Nervous tissue, also called neural tissue or nerve tissue, is the main tissue component of the nervous system. The nervous system regulates and controls bodily functions and activity and consists of two parts: the central nervous system (CNS) comprising the brain and spinal cord, and the peripheral nervous system (PNS) comprising the branching peripheral nerves. It is composed of neurons, or nerve cells, which receive and transmit impulses, and neuroglia, also known as glial cells or glia, which assist the propagation of the nerve impulse as well as provide nutrients to the neurons.
A dendritic spine is a small membranous protrusion from a neuron's dendrite that typically receives input from a single axon at the synapse. Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body. Most spines have a bulbous head, and a thin neck that connects the head of the spine to the shaft of the dendrite. The dendrites of a single neuron can contain hundreds to thousands of spines. In addition to spines providing an anatomical substrate for memory storage and synaptic transmission, they may also serve to increase the number of possible contacts between neurons.
Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cortex and the corticospinal tract. Pyramidal neurons are also one of two cell types where the characteristic sign, Negri bodies, are found in post-mortem rabies infection. Pyramidal neurons were first discovered and studied by Santiago Ramón y Cajal. Since then, studies on pyramidal neurons have focused on topics ranging from neuroplasticity to cognition.
DSCAM and Dscam are both abbreviations for Down syndrome cell adhesion molecule. In humans, DSCAM refers to a gene that encodes one of several protein isoforms.
Basket cells are inhibitory GABAergic interneurons of the brain, found throughout different regions of the cortex and cerebellum.
An apical dendrite is a dendrite that emerges from the apex of a pyramidal cell. Apical dendrites are one of two primary categories of dendrites, and they distinguish the pyramidal cells from spiny stellate cells in the cortices. Pyramidal cells are found in the prefrontal cortex, the hippocampus, the entorhinal cortex, the olfactory cortex, and other areas. Dendrite arbors formed by apical dendrites are the means by which synaptic inputs into a cell are integrated. The apical dendrites in these regions contribute significantly to memory, learning, and sensory associations by modulating the excitatory and inhibitory signals received by the pyramidal cells.
Stellate cells are any neuron in the central nervous system that have a star-like shape formed by dendritic processes radiating from the cell body. Many Stellate cells are GABAergic and are located in the molecular layer of the cerebellum. Stellate cells are derived from dividing progenitors in the white matter of postnatal cerebellum. Dendritic trees can vary between neurons. There are two types of dendritic trees in the cerebral cortex, which include pyramidal cells, which are pyramid shaped and stellate cells which are star shaped. Dendrites can also aid neuron classification. Dendrites with spines are classified as spiny, those without spines are classified as aspinous. Stellate cells can be spiny or aspinous, while pyramidal cells are always spiny. Most common stellate cells are the inhibitory interneurons found within the upper half of the molecular layer in the cerebellum. Cerebellar stellate cells synapse onto the dendritic arbors of Purkinje cells and send inhibitory signals. Stellate neurons are sometimes found in other locations in the central nervous system; cortical spiny stellate cells are found in layer IVC of the V1 region in the visual cortex. In the somatosensory barrel cortex of mice and rats, glutamatergic (excitatory) spiny stellate cells are organized in the barrels of layer 4. They receive excitatory synaptic fibres from the thalamus and process feed forward excitation to 2/3 layer of V1 visual cortex to pyramidal cells. Cortical spiny stellate cells have a 'regular' firing pattern. Stellate cells are chromophobes, that is cells that does not stain readily, and thus appears relatively pale under the microscope.
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron or to the target effector cell.
Martinotti cells are small multipolar neurons with short branching dendrites. They are scattered throughout various layers of the cerebral cortex, sending their axons up to the cortical layer I where they form axonal arborization. The arbors transgress multiple columns in layer VI and make contacts with the distal tuft dendrites of pyramidal cells. Martinotti cells express somatostatin and sometimes calbindin, but not parvalbumin or vasoactive intestinal peptide. Furthermore, Martinotti cells in layer V have been shown to express the nicotinic acetylcholine receptor α2 subunit (Chrna2).
