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Difficulty: MediumNervous Coordination and Sense Organs

When an animal detects a sudden noxious chemical stimulus on its skin, a rapid spinal reflex action is initiated to withdraw the affected limb. Which sequence correctly describes the directional flow of nerve impulses along the neural pathway of this reflex arc?

  1. Sense receptor →\rightarrow afferent neuron →\rightarrow spinal interneuron →\rightarrow efferent neuron →\rightarrow muscle effectorAnswer
  2. B
    Sense receptor →\rightarrow efferent neuron →\rightarrow spinal interneuron →\rightarrow afferent neuron →\rightarrow muscle effector
  3. C
    Sense receptor →\rightarrow spinal interneuron →\rightarrow efferent neuron →\rightarrow afferent neuron →\rightarrow muscle effector
  4. D
    Sense receptor →\rightarrow afferent neuron →\rightarrow muscle effector →\rightarrow spinal interneuron →\rightarrow efferent neuron

Answer

Sense receptor →\rightarrow afferent neuron →\rightarrow spinal interneuron →\rightarrow efferent neuron →\rightarrow muscle effector
The correct response accurately traces the unidirectional impulse pathway: sensory receptors detect the stimulus, sensory (afferent) neurons carry the impulse to interneurons (relay neurons) in the central nervous system, and motor (efferent) neurons carry the impulse out to the effector muscle.

Step-by-Step Solution

1
Identify the initial reception of the stimulus
The noxious chemical stimulus activates specialized cutaneous sense receptors.
Receptors detect environmental changes and initiate electrical action potentials.
2
Trace sensory conduction to the central nervous system
Impulses travel along sensory (afferent) neurons into the dorsal horn of the spinal cord.
Afferent pathways transmit sensory information toward the central nervous system.
3
Identify central integration and motor transmission
The impulse passes across synapses via spinal interneurons to motor (efferent) neurons.
Interneurons process the signal in the spinal grey matter and relay it to efferent neurons exiting via the ventral root.
4
Trace motor conduction to the target organ
Efferent neurons carry impulses to skeletal muscle effectors, causing muscle contraction and limb withdrawal.
Effector organs carry out the physical response to remove the organism from the harmful stimulus.

Key Concept

Neuron sequence in a spinal reflex arc
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Topics

Nervous Coordination and Sense Organs

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