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Lecture 09, 20 Sept 2005Chapter 13

Vertebrate PhysiologyECOL 437 (aka MCB 437, VetSci 437)

University of ArizonaFall 2005

instr: Kevin Boninet.a.: Kristen Potter

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1. Sensory Processes/Systems

Vertebrate Physiology 437

Chapter 13

Exam on Thursday

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Star-Nosed Mole

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-What ions tend to move through open nicotinic acetylcholine receptor channels?

-How does the function of the Na+-K+-2Cl- cotransporter in chloride cells of the Atlantic salmon likely change in saltwater vs. freshwater (you read about this in the Pelis et al. article for lab last week)?

-How does the membrane potential in rods and cones change (depolarize or hyperpolarize) in response to light?

- In general, how does transduction take place in vertebrate hair cells?

Other questions I thought about asking:

Draw a picture that illustrates a hypotonic cell (relative to the interstitial fluid surrounding it).Draw a graph of an action potential. Be sure to label the axes.Define transduction in the context of sensory reception. How do you calculate the emf (electromotive force) acting on an ion species?

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7-27 Randall et al. 2002

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10-24 Silverthorn 2001

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7-5 Randall et al. 2002

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Mechanisms and Molecules

Lots of Evolutionarily Conserved Elements

e.g., 7 transmembranehelices and G-proteinintermediate

e.g., Vision, olfaction, sweet and bitter taste(also muscarinic AChreceptors and many hormone receptors)

7-3 Randall et al. 2002

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Mechanisms and Molecules

Threshold of Detectione.g., 1 photon or hair cell movement of H diam.

Enzymatic Cascade to amplify

Sour (pH; H+) and salt (Na+) move directly – no amplification

To measure quality need many receptors grouped into organ; different ‘tunage’ (e.g, wavelength of light or frequency of sound)

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Enhancing Sensitivity

- Spontaneous basal activity

- Constant rate of APs

- Directionality if ↑ or ↓ AP frequency

7-12 Randall et al. 2002

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Tonic vs. Phasic receptors

5-19 Randall et al. 2002

Slow-adapting

fast-adapting

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-Accommodation

Randall et al. 2002

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Enhancing Sensitivity

- Efferent Control

e.g., stretch receptors in muscle control length so can perceive stretch

- Feedback Inhibition

Auto (helps keep in dynamic range)vs. Lateral…

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Enhancing Receptor Sensitivity

- Lateral Inhibition

e.g., improve touch sensitivity and visual acuity (edges especially)

7-14 Randall et al. 2002

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Vision

- light is focused by lens (and cornea) to create an image on the retina

- refraction by cornea (85%) and by lens (15%)

- alter focal length by altering shape and curvatureof lens

(zonular fibers and ciliary muscle ‘sphincter’)

- binocular convergence (both eyes on same part of retina)

LIGHT INTENSITY

- pupil for variable aperture via iris and radial muscle

FOCUS

7-34 Randall et al. 2002

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7-37 Randall et al. 2002

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10-27 Silverthorn 2001

1810-29 Silverthorn 2001

Out of focus

distant close

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Vision

- sclera white tough outer layer- choroid lots of blood vessels- pigment layer with photoreceptors- fovea where highest acuity and highest # cones

-(visual streak?)

- photoreceptors (rods and cones)-Transduce photons (light) into electrical signal

- rhodopsins (visual pigments)opsin (7-transmembrane lipoprotein)plus

retinal (absorbs photon)

~ANATOMY

TRANSDUCTION

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Vision

Rods and

Cones

Receptor Cells

-Dim light, low resolution

-Bright light, high resolution

7-38 Randall et al. 2002

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10-27 Silverthorn 2001

Rods and

Cones

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Rhodopsins(visual pigments)

-located in stackedlamellae

Membranes hyperpolarize in response to light

Na+ ‘dark current’

When light hits, the Na+ current into the cell is stopped and membrane hyperpolarizes stopping release of NT7-39 Randall et al. 2002

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Bleaching of retinal photoreceptors

Photoreceptors called cones respond to particular wavelengths oflight. Their response involves “bleaching” of their responsive pigment, so that for some seconds they are unable to respond again.

