Pathways to the Brain Flashcards
What is the spinothalamic tract?
The spinothalamic tract is the primary system for transmitting pain signals from the spinal cord to the brain. It is located in the anterolateral quadrant of the spinal cord and composed of three neuronal systems.
Where does the first neuron of the spinothalamic tract start and travel to?
The first neuron in the spinothalamic tract starts in the dorsal root ganglion and travels a short distance to synapse in either lamina 1, lamina 2, or connects with wide-dynamic range neurons in lamina 5 of the spinal cord.
Describe the path of the second neuron in the spinothalamic tract.
The second neuron starts in either lamina 1 or lamina 5, crosses to the opposite side of the spinal cord through the anterior commissural alba, and then ascends within the anterolateral system to reach the thalamus, specifically the ventrobasal complex of nuclei.
What is the role of the third neuron in the spinothalamic tract?
The third neuron originates in the thalamus and travels to various brain structures, particularly the cortex, allowing us to perceive pain.
What collateral branches does the spinothalamic tract send, and to which brain regions?
The spinothalamic tract sends collateral signals to the nucleus tractus solitarius in the medulla, the parabrachial nucleus (which communicates with the amygdala), and the hypothalamus. These regions are involved in cardiorespiratory changes, aversive limbic responses, and emotional responses like anger and withdrawal.
What is the significance of the parabrachial nucleus in pain processing?
The parabrachial nucleus communicates directly with the amygdala, which is responsible for fear and aversive limbic responses. This pathway bypasses the thalamus, suggesting that some components of pain processing may occur subconsciously.
What are the other tracts involved in pain transmission besides the spinothalamic tract?
Other tracts include the spinoreticular, mesencephalic, and spinal hypothalamic tracts. They play roles in transmitting pain signals and have multiple functions, though they are not solely dedicated to pain processing.
How does the spinoreticular tract differ from the spinothalamic tract?
Unlike the spinothalamic tract, which always crosses through the anterior commissural alba, the spinoreticular tract can transmit signals to both sides of the brain, which explains why brain responses to pain stimuli are often bilateral in imaging studies.
What endogenous opioid system and its role in pain control?
The endogenous opioid system is a set of brain regions that use beta-endorphin and encephalin as mediators to produce analgesia. This system includes regions like the periaqueductal grey matter (PAG) and the rostro-ventromedial medulla (RVM).
What happens when the endogenous opiod system is stimulated?
Stimulation of the endogenous opioid system, either by electrical stimuli or morphine injection, produces analgesia, effectively blocking pain signals. The PAG, RVM, and dorsolateral pontine tegmentum (DLPT) are key areas involved in this system.
How does the prefrontal-PAG circuit contribute to pain control?
The prefrontal-PAG circuit is controlled by endogenous opioids, which act as the brain’s internal painkillers. The PAG calculates the amount of anti-nociception based on information from higher brain regions, while the RVM and DLPT execute the pain-blocking signals to the spinal cord.
What are the major inputs to the PAG?
The PAG receives major inputs from the amygdala (fear region), hypothalamus (emotional control), insula, and anterior cingulate cortex (ACC). It sends signals to the spinal cord through the RVM or DLPT, which have neurons that stop pain at the spinal cord dorsal horn.
How do we know that the endogenous opioid system can stop pain?
We know this because electrical stimulation of the PAG, RVM, or DLPT in animal studies completely suppresses pain. Additionally, injecting morphine into these structures blocks pain by binding to opioid receptors, demonstrating the role of endogenous opioids in pain control.
