Anatomic features

To achieve their different effects NTs are not only released from different neurons to act on different receptors but their biochemistry is different. While the mechanism of their release may be similar (Chapter 4) their turnover varies. Most NTs are synthesised from precursors in the axon terminals, stored in vesicles and released by arriving action potentials. Some are subsequently broken down extracellularly, e.g. acetylcholine by cholinesterase, but many, like the amino acids, are taken back into the nerve where they are incorporated into biochemical pathways that may modify their structure initially but ultimately ensure a maintained NT level. Such processes are ideally suited to the fast transmission effected by the amino acids and acetylcholine in some cases (nicotinic), and complements the anatomical features of their neurons and the recepter mechanisms they activate. Further, to ensure the maintenance of function in vital pathways, glutamate and GABA are stored in very high concentrations (10 pmol/mg) just as ACh is at the neuromuscular junction. 

Fig. 4 Diagrammatic sketch of the small intestine illustrating the projection of the villi into the lumen (left) and the anatomic features of a single villus (right). (Modified from Ref. 7.)...

In-depth discussions of the anatomy of the eye and adnexa have been adequately covered elsewhere in the pharmaceutical literature [13-17] and in recent texts on ocular anatomy. Here a brief overview is presented of the critical anatomical features that influence the nature and administration of ophthalmic preparations. In this discussion, consideration will be given primarily to drugs applied topically, that is, onto the cornea or conjunctiva or into the palpebral fornices. Increasingly, drugs are being developed for administration by parenteral-type dosage forms subconjunctivally, into the anterior and posterior chambers, the vitreous chamber, Tenon s capsule, or by retrobulbar injection. 

C. Physiological and Anatomical Features Governing Lung Deposition... 

Compare and contrast anatomical features of the sympathetic and parasympathetic systems... 

Another noteworthy anatomical feature of the arteries is the presence of elastic connective tissue. When the heart contracts and ejects the blood, a portion of the stroke volume flows toward the capillaries. However, much of the stroke volume ejected during systole is retained in the distensible arteries. When the heart relaxes, the arteries recoil and exert pressure on the blood within them, forcing this "stored" blood to flow forward. In this way, a steady flow of blood toward the capillaries is maintained throughout the entire cardiac cycle. 

This evolutionary process by which a phenotypic trait is altered to serve more efficiently as a signal is called ritualization. Commonly, the process begins when some movement, anatomical feature, or physiolog-... 

Theoretical considerations including calculations based on the knowledge of anatomical features. 

Ad. 1. Theoretical considerations including calculations based on the knowledge of anatomical features. While considering whether or not it is reasonable to believe that the non-mono-exponential transverse relaxation reflects an intra- and extra-cellular compartmentalisation, it should be questioned if the slow-exchange assumption is reasonable taking into account the macroscopic features of a muscle cell from a theoretical point of view. The NMR-timescale criterion for exchange limit is comparison of the quantity (rr1 + t"1), where r, and t0 are the average lifetime of a water molecule inside and outside the cell, respectively, with Rt — R , which is the absolute difference in the intrinsic relaxation rates. If R —Rfl > (h 1 + ), the... 

Brownstein and Tarr35 considered if the size of a muscle cell could give rise to non-mono-exponential transverse relaxation by assuming simple diffusion and planar geometry, and found that under these conditions and in the slow diffusion range, multi-exponential transverse relaxation could be expected when the sample size is between 1 and 30 pm. Accordingly, as muscle cells have a diameter of 10-100 pm,36 the calculations performed by Brownstein and Tarr35 indicate that the anatomical features of muscle cells are consistent with the expectation of multi-exponential transverse relaxation. 

Ad. 4. Alteration of anatomical features. Finally, several studies have attempted to manipulate the macroscopic features of muscle/meat tissue in order to verify or disprove the intra-/extra-cellular model. Efforts have been made to disrupt cell membranes by glycerination and DMSO treatment in order to make assessment of the potential role of membranes possible.30,40,41 All these studies showed unaltered relaxation behaviour upon membrane disintegration, which suggests that intact cell membranes in themselves are not necessary for a non-mono-exponential relaxation. Irrelevance of membranes... 

