Shepherd; Synaptic Organization of the Brain
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Shepherd and Koch; Synaptic Circuits 1 Synaptic Circuits
Shepherd and Koch; Synaptic Circuits 25 Pyramidal neurons are the principal neuron in all three basic types of cortex: olfactory, hippocampal, and neocortex. 24
Shepherd and Koch; Synaptic Circuits 25 Pyramidal neurons feature a long axon that gives off collaterals that make synapses on targets within the neighborhood of the cell and at different distances from the cell. 0
Shepherd and Koch; Synaptic Circuits 28 Reptilian dorsal general cortex has been regarded as a model for the evolutionary precursor of mammalian neocortex. 3
Shepherd and Koch; Synaptic Circuits 30 Rhythmic activity can be generated by two main mechanisms -- intrinsic membrane properties and synaptic circuits. 2
Shepherd and Koch; Synaptic Circuits 30 Intrinsic membrane properties were first found in pacemaker neurons in central pattern generator circuits controlling breathing, walking, and other highly stereotyped behaviors in invertebrates. 0
Shepherd and Koch; Synaptic Circuits 30 Many types of neurons in the vertebrate central nervous system possess complex and highly nonlinear ionic conductances that allowed these cells to respond to inputs by oscillating at various frequencies. 0
Shepherd and Koch; Synaptic Circuits 30 High frequency oscillations (40-60 Hz) of a large proportion of the neuronal population in a given area appear to be a common occurrence in awake, behaving animals. 0
Shepherd and Koch; Synaptic Circuits 32 The two common fast-acting neurotransmitters -- excitatory (ACh) and inhibitory (GABA). 2
McCormick; Neurotransmitter Actions 37 Membrane Properties and Neurotransmitter Actions 5
McCormick; Neurotransmitter Actions 38 Protein macromolecules in the membrane 1
McCormick; Neurotransmitter Actions 38 Because ions are unequally distributed across the membrane, they tend to diffuse down their concentration gradient through ionic channels. 0
McCormick; Neurotransmitter Actions 50 Ionic channels that conduct Ca2+ are present in all neurons. 12
McCormick; Neurotransmitter Actions 51 Experiments by Rodolfo Llinás and colleagues 1
McCormick; Neurotransmitter Actions 57 Gap junctions are actual physical connections between neighboring neurons made by large macromolecules that extend through the membranes of both cells and contain water-filled pores. 6
McCormick; Neurotransmitter Actions 57 Gap junctions allow for the direct exchange of ions and other small molecules between cells. 0
McCormick; Neurotransmitter Actions 58 Ephaptic interactions refer to interactions between neurons based largely upon their close physical proximity. The flow of ions into and out of one neuron will set up local electrical currents that can partially pass through neighboring neurons. 1
McCormick; Neurotransmitter Actions 58 In regions that possess closely spaced neuronal elements, such as the close packing of cell bodies in hippocampus and cerebellum or the bundling of dendrites in the cerebral cortex, there is a possibility of significant ephaptic interaction. 0
McCormick; Neurotransmitter Actions 58 Release of transmitter is triggered by the entry of Ca2+ into the presynaptic terminal. 0
McCormick; Neurotransmitter Actions 59 Ephaptic interactions (diagram) 1
McCormick; Neurotransmitter Actions 59 Binding of acetylcholine (Ach) to the nicotinic postsynaptic receptor induces a conformational change in the ionic channel, thereby opening the gate and allowing ions to flow through the pore. 0
McCormick; Neurotransmitter Actions 60 Once a neurotransmitter is released, the length of time that it is present in the synaptic cleft is controlled by either: (1) hydrolysis of the transmitter, (2) reuptake into the presynaptic terminal, (3) uptake into neighboring cells, or by (4) fusion out of the cleft. 1
McCormick; Neurotransmitter Actions 60 Neuroactive substances in the nervous system have been classified as either 'neurotransmitters' or 'neuromodulators' according to the duration and functional implications of their actions. 0
McCormick; Neurotransmitter Actions 61 Substances released in neurotransmitter roles cause postsynaptic responses that are both quick in onset (<1 msec) and relatively short in duration (tens of msec). 1
McCormick; Neurotransmitter Actions 61 Substance released in a neuromodulatory role are characterized by prolonged duration and the ability to modulate the response of the neuron to other inputs. 0
McCormick; Neurotransmitter Actions 61 Most neurons in the brain are under the influence of as many as a dozen or more neuroactive active substances. 0
Shepherd; Synaptic Organization of the Brain 77 Spinal Cord: Ventral Horn 16
Shepherd; Synaptic Organization of the Brain 121 Cochlear Nucleus 44
Shepherd and Greer; Olfactory Bulb 159 Olfactory Bulb 38
Shepherd and Greer; Olfactory Bulb 170 Intrinsic neurons of all later than projection neurons. 11
Shepherd; Synaptic Organization of the Brain 205 Retina 35
Llinás; Cerebellum 255 Cerebellum 50
Llinás; Cerebellum 255 Cerebella cortex receives two types of afferents -- climbing fibers and mossy fibers, and generates a single output system, the axons of Purkinje cells. 0
Llinás; Cerebellum 255 Cerebellum as a whole is connected to the rest of the central nervous system by three large fiber bundles, the cerebellar peduncles. 0
