Ascending Sensory Pathways & Spinal Cord Tracts

50 question-and-answer flashcards covering spinal cord tracts, sensory pathways, receptors, lemnisci, and clinical correlations.

What are “long” tracts of the spinal cord?

Ascending or descending pathways that extend the entire length of the cord or reach the brain.

What characterizes “short” tracts of the spinal cord?

Fibers that start and end within the spinal cord, ascending or descending only a few segments.

List the four main long ascending tracts that carry sensations to the cerebral cortex.

Gracile tract, Cuneate tract, Lateral spinothalamic tract, Ventral spinothalamic tract.

Which tract conveys proprioception and fine touch from the lower ipsilateral half of the body?

Gracile tract.

Which tract conveys proprioception and fine touch from the upper ipsilateral half of the body?

Cuneate tract.

Name the two ascending spinocerebellar tracts.

Dorsal (posterior) spinocerebellar tract and Ventral (anterior) spinocerebellar tract.

What two additional ascending tracts project to sub-cortical structures other than the cerebellum?

Spino-olivary tract and Spino-tectal tract.

Define proprioception.

The sense of position, movement, and vibration of body parts.

Define fine touch.

Tactile localization, discrimination, and stereognosis (shape recognition by touch).

Name three proprioceptive receptors.

Muscle spindles, tendon (Golgi) spindles, and Pacinian corpuscles.

Give three receptors for fine touch.

Meissner’s corpuscles, Ruffini’s endings, and Merkel’s discs.

Where are first-order neurons for body proprioception and fine touch located?

Large cells in the dorsal (spinal) root ganglia.

Through which root division do thick myelinated fibers for fine touch enter the cord?

The medial division of the posterior (dorsal) roots.

In which dorsal column does information from sacral, lumbar, and lower thoracic segments ascend?

Gracile tract (fasciculus gracilis).

In which dorsal column does information from cervical and upper thoracic segments ascend?

Cuneate tract (fasciculus cuneatus).

Where do gracile and cuneate tracts terminate?

In their respective nuclei (gracile & cuneate nuclei) in the closed medulla on the same side.

What name is given to the decussating fibers from gracile and cuneate nuclei?

Internal arcuate fibers.

What structure is formed after the sensory decussation of internal arcuate fibers?

The medial lemniscus.

Where does the medial lemniscus terminate?

In the ventral posterolateral nucleus (VPL) of the thalamus.

Which cortical area receives third-order medial lemniscal fibers?

Post-central gyrus, Brodmann areas 3, 1, 2.

What condition results from bilateral degeneration of gracile and cuneate tracts in syphilis?

Tabes dorsalis.

What is the chief clinical sign of tabes dorsalis?

Sensory ataxia with a stamping gait due to loss of proprioception.

What receptors initiate pain and temperature sensation?

Free (naked) nerve endings.

Where are first-order neurons for pain and temperature from the body located?

Small cells in dorsal root ganglia.

Into which tract do pain and temperature fibers ascend/descend one or two segments before synapsing?

Lissauer’s tract.

Which gray-matter nucleus contains second-order neurons for pain and temperature?

Substantia gelatinosa of Rolando.

Which tract carries pain and temperature after decussation?

Lateral spinothalamic tract.

At the pons, which two tracts merge to form the spinal lemniscus?

Lateral spinothalamic and Ventral spinothalamic tracts.

What sensations does the spinal lemniscus convey?

Pain, temperature, and crude touch from the opposite side of the body.

Which receptors mediate crude (simple) touch?

Free nerve endings, Meissner’s corpuscles, Merkel’s discs, and peritrichial endings.

Which nucleus supplies second-order neurons for crude touch?

Nucleus proprius (main sensory nucleus of the cord).

Which tract carries crude touch fibers that have crossed in the anterior white commissure?

Ventral (anterior) spinothalamic tract.

State the function of the ventral spinothalamic tract.

Conveys crude (simple) touch from the contralateral side of the body.

Where do both lateral and ventral spinothalamic tracts terminate?

Ventral posterolateral nucleus (VPL) of the thalamus.

Define “lemniscus” in brain-stem terminology.

A bundle of secondary sensory fibers that terminates in specific relay nuclei of the diencephalon.

Give the definition and function of the medial lemniscus.

An ascending brain-stem bundle carrying proprioception and fine touch from the opposite side of the body.

What are the four named short tracts of the spinal cord?

Fasciculi proprii, Lissauer’s tract, Septomarginal tract, and Comma-shaped tract.

Which short tract surrounds the gray matter like a ring and coordinates intersegmental activity?

Fasciculi proprii.

Which short tract conveys pain and temperature one–two segments before synapse?

Lissauer’s tract.

Which short tract contributes to the stretch reflex arc in lower segments?

Septomarginal tract (in sacral, lumbar, lower thoracic posterior column).

Which nucleus contains the only first-order sensory neurons located inside the CNS?

Mesencephalic nucleus of the trigeminal nerve (proprioception from face).

What is the trigeminal lemniscus?

An ascending bundle carrying proprioception, pain, temperature, and simple touch from the opposite side of the face.

From which two nuclei do fibers of the trigeminal lemniscus arise?

Spinal nucleus and Main sensory nucleus of the trigeminal nerve.

Into which thalamic nucleus does the trigeminal lemniscus terminate?

Posteromedial ventral nucleus (PMV) of the thalamus.

What term describes hypersensitivity to painful stimuli?

Hyperalgesia.

Where does primary hyperalgesia occur and what mediators lower pain threshold?

In inflamed (reddened) skin; bradykinin and K⁺ lower the threshold.

What is secondary hyperalgesia and where does the lesion lie?

Exaggerated pain in normal-appearing skin due to lesions in the thalamus or spinal cord.

Which spinal tract lesion pattern leads to loss of pain and temperature but preserves fine touch on one side?

Interruption of the lateral spinothalamic tract.

Name the three orders of neurons common to major ascending sensory pathways.

1st order – dorsal root or cranial sensory ganglia, 2nd order – gray-matter nucleus (cord/brainstem), 3rd order – thalamic relay nucleus (VPL or PMV).

Which cortical area integrates all general somatic sensations?

Post-central gyrus (primary somatosensory cortex, Brodmann areas 3, 1, 2).

What is the ultimate effect of decerebrate rigidity noted in animal studies?

Marked increase in tone of antigravity muscles causing extension of neck, back, limbs, and tail.