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.

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.