Presentation 3 ( Information ) Major Descending ( Motor ) Pathway and Spinal Cord Tracts March 25, 2012

8/2/2019 Presentation 3 ( Information ) Major Descending ( Motor ) Pathway and Spinal Cord Tracts March 25, 2012

1/23

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


2/23

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


3/23

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


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.


4/23

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


5/23

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


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


6/23

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


NeuroLex ID birnlex_1643

The vestibulospinal tract is a neural tract in the

central nervous system. Specifically, it is a component


7/23

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


8/23

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,


9/23

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


10/23

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


11/23


[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]


12/23


13/23

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.


14/23

[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


15/23

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


16/23


17/23

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


18/23

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


19/23

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


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


20/23

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]


21/23

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


22/23

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


23/23

Documents

Presentation 3 ( Information ) Major Descending ( Motor ) Pathway and Spinal Cord Tracts March 25, 2012