20 Questions
Which pathway carries information about pain and temperature sensation?
Anterolateral pathway
Where do small diameter unmyelinated axons synapse in the spinal cord?
Dorsal marginal zone
Which pathway is responsible for conveying emotional and arousal aspects of pain?
Spinoreticular tract
What is the main function of the spinothalamic tract?
Mediates discriminative aspects of pain and temperature sensation
Where does the spinomesencephalic tract project to?
Midbrain periaqueductal gray matter
Which nucleus is a major relay for the spinothalamic tract?
Ventral posterior lateral nucleus
What does the anterolateral pathway consist of?
Three ascending pathways
Where do some axon collaterals ascend/descend before entering the central gray?
Lissauer's tract
What is the role of the spinoreticular tract in pain sensation?
Conveys emotional and arousal aspects of pain
Which part of the brain does the spinomesencephalic tract project to?
Midbrain periaqueductal gray matter
What does the spinoreticular tract lead to?
Feeling pain modulation
How does the second-order sensory neuron cross to the opposite side?
Through the anterior commissure
What is the consequence of a lateral cord lesion?
Affecting contralateral pain and temperature sensation
Where does the third-order sensory neuron synapse?
In the thalamus
Which area is found in the postcentral gyrus?
Somatosensory cortex
What is commonly associated with lesions in the PC-ML pathway?
Loss of discriminatory touch
"Positive" symptoms of lesions in the anterolateral pathway may include:
Tingling and numbness sensation
'Astereognosis' is associated with:
'Sensory ataxia'
'Hypo-reflexia' is most commonly related to damage in which area?
'Posterior columns'
'Allodynia' can be described as:
'Abnormal sensations that aren't painful'
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
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.
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