Chapter 11: The Auditory System

What are the 5 sensory Pathways?

Gustatory Cortex

Olfactory Cortex

Auditory Cortex

Visual Cortex

Primary Somatic Sensory Cortex

What is the olfactory pathway?

It pathways from the nose projects through the olfactory bulb to the olfactory cortex.

Where do most sensory pathways project, and what does it do?

Most project to the thalamus. The thalamus then modifies and relays information to the cortical centers.

What are the components of the auditory system?

Hears hidden sounds.

Communication by talking.

Sound: Pitch,loudness and timbre.

Specialized receptors

Analytical organ

Analytical Organ

analyzes sounds from all sources.

What are the properties of sound?

700 mph.

Pitch.

Loudness.

Timbre.

Pitch

frequency of vibration measured in hertz.

Loudness

function of sound wave intensity.

Timbre

provides information about the nature or complexity of a particular sound ( train, whistle,different instruments, my voice)-mixture of many pure sound.( pure frequencies)

Sound Waves

Hearing is our perception of energy carried by sound waves.

The physical dimension of amplitude (intensity) matches with the perceptual dimension of

Loudness

The physical dimension of frequency matches with the perceptual dimension of

Pitch

The physical dimension of complexity matches with the perceptual dimension of

Timbre

Pinna

external ear

Tympanic Membrane

eardrum

Middle Ear

hollow region containing the ossicles,between the tympanic membrane and the cochlea.

Ossicles

a set of middle ear bones.

Malleus

Incus

Stapes

Cochlea

snail shaped structure of the inner ear containing the Organ of Corti

Organ of Corti

sensory organ for the auditory system.

Basilar Membrane

Hair Cells

Tectorial Membrane

Oval Window

opening in the cochlea where the stapes is located.

Round Window

opening in the cochlea (the window is closed and elastic)

What do outer hair cells help?

They help only sensitivity and selectivity of inner hair cells.

What is the ratio of outer hair cells to inner hair cells?What are there percentages?

3:1

95% inner hair cells

5% outer hair cells

What are the three stairways of the cochlea?

Scala Vestibuli

Scala Media (organ of corti)

Scala Tympani

How is sound wave (mechanical energy) transduced to neural signals (AP)?

1. Sound wave strikes the tympanic membrane and becomes vibrations.

2.Sound wave energy is transferred to the three bones of the middle ear which vibrates.

3.The stapes is attached to the membrane of the oval window.Vibrations of the oval window create fluid waves within the cochlea.

4. Fluid waves push on the flexible membranes of the cochlear duct. Hair cells bend and ion channels open, creating an electrical signal that alters neurotransmitter release.

5.Neurotransmitter release onto sensory neurons create action potentials that travel through the cochlear nerve to the brain.

6.Energy from the waves transfer across the cochlear duct into the tympanic duct an is dissipated back into the middle ear at the round window.

Cilia

hairlike appendage of a cell involved in movement of in transducing sensory information; found on the receptors in the auditory ( and vestibular system).

Tip Link

elastic filament that attaches the tip of one cilium to the side of an adjacent one.

Insertional Plaque

point of attachment of a tip link to a cilium (show the EM slide).

What are auditory receptors?

hair cells

What moves the cilia on the hair cells?

the movement of tectorial membrane

Signal transduction in hair cells: At Rest

Some channels open.

K+ and Ca2+

Signal transduction in hair cells: Excitation

More channels open. Cation entry depolarizes cell.

Signal transduction in hair cells: Inhibition

Channels closed. Less cation entry hyper-polarizes cell.

Cochlear Nerve

( Connections With the Cochlear Nerve)

branch of the auditory nerve that transmits auditory information to the brain.

What are the components of the central auditory system?

Cochlear Nucleus

Superior Olivary Complex

Lateral Lemniscus

Medial Geniculate Nucleus

Cochlear Nucleus

( ventral and dorsal; a group of neurons) nuclei in the medulla that receive auditory information.

Superior Olivary Complex

nuclei in the medulla that receive auditory information from the cochlear nuclei.

Lateral Lemniscus

band of fibers carrying auditory information through the medulla and pons to inferior colliculs ( below superior colliculs for vision)

Medial Geniculate Nucleus (MGN)

nucleus in the thalamus that relays the auditory information to the primary cortex.

