MOTOR EFFECTS ARE SEEN IN SOMATIC NS SYMPATHETICFIBRE S ANS PARASYMPATHETIC FIBRES
Lowest level of motor neuron-LMN Primary motor area neuron in cerebral cortex-UMN
MOTOR ACTIVITY OCCURS AT 3LEVELS Spinal cord level -as a reflex action Brain stem level- as a cranial reflex action Cortical level- as a voluntary action
LMN receive input from UMN Most of the UMN synapse with interneurons Some synapse with LMN UMN originate from cerebral cortex,motor centres of brain stem,red nucleus,vestibular nucleus,sop.colliculus ,reticular formation
UMN from cerebral cortex reg.vol. motor activity UMN from brain stem reg. muscle tone,posture and equilibrium
Somatic motor pathway Direct motor/pyramidal Indirect motor/extrapyramidal IncludesReticulospinalTectospinalVestibulospinalRubrospinalolivospinal
Motor areas of brain Primary motor area located in precentral gyrus. Brodman’s area.(area 4) Betz cells are the characteristic feature of primary motor area. Topographical representaion (motor homunculus) of entire body.
Contd..• body representation in this area is inverted & unilateral with the head represented down & foot up.• Bilateral representation is seen to LMN, innervating the upper half of face,muscles of eyes,jaws,pharynx,larynx,neck,thorax & abdomen.
Contd… Supplementary motor area-medial part of frontal lobe to upper part of cingulate sulcus where the entire body representation is seen. Area 6- premotor area or motor association area. Major descending tracts which arise from these areas which control motor activity – PYRAMIDAL TRACT
PYRAMIDAL TRACT Information from cerebral cortex for voluntary motor activity. 60 % fibres arise from primary motor cortex (area 4.) 40% fibres from supplementary or secondary motor area and from sensory areas(area 3,1,2) 80% motor area. 20% sensory area.
Motor nuclei of the cranial nerves in which these axons terminate are that of 3,4,5,6,7,9,10,11,12 cranial nerves – CORTICO NUCLEAR OR CORTICO BULBAR fibres. Rest form CORTICO SPINAL fibres.
Contd… In medulla 80% of fibres cross to opp side(controlateral)as pyramidal deccusation. 20% pass uncrossed(ipsilateral). Crossed fibres occupy lat funiculus of spinal cord & go as lat corticospinal tract. Uncrossed fibres in spinal cord forms ant corticospinal tract.
Right cerebral cortex controls muscles of left side of the body and left cerebral cortex controls the muscles of right side of the body.
EXTRAPYRAMIDAL TRACTS All descending tracts other than pyramidal tract. Back ground tone, posture ,equilibrium etc. are maintained. Arise from cerebral cortex & from sub cortical structures like basal ganglia , brainstem, reticular formation, red nucleus, tectal nucleus, vestibular nucleus & olivary nucleus.
Cortically originating A) facilitatory fibres.- (+) muscle tone and stretch reflex.(area6,supp.motor area ,& area 7) B) inhibitory fibres- (-) motor activity or reflexes.(suppressor strips of diff areas of cortex like 4s 2s 8s 19s 24s etc.)
Cortically originating extra pyramidal fibres descend intermingled with pyramidal tract fibres. so any leison of pyramidal tract in brain will be associated with extra pyramidal manifestations.
Cortically occuring extra pyramidal fibres do not go directly to the alpha motor neuron instead relay in the reticular formation directly or indirectly through the basal ganglia. So reticular formation-relay & integrating centre of extrpyramidal influences.
2.Reticulospinal Fibres arising from the reticular formation 1) anterior 2) lateralConsists of 2 parts1.bulboreticular facilitatory area maintain nl muscle tone.2.caudal inhibitory area
3.Vestibulo spinal Arise from lat vestibular nucleus Recieves connection from inner ear, cerebellum, cortex, reticular formation. Facilitate activity of extensor group of muscles-those that maintain posture.
4.Rubrospinal Arise from red nucleus of mid brain. Connections to cortex, cerebellum, ret formation. 2 parts – magno cellular parvo cellular Forrel’s deccusation. Maintain flexor group of muscles.
5.Olivospinal Arise from inf. olivary nucleus in medulla. Connected to cortex,cerebellum, thalamus, red nucleus, reticular formation.
6.Tectospinal Arise from neurons in sup colliculus. Terminate in upper seg of spinal cord. Concerned with spino visual reflex.