MotorMotor systemssystems ControlControl ofof movementmovement Motor neuron DRG ElementsElements ofof motormotor systemsystem Effectors MOTOR SYSTEM Skeletal Muscle SOMATIC MOTOR SYSTEM Smooth Muscle AUTONOMIC MOTOR SYSTEM Glands (sympathetic and Parasympathetic) MajorMajor somaticsomatic motormotor systemssystems LowerLower motormotor neuronsneurons –– spinalspinal cordcord UpperUpper motormotor neuronsneurons –– neocortexneocortex CerebellumCerebellum BasalBasal gangliaganglia BasicBasic componentscomponents ofof motormotor circuitscircuits MotorMotor cortexcortex Basal ganglia Cerebellum BrainstemBrainstem centerscenters && SpinalSpinal cordcord Muscles ControlControl ofof movementmovement AnteriorAnteriorAnterior HornHornHorn CellCellCell --Lower Lower MotorMotor NeuronNeuron -- AHC MotorMotor unitunit = 11 motoneuronmotoneuron + musclemuscle fibersfibers Motor unit innervation ratios (motoneuron/muscle fibers innervated) eyes, ear - 1:10 hands - 1:100 soleus (posture) - 1:180 gastrocnemius (jumping) - 1:1000- 2000 Each muscle fiber receives input from only one motor neuron SpinalSpinal reflexesreflexes Purves, et al, Neuroscience, 3rd ed. The stretch reflex operates as a negative feedback loop to regulate muscle length Purves, et al, Neuroscience, 3rd ed. DiseasesDiseases ofof thethe motormotor unitunit (disease of nerve) (disease of muscle) Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. NeurogenicNeurogenic vsvs myopathicmyopathic diseasesdiseases ofof thethe motormotor unitunit Finding Neurogenic disease Myopathic disease Weakness + + + + Wasting + + Loss of reflexes + (ALS) 0 Fasciculations + (PN) 0 Sensory loss + (PN) 0 Hyperreflexia, Babinski sign + (ALS) 0 Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. LowerLower motormotor neuronsneurons (LMN)(LMN) SpinalSpinal CordCord AnteriorAnterior Horn Horn Cell Cell (Lamina (Lamina IX) IX) -------- --------spinal spinal n. n. BrainBrain StemStem GeneralGeneral Somatic Somatic Efferent Efferent (GSE) (GSE) Nuclei Nuclei HypoglossalHypoglossal Nucleus Nucleus -------------------- --------------------XII XII AbducensAbducens Nucleus Nucleus ------------------------ ------------------------VI VI TrochlearTrochlear Nucleus Nucleus ------------------------- -------------------------IV IV OculomotorOculomotor Nucleus Nucleus ---------------------- ----------------------III III SpecialSpecial Visceral Visceral Efferent Efferent (SVE) (SVE) Nuclei Nuclei AmbiguusAmbiguus Nucleus Nucleus ----------------------- -----------------------IX, IX, X, X, XI XI FacialFacial (Motor) (Motor) Nucleus Nucleus ------------------- -------------------VII VII TrigeminalTrigeminal Motor Motor Nucleus Nucleus -------------- --------------V V Distribution of LMN pools: somatotopic arrangement dorsal Flexor muscles (posture) (fine movement) Extensor muscles ventral SpinalSpinal locallocal circuitcircuit neuronsneurons areare alsoalso arrangedarranged somatotopicallysomatotopically MedialMedial projectproject toto manymany segmentssegments andand supplysupply medialmedial MNsMNs -- postureposture LateralLateral projectproject toto 11 oror fewfew segmentssegments andand supplysupply laterallateral MNsMNs –– finefine movementsmovements Purves, et al, Neuroscience, 3rd ed. Upper motor neurons are also arranged somatotopically BrainstemBrainstem →→ spinalspinal medialmedial MNsMNs -- postureposture NeocortexNeocortex →→ spinalspinal laterallateral MNsMNs –– finefine movementsmovements UpperUpper motormotor neuronneuron (UMN)(UMN) = pyramidalpyramidal tracttract Pyramidal tract Corticobulbar tract Corticospinal tract UMNUMN –– corticospinalcorticospinal tracttract Origin:Origin: CerebralCerebral CortexCortex BrodmannBrodmann Area Area 4 4 (Primary (Primary Motor Motor Area, Area,M M I) I) BrodmannBrodmann Area Area 6 6 (Premotor (Premotor Area, Area, PM PM ) ) BrodmannBrodmann Area Area 3,1,2 3,1,2 (Primary (Primary Somesthetic Somesthetic Area, Area, S S I) I) BrodmannBrodmann Area Area 5 5 (Anterior (Anterior Portion Portion of ofSup. Sup. Parietal Parietal Lobule) Lobule) CoronaCorona Radiata Radiata lnternallnternal Capsule, Capsule, Posterior Posterior Limb Limb CrusCrus Cerebri, Cerebri, MiddleMiddle Portion Portion LongitudinalLongitudinal Pontine Pontine Fiber Fiber