Llinás; Cerebellum 256 Integrative properties of dendritic trees. 1
Llinás; Cerebellum 256 Intrinsic excitability of the Purkinje cell and of the cerebellar nuclear cell membrane; the crystal-like organization of the synaptic connectivity of the cerebellar cortex. 0
Sherman and Koch; Thalamus 289 Thalamus 33
Sherman and Koch; Thalamus 289 Thalamus is most highly developed in mammals and especially so in primates. 0
Sherman and Koch; Thalamus 290 Schematically three-dimensional view of right thalamus with many of its major nuclei.  (Diagram) 1
Sherman and Koch; Thalamus 295 Major input to thalamus originates among layer 6 pyramidal cells of the cortex.  There seems to be at least an order of magnitude more corticothalamic axons than thalamocortical ones. 5
Sherman and Koch; Thalamus 295 Each cortical axon innervates many thalamic neurons. 0
Sherman and Koch; Thalamus 295 Strong reciprocity exists in thalamocortical connections. 0
Sherman and Koch; Thalamus 296 Corticothalamic pathway faithfully adheres to the map established in the thalamic nucleus. 1
Sherman and Koch; Thalamus 299 Roughly 25% of the cells in most thalamic nuclei are local interneurons. 3
Sherman and Koch; Thalamus 319 Rich array of membrane properties of thalamic relay cells plus their complex ensemble of inputs from various sources suggest that relay of peripheral information to cortex is not a simple, trivial affair. 20
Sherman and Koch; Thalamus 319 Gating and other transformations and thalamic relay. 0
Sherman and Koch; Thalamus 319 There seem to be three different response modes in thalamic neurons -- rhythmic bursting, arrhythmic bursting, and tonic firing. 0
Sherman and Koch; Thalamus 319 Rhythmic bursting of thalamic neurons occurs during quiet or non-REM sleep, perhaps during drowsiness, and might also occur during epileptic episodes. 0
Sherman and Koch; Thalamus 319 Arrhythmic bursting and tonic firing of thalamic neurons occur during waketime activity, meaning that both burst and tonic modes can be effective relay nodes. 0
Sherman and Koch; Thalamus 321 Perhaps burst mode is used during visual search or maybe during periods when attention is directed elsewhere as a sort a wake-up call for novel and potentially interesting or dangerous stimuli. 2
Sherman and Koch; Thalamus 321 Although burst firing may be ideal for signal detection, the nonlinear distortion during this relay mode means that the stimulus will not be accurately analyzed. 0
Sherman and Koch; Thalamus 321 Tonic mode, with its more linear relay, would permit faithful signal analysis. 0
Sherman and Koch; Thalamus 321 Brain stem and cortical afferents to thalamus in terms of their ability to affect response mode. 0
Sherman and Koch; Thalamus 323 Activity in brain stem afferents is associated with more alert behavioral states. 2
Sherman and Koch; Thalamus 324 Every thalamic nucleus appears to receive afferents from layer 6 of the relevant cortical region or regions. 1
Sherman and Koch; Thalamus 325 Layer 5 innervation pattern suggest that certain thalamic nuclei receive their primary afferents from the cortex rather than subcortically and they relay this afferent cortical activity to other cortical areas. This provides the thalamus with a much more extensive role in cortical-cortical communication. 1
Sherman and Koch; Thalamus 325 There are at least two functionally distinct corticothalamic systems.  One derives from layer 6 and serves to modulate the relay properties of its thalamic target.  The other derives from layer 5 and represents the primary information to be relayed by the target thalamic cells. These latter  thalamic relay cells are also under the modulatory influence of layer 6 input, which is ubiquitous for all thalamic nuclei. 0
Sherman and Koch; Thalamus 325 There are two types of thalamic nuclei -- one receiving its primary afferent from subcortical sources and the other, from cortical sources. 0
Sherman and Koch; Thalamus 325 First-order of thalamic relay nuclei received primary afferent from subcortical sources. 0
Sherman and Koch; Thalamus 325 Higher-order thalamic relay nuclei receive primary input from the cortex that has already received and acted on information from its first-order thalamic relays. 0
Sherman and Koch; Thalamus 325 Olfactory pathway from the olfactory bulb to olfactory paleocortex is analogous to a first-order relay without a thalamic component. 0
Sherman and Koch; Thalamus 325 Olfactory pathway to olfactory paleocortex may have evolved before thalamus and neocortex. 0
Sherman and Koch; Thalamus 326 Thalamocortical interactions permit a rich avenue of communication among cortical areas. 1
Sherman and Koch; Thalamus 326 Cortical areas can communicate through the thalamus, with some thalamocortical inputs relaying via layer 5, to another cortical area. 0
Sherman and Koch; Thalamus 326 Other cortical areas, via their layer 6 outputs, can modify the thalamic route of corticocortical communication. 0
Sherman and Koch; Thalamus 328 Relay functions served by thalamus is not limited to transferring peripheral information to cortex; certain thalamic nuclei serve chiefly to relay information from cortex to cortex; This role may prove crucial to cortico-cortical communications. 2
Wilson; Basal Ganglia 329 Basal Ganglia 1
Wilson; Basal Ganglia 329 Basal ganglia have no direct connections with either the sensory or motor organs. 0
