Fiber terminals

Blockade of histamine autoreceptors increases histamine synthesis and release and may support higher CNS functions such as arousal, cognition and learning. Peripheral histamine heteroreceptors on C liber and on postganglionic sympathetic fiber terminals diminish neuropeptide and noradrenaline release, respectively. Both inhibititory effects are beneficial in myocardial ischemia. The inhibition of neuropeptide release also explains the antimigraine effects of some agonists of presynaptic histamine receptors. 

The preganglionic fibers terminating in the adrenal medulla, the autonomic ganglia (both parasympathetic and sympathetic), and the postganglionic fibers of the parasympathetic division use acetylcholine as a neurotransmitter (Figure 4.2). Cholinergic neurons innervate voluntary muscles of the somatic system and are also found in the CNS. 

Tension wood differs less from normal wood than compression wood. It contains thick-walled fibers, terminated towards the lumen by a gelatinous layer (Fig. 1-19). This so-called G layer consists of pure and highly crystalline cellulose oriented in the same direction as the fiber axis. For this reason the cellulose content of tension wood is higher and the lignin content lower than in normal wood. 

Fiber terminal networks containing substance P, enkephalin and dynorphin are densely distributed in the ventral midbrain tegmentum (reviewed by Fallon and Loughlin, 1985, 1995). Terminal fibers containing substance P and those containing dynorphin are very dense in the SNr, and more sparsely distributed in the VTA and SNc, whereas the terminal fibers containing enkephalin are concentrated in the SNc and in the dorsal portion of the VTA. 

The cholinergic, i.e. parasympathetic system, acts through the vagal nerves by release of acetylcholine (ACh) that opposes the sympathetic stimulation. Parasympathetic preganghonic neurons originate in the medulla. Parasympathetic fibers terminate mainly on cells of the atria. Parasympathetic irmervation is denser in the SA and AV nodes than the left ventricle. The right vagus nerve innervates the SA node. The neurotransmitter ACh and adenosine promote susceptibility to atrial fibrillation, and shorten atrial refractoriness. Excessive stimulation causes bradyarrhythmia. The... 

One striking feature of hippocampal circuitry is the pattern of afferent termination. Major hippocampal afferents originating from entorhinal cortex and ipsilateral and contralateral hippocampal subfields synapse on the dendrites of the principal cells in a laminated pattern. For instance, hippocampal commissural and associafional fibers synapse within the proximal one-third of the granule cell dendritic field, which is close to the cell body layer. The massive perforant path fibers terminate topographically in the outer two-thirds of the dendritic field. Afferents also have a laminar organization in the hippocampal proper. 

It has been proposed that adrenergic fibers terminate at inhibitory B receptors on smooth muscle fibers, and at inhibitory a receptors on parasympathetic cholinergic (excitatory) ganglion cells of Auerbach s plexus. 

Neuromuscular junction— Where the nerve fibers terminate in the muscle tissue. 

Proposed model of vibrotactile representation in SI. (a) Thalamocortical arbors in SI have multiple clusters extending across millimeters of cortex (Garraghty et al., 1989). (b) Single SA, RA, or PC fibers terminate in layer IV with three arbors (colored disks). These arbors project in turn to superficial layers ll/lll. Thus, some cortical columns are dominated by a single SA, RA, or PC input, whereas others have mixed input (overlapping disks)... 

NE Innervation Pattern and Receptor Distribution A significant modulatory input to the MOB is from the pontine nucleus, locus coeruleus (LC). In the rat, all LC neurons contain the neurotransmitter, norepinephrine (NE) LC contains the largest population of NE neurons in the brain. It has been estimated that up to 40% of LC neurons (400-600 of a total of 1,600 LC neurons) project to the bulb in the rat (Shipley et al., 1985). A subset of LC neurons projecting to MOB contain NPY (Bouna et al., 1994). NE fibers terminate in MOB with laminar specificity. LC axons project mainly to the subglomerular layers of the bulb, particularly the IPL and GCL (McLean et al., 1989). The EPL and MCL are moderately innervated, whereas the GL is nearly devoid of NE input. 

Kharazia VN, Weinberg RJ (1994) Glutamate in thalamic fibers terminating in layer IV of primary sensory cortex. J Neurosci 74 6021-6032. 

Osen KK, Storm-Mathisen J. Ottersen OP, Dihle B (1995) Glutamate is concentrated in and released from parallel fiber terminals in the dorsal cochlear nucleus a quantitative immunocytochemical analysis in guinea pig. J Comp Neurol 357 482-500. 

Sandler R, Smith AD (1991) Coexistence of GABA and glutamate in mossy fiber terminals of the primate hippocampus an ultrastructural study. J Comp Neurol 303 177-192. 

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