Dr. Farah Nabil Abbas MBChB, MSc, PhD
*Located anterior to the central sulcus and occupying the posterior ⅓ of frontal lobe.Subdivided into 3 sub areasEach has its own topographical representation of muscle groups and specific motor functions of the body. *
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Corresponds to Broadmann's area No. 4. Lies in precentral gyrus of the frontal lobe. Representation of body muscles in this area is characterized by: Contralateral. Inverted. Size of represented area depends upon the movement performed by the muscles.
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Muscles perform fine movements represented by larger areas. Muscles perform gross movements represented by smaller areas. Definite somatotopic map for different parts of the body in which: Feet represented at upper medial region. Face represented at lower lateral region.
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N.B. Several facial muscles are represented bilaterally. Excitability of area 4 is high due to the presence of a large pyramidal cells called Betz cells
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1) Thalamus and somatic sensory area: Supplies motor area with information about sense of position and movements This provides sensory feed-back control of cortical motor activity. 2) Premotor and supplemental motor areas of the same side 3) Basal ganglia and cerebellum: To regulate and coordinate its motor activity.
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4) Visual and auditory areas: To provide information about spatial relations of the body to external environment. 5) Motor areas of the opposite side: To coordinate bilateral motor activities performed by both sides of the body.
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1) 30% of corticobulbospinal tract. 2) Basal ganglia: Neural pathway with cerebral cortex for planning & programming of motor actions 3) Cerebellum: Neural pathway with cerebral cortex for coordination and regulation of movements. 4) Red nucleus & brain stem reticular formation To control their activities.
controls both distal and proximal muscles initiate fine voluntary movements. facilitatory to the tone of distal muscles, particularly flexor muscles. *
Damage of area 4 leads to:Paralysis of muscles of the opposite side.Hypotonia+ve Babinski’s sign.Weak tendon jerks.Loss of superficial reflexes. *
Lies 1-3 cm anterior to 1ry motor cortex.Rough topographical representationOccupies a large share of Broadmann's area number 6.Generated nerve signals complex movement patterns, i.e., group of muscles that perform specific task. *
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Posterior part sends signals: Directly to primary motor cortex to excite specific muscles or By way of the basal ganglia and thalamus back to primary motor cortex.
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Primary and supplemental motor areas: Through afferent and efferent connectionsCerebellum: Receives an afferent pathway from cerebellum regulate and coordinate cortical motor activity.Basal ganglia: Establishes a neural circuits with motor cortex involved in planning and initiation of motor acts. *
Adjusts posture during performance of voluntary movements. Enhances the primary motor area to perform its activity. Establishing motor programs necessary for finishing of complex movements with supplemental motor area.
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Muscles weakness or ParesisHypertonia and spasticity+ve Babinski’s sign.Exaggerated tendon jerks.Motor aphasia; lesion in Broca’s area.Motor apraxia; inability to perform a skilled hand movement. *
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Lies superior to the premotor area. Body representation: Bilateral. Horizontal (head anterior and leg posterior). Less excitable - Stronger electrical stimuli required to cause muscle contraction.
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Stimulation contractions often bilateral rather than unilateral, i.e., Bilateral grasping movement of both hands simultaneously.Rotation of the trunkRotation of the handsMovement of the eyesFixation of the shoulders. *
It is connected with: Primary motor and premotor areas. Basal ganglia and cerebellum via thalamic nuclei.
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In association with premotor area provide:Postural adjustment:Supplements area 6 in performance of fine skilled motor acts by hands and fingers.Programming of complex voluntary movements:Involved in specific sequences of motor movements. *
Examples: Provide attitudinal movements Fixation movements of different segments of the body Positional movements of the head and eyes
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Broca’s AreaLocated anterior to inferior region of premotor areaPresent in one hemisphere (usually left)A motor speech area that directs muscles of tongueIs active as one prepares to speakFrontal eye fieldLocated anterior to premotor cortex and superior to Broca’s areaControls voluntary eye movement *