Anatomy & Physiology
A STUDY OF ANATOMY AND PHYSIOLOGY OF MOVEMENT OF UPPER LIMB
The procedure in lifting the hand to drink water is a complex one which involves a huge amount of technology inter-transfer between the brain and the eventual skeletal muscle . There is initiation of the movement at the brain which is transmitted via specialized white fibre tracts to the hip flexors via the intermediate spinal cord , involving a very complex mechanism at the cellular level
The initiation of the process is at the motor cortex (Ms I ) of the brain . The primary [banner_entry_middle]
motor area is located at the precentral gyrus of the frontal lobe . The area controlling the motion of the lower limbs lies towards the superior surface of the brain . Within this area lies the cell body of the primary neuron . These neurons are known as upper motor neurons (UMN . These UMNs receive modulating impulse from the inputs from the cerebellum and the basal ganglia via the extrapyramidal pathways . These tracts modulate the gross movement initiated at the frontal cortex . In turn these areas are modulated by afferent signals from ascending spino cerebellar , and spino-thalamic pathways . The signal initiated at the nucleus of the cell body is transmitted electronically via the axon of the myelinated neuron via the mode of salutatory conduction . The myelin sheath which surrounds the axon of nerves that involve fast transport , breaks at intermediate regions known as Nodes of Ranvier . The electrical impulse moves in a jumping manner at these nodes nerve transmission as a neural impulse , generated by the formation of a nerve action potential . Like all excitable tissue , nerves maintain a resting membrane potential that is the difference of voltage across the membrane of the neuron . In neurons this value is – 70 mV This voltage difference is maintained by the Na /K pump on the membranes This impulse generated at the axon hillock is transmitted via the depolarizing phase which allows sodium ions ingress into cells via opening of the Na channels . This entry of Na in one portion allows activation of other Na channels , causing depolarization of the adjacent region of the neuron . Subsequently repolarization occurs via the opening of K channels , which restores the membrane potential . Thus this process continues which allows the transmission of impulse . Many such nerves together descend as the descending cortico spinal tract in the pyramidal system , which travels through the midbrain into the spinal cord decussating at the level of midbrain ( 90 of the fibres decussating and forming the lateral spinothalamic tract ) and again at the level of spinal cord ( the other 10 , forming the anterior spinothalamic tract It is the former which is responsible for the upper limb movements . The cortico-spinal tract travels in the anterior horn cell of the spinal cord till the brachial plexus where they synapse with the spinal ventral root neuron (lower motor neuron . A single post-synaptic neuron receives signals from many neurons . At the axon terminal , the propagation of impulses leads to release of neurotransmitters , which are stored in specialized… [banner_entry_footer]
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