the central auditory system
TRANSCRIPT
The Central Auditory System
Ozarks Technical Community CollegeHIS 120
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
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
The Skull
Our brains are protected by our skull
The structures of the ear are housed in the temporal bone
Image from: cnx.org
Important Anatomy Terms to KnowExternal vs. Internal Auditory CanalAfferent vs. EfferentIpsilateral vs. Contralateral
External vs. Internal Auditory CanalYou know that the EAC is part of the outer
earThe 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
Afferent vs. EfferentAfferent 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)Afferent =“up, up, and away”
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)
Ipsilateral vs. ContralateralIpsilateral = same sideContralateral = 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.
Onto the central auditory system…
So what happens to sound after it reaches the cochlea?Most of our auditory system is AFFERENTSound travels from our cochlea UP:
to the auditory nerve, thenTo the brainstem, thenTo the brain (where it is perceived as sound)
Information from one ear, reaches both sides of the brainOur PRIMARY auditory cortex is usually
located in the left hemisphere, as are our primary speech centers
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
Afferent Auditory Pathway
Image from: Martin & Clark online
Efferent Auditory PathwaysDescending nerve fibers from the auditory cortex (brain)
to the brainstem and cochleaThe auditory efferent system is not well understood and
remains somewhat of a mysteryOur 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
Efferent Auditory Pathways
Image from: Martin & Clark online
Central Auditory ProcessesOur central auditory system is responsible for the following
auditory processes:Sound localization and lateralizationAuditory discrimination
Determining the difference between different speech soundsAuditory pattern recognition
i.e. identifying a melodyTemporal (timing) aspects of hearing
Temporal integration Temporal discrimination (e.g., temporal gap detection) Temporal ordering Temporal masking
Auditory performance in competing acoustic signalsAuditory performance with degraded acoustic signals
ASHA, 1995