Download Chapter 7 - Bakersfield College

Chapter Seven
Nonvisual Sensation and
Perception
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Audition: Sound as a Stimulus
• Intensity: amplitude of sound wave
– Vary from quiet whisper to rock band
– Logarithmic scale of intensity (decibels, dB)
• Frequency: wavelength of a sound wave
– Determines pitch
– Single frequency = pure tone
– Multiple frequencies (timbre vs. noise)
– Measured in cycles per second in units of
Hertz (Hz)
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The Auditory World Differs Across Species
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Sound Results From the Collision of
Molecules
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Sounds Vary Along the Dimensions of
Amplitude, Frequency, and Complexity
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Intensity Levels of Common Sounds
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The Structure and Function of the Auditory
System
• The outer ear
– Pinna; auditory canal
• The middle ear
– Tympanic membrane (eardrum)
– Ossicles (malleus, incus, stapes)
– Oval window
• The inner ear
– Semicircular canal; cochlea
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The Anatomy of the Ear
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The Cochlea
• Three chambers
– Vestibular canal (perilymph)
– Tympanic canal (perilymph)
– Cochlear duct (endolymph)
• Organ of Corti (inner and outer hair cells)
• Separated by membranes
– Reissner’s membrane
– Basilar membrane: tectorial membrane
– Round window
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The Cochlea
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Sound Frequencies Are Translated by the
Basilar Membrane
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The Movement of the Cilia Regulates
Neurotransmitter Release by Hair Cells
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Central Auditory Pathways
• Spiral ganglia neurons communicate with
cochlear hair cells and the dorsal and
ventral cochlear nuclei of the medulla
• Cochlear nuclei synapse directly or
indirectly with the inferior colliculus
• The inferior colliculus projects to the
medial geniculate nucleus (MGN) of the
thalamus
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The Auditory Cortex
• The MGN projects to the primary auditory
cortex
• Primary auditory cortex
– Columns respond to single frequencies
• Secondary auditory cortex
– Activated by complex stimuli
– Separate pathways process the “what” and
“where” of sound
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Auditory Pathways from the Cochlea to the
Cortex
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Tonotopic Organization is Maintained by the
Auditory Cortex
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Auditory Perception
• Pitch perception
– Tonotopic organization (place theory)
– Temporal theory
• Loudness perception
– Decibel level describes physical qualities of
sound stimulus
– Loudness is the human perception of that
stimulus
– Equal loudness contours
– Decibel range of auditory neurons
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Equal Loudness Contours
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Localization of Sound
• Horizontal plane
– Comparison of arrival times of sounds at each
ear
– Differences in intensities between each ear
– Binaural neurons
• Vertical plane
– Pinna
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We Localize Sound by Comparing Arrival
Times at Both Ears
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Hearing Disorders
• Age-related hearing loss
– Poor circulation to the inner ear; exposure to
loud noise
• Damage to outer or middle ear
– Conduction loss due to wax build-up,
infection, or otosclerosis
– Treated with hearing aids
• Damage to inner ear, auditory pathways,
or auditory cortex
– Treated with cochlear prosthetics
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Cochlear Prosthetics
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The Body Senses
• The somatosensory system provides
information related to:
– The position and movement of the body
– Touch
– Skin temperature
– Pain
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The Vestibular System
• Movement receptors of the inner ear
– Otolith organs
• Utricle and saccule
• Head position and linear acceleration
– Semicircular canals
• Rotation of the head
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The Vestibular Structures of the Inner Ear
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The Vestibular System
• Central pathways
– Axons from vestibular organs travel along
auditory nerve to the cerebellum and
vestibular nucleus
– Axons from vestibular nucleus communicate
with spinal cord and ventral posterior (VP)
nucleus
– VP nucleus projects to primary
somatosensory cortex and primary motor
cortex
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Touch
• Skin structure
– Hairy and glabrous (hairless) skin
– Epidermis, dermis, subcutaneous tissue
• Mechanoreceptors
– Encapsulated: Meissner’s and Pacinian
corpuscles
– Nonencapsulated: Merkel’s disks and Ruffini’s
endings
– Free nerve endings
– Two-point discrimination test
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Mechanoreceptors in the Skin
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Major Features of the Mechanoreceptors
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Two-Point Discrimination Thresholds
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The Four Classes of Sensory Axons Differ
in Size and Speed
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Touch Pathways
• Signals from mechanoreceptors travel
from skin along Aβ axons to the dorsal
roots of the spinal cord: dermatomes
• From the spinal cord, axons travel along
the dorsal column-medial lemniscal
pathway to the dorsal column nuclei of the
medulla
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Touch Pathways (cont’d.)