Expectation after 1

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seconds?

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Bleaching of retinal photoreceptors

Photoreceptors called cones respond to particular wavelengths oflight. Their response involves “bleaching” of their responsive pigment, so that for some seconds they are unable to respond again.

Expectation after 1

5

seconds?

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Bleaching of retinal photoreceptors

Photoreceptors called cones respond to particular wavelengths oflight. Their response involves “bleaching” of their responsive pigment, so that for some seconds they are unable to respond again.

Expectation after 1

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seconds?

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Rhodopsin mechanism: cis-trans isomerization of retinal molecule

Changes conformation of opsinmolecule and therefore initiates transduction

activa

ted

7-43 Randall et al. 2002

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Activated retinal changes conformation of opsin molecule (opsin and retinal separate) and initiates transduction

G-protein

amplific

ation

Need to reconstitutethe rhodopsin

(night blindness)7-45 Randall et al. 2002

7-44 Randall et al. 2002

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Rod and Cone details

Action spectrum (where absorb light)

3 (e.g., humans, fish)-5 (e.g,. birds)different photopigments

Different opsins, same retinal

Sensitivity vs. Acuity

Porphyropsins (different retinal) seem better than rhodopsins in freshwater

10-35 Silverthorn 2001

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Physiology Players Theatre

-2 competing casts-Judge(s)

-accuracy-enthusiasm

Actors:1. Photon 4. Transducin 7&8. Ion channel2. Retinal 5. PDE 9. Cation (Na+)3. Opsin 6. cGMP

Act IPhoton enters stage right. Other players assembled within or near membrane. …photo transduction...Dark current reduced as curtain closes.

7-49 Randall et al. 2002

Red vs. Green opsin

30Hill et al. 2004, Fig 13.11

•Horizontal•Bipolar•Amacrine•Ganglion

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Hill et al. 2004, Fig 13.16

32Hill et al. 2004, Fig 13.17

Straight-through

Lateral

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33Hill et al. 2004, Fig 13.18

Straight-through

Lateral

34Hill et al. 2004, Fig 13.21

Receptive Field of Complex Cell in Visual Cortex

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External Chemoreception (Taste and Smell)

-Taste ~ direct contact

-Smell~ distant signal source

-Chemoreception very sensitive

-Bombyx moth antenna example:

Male responds to female pheromone at low [ ] of 1 molecule in 1017 !

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Taste Chemoreception

-Taste

1. Salt2. Sour3. Sweet4. Bitter5. Umami

(“savory” or ”meaty”)

Salty

Sour

Sweet

4-5 qualities:

Usually oral cavitySome fish fins!

Differing Receptor Properties

7-17 Randall et al. 2002

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Taste

- microvilli- basal cells give rise to new receptor cells every 10 days

7-16 Randall et al. 2002

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10-14 Silverthorn 2001

human

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10-15 Silverthorn 2001

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Taste

-Quasi Labelled lines

Facial nerve

Outer tongue

Inner tongue

- multiple receptor types/neuron

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Smell/ Olfaction

-1 Nasal Cavity-turbinates (↑s.a.)

-2 Vomeronasal organ-usually conspecificcommunication

7-19 Randall et al. 2002

7-16 Randall et al. 2002

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Smell/ Olfaction

-Nasal and Vomeronasal:

-Epithelial tissue origin-Cilia or Microvilli covered in mucus

-Receptor proteins with 7-transmembrane helices-Coupled to G-protein cascade

7-21 Randall et al. 2002

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Smell/ Olfaction

- Nasal and Vomeronasal:

-Thousands of receptor proteins-but different for nasal and vomeronasal

-Receptor cells contain axons- Glomeruli in olfactory bulb/accessory olfactory bulb

7-21 Randall et al. 2002