Major Limbic Forebrain Structures

Major Limbic Forebrain Structures

pediagenosis    April 04, 2023   

The term limbic is derived from limbus, meaning ring. Many of these structures and their pathways in the limbic system form a ring around the diencephalon. They are involved in emotional behavior and individualized interpretations of external and internal stimuli. The hippocampal formation and its major pathway, the fornix, curve into the anterior pole of the diencephalon, forming precommissural (to the septum) and postcommissural (to the hypothalamus) connections in relation to the anterior commissure. The amygdaloid nuclei give rise to several pathways; one, the stria terminalis, extends in a C-shaped course around the diencephalon into the hypothalamus and basal forebrain. The olfactory tract communicates directly with several limbic forebrain areas; it is the only sensory system to entirely bypass the thalamus and terminate directly in cortical and subcortical zones of the telencephalon. Connections from the septal nuclei to the habenula (stria medullaris thalami) connect the limbic forebrain to the brain stem. The amygdaloid nuclei and hippocampus (shaded) are deep to the cortex.

Horizontal Brain Sections Showing The Basal Ganglia

Horizontal Brain Sections Showing The Basal Ganglia

pediagenosis    April 04, 2023   

Two levels of horizontal sections through the forebrain reveal the major anatomical features and the relationships among the basal ganglia, the internal capsule, and the thalamus (schematically shown in the lower illustration). The caudate nucleus is a C-shaped structure that sweeps from the frontal lobe into the temporal lobe; a horizontal section passes through this nucleus in two distinct places (head and tail). The anterior limb, genu, and posterior limb of the internal capsule contain major connections into and out of the cerebral cortex. The head and body of the caudate are medial to the anterior limb, whereas the thalamus is medial to the posterior limb. These relationships are important for understanding imaging studies and for understanding the involvement of specific functional systems in vascular lesions or strokes. The internal and external segments of the globus pallidus are located medial to the putamen. The external capsule, claustrum, extreme capsule, and insular cortex, from medial to lateral, are located lateral to the putamen. The fornix, also a C-shaped bundle, is sectioned in two sites, the crus and the column.

SCURVY

SCURVY

pediagenosis    April 03, 2023    Comment   

DIETARY SOURCES OF VITAMIN C AND CLASSIC CUTANEOUS MANIFESTATIONS OF SCURVY

Scurvy is a well-known nutritional disease that results from a lack of the water-soluble vitamin, ascorbic acid (vitamin C). Scurvy has a well-documented history. It was first recognized in the fourteenth century in sailors who spent long amounts of time at sea. The symptoms were recognized as being related to a lack of fresh foods, especially citrus products. In 1753, James Lind, a British surgeon aboard the HMS Salisbury, performed the first documented clinical trial proving that scurvy was caused by a lack of citrus fruit in the diet of sailors. After Lind’s discovery, citrus fruits were included in ships’ provisions, and the incidence of scurvy in sailors plummeted. It was not until 1928 that ascorbic acid was isolated by the Hungarian chemist, Albert von Szent-Grörgyi, who was eventually awarded the Nobel Prize for this discovery. Scurvy is still present in some areas of the world due to inadequate dietary intake of vitamin C. Scurvy is uncommon in North America but can be seen in individuals with abnormal diets.

PHENYLKETONURIA

PHENYLKETONURIA

pediagenosis    April 03, 2023   

 

NORMAL AND ABNORMAL METABOLISM OF PHENYLALANINE

Phenylalanine is an essential amino acid that serves as a substrate for many different biochemical pathways. Two end products that use phenylalanine as their precursors are melanin and epinephrine. Under normal physiological and biochemical environments, any excess amount of phenylalanine is converted into tyrosine by the liver and used for a host of biochemical processes including protein synthesis. In patients with phenylketonuria, the enzyme in the liver that converts phenylalanine into tyrosine is completely absent. This inborn error of metabolism is one of the most thoroughly researched disease states. With early detection and therapy, the severe sequelae of phenylketonuria can be avoided. Screening is performed soon after birth for all children in the United States and in most of the world. Children born in regions with poor medical infrastructure and no testing are at risk for the disease. Once the disease symptoms have appeared, therapy usually cannot reverse the damage that has been done. Phenyl-ketonuria is inherited in an autosomal recessive manner, but many genotypes have been described, and many mutations in the responsible gene have been reported. The defect is located on the long arm of chromosome 12, where the PAH gene encodes the protein, phenylalanine hydroxylase.

