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Lecture 9

PSYC 211 Lecture Notes - Lecture 9: Bottle Cap, Subcutaneous Tissue, Dorsal Root Ganglion

Course Code
PSYC 211
Yogita Chudasama

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PSYC211 Lecture 9 - Feb. 8
The Stimulus:
Sounds are vibrations of air molecules that are produced by objects
If the vibration ranges between 30 and 20,000 times per second, it stimulates receptor cells in the ear
Sound has three physical dimensions:
The pitch determines the frequency of the molecular vibrations. It is measured in hertz (Hz) or cycles per second
The loudness corresponds to the amplitude o intensity of the molecular
The timbre corresponds to the complexity of the sound. Provides information
to the nature of the sound (i.e. train’s steam whistle)
Anatomy of the Ear:
Unlike the eye, the ear does not mix sound waves that enter the ear; what you
hear is two original tones. It is auditory system that helps develop the complexity
of the tone and to identify the nature of the sound
Sound is funneled through the pinna (the external ear)
Sounds coming down the ear canal cause the tympanic membrane (the
eardrum) to vibrate. These vibrations are transferred to the middle ear
The middle ear comprises thee ossicles (small bones of the middle ear: the malleus, incus and stapes)
The cochlea is part of the inner ear. It is a long coiled tube structure
containing fluid. It also contains the receptors
Cross Section Through Cochlea:
The cochlea is divided into three longitudinal divisions: scala vesibuli, scala
media and scala tympani
The receptive organ is the organ of Corti. It consists of the basilar
membrane, the tectorial membrane and hair cells
The hair cells are the auditory receptors
Fine cilia extensions of the hair cells attach to the tectorial membrane
Sound waves cause the basilar membrane to move relative to the tectorial
membrane which bends the cilia of the hair cells. This bending of the cilia
produces receptor potentials
From the Ear to the Primary Auditory Cortex:
The organ of Corti sends auditory information to the brain by the cochlea
The axons enter the cochlear nuclei where hey synapse
The axons of the cochlear nuclei then enter the superior olivary complex
Axons from superior olivar complex pass through a bundle of fibres (lateral
lemniscus) and enter the inferior colliculus
The axons then pass to the medial geniculate nucleus of the thalamus
which make their way to the primary auditor cortex of the temporal lobe
Tonotopic Representation:
The major principle of cochlear coding is that different frequencies produce
maximal stimulation of hair cells at different points on the basilar membrane
Like the basilar membrane, the auditory cortex is also organized according
to frequency, i.e. different parts of the auditor cortex respond best to
different frequencies
This organization of different frequencies of sound that are represented in
different places of the auditory cortex is known as tonotopic representation
Perception of Complex Sounds:
A principle function of the auditory system is to identify the sound
Perception of complex sounds is accomplished by neural circuits in the auditory cortex:
Axons have voltage-dependent potassium channels that produce very short action potentials
Terminal buttons are large and therefore release large amounts of glutamate
Postsynaptic membrane contains neurotransmitter dependent ion channels which act rapidly and produce strong EPSPs
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