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Difficulty: Very hardNervous Coordination and Sense Organs

During a withdrawal reflex when a person touches a hot object, electrical impulses travel through a specific sequence of neural structures to produce an immediate somatic motor response. Which of the following correctly traces the pathway of the nerve impulse from stimulus detection to the execution of the response?

  1. Sensory receptor → Afferent neuron → Relay neuron → Efferent neuron → Skeletal muscle effectorAnswer
  2. B
    Sensory receptor → Efferent neuron → Relay neuron → Afferent neuron → Skeletal muscle effector
  3. C
    Skeletal muscle effector → Efferent neuron → Relay neuron → Afferent neuron → Sensory receptor
  4. D
    Afferent neuron → Sensory receptor → Efferent neuron → Relay neuron → Skeletal muscle effector

Answer

Sensory receptor → Afferent neuron → Relay neuron → Efferent neuron → Skeletal muscle effector
The correct response traces impulse flow in strict physiological sequence: starting at the sensory receptor (stimulus transduction), moving through the afferent neuron (sensory input to CNS), across the relay neuron in the spinal cord (integration), along the efferent neuron (motor output from CNS), and terminating at the skeletal muscle effector (response execution).

Step-by-Step Solution

1
Identify the initial site of stimulus reception
Sensory receptors in the skin detect thermal stimulus and generate action potentials.
Receptors transduce physical energy from stimuli into electrical nerve impulses.
2
Trace inward conduction toward the central nervous system
Impulses travel along the afferent (sensory) neuron into the dorsal horn of the spinal cord.
Afferent neurons transmit sensory information unidirectionally toward the spinal cord.
3
Identify synaptic integration in the spinal cord
The impulse synaptically transfers to a relay (interneuron) within the spinal cord grey matter.
Relay neurons connect sensory and motor pathways within the central nervous system for rapid reflex processing.
4
Trace outward conduction to the target organ
The relay neuron excites an efferent (motor) neuron, which conducts impulses to the skeletal muscle effector to cause contraction.
Efferent neurons conduct motor signals from the spinal cord to muscle effectors to carry out the physical response.

Key Concept

Unidirectional impulse flow in a spinal reflex arc
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Topics

Nervous Coordination and Sense Organs

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