Podcast
Questions and Answers
Which pathway carries information about pain and temperature sensation?
Which pathway carries information about pain and temperature sensation?
Where do small diameter unmyelinated axons synapse in the spinal cord?
Where do small diameter unmyelinated axons synapse in the spinal cord?
Which pathway is responsible for conveying emotional and arousal aspects of pain?
Which pathway is responsible for conveying emotional and arousal aspects of pain?
What is the main function of the spinothalamic tract?
What is the main function of the spinothalamic tract?
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Where does the spinomesencephalic tract project to?
Where does the spinomesencephalic tract project to?
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Which nucleus is a major relay for the spinothalamic tract?
Which nucleus is a major relay for the spinothalamic tract?
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What does the anterolateral pathway consist of?
What does the anterolateral pathway consist of?
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Where do some axon collaterals ascend/descend before entering the central gray?
Where do some axon collaterals ascend/descend before entering the central gray?
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What is the role of the spinoreticular tract in pain sensation?
What is the role of the spinoreticular tract in pain sensation?
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Which part of the brain does the spinomesencephalic tract project to?
Which part of the brain does the spinomesencephalic tract project to?
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What does the spinoreticular tract lead to?
What does the spinoreticular tract lead to?
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How does the second-order sensory neuron cross to the opposite side?
How does the second-order sensory neuron cross to the opposite side?
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What is the consequence of a lateral cord lesion?
What is the consequence of a lateral cord lesion?
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Where does the third-order sensory neuron synapse?
Where does the third-order sensory neuron synapse?
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Which area is found in the postcentral gyrus?
Which area is found in the postcentral gyrus?
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What is commonly associated with lesions in the PC-ML pathway?
What is commonly associated with lesions in the PC-ML pathway?
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"Positive" symptoms of lesions in the anterolateral pathway may include:
"Positive" symptoms of lesions in the anterolateral pathway may include:
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'Astereognosis' is associated with:
'Astereognosis' is associated with:
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'Hypo-reflexia' is most commonly related to damage in which area?
'Hypo-reflexia' is most commonly related to damage in which area?
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'Allodynia' can be described as:
'Allodynia' can be described as:
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Study Notes
Anterolateral Pathway
- Small diameter unmyelinated axons carrying information about pain and temperature sense enter the spinal cord via the dorsal root entry zone.
- These axons synapse immediately in the gray matter of the spinal cord, mainly in the dorsal marginal zone (lamina I) and deeper in the dorsal horn (lamina V).
- Some axons ascend/descend for a few segments in Lissauer's tract before entering the central gray.
Ascending Pathways
- The anterolateral pathway consists of three ascending pathways:
- Spinothalamic tract
- Spinoreticular tract
- Spinomesencephalic tract
Spinothalamic Tract
- Mediates discriminative aspects of pain and temperature sensation, including location and intensity of the stimulus.
- A major relay for the spinothalamic tract is the ventral posterior lateral nucleus (VPL) of the thalamus.
Spinoreticular Tract
- Conveys emotional and arousal aspects of pain.
- Terminates on the medullary-pontine reticular formation, which then projects to the intralaminar thalamic nuclei.
Spinomesencephalic Tract
- Projects to the midbrain periaqueductal gray matter and the superior colliculi.
- Involved in pain modulation.
Synapses and Pathways
- Primary sensory neurons synapse on second-order sensory neurons in the dorsal horn.
- Second-order sensory neurons cross the midline through the anterior (ventral) commissure (over 2-3 segments) to ascend in the anterolateral white matter.
- Second-order sensory neurons synapse onto third-order sensory neurons in the thalamus.
- Third-order sensory neurons project to the somatosensory cortex.
Somatosensory Cortex
- Found in the postcentral gyrus.
- Occurs on both sides.
- Maintains somatotopic organization (legs = lateral, arms = medial).
Lesion Effects
- Lateral cord lesion affects contralateral pain and temperature sensation beginning a few segments below the lesion.
- Posterior column damage does not affect crude touch sensation due to the anterolateral pathway.
Somatosensory Lesions
- Negative symptoms:
- Loss of position and vibration sense (limb orientation)
- Loss of discriminatory touch (2-point discrimination)
- Astereognosis (inability to recognize objects by touch)
- Sensory 'ataxia' (unsteady balance and gait, poorly coordinated movements)
- Positive symptoms:
- Paresthesia (dysesthesia): abnormal sensations that are not painful
- Hyperathia/allodynia: sensation of pain in stimuli that is not normally painful
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Description
Explore the pathway through which small diameter unmyelinated axons carrying information about pain and temperature sense enter the spinal cord and synapse in the gray matter. Learn about the three ascending pathways involved in this process.
