Biological Systems MCAT Practice Exam

What is the key characteristic of a monosynaptic reflex arc?

1. Involves multiple synapses

2. Direct connection between sensory and motor neurons

3. Requires brain input for response

4. Involves interneurons as mediators

The correct answer is: Direct connection between sensory and motor neurons

A monosynaptic reflex arc is characterized by a direct connection between sensory and motor neurons, making it the fastest type of reflex. In this type of reflex, when a sensory neuron detects a stimulus, it sends an immediate signal directly to a motor neuron, which then elicits a response in a muscle or gland without the involvement of interneurons or additional synapses. This direct pathway allows for a quick response to stimuli, such as the knee-jerk reflex, where tapping the patellar tendon stretches the quadriceps muscle and causes an immediate contraction through the connected sensory and motor neurons. The simplicity of this pathway is a defining feature of monosynaptic reflexes, distinguishing them from other reflexes that involve more complex pathways with multiple synapses and interneurons.