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Neural Pathways of the Nervous System

Q: In which specific sulcus or gyrus of the cortex does the optic radiation terminate?

The optic radiation (radiatio optica) terminates in the cortex of the occipital lobe of the brain, specifically along the banks of the calcarine sulcus (sulcus calcarinus). This area houses the cortical center of the visual analyzer (Brodmann area 17). Anatomical landmarks of the visual cortex projection also include the cuneus and the lingual gyrus (gyrus lingualis).

Q: In which specific thalamic nuclei do the fibers of the medial lemniscus terminate?

The fibers of the medial lemniscus (lemniscus medialis) terminate in the ventrolateral nuclei of the thalamus. These nuclei contain the cell bodies of the third-order sensory neurons onto which neural excitation is relayed. From here, the axons of the third-order neurons project through the posterior limb of the internal capsule to the cortex of the postcentral gyrus.

Tractus systematis nervosi

For medical students3 min readUpdated 2026-10-10

Neural pathways are systems of nerve fibers that transmit impulses from receptors to the brain and from motor centers to effector organs. They connect various parts of the central nervous system, ensuring sensation, coordination, and voluntary movement.

Fiber groupsMedial (thick) and lateral (thin) groups in the dorsal roots

Voluntary movementControlled by the pyramidal tract originating from the precentral gyrus

Sensory filterThe thalamus integrates sensory pathways before sending them to the cortex

Auditory pathwayPasses through the trapezoid body to the superior temporal gyrus

Ascending Spinal Cord Pathways

Sensory (afferent) pathways originate from first-order neurons whose cell bodies lie in the dorsal root ganglia. Their axons enter the spinal cord via the dorsal roots and divide into two components:

Medial group (thick, heavily myelinated fibers) enters the posterior funiculus. Here, each fiber bifurcates in a T-shape. Ascending branches travel to the dorsal horn and substantia gelatinosa, and some reach the medulla oblongata, forming the fasciculus gracilis and fasciculus cuneatus. Descending branches descend 6–7 segments, synapsing with the gray matter of the posterior horns (forming a medial tract in the lumbar region and adjoining the fasciculus gracilis in the sacral region).
Lateral group (thin fibers) proceeds to the marginal nucleus and then to the posterior column. Subsequently, axons ascend in the lateral funiculus (partially crossing via the anterior white commissure to the contralateral side).

Pathway Name	Course and Localization	Function
Spinothalamic tracts (anterior and lateral)	2nd neuron: proper nucleus of the posterior horn. Decussation in the white commissure. Ascends to the thalamus as the spinal lemniscus	Lateral: pain and temperature. Anterior: tactile sensation
Posterior spinocerebellar tract	2nd neuron: Clarke's nucleus. Travels laterally in the dorsolateral part of the lateral funiculus, entering the cerebellum via the inferior cerebellar peduncle	Proprioception (from muscles and tendons)
Anterior spinocerebellar tract	2nd neuron: intermediomedial nucleus. Partial decussation. Via the superior cerebellar peduncle to the cerebellar vermis	Proprioception
Spino-olivary tract	From posterior horn cells, crosses, goes to the inferior olivary nucleus	Information from cutaneous, muscle, and tendon receptors

Additionally, the spinoreticular tract (uncrossed, projecting to the brainstem reticular formation) and spinotectal tract (terminating in the midbrain tectum) are distinguished.

Ascending Pathways of the Brainstem

At the brainstem level, major sensory collection systems are formed:

Medial lemniscus (lemniscus medialis). A direct continuation of the fasciculus gracilis and fasciculus cuneatus. The axons of their second-order neurons (in the corresponding nuclei of the medulla oblongata) form internal arcuate fibers, decussate, and head to the thalamus.
Trigeminal lemniscus (lemniscus trigeminalis). Collects fibers from the sensory nuclei of cranial nerves V, VII, IX, and X, crosses to the contralateral side, and also terminates in the thalamus.
Auditory pathway. Begins at the spiral ganglion. Second-order neurons lie in the anterior and posterior cochlear nuclei. After decussation (in the trapezoid body), fibers form the lateral lemniscus. The pathway passes through the medial geniculate body and auditory radiation to reach the cortex of the superior temporal gyrus.
Radiations. Transmit signals from subcortical centers to the cortex. Optic radiation (radiatio optica) connects the lateral geniculate body to the occipital lobe. Thalamic radiations connect its nuclei to the cortex (anterior radiation to the frontal lobe, central radiation to the postcentral gyrus).