Figure 2.1 Light photomicrographs of wood cross-sections illustrating different anatomical features of softwood and hardwood (a) pine (softwood), (b) birch (diffuse porous hardwood), (c) oak (ring porous hardwood). Scale bar = 200 m.

What happens in the body to consumed food is a matter of primary concern to biochemists. We shall therefore indicate some of the variable anatomical features which bear on this problem. 

Comparatively little definitive data are available with respect to neuroanatomical variations. Some idea of the extent of the variation may be gained, however, from a consideration of Figure 12 in which are depicted eight patterns of the facial nerve. It may be observed that, as among other anatomical features, there is no single pattern (or even two or three patterns) and that there are no set or normal positions for anastomoses. 

Riddle s extensive study (p. 21) which included numerous breeding experiments showed clearly that the endocrines, as well as other anatomical features, of pigeons and doves showed wide inter-individual and interstrain differences. 

Sheldon s extensive classification of body types constitutes an important contribution to the understanding of the human differences which make for susceptibility to numerous diseases. 5 What he has done with body form is just a beginning anatomical features... 

For common preclinical laboratory specimens such as mouse and rat, it is possible to image the skeletal features associated with different developmental stages of serial end-point harvested specimens (Fig. 1). Additionally, with the use of radio-opaque contrast agents, it is possible to image capture the soft tissue features of these specimens (Fig. 2). The combined imaging can be used to illustrate various anatomical features of interest within the same specimen (Fig. 3). This imaging technique therefore has an added potential of conferring multi-modality to an individual micro-CT machine. 

Fig. 3. Skeletal and soft tissue anatomical features can be scrutinized and labeled for compilation purposes. (Left) A rat gestational day 21 (GD21) skeletal specimen, 3D volume rendering. (Middle) fsA PO specimen with on-screen thresholding optimized to detail the skeletal features of inferesf. (Right) The same rat PO specimen, processed for soff fissue visualization, with relevant soft tissue features of inferesf highlighted.

An important anatomical feature of the LC is the rich innervation by afferents from the sensory systems. This puts the LC in the position to monitor the internal and external environments. The widespread LC efferents in turn then lead to an inhibition of spontaneous discharge in the target neurons. Therefore, the LC is thought to be crucial for fine-tuning the attentional matrix of the cortex and the activity in limbic structures. Anxiety disorders may be due to perturbations of this system. 

The individual unit of the nervous system is the neuron, a specialized cell that both receives and transmits information. The nervous system contains more than 100 billion neurons and is a major user of metabolic energy in the human body. It is also a region particularly susceptible to injury from toxic chemicals, lack of oxygen, and other assaults. Depending on the nervous region in which they reside, neurons may have different anatomical features and may use different chemical transmitters. Neurons communicate with each other and with their end organs by these chemical signals, which are released from the nerve terminal and interact with specific receptors on adjacent neurons or cells. 

Nowhere are the effects of the permeability of the placental membrane more graphic than in the incidence of fetal alcohol syndrome (FAS) in the children of alcoholic mothers. FAS produces distinctive anatomical features and mental retardation. Ethanol is called a teratogen because it causes genetic malfunction. Recall that thalidomide was a teratogen. 

Li XJ, Hou JH, Zhangb GL, Liu RS, Yang YG, Hu YX, Lin JX. 2004. Comparison of anthocyanin accumulation and morpho-anatomical features in apple skin during color formation at two habitats. Sci Hortic 99 41-53. 

In vivo RRS spectroscopy of the macula can take advantage of favorable anatomical features of the tissue structures encountered in the excitation and light scattering pathways. The major site of macular carotenoid deposition is the Henle fiber layer, which has a thickness of only about 100 pm, and to a lesser extent the plexiform layer (Fig. 12.8). Considering that the optical density of MP in the peak of the absorption band is typically quite a bit smaller than 1, as determined from direct absorption measurements of MP in excised... 

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