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Biology 226 spring 2012Presentation 3
March 25,2012
Major Descending ( Motor )
Pathway and spinal CordTracts
Direct ( Pyramidal )
Lateral corticospinal
tractFrom Wikipedia, the free encyclopedia
Lateral corticospinal tract
Lateral corticospinal tract labeled in red at upper left.
Latin tractus corticospinalis lateralis, fasciculus
cerebrospinalis lateralis
Gray's subject #185 759
The lateral corticospinal tract (also called the crossed
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pyramidal tract or lateral cerebrospinal fasciculus) is
the largest part of the corticospinal tract. It extends
throughout the entire length of the medulla spinalis,
and on transverse section appears as an oval area infront of the posterior column and medial to the
posterior spinocerebellar tract.
Its fibres arise from cells in the motor area of the
cerebral hemisphere of the opposite side.
They pass downward in company with those of the
anterior corticospinal tract through the same side of
the brain as that from which they originate, but they
cross to the opposite side in the medulla oblongata
and descend in the lateral funiculus of the medulla
spinalis.
The lateral corticospinal tract controls movement of
ipsilateral limbs(albeit contralateral to the
corresponding motor cortex) as it lies distal to thepyramidal decussation. Control of more central axial
and girdle muscles comes from the anterior
corticospinal tract.[1]
[edit]References
Anterior corticospinal
tract
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From Wikipedia, the free encyclopedia
(Redirected from Ventral corticospinal tract)
Anterior corticospinal tractAnterior corticospinal tract seen in red at bottom
center in figure (text tag found at upper-left).
Decussation of pyramids. Scheme showing passage of
various fasciculi from medulla spinalis to medulla
oblongata. a. Pons. b. Medulla oblongata. c.
Decussation of the pyramids. d. Section of cervical
part of medulla spinalis. 1. Anterior cerebrospinal
fasciculus (in red). 2. Lateral cerebrospinal fasciculus
(in red). 3. Sensory tract (fasciculi gracilis et cuneatus)
(in blue). 3. Gracile and cuneate nuclei. 4. Antero-
lateral proper fasciculus (in dotted line). 5. Pyramid. 6.
Lemniscus. 7. Medial longitudinal fasciculus. 8. Ventral
spinocerebellar fasciculus (in blue). 9. Dorsal
spinocerebellar fasciculus (in yellow).
Latin tractus corticospinalis anterior, fasciculus
cerebrospinalis anterior
Gray's subject #185 759
The anterior corticospinal tract (also called the ventral
corticospinal tract, medial corticospinal tract, direct
pyramidal tract, or anterior cerebrospinal fasciculus) is
a small bundle of descending fibers that connect the
cerebral cortex to the spinal cord. It is usually small,
varying inversely in size with the lateral corticospinal
tract, which is the main part of the corticospinal tract.
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It lies close to the anterior median fissure, and is
present only in the upper part of the medulla spinalis;
gradually diminishing in size as it descends, it ends
about the middle of the thoracic region.It consists of descending fibers that arise from cells in
the motor area of the ipsilateral cerebral hemisphere,
and that, as they run downward in the medulla
spinalis, cross in succession through the anterior
white commissure to the opposite side, where they
end, either directly or indirectly, by arborizing around
the motor neurons in the anterior column.
A few of its fibers pass to the lateral column of the
same side and to the gray matter at the base of the
posterior column.[citation needed]
They conduct voluntary motor impulses from the
precentral gyrus to the motor centers of the cord.
[edit]Additional images
Indrect ( Extrapyramidal )
Pathways
Tectospinal tractTectospinal tract
Diagram showing posFrom Wikipedia, the free
encyclopedia
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sible connection of long descending fibers from higher
centers with the motor cells of the ventral column
through association fibers. ("Tectospinal fasciculus"
labeled at center right.)Diagram of the principal fasciculi of the spinal cord.
("Tectospinal fasciculus" labeled at center right, in
red.)
