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PSYC 211 Study Guide - Midterm Guide: Medium Frequency, Nigrostriatal Pathway, Fastigial Nucleus

Course Code
PSYC 211
Yogita Chudasama
Study Guide

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Chapter 7: Audition & Chemosensory
The Stimulus
-Sounds are produced by objects that vibrate and set molecules of air into motion, producing waves, so that if the waves
range between 30-20 000 times per second, it becomes audible
-Sounds have three dimension:
oPitch: frequency of vibration, measured by hertz (Hz), or cycles per second
oLoudness: function of intensity; the degree to which condensations and rarefactions differ from each other in
oTimbre: the complexity or the nature of the sound depending on the particular mixture of different frequencies
Anatomy of the Ear
-Sound is funnelled by the pinna, or the shell of the outer ear, to the tympanic membrane, also known as the eardrum
-The malleus (hammer) connects with the tympanic membrane and transmits vibrations via the incus (anvil) and the
stapes (stirrup) to the cochlea, which contains auditory transducing mechanisms
oOval window: an opening in the bone surrounding the cochlea that reveals a membrane, against which the
baseplate of the stapes presses; transmits sound vibrations into the fluid within the cochlea
oRound window: an opening in the bone surrounding the cochlea that allows the fluid inside the cochlea to
move back and forth according to pressure changes
Cochlea (fig. 7.4)
oA coiled tubular structure, divided longitudinally into three sections: the scala vestibule, the scala media, and the
scala tympani
oThe organ of Corti contains inner (numbering approximately 3500) and outer hair cells (12000) which are
anchored by Deiter’s cells to the basilar membrane, which sits underneath the tectorial membrane
oProjections from the hair cells, called cilia, pass through the reticular membrane and come to rest on the
underside of the tectorial membrane
Sound waves cause movement of the basilar membrane and bending of the cilia, which produces
action potentials in the hair cells
High frequencies affect primarily the end nearest the oval window (the base), and low frequencies
affect primarily the end nearest the round window (the apex)
Auditory Hair Cells and the Transduction of Auditory Information
-Cilia: contain a core of acting filaments surrounded by myosin filaments and are linked adjacently by elastic tip links at the
points of attachment known as insertional plaques
-Hair cells form synapses with dendrites of bipolar neurons whose axons bring auditory information to the brain
-Where movement of the outer hair cell cilia is caused by direct contact with the flexing tecticular membrane, and the inner
hair cell cilia movement is caused by indirect inner ear fluid flow movement
oOuter hair cells are known as effector cells, which influence the effects of sound vibrations on the inner hair
oMovement toward the tallest cilium increases tension on the tip links which opens ion channels and increases
the influx of K+ and Ca2+ ions, causing depolarization; movement in the opposite direction prevents the opening
of these channels
Auditory Pathway
Cochlear nerve – the branch of the auditory nerve that transmits auditory information from the cochlea to the brain; composed of
the axons of bipolar neurons whose somas lie in the cochlear nerve ganglion, aka spiral ganglion
-The dendritic ends respond with excitatory postsynaptic potentials triggered by the glutamate released by the hair cells,
exciting the neuronal pathway that extends into the medulla
-Axons enter the cochlear nucleus of the medulla where they synapse and subsequent neurons connect to the superior
olivary complex
-From the medulla, axons travel by way of the lateral lemniscus to the inferior colliculus of the dorsal midbrain
-From the inferior colliculus axons travel to the medial geniculate nucleus of the thalamus, which sends its axons to the
auditory cortex of the temporal lobe
-A disproportion exists in the connections between the inner hair cells and the cochlear nerve axons, so that the inner hair
cells, which amount to 29% of total hair cells, connect to 95% of the cochlear nerve
oStudies show that the outer hair cells are just effector cells involved in influencing the effects of sound vibrations
on inner hair cells
-Olivocochlear bundle: efferent axons of the cochlear nerve begin at the superior olivary complex of the medulla and end
at the auditory hair cells where they secrete acetoylcholine to inhibit hair cell potentials
-Each brain hemisphere receives information from both ears but primarily processes contralaterally
oTonotopic representation: a topographically organized mapping of different frequencies of sound that are
represented in a particular region on the brain
Core region – the primary auditory cortex, located on a gyrus on the dorsal surface of the temporal lobe; consists of three regions
which each receives a separate tonotopic map of auditory information
Belt region – the first level of the auditory association cortex that surrounds the primary auditory cortex and consists of at least
seven divisions
Parabelt region – the second level of the auditory association cortex that surrounds the belt region (fig. 7.10)
Two streams of the auditory cortex:
oDorsal stream terminates in the posterior parietal cortex and is involved in sound localization
oVentral stream terminates in the parabelt region of the anterior temporal lobe and is involved in the analysis of
complex sounds
Perception of Pitch
