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Descending Motor Tracts
NBIO 401 – Wednesday October 30, 2013
Objectives:
-Be able to describe the origin, pathway, and termination of
each of the four major descending motor tracts in the brain.
-Be able to describe the deficits that follow severing the
corticospinal tract, both initially and after recovery.
-Be able to describe the evidence that rubrospinal fibers help
compensate for the loss of the corticospinal system.
MEDIAL AND LATERAL DESCENDING MOTOR TRACTS
MEDIAL AND LATERAL DESCENDING MOTOR TRACTS
LATERAL
DESCENDING
MOTOR TRACTS
CORTICOSPINAL
TRACT
CORTICOSPINAL TRACT
CORTICOSPINAL SYSTEM
CORTICOSPINAL SYSTEM (tract somatotopy)
A
B
CORTICOSPINAL SYSTEM
CORTICOSPINAL SYSTEM (tract somatotopy)
A
B
CORTICOSPINAL SYSTEM (tract somatotopy)
A
B
CORTICOSPINAL SYSTEM
(Decussation)
Right
corticospinal fibers
from left cortex
Left
~90% of corticospinal fibers from
left cortex in the dorsolateral part
of white matter in the right side
of the cord
Right
Left
pyramidal
decussation
(crossing
corticospinal
fibers)
~90% of corticospinal fibers
~10% of corticospinal fibers from
from left cortex enter
dorsolateral part of white matter left cortex enter ventromedial part
of white matter right in the left
in the right side of the cord
side of the cord
~10% of corticospinal fibers from
left cortex in the ventromedial
part of white matter right in the
left side of the cord
CORTICOSPINAL SYSTEM
(summary of the course of the
descending fibers)
CORTICOSPINAL SYSTEM
(facial nucleus input)
CORTICOSPINAL SYSTEM
(facial nucleus input)
CORTICOSPINAL SYSTEM
(facial nucleus input)
RUBROSPINAL
TRACT
RUBROSPINAL SYSTEM (location of nucleus and tract)
RUBROSPINAL SYSTEM (location of nucleus and tract)
Edinger Westphal nucleus
(constricts the pupil)
Red Nucleus
Oculomotor nucleus
(motoneurons for
eye muscles)
Oculomotor nerve
(to eye muscles & pupil muscles)
RUBROSPINAL SYSTEM (location of nucleus and tract)
RUBROSPINAL SYSTEM
(location of tract
in transverse sections)
PYRAMIDS
PYRAMIDS
PYRAMIDS
RUBROSPINAL SYSTEM
(labeled inputs and outputs)
FIBERS IN
SUPERIOR CEREBELLAR
PEDUNCLE
INTERPOSITUS NUCLEI
ANTERIOR
RUBROSPINAL
TRACT
POSTERIOR
RUBROSPINAL
TERMINATIONS IN
INTERMEDIATE SPINAL
GRAY MATTER
RUBROSPINAL
TRACT
RUBROSPINAL SYSTEM (function)
MEDIAL
DESCENDING
MOTOR TRACTS
VESTIBULOSPINAL
TRACT
Relationship between Cochlear & Vestibular Parts of VIIIth Nerve
Vestibulocochlear
Nerve VIII
32
Relationship between Cochlear & Vestibular Parts of VIIIth Nerve
Vestibulocochlear
Nerve VIII
33
Relationship between Cochlear & Vestibular Parts of VIIIth Nerve
Superior Cochlear
nucleus
Vestibulocochlear
Nerve VIII
34
Relationship between Cochlear & Vestibular Parts of VIIIth Nerve
Superior Cochlear
nucleus
Vestibulocochlear
Nerve VIII
35
Relationship between Cochlear & Vestibular Parts of VIIIth Nerve
Superior Cochlear
nucleus
Vestibulocochlear
Nerve VIII
36
Relationship between Cochlear & Vestibular Parts of VIIIth Nerve
Superior Cochlear
nucleus
Vestibulocochlear
Nerve VIII
Vestibular nuclei
37
Relationship between Cochlear & Vestibular Parts of VIIIth Nerve
Superior Cochlear
nucleus
Vestibulocochlear
Nerve VIII
Vestibular nuclei
38
VESTIBULOSPINAL
SYSTEM
(location and function of
the vestibular nuclei)
VESTIBULOSPINAL
SYSTEM
(location and function of
the vestibular nuclei)
VESTIBULOSPINAL
SYSTEM
(location and function of
the vestibular nuclei)
VESTIBULOSPINAL
SYSTEM
(location and function of
the vestibular nuclei)
VESTIBULOSPINAL
SYSTEM
(location and function of
the vestibular nuclei)
Relationship between Cochlear & Vestibular Parts of VIIIth Nerve
Superior Cochlear
nucleus
Vestibulocochlear
Nerve VIII
Vestibular nuclei
44
VESTIBULOSPINAL SYSTEM
VIIIth
nerve
VIIIth
nerve
VESTIBULOSPINAL SYSTEM
superior
cochlear
nucleus
VIIIth
nerve
superior
cochlear
nucleus
VIIIth
nerve
VESTIBULOSPINAL SYSTEM
superior
cochlear
nucleus
inferior cerebellar
peduncle
VIIIth
nerve
inferior cerebellar
peduncle
superior
cochlear
nucleus
VIIIth
nerve
VESTIBULOSPINAL SYSTEM
medial
vestibular
nucleus
superior
cochlear
nucleus
inferior cerebellar
peduncle
VIIIth
nerve
inferior cerebellar
peduncle
superior
cochlear
nucleus
VIIIth
nerve
VESTIBULOSPINAL
SYSTEM
(descending tracts)
VESTIBULOSPINAL
SYSTEM (function)
C. Head and trunk together (vestibular stimulation)
head up
head normal
head down
VESTIBULOSPINAL
SYSTEM (function)
C. Head and trunk together (vestibular stimulation)
head up
head normal
head down
VESTIBULOSPINAL
SYSTEM
RETICULOSPINAL
TRACT
Pontine reticular formation
Pontine reticular formation
Pontine reticular formation
pontine reticular
formation
Medullary reticular formation
Medullary reticular formation
Medullary reticular formation
medullary reticular
formation
RETICULOSPINAL SYSTEM
(course and function)
ende
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