PERCEPTION: ch. 11 - sound localization

What is the ACCESSORY STRUCTURE of the auditory system?

• The Pinna

What is the PINNA (structurally)?

• The external fleshy covering on each side of one’s head

What 3 FUNCTIONS does the PINNA serve? HOW are its functions SHAPED?

1. Acts as a funnel to catch sound waves and channel them into the ear 

2. Provides minor amplification of the signal 

3. May serve additional functions (such as heat dispersion)

• Shaped by evolution to aid survival and reproduction

WHERE does AUDITORY TRANSDUCTION occur?

• Outer ear

• Middle ear

• Inner ear

What STRUCTURES in OUTER EAR are in charge of AUDITORY TRANSDUCTION?

1. External Auditory Canal

2. Eardrum

What does the EXTERNAL AUDITORY CANAL do in AUDITORY TRANSDUCTION (1 functions)? What FREQUENCIES does it AMPLIFY? How BIG is it (height & diameter)?

• Conducts/channels vibrations to middle ear

• Amplifies certain frequencies–2000-5000 Hz

• ~1 inch long, 0.3 inch in diameter

What IS (structurally) the EARDRUM?

1. HOW does the EARDRUM CONDUCT its part of AUDITORY TRANSDUCTION?

2. What OTHER FUNCTIONS does it serve?

• Thin, fibrous membrane–easily damaged 

• Vibrates in response to sound wave coming through external auditory canal

• Ear’s only main defense against damage 

WHAT STRUCTURE in the MIDDLE EAR helps AUDITORY TRANSDUCTION?

The ossicles

WHAT are THE OSSICLES composed of? 

Three bones:

1. malleus,

2. incus,

3. stapes 

What 2 FUNCTIONS do THE OSSICLES serve in AUDITORY TRANSDUCTION?

• Receives and delivers vibrations (to oval window of cochlea) 

• Can decrease amplification to protect against very intense sounds

What is UNIQUE about the OSSICLES?

• they can fuse/degenerate; a cause of conduction loss—They are replaceable!

WHAT STRUCTURE in the INNER EAR helps AUDITORY TRANSDUCTION?

The Cochlea

WHAT 2 FUNCTIONS does the COCHLEA serve in AUDITORY TRANSDUCTION?

• Where Transduction Occurs–converts sound waves into neural responses

• Origin of Auditory Nerve–takes signal to the brain

WHAT 3 STRUCTURES is the COCHLEA composed of? HOW MANY of each are there?

1. Three Canals

2. Three Membranes

3. One Critical Structure

WHAT THREE CANALS is the COCHLEA composed of? WHERE are they located?

1. Scala vestibuli (upper)

2. Scala media (middle)

3. Scala tympani (lower)

• Run the length of cochlea

WHAT THREE MEMBRANES is the COCHLEA composed of? WHERE are they located?

• Reissner’s membrane–separates top & middle

• Tectorial membrane

• Basilar membrane–separates middle & lower; CRITICAL for processing 

What CRITICAL STRUCTURE is in the COCHLEA?

The organ of Corti

WHAT is the ORGAN OF CORTI (structure/location)?

• Structure on the basilar membrane covered by the tectorial membrane

WHAT FUNCTION does the ORGAN OF CORTI serve in AUDITORY TRANSDUCTION? WHAT does it CONTAIN?

• Conducts transduction–contians auditory sensory receptors

WHAT are the AUDITORY SYSTEM’S SENSORY RECEPTORS?

1. WHERE are they located?

2. HOW MANY RECEPTORS are there?

3. WHAT TYPES of receptors are there? HOW MANY are there of each type?

4. HOW MANY in TOTAL are there?

• Columns of hair cells (cilia)

1. located in ORGAN OF CORTI

2. ~24,000 NONREGENERATIVE hair cells

3. 3500 inner (TRANSDUCERS); 20,000 outer hair cells (AMPLIFIERS).

4. 50-300 cilia–OVER 1 MILLION total receptors

HOW does the INNER EAR conduct AUDITORY TRANSDUCTION? What do the structures DO?

• hair cells making CONTACT with the tectorial membrane—sound waves making the basilar membrane rise

  • CONTACT = conversion from sensory energy to NEURAL RESPONSES

HOW SHOULD the HAIR CELLS touch the TECTORAL MEMBRANE in AUDITORY TRANSDUCTION? WHY?

• GENTLY

  • Intense signals lead hair cells press too hard against the tectorial membrane—may cause damage (snapping)

HOW can the ORGAN OF CORTI be STIMULATED? HOW is it ORGANIZED - what does this MEAN?

1. WHERE do SIMILAR frequencies go?

2. WHERE do HIGHER frequencies go?

• stimulated by bone conduction

  • Listening to voice in our head vs. in recordings

• Organized tonotopically–specific frequencies are mapped to certain locations/nerve fibers

1. Similar frequencies in adjacent regions. 

2. Higher frequencies closer to stapes.  

What MODERN MEDICAL MIRACLE was made for the ORGAN OF CORTI?