Place code (von Bekesy) – the system by which information about different frequencies is coded by different locations on the basilar
membrane, so that the firing of particular axons in the cochlear nerve tells the brain about the presence of particular frequencies of
-A given frequency causes a large portion of the basilar membrane to be deformed, given that the subject is not alive and
well; otherwise place coding is very precisely localized

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-Contraction of the outer hair cells alters the mechanical characteristics of the basilar membrane, and by extension, the
Response properties of the inner cells
Cochlear implants: an electronic device surgically implanted in the inner ear that can enable a deaf person to hear by
duplicating the place coding of pitch on the basilar membrane; most effective in young children
Rate code (Kiang) – the system by which information about the lower frequencies is coded by the rate of firing of neurons in the
auditory system synced to the movements of the apical end of the basilar membrane
Perception of loudness
-The softest sounds that can be detected appear to move the tip of the hair cells 1-100 picometres (one trillionth of a
-Loudness is informed by the different rates of firing by the axons of the cochlear nerve, where louder sounds produce
more intense vibrations of the eardrum and the cilia, thereby releasing more neurotransmitters
oIn lower frequencies, it is believed that loudness is signalled by the number of axons arising from active
neurons; vice versa occurs in cases of higher frequencies
Perception of Timbre
Fundamental frequency – the lowest, and usually most intense, frequency of a complex sound; most often perceived as a sound’s
basic pitch
Overtone – the frequency of complex tones that occurs at multiples of the fundamental frequency
-Different portions of the basilar membrane respond to each of the overtones
-The auditory cortex analyze a complex sequence of multiple frequencies that appear, change in amplitude, and disappear
Perception of complex sounds
-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, achieved by rapid transmission by specialized neurons which enable strong EPSPs
-Auditory cortex is also divided between two processing streams; the dorsal where and the ventral what
oDamage to either of the streams will cause auditory agnosias (impairments of various aspects of auditory
-Physiological overlap between the visual and auditory processing regions in the brain aids individuals recognizing the
nature of the origin of a sound by association
-Musical perception requires recognition of sequences of notes (i.e. the melody) their adherence to rules that govern
permissible pitches and harmony
oPitch is determined by the fundamental frequency and timbre is determined by the mixture of overtones
-Pure tones are perceived in the primary auditory cortex, and recognition of complex pitch is done so by the auditory
association cortex
-Different brain regions are involved in different aspects of music perception; for example, the inferior frontal cortex is
involved in recognition of harmony, the left auditory cortex involved in superimposed rhythmic patterns, the cerebellum
and basal ganglia in timing, etc.
-The volume of the primary auditory cortex of musicians are greater than those who aren’t, among other factors and
-Amusia: loss or impairment of musical abilities, produced by hereditary factors or brain damage
oCongenital cases appear to involve abnormalities of the right superior temporal gyrus and the right inferior
frontal gyrus; related inversely in thickness to ability
Perception of Complex Sounds:
Hearing has three primary functions: to detect sounds, to determine the location of their sources, and to recognize the
identity of these sources
The axons in the cochlear nerve contain a constantly changing pattern of activity corresponding tot he constantly changing
mixtures of frequencies that strike the eardrums. Somehow, the auditory system of the brain recognizes particular patterns
that belong to particular sources, and those are perceived each independently
Perception of Environmental Sounds and Their Location:
Identifying sound sources is one of pattern recognition
Perception of complex sounds appears to be accomplished by circuits of neurons in the auditory cortex
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. Neurons that convey information to the auditory cortex contain special features that permit them
to conduct this information rapidly and accurately. Their axons contain special low-threshold voltage-gated potassium
channels that produce very short action potentials. Their terminal buttons are large and release large amounts of glutamate,
and the postsynaptic membrane contains neurotransmitter-dependent ion channels that act unusually rapidly, producing very
strong EPSPs
Neurons in the ‘what’ system discriminated between different monkey calls, while neurons in the ‘where’ system discriminate
between locations of loudspeakers presenting these calls
The dorsal stream of both systems overlap in the parietal lobe so that we can use the convergence of sight and sound to
recognize which of several objects in the environment is making a noise. In addition, we can learn the association between
the sight of an object and the sounds it makes
Perception of the identity of sounds activated the ventral stream of the auditory cortex and perception of the location of
sounds activated the dorsal stream
Perception of Music:
Music consists of sounds of various pitches and timbres played in a particular sequence with an underlying rhythm.
