1. The “Ear” is housed within the
TEMPORAL BONE

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

3. Pinna Landmarks Helix Antihelix Concha Tragus Intertragal Notch
Antitragus

4. 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.

5. Outer Ear Functions
Amplification / Filtering
Protection
Localization

6. 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

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

8. 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

9. Middle Ear Functions
Impedance Matching
Filtering
Acoustic Reflex

10. These sounds get through the middle ear most readily

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

15. Within S. Media is the Organ of Corti

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

17. 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

18. Afferent & Efferent Neurons

19. IHC activation alters firing rate

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

21. 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

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

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

24. 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

25. 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