Spinal reflexes, modulation

A reflex occurs when a particular stimulus always elicits a particular response. This response is automatic and involuntary in other words, it occurs without conscious effort. Therefore, reflexes are specific, predictable, and, furthermore, often purposeful. For example, the withdrawal reflex causes a body part to be pulled away from a painful stimulus so that tissue injury is avoided. Spinal reflexes require no input from the brain because they are elicited entirely at the level of the spinal cord. However, while the reflex is underway, nervous impulses are also transmitted to the brain for further processing. In fact, input from the brain may modulate a reflex or alter the response to a stimulus through conscious effort. 

A comprehensive review and discussion of studies investigating serotonergic modulation of spinal reflexes has been presented previously (10). This section... 

Initially, Gly was described to be restricted to the mammalian spinal cord, but subsequently it has been detected supraspinally as well (Legendre, 2001). Gly receptors (GlyRs) belong to the superfamily of receptor channels, which are generally composed of five subunits (al-4, P) (Webb and Lynch, 2007). The different a-and P-subunits are differently localized. The GlyR is a pentameric chloride channel, and it is classically known for mediating inhibitory synaptic transmission between interneurons and motor neurons in reflex circuits of the spinal cord, but they are also found presynaptically, where they modulate neurotransmitter release (Lynch, 2009 Webb and Lynch, 2007). The picture is complicated by the fact that Gly also binds to and activates NMDA receptors, therefore, it can influence the pain threshold by this action as well (see above. Section 2.3.1) (Zeilhofer, 2005). 

Helmstetter FJ, Bellgowan PS, Tershner SA (1993) Modulation of spinal nociceptive reflexes by the microinjection of morphine into the amygdala. NeuroReport 4 471-474... 

Bonham AC, Chen CY, Sekizawa S, Joad JP (2006) Plasticity in the nucleus tractus solitarius and its influence on lung and airway reflexes. J Appl Physiol 101 322-327 Budai D, Wilcox GL, I rson AA (1992) Modulation of A-methyl-D-aspartate and (R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) responses of spinal nociceptive neurons by a N-terminal fragment of substance P. Eur J Pharmacol 216 441 44 Carr Ml, Lee LY(2006) Plasticity of peripheral mechanisms of cough. Respir Physiol Neurobiol 152 298-311... 

Three channels for bilateral sacral root stimulation (S2-4) for bladder control (bowel control and erection, if possible) were provided. Sacral root stimulation was achieved by three pairs of LPR electrodes (10-mm long, solid platinum tubing of 1.0-mm diameter) inserted into the external sacral foramina in a lateral direction to follow and to stimulate the nerve roots epidurally. One further channel was connected to an epidural spinal cord stimulating electrode (Pisces Quad Medtronic Inc., Minneapolis, MN) for conus medullaris modulation of spastic bladder and bowel reflexes. 

As an alpha-2 agonist, tizanidine decreases presynaptic excitatory neurotransmitter release and postsyn-aptic neurotransmitter effectiveness. Alpha-2 receptor agonists attenuate monosynaptic and polysynaptic reflexes in the spinal cord [25]. Tizanidine decreases excitatory neurotransmitter release and Substance P release from small sensory afferents [28]. Tizanidine decreases locus coeruleus activity, thereby modulating descending motor regulatory pathways [28]. Tizanidine decreases activity of both alpha and gamma motor neurons [28]. 

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