Final Voluntry Movement

VOLUNTRY MOVEMENT

REM EMB ER……  Every voluntary movement requires postural adjustment which are mostly automatic & make use of reflexes .  Complex movements (walking) involve complicated sequences which are controlled without conscious attention although can be voluntarily interrupted & other movements can superimposed upon them .

WHERE I S VOL UNT RY MO VEME NT INI TI ATED ?

 Large areas of cerebral cortex are devoted to fine movements of hand , mouth , tongue & feet .  Large conspicuous pathway from a part of cerebral cortex , just anterior to the central sulcus , into the brain stem & so on to the spinal cord .  Lesions in the motor area were known to result in profound disturbances of movement

PI ECES TO BE COLL ECTED & PAR TS TO BE INTEG RATE D  The large motor pathway running from the cortex into the spinal cord is called PYRAMIDAL TRACT after the pyramid = a cone shaped structure in the brain stem , all other pathways involved in movement are called EXRAPYRAMIDAL

 Most of the large pyramidal shaped cells in the motor cortex were connected polysynaptically through chains of excitatory & inhibitory neurons to the extrafusal alpha motor neurons.

 About 10% of the pyramidal tract fibers in primate are connected monosynaptically to extrafusal fibers .  Monosynaptic pathway is thought to be of special use for rapid voluntary movement of the hand .  When very careful lesions were made in pyramidal tracts in monkeys , only the finest of finger movement were lost especially those of the thumb & index finger while great variety of voluntary movements remained .  Before movements begin from a motor control centre , the pyramidal tract neurons discharge action potentials 50 – 100 msec before movement .

WHA T A RE TH E F UN CTIO NS OF OTH ER B RAIN ST RUC TUR ES K NOW N TO BE IN VOL VE D I N MOV EME NT ?

 Cerebellum & basal ganglia play a subsidiary but important role in the control of voluntary movement .  Movements are not elicited on stimulation of the above structures BUT profound movement disturbances occur when they are damaged or diseased .

IN TE GRAT IO N  Movement is initiated by the entire motor nervous system & no centre is above the others or control the rest but coordinated sensible voluntary movement is initiated by the concerted integrated action of the cerebellum , motor cortex , basal ganglia & all other areas of pyramidal & extra pyramidal systems .

CEREB ELL U M

 Cerebellum might supply feed back information mainly from joints & muscle receptors to the motor cortex .  Functionally , it consists of a midline portion ( lesions affect balance & equilibrium ) & lateral portion ( more involved with voluntary movement = 1-decreased muscle tone,2- late in starting,3- not accurately terminated ) .

 In summary , the lateral lobe & nuclei of the cerebellum appear to assist in ordering the sequence of contraction in different muscles & to ensure that contraction occurs at the right moment during voluntary movement .  Cerebellum receives an “advance report” of activity in the pyramidal tract . Proprioceptive information processed by the cerebellar cortex influences & modifies the output of the cerebellar nuclei & subsequently the motor centers & plays an important role in the coordination of voluntary movement .

BASA L GANGL IA

 Lesions in it result in purposeless unwanted movements .  In animals , it is the major motor centre

MOTO R COR TEX  Somatic representation in the motor cortex

shows that the upper most part of it contains neurons that supply the leg & foot musculatures while the lower part of it supplies the face & tongue . The main output from it is from the pyramidal shaped cells which project to both pyramidal & extrapyramidal pathways . This is in part explains the profound paralysis which results from destruction motor cortex while pyramidal tract damage results only in loss of very fine movements