The “Ear” is housed within the TEMPORAL BONE

The Outer Ear Consists of: The Pinna - cartilaginous, highly variable in appearance, some landmarks. External Auditory Canal (or external auditory meatus) - 2.5 cm tube.

Pinna Landmarks Helix Antihelix Concha Tragus Intertragal Notch Antitragus

External Auditory Canal lateral portion-cartilage medial portion-osseous lined with epidermal (skin) tissue hairs in lateral part cerumen (ear wax) secreted in lateral part.

Outer Ear Functions Amplification / Filtering Protection Localization

The Middle Ear: A cleft within the temporal bone Lining is mucous membrane Tympanic Membrane separates it from EAC Eustachian tube connects it to nasopharynx Also Connected to Mastoid Air Cells

Middle Ear Structures 1- Malleus 2- Incus --Ossicles 3- Stapes 4- Tympanic Membrane (Eardrum) 5- Round Window 6- Eustachian Tube

Middle Ear Muscles 1. The Stapedius Attaches to Stapes,Contracts in Response to Loud sounds, chewing, speaking; Facial (VIIth cranial) nerve 2. The Tensor Tympani Helps open Eustachian tube

Middle Ear Functions Impedance Matching Filtering Acoustic Reflex

These sounds get through the middle ear most readily

INNER EAR Two Halves: Vestibular--transduces motion and pull of gravity Cochlear--transduces sound energy (Both use Hair Cells)

Within S. Media is the Organ of Corti

The Stereocilia on IHCs and OHCs OHCs (at top) V or W shaped ranks IHC (at bottom) straight line ranks

Cochlear Functions Transduction- Converting acoustical-mechanical energy into electro-chemical energy. Frequency Analysis-Breaking sound up into its component frequencies Bekesy’s Traveling Wave Active Tuning from OHCs

Afferent & Efferent Neurons

IHC activation alters firing rate

Afferent neurons have their cell bodies in the Spiral Ganglion (4)

Major Components of the Central Auditory Nervous System (CANS) VIIIth cranial nerve Cochlear Nucleus Superior Olivary Complex Lateral Lemniscus Inferior Colliculus Medial Geniculate Body Primary Auditory Cortex <Trapezoid Body> Brainstem Mid-brain Thalamus Temporal Lobe

AUDITORY CORTEX MEDIAL GENICULATE BODY INFERIOR COLLICULUS LATERAL LEMNISCUS SUPERIOR OLIVARY COMPLEX COCHLEAR NUCLEUS

Mid-Saggital View of Brain 4th Ventricle Corpus Callosum Cerebellum Thalamus Pons

Cortical Processing Pattern Recognition Duration Discrimination Localization of Sounds Selective Attention Difficult to assign specific functional roles. a) lesion studies provide some info * lesions affect localization ability in opposite hemifield. * lesions affect performance in contralateral ear in attention studies i) but man may or may not equal animal performance ii) and lesions in man are typically diffuse, not isolated. b) single cell responses show correlation to functions i) responses to interaural time differences which show up at SOC earliest, are preserved in auditory cortex. ii) Primary Auditory cortex fiber responses show preferential response to certain transient intervals, but do not show response to fundamental. :: Q.E.D., pitch info not necessarily disrupted by lesions of primary auditory cortex

Cerebral Dominance/Laterality Language Processing in the left hemisphere. (Remember the right ear has the strongest connections to the left hemisphere) Most people show a right-ear advantage in processing linguistic stimuli