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

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.

AMNESIA

AMNESIA

AMNESIA

The term “amnesia” is used generally to describe impairment or loss of memory. It is often subclassified as being either retrograde or anterograde. With retro- grade amnesia, memories that had previously been stored are no longer available. With anterograde amnesia, information occurring in real time does not enter long-term storage. Memory is a complex process comprising three different functions: (1) registration of information, (2) storage by reinforcement, and (3) retrieval.

MEMORY CIRCUITS

MEMORY CIRCUITS

MEMORY CIRCUITS

Long-term memory is a term that encapsulates the brain’s ability to store information. It is subdivided into two main types: explicit memory (also known as declarative memory) and implicit memory (also known as nondeclarative memory). Explicit memory refers to the acquisition of information about objects, stimuli, and information that is consciously noted and recallable. The mesial temporal lobe, which includes the hippocampal formation (CA1, CA3, and dentate gyrus) and ento- rhinal cortex, is the region responsible for this process. While the hippocampal formation stores memories, the entorhinal cortex mediates learning and memory via its interaction with the hippocampus and neocortex. For instance, neocortical information from a visual stimulus is translated via the entorhinal cortex to higher-order complex memory representations such that an emotion can trigger a visual memory. Layer II of the entorhinal cortex is the first region affected in Alzheimer disease (AD). The memory circuit that integrates the mesial temporal lobe and hippocampal formation includes several pathways: the perforant pathway (input to the hippocampus from the entorhinal cortex), Mossy fiber pathway (dentate gyrus to CA3 region), Schaffer collateral/associational commissural pathway (from CA3 to CA1 region), and CA1-subiculum-entorhinal cortex pathway (the principal output of the hippocampus).

TESTING FOR DEFECTS OF HIGHER CORTICAL FUNCTION

TESTING FOR DEFECTS OF HIGHER CORTICAL FUNCTION

TESTING FOR DEFECTS OF HIGHER CORTICAL FUNCTION

It is useful to test functions that can be localized to individual brain regions because abnormalities on these tests can help localize a neuroanatomic defect and thereby suggest a specific etiology. Screening for disorders of higher cortical function can be completed within the context of an office visit, whereas extensive examinations can take up to several hours.

ASTROCYTES

ASTROCYTES

ASTROCYTES

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 provide myelination of axons in the CNS. Microglia are scavenger cells that participate in phagocytosis, inflammatory responses, cytokine and growth factor secretion, and some immune reactivity in the CNS. Perivascular cells participate in similar activities at sites near the blood vessels. Schwann cells provide myelination, ensheathment, trophic support, and actions that contribute to the growth and repair of peripheral neurons. Activated T lymphocytes normally can enter and traverse the CNS for immune surveillance for a period of approximately 24 hours.

Friday, February 12, 2021

SUMMATION OF EXCITATION AND INHIBITION

SUMMATION OF EXCITATION AND INHIBITION

SUMMATION OF EXCITATION AND INHIBITION

Summation of excitation and inhibition is the vital principle on which the functioning of the CNS is based. The illustration shows the various intracellular potential changes observed during temporal and spatial summation of excitation and inhibition, as voltage- versus-time tracings similar to those produced by an oscilloscope.

CHEMICAL SYNAPTIC TRANSMISSION

CHEMICAL SYNAPTIC TRANSMISSION

CHEMICAL SYNAPTIC TRANSMISSION

Chemical synaptic transmission proceeds in three steps: (1) The release of the transmitter substance from the bouton in response to the arrival of an action potential, (2) The change in the ionic permeabilities of the post-synaptic membrane caused by the transmitter, and  (3) the removal of the transmitter from the synaptic cleft. Depending on the type of permeability changes produced in the second step, synaptic activation may have either an excitatory or an inhibitory effect on the post-synaptic cell.

NEURONAL STRUCTURE AND SYNAPSES

NEURONAL STRUCTURE AND SYNAPSES

NEURONAL STRUCTURE AND SYNAPSES

NEURONAL STRUCTURE

A typical neuron of the central nervous system consists of three parts: dendritic tree, cell body (soma), and axon. The highly branched dendritic tree has a much greater surface area than the remainder of the neuron and is the receptive part of the cell. Incoming synaptic terminals make contact directly with the dendritic surface or with the small spines (gemmules) that protrude from it. The membrane potential induced in the dendrites spreads passively onto the cell soma, which allows all inputs acting on the neuron to summate in controlling the rate of neuronal discharge through the axon.

THALAMOCORTICAL RADIATIONS

THALAMOCORTICAL RADIATIONS

THALAMOCORTICAL RADIATIONS

All pathways carrying information from the periphery or the brainstem to the neocortex relay in the nuclei of the posterior thalamus. These nuclei can be divided into two groups on the basis of their structure, connections, and function.

FOREBRAIN REGIONS ASSOCIATED WITH HYPOTHALAMUS

FOREBRAIN REGIONS ASSOCIATED WITH HYPOTHALAMUS

FOREBRAIN REGIONS ASSOCIATED WITH HYPOTHALAMUS

The cerebral cortex influences the “autonomic” neurovisceral outflow and the neurohumoral output of the endocrine glands, as can be demonstrated experimentally by stimulating the orbitofrontal cortex of the cingulate gyrus to produce respiratory, cardiovascular, and digestive responses, as well as certain emotional reactions. The responses are less marked than those produced by stimulating the hypothalamus but are still striking; some of them, moreover, do not depend upon the integrity of the hypothalamus, a fact that suggests mediation by corticoreticular fibers to lower “centers.” In humans, subjective emotional experiences are associated with autonomic discharges (e.g., tachycardia, increased blood pressure, blushing) and changes in endocrine activity (e.g., stress-induced amenorrhea or anorexia nervosa).

