Crossed extensor reflex

Figure 7.4 The withdrawal reflex coupled with the crossed-extensor reflex. A painful stimulus will elicit the withdrawal reflex, which causes flexor muscles to contract and move the affected body part away from the stimulus. At the same time, the crossed-extensor reflex causes extensor muscles in the opposite limb to contract. The straightening of the opposite limb provides support for the body.

Alkaloid Contraction of guinea pig ileum Pressor action in pithed rat Release of catecholamines from cat adrenal Contraction of frog rectus Blockade of contraction of diaphragm Inhibition of cat knee jerk Inhibition of cat flexor reflex Inhibition of chick flexor reflex Inhibition of chick crossed extensor reflex... 

Fig. 9.21. Muscular actuators in feedback systems. Crossed extensor reflex - a more complicated reflex...

The four main alkaloids are coniine, y-coniceine, iV-methylconiine, and conhydrine. Conhydrine occurs in the smallest proportions and has the weakest pharmacological action [3,4,19,20, 31,67, 85, 87]. The most distinctive action of the three other hemlock alkaloids plus nicotine is their ability, provided the dose is small, to inhibit the crossed extensor reflex and the so-called knee-jerk by an action potential in the spinal cord. Since neurons in the spinal cord may both be inhibited and activated by the action of hemlock, the mechanisms involved are a bit complicated. If the alkaloids initially stimulate inhibitory neurons rather than blocking excitatory ones, the antagonistic relationship of the two substances may be explained. There is evidence that its central synapse is controlled by polysynaptic inhibitory pathways, although the patellar reflex is monosynaptic [3, 19, 67]. It is possible that the C. maculatum piperidine alkaloids may act upon the mechanism that regulates the amniotic liquid, adding to the production of malformations. Finally, lack of fetal movement, whatever its origin, can also cause limb malformations. 

The crossed extensor reflex is the response elicited by stimulation of a given muscle (e.g., the biceps of the right arm, causing flexion) in the muscle of opposite function on the opposite side of the body (e.g., contraction of the triceps in the left arm, creating extension). The crossed extensor reflex is mediated via many sensory and motor interneurons in the spinal cord. Some act to inhibit the contralateral agonist and stimulate the contralateral antagonist. The reflex usually... 

FIG. 6-6 Crossed extensor reflex with reoiprooal inhibition. 

Crossed extensor reflex. This is used in active myofascial techniques with resistance. When a stretch reflex excites one muscle, it simultaneously relaxes the contralateral agonist muscle. Motion is created that crosses from one side of the spine to the other in an X pattern e.g., the stretch reflex excites the right biceps, and the crossed extensor reflex relaxes the left biceps. 

Active indirect techniques are those in which the patient is asked to contract the ipsilateral antagonist muscles or the same muscles on the contralateral side. This method uses either the reciprocal inhibition or the crossed extensor reflexes to relax the muscles being treated. In these techniques, the physician typically applies isokinetic resistance to the patient s contraction, (hokinetic resistance The physician applies a resistive force such that the muscle contraction increases very little with the gradual decrease in muscle length i.e., the joint is allowed to move and the resistance is gradually increased.)... 

FIG. 26-9 Active indirect stretch of the paravertebral muscles using crossed extensor reflex (A) Starting position. (B) Midway through the maneuver, with the patient attempting to bring his chin to his right shoulder as the physician applies isokinetic resistance. (C) A passive stretch ends the technique. 

Crossed Extensor With the animal in lateral recumbency, each limb is sharply flexed by proximal movement. The contralateral limb is observed for an extension reflex. 

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