Outer innervations

The termination pattern exhibited by A -fibres is entirely different from that of large AjS-fibres. A -fibres travel extensively in Lissauer s tract, overlying the dorsal horn and their terminals form a plexus at the surface of the spinal cord A(5-fibres from high-threshold mechanoreceptors distributed to laminae I, II outer and V. Projections also appear to terminate on the contralateral side, in lamina V. A(5-fibre innervations from deep tissues (muscles and joint) have been shown to terminate exclusively in lamina I, or in laminae IV and V. 

An anatomic circumstance that sometimes creates exceptions to the above rules for differential nerve block is the location of the fibers within the peripheral nerve bundle. In large nerve trunks, fibers located circumferentially are the first to be exposed to the local anesthetic when it is administered into the tissue surrounding the nerve. In the extremities, proximal sensory fibers are located in the outer portion of the nerve trunk, whereas the distal sensory innervation is located in the central core of the nerve. Thus, during infiltration block of a large nerve, sensory analgesia first develops proximally and then spreads distally as the drug penetrates deeper into the core of the nerve. 

Within the adrenal gland, steroids are synthesized by the outer layer of cortical cells, while the central core of medullary cells is innervated by sympathetic preganglionic neurons, which stimulate it to produce and release epinephrine. The adrenal cortex is comprised of three... 

The uveal tract constitutes the middle tunic of the eye, located between the innermost retina and the outer protective scleral coat. This tissue and its constituent parts are both richly vascularized and highly innervated. The iris defines the anterior-most part of the uvea. It serves primarily as a diaphragm to admit light into the eye. Just posterior to the iris is the ciliary body, responsible for aqueous production and accommodation of the lens. Finally, the choroid defines the posterior-most aspect of the uvea. The choroid, via the choriocapil-laris, is responsible for blood supply to the outer one-third of the retina. It also serves as a pathway for numerous sensory and autonomic neurons traveling to the anterior eye. 

The cornea, the protective outer layer of the eye, is heavily innervated with sensory neurons, triggering the blink reflex and tear duct secretion in response to irritation. The cornea is also an essential optical element, supplying two thirds of the total refraction in the eye. Behind the cornea is a clear fluid, the aqueous humor, in which the central aperture of the iris, the pupil, is free to constrict or dilate. The two actions are accomplished by opposing sets of muscles. 

The ultrastructures of the taste buds of the above mentioned species are now compared to each other. With the exception of the catfishes (where the taste buds are located also in the body s outer skin, especially on the barbels) taste buds occur only in the lips and oropharyngobranchial cavity. In each case, taste buds consist of an elongated, pear-shaped sensory epithelium that is composed of different electron-lucent and electon-dense cells and that rests in a vertical position in the stratified squamous epithelium. At their apical poles these cells bear microvilli, the so-called receptor villi, which form together the receptor area of the taste buds. The border with the adjacent and non-specialized epithelial cells is formed by marginal cells. Besides this relatively big uniformity of the taste buds sensory epithelium, the taste buds of different fish vary in their innervation, in the number, morphology and position of their basal cells, and their position within the epidermis and on the top of a dermal papilla. The results of this comparison are listed in Table 1 and schematically de-... 

The intrinsic innervation of the GIT is considered as a separate autonomic division, called the enteric nervous system (ENS) (Schemann and Neunlist 2004). Neurons and enteric glia of the ENS are embedded within the gut wall and arranged in three plexuses (Hall 2011). The myenteric (Auerbach s) plexus is located between the inner and outer circular muscle layers and the submucosal (Meissner s) plexus between the circular muscle and muscularis mucosa. The deep muscle plexus separates inner and outer circular muscle layers in the small intestine. In the large intestine, it is located at the inner border of circular muscle and is called submucosal plexus. 

Chapman s reflexes are also located along the extremities. This is because of the fact that the upper and lower extremities are innervated by T2-8 and T1 1-L2, respectively. The arm and leg share sympathetic fibers with the viscera. For example, the colon and thigh are innervated by the sympathetic cell bodies ofTl 1-L2. If the patient has colitis, the resulting Chapman s reflex will manifest as quarter-sized or half-dollar-sized "shotty plaque(s)" along the outer thigh. Likewise, disorders ofthe eye may exhibit tissue texture changes along the anterior superior aspect of the humerus. 

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