• Cochlear implants

What is the AUDITORY SYSTEM’S (4-step) TRANSMISSION PATHWAY TO THE BRAIN?

1. Superior Olive Complex

2. Inferior Colliculus 

3. Medial Geniculate Nucleus (MGN) of Thalamus

4. Primary Auditory Cortex in Temporal Lobe

What FUNCTION does the SUPERIOR OLIVE COMPLEX have in AUDITORY TRANSMISSION?

• Sound localization–VITAL

  • hindbrain

What FUNCTION does the INFERIOR COLLICULUS have in AUDITORY TRANSMISSION?

• Auditory Reflexes

• midbrain

What FUNCTION does the MGN of the THALAMUS have in AUDITORY TRANSMISSION?

• Sensory Relay Station

• midbrain

What FUNCTION does the PRIMARY AUDITORY CORTEX have in AUDITORY TRANSMISSION (through WHAT KIND of representations)? Where is it LOCATED?

• processing of pitch and loudness—Tonotopical representations

• Forebrain

HOW MANY AUDITORY SIGNALS do RECEPTOR CELLS respond to in PRIMARY AUDITORY CORTEX? WHICH 2 COMPONENTS OF SOUND does it help us code?

• Each cell responds best to ONE tone (HOW WE CODE FOR FREQUENCY/PITCH)

WHAT SECONDARY AUDITORY CORTEX (structure)? What 2 FUNCTIONS does it have in AUDITORY TRANSMISSION?

• Surrounds primary auditory cortex

  • Forebrain

1. sound localization

2. Analyzes complex combinations of sounds

What is CONDUCTION HEARING LOSS? 

• Problems in signal transmission (hearing actual sound)

What CAUSES CONDUCTION HEARING LOSS (5)?

1. External ear infection–Otitis externa (swimmer’s ear)

2. Middle Ear infection–Otitis media

3. Ruptured eardrum

4. Earwax buildup

5. Otosclerosis (abnormal bone growth)

What is SENSORINEURAL HEARING LOSS?

Damage to auditory nerve

What CONDITIONS EMERGE from SENSORINEURAL HEARING LOSS (4)?

1. Tinnitus (persistent ringing in ear(s))

2. Presbycusis (age related changes)

   1. Hair Cell Loss, HBP, Diabetes, Medication Effects, Reduced Elasticity, Otosclerosis, etc

3. Noise-Induced Hearing Loss

4. Meniere's disease

HOW does the AUDITORY SYSTEM CODE (D.I.L.T.)?

1. Duration: Onset and offset of firing; well identified.

2. Intensity: Number of neurons firing and firing rate

3. Location: Excellent for both distance (firing rate) and spatial location (interaural time differences).

4. Type: Different types of sounds–speech, music, background noise

THROUGH WHAT COMPONENT OF SOUND do we ORGANIZE TYPES of sound?

by PITCH.

HOW do we code for PITCH? (2 theories)

1. Place Theory of Pitch Perception

2. Frequency Theory of Pitch Perception

WHAT is the PLACE THEORY OF PITCH PERCEPTION of AUDITORY CODING? WHERE do high & low pitches GET MAPPED?

1. What is its PROBLEM?

2. What is its REVISION?

• Pitch perception = WHICH neurons fire—different pitches activate different places on the basilar membrane (von Helmholtz)

  • High pitch = base of cochlea

  • Low pitch = apex (top) of cochlea

1. PROBLEM = Doesn’t explain ability to make PRECISE PITCH DISCRIMINATIONS

2. REVISION = “Traveling wave form”: different frequencies peak at different locations along the basilar membrane. (von Bekesy)

WHAT is the FREQUENCY THEORY OF PITCH PERCEPTION of AUDITORY CODING?

1. What is its PROBLEM?

2. What is its REVISION? 

• Pitch Perception = neuronal firing RATE—Basilar membrane vibrates at the same frequency as the sound (Rutherford) –EX: vibrates 100x per sec. for 100 Hz sound

1. PROBLEM = LIMIT TO NEURON FIRING RATE LOWER THAN AUDITORY CAPACITY (1000x per sec. < 23,000 Hz)

2. REVISION = Neurons work together to match frequency (Wever)

WHICH of the 2 theories of AUDITORY CODING is CORRECT?

BOTH! (The Duplex Theory)

What is the DUPLEX THEORY of AUDITORY CODING? WHAT TYPE OF FREQUENCY corresponds to each component?

• Neurons work together to match the original frequency–Combination of PLACE AND FREQUENCY THEORIES OF PITCH PERCEPTION

  • PLACE THEORY = higher frequencies

  • FREQUENCY THEORY = lower frequencies