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Sensory Reception
Chapter 35
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Sensory Systems
• The means by which organisms receive
signals from the external world and
internal environment
• Many animals can sense stimuli that
humans cannot
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Sensory Receptors
Convert the energy of a stimulus into
action potentials
Mechanoreceptors
Thermoreceptors
Pain receptors
Chemoreceptors
Osmoreceptors
Photoreceptors
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Assessing a Stimulus
• Action potentials don’t vary in amplitude
• Brain tells nature of stimulus by:
– Particular pathway that carries the signal
– Frequency of action potentials along an axon
– Number of axons recruited
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Recordings of Action Potentials
Figure 35.3Page 609
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Sensory Adaptation
A decrease in response to a stimulus being maintained at constant strength
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Somatic Sensations
• Touch
• Pressure
• Temperature
• Pain
• Motion
• Position
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Somatosensory Cortex
Figure 35.4Page 610
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Receptors in Skin
• Free nerve ending
• Ruffini ending
• Pacinian corpuscle
• Bulb of Krause
• Meissner’s
corpuscle
Figure 35.5Page 611
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Referred Pain
• Sensations of pain from internal organs
may be wrongly projected to part of the
skin surface
• Heart attack can be felt as pain in skin
above the heart and along the left
shoulder and arm
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Taste
• A special sense
• Chemoreceptors
• Five primary
sensations:
– sweet, sour, salty,
bitter, and umami
Figure 35.8Page 612
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Smell
• A special sense
• Olfactory receptors
• Receptor axons lead to olfactory lobe
olfactorybulb
receptor cell
Figure 35.7Page 612
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Balance and Equilibrium
• In humans, organs
of equilibrium are
located in the
inner ear
• Vestibular
apparatus vestibular apparatus
saccule
utricle
semicircular canals
Figure 35.9bPage 613
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• Moving in response to gravity, otoliths bend projections of hair cells and stimulate the endings of sensory neurons
Acceleration-Deceleration
hair cellotoliths membrane
vestibular nerve
Figure 35.9bPage 613
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Dynamic Equilibrium
• Rotating head movements cause pressure waves that bend a gelatinous cupula and stimulate hair cells inside it
cupula
Figure 35.9cPage 613
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Properties of Sound
• Ear detects pressure waves
• Amplitude of waves corresponds to
perceived loudness
• Frequency of waves (number per
second) corresponds to perceived pitch
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Anatomy of Human Ear
cochlea
auditory nerve
eardrumauditory canal
hammer
anvilstirrup
Fig. 35.11a Page 614
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Sound Reception
• Sound waves make the eardrum vibrate
• Vibrations are transmitted to the bones
of the middle ear
• The stirrup transmits force to the oval
window of the fluid-filled cochlea
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Sound Reception
• Movement of oval window causes waves in the fluid inside cochlear ducts
Figure 35.11bPage 615
eardrum round window
oval window(behind stirrup) scala vestibuli
scala tympani
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Sound Reception
hair cells in organ of Corti tectorial
membrane
lumen of cochlear duct
basilar membranelumen of scala tympani
to auditory nerve
Figure 35.11cPage 615
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Vision
• Sensitivity to light does not equal
vision
• Vision requires two components
– Eyes
– Capacity for image formation in the
brain
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Invertebrate Eyes
Limpet ocellus
sensory neuron
epidermis
cuticle
lens
Land snail eye
Compound eye of a deerfly
ommatidium
Figures 35.13 & 35.14Pages 616 & 617
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Human Eye sclera
choroid
iris
lens
pupil
cornea
aqueoushumor
ciliary muscle
vitreous body
retina
fovea
opticdisk
part ofopticnerve
Figure 35.17Page 618
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Pattern of Stimulation
• Light rays pass through lens and
converge on retina at back of eye
• The image that forms on the retina is
upside down and reversed right to left
compared with the stimulus
• Brain accounts for this during processing
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Pattern of Stimulation
Figure 35.18Page 619
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Visual Accommodation
• Adjustments of the lens
• Ciliary muscle encircles lens
• When this muscle relaxes, lens flattens,
moves focal point farther back
• When it contracts, lens bulges, moves
focal point toward front of eye
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Organization of Retina
• Photoreceptors lie at the back of the
retina, in front of a pigmented epithelium
• For light to reach the photoreceptors, it
must pass layers of neurons involved in
visual processing
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Organization of Retina
• Signals from
photoreceptors
are passed to
bipolar sensory
neurons, then to
ganglion cells
Figure 35.21aPage 620
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The Photoreceptors
• Rods – Contain the pigment rhodopsin
– Detect very dim light, changes in light intensity
• Cones– Three kinds; detect red, blue, or green
– Provide color sense and daytime vision
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Receptive Fields
• Restricted areas that influence the activity of individual sensory neurons
• Response of neuron to orientation of bar
signals tooscilloscope
time (sec)Figure 35.22Page 621
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Retina to Brain
retinaoptic nerve
lateral geniculate
nucleus
visual cortex
Figure 35.31Page 621
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Disorders of the Eye (1)
• Color blindness
• Focusing problems– Nearsightedness and farsightedness
• Eye diseases– Trachoma
– Histoplasmosis
– Herpes simplex infection
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Disorders of the Eye (2)
• Age-related problems– Cataracts– Macular degeneration– Glaucoma
• Injuries– Retinal detachment