Neuroanatomy Quiz: White Matter Functions

Ascending Tracts (Sensory Pathways)

• Information is divided into two main groups: Exteroceptive and proprioceptive.
• Exteroceptive information originates from outside the body (pain, temperature, touch).
• Proprioceptive information originates from inside the body (muscles, joints).

Three-Neuron Pathways

• Primary sensory neurons (1st order): from external receptors, travel through dorsal roots of spinal cord.
• Secondary sensory neurons (2nd order/interneurons): give rise to an axon that decussates and ascends to a higher level of the central nervous system.
• Tertiary sensory neurons (3rd order/thalamic neurons): originate from the thalamus, project to primary sensory cortex, travel through the internal capsule.

A) Anterolateral Spinothalamic Tract

• Carries information about pain, temperature, crude touch, and pressure.
• 1st order neuron enters spinal cord via dorsal root, synapses on 2nd order neuron, decussates, ascends to brain, synapses on 3rd order neuron (in thalamus), terminates in somatosensory cortex.

Lateral Spinothalamic Tract

• Carries impulses concerned with pain and temperature (thermal sensations).
• Axons of 1st order neurons enter the spinal cord from the posterior root ganglion, proceed to the posterior gray column, divide into ascending and descending branches, and travel for a distance of one or two segments as the posterolateral tract of Lissauer.
• Fibers of the first-order neuron terminate by synapsing with cells in the posterior gray horn, including cells in the substantia gelatinosa.
• Axons of 2nd order neurons decussate obliquely within one segment of their origin, passing through the ventral white commissure and terminate on 3rd order neurons in the ventral posterolateral nucleus of the thalamus.
• Thalamic neurons project to the somatosensory cortex through the posterior limb of the internal capsule.

B) Posterior (Dorsal) Column (Fasciculus Gracilis and Fasciculus Cuneatus) and Medial Lemniscus

• Contains two tracts: Fasciculus gracilis (FG) and Fasciculus cuneatus (FC).
• Carries information of conscious proprioception (muscle joint sense), discriminative touch, and vibratory sense.

C) Spinocerebellar Tract

• The spinocerebellar system consists of a sequence of two neurons.
• Two tracts: posterior (ipsilateral) and anterior (contralateral).
• Carries information of proprioception derived from muscle spindles, Golgi tendon organs, and tactile receptors (Merkel's disks, Meissner's corpuscles, Ruffini endings, Pacinian corpuscle, and Krause end bulbs).
• Terminates in the cerebellum.
• Controls posture and coordination of movements.

Posterior Spinocerebellar Tract

• Present only above level L3.
• Cell bodies of 2nd order neuron lie in Clark's column (dorsal or posterior thoracic nucleus).
• Axons of 2nd order neurons terminate ipsilaterally in the cerebellar cortex by entering through the inferior cerebellar peduncle.

Anterior Spinocerebellar Tract

• Cell bodies of 2nd order neuron lie in the base of the dorsal horn of the lumbosacral segments.
• Axons of 2nd order neurons cross to the opposite side, ascend to the midbrain, and enter the superior cerebellar peduncle.
• The fibers cross the midline again within the cerebellum before terminating in the cerebellar cortex.
• Both spinocerebellar tracts convey sensory information to the same side of the cerebellum.

D) Spinotectal Tract

• From the posterior root ganglion, axons enter the spinal cord and proceed to the grey matter to form synapses with unidentified second order neurons.
• The second-order neurons' axons climb as the spinotectal tract in the anterolateral column after crossing the median plane.
• They terminate by forming synapses with neurons in the superior colliculus of the midbrain.
• This pathway provides afferent information for spinovisual reflexes and brings about movements of the eyes and head towards the source of the stimulation.

E) Spinoreticular Tract

• From the posterior root ganglion, axons enter the spinal cord and proceed to the grey matter to form synapses with unknown second-order neurons.
• These second-order neurons' axons ascend the lateral white column as the spinoreticular tract.
• The majority of the fibers are uncrossed and come to an end by making synapses with reticular formation neurons in the midbrain, medulla oblongata, and pons.
• The reticular formation receives afferent fibers from the spinoreticular tract, which is crucial in determining consciousness levels.

F) Spino-olivary Tract

• The axons enter the spinal cord from the posterior root ganglion and terminate on unknown second-order neurons in the posterior gray column.
• The second-order neurons ascend after crossing the midline at the junction of the anterior and lateral white columns as the spino-olivary tract.
• In the inferior olivary nuclei of the medulla oblongata, axons terminate by forming synapses with third-order neurons.
• The axons of the third-order neurons enter the cerebellum via the inferior cerebellar peduncle after crossing the midline.
• The spino-olivary tract conveys information to the cerebellum from cutaneous and proprioceptive organs.

References

• Clinical neuroanatomy / Richard S. Snell. — 7th ed. Lippincott Williams & Wilkins-Philadelphia
• Netter's Clinical Anatomy
• Last's anatomy Regional and applied
• Gray's Anatomy

Test your knowledge on the functions and structures of white matter in the spinal cord. This quiz covers topics including neuroglial cells, sensory information pathways, and the relationship between consciousness and neuroanatomical structures. Challenge yourself with questions related to ascending tracts and the roles of specific neural pathways.