23: Physiology of Senses Special vs Somatic Senses Olfaction
Vision
Hearing/Balance
hedgehog tree shrew monkey
rhinal fissure
Estimating the size of a brain subunit: the neocortex of mammals:
1) rhinal fissure placement
2) cerebral sulcation
3
Q: High-level cognition without selection (i.e., neocortex) of the forebrain?
Burish, Kueh, and Wang. 2002.
Q: What aspect(s) of bird behavior correlate most strongly with a large telencephalic (≈ forebrain) fraction of the brain?
Burish, Kueh, and Wang. 2002.
0.552
Pigeons have a telencephalic fraction of 0.552…..
…and can distinguish paintings by Picasso and Monet. Watanabe et al. 1995
Brain to body connection
Q. How does brain receive and send information?
Signal Transduction
Q: How do environmental stimuli initiate APs? See text box, p. 338
CNS vs PNS **
*
General vs special senses
chemical energy electromagenetic
energy
mechanical energy
smell
hearing and balance
visionthermo-reception
General sensation enters the CNS via the sensory component of the general cranial nerves – V, VII, IX, X – as well as spinal nerves from the rest of the body Special sensation enters the CNS via the special sensory nerves – cranial nerves I, II, and VIII. They lack motor components and are located only in the head.
general or somatic senses special senses
touch
taste
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Afferent Pathways to/in brain
12
Senses: G Protein Coupled Receptors
Special Sensation
Electromagnetic energy
Mechanical energy
Chemical energy
The principle of “labeled lines”
Q: Does an incoming sensory AP reflect the environmental modality that generated it?
Northcutt 2002
Cranial nerves I II VIII Special senses
The same basic brain areas that: 1) are stimulated by a particular type of environmental energy 2) transduced in a specialized sense organ 3) reaches the brain via a “dedicated” special sensory cranial nerve
can be recognized in all vertebrate brains
Clark et al. 2001
Size comparison of of special sense referral areas often allows identification of dominant sensory modalities in non-mammals.
Secondary integration in the cerebrum obscures this pattern in mammals.
Special senses: Olfaction
The signal cascade of olfaction in mammals
APs generated by olfactory neurons are integrated in glomeruli of the olfactory bulb.
Shepherd 2006
Olfaction is used in near sensing,
remote sensing, and
to signal territories or sexual receptivity
Q: Why do some sharks have hammer heads?
Kaijura et al. 2005
Hammerheads sample a broader sample of water and have increased “klinotaxis” (but not larger olfactory epithelia) than other sharks
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Humans: 5-10 millionRodents: 15-20 millionDogs: 200 million
Each ON has one gene coding for receptor
Rodents: 1000 functional OR genes/1300 total genesChimps: 500 functional OR genes/1000 total genesHumans: 300 functional OR genes/1000 total genes
Q: How well do humans smell?
1. Relatively small olfactory bulbs (30% volume relative to brain size)3. Fewer functioning olfactory receptors (ORs)2. Fewer olfactory neurons (ONs)
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Q: Are our assumptions correct?
We’re bipedal
We don’t sniff deeply very often
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Porter et al. 2007
10 meter long scent trail: 67% successAble to detect direction (left vs right nose)
Q: How well do humans smell when we try?
23
VISIONTransduction in vision Accommodation
Color visionEcophysiology of vision
Terrestrial vs aquatic vision Diurnal vs nocturnal vision
Q: How does the retina generate receptor potentials?
1878 experiments by Wilhelm Kühne
Rhodopsin retinal + opsin
light
Rhodopsin is composed of
retinal
opsin
cell membrane
When exposed to light, rhodopsin
dissociates
changes color (“bleaches”)
Anatomy and physiology of rods
In the light:
cGMP is enzymatically degraded
Na+ channels close, and receptor cells hyperpolarize
In the dark:
Na+ channels are open(cGMP is bound)
Na+ entry and K+ exit is countered by the Na+/K+ pump
“dark current”
light
Integrative cell layers in the retina
Axons of ganglion cells exit as the optic nerve, creating a “blind spot.”
light
Eye structure
Pathways of visual information from the eye
Refractive indices air 1.0 water 1.3 cornea 1.3 lens of eye 1.4 glass 1.5 diamond 2.4
low refractive indexhigh refractive index
Accommodation (focusing light on the retina) requires:
1. materials of different refractive index
2. oblique orientation of light and refractor
Most vertebrate eyes have two refractors - one fixed and one variable
Close and distant vision require different degrees of refraction
The cornea is a fixed refractor The lens is a variable refractor
“Spectral tuning” in coho salmon ontogeny
Wavelength of maximum absorbance in cones of of different ontogenetic stages / environments. Temple et al. 2008
alevins freshwater
parr freshwater
smolts oceanic
Color vision
rods
rods and cones
Hearing Transduction in hair cells Lateral-line system
Electroreception Vestibular and acoustic systems
Characteristics of sound Inner, middle, and outer ears
Sound for communication and navigation
Transduction in hair cells
1) External structure deflected
2) Deformation opens cation channels
3) Change in cell membrane potential
4) Inhibition or promotion of APs in the integrative cells that synapse with the transducing cell.
Hair cell development and occurrence
Placodes “sink” into the dermis (lateral line and ampullae of Lorenzini) or dermal bone (inner ear) during development.
1. Lateral line
3. Vestibular and acoustic systems of the inner ear
2. Ampullae of Lorenzini
Blinded fish can still school if their lateral line system is intact.
…or in linear canals beneath scales (many fish).
1. Hair cells of the lateral line system :
located superficially in frogs…..
2. Ampullae of Lorenzini – passive electroreception
Scyliorhinus (catshark)
Kalmijn 1971
3. Acoustic (hearing) and Vestibular (balance) systems
located in the INNER ear = a WATER-BASED system based on fluid movement and the deflection of hair cell cilia.
bony fish bird mammal
VV V
AA
Vestibular system
Hair cells in the semicircular canals detect angular movements of the head.
Hair cells in the maculae of the utricle and sacculus detect linear acceleration.
otoliths
“X”“Y”
Acoustic System Mechanical disturbances of the environment, transferred to the endolymph of the cochlea, are detected by hair cells.
Deflection of stereocilia during basilar membrane vibration
Nerve VIII
Central nervous system referrals of acoustic system action potentials are interpreted as sound.
Q: is “ringing in your ears” really sound?