Senses Aristotle: classical “five senses”: •Sight •Hearing •Taste •Smell •Touch •This is not all: what did Aristotle leave out? •There are other somatosensory modalities - temperature, pain, proprioception - which could be included in a broader “sense of touch” •These modalities are handled by the somatosensory system 1
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Senses Aristotle: classical “five senses”: Sight Hearing Taste Smell Touch This is not all: what did Aristotle leave out? There are other somatosensory.
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•There are other somatosensory modalities - temperature, pain, proprioception - which could be included in a broader “sense of touch”•These modalities are handled by the somatosensory system
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The somatosensory system: what does it tell us?
Information we need about external stimuli:•what is it? (modality)•where is it? (location)•when did it happen? (timing)•how strong was the stimulus? (intensity)
From Descartes “De Homine” (1662)
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Sensory qualities in terms of receptors
•Modality: which receptor type is stimulated?
•Location: which area of skin (or body interior) is innervated by the receptor?
•Timing/Intensity: action potential frequency
•First: where do our ideas about receptors originate?
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Sensory spots and sensory receptors
Skin sensations are localised: e.g. 2 x 2.5 cm on wrist
Cold
Warm
Light touch
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What’s under the sensory spots?
Sensory nerve terminals in the skin:
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Sensory nerve terminalsare the peripheral ends of sensory neurones
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A general somatosensory pathwayThird order neurone
Thalamus
Second order neurone(crosses midline)
Primary sensory neurone(DRG neurone)
Receptor7
A general somatosensory pathway
We’ll focus on these stages:
receptors
central processing
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Low-threshold mechanoreceptors:•Pressure )•Vibration ) cutaneous “touch”•Tapping )•Muscle stretch )•Tendon stretch ) deep “proprioception”•Joint position )