23: Physiology of Senses Special vs Somatic Senses Olfaction Vision Hearing/Balance

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1 23: Physiology of Senses Special vs Somatic Senses Olfaction Vision Hearing/Balance

2 Estimating the size of a brain subunit: the neocortex of mammals: 1) rhinal fissure placement hedgehog tree shrew monkey 2) cerebral sulcation rhinal fissure

3 Q: High-level cognition without selection (i.e., neocortex) of the forebrain? 3

4 Q: What aspect(s) of bird behavior correlate most strongly with a large telencephalic ( forebrain) fraction of the brain? Burish, Kueh, and Wang

5 Pigeons have a telencephalic fraction of Burish, Kueh, and Wang

6 and can distinguish paintings by Picasso and Monet. Watanabe et al. 1995

7 Brain to body connection Q. How does brain receive and send information?

8 Signal Transduction Q: How do environmental stimuli initiate APs? See text box, p. 338

9 General vs special senses CNS vs PNS * * *

10 general or somatic senses special senses chemical energy taste smell electromagenetic energy thermoreception vision mechanical energy touch hearing and balance 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.

11 Afferent Pathways to/in brain 11

12 Senses: G Protein Coupled Receptors 12

13 Special Sensation The principle of labeled lines Electromagnetic energy Mechanical energy Chemical energy Q: Does an incoming sensory AP reflect the environmental modality that generated it?

14 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 Cranial nerves I II VIII Special senses Northcutt 2002

15 Size comparison of of special sense referral areas often allows identification of dominant sensory modalities in non-mammals. Clark et al Secondary integration in the cerebrum obscures this pattern in mammals.

16 Special senses: Olfaction The signal cascade of olfaction in mammals

17 Shepherd 2006 APs generated by olfactory neurons are integrated in glomeruli of the olfactory bulb.

18 Olfaction is used in near sensing, remote sensing, and to signal territories or sexual receptivity

19 Q: Why do some sharks have hammer heads? Kaijura et al Hammerheads sample a broader sample of water and have increased klinotaxis (but not larger olfactory epithelia) than other sharks

20 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) Humans: 5-10 million Rodents: million Dogs: 200 million Each ON has one gene coding for receptor Rodents: 1000 functional OR genes/1300 total genes Chimps: 500 functional OR genes/1000 total genes Humans: 300 functional OR genes/1000 total genes 20

21 Q: Are our assumptions correct? We re bipedal We don t sniff deeply very often 21

22 Q: How well do humans smell when we try? Porter et al meter long scent trail: 67% success Able to detect direction (left vs right nose) 22

23 23

24 VISION Transduction in vision Accommodation Color vision Ecophysiology of vision Terrestrial vs aquatic vision Diurnal vs nocturnal vision

25 Q: How does the retina generate receptor potentials? 1878 experiments by Wilhelm Kühne

26 cell membrane Rhodopsin is composed of retinal opsin light Rhodopsin retinal + opsin When exposed to light, rhodopsin dissociates changes color ( bleaches )

27 Anatomy and physiology of rods In the dark: Na+ channels are open (cgmp is bound) Na+ entry and K+ exit is countered by the Na + /K + pump dark current In the light: cgmp is enzymatically degraded Na + channels close, and receptor cells hyperpolarize

28 Eye structure Integrative cell layers in the retina light light Axons of ganglion cells exit as the optic nerve, creating a blind spot.

29 Pathways of visual information from the eye

30 Accommodation (focusing light on the retina) requires: 1. materials of different refractive index 2. oblique orientation of light and refractor Refractive indices air 1.0 water 1.3 cornea 1.3 lens of eye 1.4 glass 1.5 diamond 2.4 high refractive index low refractive index

31 Most vertebrate eyes have two refractors - one fixed and one variable The cornea is a fixed refractor The lens is a variable refractor Close and distant vision require different degrees of refraction

32 Color vision Spectral tuning in coho salmon ontogeny Wavelength of maximum absorbance in cones of of different ontogenetic stages / environments. Temple et al rods and cones rods alevins freshwater parr freshwater smolts oceanic

33 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

34 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.

35 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 2. Ampullae of Lorenzini 3. Vestibular and acoustic systems of the inner ear

36 1. Hair cells of the lateral line system : located superficially in frogs.. or in linear canals beneath scales (many fish). Blinded fish can still school if their lateral line system is intact.

37 2. Ampullae of Lorenzini passive electroreception Scyliorhinus (catshark) Kalmijn 1971

38 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 V V V A A

39 Vestibular system Hair cells in the semicircular canals detect angular movements of the head. X Y Hair cells in the maculae of the utricle and sacculus detect linear acceleration. otoliths

40 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

41 Central nervous system referrals of acoustic system action potentials are interpreted as sound. Nerve VIII Q: is ringing in your ears really sound?