Wilson; Basal Ganglia 329 Basal ganglia diseases produce severe deficits of movement. Parkinson's disease, movements are more difficult to make. Huntington's disease, useless and unintended movements interfere with intended ones. 0
Wilson; Basal Ganglia 329 Only voluntary, purposive movements affected, reflexive movements relatively unaffected. 0
Wilson; Basal Ganglia 329 Anatomical connections of the basal ganglia link it to elements of the sensory, motor, cognitive, and motivational apparatus of the brain. 0
Wilson; Basal Ganglia 329 Major structures of the basal ganglia are the caudate nucleus, putamen, globus substantia nigra, and subthalamic nucleus. 0
Wilson; Basal Ganglia 329 Two largest sources of input to the basal ganglia, the cerebral cortex and the thalamus. 0
Wilson; Basal Ganglia 329 Most of the input to the basal ganglia from other brain structures arrives in the neostriatum, which consists of the caudate nucleus, putamen, and nucleus accumbens. 0
Wilson; Basal Ganglia 330 Within the caudate nucleus and the putamen, inputs from sensory, motor; and association cortical areas converge with inputs from the thalamic intralaminar nuclei, dopaminergic inputs from the substantia nigra pars compacta, and serotoninergic inputs from the dorsal raphe nucleus. Connections arising from the limbic cortex and hippocampus are formed in a third structure, the nucleus accumbens. 1
Wilson; Basal Ganglia 331 Three input structures of the basal ganglia (caudate nucleus, putamen, nucleus accumbens.)  1
Wilson; Basal Ganglia 332 Input fibers to the neostriatum arise primarily from the cerebral cortex, the intralaminar nuclei of the thalamus, the dopaminergic neurons of the substantia nigra (pars compacta), the serotoninergic neurons of the dorsal raphe nucleus, and the basolateral nucleus of the amygdala. Less numerous inputs also arise from the external segment of the globus pallidus and from the substantia nigra, pars reticulata. 1
Wilson; Basal Ganglia 345 The neostriatum is unusual in that the principal neurons, as well as many of the interneurons, are inhibitory. The principal neuron of the globus pallidus and substantia nigra is also inhibitory. Excitatory influences in the basal ganglia arise mostly from incoming fibers.
Wilson; Basal Ganglia 345 Neostriatal spiny cells fire very rarely and in episodes that last for only about 0.1 to 3 sec.  0
Wilson; Basal Ganglia 346 Cells in the globus pallidus and substantia nigra fire tonically at very high rates. Their tonic firing produces a constant inhibition of neurons in the thalamus and superior colliculus.  1
Wilson; Basal Ganglia 347 Firing of spiny neostriatal neurons can cause a transient pause in tonic inhibition, releasing thalamic and superior colliculus neurons to respond to excitatory inputs that would otherwise be subthreshold. 1
Wilson; Basal Ganglia 347 The neostriatum acts to disinhibit neurons in the thalamus and superior colliculus; interneurons of the neostriatum help regulate the duration, strength, and spatial pattern of the disinhibition. 0
Wilson; Basal Ganglia 373 Cells in globus pallidus and in substantia nigra pars reticulata have very high rates of tonic activity. Fire rhythmically at a rate determined by membrane characteristics. 26
Wilson; Basal Ganglia 373 Inhibition exerted by (usually silent) neostriatal spiny neurons during their brief episodes of friring causes a momentary decrease in the rate of the tonic firing.  0
Wilson; Basal Ganglia 373 Fast-firing cells of the globus pallidus and substantia nigra are GABAergic neurons, which exert a tonic inhibition on the target cells of the thalamus and superior colliculus. 0
Wilson; Basal Ganglia 373 Overall, excitation of neostriatal spiny neurons leads to a disinhibition of the otherwise suppressed activity of neurons in the thalamus and superior colliculus. 0
Haberly; Olfactory Cortex 377 Olfactory Cortex 4
Haberly; Olfactory Cortex 380 In the neocortex, subtle differences in cytoarchitecture and connections reflect functional specialization. 3
Johnston; Hippocampus 417 Hippocampus 37
Johnston; Hippocampus 417 Hippocampus is one of the most thoroughly studied areas of the mammalian central nervous system. 0
Johnston; Hippocampus 417 Hippocampal formation includes the dentate gyrus, the hippocampus, the subiculum, presubiculum and parasubiculum, and the entorhinal cortex.  0
Johnston; Hippocampus 417 The dentate gyrus, hippocampus, and subiculum have a single cell layer with less cellular or acellular layers located above and below it. The other parts of the hippocampal formation have several cellular layers.  0
Johnston; Hippocampus 417 A patient known by his initials, H.M., underwent bilateral hippocampal removal for the treatment of intractable epilepsy. He was left with a permanent loss of the ability to encode new information into long-term memory.  0
Johnston; Hippocampus 417 In addition to memory studies, the hippocampus is also of interest because of its high seizure susceptibility. It has the lowest seizure threshold of any brain region. Most patients with epilepsy have seizures that involve the hippocampus, and these seizures are often the most difficult to control medically. 0
Johnston; Hippocampus 418 Portions of the hippocampal formation, particularly the entorhinal cortex, are prime targets for the pathology associated with Alzheimer's disease, and the hippocampus is very vulnerable to the effects of ischemia and anoxia. 1
