Download Chapter 12

Human Biology Concepts and Current Issues
Seventh Edition
Michael D. Johnson
12
Sensory
Mechanisms
© 2014 Pearson Education, Inc.
Lecture Presentations by
Robert J. Sullivan
Marist College
Receptors Receive and Convert Stimuli
 Stimulus:
 A change in the environment
– Heat, pressure, pain, touch, sound, light, chemical
 Receptor: a structure sensitive to a specific stimulus
and converts its energy into electric signals
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Receptors Are Classified According to Stimulus
 Mechanoreceptors
– Respond to mechanical stimuli
– Example; respond to touch, pressure
 Thermoreceptors
– Respond to heat or cold
 Pain receptors
– Respond to tissue damage or excessive heat or pressure
 Chemoreceptors
– Respond to presence of chemicals example, taste
receptors
 Photoreceptors
– Respond to light
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CNS Interprets Nerve Impulses
 Nerve impulses are transmitted from receptors to
specific portions of brain
 Sensations are perceived in the brain, example
sensation of pain, heat, cold, vision
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General (somatic) Sensations and Special Senses
Provide Sensory Information
 General (somatic) sensations
– Arise from sensory receptors located throughout the
body
– Temperature, pressure, touch, vibration, pain, of body
position
 Special senses
– Arise from sensory receptors restricted to specific
areas of the body
– Taste, smell, hearing, balance, vision
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General (somatic)Sensations Arise from Receptors
Throughout the Body
 Somatic receptors include sensory receptors in skin, muscle,
joints, ligaments
 Nerve impulses from general (somatic) receptors sent to the
primary somatosensory area of parietal lobe of cerebral
cortex
 Somatosensory area processes the information and
perception of sensation happens here
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Figure 12.1
Skin receptors
Hair
Epidermis
Merkel disks:
light touch
Dermis
Meissner’s
corpuscle:
light touch
Ruffini endings:
pressure
Pacinian
corpuscle:
deep pressure
and highfrequency
vibration
Thermolight touch,
and pain
receptors
Receptors
that sense
changing
position
of hairs
Subcutaneous
layer
Modified and encapsulated
nerve endings
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Unencapsulated
dendritic endings
Special Senses: Taste
 Taste buds
– Chemoreceptors bind with dissolved substances
– Most are distributed around edge, front, back of
tongue
 Taste categories
–
–
–
–
Sweet
Salty
Sour
Bitter
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Special Senses: Smell
 Olfactory receptor cells
– Chemoreceptors that bind with odorants
– Detect 1,000 different odorants
Olfactory
bulb
Sense of smell is perceived in
the temporal lobe
of the brain
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Olfactory
epithelium
Figure 12.9
Special Senses- Hearing: receptors detect
sound waves
Outer ear
Pinna
Middle ear
Inner ear
Incus (anvil)
Malleus
(hammer)
Semicircular canals
Vestibulocochlear
nerve ( VIII) Nerve
Vestibular nerve
Cochlear nerve
Vestibule
Oval window
(behind stirrup)
Stapes (stirrup)
Cochlea
Auditory canal
Tympanic membrane
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Round window
Auditory tube
The Outer Ear
 Pinna: visible portion of ear, directs sound waves to
auditory canal
 Auditory canal: directs sound waves to the
tympanic membrane
 Tympanic membrane (ear drum): separates outer
ear from middle ear, vibrates in response to sound
waves and passes along vibrations to the ear bones
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The Middle Ear
 Air-filled space with three small bones
 vibrations of tympanic membrane, passed to these
three bones in sequence
 vibrations passed to inner ear
 Auditory tube (eustachian tube)
– Connects to throat
– Equalizes pressure
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The Inner Ear & hearing
 Bony cochlea (looks like a snail),contains a cochlear
duct- has receptors for hearing which get stimulated
 Sound waves converted to action potentials (nerve
impulses)
 Nerve impulses carried by VIII cranial nerve
(vestibulocochlear nerve) to auditory area in the
temporal lobe of the brain
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Inner Ear also plays an essential role in balance
 Vestibular apparatus
 Helps maintain equilibrium
– Three semicircular canals and vestibule
– Contain receptors for detecting changes in position of
head
 Sensing rotational movement
– Detected by receptors in semicircular canals
 linear movement
– Detected by receptors in vestibule
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Inner Ear
Semicircular canals
for balance
Cochlea (for hearing)
Vestibule
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Eye & Vision
 Vision involves converting light energy to nerve
impulses and transmitting them to the occipital lobe
of the brain
 Eye ball structures
–
–
–
–
–
–
Sclera (white of the eye) and cornea
Iris, choroid
lens
Aqueous humor & vitreous humor
Retina, macula
optic nerve, optic disc
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Figure 12.14
Macula
Fovea
centralis
Optic
nerve
Optic
disk
Sclera
Canal of
Schlemm
Cornea
Aqueous
humor
Iris
Pupil
Lens
Vitreous
humor
Ciliary muscle
Choroid
Retina
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Table 12.4
© 2014 Pearson Education, Inc.
Figure 12.18
Retina- contains photoreceptors: rods
and cones
Retina
Blind spot
Artery
Axons of
ganglion cells
To optic nerve
Ganglion cell layer
Bipolar cell layer
Rod cell and cone cell layer
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Vein
Rod
Cone
Photoreceptor
cells
Pigmented
cell layer
Photoreceptors






Photoreceptors contain photo pigments
Rods- provide vision in dim light
Contain single type of photo pigment
In dim light, vision primarily dependent on rods
Cones- provide color vision and accurate images
Three types of cones, according to three types of
photopigments- red, green, blue
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Disorders
Otitis media
Deafness
Retinal
detachment
Cataract
Glaucoma
Color blindness
© 2014 Pearson Education, Inc.