Immunity To Worms

Immunity To Worms

pediagenosis    March 26, 2023   

Immunity To Worms

Parasitic worms of all three classes (roundworms, tapeworms and flukes) are responsible for numerous human diseases, including three of the most unpleasant (upper left): onchocerciasis, elephantiasis and schistosomiasis. These worms are transmitted with the aid of specific insect or snail vectors, and are restricted to the tropics, while the remainder (lower left) can be picked up anywhere by eating food contaminated with their eggs, larvae or cysts. A feature of many worm infections is their complex life cycles and circuitous migratory patterns, during which they often take up residence in a particular organ (see figure).

Large Intestine

Large Intestine

pediagenosis    March 26, 2023    Comment   

Large Intestine

The large intestine comprises the caecum, ascending, transverse, descending and sigmoid colon, rectum and anal canal (Fig. 41a). It is approximately 1.2 m in length and between 6 and 9 cm in diameter. Approximately 1.5 L of chyme enters the large intestine per day through a sphincter called the ileocaecal sphincter. Distension of the terminal ileum results in the opening of the sphincter and distension of the caecum causes it to close, thereby maintaining the optimum rate of entry to maximize the main function of the large intestine, which is to absorb most of the water and electrolytes. The initial 1.5 L is reduced to about 150 g of faeces consisting of 100 mL of water and 50 g of solids.

Genetic Imprinting

Genetic Imprinting

pediagenosis    March 26, 2023    Comment   

Genetic Imprinting

Besides autosomal and sex-linked genes and mitochondrial inheritance, it was found that certain genes exhibit a “parent of origin” type of transmission in which the parental genomes do not always contribute equally in the development of a person (Fig. 6.10). The transmission of this phenomenon is called genetic imprinting. Although rare, it is estimated  that  approximately  100  genes  exhibit  genetic imprinting. Evidence suggests a genetic conflict occurs in the developing embryo: the male genome attempts to establish larger offspring, whereas the female prefers smaller off-spring to conserve her energy for the current and subsequent pregnancies.

Pedigree

Pedigree

pediagenosis    March 26, 2023   

Pedigree

A pedigree is a graphic method (see Figs. 6.10 and 6.11) for portraying a family history of an inherited trait. It is constructed from a carefully obtained family history and is useful for tracing the pattern of inheritance for a particular trait.

Cells Of The Nervous System I Neurones

Cells Of The Nervous System I Neurones

pediagenosis    March 23, 2023   

Cells Of The Nervous System I: Neurones

There are two major classes of cells in the nervous system: the neuroglial cells and neurones, with the latter making up only 10– 20% of the whole population. The neurones are specialized for excitation and nerve impulse conduction (see Chapters 14, 15 and 17), and communicate with each other by means of the synapse (see Chapter 16) and so act as the structural and functional unit of the nervous system.

Membrane Potentials

Membrane Potentials

pediagenosis    March 23, 2023   

Membrane Potentials

Electrochemical potentials are present across the membranes of virtually all cells in the body. Some cells, such as nerve and muscle cells, are capable of generating rapidly changing electrical impulses, and these impulses are used to transmit signals along their membranes. In other cells, such as glandular cells, membrane potentials are used to signal the release of hormones or activate other functions of the cell. Generation of membrane potentials relies on (1) diffusion of current-carrying ions, (2) development of an electrochemical equilibrium, (3) establishment of a RMP, and (4) triggering of action potentials.