Latin tractus tectospinalis
Gray's subject #185 760
In humans, the tectospinal tract (also known as
colliculospinal tract) is a nerve pathway which
coordinates head and eye movements. It is part of the
indirect extrapyramidal tract. Specifically, the
tectospinal tract connects the midbrain tectum and
the spinal cord.
It is responsible for motor impulses that arise fromone side of the midbrain to muscles on the opposite
side of the body. The function of the tectospinal tract
is to mediate reflex postural movements of the head
in response to visual and auditory stimuli.
The portion of the midbrain from where this tract
originates is the superior colliculus, which receives
afferents from the visual nuclei (primarily theoculomotor nuclei complex), then projects to the
contralateral (decussating ventral to the
mesencephalic duct) and ipsilateral portion of the first
cervical neuromeres of the spinal cord, the
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oculomotor and trochlear nuclei in the midbrain and
the abducens nucleus in the caudal portion of the
pons.
The tract descends to the cervical spinal cord toterminate in Rexed laminae VI, VII, and VIII to
coordinate head, neck, and eye movements, primarily
in response to visual stimuli.
[edit]See also
Upper motor neuron
Spinotectal tract
Vestibulospinal tractFrom Wikipedia, the free encyclopedia
Brain: Vestibulospinal tract
Vestibulospinal tract is labeled, in red at bottom left.
Diagram of the principal fasciculi of the spinal cord.
(Vestibulospinal fasciculus labeled at bottom right.)
Latin tractus vestibulospinalis
Gray's subject #185 760
NeuroLex ID birnlex_1643
The vestibulospinal tract is a neural tract in the
central nervous system. Specifically, it is a component
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of the extrapyramidal system and is classified as a
component of the medial pathway. Like other
descending motor pathways, the vestibulospinal fibers
of the tract relay information from nuclei to motorneurons.[1] The vestibular nuclei receive information
through the vestibulocochlear nerve about changes in
the orientation of the head. The nuclei relay motor
commands through the vestibulospinal tract. The
function of these motors commands are to alter
muscle tone, extend, and change the position of the
limbs and head with the goal of supporting posture
and maintaining balance of the body and head.[1]
Contents [hide]
1 Classification
2 Function
3 Anatomy
3.1 Lateral vestibulospinal tract
3.2 Medial vestibulospinal tract
4 Reflexes
4.1 Example of vestibulospinal reflex
4.2 Tonic labyrinthine reflex
4.3 Righting reflex
5 Development
5.1 CNS development
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5.2 Specification of ventral motor neurons by SHH
6 Damage
7 Current/Future Research8 See also
9 External links
10 References
[edit]Classification
Main article: extrapyramidal system
The vestibulospinal tract is part of the "extrapyramidal
system" of the central nervous system. In human
anatomy, the extrapyramidal system is a neural
network located in the brain that is part of the motor
system involved in the coordination of movement.[2]The system is called "extrapyramidal" to distinguish it
from the tracts of the motor cortex that reach their
targets by traveling through the "pyramids" of the
medulla. The pyramidal pathways, such as
corticospinal and some corticobulbar tracts, may
directly innervate motor neurons of the spinal cord or
brainstem. This is seen in anterior (ventral) horn cells
or certain cranial nerve nuclei. Whereas the
extrapyramidal system centers around the modulation
and regulation through indirect control of anterior
(ventral) horn cells. The extrapyramidal subcortical
nuclei include the substantia nigra, caudate, putamen,
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globus pallidus, thalamus, red nucleus and
subthalamic nucleus.[3]
The traditional thought was that the extrapyramidal
system operated entirely independently of thepyramidal system. However, more recent research
has provided a greater understanding of the
integration of motor control. Motor control from both
the pyramidal and extrapyramidal systems have
extensive feedback loops and are heavily
interconnected with each other.[1] A more
appropriate classification of motor nuclei and tractswould be by their functions. When broken down by
function there are two major pathways: medial and
lateral. The medial pathway helps control gross
movements of the proximal limbs and trunk. The
lateral pathway helps control precise movement of the
distal portion of limbs.[1] The vestibulospinal tract, as
well as tectospinal and reticulospinal tracts areexamples of components of the medial pathway.[1]
[edit]Function
The vestibulospinal tract is part of the vestibular
system in the CNS. The primary role of the vestibular
system is to maintain head and eye coordination,upright posture and balance, and conscious realization
of spatial orientation and motion. The vestibular
system is able to respond correctly by recording
sensory information from hairs cells in the labyrinth of
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the inner ear. Then the nuclei receiving these signals
project out to the extraocular muscles, spinal cord,
and cerebral cortex to execute these functions.[4]
One of these projections, the vestibulospinal tract, isresponsible for upright posture and head stabilization.
