pediagenosis: Nervous
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Showing posts with label Nervous. Show all posts
Showing posts with label Nervous. Show all posts

Wednesday, April 28, 2021

NEURONAL STRUCTURE

NEURONAL STRUCTURE


NEURONAL STRUCTURE
Neuronal structure reflects the functional characteristics of the individual neuron. Incoming information is projected to a neuron mainly through axonal terminations on the cell body and dendrites. These synapses are isolated and are protected by astrocytic processes. The dendrites usually make up the greatest surface area of the neuron. Some protrusions from dendritic branches (dendritic spines) are sites of specific axodendritic synapses. 
NEURONAL STRUCTURE

Each specific neuronal type has a characteristic dendritic branching pattern called the dendritic tree, or dendritic arborizations. The neuronal cell body varies from a few micrometers (µm) in diameter to more than 100 µm. The neuronal cytoplasm contains extensive rough endoplasmic reticulum (rough ER), reflecting the massive amount of protein synthesis necessary to maintain the neuron and its processes. The Golgi apparatus is involved in packaging potential signal molecules for transport and release. Large numbers of mitochondria are necessary to meet the huge energy demands of neurons, particularly those related to the maintenance of ion pumps and membrane potentials. Each neuron has a single (or occasionally no) axon, usually emerging from the cell body or occasionally from a dendrite (e.g., some hip- pocampal CA neurons). The cell body tapers to the axon at the axon hillock, followed by the initial segment of the axon, which contains the Na+ channels, the first site where action potentials are initiated. The axon extends for a variable distance from the cell body (up to 1 m or more). An axon larger than 1 to 2 µm in diameter is insulated by a sheath of myelin provided by oligodendroglia in the central nervous system (CNS) or Schwann cells in the peripheral nervous system (PNS). An axon may branch into more than 500,000 axon terminals, and may terminate in a highly localized and circumscribed zone (e.g., primary somatosensory axon projections used for fine discriminative touch) or may branch to many disparate regions of the brain (e.g., noradrenergic axonal projections of the locus coeruleus). A neuron whose axon terminates at a distance from its cell body and dendritic tree is called a macroneuron or a Golgi type I neuron; a neuron whose axon terminates locally, close to its cell body and dendritic tree, is called a microneuron, a Golgi type II neuron, a local circuit neuron, or an interneuron. There is no typical neuron because each type of neuron has its own specialization. However, pyramidal cells and lower motor neurons are commonly used to portray a so-called typical neuron.
TYPES OF SYNAPSES

TYPES OF SYNAPSES


TYPES OF SYNAPSES
A synapse is a site where an arriving action potential, through excitation-secretion coupling involving Ca2+ influx, triggers the release of one or more neurotransmitters into the synaptic cleft (typically 20 µm across). 
TYPES OF SYNAPSES
The neurotransmitter acts on receptors on the target neuronal membrane, altering the membrane potential  from  its  resting state. These  postsynaptic potentials are called graded potentials. Most synapses carrying information toward a target neuron terminate as axodendritic or axosomatic synapses. Specialized synapses, such as reciprocal synapses or complex arrays of synaptic interactions, provide specific regulatory control over the excitability of their target neurons. Dendrodendritic synapses aid in the coordinated firing of groups of related neurons such as the phrenic nucleus neurons that cause contraction of the diaphragm.
NEURONAL CELL TYPES

NEURONAL CELL TYPES


NEURONAL CELL TYPES
Local interneurons and projection neurons demonstrate characteristic size, dendritic arborizations, and axonal projections. In the CNS (denoted by dashed lines), glial cells (astrocytes, microglia, oligodendroglia) provide support, protection, and maintenance of neurons. Schwann cells and satellite cells provide these functions in the PNS. 
NEURONAL CELL TYPES
The primary sensory neurons (blue) provide sensory transduction of incoming energy or stimuli into electrical signals that are carried into the CNS. The neuronal outflow from the CNS is motor (red) to skeletal muscle fibers via neuromuscular junctions, or is autonomic preganglionic (red) to autonomic ganglia, whose neurons innervate cardiac muscle, smooth muscle, secretory glands, metabolic cells, or cells of the immune system. Neurons other than primary sensory neurons, LMNs, and preganglionic autonomic neurons are located in the CNS in the brain (enclosed by upper dashed lines) or spinal cord (enclosed by lower dashed lines). Neurons and glia are not drawn to scale.

Wednesday, April 14, 2021

3D NEURONAL STRUCTURE AND NEUROHISTOLOGY

3D NEURONAL STRUCTURE AND NEUROHISTOLOGY


3D NEURONAL STRUCTURE AND NEUROHISTOLOGY
3D NEURONAL STRUCTURE AND NEUROHISTOLOGY
        A. Spinal cord lower motor neuron. Nissl substance (rough endoplasmic reticulum) stains purple. The nucleolus is stained in the clear nucleus. Cresyl violet stain.
B.Cerebellar Purkinje neurons. Large dendrites branch from the cell body. Intraneuronal neurofibrils and background neural processes (neuropil) stain densely. Silver stain.
GLIAL CELL TYPES

GLIAL CELL TYPES


GLIAL CELL TYPES
Astrocytes provide structural isolation of neurons and their synapses and provide ionic (K+) sequestration, trophic support, and support for growth and signaling functions to neurons. Oligodendroglia (oligodendrocytes) provide myelination of axons in the CNS.
ASTROCYTE BIOLOGY

ASTROCYTE BIOLOGY


ASTROCYTE BIOLOGY
Astrocytes are the most abundant glial cells in the CNS. They arise from neuroectoderm and are intimately associated with neural processes, synapses, vasculature, and the pial-glial membrane investing the CNS. Astrocytes in gray matter are called protoplasmic astrocytes, and in white matter they are called fibrous astrocytes.
MICROGLIAL BIOLOGY

MICROGLIAL BIOLOGY


MICROGLIAL BIOLOGY
MICROGLIAL BIOLOGY
Microglial cells are mesenchymal cells derived from yolk sac that come to reside in the CNS. They are a unique resident population with the capacity for self-renewal. Microglia provide constant surveillance of the local microenvironment, moving back and forth up to 1.5 µm/min. Microglial processes can grow and shrink up to 2-3 µm/min. They have a territory 15-30 µm wide, with little overlap with each other. Resting microglia have soma of 5-6 µm diameter, and activated microglia are ameboid in appearance, with soma of approximately 10 µm diameter.
OLIGODENDROCYTE BIOLOGY

OLIGODENDROCYTE BIOLOGY


OLIGODENDROCYTE BIOLOGY
OLIGODENDROCYTE BIOLOGY
Oligodendrocytes are neuroectodermally derived glial cells that have the major role of myelinating central axons. The trigger for myelination may include associated axonal size and signal molecules (such as ATP, K+, glutamate, GABA, and some cell adhesion molecules). 

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