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Draft Figure Dendrogram Proposal.Ai ] The NEURONS and NEURAL SYSTEM: a 21st CENTURY PARADIGM This material is excerpted from the full β-version of the text. The final printed version will be more concise due to further editing and economical constraints. A Table of Contents and an index are located at the end of this paper. A few citations have yet to be defined and are indicated by “xxx.” James T. Fulton Neural Concepts 1 (949) 759-0630 [email protected] December 25, 2011 Copyright 2011 James T. Fulton 1 2 Neurons & the Nervous System [ phase out SSC’s in favor of OR’s or GR’s. [ edit carbonyl (C=O) versus carboxyl (COOH) usage. screwed up in places ] [ sulfide in america; sulphide in britain ] [ establish a clear demarcation between using H-best and C-best ] [ be sure Section 8.2 and 8.3 touch on anatomical computation to support chapter 0. 8 Stage 1 & 2, Signal Generating & Processing Neurons1 “Science is made up with facts as a house is made from stones. But a collection of facts is no more a science than a pile of stones is a house.” —Poincare' , Hypotheses in Physics (1952) “In order to understand any part of nature, one must have both experimental data and a theory for interpreting the data and predicting new data.” – Shepherd, Outline of a Theory of Olfaction, 2005 8.1 Introduction The sensory neurons serve disparate purposes but exhibit a remarkable uniformity at the morphological, cytological and electrophysiological level. The visual and auditory modalities are focused on sensing of the distant external environment. The olfactory and gustatory modalities are focused on the near and even nearer external environments. The remainder of the external sensory modalities typically (with the exception of radiant heat) involve physical contact with the source of the stimulation. Adopting Poincare’s above thesis, the goal of this chapter is to show how our collection of facts describe an architecturally identifiable structure of complexity and beauty. The signal processing (stage 2) neurons immediately behind the sensory neurons vary more widely than do the sensory neurons, primarily in whether they are present at all. The retina and the olfactory modalities employ significant signal processing immediately adjacent to their sensory neurons. The auditory and gustatory modalities on the contrary, avoid stage2 signal processing adjacent to the sensory neurons and employ stage 3 signal projection channels between the sensory neurons and more distant signal processing elements that may be considered part of the divergent stage 2 signal processing or or of the convergent stage 4 signal manipulation elements of the modality architecture. When discussing the sensory neurons in a consistent lexical context, there is a problem with the use of the terms cilia and microvilli. Elsaesser & Paysan wrote an elaborate paper addressing this duality without defining their terms and coming to any conclusion about the correct terminology2. They did provide over one hundred citations. The term cilium is from the Latin for eyelash and generally is considered a rigid structure. Unfortunately, villium also comes from the Latin and colloquially refers to curly hair. These terms are often used interchangeably in the literature. In this work, the goal is to use cilium and cilia when referring to structures emanating from the dendritic structure of a sensory neuron that are “rigid” or must maintain a column like character. The rigid structures are typically filled with rigid liquid crystalline proteins participating in a piezoelectric transduction process. The photoreceptors maintain a column-like structure for optimal optical 1December 25, 2011 2Elsaesser, R. & Paysan, J. (2007) The sense of smell, its signaling pathways, and the dichotomy of cilia and microvilli in olfactory sensory cells BMC Neurosci vol 8(Suppl 3):S1 Signal Generation & Processing 8- 3 efficiency. Villium and villi will be used when referring to structures emanating from the dendritic structure of a sensory neuron that are not rigid and need not maintain a column-like structure. These structures are typically filled with a fluid like material and reticuli that are flexible in character. At the cytological level, the protein filled cilia transfer their signal to a first amplification stage within the soma of the neuron whereas, the microvilli of sensory neurons have been modified to create an active electrolytic device between their outer lemma and their inner reticulum. In this work, the visual, olfactory and gustatory sensory neurons exhibit microvilli; the auditory and many of the somatosensory sensory neurons exhibit cilia that are sensitive to dynamic loadings and motions. All of the sensory modalities appear to employ the same type of signaling and present a nearly identical interface to the saliency map within the CNS. It will be shown that the signaling architecture, methodologies and techniques within the different sensory modalities are essentially identical. While the visual and auditory modalities are very well understood and interpreted (especially employing the Electrolytic Theory of the Neuron) the modalities employing chemo– thermo– and mechanico–receptors are less well understood. The literature of these modalities at the electrophysiological level is relatively thin. As a result, this work will hypothesize in these areas based on the similarity to the more studied modalities. Only additional laboratory work, based on these hypotheses will allow confirmation or refutation of these hypotheses. One area supporting the theory and the comparability of the sensory modalities is the adaptation characteristic 2.1 Introduction The signal generating neurons have the basic task of converting some source of energy into an electrical signal that can be processed and interpreted by the remainder of the neural system prior to taking some responsive action (when appropriate). An initial list of the sensory neurons generally includes those associated with seeing, hearing, touch, taste and smell. Less frequently, the sensory neurons associated with orientation are added to this list. Each of these broad designations can usually be subdivided into several additional descriptors. As an example, the photoreceptors of sight (the visual system) are further divided into spectrally sensitive types. The neurons associated with touch are frequently subdivided into those sensing relative motion and those sensing temperature. These subdivisions of a given modality are sometimes described as qualities within a modality. Shepherd has provided a table of sensory modalities, that he credits to Ganong (1985), that shows some of these groupings3. His listing speaks of the form of incident energy when he generally means the source of the incident energy. The listing by Shepherd only includes a mixture of generic names for the types of sensory cells. Feducci, editing Torrey’s 5th Edition, provides a brief introduction to the evolution of the sensory neurons4. Shepherd also provided an interpretation (pg 208) of a figure by Bodian (1967) that will be expanded upon here. The caricatures for the modalities other than vision do not allow for signal processing within the neural system supporting that modality. However, it is readily shown that most individual sensory neurons are not connected to the brain by a unique and exclusive neural circuit. Stage 2 signal processing is an effective method of economizing on neural circuitry and is found in nearly every sensing modality. This work will postulate that the excitation energy is quantum-mechanical in form for most, if not all, of the sensory modalities. This prediction is made based on the impulse response reported for a range of these modalities. The result of the postulate is confirmation of the “law of specific nerve energies” attributed to J. Muller in the 1830's. However, the modern interpretation of that law is quite different. The next section will calculate the minimum energy required to excite any sensory 3Shepherd, G. (1988) Neurobiology, 2nd ed. NY: Oxford University Press pg 207 4Feducci, xxx Torrey’s 5th Ed. pg 449 4 Neurons & the Nervous System neuron and create a free electron within the signaling system. Later sections will show that this minimum energy is a critical design parameter within the overall neural system. It defines the technology available to support different sensing modalities. As a guide, these technologies involve the photoelectric, piezoelectric and electrostenolytic effects. These effects are all quantum- mechanical in nature. Both the piezoelectric and electrostenolytic effects appear to be used in multiple implementations that show striking morphological differences. The conversion of the input stimulus to a free electron is known as transduction. It does not rely upon the release or transport of any protein within the neural system. All signaling is performed by the transport of fundamental electrical charges (or the propagation of energy resulting from the motion of such fundamental charges). The last caveat will be discussed in Section xxx where the mode of propagation of action potentials will be addressed. While much of the literature uses the term conductance change to describe a mechanism that either generates or supports the transmission of a neural signal, this work does not. Simple changes in the conductance of an electrical element, other than those associated with the response function of diodes and the Activa, do not occur within the neural system. The changes in conductance associated with diodes (a fixed nonlinear current-voltage
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