Lecture 07, 13 Sept 2005 Vertebrate Physiology ECOL 437 ...eebweb.arizona.edu/courses/Ecol437/437Lect7_CH12n13_2005.pdf · Vertebrate Physiology ECOL 437 (aka MCB 437, VetSci 437)

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Lecture 07, 13 Sept 2005Chapters 12 and 13

Vertebrate PhysiologyECOL 437 (aka MCB 437, VetSci 437)

University of ArizonaFall 2005

instr: Kevin Boninet.a.: Kristen Potter

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2. Sensory Processes/Systems

Vertebrate Physiology 437

Chapter 13

Chapter 12

1. Synapses,Neurotransmitters

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Hill et al. 2004, Fig. 11.17

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Hill et al. 2004, Fig. 11.18

Voltage-gated channel superfamily

4 identical subunits

4 different domains

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5Voltage-gated Channels

Proposed Evolution

Hill et al. 2004, pg. 301

6Silverthorn 2001. 2nd ed. Human Physiology. Prentice Hall

Frequency and number!

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SYNAPSES

-communication between neuronsor between neuron and effector organ

1-electrical (rapid)2-chemical(‘fast’ or slow)

1. De- or hyper-polarize

2. Change # ion channels in membrane

3. Alter rate of ion channel activity

4. Modify sensitivity to activation signals

In postsynaptic neuron:

6-22 Randall et al. 2002

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Electrical Synapse (rapid)- direct ionic coupling via gap junctions-examples in retina, CNS, smooth muscle, cardiac muscle, etc.

gap junctions



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Agonist (mimics)(e.g., heroin mimics natural opiates)

vs.

Antagonist (blocks)(e.g., curare blocks ACh reception)

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Hill et al. 2004, Fig 12.1

Chemical Electrical

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Chemical (neurotransmitter)20-30nm apart

Electrical(gap junction, connexons)3nm apart

Hill et al. 2004, Fig 12.2,3

1 amplify2 excitatory or inhibitory3 ~one-way4 modifiable

12Hill et al. 2004, Fig 12.4

ionotropic metabotropic

Chemicalsynapses

Role of Ca++

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Silverthorn 2001. 2nd ed. Human Physiology. Prentice Hall SlowFast

14Hill et al. 2004

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Postsynaptic Neurotransmitter Effects

1. Fast and direct

2. Slow and indirect

e.g., ACh receptors

1. Nicotinic (muscles, autonomic/sympathetic NS)

2. Muscarinic (parasympathetic, indirect)

NT role depends primarily on receptor characteristics on postsynaptic neuron

16Hill et al. 2004, Fig 12.18

•Norepi•G-protein•cAMP 2nd messenger•Phosphorylation (kinases)•(amplification)

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17Hill et al. 2004, Fig 12.19

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Postsynaptic Neurotransmitter

Effects

e.g., indirect, metabotropicmuscarinic AChreceptors acting to reduce heart cell excitability


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Postsynaptic Neurotransmitter Effects

e.g., fast nicotinic ACh receptors1. Fast and direct



20Hill et al. 2004, Fig 12.16

Nicotinic ACh receptor

ACh binds alpha subunits

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Neuromuscular Junction

Quantal packets(~5,000 Ach/vesicle)

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Neurotransmitters:

1. small-molecule neurotransmitters(often made in axon terminals)

2. neuroactive peptides(often made in soma and shipped down axon)

Nematodes use a lot of the same neurotransmitters.

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(IPSP)

(IPSP)

(abundant and widespread)

(1%)

(10%)

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•Change synaptic efficacy•Alter rate of NT production and release

•Learning and Memory

•Facilitation vs. antifacilitation/depression

•Calcium-dependent-Research on-going

Synaptic Plasticity

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•Hippocampus

•Learning and Memory

•“Neurons that fire together wire together”

•NMDA glutamate receptors

Longterm Potentation

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Doogie Mice?

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Vertebrate Physiology 437

2. Sensory Processes/SystemsChapter 13

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Sensing the Environment

Sensory Reception-Environment-Within body

Integrated and Processed by NS

Sensory Receptors send signals to brain so perceive sensations

Sensory Receptor cells 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


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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)

2- Signal often amplified

3- Ion channels opened directly or indirectly

4- Current flows across membrane (often Na+)

5-Vm changes (akareceptor potential changes)

6- AP sent or NTreleased causing AP

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Mechanisms and Molecules

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 frequency

Detectable 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)

38Hill et al. 2004, Fig 13.5

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Sensory Adaptation; Pacinian Corpuscle - Touch Example

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


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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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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


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Tonic vs. Phasic receptors


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)


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Vision

- light is focused by cornea to create animage 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


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10-27 Silverthorn 2001

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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


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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

5

seconds?

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Expectation after 1

5

seconds?

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Expectation after 1

5

seconds?

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Rhodopsin mechanism: cis-trans isomerization of retinal molecule

Changes conformation of opsinmolecule and therefore initiates transduction

activa

ted


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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


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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


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Physiology Players Theatre

-2 competing casts-Judge(s)

-accuracy-enthusiasm

Actors:1. Photon 4. Transducin 7. Ion channel2. Retinal 5. PDE 8. 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.


Red vs. Green opsin

Documents

Lecture 07, 13 Sept 2005 Vertebrate Physiology ECOL 437 ...eebweb.arizona.edu/courses/Ecol437/437Lect7_CH12n13_2005.pdf · Vertebrate Physiology ECOL 437 (aka MCB 437, VetSci 437)