Transcript How is information about touch relayed to the brain?

Psychology 304:
Brain and Behaviour
Lecture 27
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The Somatosensory System and the Auditory System
1. What are the receptors for touch? (continued)
2. How is information about touch relayed to the brain?
3. What are the major areas of the brain that are
associated with the perception of touch?
4. What are the physical and perceptual dimensions of
sound?
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By the end of today’s class, you should be able to:
1. differentiate between the structure and function of the
four somatosensory receptors.
2. define the term “dermatome.”
3. review the pathway by which somatosensory
information is transmitted from receptors to the brain.
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4. identify the locations and functions of the primary
cortex, secondary cortex, and association areas for
touch.
5. describe the condition “asomatognosia.”
6. describe the three physical and three perceptual
dimensions associated with sound.
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What are the receptors for touch? (continued)
• Four types of touch receptors have been identified:
 Pacinian corpuscles: Encapsulated (onion-like)
receptors. Detect vibration. Fast-adapting
(i.e., phasic, highly sensitive to change). Large
receptive fields.
 Meissner’s corpuscles: Encapsulated receptors.
Detect light touch. Fast-adapting. Small receptive
fields.
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 Merkel’s discs: Non-encapsulated receptors.
Detect light touch. Slow-adapting (i.e., tonic, not
highly sensitive to change). Small receptive fields.
 Ruffini’s corpuscles (Ruffini’s endings): Nonencapsulated receptors. Detect stretching. Slowadapting. Large receptive fields.
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Touch Receptors
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How is information about touch relayed to the brain?
• The surface of the skin can be divided into dermatomes:
sections of skin for which distinct spinal nerves carry
information about touch to the spinal cord.
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Dermatomes
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• Touch information is relayed to the brain via the dorsalcolumn medial-lemniscus pathway:
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Dorsal-Column Medial-Lemniscus Pathway
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What are the major areas of the brain that are associated
with the perception of touch?
• The majority of thalamic neurons that receive touch
information subsequently project the information to the
primary somatosensory cortex (SI). Thereafter,
information is projected to the secondary somatosensory cortex (SII) and the posterior parietal cortex.
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Primary Somatosensory Cortex (SI)
Somatosensory Association
Cortex
Secondary Somatosensory
Cortex (SII)
Somatosensory Areas of the Brain
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• SI is somatotropically organized—that is, organized
according to a map of the body.
• The somatotropic map found in SI is referred to as the
somatosenosry homunculus. The representation of the
body in the somatosensory homunculus is distorted.
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The Primary Somatosensory Cortex
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The Nerve-Weighted Man
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What are the physical and perceptual dimensions of
sound?
• Sounds are produced by objects that cause air
molecules to vibrate.
• As they vibrate, the air molecules alternately condense
and expand, producing sound waves.
• Sound waves vary on three physical dimensions. Each
physical dimension uniquely influences our perception of
sound.
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Physical and Perceptual Dimensions of Sound Waves
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The Somatosensory System and the Auditory System
1. What are the receptors for touch? (continued)
2. How is information about touch relayed to the brain?
3. What are the major areas of the brain that are
associated with the perception of touch?
4. What are the physical and perceptual dimensions of
sound?
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