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Chapter 10

Chapter 10 notes


Department
Biological Sciences
Course Code
BIOD27H3
Professor
A.Elia
Chapter
10

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Chapter 10- Sensory Physiology
-sensory stimuli whose processing reaches the conscious level of perception
-these stimuli are those associated with the special senses of vision, hearing, taste, smell,
and equilibrium
-somatic senses; touch, temperature, pain, itch, and Proprioception
-Proprioception; awareness of body movement and position in space is mediated by
muscle and joint sensory receptors called proprioceptors and maybe unconscious or
conscious
General Properties of Sensory Systems
-sensory pathways begin with a stimulus that is converted by a receptor into an electrical
potential
-if the stimulus is above threshold, action potentials pass along a sensory neuron to the
CNS. We become aware of some stimuli but are never conscious of others.
-Sensory receptors vary from free nerve endings to encapsulated nerve endings to
specialized receptor cells
-4 types of sensory receptors based on stimulus to which they are most sensitive to;
chemoreceptors, mechanoreceptors, thermoreceptors, and photoreceptors
-Each receptor type has an adequate stimulus, a particular form of energy to which it is
most responsive
-A stimulus that is above threshold creates a graded potential in the receptor
-Multiple sensory neurons converge on one secondary neuron and create a single large
receptive field
-Sensory information from the spinal cord projects to the thalamus, then on to the sensory
areas of cerebral cortex. Olfactory information does not pass through the thalamus
-The CNS is able to modify our level of awareness of sensory input. The perceptual
threshold is the level of stimulus intensity necessary for us to be aware of a particular
sensation.
-The modality of a signal and its location are indicated by which sensory neurons are
activated. The association of a receptor with a specific sensation is called labelled line
coding.
-Localization of auditory information depends on the timing of receptor activation in each
ear
-Lateral inhibition enhances the contrast between the center of the receptive field and the
edges of the field. In population coding the brain uses input from multiple receptors to
calculate location and timing of a stimulus
-Stimulus intensity is coded by the number of receptors activated and by the frequency of
their action potentials
-Tonic receptors; sensory neuron fires action potentials as long as the receptor potential is
above threshold. Phasic receptors respond to a change in stimulus intensity but adapt if
the strength of the stimulus remains constant
Somatic Senses
-there are 4 somatosensory modalities; touch Proprioception, temperature, and nociception
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