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CNS: Anatomy# Ascending Sensory Pathways
Q1. All of the following statements regarding the three-neuron chain of ascending sensory pathways are correct EXCEPT:
It is the most common anatomical arrangement for conscious sensation
The first-order neuron is pseudo-unipolar
The first-order neuron cell body is located in the dorsal root ganglion
The first-order neuron synapses directly with the cerebral cortex
Explanation:
First-order neurons synapse with second-order neurons, not directly with the cortex.
Q2. Regarding the first-order sensory neuron, all of the following are true EXCEPT:
It has a peripheral and a central process
Its peripheral process may terminate as a free nerve ending
Its central process exits the spinal cord via the anterior root
Its cell body lies in the posterior root ganglion
Explanation:
The central process enters via the posterior root.
Q3. All of the following regarding second-order neurons in ascending pathways are correct EXCEPT:
They decussate to the opposite side
They are located in the dorsal root ganglion
They ascend to higher CNS levels
They synapse with third-order neurons
Explanation:
Second-order neurons are in the spinal cord or medulla.
Q4. Concerning third-order neurons of ascending sensory pathways, all are true EXCEPT:
They are commonly located in the VPL nucleus of the thalamus
Their axons form thalamo-cortical projections
They pass through the posterior limb of the internal capsule
They decussate within the spinal cord
Explanation:
Decussation occurs at the second-order neuron.
Q5. All of the following statements about the lateral spinothalamic tract are correct EXCEPT:
It ascends ipsilaterally in the spinal cord
It carries pain and temperature sensation
Pain fibers lie anterior to temperature fibers
Sacral fibers are located laterally in upper segments
Explanation:
It ascends contralaterally.
Q6. All of the following characterize slow pain EXCEPT:
Conducted by C fibers
Poorly localized
Involves multiple synapses in posterior gray horn
Conducted rapidly at 30 m/sec
Explanation:
Rapid conduction is a feature of fast pain.
Q7. The spinal lemniscus includes all of the following tracts EXCEPT:
Lateral spinothalamic tract
Anterior spinothalamic tract
Medial lemniscus
Spinotectal tract
Explanation:
Medial lemniscus is a separate pathway.
Q8. All of the following are functions of the primary somesthetic cortex EXCEPT:
Precise localization of fast pain
Initiation of autonomic responses to pain
Assessment of pain intensity
Interpretation based on past experience
Explanation:
Autonomic responses are mediated by insula/limbic areas.
Q9. According to the gating theory, all are true EXCEPT:
Pain fibers stimulate the connector neuron
Touch fibers excite inhibitory interneurons
The gate is located in the substantia gelatinosa
Massage can reduce pain transmission
Explanation:
Pain fibers inhibit the connector neuron.
Q10. All of the following structures are part of the brain’s analgesia system EXCEPT:
Periaqueductal gray matter
Periventricular nuclei
Nucleus raphe magnus
Primary somesthetic cortex
Explanation:
Primary somesthetic cortex is not part of the analgesia system.
Q11. All of the following regarding nucleus raphe magnus are correct EXCEPT:
Contains serotonergic neurons
Receives input from periaqueductal gray matter
Enhances substance P release
Participates in pain inhibition
Explanation:
It inhibits substance P release.
Q12. Light (crude) touch is characterized by all of the following EXCEPT:
Poor localization
Free nerve endings as receptors
Second-order neurons in substantia gelatinosa
Transmission via posterior columns
Explanation:
Crude touch uses anterior spinothalamic tract.
Q13. All of the following are true regarding the anterior spinothalamic tract EXCEPT:
It conveys discriminative touch
It crosses in the anterior commissure
It carries crude touch and pressure
It contributes to the spinal lemniscus
Explanation:
Discriminative touch is via dorsal columns.
Q14. In the anterior spinothalamic tract at upper cervical levels, which fibers are most medial?
Sacral
Lumbar
Cervical
Thoracic
Explanation:
Cervical fibers are most medial.
Q15. All of the following receptors are involved in conscious proprioception EXCEPT:
Muscle spindles
Free nerve endings
Golgi tendon organs
Pacinian corpuscles
Explanation:
Free nerve endings are not proprioceptive.
Q16. Long ascending fibers of proprioception primarily ascend in:
Lateral spinothalamic tract
Anterior spinothalamic tract
Spinocerebellar tracts
Posterior white column
Explanation:
They ascend in posterior columns.
Q17. All of the following statements about fasciculus gracilis are correct EXCEPT:
It contains fibers from cervical spinal nerves
It is present throughout the spinal cord
It lies medial to fasciculus cuneatus
It conveys information from lower body
Explanation:
Cervical fibers run in fasciculus cuneatus.
Q18. Decussation of dorsal column fibers occurs at the level of:
Spinal cord
Thalamus
Medulla oblongata
Internal capsule
Explanation:
Occurs via internal arcuate fibers in the medulla.
Q19. All ascending sensory pathways share all of the following EXCEPT:
First-order neuron in dorsal root ganglion
Second-order neuron that decussates
Third-order neuron in the VPL nucleus
Relay in cerebellar cortex
Explanation:
Cerebellum is not involved in conscious sensation.
Q20. All of the following sensations reach consciousness via the VPL nucleus EXCEPT:
Pain
Olfaction
Crude touch
Proprioception
Explanation:
Olfaction bypasses the thalamus.