What are the component of pitch perception?

Place coding and Rate coding.

Place Coding

Coding of frequencies by different locations on the

basilar membrane (moderate to high Hz)

Experiments: kanamycin and neomycin to kill

progressively the high to low Hz receptors

Rate Coding

Coding of frequencies by the rate of firing of neurons

in the auditory system (Low Hz)

What is the sensory coding for pitch?

Place coding

Cochlear Implant

is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. Also commonly referred to as bionic hearing.

Who are cochlear implants for

provides hearing in patient that are deaf due to damage to sensory hair cells in their cochlea.

Key to cochlear implant: an example of neural coding for sound

to electrically stimulate auditory nerves at different locations of the basilar membrane using place coding, and rate coding principles. Electrical electrodes for high frequency sound should be placed on the basilar membrane in close to the oval window.

Perception of Loudness

Detect the sound when the eardrum vibrates less than the diameter of a hydrogen atom. The firing frequency of a single axon here represent the loudness, and the location at the basilar membrane indicates the sound frequency.

How is perception of loudness achieved in the most part of the basilar membrane

it is achieved by the firing frequency of cochlear nerve axons (Moderate and High frequency: rating firing > 200 hz.).

How is perception of loudness achieved at the apical end of the basilar membrane

it is achieved by the number of axons firing at a given time. (very low frequency <200 Hz: number of axon firings).

At the apical end of the basilar membrane the firing frequency represents

a single axon here represents the sound frequency and the number of axons firing at the same time represent the sound intensity.

What are the components of Perception of timbre

Fundamental Frequency

Overtone

Fundamental Frequency

lowest and usually most intense frequency of a complex sound.

Overtone

frequency of complex tones that occurs at multiples of fundamental frequency

Perception of timbre

In the basilar membrane different portions respond to each of the overtones. The unique anatomically coded pattern of the activity of the auditory nerve is perceived by the auditory cortex (In mathematical term:Fourier analysis)

Static and Dynamic

What is the primary auditory cortex?

where the brain puts all the pieces together.

Where is the auditory cortex located?

Situated in the temporal cortex on the bottom of the lateral fissure.

Central Auditory Cortex

Primary Cortex

Association Cortex

Ventral Stream

Dorsal Stream

Primary Cortex

Core

Association Cortex

Belt and Parabelt

Ventral stream to the para-belt region of the anterior temporal lobe

What: analysis of pattern or identify of sounds: dogs or monkeys

Dorsal stream to posterior parietal cortex

Where: sound location

Phase differences

Difference in arrival times of sound waves at each

eardrum.

Localization by Means of Intensity Differences

Some neurons respond differently to binaural (both ears) stimuli of different intensity in each ear due to the head absorbs high frequencies producing a "sonic shadow" (high Hz).

Localization by Means of Timbre

The pattern of reflection of sounds by the pinna (folds and ridges) will change depending on the location of the source (at different elevations), altering the timbre.

Where:Localization by mean of Timbre

Outer ear: folds and ridges (echoes) can change the timbre

Dorsal cochlear nuclei

Learning experience individually

Hearing

detect sounds, determine the locations of the sound sources, and recognize the identity of the sounds

Perception of Environmental Sounds and Their Location components

-Pattern Recognition

-Complex sound perception is conducted by circuits of neurons in the auditory cortex.

- What system

-Where system

Pattern Recognition -

recognition that particular patterns of constantly changing activity belong to different sound sources (cars honking, birds chirping, people coughing, doors slamming at the same time)---auditory system: analytic organ, hearing all these at the same time

What system:

detects different monkeys' calls: (Ventral stream to the parabelt region of the anterior temporal lobe: analysis of pattern of sounds and identity

Where system:

detects different locations of these calls (Dorsal

stream to posterior parietal cortex: sound location )

Patient F D: recognition of Environmental sound, but not

the location and movement

of the sound source

loss of where

Patient C Z: aware of

Movement and location of sound, But not recognition of Environmental sound

loss of what

Patient M.A. not deaf, but can not

recognize the sound

nor the location and

movement—loss of what and where

Inferior temporal lobe

harmony

Right auditory cortex

beat of music

Left auditory cortex

pattern

Cerebellum

timing of music pattern and movement

Amusia

loss of the ability to perceive or produce melodic or rhythmic aspects of music