Textbook Notes (362,768)
Canada (158,052)
Psychology (1,390)
PSYC 211 (154)
Chapter 7

Chapter 7 Notes.docx

14 Pages
Unlock Document

McGill University
PSYC 211
Yogita Chudasama

Chapter 7: Audition, the Body Senses, and the Chemical Senses Notes taken by: Ashley Brown Contact for mistakes: [email protected] Audition The Stimulus Sounds refers to vibrations moving through any medium - humans can detect sound waves between 30 and 20,000 Hz - vary in their picth, loudness, and timbre o pitch corresponds to the fundamental frequency of vibration measured in hertz (Hz) o loudness corresponds to intensity or the degree to which condensations and rarefactions differ from each other (amplitude) o timbre corresponds to complexity; it provides information to the nature of the sound The ear is an analytical organ (as opposed to the eye which is a synthetic organ) - when 2 different frequencies of sound wave are mixed we do not perceive an intermediate tone but instead we hear both original tones - this gives us the ability to identify the nature of particular sounds Anatomy of the Ear Sound is funneled via the pinna, or the external ear through the ear canal to the tympanic membrane, or the eardrum, which vibrates with the sound The middle ear is the hollow region behind the tympanic membrane - contains the bones of the middle ear called the ossicles which are set into vibration by the tympanic membrane o malleus, or the hammer, connects with the tympanic membrane, is the first of the three o incus, or the anvil, is the second o the stapes, or the stirrup, is the last of the ossicles The ossicles transmit vibrations to the cochlea, the structure in the inner ear that contains the receptors - the baseplate of the stapes presses against the membrane behind the oval window, an opening in the bone surrounding the cochlea, and transmits sound vibrations into the fluid within the cochlea - this process is really efficient because it vibrates with smaller but more forceful excursions against the oval window than the tympanic membrane does against the malleus  compensates for the fact that sound waves must travel from air to the liquid medium of the cochlea Breakdown of Cochlea structure - shaped like a snail - fluid filled - divided into three sections o scala vestibuli: the vestibular stairway o scala media: the middle stairway o scala tympani: the tympanic stairway - the round window is a membrane-covered opening in the bone surrounding the cochela that makes it not a closed system and thus permitting the transmission vibration from the oval window to the fluid of the cochlea o pretty sure this is like the exit while the oval window is the entrance Organ of Corti is the receptive organ - consist of the basilar membrane, the hair cells, and the tectorial membrane o basilar membrane: is a membrane in the cochlea and contains the organ of Corti (how they contain each other is past me) o hair cells: the receptive cell of the auditory apparatus, they are anchored by rodlike Deiter’s cells (which are just supporting cells) to the basilar membrane o tectorial membrane is located above the basilar membrane and serves as a shelf against which the cilia of the auditory hair cells move; is fairly rigid - sound waves cause the basilar membrane to move relative to the tectorial membrane, which bends the cilia of the hair cells o bending produces receptor potentials o the basilar membrane bending is determined the frequency of the sound  high frequency sounds cause the end nearest the oval window to bend, the basal end Vibration of baseplate of stapes against membrane behind oval window  sound waves of low or high frequency into the cochlea  vibrations cause part of the basilar membrane to flex back and forth  pressure changes in the fluid underneath the basilar membrane are transmitted to the membrane of the round window  this moves in and out in a manner opposite to the movements of the oval window There exist a middle ear disorder in which bone grows over the round window which causes severe hearing loss because the basilar membrane can’t flex - can be fixed by fenestration, or drilling a tiny hole in the bone where the round window should be Auditory Hair Cells and the Transduction of Auditory Information Two types of auditory receptors, inner and outer auditory hair cells, are located on the basilar membrane - contain cilia which are fine hairlike appendages that arranged in rows according to height that are involved in transducing sensory information o contain a core of actin filaments surrounded by myosin filaments that make them stiff and rigid o adjacent cilia are linked to each other by elastic filaments known as tip links which attach the tip of one cilium to the side of the adjacent one at points of attachment called insertional plaques which is where receptor potentials are triggered  normally tip links are under a small amount of tension because they are slightly stretched, so movement in one direction stretches them more and the other relaxes them o the bending of bundles of cilia causes receptor potentials  fluid surrounding hair cells is rich in potassium  each insertional plaque contains a single cation channel, identified as TRPA 1 which opens when the bundles move toward the tallest one because it increases the tension and then this opening causes depolarization of the membrane and NT release is increased (when it moves towards the shorter they are shut, hyperpolarized, and decreased NT release) - humans have approx. 3500 inner hair cells and 12,000 outer hair cells - these cells form synapses with dendrites of bipolar neurons who axons bring auditory information to the brain Sound waves cause both the basilar membrane and the tectorial membrane to flex up and down - these movements bend the cilia one direction or the other - the tips of the cilia of outer hair cells are attached directly to the tectorial membrane o the cilia of the inner hair cells which aren’t attached bend back and forth because of the relative motion of the fluid within the cochlea The Auditory Pathway Connections with the Cochlear Nerve The organ of Corti sends auditory information to the brain through the cochlear nerve, a branch of the auditory nerve - the neurons that compose the afferent axons are of the bipolar type o their cell bodies are in the cochlear nerve ganglion, also called the spiral ganglion o have axonal processes that are capable of sustaining action potentials that protrude from both ends of the soma  one end acts like a dendrite  responds with excitatory postsynaptic potentials when the NT is released by the auditory hair cells and this triggers action potentials in the auditory nerve axons which form synapses with neurons in the medulla o each cochlear nerve has approx. 