Nov 16, Neuroanatomy: an Illustrated Colour Text, 5e Alan R. Crossman PhD Author: Alan R. Crossman PhD DSc, David Neary MD. Paperity: the 1st multidisciplinary aggregator of Open Access journals & papers. Free fulltext PDF articles from hundreds of disciplines, all in one place. Any information contained in this pdf file is automatically generated from digital .. "Neuroanatomy, an illustrated colour text" A.R. Crossman and D. Neary.
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Neuroanatomy: An illustrated colour text. Ruth E. M. Bowden Professor by A.R. Crossman and D. Neary. pp. Edinburgh: Churchill Livingstone, Neuroanatomy: an Illustrated Colour Text. 5th Edition. Authors: Alan Crossman David Neary. Paperback ISBN: eBook ISBN: Veja grátis o arquivo Neuroanatomy An Illustrated Colour Text Crossman 5th Ed [ PDF] enviado para a disciplina de Neuroanatomia e Neurofisiologia 1.
The toluidine blue counterstaining reveals the nuclei of surrounding glial cells. By permission from Young, B. Churchill Livingstone, Edinburgh. Some axons are almost filled by neurofilaments. Dendrites usually have more microtubules than axons.
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Why not share! Embed Size px. Start on. Show related SlideShares at end. WordPress Shortcode. AmieHarrell53 Follow. Published in: Full Name Comment goes here. Are you sure you want to Yes No. Be the first to like this. No Downloads. Fast anterograde transport carries vesicles, including synaptic vesicles containing neurotransmitters, from the soma to the axon terminals.
Retrograde axonal transport accounts for the flow of mitochondria, endosomes and lysosomal autophagic vacuoles from the axon terminals into the soma. Retrograde transport mediates the movement of neurotrophic viruses e. They are described separately in Chapter Synapses can occur between almost any surface regions of the participating neurones. The most common type occurs between an axon and either a dendrite or a soma, when the axon is expanded as a small bulb or bouton see Figs.
This may be a terminal of an axonal branch terminal bouton or one of a row of bead-like endings, with the axon making contact at several points and often with more than one neurone bouton de passage.
Boutons may synapse with dendrites, including dendritic spines or the flat surface of a dendritic shaft; a soma, usually on its flat surface, but occasionally on spines; the axon hillock and the terminal boutons of other axons. The connection is classified according to the direction of transmission, with the incoming terminal region named first. Most common are axodendritic synapses, although axosomatic connections are frequent.
All other possible combinations are found, but they are less common: axoaxonic, dendroaxonic, dendrodendritic, somatodendritic and somatosomatic. Axodendritic and axosomatic synapses occur in all regions of the CNS and in autonomic ganglia, including those of the ENS. The other types appear to be restricted to regions of complex interaction between larger sensory neurones and microneurones, such as in the thalamus.
Ultrastructurally, synaptic vesicles may be internally clear or dense and of different sizes loosely categorized as small or large and shape round, flat or pleomorphic, i. The submembranous densities may be thicker on the postsynaptic than on the presynaptic side asymmetric synapses or equivalent in thickness symmetric synapses. Synaptic ribbons are found at sites of neurotransmission in the retina and inner ear.
They have a distinctive morphology, in that the synaptic vesicles are grouped around a ribbon- or rod-like density oriented perpendicular to the cell membrane see Fig.
Synaptic boutons make obvious close contacts with postsynaptic structures, but many other terminals lack specialized contact zones.
Areas of transmitter release occur in the varicosities of unmyelinated axons, where the effects are sometimes diffuse e. In some instances, such axons may ramify widely throughout extensive areas of the brain and affect the behaviour of very large populations of neurones e.
Pathological degeneration of these pathways can therefore cause widespread disturbances in neural function. Neurones express a variety of neurotransmitters, either as one class of neurotransmitter per cell or, more often, as several.
Good correlations exist between some types of transmitters and specialized structural features of synapses. In general, asymmetric synapses with relatively small spherical vesicles are associated with acetylcholine ACh , glutamate, serotonin 5-hydroxytryptamine, or 5-HT and some amines; those with dense-core vesicles include many peptidergic synapses and other amines e.