Descending Pathways

Descending (efferent) pathways originate in the cerebral cortex, brainstem nuclei, or cerebellum. They terminate on the motor nuclei of the brainstem or in the anterior horns of the spinal cord, producing a motor response.

1. Pyramidal System Responsible for voluntary (conscious) movements. The pyramidal tract (tractus pyramidalis) starts in the precentral gyrus of the cortex, passes through the corona radiata, the posterior limb of the internal capsule, the cerebral peduncles, and the pons. Decussation occurs in the pyramids of the medulla oblongata, after which the pathway divides into the lateral and anterior corticospinal tracts. A similar function for the head and neck muscles is performed by corticinuclear fibers (fibrae corticonucleares), running to the motor cranial nerve nuclei.

2. Extrapyramidal System Provides unconscious regulation of muscle tone, balance, and movement coordination. It includes several tracts:

Rubrospinal tract (tractus rubrospinalis);
Tectospinal tract (tractus tectospinalis);
Vestibulospinal tract (tractus vestibulospinalis, divided into lateral and medial);
Pontine and medullary reticulospinal tracts;
Olivospinal tract (tractus olivospinalis);
Central tegmental tract (tractus tegmentalis centralis).

Mnemonic

Note the localization of second-order neurons: for the spinothalamic tracts (pain, temperature, touch), they are located directly within the spinal cord (decussation occurs immediately), whereas for the tracts of Goll and Burdach (gracilis and cuneatus — proprioception), they ascend to the medulla oblongata, where the decussation of the medial lemniscus takes place.

Frequently asked questions

What exact type of sensation do the tracts of Goll and Burdach (gracilis and cuneatus) conduct?

The gracile and cuneate fasciculi (tracts of Goll and Burdach) conduct conscious proprioceptive and tactile sensation. These modalities include:

Conscious proprioceptive sensation — muscle-joint sense and body position;
Vibratory sensation — perception of vibration;
Touch and pressure — tactile sense;
Discriminative sensation — the ability to distinguish two points of touch.

These pathways provide a conscious reaction to the listed stimuli.

In which specific sulcus or gyrus of the cortex does the optic radiation terminate?

The optic radiation (radiatio optica) terminates in the cortex of the occipital lobe of the brain, specifically along the banks of the calcarine sulcus (sulcus calcarinus). This area houses the cortical center of the visual analyzer (Brodmann area 17). Anatomical landmarks of the visual cortex projection also include the cuneus and the lingual gyrus (gyrus lingualis).

In which specific thalamic nuclei do the fibers of the medial lemniscus terminate?

The fibers of the medial lemniscus (lemniscus medialis) terminate in the ventrolateral nuclei of the thalamus. These nuclei contain the cell bodies of the third-order sensory neurons onto which neural excitation is relayed. From here, the axons of the third-order neurons project through the posterior limb of the internal capsule to the cortex of the postcentral gyrus.

Which descending tracts run in the anterior funiculus of the spinal cord?

The anterior funiculus of the spinal cord contains the following descending motor tracts:

Anterior corticospinal tract (tractus corticospinalis anterior) — formed by uncrossed fibers of the pyramidal tract that decussate in the white commissure of the spinal cord;
Tectospinal tract (tractus tectospinalis) — situated immediately adjacent to the anterior median fissure of the spinal cord, providing unconscious reflex motor reactions.

Where are the cell bodies of the first-order neurons for all sensory ascending pathways located?

The cell bodies of first-order neurons for all types of sensation always lie outside the CNS—in the dorsal root ganglia.

What is the difference between the lateral and anterior spinothalamic tracts?

The lateral spinothalamic tract conducts pain and temperature sensation, whereas the anterior tract is responsible for tactile sensation.

What is the medial lemniscus and how is it formed?

The medial lemniscus is a fiber bundle in the brainstem. It is formed by the axons of second-order neurons of the gracile and cuneate nuclei after they decussate (forming internal arcuate fibers).

Where does the pyramidal tract decussate?

Decussation of the pyramidal tract fibers occurs in the region of the pyramids of the medulla oblongata.

Go deeper

Topography of neural pathways in a transverse section of the spinal cord.
Detailed fiber course of the extrapyramidal system and their influence on muscle tone.
Internal capsule: arrangement of ascending and descending tracts within its limbs.
Formation of the lateral lemniscus and the centers of the auditory analyzer.
Role of the reticular formation and the spinoreticular tract.