Functional Organisation of the Central Nervous System - The Motor System


Motor system Movements be the consequence of coordinated contraction and rest of groups of muscles. The main movers contract with reciprocal leisure of the antagonists. Synergists are those muscles that stabilize the proximal joints and maintain proper postures to help make the motion most effective. Voluntary action is set up by the top of moter neuron (UMN) that contains neurons of the motor cortex (precentral area) and its fiber connections. The relaxation of the antagonists and activity of the synergists are synchronised by the cerebellum. The upkeep of posture is mediated largely through the extrapyramidal system and the vestibular and spinal reflexes. The influences from the top of motor neuron, extrapuramidal system and cerebellum act upon the anterior horn cell of the spinal cord or the engine nuclei of the human brain stem, that contain connections to groups of muscle fibers. The lower motor device which will be the final most common path consists of the anterior horn cell and its efferent connections. Whereas the lower motor neuron (LMN) innervates groups of muscle fibers, the top motor neuron mediates movements.

Engine system

The upper motor neuron (UMN) This consists of the cortical cells (pyramidal cells) which are put in the motor region (pre-central gyrus) as well as their axons that pass down the brain stem as well as spinal cord to reach the brain stem nuclei or anterior horn cells of the complete opposite side. In the motor area, which in turn symbolizes the opposite side of the areas of the body are represented from above downwards in the order here (i thought about this) of perineum, feet, leg, thigh, trunk, arm, of representation is proportional to the functional significance of the part, so that the hands, deal with, and feet are given a broader area of the motor cortex than the other components.
By the motor cortex, the fibers project down through the subcortical region to attain the internal capsule in which the motor fibres come into good communication and they occupy the anterior two thirds of the posterior limb of the internal capsule. In the internal capsule, the fibers due to the head are in front and those for the lower limbs are behind. Nonetheless more behind in the posterior limb of the internal capsule are the sensory fibers, auditory fibers, and visual fibers. From the internal capsule, the motor ibers pass throughout the midbrain (where they're kept in the cerebral penduncles), the pons (where they break-up into little fasciculi and are criss-crossed by other fiber tracts), along with the medualla (where they aggregate to form the medullary pyramids). In the mid brain, the pyramid tract is in close relation with the 3rd nerve nucleus, in the pons it's in close proximity to the 7th nerve nucleus, and in the medulla it is closer to the 12th nerve nucleus. Consequently lesions at these levels likewise entail the corresponding cranial nerve nuclei. In the brain stem (mid-brain, pons, and medulla) the pyramidal region gives UMN fibers to the cranial nerve nuclei of the complete opposite side. At the lower end of the medulla, the main section of the pyramidal tract (about 80 %) crosses over to the opposite side and this also crossed pyramidal tract descends in the lateral corticospinal area along the total length of the spinal cord to provide the anterior horn cells. The uncrossed fibers descend in the spinal cord as the anterior corticospinal area and also at different spinal segments they also cross to the opposite side to supply the anterior horn cells. Thus it may be seen that the upper motor neuron controls the brain stem and spinal nuclei of the opposite side.
Lesions of the pyramidal tract result in loss of voluntary activity. since the UMN usually carries fibres that hinder the stretch reflexes mediated by the LMN wounds of the UMN result in exaggeration of these stretch reflexes. The superficial reflexes (cutaneous protective reflexes) also are changed. Top motor neuron lesions are scientifically characterised by the following signs:
1. Loss of voluntary power
2. Increase in tone clasp knife rigidity additionally called spasticity. In this the resistance to passive movement. Muscles relax, after this stage is overcome. The flexor muscles of the top of limb as well as extensor muscles of the lower limb are maximally affected.
3. Exaggerated deep tendon reflexes: When the deep tendon reflexes are exaggerated, straightforward increased in amplitude might occur even with no neurological disorders, eg. anziety. Inequality between corresponding reflexes on either side is of excellent analysis worth. In bilateral UMN lesions above the amount of the Pons, the chin jerk is exaggerated. When the UMN lesion is well established, clonus could develop. In clinical practice, patellar clonus as well as ankle clonus would be the ones commonly looked for.
4. Alteration in superficial reflexes: the abdomina and Cremasteric reflexes are lost.
The plantar response: This will become extensor. This's defined as the Babinski's indication. Normally on stroking the lateral aspect of the feet from the heel on the heel of the huge toe with a sharp object a set of reactions takes place. The fundamental toe flexes, the lateral four toes in addition crowd and flex together. Minimal contraction of the tensor fascia lata, the adductors of the thigh and sartorius occurs. This particular whole response is described as the' flexor' plantar effect.