Synapses Transmission of impulses across specialized junctions synapses between two neurones is largely chemical. It depends on the release of neurotransmitters from the presynaptic side; this causes a change in the electrical state of the postsynaptic neuronal membrane, resulting in either its depolarization or its hyperpolarization.
The patterns of axonal termination vary considerably. A single axon may synapse with one neurone, such as climbing fibres ending on cerebellar Purkinje neurones; more often, it synapses with many, such as cerebellar parallel fibres, which provide an extreme example of this phenomenon. In synaptic glomeruli e. Electrical synapses direct communication via gap junctions are rare in the human CNS and are confined largely to groups of neurones with tightly coupled activity, such as the inspiratory centre in the medulla.
They are not discussed further here. Classification of Chemical Synapses Chemical synapses have an asymmetric structural organization Figs 2. Typical chemical synapses share a number of important features. They all display an area of presynaptic membrane apposed to a corresponding postsynaptic membrane; the two are separated by a narrow 20 to 30 nm gap, the synaptic cleft. Synaptic vesicles containing neurotransmitters lie on the presynaptic side, clustered near an area of dense material on the cytoplasmic aspect of the presynaptic membrane.
A corresponding region of submembrane density is present on the postsynaptic side. Together these define the active zone, the area of the synapse where neurotransmission takes place. Chemical synapses can be classified according to a number of different parameters, including the neuronal regions forming the synapse, their ultrastructural characteristics, the chemical nature of their neurotransmitters and their effects on the electrical state of the postsynaptic neurone.
The classification described here is limited to associations between neurones. Neuromuscular junctions share many although not all of these parameters A B Fig. The directions of transmission are shown by the arrows.
B, Synaptic cartridge with a group of synapses surrounding a dendritic segment. Each complex unit is enclosed within a glial capsule green.
A, Pale cross-section of a dendrite on which two synaptic boutons end. The upper bouton contains round vesicles, and the lower bouton contains flattened vesicles of the small type. A number of pre- and postsynaptic thickenings mark the specialized zones of contact.
B, Type I synapse containing both small, round, clear vesicles and large, dense-core vesicles of the neurosecretory type. C, Large terminal bouton of an optic nerve afferent fibre, making contact with a number of postsynaptic processes, in the dorsal lateral geniculate nucleus of a rat.
D, Reciprocal synapses between two neuronal processes in the olfactory bulb. A and C, Courtesy of A. The neurosecretory endings found in various parts of the brain and in neuroendocrine glands have many features in common with presynaptic boutons. They all contain peptides or glycoproteins within dense-core vesicles of characteristic size and appearance. These are often ellipsoidal or irregular in shape and relatively large; for example, oxytocin and vasopressin vesicles in the neurohypophysis may be up to nm across.
Synapses may cause depolarization or hyperpolarization of the postsynaptic membrane, depending on the neurotransmitter released and the classes of receptor molecule in the postsynaptic membrane.
Depolarization of the postsynaptic membrane results in excitation of the postsynaptic neurone, whereas hyperpolarization has the effect of transiently inhibiting electrical activity. Subtle variations in these responses may also occur at synapses where mixtures of neuromediators are present and their effects are integrated.
Type I and II Synapses There are two broad categories of synapse: type I synapses, in which the subsynaptic zone of dense cytoplasm is thicker than on the presynaptic side, and type II synapses, in which the two zones are more symmetric but thinner. Other differences include the widths of the synaptic clefts, which are approximately 30 nm in type I and 20 nm in type II synapses, and their vesicle content.
Type I boutons contain a predominance of small spherical vesicles approximately 50 nm in diameter, and type II boutons contain a variety of flat forms. The general principle that broadly applies throughout the CNS classifies type I synapses as excitatory and type II as inhibitory.
In a few instances, type I and II synapses are found in close proximity, oriented in opposite directions across the synaptic cleft a reciprocal synapse.
Mechanisms of Synaptic Activity Synaptic activation begins with the arrival of one or more action potentials at the presynaptic bouton, which causes the opening of voltage-sensitive calcium channels in the presynaptic membrane. The response time in typical fast-acting synapses is then very rapid; classic neurotransmitter e.