The control systems: nervous and endocrine
Nick Draper, Helen Marshall in Exercise Physiology, 2014
The sub-arachnoid space (between arachnoid and pia maters) is filled with cerebrospinal fluid (CSF) which is a clear liquid produced by the walls of the ventricles within the brain. In addition to acting as a shock absorber, the CSF plays an important role in regulating the extracellular environment of nerve cells, and provides the brain and spinal cord with nutrients and electrolytes. The pia mater, the innermost meningeal layer, sticks to the surface of the brain, following every contour. Blood vessels run along the surface of the pia mater, supplying the brain and spinal cord with nutrients and oxygen. Unique to the brain is the blood-brain barrier, a vital protective mechanism to ensure a stable internal environment is maintained. The majority of capillaries in the brain are surrounded by the blood-brain barrier which functions to separate the general circulation from the neural tissue of the brain. This prevents the free flow of substances into the brain and is effective in protecting the brain from chemicals that might disrupt neural function, or from blood-borne bacterial infections. A basic pattern of the distribution of matter in the CNS exists with slight variation depending on the region of the brain or spinal cord. In general, the central cavity is surrounded by grey matter with white matter lying externally. A slight variation on this is found in the cerebellum where an outer layer of gray matter exists which is known as the cortex. The grey matter contains neuronal cell bodies and their dendrites, whereas the white matter consists of myelinated neurons.
Biological Basis of Behavior
Mohamed Ahmed Abd El-Hay in Understanding Psychology for Medicine and Nursing, 2019
Glial cells or glia play a supporting role for nervous tissue. Neurons are composed of: (1) a cell body that contains the nucleus and most of the cell’s biosynthetic machinery and keeps the cell alive; (2) branching tree-like fibers called dendrites, which extend from the cell body, collect information from other cells and send the information to the cell body; (3) an axon, which transmits information away from the cell body to other neurons or to the muscles and glands; and (4) specialized regions, at the end of axons, called synaptic buttons or synaptic endings, where communication with other nerve cells or special effector tissues (such as gland or muscle cells) is carried out (Figure 5.2). Neurons are differentiated according to their function into sensory and afferent neurons that carry information from the sensory receptors, and motor or efferent neurons that transmit information to the muscles and glands. Interneurons are the most common type of neurons, and are located primarily within the central nervous system (CNS) and are responsible for communication among the neurons. Interneurons allow the brain to combine the multiple sources of available information to create a coherent picture of the sensory information being conveyed. The human nervous system is organized into the CNS and the peripheral nervous system (PNS). The CNS includes the brain and the spinal cord. There are two general types of tissue in the CNS: gray matter and white matter. Gray matter consists of nerve cell bodies, dendrites, and axons. Neurons in gray matter organize either in layers, as in the cerebral cortex, or as clusters called nuclei. White matter consists mostly of axons, causing it to look white due to the myelin sheathing of the axons. The three major components of the brain are the cerebrum, the cerebellum, and the brain stem.
The cerebrum is divided into right and left hemispheres: each is composed of four major sections called lobes—the frontal, temporal, parietal, and occipital lobe—each separated by folds known as fissures.
The cerebral cortex is the outside portion of the cerebrum.
Deep in the cortex is the cerebral white matter.
The white matter provides communication between the cortex and lower central nervous system centers.
The two cerebral hemispheres are connected by the corpus callosum, the anterior commissure, the hippocampal commissure, and the habenular commissure.
Studying the brain structure and functions can be achieved by the following means:
Studying the brains of cadavers to discover brain structures.
These studies are limited as the brain is no longer active.
Lesion studies: the effects of lesions on different brain regions are informative about possible functions of those regions.
The brain
Nan Stalker in Pain Control, 2018
White matter consists of nerve fibres running to, from and between the cells of the cortex. Motor fibres run from the motor centres of the cortex out through the base of the brain into the spinal cord, carrying impulses from the brain. Sensory fibres run in from the base of the brain to the sensory centres of the cortex. These carry impulses to the cerebral nerve centres. Association or connector fibres run from one nerve centre to another and from hemisphere to hemisphere linking them to one another, so that the various centres of the brain can work as a whole and communicate with one another. A mass of connector neurones made up of fibres linking the two hemispheres form a bridge-like structure at the base of the fissure which separates the hemispheres from one another: this is called the corpus callosum. Returning to our telephone exchange analogy from Session One, the nerve endings not only receive messages, they also store them so that they can be recalled, giving rise to memory, and can be used as a guide to the action to be taken when a similar stimulus is received again. Nerve fibres run towards a point at the centre of the base of the cerebrum, where they form stalks which pass to the midbrain. Between them in the base of the cerebrum is a small cavity — the third ventricle — into which the lateral ventricles lead. There is also a small amount of grey matter, which consists almost entirely of sensory cells. These cells receive the stimuli which are being brought into the brain by the afferent nerve fibres, and relay the stimuli on via fresh neurones to the nerve centres of the cortex.
