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). 

Tuesday, April 13, 2021

NEURONAL GROWTH FACTORS AND TROPHIC FACTORS

NEURONAL GROWTH FACTORS AND TROPHIC FACTORS


NEURONAL GROWTH FACTORS AND TROPHIC FACTORS

NEURONAL GROWTH FACTORS AND TROPHIC FACTORS
Neuronal growth factors and trophic factors are signal molecules produced by neurons, glia, and target tissues that can influence neuronal differentiation, growth of neurites, establishment of contacts for signaling, maintenance of neural contacts with their central or peripheral targets, and other functions. 

Saturday, April 3, 2021

Motor Control And The Cerebellum

Motor Control And The Cerebellum

Motor Control And The Cerebellum
Motor control
Motor control is defined as the control of movements by the body. These movements can be both influenced and guided by the many sensory inputs that are received, or can be triggered by sensory events. They can also be triggered by the need to move using internal mechanisms. The major division of the body into sensory and motor functions is artificial, because almost all motor areas in the central nervous system (CNS) receive sensory inputs.
The organization and physiology of motor systems have been represented as a number of hierarchical structures, but these must be viewed with caution, as they are again artificial and, by necessity, oversimplified.
Motor Control And The Cerebellum
        Figure 59a shows the major ascending sensory inputs and descending motor outputs, and Figure 59b shows the main looped pathways within the CNS.

Tuesday, March 9, 2021

FRONTOTEMPORAL DEMENTIA

FRONTOTEMPORAL DEMENTIA

FRONTOTEMPORAL DEMENTIA

Frontotemporal dementia (FTD) is a heterogeneous spectrum of disorders marked by degeneration in the frontal and anterior temporal lobes, resulting in various symptoms of disturbed personality, behavior, and language. FTD is the third most common form of neuro- degenerative dementia, ranking after Alzheimer disease and dementia with Lewy bodies, accounting for perhaps 5% of all dementia cases. FTD generally presents at a younger age than Alzheimer disease and has a mean age at onset of 58 years.

DEMENTIA WITH LEWY BODIES

DEMENTIA WITH LEWY BODIES

DEMENTIA WITH LEWY BODIES

Dementia with Lewy bodies (DLB) is the second most common cause of dementia, accounting for 10% to 15% of dementia cases. The pathologic hallmark of DLB is the presence of Lewy bodies in neurons of the brainstem, primarily the substantia nigra, and through-out the cerebral cortex. Lewy bodies are primarily composed of abnormal aggregations of the synaptic protein alpha-synuclein. Interestingly, brain changes of Alzheimer disease (plaques and tangles) frequently co-occur with typical Lewy body pathology.

VASCULAR DEMENTIA

VASCULAR DEMENTIA

VASCULAR DEMENTIA

Vascular dementia is interesting in that many of those who do have a true vascular dementia are not diagnosed with it, while many who probably do not have a vascular dementia are diagnosed with it. The most straightfor-ward presentations are those in which an individual with normal cognition has a large stroke that causes a combination of cognitive signs, such as aphasia and a memory retrieval problem. If the patient cannot resume their prestroke day-to-day level of function because of these new cognitive deficits, the criteria for vascular dementia are met, but because the stroke so clearly caused the deficits, they are held to simply represent the consequences of a stroke (as opposed to a frank vascular dementia). On the other hand, some patients will present with a gradually progressive dementia, a retention-type memory deficit, no motor signs, no history of sensory or motor changes, and a neuroimaging study that shows subcortical changes that could be consistent with “small vessel cerebrovascular disease.” In the elderly, such patients almost always have the plaques and tangles that are expected in Alzheimer disease. In such cases, despite the neuroimaging changes, it is probably more appropriate to consider Alzheimer disease as the primary etiology. Still, the frequent association between Alzheimer disease and cerebrovascular pathology suggests these conditions may be linked in some way.

TREATABLE DEMENTIAS

TREATABLE DEMENTIAS

TREATABLE DEMENTIAS

Although in some ways cognitive performance abilities evolve throughout adulthood, many elderly people remain mentally sharp into their ninth and tenth decades. The emergence of uncharacteristic changes in an individual’s cognition that impacts their usual activities should, therefore, trigger an evaluation for possible etiologies.

