Chapter 16 - Section 16.2 - Study Guide - Assess Your Learning Outcomes - Page 625: 8

The transmission of pain signals from peripheral tissues to the cerebral cortex involves a three-neuron pathway that helps relay sensory information and generate the perception of pain. This pathway is known as the spinothalamic pathway, which is a specific subset of the larger somatosensory pathway. Here's an overview of the general three-neuron pathway taken by pain signals: 1. **First-Order Neuron (Peripheral Nerve to Spinal Cord):** - The journey of a pain signal begins at the site of injury or stimulation in the peripheral tissues (skin, muscles, etc.). - Nociceptors, specialized sensory nerve endings that detect painful stimuli, are activated by noxious stimuli such as heat, pressure, or chemical irritants. - These activated nociceptors send pain signals, in the form of electrical impulses, through their associated sensory neurons. The sensory neurons are part of peripheral nerves. - The peripheral nerve fibers carrying pain signals enter the spinal cord through the dorsal roots, which contain cell bodies located in the dorsal root ganglia. - In the spinal cord, the central terminal of the first-order neuron synapses with second-order neurons in the dorsal horn of the spinal gray matter. 2. **Second-Order Neuron (Spinal Cord to Thalamus):** - The second-order neurons decussate (cross over to the opposite side of the spinal cord) soon after entering the spinal cord. - The decussation allows pain signals from one side of the body to be processed in the opposite side of the brain. - These second-order neurons ascend the spinal cord within the spinothalamic tract, relaying the pain signals to the brainstem and thalamus. - The second-order neurons synapse with third-order neurons in the thalamus, specifically in the ventral posterolateral nucleus (VPL). 3. **Third-Order Neuron (Thalamus to Cerebral Cortex):** - The third-order neurons receive the pain signals from the second-order neurons in the thalamus. - From the thalamus, these neurons project to various regions of the cerebral cortex, primarily the somatosensory cortex (postcentral gyrus) in the parietal lobe. - The somatosensory cortex processes the pain signals and generates the conscious perception of pain, allowing us to localize, interpret, and respond to painful stimuli appropriately. In summary, the general three-neuron pathway for pain signals involves the transmission of nociceptive information from peripheral tissues to the cerebral cortex. The first-order neuron carries the signal from the peripheral nerve to the spinal cord, the second-order neuron relays it from the spinal cord to the thalamus, and the third-order neuron carries it from the thalamus to the somatosensory cortex in the cerebral cortex. This pathway enables us to perceive and respond to painful stimuli.

The transmission of pain signals from peripheral tissues to the cerebral cortex involves a three-neuron pathway that helps relay sensory information and generate the perception of pain. This pathway is known as the spinothalamic pathway, which is a specific subset of the larger somatosensory pathway. Here's an overview of the general three-neuron pathway taken by pain signals: 1. **First-Order Neuron (Peripheral Nerve to Spinal Cord):** - The journey of a pain signal begins at the site of injury or stimulation in the peripheral tissues (skin, muscles, etc.). - Nociceptors, specialized sensory nerve endings that detect painful stimuli, are activated by noxious stimuli such as heat, pressure, or chemical irritants. - These activated nociceptors send pain signals, in the form of electrical impulses, through their associated sensory neurons. The sensory neurons are part of peripheral nerves. - The peripheral nerve fibers carrying pain signals enter the spinal cord through the dorsal roots, which contain cell bodies located in the dorsal root ganglia. - In the spinal cord, the central terminal of the first-order neuron synapses with second-order neurons in the dorsal horn of the spinal gray matter. 2. **Second-Order Neuron (Spinal Cord to Thalamus):** - The second-order neurons decussate (cross over to the opposite side of the spinal cord) soon after entering the spinal cord. - The decussation allows pain signals from one side of the body to be processed in the opposite side of the brain. - These second-order neurons ascend the spinal cord within the spinothalamic tract, relaying the pain signals to the brainstem and thalamus. - The second-order neurons synapse with third-order neurons in the thalamus, specifically in the ventral posterolateral nucleus (VPL). 3. **Third-Order Neuron (Thalamus to Cerebral Cortex):** - The third-order neurons receive the pain signals from the second-order neurons in the thalamus. - From the thalamus, these neurons project to various regions of the cerebral cortex, primarily the somatosensory cortex (postcentral gyrus) in the parietal lobe. - The somatosensory cortex processes the pain signals and generates the conscious perception of pain, allowing us to localize, interpret, and respond to painful stimuli appropriately. In summary, the general three-neuron pathway for pain signals involves the transmission of nociceptive information from peripheral tissues to the cerebral cortex. The first-order neuron carries the signal from the peripheral nerve to the spinal cord, the second-order neuron relays it from the spinal cord to the thalamus, and the third-order neuron carries it from the thalamus to the somatosensory cortex in the cerebral cortex. This pathway enables us to perceive and respond to painful stimuli.