Johnston; Hippocampus 420 The principal neurons in the dentate gyrus are the granule cells, and in the hippocampus they are the pyramidal neurons. 2
Johnston; Hippocampus 420 The pyramidal cell layer of the hippocampus has been divided into three regions designated CA1,  CA2,  CA3 based on the size and appearance of the neurons. 0
Johnston; Hippocampus 421 Vast majority of interneurons in the dentate gyrus and hippocampus have locally restricted target regions, lack spines, and are GABAergic. 1
Johnston; Hippocampus 423 Hippocampal interneurons with cell bodies in or near the pyramidal cell layer can be classified into three groups on the basis of their synaptic targets -- axo-axonic cells, basket cells, and bistratified cells.  2
Johnston; Hippocampus 423 Axo-axonic cells synapse onto the initial segments of pyramidal neurons and thus exert a strong control over action potential initiation.  0
Johnston; Hippocampus 423 Basket cells synapse onto the somata of pyramidal neurons. Each basket cell can make multiple contacts onto a pyramidal neuron, forming what looks like a "basket" into which the soma sits. 0
Johnston; Hippocampus 423 Bistratified cells make synaptic contacts onto apical and basal dendrites of pyramidal neurons. 0
Johnston; Hippocampus 423 Mutual inhibitory connections among these interneurons. 0
Johnston; Hippocampus 423 Mutual inhibitory connections synchronize interneurons, producing oscillations at various frequencies, including theta (5 Hz) and gamma (40 Hz) frequencies. 0
Johnston; Hippocampus 423 Many GABAergic interneurons also contain and release neuroactive peptides. 0
Johnston; Hippocampus 423 Interneurons whose post-synaptic targets are exclusively other interneurons. 0
Johnston; Hippocampus 423 Basic circuitry of the hippocampal formation has been known since the time of Ramon y Cajal (1911). 0
Johnston; Hippocampus 424 Unidirectional progression of excitatory pathways that link each region of the hippocampal formation -- the trisynaptic circuit. 1
Johnston; Hippocampus 424 Entorhinal cortex is considered the starting point of the trisynaptic circuit since much of the sensory information that reaches the hippocampus enters through the entorhinal cortex. 0
Johnston; Hippocampus 424 Neurons located in layer II of the entorhinal cortex give rise to a pathway, the perforant path, that projects through (perforates) the subiculum and terminates both in the dentate gyrus and in the CA3 field of the hippocampus. 0
Johnston; Hippocampus 424 Dentate gyrus is the next step in the progression of connections, and it gives rise to the mossy fibers that terminate on the proximal dendrites of the CA3 pyramidal cells. 0
Johnston; Hippocampus 425 The CA3 pyramidal cells project heavily to other levels of CA3 as well as to CA1. The projection to CA1 is typically called the Schaffer collateral projection. 1
Johnston; Hippocampus 425 Information entering the entorhinal cortex from a particular cortical area can traverse the entire hippocampal circuit through the excitatory pathways and ultimately be returned to the cortical area from which it originated. The transformations that take place through this traversal are presumably essential for enabling the information to be stored as long-term memories. 0
Johnston; Hippocampus 427 The major input to the dentate gyrus is from the entorhinal cortex. 2
Johnston; Hippocampus 428 Subcortical inputs to the dentate gyrus originate mainly from the septal nuclei, supramamillary region of the posterior hypothalamus, and several monoaminergic nuclei in the brainstem, especially the locus coeruleus and raphe nuclei. 1
Johnston; Hippocampus 428 Dentate gyrus receives a particularly prominent noradrenergic input, primarily from the locus coeruleus.  0
Johnston; Hippocampus 428 Serotonergic projection originates from the raphe nuclei. 0
Johnston; Hippocampus 430 Many of the cells in the raphe nuclei that project to the hippocampal formation appear to be nonserotonergic. 2
Johnston; Hippocampus 430 Dentate gyrus receives a lighter and diffusely distributed dopaminergic projection that arises mainly from cells located in the ventral tegmental area. 0
Johnston; Hippocampus 430 Dentate gyrus does not project to other brain regions. Within the hippocampal formation, it only projects to CA3 via the mossy fibers. 0
Johnston; Hippocampus 431 CA3 pyramidal cells give rise to highly collateralized axons that distribute fibers both within the hippocampus (to CA3, CA2, CA1), to the same fields in the contralateral hippocampus (the commissural projections), and subcortically to the lateral septal nucleus. 1
Johnston; Hippocampus 431 CA3 cells, especially those located proximally in the field, and CA2 cells contribute a small number of collaterals that innervate the polymorphic layer of the dentate gyrus. 0
Johnston; Hippocampus 431 All of the CA3 and CA2 pyramidal cells give rise to highly divergent projections to all portions of the hippocampus. The projections to CA3 and CA2 are typically called the associational connections, and the CA3 projections to the CA1 field are called the Schaffer collaterals.  0
Johnston; Hippocampus 431 Highly ordered and spatially distributed pattern of projections from CA3 to CA3 and from CA3 to CA1. 0
