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CHAPTER V Movement disorders Part I: Anatomy and physiology of motor system Motor systems • Motor systems are complex and include sophisticated control systems the purpose of which is to serve locomotion, posture and work. Several feedback systems monitor muscle activity The length of muscles and the strength of contractions are monitored by: – Input from proprioceptive receptors in muscles, joints and tendons – Local feedback from motor nerves (Renshaw inhibition) Posture Monitored by • proprioceptors, • vestibular system • vision Causes of movement disorders • More or less anatomically specific neural degeneration • Injuries (trauma, strokes, surgery, etc) • Chemicals (alcohol, drugs) • Inflammations and infections (viral) • Tumors • Genetic • Neural plasticity • Genetic • Idiopathic Motor disorders • Lack of function • Inadequate function • Hyperactivity Disorders of motor systems • Hypokinesia • Hyperkinesia – Spasticity • Ataxia • Gait and balance disturbances Two different descending motor pathways: • Lateral system – Fine movements • Medial system – Posture etc. Midline Lateral system Cortex (MI) Internal capsule Nucleus ruber Brainstem Pyramids Propriospinal interneuron Spinal cord a motoneuron Distal limb muscles Medial system Motor pathways The motoneurons (alpha motoneurons) are the final common pathways The alpha-motoneurons (common final pathway) receive many inputs Some are facilitating and some are inhibitory Motor pathways Somatotopic organization of the motor cortex Two motoneurons receiving input from cortical cells Colony Colony Terminations of the corticospinal tract projections of sensory pathways Motor areas Sensory areas Renshaw inhibition Midline Corticospinal tracts Propriospinal interneuron Fibers of the corticospinal tract terminate on motoneurons or interneurons a motoneuron a motoneuron Renshaw cell Muscle Supraspinal input Segmental input Ia interneuron Extensive processing of motor command occurs in the spinal cord (and brainstem) • Spinal reflexes play an important role in all motor functions • Some functions such as walking is programmed in the spinal cord Monosynaptic stretch reflex Presynaptic (Axo-axonic) synapse Muscle spindel afferent From supraspinal sources Interneuron DRG la fibers Muscle a motoneuron A Hoffman reflex Stimulus EMG Motor Antidromic motor Orthodromic motor (reflex) M-wave B H-reflex 10ms Stimulus C M 8 6 H 4 2 0 40 80 Stimulus strength (V) 120 Reflexes are modulated from supraspinal sources Reciprocal spinal reflex Supraspinal input la interneuron Stretch reflex arc Inhibition on a motoneuron DRG Muscle spindel Agonist muscle a motoneuron Antagonist muscle From semicircular canals Descending vestibular pathways Medial vestibular nucleus From uticulus Lateral vestibular nucleus Medial vestibular spinal tract Lateral vestibular spinal tract a motoneurons motoneurons Spinal cord Medial system Posture and automatic functions Tendon reflex Reticulospinal tract Golgi tendon afferent Tendon Muscle la interneuron DRG a Motoneuron (inhibitory input) Flexor reflex Reticulospinal pathway Flexor reflex afferents la interneuron Inhibitory interneuron Excitatory interneuron a Motoneuron a Motoneuron Extensor muscle Flexsor muscle Convergence of excitatory inputs Convergence of inhibitory and excitatory inputs A A B B a motoneuron a motoneuron Input A Input B Intracellular potential in a motoneuron Interneuron Input A Input B Intracellular potential in a motoneuron Input to propriospinal neurons of the forelimb of the cat Decending motor tracts Forelimb afferents lb inhibitory la excitatory a motoneuron Muscle Magnetic stimulation of motor cortex in an awake individual From Rosler Fig 2B Input to an Ia inhibitory interneuron Ipsi. vestibular tract Propriospinal input FRA Corticospinal tract and interneurons Contralat. Vest. Spinal, FRA etc. Renshaw From agonist muscle spindle la afferents Agonist a motoneuron Muscle From antagonist muscle spindle Antagonist a motoneuron Muscle Input to an Ib (inhibitory) interneuron Decending motor tracts Joint receptors Dorsal reticular spinal tract Skin receptors Norepinephrine serotonin tract la lb a motoneuron Muscle BASAL GANGLIA Extrapyramidal system Pyramidal system Cortex Thalamus Basal ganglia To spinal cord Motor cortex Two descending motor tracts The alphamotoneuron is the final common pathway Basal ganglia Thalamus Cerebellum Corticospinal tract Brain stem motor pathways Interneurons a motor neuron muscle Anatomical localization motor pathways Fig 5.27B Motor cortex Caudate nucleus Claustrum Thalamus Putamen Globus pallidus Substantia nigra Subthalamic nucleus Basal ganglia Parkinson’s disease Huntington’s disease Direct and indirect pathways SMA/PMC/CM Indirect Direct Putamen GPe STN Brainstem Spinal Cord GPi/SNr VLo VApc/mc CM Basal ganglia connect to supplementary motor areas and primary motor cortex SMA MI Putamen SMA: Supplementary motor area STN: Subthalamic nucleus Globus pallidus Thalamus Vlo-CM STN Involvement of the cerebellum Cortex Thalamus Dentate nucleus Pontine nuclei Cerebellar cortex Involvement of the cerebellum and pontine nuclei Cerebral cortex (MI and SI) Thalamus Red nucleus Cerebellar nucleus Pontine nuclei Cerebellar cortex Rubrospinal tract From spinal cord Overview of motor pathways ANATOMICAL LOCATIONS OF THE BASAL GANGLIA Middle cerebral artery BASAL GANGLIA ANATOMICAL LOCATION OF THE CAUDATE NUCLEUS Somatotopic organization of the motor cortex Cortical motor areas The central sulcus divides motor and sensory areas Overview of motor pathways Motor cortex Two descending motor tracts The alphamotoneuron is the final common pathway Basal ganglia Thalamus Cerebellum Corticospinal tract Brain stem motor pathways Interneurons a motor neuron muscle Motor cortex Thalamus Basal ganglia Cerebellum Brainstem Spinal cord Effect from spasticity 120 Soleus H-reflex: Effect on Ib inhibition on reflex response 110 Hemiplegic side 100 90 Normal side 80 2 3 4 5 6 7 8 9 Conditioning-test interval (ms) 10 Inhibitory supraspinal input to motoneuron pool Supraspinal input Segmental input la (from muscle spindles) lb (from Golgi tendon organs) a motoneuron Muscle Visceral afferent innervation in the lower body and motor (efferent) innervation. Spinal cord DRG T11-L4 Viceral afferents DRG Viceral afferents S 3-S 4 Viceral afferents Uterus Efferent Viceral receptors Pain fibers Bladder Nociceptors