17 - Neurons

17 - Neurons - Bi9 lecture 5/24/10 Introduction to Neurons...

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Bi9 lecture 5/24/10 Introduction to Neurons Kai Zinn
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Neurons and epithelial cells Neurons evolved from epithelial cells that had apical and basal compartments. These became, respectively, the axonal (output) and dendritic (input) processes of the neuron. Neurons are highly polarized; spinal motor neurons have axons up to several feet long, and everything needed at the end of the axon must be delivered there by various forms of axonal transport.
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Neuronal geometry This overall pattern (basolateral dendrites, apical axons) can be used to create many different neuronal geometries. These geometries fit the functions of the neurons.
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How does a neuron work? Summarize: electrochemical potential, ion channels How ion channel properties allow creation and propagation of action potentials Transmitter release Coupling of transmitter release to action potentials
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Reception of neurotransmitter by neurons Summarize: neurotransmitter receptors Depolarization in response to neurotransmitter Propagation and summation of depolarization Hyperpolarizing neurotransmitter responses Coupling synaptic input to output
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Versatility of the neuronal plan Summarize: diversity of depolarizing/hyperpolarizing inputs (sensory signals, various neurotransmitters) Coupling to different outputs: small molecule neurotransmitters Modulatory peptide neurotransmitters
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Organization of neuronal circuits Summarize: Neurons can be connected in series and in parallel, in any pattern The simplest circuit (reflex) is a sensory input coupled to a motor output Nervous systems have many interneuronal layers that process sensory input and determine the appropriate motor output
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Sensory circuits 5 main sensory modalities in humans: vision, hearing, touch, smell, taste Each has a circuit that is optimized for the type of input. The first element in each circuit is a specialized sensory neuron that can detect the signal from the environment.
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Vision
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A simplified diagram of retinal circuits
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Photoreceptor morphology
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Characteristics of rods and cones Rods have high sensitivity to light, can do single photon detection, used for night vision. Rods use rhodopsin as their sole photopigment. Rod vision is low acuity and has poor temporal resolution. Rods are located in the peripheral region of the retina. Cones have lower sensitivity, used for high-acuity day (color) vision. Cones have one of three types of photopigment, each most sensitive to a different part of the spectrum. Cones are concentrated in fovea.
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Rhodopsin is a 7- transmembrane protein in rod outer segments with a covalently bound retinal chromophore that absorbs visible light. Light converts 11-
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This note was uploaded on 01/12/2012 for the course BI 9 taught by Professor Aravin during the Spring '10 term at Caltech.

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17 - Neurons - Bi9 lecture 5/24/10 Introduction to Neurons...

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