Spinal cord composition

Figure 11.10 Glycine receptor pharmacology and structure, (a) Amino acids that act as agonists at glycine receptors, and strychnine a competitive antagonist, (b) Subunit composition of foetal and adult glycine receptors in the spinal cord. The receptors are shown with a pentameric assembly but the a. and subunits are distinct from those that form GABAa receptors. Picrotoxin is also an effective glycine antagonist and in recombinant systems is selective for homomeric receptors...

Lamina VI forms the base of the dorsal horn and can be found only in certain levels of the spinal cord, the cervical and lumbar regions. Few data have been reported on the cell composition of lamina VI. Cells of lamina VI are small compared to those of lamina V and some axons appear to contribute to the STT and SCT pathways. 

The data in Table 4-1 indicate that myelin accounts for much of the total lipid of white matter, and that the lipid composition of gray matter is quite different from that of myelin. The composition of brain myelin from all mammalian species studied is very much the same. There are, however, some species differences for example, myelin of rat has less sphingomyelin than does that of bovine or human (Table 4-1). Although not shown in the table, there are also regional variations for example, myelin isolated from the spinal cord has a higher lipid-to-protein ratio than brain myelin from the same species. 

Neurokinin A and B are both decapeptides discovered by Kimura et al. (142) from the porcine spinal cord. Both have very similar amino acid composition and sequence homology to the undecapeptide substance P, and they also have similar biological activities as substance P. They are potent bronchoconstrictors, constrict smooth muscle, and activate the micturition reflex. 

The motor unit has four components a motor neuron in the brain or spinal cord, its axon and related axons that comprise the peripheral nerve, the neuromuscular junction, and all the muscle fibers activated by the neuron. Like other cells, nerve and muscle cells have an external membrane that separates the inner fluids from those on the outside. The fluid on the inside is rich in potassium (K), magnesium (Mg), and phosphorus (P), whereas the fluid on the outside contains sodium (Na), calcium (Ca), and chloride (Cl). When all is quiet, the internal chemical composition of both nerve and muscle cells is remarkably constant and is called resting membrane potential. A primary reason for this constancy lies in the cells ability to regulate the flow of sodium— thanks to an enzyme in the membrane called Na+/K+ ATP-ase. Because the inside of the cell has less sodium than the outside, there is a negative potential (like a microscopic battery) of 70-90 mV. Under ordinary circumstances, the interior of the cell is 30 times richer in potassium than the extracellular fluid and the sodium concentration is 10-12 times greater on the outside of the cell. At rest, sodium tends to flow into cells and potassium oozes out. 

The formulation of parenteral products involves careful consideration of the proposed route of administration and the volume of the injection. Injections are administered to the body by many routes into various layers of the skin, the subcutaneous and muscle tissue, into arteries or veins, into or around the spinal cord, or directly into various organs (e.g., the heart or the eye). The volume to be injected can range from microliters, typically diagnostic agents administered intradermally or insulin administered subcutaneously, to several liters administered intravenously as infusions. The route of administration and the volume to be injected affect the composition of the formulation. 

Studies on spinal cord myelin lipid composition in mouse model of ALS indicate that levels of lipids, phospholipids, cholesterol, and cerebrosides are decreased compared to wild-type mice (Table 8.4) (Niebroj-Dobos et al., 2007). Although a progressive decrease in proteolipid, DM-20, and Wolfgram proteins occurs in this ALS model, myelin basic proteins I and n are not affected. Electron microscopy indicates massive myelin disorganization (Niebroj-Dobos et al., 2007). Production... 

Niebroj-Dobos I, Rafalowska J, Fisziariska A, Gadamski R, Grieb P (2007) Myelin composition of spinal cord in a model of amyotrophic lateral sclerosis (ALS) in SOD1G93A transgenic rats. Foha Neuropathol 45 236-241... 

Fetal or neonatal brain prior to myelination contains relatively little cholesterol and in this respect the composition is similar to that of other body tissues. However, during this period before myelin is laid down, microscopic examination shows that small lipid droplets appear in variable number within the nervous tissue. In the human spinal cord droplets appear up to the twenty-second week of fetal life and in the chick embryo up to the sixteenth day of incubation. It would appear from histochemical reactions (Adams and Davison, 1959) that these droplets contain hydro-phobic lipids such as cholesterol esters or triglyceride. Chemical analyses... 

The respiration rate is altered by changes in the chemical composition of the blood, and also as a result of emotional stress or voluntary efforts. Passing from quiet respiration to dyspnea affects different nerves, such as the intercostal nerve. Breathing patterns are controlled by a complex network of neurons connected to efferent fibers chemoreceptors, stretch receptors, pressure receptors. The efferent fibers send impulses to the motor nuclei in the spinal cord, and from there the impulse is transferred to the respiratory muscles. 

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