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Difficulty: HardNervous Coordination and Sense Organs

A barefoot individual stepping on a sharp glass fragment experiences an immediate withdrawal of the foot via a spinal reflex arc. Which sequence accurately traces the anatomical pathway traversed by the nerve impulse from the sensory receptor to the effector muscle?

  1. Cutaneous pain receptor →\rightarrow Afferent neuron →\rightarrow Dorsal root of spinal nerve →\rightarrow Relay interneuron →\rightarrow Ventral root of spinal nerve →\rightarrow Efferent neuron →\rightarrow Effector muscleAnswer
  2. B
    Cutaneous pain receptor →\rightarrow Efferent neuron →\rightarrow Ventral root of spinal nerve →\rightarrow Relay interneuron →\rightarrow Dorsal root of spinal nerve →\rightarrow Afferent neuron →\rightarrow Effector muscle
  3. C
    Cutaneous pain receptor →\rightarrow Afferent neuron →\rightarrow Ventral root of spinal nerve →\rightarrow Relay interneuron →\rightarrow Dorsal root of spinal nerve →\rightarrow Efferent neuron →\rightarrow Effector muscle
  4. D
    Cutaneous pain receptor →\rightarrow Efferent neuron →\rightarrow Dorsal root of spinal nerve →\rightarrow Relay interneuron →\rightarrow Ventral root of spinal nerve →\rightarrow Afferent neuron →\rightarrow Effector muscle

Answer

Cutaneous pain receptor →\rightarrow Afferent neuron →\rightarrow Dorsal root of spinal nerve →\rightarrow Relay interneuron →\rightarrow Ventral root of spinal nerve →\rightarrow Efferent neuron →\rightarrow Effector muscle
The correct answer accurately details the unidirectional flow of neural information in a spinal reflex arc. Sensory stimuli trigger action potentials in receptors, which travel through afferent neurons into the dorsal root of the spinal cord. Inside the spinal cord gray matter, interneurons transfer the signal to efferent neurons exiting via the ventral root to trigger contraction in the effector muscle.

Step-by-Step Solution

1
Identify the primary stimulus reception point
The painful mechanical stimulus activates cutaneous pain receptors in the skin of the foot.
Receptors detect environmental changes and initiate electrical action potentials.
2
Trace sensory nerve input into the central nervous system
Impulses travel along afferent (sensory) neurons and enter the spinal cord via the dorsal root.
Sensory neurons always conduct impulses toward the central nervous system via dorsal roots.
3
Determine spinal cord processing
The impulse synapses with a relay neuron (interneuron) within the gray matter of the spinal cord.
Relay neurons process and transmit signals from sensory neurons to motor neurons in polysynaptic reflex arcs.
4
Trace motor output to the responding muscle
The relay neuron passes the impulse to an efferent (motor) neuron, which exits through the ventral root to stimulate flexor muscle contraction.
Motor neurons conduct impulses away from the central nervous system through ventral roots to effectors.

Key Concept

Spinal Reflex Arc Impulse Pathway
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Topics

Nervous Coordination and Sense Organs

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