molecule located on the cilia of a
receptor cell, the cell becomes excited
This excitation is passed on to the brain by the axon of the receptor cell
Humans can recognize up to 10,000 different odourants
A particular odourant binds to more than one receptor; the brain eventually receives signals
from several receptors
The task of chemical recognization is thereby transformed into a task of pattern
The somatosenses (body senses) are bodily sensations; sensitivity to such stimuli as touch,
pain, and temperature
Entire surface of human body is innervated (supplied with nerve fibres) by the dendrites of
neurons that transmit somatosensory information to the brain
All somatosensory information is detected by the dendrites of neurons
Some of these dendrites have specialized endings that modify the way they transduce
energy into neural activity
Free nerve ending: the most common type of skin sensory receptor; a dendrite of
somatosensory neurons (resembles the fine roots of a plant)
Pacinian Capsule: a specialized somatosensory nerve ending that detects mechanical
stimuli especially vibrations
When they are moved, their axons fire a brief burst of impulses
Two-point discrimination threshold: the minimum distance between two small points that
can be detected as separate stimuli when pressed against a particular region of the skin
There are three types of pain receptors; referred to as nociceptors (detectors of noxious
Pain also involves emotional component; a given sensory input to the brain might be
interpreted as pain in one situation and as pleasure in another
Opiates, such as morphine, diminish the sensation of pain by stimulating opioid receptors
on neurons in the brain; these neurons block the transmission of pain information to the
In contrast, some tranquilizers (valium) depress neural systems that are responsible for the
emotional reaction to pain, but do not diminish the intensity of the sensation
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