c 55 motor cortex & corticospinal tract

8/6/2019 C 55 Motor Cortex & Corticospinal Tract

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Motor Cortex &Corticospinal Tract

By

Prof. Dr. Abdul MajidMBBS, M.Phil, FCPS


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Motor Areas

1. Primary motor area.

2. Pre-motor area.

3. Supplementary motor area.Primary motor area:

Extent.

Brodmanns area 4. Representation of body parts.

Greater representation.


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Cont

Electrical stimulation-contraction

of group of muscles.

Initiation of voluntary movements.


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Motor & Somato Sensory Cortical

Areas


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Degree of Representation of

Different Muscles of the Body


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Pre-Motor Area

Location.

Extent.

Brodmanns area 6. Electrical stimulation produces

more complex patterns of

movements. Sends signals to primary motor

area directly as well as indirectly

through basal ganglia.


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Specialized Areas in Pre-Motor

Cortex


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Specialized Areas in the

Pre-Motor CortexFrom below upwards these

include:

Brocas area for speech: Brodmanns area 44

Word formation area.

Damage to this area does notprevent a person from vocalization

but he can not speak whole words.


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Cont:

Voluntary eye movement field

area:

Location. Brodmanns area 8.

This area is concerned with

voluntary moving of eyes towardsdifferent objects.

Also controls eye movements

such as blinking.


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Cont:

Head rotation area:

Location.

Stimulation of this area rotates thehead toward different objects.

Area for hand skills:

Location.

Damage to this area results inuncoordinated & non-purpose fullmovements in the hands called

motor apraxia.


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Transmission of Signals from the

Motor Cortex to the Muscles

Motor signals are transmitted

directly from cortex to the spinal

cord through the corticospinal

(pyramidal) tract & indirectly

through multiple accessory

pathways (rubrospinal, olivospinal,

tactospinal, vestibulospinal &reticulospinal tracts)


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Cont:

that involve the basal ganglia,

cerebellum & various nuclei of the

brain stem.

In general, the direct pathways are

concerned more with discrete &

detailed movements, especially of

distal segments of the limbs,particularly the hands & fingers.


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Pyramidal Tract


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Cont:

Formation:

30% from the primary motor

cortex. 30% from premotor &

supplementary motor cortex.

40% from the somato sensoryareas.


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Cont:

Course:

After leaving the cortex it passes

through the posterior limb of theinternal capsule (b/w caudate

nucleus & putamen of basal

ganglia) & then through the brain

stem, forming the pyramids of themedulla.


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Cont:

the majority of pyramidal fibers

then cross in the lower medulla to

the opposite side & descend into

lateral corticospinal tracts. The

fibers which do not cross in the

lower medulla they descend down

words ipsilaterally in the ventralcorticospinal tracts. Many if not

most of these fibers eventually

cross to


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Cont:

the opposite side of the cord either

in the neck or in the upper thoracic

region.

Termination: The majority of

pyramidal tracts finally terminate

mainly on interneuron's, a few

terminate on sensory relayneurons in the dorsal horn,


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Cont:

& a very few terminate on the

anterior motor neurons. The fibers

of ventral corticospinal tracts may

be concerned with the control of

bilateral postural movements by

the supplementary motor cortex.

Number of fibers: in eachcorticospinal tract there are more

then 1 million fibers.


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Cont:

Out of these 3% of the total fibers

are large myelinated fibers

heaving diameter 16 micron

meters which come from 34

thousand giant pyramidal cells,

called Betz cells. 97% of the fibers

are mainly smaller then 4 micronin diameter


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Cont:

which conduct background tonic

signals to the motor areas of the

cord.

Role of lower motor neurons:

Finally motor fibers from anterior

horn cells pass to skeletal muscles.

Function of corticospinal tract: It

controls fine, discrete movements

of fingers which become impaired if

there is lesion of this tract.


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Cont:

putamen due to rupture of blood

vesicle or by thrombosis of 1 of

the major arteries supplying to the

brain. This results in upper motor

neuron lesion disease called

hemiplegia. In hemiplegia there is

loss of voluntary movements in theopposite half of the body.


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Cont:

Monoplegia: Means paralysis of

muscles of one limb.

Quadriplegia: Means paralysis ofmuscles of all the four limbs.

Paraplegia: paralysis of muscles

of both legs due to lesion at

lumber region of the spinal cord

due to gun short wound or fall

from a tree or roof.


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Corticorubrospinal Pathway


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Cont:

fallows a course immediately

adjacent and anterior to the

corticospinal tract.

Final termination: The fibers

mostly terminate on inter neurons,

but some terminate directly on

anterior motor neurons.


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Cont:

Function: This tract controls fine

discrete movements of the wrist

joint. Anatomically this tract

belongs of extra pyramidal tracts

but functionally it provides

accessory pathway to

corticospinal tract.


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Role of the Brain Stem in

Controlling Motor Functions

Control of respiration.

Control ofCVS.

Partial control of GIT functions. Control of many stereo typedmovements of the body.

Control of equilibrium.

Control of eye movements.

Serves as a way station forcommand signals from higher

neural centers.


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Location of Nuclei in the Brain Stem


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Cont:

Reticular & vestibular nuclei

support the body against gravity.

The reticular nuclei are divided into two major groups;

1. Pontine reticular nuclei, located

slightly posteriorly & laterally in

the pons & extending into

mesencephalon.


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Cont:

2. Medullary reticular nuclei which

extend through the entire

medulla, lying ventrally &

medially near the medal eye.

3. The two sets of nuclei function

mainly antagonistically to each

other, with a pontine exciting theantigravity muscles & the

medullary relaxing the same

muscles.


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Cont:

Pontine reticular system: The

pontine reticular nuclei transmit

excitatory signals through pontine

reticulospinal tract in the anterior

column of the cord.

The fibers terminate on medial

anterior motor neurons to exciteaxial muscles


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Cont:

Medullary reticular system:

Medullary reticular nuclei

transmit inhibitory signals to the

same antigravity neurons by way

of a medullary reticulospinal tract

located in the lateral column of

the cord. The medullary reticularnuclei receive strong input

signals from;


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Cont:

1. Corticospinal tract.

2. Rubrospinal tract.

3. Other motor pathways.When pontine & medullary

reticular systems are working

normally the body muscles arenot abnormally tense.


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Vestibulospinal & Reticulospinal

Tracts


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c 55 motor cortex & corticospinal tract

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