The central auditory system

1. The Central Auditory System Ozarks Technical Community College HIS 120

2. The Central Nervous System The central nervous system contains the   brain the   spinal cord The average adult brain weighs about 3 pounds The brain contains about 100 billion neurons that transmit information about our bodies up to our brains, where that information is processed Image from: faculty.washington.edu

3. The Brain Image from: faculty.vassar.edu Our brains are divided into four lobes: Frontal Temporal Parietal Occipital The temporal lobe is where auditory information is sent to be processed

4. The Skull Our brains are protected by our skull The structures of the ear are housed in the temporal bone Image from: cnx.org

5. Important Anatomy Terms to Know External vs. Internal Auditory Canal Afferent vs. Efferent Ipsilateral vs. Contralateral

6. External vs. Internal Auditory Canal You know that the EAC is part of the outer ear The internal auditory canal (IAC) or internal auditory meatus is an opening in the temporal bone where the facial nerve (CN VII) and auditory nerve (CN VIII) travel to the brainstem

7. Afferent vs. Efferent Afferent refers to the ascending pathway of sensory information that travels from our peripheral system to our central system. Another way to think about this is the transmission of information about all of our senses up to our brain. (i.e. when you touch a hot pan, the afferent nervous system sends the pain signal to your brain) A fferent =“up, up, and a way” Efferent refers to the descending pathway of information from our brain to a part of our body. (i.e. after your brain receives the pain signal from touching the hot pan, an efferent message is sent to your hand to pull away from the pan)

8. Ipsilateral vs. Contralateral Ipsilateral = same side Contralateral = opposite side Examples : When using nasal spray in the right nostril, you should point the tip of the nasal spray at the corner of the ipsilateral ( right ) eye During audiometric testing of the right ear, you present masking noise to the contralateral ear ( left ear in this case) in order to isolate the test ear.

9. Onto the central auditory system…

10. So what happens to sound after it reaches the cochlea? Most of our auditory system is AFFERENT Sound travels from our cochlea UP: to the auditory nerve, then To the brainstem, then To the brain (where it is perceived as sound) Information from one ear, reaches both sides of the brain Our PRIMARY auditory cortex is usually located in the left hemisphere, as are our primary speech centers

11. Afferent Auditory Pathway Cochlea CN VIII Brainstem: Cochlear Nucleus Superior Olivary Complex Lateral Lemniscus Inferior Colliculus (crossover) Medial Geniculate Body Brain: Auditory cortex/Temporal Lobe

12. Afferent Auditory Pathway Image from: Martin & Clark online

13. Efferent Auditory Pathways Descending nerve fibers from the auditory cortex (brain) to the brainstem and cochlea The auditory efferent system is not well understood and remains somewhat of a mystery Our auditory efferent system is responsible for: Sending inhibitory messages to the outer hair cells in the cochlea to control stiffness and membrane vibration Innervation of the stapedius and tensor tympani muscles in the middle ear Our efferent system is believed to play a role in: detection of signals in noise, protection in noise-induced cochlear damage, development of hearing and processing of complex auditory signals

14. Efferent Auditory Pathways Image from: Martin & Clark online

15. Central Auditory Processes Our central auditory system is responsible for the following auditory processes: Sound localization and lateralization Auditory discrimination Determining the difference between different speech sounds A uditory pattern recognition i.e. identifying a melody Temporal (timing) aspects of hearing T emporal integration Temporal discrimination (e.g., temporal gap detection) Temporal ordering Temporal masking A uditory performance in competing acoustic signals A uditory performance with degraded acoustic signals ASHA, 1995