Types of movements

  • Unintentional – involuntary
  • Intentional – voluntary

Purpose of movements

  • Protection/maintenance of posture
  • To execute a voluntary movement in response to a thought/ idea or external stimulus [ from eyes, ears, touch, etc]

Posture provides background for movement
Movement starts with one posture and ends with another
Coordination before and after movement

  • Initiation & coordination of movement is carried out by a complex system of
    • hierarchical control
    • feedbacks
    • continuous adjustment
  • Eg. Walking
    • left upper limb coordinated with right lower limb
      • smooth & balanced

Servo systems

  • No control system
  • Feedforward system
  • Feedback system

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Scheme of motor movement

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  • Idea
    • eg. i want to touch my toes
  • Planning & programming
    • Cerebral cortex (Cortical association areas)
      • plans and execute movement
    • Basal ganglia
      • initiates movement
    • Lateral cerebellum
      • refines movement
  • Thalamus
  • Premotor & motor cortex
    • Pyramidal system
      • to corticospinal tract
    • Extrapyramidal system
      • Rubospinal
      • Reticulospinal
      • Tectospinal
      • Vestibulospinal
  • Alpha motor neuron (lower motor neuron)
    • final common pathway
  • Execution
    • muscles
  • Monitoring
    • intermediate cerebellum
  • Feedback
    • back to premotor & motor cortex

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The basal ganglia

Responsible for planning and programming of movements.

Disorders of movements

  • Hyperkinetic
    • Chorea
      • Huntington’s chorea
    • Athetosis
      • slow and writhing
      • like a snake dance
    • Ballism
      • ballistic!
      • hemiballism
        • resulting from the destruction of subthalamic nuclei on the same side
  • Hypokinetic
    • Akinesia
      • inability to initiate movement due to difficulty selecting and/or activating motor programs in the central nervous system
    • Bradykinesia
      • slowness of movement and has been linked to Parkinson’s disease and other disorders of the basal ganglia

Related structures of basal ganglia

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  • Corpus striatum
    • Striatum (neostriatum)
      • caudate nucleus
      • putamen
      • nucleus accumbens
    • Globus pallidus (pallidum/paleopallidum)
      • medial (internal) segment
      • lateral (external) segment
      • ventral pallidum
  • Substantia nigra
    • pars compacta
    • pars reticularis
  • Subthalamic nuclei
  • Ventral tegmental area

Different pathways

  • Nigrostriatal dopaminergic pathway
    • dopamine releasing neurones going from Substatia nigra to the putamen (striatum)
    • degeneration of this pathway –> Parkinsonism
  • Intrastriatal cholinergic system
    • loss in Huntington’s disease
  • GABA-ergic neurons from striatum to globus pallidus (external) and Substantia Nigra
    • loss in Huntington’s disease

Parkinsonism

  • disorder of the extrapyramidal system, that is, the motor structures in the basal ganglia
    • may be caused by degeneration of dopamine-producing cells in the substantia nigra, resulting in decreased levels of dopamine in the striatum
  • Pathogenesis
    • loss of dopamine and dopamine receptors
      • normal aging process
      • however accelerated in Parkinson’s disease
    • loss of balance between cholinergic (exci
      tatory) and dopaminergic (inhibitory) discharge

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Schematic representation of the basal ganglia - t...

Pathophysiology of Parkinsonism
Refer diagrams above

Normally,

  • The cerebral cortex plans and programs the movement
  • Then signals the striatum to secrete dopamine (1 and 2)
  • 2 pathways
    • Direct pathway
      • cortex→striatum→GPi→thalamus→cortex
      • outflow from striatum
        • Secrete D1
      • directly inhibits GPi and Substantia nigra (SNr)
        • GPi usually inhibits thalamus
        • So if GPi is inhibited, so there is no longer inhibition of the thalamus (disinhibition) –> stimulate thalamus
      • sends inhibitory output to the ventral lateral (VL) nucleus of the thalamus
        • stimulate THALAMUS
        • excites cortex
      • initiate movement
        • In parkinson’s: opposite of everything
        • Difficulty in initiating movement
    • Indirect pathway
      • cortex→striatum→GPe→STN→GPi→thalamus→cortex
      • inhibit GPe and Subthalamic nucleus
      • excites GPi
        • further inhibit the thalamus
      • inhibit thalamus
        • does not excite cortex
      • supresses involuntary movement
        • In parkinson’s: opposite of everything
        • Increases involuntary movement

Clinical features of Parkinson’s disease

  • Hypokinetic features (pallidectomy is beneficial)
    • akinesia
      • difficulty in initiating movements
    • bradykinesia
      • slow performance of voluntary movement
      • eg shuffling gait
    • hypokinesia
      • difficulty in initiating continuous movement
    • inability to execute simultaneous movement
    • Hypomimia/ defective kinetic automatism / masked facies
      • loss of associated movements
      • eg facial expressions, unconscious movements (swinging of arms), gestures, fidgety actions
    • festinating gait
      • bends lightly forward and walks with short quite step
    • swallowing & speaking difficulties
  • Hyperkinetic features
    • rigidity
      • cogwheel rigidity
    • tremor at rest
      • pin-rolling tremor
    • loss of braking action
      • can’t stop himself when pushed

Test for Parkinsonism

  • Observe
    • masked facies (loss of facial expression)
    • loss of associated movements (swinging of arms when walking)
    • shuffling gait
    • pin-rolling movements
  • Test for rigidity
    • lead pipe rigidity/ cogwheel rigidity
  • Push him
    • can he brake himself?
    • be sure to have someone catch him when he falls

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Cerebellum

  • Planning execution of movement
  • Learning of skilled motor tasks
  • Receives afferent from:
    • labyrinths
      • through vestibulocerebellar pathway
      • to maintain balance
    • Proprioceptors and enteroceptors
      • through spinocerebellar pathway
      • postural control
      • feedback during movement
    • Proprioceptors from head and neck
      • through cuneocerebellar pathway
    • Proprioceptors from whole body
      • through olivocerebellar pathway
    • Ear and eye
      • through tectocerebellar pathway
    • Cerebral cortex
      • through pontocerebellar pathway
  • -> goes to spinocerebellum
    • medial and lateral descending systems
  • Sends efferents to:
    • lateral cerebellum (cerebrocerebellum)
      • motor & premotor cortex
        • motor planning
      • vesticular nuclei
        • balance & eye movements
    • vesticulocerebellum
      • diving

Cerebellar dysfunction

  • May show no abnormality at rest
  • Ataxia (with movement)
    • errors in rate, force, range and direction in movement
  • Defect in skilled movement
    • slurred/scanned speech
    • Dysmetria (past-pointing)
    • Intentional tremors
      • due to overcorrection
    • Adiadochokinesia
      • an inability to perform rapidly alternating movements, such as pronation and supination or flexion and extension
    • Decomposition of movement
      • movements dissected like a puppet

Tests for cerebellar dysfunction

  • Speak to the patient
    • slurring of speech?
  • Observe
    • intentional tremors
  • Walk to straight line
    • ataxia
  • Finger-nose test
    • past-pointing to the ear
  • Supinate and pronate hands quickly
    • adiodochokinesia
  • heel-to-knee (or to shin) test
    • heel cannot slide down shin in a straight line

Differentiating atax
ia – sensory or motor.

  • Rhomberg’s test
    • stand with feet together, hands at the side
    • Sensory ataxia
      • eyes open – steady
      • eyes closed – unsteady
    • Motor ataxia
      • eyes open – unsteady
      • eyes closed – unsteady
      • (RHOMBERG’S SIGN +VE)

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