Which component carries the stimulus into the central nervous system?

Which component carries the stimulus into the central nervous system?

• A. First Order Neuron
• B. Second Order Neuron
• C. Third Order Neuron
• D. Fourth Order Neuron

Answer: (A)

The key idea is how sensory signals enter the brain. The first-order neuron is responsible for bringing the stimulus from the peripheral receptor into the central nervous system. Its cell body sits in a dorsal root (or cranial nerve) ganglion, with a peripheral branch to the receptor and a central branch that enters the spinal cord or brainstem to synapse on second-order neurons. From there, the signal is relayed upward by second-order neurons to the thalamus, and then by third-order neurons from the thalamus to the cortex. There isn’t a fourth-order neuron in the usual pathway. So the component that directly carries the stimulus into the CNS is the first-order neuron.

The key idea is how sensory signals enter the brain. The first-order neuron is responsible for bringing the stimulus from the peripheral receptor into the central nervous system. Its cell body sits in a dorsal root (or cranial nerve) ganglion, with a peripheral branch to the receptor and a central branch that enters the spinal cord or brainstem to synapse on second-order neurons. From there, the signal is relayed upward by second-order neurons to the thalamus, and then by third-order neurons from the thalamus to the cortex. There isn’t a fourth-order neuron in the usual pathway. So the component that directly carries the stimulus into the CNS is the first-order neuron.