Fragile X tremor ataxia syndrome and white matter dementia
Published in The Clinical Neuropsychologist, 2016
Objective: Fragile X tremor ataxia syndrome (FXTAS) is an inherited neurodegenerative disease in which dementia is common and disabling. The pathogenesis of dementia in FXTAS is poorly understood, but the salience of executive dysfunction and slowed processing speed, the frequent presence of the middle cerebellar peduncle sign on magnetic resonance imaging (MRI), and striking neuropathological alterations of white matter all suggest that myelinated tracts are significantly involved. This paper considers the role of white matter disease in FXTAS dementia, particularly with regard to the concept of white matter dementia (WMD). Method: A focused review of FXTAS in relation to known white matter disorders is provided to propose that the concept of WMD may illuminate the basis of dementia in FXTAS. The putative pathogenetic contribution of white matter involvement in other neurodegenerative diseases is also considered. Results: Considerable evidence supports the importance of white matter disease in the pathogenesis of dementia in FXTAS. Whereas, gray matter regions are also involved, white matter degeneration is prominent, even early in the disease, and correlates with executive dysfunction and slowed processing speed. Evidence for white matter involvement in other neurodegenerative diseases lends additional support to the relevance of white matter in FXTAS. Conclusion: The dementia of FXTAS is closely related to the profile of WMD, and white matter involvement is also supported by MRI and neuropathological observations. White matter pathology is also relevant to the pathogenesis of other neurodegenerative diseases. Further study of white matter promises to clarify the origin of dementia in FXTAS.
White Matter in Aging and Cognition: A Cross-Sectional Study of Microstructure in Adults Aged Eighteen to Eighty-Three
Published in Developmental Neuropsychology, 2010
Barbara Bendlin, Michele Fitzgerald, Michele Ries, Guofan Xu, Erik Kastman, Brent Thiel, Howard Rowley, Mariana Lazar, Andrew Alexander, Sterling Johnson
Structural brain change and concomitant cognitive decline are the seemingly unavoidable escorts of aging. Despite accumulating studies detailing the effects of age on the brain and cognition, the relationship between white matter features and cognitive function in aging have only recently received attention and remain incompletely understood. White matter microstructure can be measured with diffusion tensor imaging (DTI), but whether DTI can provide unique information on brain aging that is not explained by white matter volume is not known. In the current study, the relationship between white matter microstructure, age, and neuropsychological function was assessed using DTI in a statistical framework that employed white matter volume as a voxel-wise covariate in a sample of 120 healthy adults across a broad age range (18–83). Memory function and executive function were modestly correlated with the DTI measures while processing speed showed the greatest extent of correlation. The results suggest that age-related white matter alterations underlie age-related declines in cognitive function. Mean diffusivity and fractional anisotropy in several white matter brain regions exhibited a nonlinear relationship with age, while white matter volume showed a primarily linear relationship with age. The complex relationships between cognition, white matter microstructure, and white matter volume still require further investigation.
Correlation between pyramidal tract degeneration and widespread white matter involvement in amyotrophic lateral sclerosis: A study with tractography and diffusion-tensor imaging
Published in Amyotrophic Lateral Sclerosis, 2009
Joe Senda, Mizuki Ito, Hirohisa Watanabe, Naoki Atsuta, Yoshinari Kawai, Masahisa Katsuno, Fumiaki Tanaka, Shinji Naganawa, Hiroshi Fukatsu, Gen Sobue
Our aim was to evaluate the location and extent of white matter involvement in patients with amyotrophic lateral sclerosis (ALS) using diffusion-tensor magnetic resonance imaging (DTI). We obtained fractional anisotropy (FA) values from the internal capsule and various white matter regions of 46 patients with sporadic ALS and 19 control subjects. In ALS patients, FA values in the internal capsule, frontal white matter, genu and splenium of the corpus callosum (p<0.001), parietal and temporal lobe white matter, and posterior cingulum (p<0.05) were significantly lower than in controls. FA values in frontal white matter were lower than in parietal white matter (p<0.001). Decreased FA values in frontal, parietal, and temporal white matter, and the genu of the corpus callosum, correlated significantly with those in the internal capsule (r=0.66 and p<0.001, r=0.47 and p=0.001, r=0.33 and p=0.021, r=0.41 and p=0.005, respectively). No such correlations were found for FA values in other white matter areas or in controls. Patient FA values generally were not correlated with disease duration. DTI demonstrated more widespread involvement of the cerebral white matter in ALS patients than previously believed. The severity of involvement in the frontal, temporal and parietal white matter correlated with severity in the pyramidal tract.
Related Knowledge Centers
- Cerebrum
- Lipid
- Myelin
- Magnetic Resonance Imaging
- Central Nervous System
- Axon
- Neuroglia