motor areas of cerebral cortex
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Transcript of motor areas of cerebral cortex
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