NEUROLOGY PATHWAYS
DESCENDING TRACT
Extrapyramidal system
Definition: It is a network of subcortical nuclei and descending
motor pathways that regulate posture, muscle tone, balance
and involuntary or automatic movements, acting mainly via
brainstem pathways and modulating the execution of voluntary
motor activity.
Main components:
a) Basal ganglia: caudate nucleus, putamen, globus pallidus,
subthalamic nucleus, substantia nigra.
b) Descending tracts: rubrospinal, reticulospinal,
vestibulospinal, tectospinal.
Function:
Regulation of muscle tone
Maintenance of posture
, Control of automatic and semi-automatic movements
(gait, arm swing, postural adjustments)
Coordination of gross motor activity
Integration of reflexes
Modulation of voluntary movements
Descending extrapyramidal tracts:
1. Rubrospinal tract:
Origin: red nucleus, midbrain tegmentum
Decussation: ventral tegmental decussation in midbrain;
early and contralateral crossing
Course:
Red nucleus (midbrain)
Ventral tegmental decussation
(immediate crossing)
Descends in lateral funiculus of
spinal cord
Cervical/thoracic anterior horn of
spinal cord
, Termination: cervical spinal cord anterior horn, via
interneurons influencing alpha motor neurons (mainly
upper limb flexors).
Function:
Facilitates flexor muscles of upper limb
Inhibits extensor muscles (via interneuronal circuits)
Has limited compensatory role for corticospinal tract
function in humans
2. Vestibulospinal tract
Origin: vestibular nuclei (pons and medulla)
Types: Lateral vestibulospinal tract (LVST)
Medial vestibulospinal tract (MVST)
Decussation:
LVST: predominantly uncrossed (ipsilateral)
MVST: partial crossing (bilateral)
Termination:
LVST: Extensor motor neurons (trunk/limbs)
Anterior horn
MVST: Neck/upper trunk motor neurons
DESCENDING TRACT
Extrapyramidal system
Definition: It is a network of subcortical nuclei and descending
motor pathways that regulate posture, muscle tone, balance
and involuntary or automatic movements, acting mainly via
brainstem pathways and modulating the execution of voluntary
motor activity.
Main components:
a) Basal ganglia: caudate nucleus, putamen, globus pallidus,
subthalamic nucleus, substantia nigra.
b) Descending tracts: rubrospinal, reticulospinal,
vestibulospinal, tectospinal.
Function:
Regulation of muscle tone
Maintenance of posture
, Control of automatic and semi-automatic movements
(gait, arm swing, postural adjustments)
Coordination of gross motor activity
Integration of reflexes
Modulation of voluntary movements
Descending extrapyramidal tracts:
1. Rubrospinal tract:
Origin: red nucleus, midbrain tegmentum
Decussation: ventral tegmental decussation in midbrain;
early and contralateral crossing
Course:
Red nucleus (midbrain)
Ventral tegmental decussation
(immediate crossing)
Descends in lateral funiculus of
spinal cord
Cervical/thoracic anterior horn of
spinal cord
, Termination: cervical spinal cord anterior horn, via
interneurons influencing alpha motor neurons (mainly
upper limb flexors).
Function:
Facilitates flexor muscles of upper limb
Inhibits extensor muscles (via interneuronal circuits)
Has limited compensatory role for corticospinal tract
function in humans
2. Vestibulospinal tract
Origin: vestibular nuclei (pons and medulla)
Types: Lateral vestibulospinal tract (LVST)
Medial vestibulospinal tract (MVST)
Decussation:
LVST: predominantly uncrossed (ipsilateral)
MVST: partial crossing (bilateral)
Termination:
LVST: Extensor motor neurons (trunk/limbs)
Anterior horn
MVST: Neck/upper trunk motor neurons