AMYGDALA

AMYGDALA

AMYGDALA

The amygdala is an almond-shaped complex located in the medial temporal lobe, and contains approximately 13 nuclei. The three main regions are the corticomedial nuclei, basolateral nuclei (both receive afferents and project axons to target structures), and central nucleus (which provides mainly efferent projections to the brainstem). Afferent connections to the amygdala originate from cortical and thalamic areas, and hypothalamic and brainstem areas. Its function is to provide emotional relevance to external and internal sensory information and to provide a behavioral and emotional response, particularly a fearful and aversive response, to a sensory input.

Friday, February 5, 2021

FORNIX

FORNIX

FORNIX

The fornix is an almost circular arrangement of white fibers conveying the great majority of the hippocampal efferents to the hypothalamus and carrying commissural fibers to the opposite hippocampus and habenular trigone. The fornix rises out of the fimbria of the hippocampus, which turns upward beneath the splenium of the corpus callosum and above the thalamus to form the crura (posterior columns) of the fornix. Anterior to the commissure of the fornix, the two crura unite for a variable distance in the midline and create the triangular body of the fornix. The free lateral edges of the fornix help to bind the choroid fissure, through which the pia mater of the telachoroidea becomes invaginated into the lateral ventricles.

HIPPOCAMPUS

HIPPOCAMPUS

HIPPOCAMPUS

Hippocampal Formation. The hippocampus, the posterior part of the dentate gyrus and the indusium griseum are sometimes grouped together as the hippocampal formation. In humans, the attenuated gray and white structures of this formation are produced by the enormous enlargement of the corpus callosum, which encroaches upon the parahippocampal and dentate gyri and the hippocampi, thus expanding them. The hippocampus is a part of the marginal cortex of the parahippocampal gyrus that has been invaginated, or rolled, into the floor of the inferior horn of the lateral ventricle by the exuberant growth of the nearby temporal cortex. The curved hippocampal eminence is composed mostly of gray matter, and its anterior end is expanded and grooved like a paw, the pes hippocampi. Axons conveying efferent impulses from the pyramidal cells of the hippocampus form a white layer on its surface, the alveus, and then converge toward its medial edge to form a white strip, the fimbria. The hippocampus is an important part of the olfactory apparatus in lower animals; in humans, few or no secondary olfactory fibers end in it. However, it possesses substantial connections with the hypothalamus, which regulates many visceral activities that influence emotional behavior and with temporal lobe areas reputedly associated with memory.

RHINENCEPHALON AND LIMBIC SYSTEM

RHINENCEPHALON AND LIMBIC SYSTEM

RHINENCEPHALON AND LIMBIC SYSTEM

The rhinencephalon is a term that describes quite literally the “nose” or “smell” regions of the brain. The limbic system refers to the structures and tracts involved with emotion, including memory formation, as well as autonomic and endocrine response to emotional stimuli. The terms rhinencephalon and limbic system are sometimes used synonymously, but the rhinencephalon refers to olfactory structures and related pathways. Located in the medial and inferior surface of the forebrain, these parts include the olfactory bulb, tract and striae, the anterior perforated substance, the uncus, the hippocampus, the dentate gyrus, the gyrus fasciolaris, the indusium griseum, the habenular trigone, the subcallosal area, the paraterminal gyrus, the fornix, and the amygdaloid body as direct olfactory afferents project to the amygdala. The olfactory pathway is described and illustrated in Plate 5-8.

CORPUS CALLOSUM

CORPUS CALLOSUM

CORPUS CALLOSUM

The corpus callosum is the major commissure of the forebrain, connecting homologous cortical regions of the two cerebral hemispheres. The corpus callosum is divided into anterior and posterior parts, known as the genu and splenium, respectively. The genu includes fibers of the frontal forceps (forceps minor) interconnecting frontal areas. Posteriorly, the splenium includes the occipital forceps (forceps major), interconnecting the parietal, occipital, and temporal lobes. A corpus callosotomy, a surgical lesioning of the corpus callosum, has been performed in patients with medication-refractory epilepsy. The goal of this surgery is to prevent seizure spread from one hemisphere to another. Agenesis of the corpus callosum (ACC) is a congenital birth defect characterized by an absence of a corpus callosum. This condition can occur in isolation (with little to no impact on cognitive performance) or can occur as part of abnormalities such as Dandy-Walker syndrome, Arnold-Chiari malformation, schizencephaly, holoprosencephaly, Andermann syndrome, or Aicardi syndrome (a syndrome more commonly seen in females). Midline facial defects often accompany ACC.

CORTICOCORTICAL AND SUBCORTICOCORTICAL PROJECTION CIRCUITS

CORTICOCORTICAL AND SUBCORTICOCORTICAL PROJECTION CIRCUITS

CORTICOCORTICAL AND SUBCORTICOCORTICAL PROJECTION CIRCUITS

The cerebral white matter consists of myelinated axons that link cortical areas with both cortical and subcortical regions. There exist three main categories of efferent fibers from a cortical area: association fibers, striatal fibers, and commissural/subcortical fibers. Corticocortical projections allow both adjacent and distant cortical regions to communicate, whereas corticosubcortical projections allow reciprocal communication between cortical regions and subcortical structures. These subcorticocortical projections connect the cortex to the thalamus, the pontocerebellar system, brainstem, and spinal cord.

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