Johnston; Hippocampus 432 Each CA3 neuron makes contacts with many CA1 pyramidal cells. It has been estimated that a single CA1 neuron may be innervated by more than 5,000 ipsilateral CA3 pyramidal cells. 1
Johnston; Hippocampus 432 Projections from CA3 to CA1 terminate as asymmetric, axospinous synapses located on the apical and basal dendrites of the CA1 pyramidal cells. The sizes and shapes of the spines and presynaptic profiles in this region are quite variable and may be related to the physiological efficacy of the synapses in CA1. 0
Johnston; Hippocampus 432 CA3-to-CA3 associational and CA3-to-CA1 Schaffer collateral projections are both divergently distributed along the septotemporal axis. 0
Johnston; Hippocampus 432 Single CA3 and CA2 pyramidal cells give rise to highly arborized axonal plexuses that distribute to as much as 75% of the septotemporal extent of the ipsilateral and contralateral CA1 fields. 0
Johnston; Hippocampus 432 Total length of the axonal plexus from single CA3 neurons can be as long as 150-300 mm, and a single CA3 cell may contact as many as 30,000 to 60,000 neurons in the ipsilateral hippocampus. 0
Johnston; Hippocampus 432 The only sizable subcortical projection from CA3 is to the lateral septal nucleus. 0
Johnston; Hippocampus 432 Some CA3 fibers cross in the ventral hippocampal commissure to innervate the homologous region of the contralateral lateral septal nucleus. 0
Johnston; Hippocampus 432 Essentially all of the CA3 cells give rise to projections both to CA1 and to the lateral septal nucleus. 0
Johnston; Hippocampus 433 CA3 field receives inputs from the noradrenergic nucleus locus coeruleus. 1
Johnston; Hippocampus 435 Highly structured and organized arrangement of synaptic pathways makes the hippocampus ideal for studying synaptic actions in vivo or in vitro. Single-shock electrical stimulations to the perforant path, mossy fibers, or Schaffer collaterals result in a characteristic sequence of excitation followed by inhibition in the appropriate target neurons.  2
Johnston; Hippocampus 438 Electrophysiological behavior of the different neurons in the hippocampus is variable. 3
Johnston; Hippocampus 438 Dentate granule and CA1 pyramidal neurons can fire repetitively at up to several hundred Hz. 0
Johnston; Hippocampus 438 CA3 pyramidal neurons tend to fire in short bursts of 5-10 action potentials. 0
Johnston; Hippocampus 438 Bursting properties of CA3 hippocampal neurons are thought to be important for explaining the seizure susceptibility of the hippocampus. 0
Johnston; Hippocampus 438 A prominent feature of hippocampal neurons firing repetitively is that the frequency of action potentials declines or accomodates during the train, and there is a slow afterhyperpolarization (AHP) at the end of the train. 0
Johnston; Hippocampus 438 Both the frequency accomodation and the slow AHP result in part from the activation of potassium channels by the influx of calcium ions during the train. 0
Johnston; Hippocampus 438 Presynaptic mechanisms, including the quantal hypothesis for transmitter release and the role of presynaptic calcium, have been studied directly at both mossy fiber and Schaffer collateral synapses. 0
Johnston; Hippocampus 439 Because excitatory synapses and some inhibitory synapses terminate on dendrites, the physiology and biophysics of synaptic transmission is complicated by the properties of dendrites. 1
Johnston; Hippocampus 439 Basic sequence of synaptic transmission begins with an action potential in the presynaptic axon that elicits Ca2+ influx into the bouton, and through a number of poorly understood steps, neurotransmitter is released into the cleft from transmitter-containing vesicles in the presynaptic terminal. 0
Johnston; Hippocampus 439 Transmitter molecules diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic neuron, opening ion channels. 0
Johnston; Hippocampus 439 Single boutons may have as few as 1 active zone in some Schaffer collateral boutons to as many as 37 active zones on some of the largest mossy fiber terminals. 0
Johnston; Hippocampus 439 A prominent theory is that one vesicle per action potential is released at each active zone with a mean probability of about 1 release every fourth action potential. 0
Johnston; Hippocampus 439 Vesicles can sometimes release their transmitter spontaneously in the absence of a presynaptic action potential. 0
Johnston; Hippocampus 439 Inhibitory neurons can fire repetitively at rates much higher than is typical for excitatory neurons. 0
Johnston; Hippocampus 439 Excitatory input to inhibitory interneurons may trigger a high-frequency train of action potentials in the interneurons, leading to longer-lasting transmitter release and a longer-lasting inhibition of the post-synaptic neuron than from the excitatory response. 0
Johnston; Hippocampus 439 Major excitatory neurotransmitter in the hippocampus is glutamate. 0
Johnston; Hippocampus 440 Major inhibitory neurotransmitter in the hippocampus is GABA . 1
Johnston; Hippocampus 442 It was once believed that inhibitory synapses were primarily on the cell bodies of pyramidal neurons. There is now much evidence that GABAergic synapses occur both on the cell bodies as well as throughout the dendritic tree. 2
Johnston; Hippocampus 442 Neuromodulatory neurotransmitters acting pre- and/or postsynaptically that under some conditions can be considered inhibitory. These include norepinephrine, serotonin, dopamine, and neuroactive peptides. 0
