437Lect9b SensoryProcesses-CH13 sp2009

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9th Lecture (9b)Wed 04 Feb 2009

Vertebrate PhysiologyECOL 437 (MCB/VetSci 437)Univ. of Arizona, spring 2009

Kevin Bonine & Kevin Oh

Sensory ProcessingChapter 13

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Sensory ProcessesSensory SystemsCh13 in your text

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Sensing the Environment

Sensory Reception-Environment-Within body

Integrated and Processed by NS

Sensory Receptorssend signals to brain so perceive sensations

Sensory Receptorcells often organized into organs 7-1 Randall et al. 2002

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Properties of Receptor Cells

Sensory Modality

Qualities within each modality

Modalities include:vision, hearing, touch, taste, smell, chemical,thermal, proprioceptors

e.g., Red or yellow;High or low-pitched

7-1 Randall et al. 2002

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etc.

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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

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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

- Efferent Controle.g., stretch receptors in muscle

control length so can perceive stretch

- Feedback InhibitionAuto (helps keep in dynamic range)vs. Lateral…

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Receptor Cells- Specialized- Selective for energy type and modality

-either is a neuron or-Synapses immediately on a neuron

(1° afferent neuron to CNS)

Stimulus modifies conformation of receptor


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Transduction=Stimulus energy converted to nerve impulse

1- Proteins respond to membrane distortion

ExampleMechanoreceptors (touch)

5- Signal often amplified

2- Ion channels opened directly or indirectly

3- Current flows across membrane (often Na+)

4-Vm changes (aka receptor potential changes)

6- AP sent or NTreleased causing AP

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Sensory Adaptation

- orders of magnitude different stimulus strength

Type of stimulus received depends on where in CNS (~brain) AP arrives (LABELED LINES).

- often controlled via Ca++ availability- local control or feedback from CNS

Rub eyes and see light!

Intensity signalled by frequency of APs, but…

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Stimulus Intensity and Dynamic RangeFrom lowest threshold, to upper limit imposed by refractory period:

Note log axis


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Dynamic Range

Shifting range of appropriate AP frequencyDetectable light intensity varies over 9 orders magnitude

Detectable sound intensity varies over 12 orders magnitude

Range Fractionation- Function of sensory adaptation- Also recruit receptors with

different ‘tunage’ or sensitivity(e.g., rods and cones in eye)

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Sensory Adaptation Possibilities:

1. Receptor cell mechanical properties may filter

2. Receptor cells may be depleted (e.g., visual pigments; need to be regenerated)

3. Enzyme cascade (during amplification) may be inhibited by (intermediate) product

4. Electrical properties change b/c ↑ [Ca++]

5. Accommodation of spike initiating zone

6. Sensory adaptation in downstream neurons (CNS)

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-Accommodation

Randall et al. 2002

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Enhancing Sensitivity

- Spontaneous basal activity- Constant rate of APs

- Directionality if ↑ or ↓ AP frequency


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Tonic vs. Phasic receptors


Slow-adapting

fast-adapting

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Hill et al. 2004, Fig 13.5

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Sensory AdaptationPacinian Corpuscle - Touch Example

Movement of Oil between layers is what triggers APsSignal changes in pressure, not steady pressure


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Star-Nosed Mole

(↑ # neurons, ↑ subtlety)

(receptor field size?)

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Mechanoreception

- Several Types:

1 Undifferentiated nerve endings in connective tissue2 More specialized

e.g., Pacinian Corpusclee.g., Muscle stretch receptors

3 hairlike sensory receptors

Activated by stretch or distortion of plasma membrane

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Whiskering

Are these the hair cells we are talking about?

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Mechanoreception

- Hair Cells in cupulaone Kinocilium (or none)many stereociliae.g., -lateral line system in

fish and amphibians(motion/electricity)

-hearing and equilibrium



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Hearing and Equilibrium

Equilibrium:2 chambersSacculusUtriculus w/ 3 semicircular canals in

three perpendicular planes

These three planes can detect movement in any direction as endolymph moves and cilia are bent

Sacculus and Utriculusalso contain patches of hair cells that detectposition relative to gravity via otoliths


- Both are functions of the ear

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10-24 Silverthorn 2001

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Hearing (in a nutshell…1)

- external ear funnels sound

- sound is oscillating air pressure

- funneled to tympanic membrane (eardrum)

- auditory ossicles transfer sound across air-fluidboundary to oval window (another membrane)

- [auditory ossicles are malleus, incus, stapes]

- tympanum area 19x oval window area= amplification

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Hearing (in a nutshell…2)

- cochlea is fluid filled chamber on other side of oval window and it contains hair cells

- hair cells in cochlea bathed in endolymph (high in K+)

- when cilia bent, ion channels for K+ open and cell depolarizes, causing transduction

- different hair cells (and location in cochlea) for different frequencies of sound

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Basilar membrane

Mammalian Cochlea

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Barn Owl

Konishi and Knudsen (1977) identified an area in the midbrain containing cells called space-specific neurons that fired only when sounds were presented in a particular location. Astonishingly, the cells were organized in a precise topographic array, similar to maps of cells in the visual cortex of the brain. Aggregates of space-specific neurons, corresponding to the precise vertical and horizontal coordinates of the speaker, fired when a tone was played at that location.

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Type of sensation received depends on where in CNS (~brain) AP arrives

(LABELED LINES).

Rub eyes and see light!

Synesthesia:e.g., smell colors

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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)


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etc.

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437Lect9b SensoryProcesses-CH13 sp2009