PyramidPyramid - -pyramidal pyramidal decussation decussation CorticospinalCorticospinal Tract Tract - -Lateral Lateral and and Anterior Anterior Termination:Termination: SpinalSpinal GrayGray ( (RexedRexed IV IV-IX)-IX) CorticospinalCorticospinal TractTract BA 4 L T Posterior Limb IC A Cerebral Peduncles F Longitudinal Fibers Pons Pyramids ±Decussation Origin: Primary motor cortex (BA 4) Spinal Cord Course: Post Limb IC, Pyramids 90% Lat, 10% Ant Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal TractTract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal TractTract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal TractTract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal TractTract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal TractTract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal TractTract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal TractTract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) CorticospinalCorticospinal TractTract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) 90% of the fibers decussate and become the lateral corticospinal CorticospinalCorticospinal TractTract tract; the remaining 10% of fibers remain ipsilateral and become the anterior corticospinal tract Origin: Primary motor cortex (BA 4) Course: Post Limb IC, Pyramids Termination: Spinal cord ventral horn Laterality: CONTRA (lateral), IPSI (anterior) Lateral CorticospinalCorticospinal TractTract CST Anterior CST Descending neurons synapse on Origin: Primary motor cortex (BA 4) interneurons or Course: Post Limb IC, Pyramids motoneurons in the Termination: Spinal cord ventral horn ventral horn of the Laterality: CONTRA (lateral), IPSI (anterior) spinal cord CCorticospinalorticospinal tracttract -- summarysummary Terminates on inhibitory INs in spinal cord Essential for skill and precision in movement and the execution of discrete fine finger movements Myelination completes by 2 nd year → time of standing/walking Lesions of CST result in paralysis (UMN disease) lesion above decussation → paralysis is contralateral lesions below decussation → paralysis is ipsilateral Corticospinal tract - summary UMNUMN vsvs LMNLMN diseasedisease Fundamentals of neurologic disease : an introductory text / Larry E. Davis, 2005 BabinskiBabinski signsign →→ UMNUMN damagedamage Purves, et al, Neuroscience, 3rd ed. AtrophyAtrophy →→ LMNLMN damagedamage Distinguish neurogenic from myopathic atrophy! UMNUMN –– corticobulbarcorticobulbar tracttract - Corticofugal fibers projecting to, and terminating in the portions of lower brainstem - Termination: 1) motor nuclei (upper motor neuron pathway) hypoglossal, ambiguus , facial motor, trigeminal motor, abducens , trochlear and oculomotor nucleus 2) sensory relay nuclei nuclei gracilis and cuneatus, trigeminal sensory nucleus, solitary tract nucleus 3) reticular formation (corticoreticular fiber) Corticobulbar Tracts L T A F Origin: Primary motor cortex (BA 4), face portion Course: Internal Capsule (genu), cerebral peduncles, longitudinal fibers of the pons, pyramids Termination: Motor nuclei of the cranial nerves Laterality: CN motor nuclei – V , VII (upper face), Ambiguus: BILATERAL CN motor nuclei - VII (lower face), XII: Contralateral Corticobulbar Tracts Genu of internal capsule Origin: Primary motor cortex (BA 4), face portion Course: Internal Capsule (genu), cerebral peduncles, longitudinal fibers of the pons, pyramids Termination: Motor nuclei of the cranial nerves Laterality: CN motor nuclei – V , VII (upper face), Ambiguus: BILATERAL CN motor nuclei - VII (lower face), XII: Contralateral Corticobulbar Tracts – Motor V Origin: Primary motor cortex (BA 4), face portion Course: Internal Capsule (genu), cerebral peduncles, longitudinal fibers of the pons, pyramids Termination: Motor nuclei of the cranial nerves Laterality: CN motor nuclei – V , VII (upper face), Ambiguus: BILATERAL CN motor nuclei - VII (lower face), XII: Contralateral Corticobulbar Tracts – Motor VII Upper part only Origin: Primary motor cortex (BA 4), face portion Course: Internal Capsule (genu), cerebral peduncles, longitudinal fibers of the pons, pyramids Termination: Motor nuclei of the cranial nerves Laterality: CN motor nuclei – V , VII (upper face), Ambiguus: BILATERAL CN