Because Alzheimer disease is the most common cause of intellectual decline in later life, symptoms or signs that are unusual in Alzheimer disease should particularly alert the physician to a different diagnosis and the possibility of reversing the dementing process. Such features include early age at onset; prominent headache; disturbances of gait or incontinence early in the course of the illness; epileptic seizures; fever; precipitous decline over a period of weeks or months; alteration of consciousness, especially sleepiness, stupor or delirium; history of head trauma; focal neurologic signs, such as lateralized visual, motor, or sensory abnormalities; accompanying dysfunction of peripheral nerves characterized by paresthesias and absent distal reflexes; and known systemic cancer, collagen vascular disease, or endocrinopathy. The presence of any of these features should dictate further evaluation and consideration of the following treatable dementias.

TREATABLE DEMENTIAS


Metabolic Disease with Encephalopathy. When intellectual decline is caused by systemic metabolic disease, there are usually four associated features: diminished alertness; asterixis; a global decrease in mental function, often with a flight of ideas; and variability of intellectual function during the day. The metabolic dysfunction can be either endogenous or exogenous. An endogenous abnormality indicates too much or too little of a substance or metabolite usually found in the body, such as calcium, sodium, thyroid hormone, sugar, and so forth, may be responsible.

ALZHEIMER DISEASE: CLINICAL MANIFESTATIONS, PROGRESSIVE PHASES

ALZHEIMER DISEASE: CLINICAL MANIFESTATIONS, PROGRESSIVE PHASES

ALZHEIMER DISEASE: CLINICAL MANIFESTATIONS, PROGRESSIVE PHASES

The earliest stages of Alzheimer disease are generally marked by cognitive changes in multiple domains of cognition, including memory, executive function, language, and visuospatial function. Of importance, these cognitive changes are often well-compensated, and individuals may still be independent in many activities in the community, and their symptoms may not be readily apparent in casual conversation. Observations from an attentive family member, relative, or friend describing cognitive changes interfering even mildly with the subject’s usual function is a sensitive indicator of the earliest stages of AD.

Thursday, February 18, 2021

PYELOPLASTY AND ENDOPYELOTOMY

PYELOPLASTY AND ENDOPYELOTOMY

PYELOPLASTY AND ENDOPYELOTOMY

A pyeloplasty or endopyelotomy may be performed to treat an obstruction of the ureteropelvic junction (UPJ, see Plate 6-6). A pyeloplasty consists of surgical reconstruction of the UPJ, whereas endopyelotomy consists of intraluminal, endoscopic incision of the obstruction.

ALZHEIMER DISEASE: PATHOLOGY

ALZHEIMER DISEASE: PATHOLOGY

ALZHEIMER DISEASE: PATHOLOGY

Alzheimer disease (AD) is the most common neurodegenerative disorder and affects 10% of people older than age 65 years and nearly 50% of those 85 years and older. The brain affected by AD has gross changes of brain atrophy accompanied by microscopic changes of amyloid plaques and neurofibrillary tangles.

Wednesday, February 17, 2021

NONDOMINANT HEMISPHERE HIGHER CORTICAL DYSFUNCTION

NONDOMINANT HEMISPHERE HIGHER CORTICAL DYSFUNCTION

NONDOMINANT HEMISPHERE HIGHER CORTICAL DYSFUNCTION

When it comes to stroke-induced lateralized deficits, patients with left-sided hemiplegia caused by damage to the nondominant right cerebral hemisphere frequently do not recover as well as patients with similar left hemisphere lesions, despite the fact that they are not aphasic. Return to the work place and previous home and family participation occur less frequently after a stroke causing left-sided hemiplegia. Although disturbances of higher cortical function and behavior in patients with right hemisphere disease are more subtle, they are equally or more functionally disabling than the more obvious aphasia caused by left hemisphere disease. Deficits in right hemisphere disease include the following.

DOMINANT HEMISPHERE LANGUAGE DYSFUNCTION

DOMINANT HEMISPHERE LANGUAGE DYSFUNCTION

DOMINANT HEMISPHERE LANGUAGE DYSFUNCTION

Aphasia, a disorder of language usage and comprehension, should be distinguished from dysarthria, impaired articulation, and mutism, the absence of speech. Usually, the presence of aphasia accurately localizes dysfunction to the cerebral hemisphere concerned with speech.

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