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Biology 220
Anatomy & Physiology I
Unit X
SPECIAL SENSES
Chapter 16
pp. 558 - 607
E. Gorski/ E. Lathrop-Davis/ S. Kabrhel
Special Senses
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Vision
Hearing
Equilibrium
Taste
Smell
Vision
1. Location
– receptors found in retina of eye
(70% of all sensory receptors in
the body)
2. Structure/receptors
– rods - respond to light intensity
(shades of gray)
– cones - respond to light of
specific wavelengths (color
vision)
° Visible light = 400 - 700 nm
Fig. 16.13, p. 574
Vision
3. Nerve pathway
– optic nerve carries impulse from eye (enters
cranium through optic foramen)
– fibers from medial portion of retina cross over at
optic chiasma
– fibers continue toward thalamus via optic tracts
(some fibers to superior colliculi - visual reflex)
4. Relays (synapses)
– fibers synapse in thalamus (lateral geniculate
bodies) and are relayed to primary visual cortex
Vision
5. Final destinations
– primary visual cortex on posterior medial
occipital lobe
– visual association area allows recognition
of shapes, objects, letters, etc.
Visual Fields of the Eyes
Fig. 16.12, p. 584
Visual Fields Defects
Right eye Left eye
1.
1
2
2.
3
3.
4.
4
Hearing
1. Location
– receptors found in inner ear
2. Structure/receptors
– organ of Corti
° found in cochlea of inner ear
° contains “hairs” that respond to
vibration
3. Nerve pathway
– cochlear branch of vestibulocochlear
nerve carries impulses from inner
ear; enters cranial cavity through
internal auditory meatus
Fig. 16.24,p. 587; Fig.16.27, p. 590
Hearing
4. Synapses
– fibers synapse in medulla
oblongata (twice)
– fibers from medulla synapse
in inferior colliculus
(midbrain)
– fibers from inferior colliculus
synapse in thalamus and are
relayed to primary auditory
cortex
5. Final destination
– primary auditory cortex (on
temporal lobe)
Fig. 16.33, p. 595
Hearing
Transmission of sound:
• airborne sound enters external auditory canal --> strikes
tympanic membrane causing vibration
• vibration amplified by ossicles (malleus, incus, stapes) in
middle ear and transferred to oval window
• perilymph in inner ear moves basilar membrane -->
endolymph in cochlear duct disturbed
• hair cells of Organ of Corti pushed up against the
tectorial membrane and stimulated --> send impulses
through cochlear branch of vestibulocochlear nerve
• pressure relieved when pressure waves enter scala
vestibuli, move through and are relieved at round
window
Cochlea/Resonance of Membrane
Amplitude -intensity (energy)
• healthy adult can pick up sounds between 1-120 dB
– 130dB - pain
Frequency - number of waves/time
• range of human 20-20,000 Hz
• most sensitive to 1500-4000 Hz
– low frequency sounds to apex
– high frequency sounds to base
Fig. 16.31, p. 594
Equilibrium
1. Location - inner ear
2. Structure/receptors
– receptors in utricle and
saccule for static equilibrium
(head position, linear
acceleration - changes in
speed and direction)
– receptors in semicircular
canals for dynamic
equilibrium (rotatory
movements)
Fig. 16.34, p. 597
Equilibrium
3. Nerve pathways
– vestibular branch of
vestibulocochlear nerve
carries impulse to brainstem
(medulla)
4. Synapses - complex pathways
5. Final destinations
– cerebellum
– brain stem
Taste (Gustation)
1.
2.
Location - oral cavity (mostly in papillae of tongue)
Structures/receptors - chemoreceptors (respond to
chemicals dissolved in saliva)
3. Nerve pathways from taste buds in:
• mouth/tongue: facial (anterior 2/3 of tongue) and
glossopharyngeal (posterior 1/3)
• lower pharynx and epiglottis: vagus
Fig. 16.1, p. 560
Taste
4. Synapses
– facial, glossopharyngeal and vagus nerves carry
impulses to medulla
– some fibers from medulla synapse with
parasympathetic fibers to initiate reflexes for saliva and
gastric juice secretion (also gagging or vomiting)
– other fibers from medulla carry impulses to thalamus
– fibers from thalamus carry impulses to gustatory area
(parietal lobe), hypothalamus and cerebral limbic
system
Taste
5. Final destinations:
– gustatory area (parietal lobe), hypothalamus and
cerebral limbic system
• NOTE:
– receptors for taste and smell complement each other
and respond to many of the same stimuli
– most (~80%) of what we call taste is really smell
– mouth also contains: thermoreceptors,
mechanoreceptors, nociceptors (carried by trigeminal
nerve)
Smell (Olfaction)
1. Location
– nasal mucosa in roof of
nasal cavity
2. Structure/receptors
– olfactory receptor cells
in nasal mucosa (nerve I)
– olfactory cilia (increase
receptive surface area)
• NOTE: these neurons
(olfactory receptor cells)
reproduce
Fig. 16.2, p. 562
Smell
3. Nerve
– olfactory nerves enter cranium through olfactory
foramina of cribriform plate (of the ethmoid bone)
4. Synapses
– olfactory nerves synapse with neurons in olfactory bulb
– fibers from olfactory bulb run through olfactory tracts
– olfactory tracts carry impulses to thalamus or to other
parts of the limbic system
– fibers from thalamus eventually reach olfactory cortex of
temporal lobe
Smell
5. Final destinations
– limbic system (for emotional response to smell)
– olfactory cortex of temporal lobe (for smell
recognition)