Question: 100% NCERT covered from Particular Keyword.Explanations are 100% from NCERT | [Difficult level: Hard] From NCERT NEET Derived Question.
Which of the following statements about the neural basis of
the knee-jerk reflex in humans is false ?
(a) The leg extensor is stimulated to contract by the motor
neuron in this reflex loop.
(b) The only synapses between neurons involved in this
loop occur in the spinal cord.
(c) The basic response is a polysynaptic circuit containing
several interneurons.
(d) Conscious action can modify the basic reflex because
of the action of interneurons.
Answer: c
At first it seems like it is out of NCERT question but actually it is also based on NCERT.
Let's see NCERT XI class , Page 322 .
REFLEX ACTION AND REFLEX ARC
You must have experienced a sudden withdrawal of a body part which
comes in contact with objects that are extremely hot, cold pointed or
animals that are scary or poisonous. The entire process of response to a
peripheral nervous stimulation, that occurs involuntarily, i.e., without
conscious effort or thought and requires the involvment of a part of the
central nervous system is called a reflex action. The reflex pathway
comprises at least one afferent neuron (receptor) and one efferent (effector
or excitor) neuron appropriately arranged in a series (Figure 21.5). The
afferent neuron receives signal from a sensory organ and transmits the
impulse via a dorsal nerve root into the CNS (at the level of spinal cord).
The efferent nueuron then carries signals from CNS to the effector. The
stimulus and response thus forms a reflex arc as shown below in the
knee jerk reflex. You should carefully study Figure 21.5 to understand
the mechanism of a knee jerk reflex.
Now see option two and three, both contracting each other,
option b is saying if one neuron involved.
Option C is saying if many neuron involved.
Now see NCERT Highlighted point.
From Above comparison, we conclude that option C is incorrect. So correct answer for the question is C.