Posture Prof K Sivapalan Posture Regulating Mechanisms Posture

Posture. Prof. K. Sivapalan

Posture Regulating Mechanisms • Posture regulation involves many nuclei in spinal cord, brain stem, and the cerebral cortex. • They are concerned with static posture and initiation and control of movement. • Segmental coordination developed in lower animals. • These mechanisms are dominated and movements are integrated by higher structures as evolution progressed. • Transaction of neural axis at different levels release the higher control. • The local [or lower] mechanisms appear to be accentuated after transaction. 6/17/2021 Posture 2

Spinal Shock • It is profound depression of all spinal reflex responses for a period following transaction of spinal cord. • The duration of spinal shock is proportional to the degree of encephalization • In frogs and rats it is only a few minutes. • In dogs and cats it is about 1 to 2 hours • It is few days in monkeys and 2 weeks in human. • When reflex responses return, they are hyperactive. 6/17/2021 Posture 3

Responses in Chronic Spinal Animals and Humans • Minor noxious stimuli may cause prolonged withdrawal of stimulated extremity and marked flexion – extension patterns in the other three limbs. • Stretch reflex is hyper reactive. • Positive supporting reaction [magnetic reaction]: when the sole of a spinal animal touched by a finger and withdrawn, the leg extends following the finger. • This involves tactile and proprioceptive afferents to support against gravity. • Extension of a limb results in negative supporting reaction. 6/17/2021 Posture 4

Locomotion Generator • There are two pattern generators, one in cervical and the other in lumbar regions. • They are influenced by discharge from midbrain - mesencephalic locomotor region. • Spinal animal shows spontaneous diagonal stepping movements. • This shows release of higher control and communication between the two centers through spinal cord. 6/17/2021 Posture 5

Autonomic Reflexes • Bladder and rectum contract reflexly when distended without voluntary control. • Bladder may not empty completely. • Bladder will be shrunken by the hyperactive reflexes and fibrosis may occur. • Afferent stimuli can radiate from one to another reflex and result in mass reflex. • Blood pressure is normal at rest but baroreceptor reflex cannot operate and it will result in wide swings in pressure. • Genetal manipulation cause erection and ejaculation in males and copulatory position in females. 6/17/2021 Posture 6