Coordination of movement

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

Scheme of motor movement

• 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

• 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

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)