Lecture 07, 13 Sept 2005 Vertebrate Physiology ECOL 437...
Transcript of Lecture 07, 13 Sept 2005 Vertebrate Physiology ECOL 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
6-22 Randall et al. 2002
6-9 Randall et al. 2002
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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
6-37 Randall et al. 2002
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Postsynaptic Neurotransmitter Effects
e.g., fast nicotinic ACh receptors1. Fast and direct
6-32 Randall et al. 2002
6-34 Randall et al. 2002
20Hill et al. 2004, Fig 12.16
Nicotinic ACh receptor
ACh binds alpha subunits
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Hill et al. 2004, Fig 12.7
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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Hill et al. 2004, Fig 12.27
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
7-1 Randall et al. 2002
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Properties of Receptor Cells
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
7-2 Randall et al. 2002
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Properties of Receptor Cells
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
7-7 Randall et al. 2002
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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
7-10 Randall et al. 2002
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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 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
7-34 Randall et al. 2002
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7-37 Randall et al. 2002
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10-27 Silverthorn 2001
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5110-29 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
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
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
5
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. 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.
7-49 Randall et al. 2002
Red vs. Green opsin