When the vestibular sensory neurons detect small
movements of the body, the vestibulospinal tract
commands motor signals to specific muscles to
counteract these movements and re-stabilize the
body.
The vestibulospinal tract is an upper motor neuron
tract consisting of two sub-pathways:
The medial vestibulospinal tract projects bilaterally
from the medial vestibular nucleus within the medial
longitudinal fasciculus to the ventral horns in the
upper cervical cord (T6 vertebra).[5] It promotes
stabilization of head position by innervating the neckmuscles, which helps with head coordination and eye
movement.
The lateral vestibulospinal tract provides excitatory
signals to interneurons, which relay the signal to the
motor neurons in antigravity muscles.[6] These
antigravity muscles are extensor muscles in the legs
that help maintain upright and balanced posture.
[edit]Anatomy
Medulla Spinalis
Latin medullae spinalis
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Gray's subject #185 753
[edit]Lateral vestibulospinal tract
The lateral vestibulospinal tract is a group ofdescending extrapyramidal motor neurons, or efferent
fibers.[2] This tract is found in the lateral funiculus, a
bundle of nerve roots in the spinal cord. The lateral
vestibulospinal tract originates in the lateral vestibular
nucleus or Deiters nucleus in the pons.[2] The
Deiters' nucleus extends from pontomedullary
junction to the level of abducens nerve nucleus in the
pons.[2]
Lateral vestibulospinal fibers descend uncrossed, or
ipsilateral, in the anterior portion of the lateral
funiculus of the spinal cord.[2][7] Fibers run down the
total length of the spinal cord and terminate at the
interneurons of laminae VII and VIII. Additionally,
some neurons terminate directly on the dendrites ofalpha motor neurons in the same laminae.[2]
[edit]Medial vestibulospinal tract
The medial vestibulospinal tract is a group of
descending extrapyramidal motor neurons, or efferent
fibers found in the anterior funiculus, a bundle of
nerve roots in the spinal cord. The medialvestibulospinal tract originates in the medial
vestibular nucleus or Schwalbe's nucleus.[2] The
Schwalbe's nucleus extends from the rostral end of
the inferior olivary nucleus of the medulla oblongata
to the caudal portion of the pons.[2]
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as the vestibular nucleus.
These impulses are transmitted down both the lateral
and medial vestibulospinal tracts to the spinal cord.
The spinal cord induces extensor effects in the muscle
on the side of the neck to which the head is bent, and
flexor effects in the muscle in the side of the neck
away from the direction of the displaced head.
[edit]Tonic labyrinthine reflex
The tonic labyrinthine reflex is a reflex that is present
in newborn babies directly after birth and should be
fully inhibited by 3.5 years.[9] This reflex helps the
baby master head and neck movements outside of the
womb as well as the concept of gravity. Increased
muscle tone, development of the proprioceptive and
vestibular senses and opportunities to practice with
balance are all consequences of this reflex. During
early childhood, the TLR matures into more developed
vestibulospinal reflexes to help with posture, head
alignment and balance.[10]
The tonic labyrinthine reflex is found in two forms.
