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Difficulty: EasyNervous Coordination and Sense Organs

Arrange the following physiological events in the correct sequence to describe the pathway of a spinal reflex action when a hand touches a hot stove.

  1. 1Thermal receptors in the skin detect the heat stimulus.
  2. 2Sensory neuron transmits the nerve impulse to the spinal cord.
  3. 3Relay neuron passes the impulse across a synapse in the spinal cord.
  4. 4Motor neuron transmits the impulse from the spinal cord to the arm muscle.
  5. 5Arm muscle contracts to withdraw the hand.

Answer

The correct order of events in a spinal reflex arc is: receptor detection of heat stimulus, transmission along the sensory neuron, relay neuron processing in the spinal cord, motor neuron transmission, and contraction of the effector muscle.
A spinal reflex arc follows an unidirectional pathway: stimulus detection by a receptor, impulse transmission via sensory neurons into the spinal cord, relay neuron integration, motor neuron output, and muscle effector response.

Step-by-Step Solution

1
Identify the initial sensory detection.
Thermal receptors in the skin detect the heat stimulus.
Reflex actions always originate at sensory receptors responding to a stimulus.
2
Trace signal propagation into the central nervous system.
Sensory neuron transmits the nerve impulse to the spinal cord.
Afferent (sensory) neurons carry signals from sensory organs toward the spinal cord.
3
Identify central nervous system integration.
Relay neuron passes the impulse across a synapse in the spinal cord.
Interneurons in the spinal cord bridge the pathway from afferent to efferent pathways without immediate brain intervention.
4
Trace signal output from the spinal cord.
Motor neuron transmits the impulse from the spinal cord to the arm muscle.
Efferent (motor) neurons conduct impulses away from the spinal cord to target tissues.
5
Determine the physical response.
Arm muscle contracts to withdraw the hand.
The effector muscle responds directly to motor nerve stimulation.

Key Concept

Spinal Reflex Arc Pathway (Receptor -> Sensory Neuron -> Relay Neuron -> Motor Neuron -> Effector)
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Topics

Nervous Coordination and Sense Organs

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