1 Psychology 304: Brain and Behaviour Lecture 24

2 The Auditory System and the Vestibular System 1. What is the structure of the ear and where are the receptors for sound? (continued) 2. How is information about sound relayed to the brain? 3. What are the major areas of the brain that are associated with the perception of sound? 5. What are the biological mechanisms associated with vestibular perception? 4. What is the neurological basis of deafness?

3 The Structure of the Ear What is the structure of the ear and where are the receptors for sound? (continued)

4 Inner Hair Cells Outer Hair Cells Inner and Outer Hair Cells

5 Outer Hair Cell Contact with the Tectorial Membrane Auditory nerve

6 When hair cells are stimulated, action potentials are triggered that pass down axons of the auditory nerve—a branch of cranial nerve VIII. The vibrations of the cochlear fluid are ultimately dissipated by the round window. High frequencies stimulate hair cells close to the oval and round windows. Low frequencies stimulate hair cells at the tip of the cochlea.

7 How is information about sound relayed to the brain? Sound information is relayed to the brain via a network of auditory pathways.

8 Pathways of the Auditory System

9 What are the major areas of the brain that are associated with the perception of sound? The majority of thalamic neurons that receive sound information subsequently project the information to the primary auditory cortex. Thereafter, information is projected to the secondary auditory cortex (SII) and association areas.

10 Auditory Areas of the Brain

11 Current theory suggests two large areas of auditory association cortex: the prefrontal cortex and the posterior parietal cortex. The anterior auditory pathway leading to the prefrontal cortex is thought to be involved in identifying sounds; the posterior auditory pathway is thought to be involved in locating sounds.

12 Pathways to Auditory Association Cortex

13 What is the neurological basis of deafness? Although impaired hearing is a common human disability, complete deafness is rare. There are three common classes of hearing impairments: conductive deafness (outer or middle ear damage), sensorineural deafness (inner ear damage), and central deafness (cortical damage). Cochlear implants can improve the hearing of those who have sensorineural deafness.

14 Cochlear Implant

15 Cochlear Implant

16 What are the biological mechanisms associated with vestibular perception? The functions of the vestibular system include the detection of head movement, balance, and the maintenance of the head in an upright position. The vestibular system has two components: the semicircular canals and the vestibular sacs.

17 Vestibular Sacs and Semicircular Canals

18 Vestibular receptors are found in enlargements on the semicircular canals called ampullae. These receptors respond to angular (i.e., rotational) acceleration of the head.

19 Receptor Cells in the Semicircular Canals

20 The Auditory System and the Vestibular System 1. What is the structure of the ear and where are the receptors for sound? (continued) 2. How is information about sound relayed to the brain? 3. What are the major areas of the brain that are associated with the perception of sound? 5. What are the biological mechanisms associated with vestibular perception? 4. What is the neurological basis of deafness?