Forward: When the head bends forward, the whole
body, arms, legs and torso curl together to form the
fetal position.
Backwards: When the head is bent backward, the
whole body, arms, legs and torso straighten and
extend.
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[edit]Righting reflex
The righting reflex is another type of reflex. This reflex
positions the head or body back into its "normal"
position, in response to a change in head or bodyposition. A common example of this reflex is the cat
righting reflex, which allows them orient themselves
in order to land on their feet. This reflex is initiated by
sensory information from the vestibular, visual, and
the somatosensory systems and is therefore not only
a vestibulospinal reflex.[8]
[edit]Development
[edit]CNS development
Four stages in the development of the neural tube in
the human embryo
Main article: neural development
During the gastrulation stage of vertebraldevelopment, the blastula divides into three distinct
germ layers. These three layers are the endoderm,
mesoderm, and ectoderm. The ectoderm is the
outermost of these layers and eventually becomes the
nervous system, the epidermis, and the lining of
various external orifices. The next stage in the
development of the nervous system is neurulationwhich is the name for organogenisis of the nervous
system. This stage begins with the formation of the
notochord, a thin layer of mesodermal cells in the
most dorsal portion of the embryo. The notochord
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signals the ectodermal cells above it to form the
neural tube.[11] The formation of the neural tube is
done specifically by the folding of the neural plate into
a circle which is accomplished with the help of themedial and dorsolateral hinge point cells. This
structure, the neural tube, gives rise to the brain and
spinal cord.[12]
[edit]Specification of ventral motor neurons by SHH
When the neural tube begins to form into spinal cord,
there are two different plates, the alar and basil
plates. These two plates are separated by the sulcus
limitans. The alar plate will turn into the dorsal horn,
consisting of sensory neurons and the basil plate will
turn into the ventral horn consisting of motor neurons.
The differentiation of the ventral horn is achieved by
the secretion of sonic hedgehog, or SHH from the
notochord during neural tube development. The SHH
produced by the notochord travels extracellularly, to
the most ventral side of the neural tube.[13] It was
determined through experimentation that the
notochord is essential in floor plate formation. This
was shown by inserting a second notochord at a
different location near the neural tube and observing
the formation of a second, ectopic, floor plate.[14] In a
normal neural tube, the floor plate separates the rightand left sides of the basil plate. In this way, the floor
plate mediates which neurons will cross the mid line,
an important aspect of proper ipsilateral and bilateral
neuron formation. SHH is a critical morphogen in
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vestibulospinal tract, the person will likely sway to
that side and fall when walking. This occurs because
the healthy side "over powers" the weak side in a way
that will cause the person to veer and fall towards theinjured side.[6] Potential early onset of damage can
be witnessed through a positive Romberg's test.[6]
Patients with bilateral or unilateral vestibular system
damage will likely regain postural stability over weeks
and months through a process called vestibular
compensation.[16] This process is likely related to a
greater reliance on other sensory information.
[edit]Current/Future Research
Recent research has shown that damage to the
medial vestibulospinal tract alters vestibular evoked
myogenic potential in the sternocleidomastoid muscle
(SCM),[17] which are involved in head rotation. Thevestibular evoked myogenic potential is an
assessment of the sacculo-collic reflex and a test of
function in otolithic organs. Also, lesions to the tract
impair ascending efferent fiber signaling, which led to
nystagmus.[17]
There is has also been recent research to determine if
there is a difference in vestibulospinal function whenthere is damage to the superior vestibular nerve as
opposed to the inferior vestibular nerve and vice
versa. They defined vestibulospinal function by ability
to have proper posture, as well as by self reported
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dizziness. The results were determined by using the
Sensory Organization Test (SOT) of the computerized
dynamic posturography (CDP) as well as the dizziness
handicap inventory (DHI). It was determined thatsubjects with damaged inferior spinal nerve
performed worse on the posture test than the control
group, but performed better that patients with
superior vestibulo nerve damage. With this they
determined that the superior vestibular nerve plays a
larger in balance than the inferior vestibulo nerve but
that they both play a role. In terms of the DHI is was
concluded that there was no difference between the
patients with the two different impairments.[18]
Vestibular compensation after unilateral or bilateral
vestibular system damage can be accomplished by
sensory addition and sensory substitution. Sensory
substitution occurs when any remaining vestibular
function, vision, or light touch of a stable surfacesubstitute for the lost function. Postural sway and gait
ataxia can be reduced by augmenting sensory
information for balance control. Recent research has
shown that as little as 100 grams of light touch of a
fingertip can provide enough sensory reference to
reduce sway and ataxia during gait.[16]
[edit]See also
Gait abnormality
Spinal cord injury
Upper motor neuron
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Rubrospinal tractFrom Wikipedia, the free encyclopedia
Rubrospinal tract
Rubrospinal tract is labeled in red on the left of the
diagram.
