Neuroanatomy – Tracts © by Matthias Heyner 2008
Tracts
Pathway
Function
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Crude touch
pressure sensation
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Pain
Temperature
Itch
Tickle
Sexual sensation
Ascending tracts of the Spinal cord
Spinothalamic tracts
Anterior Spinothalamic tract
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Posterior Spinothalamic tract
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1st neuron (primary afferent neuron): Spinal ganglia
o Impulses from tactile corpuscles and receptors about hair follicles
o pass through dorsal root and enter gray matter
o branch in T shaped pattern (branches descend 1-2 segments and
ascend 2-15 segments)
o Terminate on neurons in the posterior column
2nd neuron: Neurons in the posterior column form anterior spinothalamic
tract)
o Cross at anterior commissure and ascend in the opposite anterior
funiculus.
o In the mesencephalon the tract runs in the medial lemniscus as
spinal lemniscus
o terminate in the posterolateral ventral nucleus of the thalamus
3rd neuron: Posterolateral ventral nucleus of the thalamus
o Terminate in the primary somatosensory cortex in the postcentral
gyrus.
st
1 neuron: Spinal ganglia
o Impulses come from free nerve endings
o Pass through dorsal roots into spinal cord
o Terminate on projection neurons in substantia gelatinosa
2nd neuron: Substantia gelatinosa
o Cross in the anterior commissure in the corresponding spinal cord
segment
o Ascend in the anterolateral funiculus of the opposite side
o Terminate in Thalamus
3rd neuron: (Thalamus)
o Terminate in the primary somatosensory cortex in the postcentral
gyrus
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Neuroanatomy – Tracts © by Matthias Heyner 2008
Fasciculus gracilis & fasciculus
cuneatus
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Fasciculus gracilis
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Fasciculus cuneatus
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Have descending axons which form different shapes at different levels
o Comma tract of Schultze (interfascicular fasciculus) in cervical cord
o Oval area of Flechsig (septomarginal fasciculus) in thoracic cord
o Philippe-Gombault triangle in sacral cord
o Concerned with somatosensory innervation
o Parts of the intrinsic circuits of spinal cord
1st neuron: Spinal Ganglia
o Impulses come from muscle receptors, tendon receptors, Vater –
Pacini corpuscles, receptors about hair follicles.
o Ascend uncrossed in the posterior funiculi to the nucleus gracilis in
the medulla oblongata
2nd neuron: Nucleus gracilis
o Cross in the medial lemniscus to the thalamus
3rd neuron: Thalamus
o Terminate in the primary somatosensory cortex in the postcentral
gyrus
st
1 neuron: Spinal Ganglia
o Impulses come from muscle receptors, tendon receptors, Vater –
Pacini corpuscles, receptors about hair follicles.
o Ascend uncrossed in the posterior funiculi to the nucleus cuneatus
in the medulla oblongata
2nd neuron: Nucleus cuneatus
o Cross in the medial lemniscus to the thalamus
3rd neuron: Thalamus
o Terminate in the primary somatosensory cortex in the postcentral
gyrus
Not Present below level of T3
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Fine touch of lower limb
Conscious proprioception of lower
limb
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Fine touch of upper limb
Conscious proprioception of upper
limb
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Neuroanatomy – Tracts © by Matthias Heyner 2008
Spinocerebellar tracts
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Anterior Spinocerebellar tract
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Posterior Spinocerebellar tract
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Located in the lateral funiculus
Their projection fibers ascend both ipsilaterally and contralaterally to the
cerebellum via the cerebellar peduncle
Both have the same somatotopic organization from front to back:
o Thoracic
o Lumbar
o Sacral
st
1 neuron: Spinal ganglion (pseudounipolar)
o Impulses come from muscle spindles and tendon receptors
o Terminate at the center of the posterior column
2nd neuron: Center of the posterior column (Projection neurons of the
anterior Spinocerebellar tract)
o Axons ascend both ipsilaterally and contralaterally to the
cerebellum
o Pass through the floor of the rhomboid fossa to the midbrain
o Axons then change direction to pass through the superior
cerebellar peduncle and superior medullary velum
o Terminate at the vermis of the cerbellum
1st neuron: Spinal ganglion (pseudounipolar)
o Impulses come from muscle spindles and tendon receptors
o Terminate at the posterior column
2nd neuron: Center of the posterior column (Projection neurons of the
anterior Spinocerebellar tract)
o Are contained in the thoracic nucleus which spans spinal cord
segments C8 to L2.