50,000 afferent axons  95% of which that have dendrites that form synapses with inner hair cells; these have thick and myelinated axons  shows that even though there are less inner hair cells that they are of primary importance in the transmission of auditory information to the CNS  inner hair cells necessary for normal hearing, while the outer hair cells are just effector cells (involved in altering the mechanical characteristics of the basilar membrane and therefore influencing the effects of sound vibration on inner hair cells)  other 5% form synapses with the outer hair cells, with one fiber being paired to on average 30 outer hair cells; these have thin and unmyelinated axons o NT at the afferent synapses is glutamate - Efferent axons come from the superior olivary complex, a group of nuclei in the medulla o Constitute the olivocochlear bundle o Form synapses directly on outer hair cells and on the dendrites that serve the inner hair cells o Terminal buttons secrete acetylcholine, which has an inhibitory effect on the hair cells The Central Auditory System SEE FIGURE 7.9 ON PAGE 220 1. The organ of Corti sends auditory information to the brain by the cochlear nerve. 2. The axons enter the cochlear nuclei (in the medulla) where they synapse. 3. The axons of the cochlear nuclei then enter the superior olivary complex (also in medulla) 4. Axons from superior olivary complex pass through a bundle of fibres (lateral lemniscus) and enter the inferior colliculus which is located in the dorsal midbrain 5. The axons then pass to the medial geniculate nucleus of the thalamus which make their way to the primary auditory cortex of the temporal lobe Each hemisphere receives information from both ears but primarily from the contralateral one Auditory information is relayed to the cerebellum and reticular formation as well. Tonotopic representation: a topographically organized mapping of different frequencies of sound that are represented in a particular region in the brain; describes the relationship between the cortex and the basilar membrane - the basal end (the end toward the oval window) is represented most medially in the auditory cortex - the apical end is represented most laterally in the auditory cortex - The major principle of cochlear coding is that different frequencies produce maximal stimulation of hair cells at different points on the basilar membrane. The auditory cortex is organized in hierarchy (like V1) - the primary auditory cortex is hidden on the upper hank of the lateral fissure aka on the gyrus on the dorsal surface of the temporal lobe - the core region consist of the primary auditory cortex actually consist of 3 regions each of which receive a separate Tonotopic map of auditory information from the ventral division from the medial geniculate nucleus - the auditory association has different levels o first level is the belt region which surrounds the primary auditory cortex  consist of at least 7 divisions  receives information both from A1 and the medial devisions of the medial geniculate nucleus o the highest level is the parabelt region and it receives information from the belt region and divisions of the medial geniculate nucleus that project to it - arranged into 2 streams: dorsal and ventral o Dorsal stream: terminates in the posterior parietal cortex and is involved in sound locations o Ventral stream: terminates in the parabelt region of the anterior temporal lobe and is involved in analysis of complex sounds Perception of Pitch Pitch corresponds to frequency. The cochlea detects frequency by two means: moderate to higher frequencies by place coding and low frequencies by rate coding Place Coding Different frequencies cause different parts of the basilar membrane to flex back and for the - higher frequencies produce more displacement at the basal end (toward the stapes) - place code: the system by which information about different frequencies is coded by different locations on the basilar membrane o cochlear implants, electronic devices surgically impanted in the inner ear that can enable deaf people to hear, provide good evidence for place coding (not sure why I skimmed, don’t think it matters terribly much) o the point of maximum vibration of the basilar membrane to a particular frequency is very precisely located but only when the cells in the organ of Corti are alive and healthy  outer hair cells serve a mechanical purpose, by selectively tuning and the amplification of vibration from the basilar membrane  contractile proteins contract the outer hair cells when exposed to an electric current or Ach Rate Coding Lower frequencies cannot be accounted by place coding. Appear to be detected by neurons that fire in synchrony to the movements of the apical end of the basilar membrane Rate coding: the system by which information about different frequencies is coded by the rate of firing of neurons in the auditory system Perception of Loudness Cochlea is very sensitive, only the smallest vibration is needed to produce a perceptible sound Axons of the cochlear nerve inform the brain of loudness by altering their rate of firing - louder sounds produce more intense vibrations of the eardrum which produce a more intense shearing force on the cilia of the auditory cells and so they release more NT which consequently causes then to have a higher rate of firing - the loudness of low-frequency sounds is signaled by the number of axons arising from these neurons at a given time Perception of Timbre We hear sounds with a rich mixture of frequencies, and can distinguish because of this stuff like the difference between a clarinet sound and a flute sound Fundamental frequency: the lowest, and usually most intense, frequency of a complex sound; most often perceived as the sound’s basic pitch Overtone: the frequency of complex tones that occurs at multiples of the fundamental frequency Perception of Complex Sounds Hearing has 3 primary functions: (1) to detect sounds, (2) to determine the location of their sources, and (3) to recognize the identity of these sources (along with their meaning and relevance to us) The brain recognizes particular patterns that belong to particular sources and we perceive them each as an independent entity Perception of Environmental Sounds and Their Location The task of the auditory system in identifying sound sources is one of pattern recognition - must recognize that particular patterns of constantly changing activity belong to different sound sources - recognition of complex sounds requires that the timing of changes in the components of the sounds be preserved all the way to the auditory cortex o neurons that convey info to the auditory system contain special structures that permit them to conduct this info rapidly and accurately  axons contain special low-threshold voltage-gated potassium channels that produce very short action potentials  terminal buttons are large and release large amounts of
More Less

Related notes for PSYC 211

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.