Introduction.

Control of motor system.

Area 4.

Area 6.

Aphasia .

Supplementary Area.

Area 4s .

References.

Motor nervous systemMost of voluntary movements initiated

by cerebral cortex achieved when

the cortex activates patterns of

function stored in lower brain areas

{brainstem, basal ganglia,

cerebellum}

these centers send specific control

signals to anterior motor neurons of

spinal cord that control muscle

Cerebral cortex• Cerebral cortex is the highest centre of

brain.

• It has a total surface area 0.2-0.25 m of

which about one third is exposed.

• The total cerebral cortex contain 100 billion

neurons.

It is divided by mean of primary fissures into

[frontal, parietal ,temporal,occipital,limbic

lobe]

It is divided by mean of secondary fissures

into gyri [eg. post central gyrus]

Cerebral cortex may be functionally classified into :

A-sensory areas.

Somato sensory areas

primary somato sensory area(area3,1,2(

Secondary somato sensory area(area 40(

olfactory sensory area

visual sensory (area area 17)

auditory sensory area (area 41,24(

B-motor areas.

C- association areas .

D-autonomic areas.

-N.B.

There is however considerable overlap in the

functions between these cortical area

Several areas of the cerebral cortex are

responsible for coordinated movements.

These areas are :

1- Primary motor area (area 4).

2- Premotor area (area 6).

Highly specialized motor areas have been

found in premotor area these are :

-broca‘s area .

-frontal eye movement area.

-head rotation area .

-area for hand skills (exner‘s area ).

3- area 4s (suppressor area 4 ).

4- supplementary area .

N.B. :-

somatic sensory area 1 (area 3,1,2) and area 11

are considered in participation of coordinated

voluntary movement .

Proper performance of voluntary movements

requires integrity of :

1- higher (cortical ) level .

2- subcortical level.

3- spinal cord level .

It is carried out in 2 stages :

(1) planning : this occurs as follows:

Ideas and purpose of movements originate in

cortical association areas , which discharge signals

to both basal ganglia as well as lateral cerebellum

(cerebrocerebellum).

Basal ganglia converts thoughts into a motor plan

and put program of performance (especially for

slow movements) then discharge to cortical motor

area (which also , shares in planning and

programming processes ,( especially premotor and

supplementary areas )

Cerebrocerbellum shares in planning and

programming (especially for rapid movements)

(2) Execution : this occurs as follows :

Motor cortex discharges signals to spinal and cranial

motor neurons as well as to intermediate

cerebellum (spinocerebellum ).

Motor neurons discharge final signals to skeletal

muscles .

Skeletal muscles contract according to the plan

Producing required movement coordinately .

ideasPrefrontal

association area

Basal ganglion

Lateral cerebellum

Motor cortex

AHC and cranial nuclei

Skeletal muscle

Sensory feedback control

Sensory feedback control

Intermediate cerebellum

executePlan

PRIMARY MOTOR CORTEX (also known as M-1

or Brodmann’s Area 4; part of the neocortex,

“gray matter”)

Position:-

-Located in precentral gyrus area of the frontal

lobe of the cerebral cortex

body representation :-

-body representation is mainly contralateral;

exception muscles of respiration , muscles of the

upper part of the face and abdominal muscles

which are bilateraly respresented

-it is inverted ;the body is represented upside

down with the exception of the head which is not

inverted

-small, distorted, discontinuous map of the body ,

larger areas devoted to body regions characterized

by fine or complex movements "delicate highly

skilled movements “ and smaller areas to body

regions characterized by gross movements involving

few muscles

-Hand, face, intraoral and, to some extent, foot

muscles are particularly well represented while

muscles of the thigh are represented by small areas

“gross movement”

body representation :-

1-the main function is to initiate and control fine descretemovements of the distal parts of the body on the opposite side

2-shares area 6 in its function in controlling gross movements

3-facilitates stretch reflex

4-necessary for superficial somatic reflexes

5-electrical stimulation of a particular area of area 4 leads to contraction of a particular skeletal muscle or group of muscles that is/are responsible for fine discrete movements

6-histologically the cerebral cortex is formed of many layers of cell arranged in columns. Stimulation of a given motor column of area 4 may activate a single muscle

7- It shares information of the pyramidal tracts by 30% of fibers of the pyramidal tract

unilateral lesion leads to the following

manifestations on the opposite side of the

body :

a)Monoplegia :- paralysis of muscles of one

limb

*permanent loss of fine movements and

temporary loss of gross movements

*later ,there is recovery of gross movements.

b)Hypotonia and weak tendon jerk:

due to loss of facilitatory impulses to stretch

reflex.

c)positive Babniski sign:

scratch of lateral side of sole of foot leading to

dorsiflexion of big toe (one component of Babniski

sign ) without fanning of the other toes (the

second component of this sign)

d) loss of the superficial reflexes:

e.g(flexion withdrawal reflex , planter reflex

,Grasp reflex)

descending tracts :-

1. Corticospinal tract:

a. axons pass through the internal capsule (a frequent site of stroke injury), then through the ipsilateral diencephalon, midbrain, pons, and into the medulla, where they form the medullary pyamids

