Reciprocal innervation

Stretching of the muscle is sensed in the muscle spindle and leads to firing in muscle spindle afferent. These nerves travel via the dorsal root and synapse in the anterior horn of the spinal cord directly with the motor neurone to that muscle. They stimulate firing of the motor neurones, which causes contraction of the muscle that has just been stretched. The muscle spindle afferent also synapses with inhibitory interneurons, which inhibit the antagonistic muscles. This is called reciprocal innervation. 

The oculomotor plant and saccade generator are the basic elements of the saccadic system. The oculomotor plant consists of three muscle pairs and the eyeball. These three muscle pairs contract and lengthen to move the eye in horizontal, vertical, and torsional directions. Each pair of muscles acts in an antagonistic fashion due to reciprocal innervation by the saccade generator. For simplicity, the models described here involve only horizontal eye movements and one pair of muscles, the lateral and medial rectus muscle. 

Reciprocal innervation is the stretching of a given muscle, stimulating the contraction of that muscle via the muscle spindle. The antagonist muscle is inhibited. 

Reciprocal innervation. When a stretch reflex excites one muscle, it simultaneously inhibits the antagonist muscle. Reciprocal... 

Mitscle energy treatmerrt combines elements of the Golgi tendon reflex, reciprocal innervation. 

In reciprocal innervation when a stretch excites one muscle, it simrtltaneously inhibits its antagorrist. 

Central/Tertiary structures The fish olfactory bulb is a fourlayered structure much as in higher vertebrates. Within the 2nd layer, the first synapse for olfactory input is on the dendrites of the mitral cells (MC). About 1000 ORN axons converge on one MC, a ratio similar to mammals. The MC output, from cells at various levels, leads into several glomeruli and receives (inhibitory) input from granule cells. The latter also innervate a distinct cell type in the MC layer of teleosts — the ruffed cells (RC), with which they have reciprocal synapses [Fig. 2.18(a)] both relay cells send ascending fibres to forebrain centres (Kosaka and Hama, 1982). The RC are unlike the MC since they are not stimulated by the ORNs directly. Their interactions (Chap. 5) may contribute to the processing of pheromonal stimuli (Zippel, 2000). The main bulbar pathways project to several nuclei in the forebrain via two ipsilateral tracts, the lateral and medial [Fig. 2.18(b)], the latter mediates sexual behaviour and the former probably other behaviours (Hara,... 

Kurasawa I, Toda K, Nakamura Y (1990) Non-reciprocal facilitation of trigeminal motoneurons innervating jaw-closing and jaw-opening muscles induced by iontophoretic application of serotonin in the guinea pig. Brain Res 515 126-134... 

A variety of chemically-identified neurons within the ARC receive both indirect (extrinsic) and direct (intrinsic) enkephalinergic neuronal input (Magoul et al., 1993) suggesting a role for enkephalin in the neuroendocrine regulation of pituitary hormone secretion. Enkephalin-IR perikarya in the bed nucleus of the stria terminalis, medial preoptic nucleus, periventricular nucleus and dorsomedial nucleus all provide extrinsic input to the rostral ARC, whereas intrinsic enkephalin neurons connect the rostral and caudal portions of the ARC (Magoul et al., 1993). Enkephalin-IR neurons innervate TH-IR neurons (perikarya and dendrites) in the DM-ARC (but not in the VL-ARC), (5-endorphin neurons in the VL-ARC, and NPY neurons in the ventromedial ARC (Magoul et al., 1994). There are symmetrical synaptic connections between enkephalin axon terminals and POMC perikarya in the ARC (Zhang et al., 1987), and reciprocal synaptic associations with NPY neurons in the ventromedial ARC (Li et al., 1993). 

At this juncture, a new type of interneuronal communication, i.e., the capacity of neuropeptides to act as neurotransmitters, had become established. Moreover, the structural parameters of peptidergic innervation were seen to include junctional complexes between two peptidergic neurons that seem to enable a reciprocal exchange of signals. 

The size of the pupil is determined by the balance of forces exerted by the dilator muscles fibers (sympathetically innervated and radially arranged) and the constrictor muscle fibers (parasympathetically innervated and circularly arranged) of the iris. Normally both sets of muscle fibers have a constant degree of tonus and act reciprocally to dilate or constrict the pupil. Any substance that paralyzes the constrictor muscle fibers (parasympathol3d ic) allows the unopposed tone of dilator muscle fibers to widen the pupil. 

Once antibodies to the anandamide-degrading enzyme, namely fatty acid amide hydrolase (FAAH), became available, it was apparent that in many regions FAAH and CBl expression is reciprocal in nature (Egertova et al. 1998, 2003 Tsou et al. 1998b). For example, FAAH, but not CBi is highly expressed in the somata and proximal dendrites of hippocampal pyramidal cells and cerebellar Purkinje neurons. These neurons are, in turn, densely innervated by CBi-positive fibers. Thus, it has been proposed that anandamide, despite its possible presynaptic site... 

Evidence has been presented for a correlation between the density of mature sympathetic innervation and the concentration of both NGF and mRNA ", although this has not been established for more than a few tissues and does not take into account the presence of sensory neurons (Korsching and Thoenene, 1983 Shelton and Reichardt, 1984 Harper and Davies, 1990). Nevertheless, this finding alone implies a close reciprocal regulation of NGF synthesis and neuronal metabolism by nerve and NGF, respectively. However, no clear evidence for an influence of nerve on NGF synthesis in peripheral effector tissues has been found (see Section 9). 

Complex organ control— the eye The eye contains multiple tissues with various functions, several of them under autonomic control (Figure 6-5). The pupil, discussed above, is under reciprocal control by the SANS (via alpha receptors) and the PANS (via muscarinic receptors) acting on two different muscles in the iris. The ciliary muscle, which controls accommodation, is under primary control of muscarinic receptors innervated by the PANS, with insignificant contributions from the SANS. The ciliary epithelium, on the other hand, has important beta receptors that have a permissive effect on aqueous humor secretion. 

The autonomic nervous system guides the electrical and mechanical functions of the heart. The heart is innervated by both the sympathehc and parasympathetic systems, which have opposite effects and are activated reciprocally. They play important roles in arrhythmia susceptibility. Sympathetic shmulation originates from the intermediolateral column of the thoracic spinal cord. Its neurotransmitter, norepinephrine, is released from neurons of postganglionic fibers of stellate ganglia and epinephrine is released from the adrenal medulla. Both of these act on cardiac p-adrenergic receptors. Sympathetic nerves are predominantly on... 

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