Question

The delay in transmission from the dorsal to the ventral root across the spinal cord for the reflex pathways 'A', 'B', 'D' and 'C' respectively is 0.5 ms,1.0 ms, 1.5 ms, and 2.0 ms.Identify the correct option: (Average synaptic delay =0.5 ms)

• A. A=monosynaptic , B= trisynaptic , D=bisynaptic
• B. A=monosynaptic , C=trisynap tic , D=quadrisynaptic
• C. A=monosynaptic , B=bisynaptic , C=trisynaptic
• D. A=monosynaptic , D=trisynaptic , C=quadrisynaptic

Answer 1

Answer: (D)

Monosynaptic transmission involves only two neurons, one sensory and one motor. In this, the signal is passed from one neuron to another neuron. In multisynaptic transmission, more than two neurons are involved. In this case, there is some delay in transmission of neural signal at the synapses. This is because more synapses are encountered in a reflex pathway and hence it takes more time to effect the reflex. In the given problem, it is given than average synaptic delay is 0.5 ms. Reflex pathway A is monsynaptic as it is taking 0.5 ms for transmission of signal. Reflex pathway B is disynaptic as it is taking 1.0 ms for signal transmission. This is because there are three neurons are involved. From sensory neuron each motor neuron takes 0.5 ms for transmission of signal. Reflex pathway for D is trisynaptic as it is having 1.5 ms of synaptic delay. Similarly, reflex pathway for C is quadrisynaptic as it is having 2.0 ms of synaptic delay.

The correct answer is option D.