The expression "knee-jerk reaction" refers to someone doing something automatically without thinking. In biological terms, which of the following statements is true regarding this expression?
A) In the nervous system, this expression implies the involvement of higher brain regions before executing a spinal reflex.
B) In the nervous system, this expression implies the lack of brain input when executing a spinal reflex.
C) This expression implies that the knee-jerk reaction will be shortened in duration following input from higher brain regions.
D) This expression implies that only children exhibit this type of unthinking behavior.

Question

Quizplus · Accepted Answer

The knee-jerk reaction is a spinal reflex that does not involve higher brain regions. It is an automatic response triggered by the tapping of the patellar tendon, which stimulates sensory neurons that synapse directly with motor neurons in the spinal cord, causing the leg to kick out. Therefore, the expression "knee-jerk reaction" implies the lack of brain input when executing a spinal reflex.

The Expression "Knee-Jerk Reaction" Refers to Someone Doing Something Automatically