sensory reception chapter 14. sensory systems the means by which organisms receive signals from the...
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Sensory Reception
Chapter 14
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Sensory Systems
• The means by which organisms receive
signals from the external world and
internal environment
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Sensation and Perception
• Sensation is conscious awareness of a
stimulus
• Perception is understanding what a
sensation means
• A perception of wetness arises from
numerous sensations
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Types of Receptors
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
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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
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Receptors in Skin
• Free nerve ending
• Ruffini ending
• Pacinian corpuscle
• Bulb of Krause
• Meissner’s
corpuscle
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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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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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Taste
• A special sense
• Chemoreceptors
• Five primary
sensations:
– sweet, sour, salty,
bitter, and umami
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Smell
• A special sense
• Olfactory receptors
• Receptor axons lead to olfactory lobe
olfactorybulb
receptor cell
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Anatomy of Human Ear
cochlea
auditory nerve
eardrumauditory canal
hammer
anvilstirrup
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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
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Sound Reception
• Organ of Corti senses fluid movement
• Hair cells are bent against overlying tectorial membrane, and they fire
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Balance and Equilibrium
• In humans, organs
of equilibrium are
located in the
inner ear
• Vestibular
apparatus
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Dynamic Equilibrium
• Rotating head movements cause pressure waves that bend a gelatinous cupula and stimulate hair cells inside it
cupula
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HEAD LEVEL
HEAD TILTED
• Moving in response to gravity, otoliths bend projections of hair cells and stimulate the endings of sensory neurons
Acceleration-Deceleration
otolithhair cell
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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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Human Eye sclera
choroid
iris
lens
pupil
cornea
aqueoushumor
ciliary muscle
vitreous body
retina
fovea
opticdisk
part ofopticnerve
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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
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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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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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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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To the Visual Cortex (1)
• Signals from
photoreceptors
are passed to
bipolar sensory
neurons, then to
ganglion cells
rod
cone
ganglion cell
bipolar cell
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To the Visual Cortex (2)
Visual cortex
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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