• Axons from the dorsal column nuclei cross
the midline to the contralateral ventral (VP)
posterior nucleus of the thalamus, then
project to the primary somatosensory
cortex
• Touch information from the head travels to
the VP nucleus via the cranial nerves
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Dermatomes Are Areas of Skin Served by
the Dorsal Roots of One Spinal Nerve
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Touch Pathways
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Somatosensory Areas of the Thalamus
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The Sensory Homunculus
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The Plasticity of Touch
• Somatosensory cortex rearranges itself in
response to changes in the amount of
input it receives
– Phantom pain
– Referred sensations
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Somatosensory Disorders
• Damage to the primary somatosensory
cortex
– Sensation and movement deficits
• Damage to the secondary somatosensory
cortex
– Neglect syndrome
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Pain
• A purpose for pain
– Emotional, cultural, and experiential
components
– Relays information about tissue injury
• Receptors for pain
– Nociceptors
– Mechanical injury, extreme temperature, and
certain chemicals activate nociceptors
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Ascending Pain Pathways to the Brain
• Ascending pain fibers
– Myelinated Aδ (quick, sharp pain)
– Unmyelinated C fibers (dull ache)
– Glutamate and substance P
• Spinal cord to the substantia gelatinosa to
the spinothalamic pathway; synapse in the
thalamus
– Pain signals from head/neck travel along the
trigeminal nerve, synapse in the spinal
trigeminal nucleus; forms trigeminal lemniscus
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Ascending Pain Pathways to the Brain
(cont’d.)
• Spinothalamic and trigeminal lemniscus
fibers synapse in VP nucleus or
intralaminar nuclei of the thalamus
• Communicate with the anterior cingulate
cortex and somatosensory cortex
• Gate theory of pain
– Explains the effect of context on pain
perception
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Ascending Pain Pathways
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Descending Pain Pathways to the Brain
• Higher level brain structures project to the
periaqueductal gray (PAG) of the midbrain
• PAG projects to the raphe nuclei of the
medulla and the spinal cord
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Descending Messages Influence Pain
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Managing Pain
• Opioid activity
• Periaqueductal gray (PAG) associated
with cultural, emotional, and experiential
influences on pain sensation
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The Chemical Senses: Olfaction
• Sense of smell
• Detection of airborne molecules
• Olfactory receptors: bipolar
– Line the olfactory epithelium in the dorsal
nasal cavity
– Olfactory neurons form the olfactory nerve
– Molecules dissolve in mucus surrounding
olfactory receptors
– Depolarization sends action potentials to the
olfactory bulb via the olfactory nerve
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Olfactory Pathways
• Signals to the olfactory bulb are sorted by
glomeruli
• Olfactory bulb axons form olfactory tracts,
project to the olfactory cortex
– Does not synapse in thalamus first
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Olfactory Pathways (cont’d.)
• Olfactory cortex connects to the medial
dorsal nucleus of the thalamus, which
projects to the insula and the orbitofrontal
cortex
• Olfactory signals are interpreted as odor
identification, motivation, emotion, and
memory
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Olfactory Information Travels from the
Epithelium to the Brain
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The Chemical Senses: Gustation
• Sense of taste
– Protection from poisonous or spoiled food
– Attraction to foods is necessary for survival
• Dissolved chemicals in saliva
• Five major taste classes
– Sweet, sour, bitter, salty, umami
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Gustatory Receptors
• Found on tongue and other areas of the
mouth
• Papilla contain taste buds
• Taste buds have 50-150 receptor cells
– Receptor cells are not neurons, but can form
synapses
– Microvilli project into saliva
– Transduction mechanisms for chemical stimuli
result in depolarization of taste receptor cells
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The Taste Receptors
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Gustatory Pathways
• Taste fibers in tongue form parts of cranial
nerves VII, IX, and X
• Cranial nerves synapse with gustatory
nucleus of the medulla
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Gustatory Pathways (cont’d.)
• Axons from gustatory nucleus synapse in
the ventral posterior medial (VPM) nucleus
of the thalamus
– Projects to the gustatory cortex in the parietal
lobe for identification of primary taste qualities
– Projects to the orbitofrontal cortex in the
frontal lobe for combination with olfaction and
vision to produce flavor perceptions
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Gustatory Pathways to the Brain
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