The synaptotropic hypothesis, also called the synaptotrophic hypothesis, is a neurobiological hypothesis of neuronal growth and synapse formation. The hypothesis was first formulated by J.E. Vaughn in 1988, and remains a focus of current research efforts. The synaptotropic hypothesis proposes that input from a presynaptic to a postsynaptic cell eventually can change the course of synapse formation at dendritic and axonal arbors. This synapse formation is required for the development of neuronal structure in the functioning brain.
Protocadherins (Pcdhs) are the largest mammalian subgroup of the cadherin superfamily of homophilic cell-adhesion proteins. They were discovered by Shintaro Suzuki's group, when they used PCR to find new members of the cadherin family. The PCR fragments that corresponded to Protocadherins were found in vertebrate and invertebrate species This prevalence in a wide range of species suggested that the fragments were part of an ancient cadherin and were thus termed "Protocadherins" as the "first cadherins"; although, of the approximately 70 Pcdh genes identified in mammalian genomes, over 50 are located in tightly linked gene clusters on the same chromosome, and this kind of organization can only be found in vertebrates.
Neural backpropagation is the phenomenon in which after the action potential of a neuron creates a voltage spike down the axon another impulse is generated from the soma and propagates toward to the apical portions of the dendritic arbor or dendrites, from which much of the original input current originated. In addition to active backpropagation of the action potential, there is also passive electrotonic spread. While there is ample evidence to prove the existence of backpropagating action potentials, the function of such action potentials and the extent to which they invade the most distal dendrites remains highly controversial.
In neurophysiology, a dendritic spike refers to an action potential generated in the dendrite of a neuron. Dendrites are branched extensions of a neuron. They receive electrical signals emitted from projecting neurons and transfer these signals to the cell body, or soma. Dendritic signaling has traditionally been viewed as a passive mode of electrical signaling. Unlike its axon counterpart which can generate signals through action potentials, dendrites were believed to only have the ability to propagate electrical signals by physical means: changes in conductance, length, cross sectional area, etc. However, a large body of evidence now makes it clear that dendrites are active neuronal structures. Dendrites contain voltage-gated ion channels giving them the ability to generate action potentials. Dendritic spikes have been recorded in numerous types of neurons in the brain and are thought to have great implications in neuronal communication, memory, and learning. They are one of the major factors in long-term potentiation.
Nonsynaptic plasticity is a form of neuroplasticity that involves modification of ion channel function in the axon, dendrites, and cell body that results in specific changes in the integration of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). Nonsynaptic plasticity is a modification of the intrinsic excitability of the neuron. It interacts with synaptic plasticity, but it is considered a separate entity from synaptic plasticity. Intrinsic modification of the electrical properties of neurons plays a role in many aspects of plasticity from homeostatic plasticity to learning and memory itself. Nonsynaptic plasticity affects synaptic integration, subthreshold propagation, spike generation, and other fundamental mechanisms of neurons at the cellular level. These individual neuronal alterations can result in changes in higher brain function, especially learning and memory. However, as an emerging field in neuroscience, much of the knowledge about nonsynaptic plasticity is uncertain and still requires further investigation to better define its role in brain function and behavior.
Sholl analysis is a method of quantitative analysis commonly used in neuronal studies to characterize the morphological characteristics of an imaged neuron, first used to describe the differences in the visual and motor cortices of cats. Sholl was interested in comparing the morphology of different types of neurons, such as the star-shaped stellate cells and the cone-shaped pyramidal cells, and of different locations in the dendritic field of the same type of neurons, such as basal and apical processes of the pyramidal neuron. He looked at dendritic length and diameter and also the number of cells per volume.
The name granule cell has been used for a number of different types of neuron whose only common feature is that they all have very small cell bodies. Granule cells are found within the granular layer of the cerebellum, the dentate gyrus of the hippocampus, the superficial layer of the dorsal cochlear nucleus, the olfactory bulb, and the cerebral cortex.
An autapse is a chemical or electrical synapse from a neuron onto itself. It can also be described as a synapse formed by the axon of a neuron on its own dendrites, in vivo or in vitro.