Particular combinations of musical notes played simultaneously are perceived as consonant or dissonant, pleasant or
Melodies played with one set of rules (the major mode) usually sound happy, while those played using another set of rules
(the minor mode) generally sound sad
A melody is recognized by the relative intervals between its notes, not by their absolute value
Primary auditory cortex responds to pure tones of different frequencies but that recognition of the pitch of complex sounds is
accomplished only by the auditory association cortex
Pitch discrimination takes place in a region of the superior temporal gyrus rostral

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The cerebellum and basal ganglia are involved in timing of musical rhythms and timing of movements
4% of the population exhibits congenital amusia, a severe and persistent deficit in musical ability (auditory cortex of the right
superior temporal gyrus and the cortex of the right inferior frontal gyrus was thicker in people with congenital amusia)
Musical ability in general and congenital amusia have a genetic basis
Cutaneous sense – one of the somatosenses; includes sensitivity to stimuli that involve the skin
Proprioception – perception of the body’s position and posture
Kinesthesia – perception of the body’s own movements
Organic sense – a sense of modality that arises from receptors located within the inner organs of the body
The Stimuli
-Pressure Caused by mechanical deformations of the skin
oVibration is used as a judge of roughness
oPain is an indication of tissue damage
oKinesthesia by muscle receptors in stretch and tension
Anatomy of the Skin and its Receptive Organs
-Skin consists of subcutaneous tissue, dermis, and epidermis
Hairy skin:
-Free (unencapsulated) nerve endings are found interwoven around the bases of hair follicles and around the emergence
of hair shafts in order to detect hair movement; also located just under the surface of the skin to detect changes in
temperature and pain
-Ruffini corpuscles: slow response receptors with large diffuse borders that respond to indentations of the skin
-Pacinian corpuscles: specialized, encapsulated nerve endings that detect mechanical stimuli such as vibrations; the
largest sensory end organs consisting of up to 70 onion-like layers wrapped around the dendrite of a single myelinated
axon; rapid adaptation with large diffuse borders
Glabrous skin (skin that does not contain hairs and is more active in touch/use/contact)
-in addition to what is found under hairy skin:
-Meissners corpuscles: located in the papillae that project up into the epidermis, enervated by two to six axons; rapid
adaptation to objects with small, sharp borders and in vibrations and taps
-Merkel’s disks: also found in the papillae of glabrous skin at the base of the epidermis adjacent to sweat ducts; responds
slowly to objects with small sharp borders
Perception of Cutaneous Stimulation
-Movement on skin causes ion channels to open; influx and efflux of ions in the dendrite results in action potential
transmission by small-diameter unmyelinated axons in cases of sensitive touches and temperature, otherwise
transmission occurs by fast-conducting myelinated axons
-movement between skin and object is needed for information to be conveyed about the object, such as shape, mass,
texture, etc; therefore the somatosenses work dynamically with the motor system to manipulate the objects
-prolonged repetitive tactile experience also shapes the relevant brain structures involved (e.g. violinists)
-perceptions of temperature is relative across the skin, depending on previous thermal stimulation experience in the area
oincreases in temperature lower the sensitivity of warmth receptors and raise the sensitivity of cold receptors;
and vice versa for decreases in temperature
-cold sensors are located just beneath the epidermis, and warmth sensors are located more deeply in the skin (table 7.2)
owarmth sensors activated by six known thermoreceptors from the transient receptor potential (TRP) family:
-pain perception is accomplished by networks of free nerve endings in the skin in at least three different types of receptors
ohigh threshold mechanoreceptors are free nerve endings that respond to intense pressure
osecond category mechanoreceptors respond to extremes of heat, acids, and capsaicin and contains TRPV1
oTRPA1 receptors are the third category and react to pungent irritants in foods and the environment that cause
-skin irritation that elicits the desire/reflex to scratch, caused by chemicals such as histamine
-pain and itching are mutually inhibitory, although certain drugs to treat one are causes of the other
Somatosensory Pathways
-axons that convey precisely localized information
(i.e. touch, kinesthesia):
neurons in the dorsal root ganglion
dorsal columns of white matter
nuclei in lower medulla
medial lemniscus in midbrain
ventral posterior nuclei of the thalamus
primary somatosensory cortex
secondary somatosensory cortex
-axons that convey poor localized information (i.e.
pain, temperature):
neurons in the dorsal root ganglion
synapses formed in the spinal cord
contralateral spinothalamic tract
ventral posterior nuclei of the thalamus
primary somatosensory cortex
secondary somatosensory cortex
-in the somatosensory cortex, cortical columns contain neurons that respond to a particular type of stimulus applied to a
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