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Question

Difficulty: MediumNervous Coordination and Sense Organs

When a physician taps the patellar tendon just below the knee cap with a rubber mallet, the lower leg involuntarily kicks forward in a knee-jerk response. Which of the following correctly traces the pathway of the nerve impulse during this reflex action?

  1. Stretch receptor →\rightarrow sensory neuron →\rightarrow spinal cord →\rightarrow motor neuron →\rightarrow quadriceps muscleAnswer
  2. B
    Stretch receptor →\rightarrow motor neuron →\rightarrow spinal cord →\rightarrow sensory neuron →\rightarrow quadriceps muscle
  3. C
    Quadriceps muscle →\rightarrow sensory neuron →\rightarrow spinal cord →\rightarrow motor neuron →\rightarrow stretch receptor
  4. D
    Stretch receptor →\rightarrow sensory neuron →\rightarrow cerebral cortex →\rightarrow motor neuron →\rightarrow quadriceps muscle

Answer

The nerve impulse pathway travels from the stretch receptor →\rightarrow sensory neuron →\rightarrow spinal cord →\rightarrow motor neuron →\rightarrow quadriceps muscle.
The correct response accurately details the monosynaptic reflex arc: a mechanical stimulus activates stretch receptors, generating an action potential conducted along an afferent sensory neuron into the spinal cord. In the spinal cord, the signal synapses with an efferent motor neuron that propagates the impulse directly to the quadriceps muscle (effector), triggering contraction.

Step-by-Step Solution

1
Identify the stimulus reception point
Tapping the tendon stretches the muscle, stimulating muscle spindle stretch receptors.
Receptors are specialized structures that detect changes in the internal or external environment.
2
Trace the afferent pathway to the central nervous system
Sensory (afferent) neurons carry the nerve impulse from the stretch receptor into the spinal cord.
Sensory neurons transmit impulses from peripheral receptors toward the central nervous system.
3
Determine the integration point and efferent pathway
In the grey matter of the spinal cord, the impulse synapses directly onto a motor (efferent) neuron, which transmits the signal out to the quadriceps muscle.
Spinal reflexes bypass conscious cerebral processing to allow rapid, automatic responses.
4
Identify the effector response
The quadriceps muscle contracts, causing the lower leg to kick forward.
Effectors (muscles or glands) execute the physical response to motor nerve stimulation.

Key Concept

Monosynaptic Spinal Reflex Arc Pathway
Estimated Time:1m 0s
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Topics

Nervous Coordination and Sense Organs

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