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.
Lateral system
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
Motor areas Sensory areas Terminations of the corticospinal tract projections of sensory pathways
Renshaw inhibition Fibers of the corticospinal tract terminate on motoneurons or interneurons
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
Hoffman reflex
Reflexes are modulated from supraspinal sources
Reciprocal spinal reflex
Descending vestibular pathways
Medial system Posture and automatic functions
Tendon reflex
Flexor reflex
Convergence of excitatory inputs Convergence of inhibitory and excitatory inputs
Input to propriospinal neurons of the forelimb of the cat
From Rosler Fig 2B Magnetic stimulation of motor cortex in an awake individual
Input to an Ia inhibitory interneuron
Input to an Ib (inhibitory) interneuron
BASAL GANGLIA Extrapyramidal system Pyramidal system
Two descending motor tracts The alpha- motoneuron is the final common pathway
Anatomical localization motor pathways
Basal ganglia
Parkinson’s disease
Huntington’s disease
Direct and indirect pathways
Basal ganglia connect to supplementary motor areas and primary motor cortex SMA: Supplementary motor area STN: Subthalamic nucleus
Involvement of the cerebellum
Involvement of the cerebellum and pontine nuclei
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
Two descending motor tracts The alpha- motoneuron is the final common pathway
Effect from spasticity Soleus H-reflex: Effect on Ib inhibition on reflex response Hemiplegic side Normal side
Inhibitory supraspinal input to motoneuron pool
Visceral afferent innervation in the lower body and motor (efferent) innervation.