o Ascend ipsilaterally to the cerebellum, entering through the inferior
cerebellar peduncle
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Unconscious coordination of
motor activities (unconscious
proprioception, automatic
processes below the conscious
level such as jogging or riding a
bike)
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Unconscious coordination of
motor activities (unconscious
proprioception, automatic
processes below the conscious
level such as jogging or riding a
bike)
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Neuroanatomy – Tracts © by Matthias Heyner 2008
Descending tracts of the spinal cord
Pyramidal (Corticospinal) Tracts
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Pyramidal Tract
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Start in Motor cortex
Most important pathway for voluntary motor function
Some axons (corticonuclear fibers) terminate at the cranial nerve nuclei
Other axons (corticospinal fibers) terminate on the motor anterior horn
cells
Third group of the axons (corticoreticular fibers) terminate at the nuclei of
the reticular formation
Origin: Motor cortex at the pyramidal cells
o Corticonuclear fibers
o Corticospinal fibers
o Corticoreticular fibers
All 3 pass through the internal capsule from the telencephalon
o Continue into brainstem and spinal cord
In the brainstem the Corticonuclear fibers terminate at the motor nuclei of
the cranial nerves
The corticospinal fibers descend to the decussation of pyramids in the
lower medulla oblongata (~80% cross to the opposite side)
o Continue into the Spinal cord
o Form the corticospinal tract (has somatotopic organization; fibers
for the sacral cord are most lateral, fibers for the cervical cord are
most medial)
20% of the corticospinal fibers continues to descend without crossing
o They form the anterior corticospinal tract bordering the anterior
median fissure in a transverse section of the spinal cord
o Particularly well developed in the cervical cord but not present in
lower thoracic, lumbar and sacral cords.
o Most of the fibers cross at the segmental level to terminate on the
same motor neurons as the lateral corticospinal tract.
o The axons on the pyramid cells terminate via intercalated cells on
alpha and gamma neurons, Renshaw cells and inhibitory
interneurons.
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Voluntary motor activity
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Neuroanatomy – Tracts © by Matthias Heyner 2008
Extrapyramidal & Autonomic tracts
Extrapyramidal tracts
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Reticulospinal tract
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Tectospinal tract
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motor regulation of muscles
flexors & extensors
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Auditory & optic muscles
(motor innervation)
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Origin: lateral vestibular nucleus
o runs to spiral cord
ends in ventral horn in alpha & gamma neurons
parts of fibers run eye muscle nucleus
Origin: Nucleus rubor
The fibers cross to the contralateral side in the tegmental decussation
Runs down with the pyramidal tract in the ventral column to the neck
ends in motor neurons in ventral horn in alpha & gamma neurons
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balance maintained
raises the tone of flexors uses the
motor neurons
motor regulation
has excitory effect on alpha and
Gamma neurons of flexors (motor
regulation)
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Origin Spinal cord
runs to inf. olive (upwards)
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Vestibulospinal tract
Rubrospinal tract
Olivospinal tract
Origin:
o Basal Ganglia (corpus striatum & globus pallidus which act on
substantia nigra)
o Substantia nigra
o Red nucleus
Reticular formation of pons of medulla
Descend in ventral column
End: In the ventral horn of the spinal cord in alpha and gamma neurons
(deiter’s neurons)
Origin: Superior colliculus
o Fibers descend in the ventral column
o Crossover in Mesencephalon
End in Spinal cord in ventral horn in neck region in alpha & gamma neurons
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Somatosensory function
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Neuroanatomy – Tracts © by Matthias Heyner 2008
Tracts in the Brainstem
Medial longitudinal fasciculus
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Connects the cranial Eye nuclei with each other
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Ventral / posterior longitudinal
fasciculus (Schütz)
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Runs from thalamus to cranial nuclei
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Lateral lemniscus
Medial lemniscus
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Connects the Trapezoid body / superior olive with the inferior colliculus
Connects the dorsal column nuclei (gracilis & cuneatus) with the thalamus
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Spinal lemniscus
(borders the medial lemniscus)
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Connects the posterior horns (lateral and anterior spinothalamic tract) with
the thalamus
Is a portion of the anterior spinothalamic tract located in the
mesencephalon. The course of the anterior spinothalamic tract in the
brainstem is not fully understood…yet.
Connects the sensory trigeminal nuclei with the thalamus
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Pain pathway for the trunks and
limbs
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Sensory Pathway for the head
Origin: Pons, Medulla (Primary sensory neurons of
cranial nerves VII, IX, X)
End in nucleus of solitary tract.
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Visceral & taste sensory
Inside the pons
Origin: Neocortex this tract contains 4 other tracts:
o 1) Frontopontine tract
o 2) temperopontine tract
o 3) occipitopontine tract
o 4) parietopontine tract
o they all come from the neocortex (different lobes)
end in the pontine nucleus
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Cerebellar motor regulation
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Trigeminal lemniscus
(borders the medial lemniscus)
All the following tracts end in the
pons:
Solitary tract
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Corticopontine tract
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Association complex of the
reticular formation
Brings fibers from autonomic
centers to the cranial nerves
Part of auditory pathway
Touch, conscious proprioception
(movement, position etc) of the
trunk and limbs
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