1. Psychology 304: Brain and Behaviour Lecture 27

2. 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?

3. 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.

4. 4. identify the locations and functions of the primary
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.

5. 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.

6. Merkel’s discs: Non-encapsulated receptors. Detect light touch
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): Non- encapsulated receptors. Detect stretching. Slow- adapting. Large receptive fields.

7. Touch Receptors

8. 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.

9. Dermatomes

10. Touch information is relayed to the brain via the dorsal-
Touch information is relayed to the brain via the dorsal- column medial-lemniscus pathway:

11. Dorsal-Column Medial-Lemniscus Pathway

12. 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 somato- sensory cortex (SII) and the posterior parietal cortex.

13. Somatosensory Areas of the Brain
Primary Somatosensory Cortex (SI)
Notes
Somatosensory Association Cortex
Secondary Somatosensory Cortex (SII)
Somatosensory Areas of the Brain

14. SI is somatotropically organized—that is, organized
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.

15. The Primary Somatosensory Cortex

16. The Nerve-Weighted Man

17. 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.

18. Physical and Perceptual Dimensions of Sound Waves

19. 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?