Note: the corticospinal tract is also termed the “pyramidal tract” (named for the medullary pyramids, not for the cortical pyramidal cells)

b. as the axons pass from the medulla into the spinal cord, most (80-90%) decussate (cross to the opposite side) and descend in the white matter of the contralateral cord, forming the lateral corticospinaltract, until they reach the region containing the alpha motoneuronsof the muscles they represent; the majority of these motoneuronsinnervate flexors

c. the non-decussating axons descend in the ipsilateral cord, forming the ventral corticospinal tract, until they reach the level of region of the body they represent, and then they decussate also; the majority of these motoneurons control extensors

2. Corticobulbar tract:

a. axons pass through the internal capsule and terminate either directly on alpha motorneurons or on interneurons innervating alpha motor neurons in the brainstem controlling somatic motor activity in the head (e.g. muscles controlling eye movement, muscles of mastication, muscles of facial expression)

b. axons innervating some somatic motor nerve cranial nuclei decussate before their termination and so control contralateral muscles; corticobulbar tracts controlling other motor nuclei split, some axons decussating and others descending ipsilateral, resulting in bilateral innervation

c. cranial nerve innervation is either direct or through interneurons, as in the corticospinal tract

3. Cortico-rubar and Cortico-reticular tracts:

a. consist of axons originating In M-1 and

terminating in the red nucleus (midbrain) and

the reticular formation (throughout the

brainstem), respectively

b. output from the red nucleus (rubrospinal

tract) and the reticular formation

(reticulospinal tract

But it less excitable than area 4 due to absence of

Betz cells

It control movement of opposite side of body.

But:There is Bilateral representation of

muscles that moves together as:

1. Muscles of eyes.

2. Respiratory muscles.

3. Abdominal muscles.

The body is represented upside down.

ButRepresentation of head is not inverted

(eye brows upward /lips are downward)

1) Muscles that are responsible for delicate

highly skilled movement are

represented by wide areas.

(e.g. muscles of fingers)

2) Muscles that are responsible for gross

movement are represented by small

areas .(e.g. muscles of thigh)

Area 6 is connected to :

1) Sensory association areas (Area 5/Area7) .

2) Primary motor area (Area 4).

3) Supplementary area .

4) Cerebellum .

5) Basal ganglia .

1) Initiation of gross movement that involve groups

of muscles on opposite side of body .

2) Postural adjustment of different parts of the

body to perform fine skilled motor acts by hand

and fingers.

3) Inhibitory to stretch reflex (muscle tone and tendon

jerks).

4) It is necessary for normal flexor response of

planter reflex .

1) It shares in planning of voluntary movement

with Area4 and supplementary area.

2) It retains memory of highly skilled movements

.

3) It is responsible for some autonomic reactions .

(e.g. increasing heart rate)

4) It inhibits grasp reflex .

5) It contains specialized areas that control

specific movement .

Broca`s areao It is the area of word formation .

o It is motor center for spoken speech .

o It stores the motor programs for verblization.

Frontal eye movement area (area 8)

o It control extrinsic movements of eye .

o Stimulation of this area causes conjugate deviation of eyes to opposite side.

Head rotation areao It directs head towards different visual objects.

Exner`s areao It is the area of hand skills .

o It stores the motor programs for skilled movements of hand and fingers .

The following manifestations occur on the opposite site of the body;

1)Paresis”weakness but not paralysis” of muscles. 2)increased muscle tone and exaggerated tendon jerks. 3) positive Babiniski sign*only fanning of lateral 4toes without dorsiflexion of big toe* 4 ) Autonomic disturbances . 5 ) Appearance of grasp reflex . 6) Motor aphasia(it is inability to speak whole words except simple ones as yes or no)due to lesion in Broca ,s area .

7)Agraphia(it is inability to write or draw but use hands for other purposes)due to lesion in Exner,sarea.

definition : it means disturbances of speech

due to a lesson in the dominant hemisphere in

absence of muscle paralysis and defects of

vision or hearing

Types:

1-sensory aphasia : it includes:-

a- auditory aphasia (word deafness) : it is due

to damage of the auditory association area

(area 22)

The patient hears spoken word but is unable

to understand their meaning

B-Visual aphasia (word blindness) : it is due to damage of the visual association areaThe patient sees written words but is unable to understand their meaning

C-General sensory aphasia : it's due to damage of the general interpretative areaThe patient is unable to understand the meaning of spoken words or written word completely or to express his thought by speaking or writing.

2-Motor aphasia : it includes :-

A-Vocal aphasia : it is due to damage of Broca's areaThe patient understands both spoken and written speech but is unable to express his thoughts by spoken words although he knows what he wants to say

B- Agraphia : it is due to damage of Exner'scenterThe patient understands both spoken and written speech but is unable to express his thoughts by written words although he knows what he wants to write

its site :

it forms a narrow strip anterior to area 4 .

Function of area 4s :

1-It suppresses the extra impulses

produced by area 4 & hence prevents

exaggeration of movements .

2-It inhibits the spinal motor neurons by

sending inhibitory signals to the inhibitory

reticular formation or by inhibiting the

adjacent motor area 4 .

It lies anterior and superior to

premotor Area (Area 6)

:-

1) Horizontal .

2) Bilateral .

i. Postural adjustment of different parts of body to

perform skilled motor acts by the hands and fingers .

ii. It is involved in planning and programming of specific

sequence of motor commands .

iii. It evokes complex movements involving both sides of

the body .

1-central nervous system “faculty of

medicine tanta university”.

2-www.acbrown.com

3-www.en.wikipedia.org