Schematic representation of the chief ganglionic
categories (Rubrospinal tract not labeled, but red
nucleus visible near center)
Latin tractus rubrospinalis
Gray's subject #192 870
This article needs additional citations for verification.
Please help improve this article by adding citations to
reliable sources. Unsourced material may be
challenged and removed. (October 2011)
The rubrospinal tract is a part of the nervous system.It is a part of the lateral indirect extra-pyramidal tract.
Contents [hide]
1 Function
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2 Path
3 See also
4 References5 External links
[edit]Function
In humans, the rubrospinal tract is one of several
major motor control pathways. It is smaller and has
fewer axons than the corticospinal tract, suggesting
that it is less important in motor control. It is one ofthe pathways for the mediation of voluntary
movement. The tract is responsible for large muscle
movement as well as fine motor control, and it
terminates primarily in the cervical spinal cord,
suggesting that it functions in upper limb but not in
lower limb control. It primarily facilitates Flexion in the
upper extremities (see decorticate posture).It is small and rudimentary in humans. In some other
primates, however, experiments have shown that over
time, the rubrospinal tract can assume almost all the
duties of the corticospinal tract when the corticospinal
tract is lesioned.
[edit]Path
In the midbrain, it originates in the magnocellular red
nucleus, crosses to the other side of the midbrain, and
descends in the lateral part of the brainstem
tegmentum.[1]
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In the spinal cord, it travels through the lateral
funiculus of the spinal cord in the company of the
lateral corticospinal tract.
[edit]See also
Upper motor neuron
Reticulospinal tractFrom Wikipedia, the free encyclopedia
(Redirected from Reticulospinal)
Brain: Reticulospinal tract
Reticulospinal tract is labeled in red, near center in
figure (text tag at left).
NeuroNames hier-802
NeuroLex ID birnlex_1471
The reticulospinal tract (or anterior reticulospinal
tract) is an extrapyramidal motor tract which travels
from the reticular formation.
Contents [hide]
1 Functions
2 Components
3 Clinical significance
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4 See also
5 External links
[edit]Functions1. Integrates information from the motor systems to
coordinate automatic movements of locomotion and
posture.
2. Facilitates and inhibits voluntary movement,
influences muscle tone.
3. Mediates autonomic functions
4. Modulates pain impulses
5. Influences blood flow to lateral geniculate
[edit]Components
The tract is divided into two parts, the medial (or
pontine) and lateral (or medullary) reticulospinaltracts (MRST and LRST).
The MRST is responsible for exciting anti-gravity,
extensor muscles. The fibers of this tract arise from
the caudal pontine reticular nucleus and the oral
pontine reticular nucleus and project to the lamina VII
and lamina VIII of the spinal cord (BrainInfo)
The LRST is responsible for the inhibiting excitatory
axial extensor muscles of movement. The fibers of
this tract arise from the medullary reticular formation,
mostly from the gigantocellular nucleus, and descend
the length of the spinal cord in the anterior part of the
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