Control of Postural Movement PDF

12/29/20 Definitions Control of postural movement 3 Assist. Prof. Dr. Cenk Serhan ÖZVEREL [email protected] Types of Posture • Postural control: Controlling bodies position in space for dual purposes of stability and orientation. • Posture: Biochemical alignment of body and orientatio...

12/29/20 Definitions Control of postural movement 3 Assist. Prof. Dr. Cenk Serhan ÖZVEREL [email protected] Types of Posture • Postural control: Controlling bodies position in space for dual purposes of stability and orientation. • Posture: Biochemical alignment of body and orientation of body to the environment. • Postural stability: Ability to control centre of mass in relationshi to the base of support. Framework of postural control • Static posture: • Body and body segments are aligned and maintained in certain positions. • Dynamic Posture: • Refers to postures in which body or body segments are moving 1 12/29/20 Types of postural TASKS Feedforward vs feedback postural control • Steady State Balance: Stability underlying sitting or standing quietly à Static balance • Reactive balance control: Movement strategies in response to brief displacements of supporting surfaces. • Proactive (anticipatory) balance control: A preprogrammed force based on anticipation of what the task requires based on previous experiences by the CNS. Physiology behind postural control: Motor Systems in postural control: • Depends on: • Motor system à Generation of coordination of appropriate muscles. à control bodys position and movement in space. • Motor / Somatosensory • Visual System • Vestibular system • Motor systems include: • High level planning àFrontal and motor cortex • Coordination à Brainstem, cerebellum and basal ganglia • Generation of forces à Motor neurons and muscles 2 12/29/20 Cortical Areas involved in Motor control Descending Pathways from the motor cortex • Corticospinal pathway / Pyramidal Tract • Corticobulbar Pathway • Extrapyramidal Pathway • Cerebellum • Basal Ganglia Corticospinal Tract Corticobulbar pathway • They are descending tracts of voluntary motor activities of body. • Also known as Corticonuclear tract • Also known as pyramidal tracts of spinal cord. • 2 neuron • White matter motor pathway • There are 2 corticospinal tracts: • 1-Anterior corticospinal tract • 2-Lateral corticospinal tract • Connects motor cortex in cerebral cortex to medullary pyramids 3 12/29/20 • Functions: • Muscle of face • Head • Neck • Innervates cranial nerve 5,7,11 and 12 • Also innervates the motor part of cranial nerve 10. Role of Extrapyramidal Pathway • Adjust body posture • Provides stable background for movement • Concerned with grosser movements and posture 4 12/29/20 Role of Cerebellum Role of Basal Ganglia • Regulates postural reflexes by Modifying muscle tone. • They are scattered masses of gray matter submerged in subcortical substance of cerebral hemisphere. • It facilitates the gamma motor neur ons in the spi nal cord via cerebell ovestibulo-s pinal ne urons in th e spinal cord and cerebellreticulp-spinal tracts. • Gamma motor neurons reflexly modify the activity of alpha motor neurons thus regulate the muscle tone. • Has 3 components: • 1-Corpıs striatum • 2- Substantia nigra • 3-Subthalamic nucleus of luys • Thus, cerebellum forms important li nkage of alpha-gamma systems responsible for muscle tone. Control of posture by BASAL GANGLIA Role of Brainstem • Controls the muscle tone • Red nucleus of brainstem ***** • In fact, gamma motor neurons are responsible for development of muscle tone. • Important in maintaining posture • Reflex muscular activities, particularly visual and labyrinthine reflexes are important in maintaining posture. • Basal gangliaà Coordination and integration of impulses for these reflex activities. • Red nucleus is a large oval or round mass of gray matter, extending between superior colliculus and hypothalamus. • Pathways: • The Ventromedial Pathway • The Lateral Reticulospinal Tract • The Rubrospinal Tract 5 12/29/20 1- Ventromedial Pathway • Vestibulospinal Tract: • Info from vestibular nucleus for reflex control of equilibrium. • Tectospinal Tract: • Originates in tectum for control of head and eye movements • Medial Reticulospinal Tract: • Originates in reticular formation for maintaining posture by activation of extensors. 2- Lateral Reticulospinal Pathway 3- The Rubrospinal Pathway • Originates in reticular formation for maintaining posture by activation of flexors. • The rubrospinal tract begins in the magnocellular red nucleus. • Terminates in the cervical segments of the spinal cord • So, it only innervates upper limbs. • à Arm swinging while walking 6 12/29/20 Role of Visual Pathway • The visual proprioceptive system has neurons that are specialized in responding movement of the retinal image across retina. Role of Vestibular Apparatus: • Labyrinth (Inner ear) • Vestibular apparatus is a part of labyrinth or inner ear. • Consist of 2 structures • Important role in maintaining posture and equilibrium through statokinetic reflexes. • 1- Bony labyrinth • 2-Membranous labyrinth 7 12/29/20 • Semicircular Canals: • Tubular structures at right angles to each other. • 1-Anterior or Superior Canal • 2-Posterior Canal • 3-Lateral or horizontal or external canal • Mechanism of semi-circular canals: • Superior Semicircular Canal: • Gives response to rotation anteroposterior plane (transverse axis), EX:front to back movements of head while saying ’YES-YES’ • Horizontal Semicircular Canal: • Gives response to rotation in horizontal plane (Vertical axis): EX: Side to Side movements of head while saying ‘No- NO’ Posture • Posterior Semicircular Canal • Gives response to rotation in vertical plane (anteroposterior axis) by which head is rotated from shoulder to shoulder. • Maintained by 2 main factors • 1-Muscle tone • 2-Postural reflexes 8 12/29/20 Muscle Tone • State of continuous and passive contraction of muscle with certain vigor and tension. • It is also called tonus. • It is also defined as resistance offered by muscle to stretch Postural Reflexes: • Help to maintain the body in upright and balanced position • Efferent pathways à alpha-motor neurons supplying skeletal muscles (Effector organs) • REFLEX ARC • Afferent pathways come from EYES, the vestibular apparatus and the proprioceptors. • Integrating centers are formed by neuronal networks in brain stem and spinal cord. 9 12/29/20 Types of Postural Reflexes • 2 types • 1- Static Reflexes • Both Static and Statokinetic reflexes are integrated at various levels in CNS from spinal cord to cerebral cortex. They are largely affected by pyramidal pathways. • Elicited by gravitational pull and involve sustained contraction of muscles. • 2- Statokinetic Reflexes • Also called phasic reflexes. • Elicited by acceleratory displacement of body. • They maintain stable postural background for voluntary activity. Maintenance of posture: • Decision for particular posture à occurs in CORTEX • ,In a standing posture • Centre of gravity pulls body to fall forward • Planning and programming à BASAL GANGLIA and CEREBELLUM • Information comes down through PYRAMIDAL TRACT to MOTOR NEURONS supplying muscles. • So antigravity muscles like extensors of neck, back, lip and legs etc. should be in contracted state 10 12/29/20 • In normal standing posture, • Upper limbs are slightly flexed • The flexor group of muscles are antigravity muscles in the upper limb • Vestibular receptors, proprioreceptors, visualreceptors etc. have important roles in maintaining posture. • In the standing posture, • Impulse coming through vestibulospinal tract and reticulospinal tract also plays important role. • If there is a change in head position, receptors in the utricle and saccule are stimulated. à Some group of muscles contract and head is held erect or in particular posture. 11 12/29/20 The End 12