Johnston; Hippocampus 442 Perforant Pathway can be separated into two groups of fibers, the lateral and medial perforant paths. Opioid peptides influence the induction of longterm potentiation in the lateral perforant path. 0
Johnston; Hippocampus 442 Hilar Pathways -- physiology of the hilar region is poorly understood, compared with the rest of the hippocampus. 0
Johnston; Hippocampus 442 Mossy Fibers. Mossy fiber boutons are among the largest synapses of the mammalian central nervous system, surpassed only by certain synapses in the cochlear nucleus. At each bouton there are multiple active zones (up to 37) resulting in multiple release sites for neurotransmitter. The boutons contain large amounts of Zn2+ and opioid peptides that are co-released with the main neurotransmitter glutamate.  0
Johnston; Hippocampus 442 Mossy fibers terminate on the proximal dendrites of CA3 pyramidal cells.  0
Johnston; Hippocampus 443 Recurrent Pathways. One of the hallmarks of the CA3 region is the prominent, recurrent excitatory connections among the pyramidal neurons. This recurrent pathway is glutamatergic, and excitatory, and represents a form of positive feedback that makes the CA3 region inherently unstable. In combination with the intrinsic bursting properties of CA3 neurons; subtle increases in the ratio of excitation/inhibition in this region can result in epileptiform activity, which is characterized by spontaneous and synchronous, rhythmic firing among large numbers of neurons. 1
Johnston; Hippocampus 444 Schaffer Collaterals are probably the best-studied synaptic pathway in the hippocampus. Each Schaffer collateral axon synapses onto thousands of CA1 pyramidal neurons, but usually with only one or two synaptic contacts per neuron. 1
Johnston; Hippocampus 444 Axons of the CA1 pyramidal neurons also form a recurrent excitatory pathway that synapses back onto other CA1 neurons, although it is much sparser and weaker than that in CA3. 0
Johnston; Hippocampus 444 Synaptic Plasticity - most of the excitatory synapses in the hippocampus exhibit various forms of use- or activity-dependent synaptic plasticity. 0
Johnston; Hippocampus 444 Short-term plasticities are facilitation, post-tetanic potentiation, and depression. They range in duration from hundreds of milliseconds to several minutes.  0
Johnston; Hippocampus 445 Long-term Plasticities -- There are several forms of synaptic plasticities at glutamatergic, excitatory synapses in hippocampus that have durations of from 30 min to hours, days, or weeks. They are called short-term potentiation and depression (STP and STD) and long-term potentiation and depression (LTP and LTD). 1
Johnston; Hippocampus 445 LTP was first described by Bliss and colleagues (Bliss and Lomo, 1973; Bliss and Gardner-Medwin, 1973) and is probably the most intensely studied of all the synaptic plasticities because of its presumed role in learning and memory. 0
Johnston; Hippocampus 445 LTP is typically induced by giving one or more high-frequency (25-200 Hz) stimulus trains to a synaptic pathway, such as the perforant path, mossy fibers, or Schaffer collaterals. This period of high-frequency stimulation trains is called the induction phase. 0
Johnston; Hippocampus 445 The induction phase of LTP is followed by an expression phase, during which a stimulus is amplified some 50-100%. Characteristically, an induction phase of only a few seconds to 1 min is much shorter than the subsequent expression phase, which may last up to several days.  0
Johnston; Hippocampus 445 Maximum duration of expression phase is difficult to ascertain, but LTP in hippocampus is unlikely to be permanent. 0
Johnston; Hippocampus 445 LTP has associative properties; synapses may exhibit LTP only when they are active at the same time as other synapses. These and other properties make LTP a candidate mnemonic device. 0
Johnston; Hippocampus 445 LTD represents a long-term depression of a synaptic response, induced by the low-frequency stimulation (1-5 Hz) of a synaptic pathway. LTD can last from 30 min to an hour or more.  0
Johnston; Hippocampus 445 Most theories for learning involve strengthening of specific synaptic pathways at the expense of others, and the existence of an LTD-like phenomenon has long been theorized. 0
Johnston; Hippocampus 445 At many synapses LTP and LTD are dependent on the activation of NMDA receptors. A requirement for the induction of LTP is that there must be a sufficient increase in the intracellular Ca2+ concentration near the stimulated synapses. This occurs by the influx of Ca2+ ions through NMDA receptors and/or voltage-gated Ca2+ channels. 0
Johnston; Hippocampus 445 At mossy fiber synapses and perhaps at lateral perforant-path synapses, LTP is facilitated by the release of opioid peptides. 0
Johnston; Hippocampus 446 STP and STD occur when the stimulation during induction is of insufficient intensity or duration to induce LTP and LTD. STP and STD have lower induction thresholds than their longer-term counterparts.  1
Johnston; Hippocampus 446 It is not clear whether STP and STD are just shorter-term versions of LTP and LTD or if they have separate mechanisms. Nonetheless, they share characteristics, such as a dependence on a rise in intracellular Ca2+ concentration in the postsynaptic neuron, and at some synapses, a requirement for NMDA receptor activation.
