In this note, we will continue examining the anatomy and function of the tracts of the brain and spinal cord.

Let’s move one to the descending tracts.

They carry motor (efferent) information from the structures of the central nervous system to effector organs. In the somatic division of the nervous system, which we are studying right now, effectors are represented by the skeletal muscles.

The descending tracts are functionally divided into two major groups:

• Pyramidal (voluntary) tracts
• Extrapyramidal (involuntary) tracts

The second group includes the basal ganglia, which we have discussed in detail in the corresponding topic from the “Central Nervous System” section,

as well as several pathways:

• Rubrospinal tract
• Tectospinal tract
• Vestibulospinal tracts (lateral and medial)
• Reticulospinal tracts (from the pons and medulla oblongata)

The activity of these pathways provides the involuntary control of skeletal muscles. Mostly this involves the muscles of the neck, trunk, and proximal muscles of the limbs.

Rubrospinal tract

The rubrospinal tract is the only pathway of the extrapyramidal system involved in the regulation of movements of the distal musculature. Specifically, it activates the flexor muscles and inhibits the extensors of the upper limbs.

The first-order neurons are located in the red nuclei within the tegmentum of the midbrain.

These nuclei receive proprioceptive information from the cerebellum.

Almost immediately after emerging from the nuclei, the fibers decussate, forming the anterior tegmental decussation.

The tract then continues within the lateral funiculus,

eventually synapsing to the second-order neuron in the anterior horn of the cervical segments of the spinal cord.

Tectospinal tract

The tectospinal tract originates from neurons of the superior colliculi.

The fibers of this pathway decussate, forming the posterior tegmental decussation.

Then the tract travels within the anterior funiculus of the spinal cord, eventually synapsing to the second-order neuron in the anterior horn of the cervical segments.

Due to its connections with the superior colliculus, the tectospinal tract provides a motor response to sudden visual stimuli.

Vestibulospinal tracts

The vestibulospinal tracts include the lateral and medial pathways. The vestibular nuclei are located in the lateral part of the rhomboid fossa. These nuclei receive sensory information from the cerebellum and vestibular receptors of the inner ear.

As a result, this complex activates the antigravity muscles, in particular the muscles of the vertebral column and the extensors of the limbs.

The lateral vestibulospinal tract originates from the lateral vestibular nucleus.

The medial vestibulospinal tract primarily originates from the medial vestibular nucleus.

The fibers of both tracts travel within the anterior funiculus of the spinal cord, and in the anterior horn, they synapse to the second-order neuron.

The medial tract affects the muscles of the head and neck, while the lateral tract activates the axial musculature and the muscles of the pelvic and shoulder girdle.

Reticulospinal tract

The reticulospinal tracts include the pontine and medullary pathways.

These pathways originate from the reticular formation of the brainstem and descend into the spinal cord.

The pontine (medial) pathway emerges from the neurons of the reticular formation of the pons, while the lateral (medullary pathway) originates from the reticular formation of the medulla oblongata (in particular the gigantocellular nucleus).

The fibers of the medial pathways travel within the anterior funiculus, and the fibers of the lateral pathways within the lateral funiculus of the spinal cord, and synapse to the second-order neuron in the anterior horn.

The pontine pathway activates the antigravity muscles, activating the muscles of the vertebral column and the limb extensors, while the medullary pathway activates the flexor muscles. This helps us to maintain posture.

Golosary

Extrapyramidal system

basal nuclei

nuclei basales

rubrospinal tract

tractus rubrospinalis

tectospinal tract

tractus tectospinalis

red nucleus

nucleus ruber

anterior tegmental decussation

decussatio tegmentalis anterior

lateral funiculus

funiculus lateralis

superior colliculi

colliculi superiores

posterior tegmental decussation

decussatio tegmentalis posterior

anterior funiculus

funiculus anterior

vestibular nuclei

nuclei vestibulares

lateral vestibulospinal tract

tractus vestibulospinalis lateralis

medial vestibulospinal tract

tractus vestibulospinalis medialis

lateral vestibular nucleus

nucleus vestibularis lateralis

medial vestibular nucleus

nucleus vestibularis medialis

pontine reticular formation

formatio reticularis pontis

medullary reticular formation

formatio reticularis medullae oblongatae

pontine reticulospinal tract

tractus pontoreticulospinalis

medullary reticulospinal tract

tractus bulboreticulospinalis