Download Chapter 17 - Martini

Special Senses
Chapter 17
The Special Senses and their modalities
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Olfaction (Smell) - chemical
Taste (Gustation) – chemical
Vision (Sight) – photo
Hearing – mechanical
Equilibrium - mechanical
Olfaction
• 10 – 100 million receptors on the roof of the
nasal cavity. (about 5 square cm)
• Three types of cells:
– Olfactory receptors (bipolar neurons)
– Supporting cells (pseudostratified columnar)
– Basal stem cells (mitotic cells producing new
receptors)
• Just about the only nuerons that replace
themselves in mature humans!
• Olfactory (Bowman’s) glands – secrete mucus
Olfactory receptors
Olfactory epithelium
Olfactory physiology
• 7 primary odors
– Floral
– Musky
– Camphorous
– Pepperminty
– Etheraeal
– Pungent
– Putrid
• About 10,000 different
odors are recognizable
• Much depends upon
experience and
synthetic processing in
the brain
• Dogs have about
30,000 times the acuity
for smell
Olfactory pathway
Gustation
• About 80% of taste is dependent upon smell
• 5 primary tastes
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Sweet
Salty
Sour
Bitter
Umami (savory)
• Lowest threshold is for bitter, highest is for
sweet
• Lowest adaptation is for bitter, highest for sweet
Taste & the
tongue
Four types of Papillae
• Circumvallate – at the back of the tongue
• Fungiform – all over
• Foliate – lateral margins of tongue, taste
buds gone after childhood
• Filiform – all over tongue but not for taste,
for friction
Different
receptors
respond to
different stimuli
Neural pathways
• Anterior tongue innervated by the facial nerve
(CN VII)
• Posterior tongue innervated by the
glossopharyngeal (CN IX)
• Lead to the solitary nucleus in the medulla and
then to the thalamus and gustatory cortex
(perception) or limbic system via the
hypothalamus
Vision
• Accessory structures
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Eyelids (palpabrae)
Eyelashes
Eyebrows
Lacrimal apparatus
Extrinsic eye muscles
• Superior & inferior rectus
• Lateral & medial rectus
• Superior & inferior obliques
The eye
Fig. 16.05
The Eyeball
The eyeball
The Tunics of the eye
The iris
Fig. 16.08
The retina
Fig. 16.09
Photoreceptors
Circulation of aqueous humor
The Optics of vision:
Refraction
Fig. 16.12
Common vision
defects and their
correction
Rods &
Cones
~ 125 million
rods
~ 6 million
cones
Physiology of
photoreception
Physiology of photoreception
Fig. 16.15
• Integration of
information from
red, green, and
blue cones
Color Sensitivity
Figure 17–16
Color Blindness
• Inability to detect certain
colors
• Normal color vision
– 16% blue
– 10% green
– 74% red
• Red-green color-blindness
– Missing red cones leads to an
inability to distinguish re from
green.
– Can be variable
– Most common form is Xlinked, leading to more male
than females
Figure 17–17
Visual peception and neural
pathways
Off-Center
Neurons
• Inhibited by light in central
zone
• Stimulated by illumination
at edges
• Aids in “Acuity”
• Cones are for precise vision
• Rods are for contrast & low
light and peripheral vision
Figure 17–18
Visual pathways
Contralateral & ipsilateral paths
The Ear
Figure 17–20
Middle Ear
Figure 17–21
Inner Ear
Figure 17–22
Anterior,
Posterior, and
Lateral
Semicircular
Ducts
Figure 17–23
Fig. 16.23
Utricle and
Saccule
Figure 17–23
Otolith
• Gelatinous matrix and statoconia
Figure 17–24
• Instructions descend in vestibulospinal tracts of
spinal cord
Peripheral Muscle Tone, Head, and Neck Movements
The Cochlea
Figure 17–26
Fig. 16.20d
Fig. 16.21
Sound
• Consists of waves of pressure through air or
water
Pressure
Wave
Figure 17–28
Pressure Wave
• Consists of region where air molecules are
crowded together
• Adjacent zone where molecules are farther
apart
• Sine waves:
– S-shaped curves
Wavelength
• Distance between 2 adjacent wave troughs
Frequency
• Number of waves that pass fixed reference
point at given time
• Physicists use term cycles instead of waves
Hertz (Hz)
• Number of cycles per second (cps)
Pitch
• Our sensory response to frequency
Amplitude
Figure 17–28
Amplitude
• Intensity of sound wave
• Sound energy is reported in decibels
The Power of
Sounds
Table 17–1
Hearing Process
• 6 basic steps
Figure 17–29
Frequency Discrimination
Figure 17–30
Hearing Range
• From softest to loudest represents
trillionfold increase in power
• Never use full potential
• Young children have greatest range
Aging Effects
• Tympanic membrane gets less flexible
• Articulations between ossicles stiffen
• Round window may begin to ossify
Deafness
• Conduction deafness – something hampers
sound conduction to the fluids of the inner
ear (e.g., impacted earwax, perforated
eardrum, osteosclerosis of the ossicles)
• Sensorineural deafness – results from
damage to the neural structures at any point
from the cochlear hair cells to the auditory
cortical cells
Other issues
• Tinnitus – ringing or clicking sound in the
ears in the absence of auditory stimuli
• Meniere’s syndrome – labyrinth disorder
that affects the cochlea and the semicircular
canals, causing vertigo, nausea, and
vomiting
Is that all?
Yes, we are finally through the
nervous system!