Douglas; Neocortex 459 Neocortex 13
Douglas; Neocortex 459 Human brain is three times as large as might be expected for a primate of equivalent weight. Human brain is not simply a scaled-up version of closest primate relative, the Bonobo chimpanzee. Greatest expansion is in the cortical structures, particularly the cerebellum and neocortex. 0
Douglas; Neocortex 459 Within the neocortex, the expansion is uneven. In comparison with nonhuman primates of equivalent body weight, the human association and premotor areas have expanded relative to the sensory areas. 0
Douglas; Neocortex 459 In all mammals the neocortex consists of a sheet of cells, about 2 mm thick. Conventionally, it is divided into 6 layers, but in many regions more than 6 laminae are in evidence. Each cubic millimeter contains approximately 50,000 neurons. 0
Douglas; Neocortex 459 Three major cytoarchitectural divisions of the neocortex. (1) granular cortex of the sensory areas, contains small, densely packed neurons in the middle layers; (2) agranular cortex of the motor and premotor cortical areas, (3) varying populations of granule cells, mostly 'association cortex'. Within each of these areas there are many subdivisions, both functional and anatomical.  0
Douglas; Neocortex 461 All three cytoarchitectural divisions of the neocortex contain the same two basic types of neurons: those whose dendrites bear spines (the stellate and pyaramidal cells) and those whose dendrites are smooth (smooth cells). 2
Douglas; Neocortex 461 Pyramidal cells form about 70% of the neurons. Smooth cells form about 20% of the neurons.  0
Douglas; Neocortex 462 Spiny cells are excitatory, whereas smooth neurons are inhibitory.  1
Douglas; Neocortex 464 Spiny neurons are called this because their dendrites bear small processes called spines, which are usually club shaped, with a head of about 1µm diameter and a shaft, or neck, of about 0.1 µm diameter.  2
Douglas; Neocortex 464 Major subtype of spiny neurons are the pyramidal cells, which constitute about two-thirds of the neurons in the neocortex.  0
Douglas; Neocortex 464 Pyramidal neurons are found in all cortical layers except layer 1. 0
Douglas; Neocortex 464 The most prominent feature of pyramidal neurons is an apical dendrite that may extend through all the layers of the cortex above the soma.  0
Douglas; Neocortex 464 Pyramidal cells are the major output neurons of the neocortex. 0
Douglas; Neocortex 464 Pyramidal cells participate both in connections between the different cortical areas and to subcortical structures such as the thalamus and superior colliculus.  0
Douglas; Neocortex 464 Pyramidal cells are a major provider of excitatory input to the area in which they are found -- each pyramidal neuron has a rich collateral network that forms part of the local cortical circuitry. 0
Douglas; Neocortex 464 Proximal shafts of the dendrites of the spiny cell types are nearly devoid of spines. 0
Douglas; Neocortex 464 Spine density varies considerably between different types of neurons. At one extreme is the sparsely spiny neuron, which may bear fewer than 100 spines over the entire dendritic tree. These neurons form a small subclass of the inhibitory neuron population. At another extreme are neurons such as the Betz cell, a large pyramidal cell that is found in the motor cortex (area 4) and bears about 10,000 spines. 0
Douglas; Neocortex 464 The most prominent pyramidal cells in the neocortex are the Betz cells of area 4, the motor cortex. The Betz cells are very large pyramidal cells located in layer 5. Their axons form part of the pyramidal tract that descends to the spinal cord. 0
Douglas; Neocortex 465 Primary visual cortex has a distinct set of exceptionally large pyramidal neurons, called the solitary cells of Meynert. These pyramidal cells, which are found in the deep layers (5 or 6, depending on species), project to other cortical areas and down to the midbrain structures such as the superior colliculus and the pons. 1
Douglas; Neocortex 465 Within layer 5 in the visual cortex, two types of pyramidal cells have been distinguished: (1) a thick apical dendrite that ascends to layer 1 where it forms a terminal tuft. These neurons have a bursting discharge response. (2) a thin apical dendrite that terminates without branching in layer 2, and has a regular discharge. 0
Douglas; Neocortex 465 Theoretical work has suggested that the shape of the dendritic tree is a major factor in controlling the pattern of spike output from neurons. 0
Douglas; Neocortex 465 A second group of spiny neurons, the spiny stellate neurons, are found exclusively in layer 4 of the granular cortex. They do not have the apical dendrite characteristic of pyramidal cells. Instead, dendrites of approximately equal length radiate from the soma, giving a star-like appearance. 0
Douglas; Neocortex 465 Occasionally, spiny stellate neurons do project to other areas, but most have axonal projections confined to the area in which they occur. 0
Douglas; Neocortex 465 Smooth neurons tend to have elongated dendritic trees, both in the radial and the tangential dimension.  0
Douglas; Neocortex 465 The most prominent smooth neuron is the cortical basket cell. 0
Douglas; Neocortex 465 As with basket cells in the cerebellum and hippocampus, the axons of basket cells form nests or baskets around the somata of their targets, usually pyramidal cells. 0
Douglas; Neocortex 466 Thalamus projects to all cortical areas and provides input to most layers of the cortex. The densest projections are to the middle layers, where they form about 5-10% of the synapses in those layers. 1
