Talk:Reflex arc
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This article is in dispute over whether the patellar reflex is monosynaptic or polysynaptic. I think the confusion is gay and may arise from the fact that while the patellar reflex is (to my knowledge) monosynaptic, it is occasionally illustrated as polysynaptic for purposes of education. For an example see http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_&_Physiology/A&P202/Nervous_System_Physiology/Patellar_Reflex.htm I have added the disputed template to this article, noting that the patellar reflex is described as polysynaptic in several other wikipedia articles. Robotsintrouble 21:21, 26 August 2006 (UTC)
I have moved the following two contradictory statements here, to the talk page. Would another editor help resolve this dispute?
- "The neural connection from the primary sensory neurons to the motor neurons is a poly-synaptic pathway (Andersen)."
Robotsintrouble 21:30, 26 August 2006 (UTC)
- "Correction: The diagram showing the classic "knee jerk" muscle stretch reflex incorrectly depicts a three-cell reflex arc with an interneuron in the spinal cord connecting the sensory and motor neurons (i.e., two synapses). According to Ganong (2001), stretch reflexes “are the best known and studied MONOSYNAPTIC reflexes in the body. Impulses originating in the muscle spindle are conducted to the CNS by fast sensory fibers that pass directly to the motor neurons which supply the same muscle. The neurotransmitter at the central synapse is glutamate.” So, where is the problem??"unsigned comment
- "Correction: The diagram showing the classic "knee jerk" muscle stretch reflex incorrectly depicts a three-cell reflex arc with an interneuron in the spinal cord connecting the sensory and motor neurons (i.e., two synapses). According to Ganong (2001), stretch reflexes “are the best known and studied MONOSYNAPTIC reflexes in the body. Impulses originating in the muscle spindle are conducted to the CNS by fast sensory fibers that pass directly to the motor neurons which supply the same muscle. The neurotransmitter at the central synapse is glutamate.” So, where is the problem??"unsigned comment
Or perhaps the issue is if the patellar reflex is being activated due to a quick tap (the typical method) or a maintained stretch. If it is a quick tap the muscle spindles stretch and the IA afferents fire, sending Ach to the alpha motor neurons. This causes the abrupt contraction of the muscle fibers. However, if there is a slow or sustained stretch both the Ia and II afferents become excited and interneurons in the spinal cord relay this to the alpha motor neurons. It sounds like the previously mentioned diagram shows the slow/sustained stretching, not the tapping seen in reflex testing. comickgirlOctober 2, 2006
I agree with Ganog (2001). The primary afferents (Ia's) are monosynaptic to the ipsilateral muscle's alpha-MN. However, the Ia inhibitory interneuron synapses on the contralateral muscle which is a disynaptic pathway (Kandell and Schwartz 2000). The same is true of the Ib pathway which responds to the Golgi tendon organ. It depends if the pathway goes contralateral. __________________________________________________________________________________________________________________________________
Hang on a minute guys and gals !
It is entirely correct to call the patellar tap reflex monosynaptic. If we only consider the actions of say, muscle spindle depolarisation on the agonist muscle, then clearly its monosynaptic. The outcome of the reflex is generally movement at the joint, whether it be plantar flexion (triceps surae contraction), or contraction of the quads (patellar tap reflex)knee jerk , adding the 1A inhibitory interneuron reduces the activity of the antagonist muscles resulting in a greater degree of movement INITIATED by the AGONIST muscle.
Also be careful, IA afferents don't send ACH to the motor nerves, IA afferents release glutamate (probably) in response to depolarisation (tap, stimuli, brief stretch) which, if of sufficient magnitude (> threshold) will result in depolarisation of the post synatpic motor neuron, which release Ach, leading to muscle contraction. Locsihc Oct 28, 2006