Douglas; Neocortex 466 The main feature of thalamic input to the cortex is that it is highly ordered. The sensory inputs are represented centrally in a way that their topographic arrangement in the periphery is preserved. 0
Douglas; Neocortex 466 Thalamocortical mapping is achieved by preserving the nearest-neighbor relationships of the arrangements of the sensory or motor elements in the periphery. Such topographic projections are a ubiquitous feature of the cortex. 0
Douglas; Neocortex 466 Precision of topographic mapping varies between areas. Primary sensory and motor areas usually preserve the highest detail of topography, degrading progressively through secondary, tertiary and higher order areas of cortex. 0
Douglas; Neocortex 466 In the visual system of the primate, the fovea of the retina contains the highest density of photoreceptors, represented in the cortex by 30 mm/degree of visual field.    In the far periphery, the ratio falls to about 0.01 mm/degree of visual field. 0
Douglas; Neocortex 467 Although the thalamus is a major source of input to the neocortex, it is not the only one. More than 20 different subcortical structures projecting to the neocortex have been identified. 1
Douglas; Neocortex 467 Subcortical structures projecting to the neocortex include the claustrum, locus coeruleus, basal forebrain, the dorsal and median raphe, and the pontine reticular system. 0
Douglas; Neocortex 468 Three main types of monoamine-containing cortical afferents have been described: (1) the dopamine-positive fibers arising from the rostral mesencephalon, (2) the noradrenaline-containing axons originating from the locus coeruleus, (3) the serotonin (5-HT) fibers that originate from the mesencephalic raphe nuclei. 1
Douglas; Neocortex 468 Locus coeruleus, a small nucleus in the dorsal pons, projects to most of the neocortex. Neurons synthesize norepinephrine. Activity in locus coeruleus is involved with the arousal response induced by sensory stimuli. 0
Douglas; Neocortex 468 Raphe nuclei and pontine reticular formation, are a complex of nuclei that contain the highest density of neurons that synthesize serotonin. These neurons project to all cortical areas with varying degrees of laminar specificity. 0
Douglas; Neocortex 468 The third monoamine projection to cortex is the dopaminergic pathway.The dopaminergic projection to the frontal cortex originates from the ventral tegmental area, the rostral mesencephalic groups, and the nucleus linearis. All layers except layer 4 receive dopaminergic input. Dopaminergic projections are strongest to the rostral cortical areas, especially the prefrontal cortex. 0
Douglas; Neocortex 469 Major input from any cortical area is from other cortical areas. 1
Douglas; Neocortex 469 Only 1:100 or even 1:1000 in white matter is involved in subcortical projection. 0
Douglas; Neocortex 469 Most of the fibers in white matter are involved in intrahemispheric connections and interhemispheric connections. 0
Douglas; Neocortex 475 Axons of cortical neurons do not extend more than a few millimeters laterally in an area. 6
Douglas; Neocortex 475 Neurons with similar functional properties are organized in 'columns' that extend from the cortical surface to the white matter. 0
Douglas; Neocortex 477 Output neurons from the cortex are generally pyramidal cells. 2
Douglas; Neocortex 477 Cortico-cortical connections arise mainly from the superficial cortical layers, and the subcortical projections arise from the deep layers. 0
Douglas; Neocortex 477 Within the deep layers, there is an output to regions that have a motor-related function, e.g., the superior colliculus, basal ganglia, brainstem nuclei, and spinal cord. 0
Douglas; Neocortex 477 Cortico-thalamic projection generally arises from the layer 6 pyramidal cells. 0
Douglas; Neocortex 477 Basic circuit for visual cortex (diagram) 0
Douglas; Neocortex 484 Long term potentiation -- brief tetanic stimulation of a set of input fibers potentiates synapses in hippocampal excitatory synapses for many hours. 7
Douglas; Neocortex 485 Processes of LTP and LTD have been studied in a number of different cortical areas. 1
Douglas; Neocortex 485 In the neocortex the main excitatory neurotransmitter is the amino acid glutamate. 0
Douglas; Neocortex 486 Activation of the NMDA receptor evokes a long-duration conductance change (tens of milliseconds), during which cations flow through the channel. 1
Douglas; Neocortex 488 A number of chemical substances have inhibitory effects on cortical neurons, but the most dominant inhibitor appears to be GABA. 2
Douglas; Neocortex 492 Establishment of the identity of cortical neurotransmitters has been one of the most tortuous activities of the last 40 years. 4
Douglas; Neocortex 494 Surface area of dendrites is one to two orders of magnitude larger than that of the soma. 2
Douglas; Neocortex 497 One of most prominent features of cortical neurons is that dendritic spines. 3
Douglas; Neocortex 497 Recent advances in imaging techniques make it possible to measure calcium dynamics in individual spines. 0
Douglas; Neocortex 497 Most of the synaptic current injected into the spine head reaches the trunk dendrite via the spine neck. 0
Douglas; Neocortex 497 Resistance to current flow through the neck is high, on the order of 100 MΩ or more. 0
Douglas; Neocortex 497 Neck resistance could be used to control the efficacy of the synapse and thus to provide a basis for a synaptic plasticity. 0
Douglas; Neocortex 497 Twitching spine hypothesis -- Francis Crick (1982) proposed that a change in spine length could be achieved quickly, by calcium activation of myosin and actin localized in the spine neck. 0
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