ALTERED MOTOR FUNCTION

1
ALTERED MOTOR FUNCTION

• Normal motor control
• Disorders of the neuromuscular unit
• Peripheral nerve disorders
• Multiple sclerosis
• Spinal cord injury

2
NORMAL MOTOR CONTROL

• Motor cortex - premotor, primary - UMNs
• ? (pyramidal tracts)
• Basal ganglia - extrapyramidal tracts
• (balance, posture)
• Cerebellum - sensory feedback, skilled
• ? motor function
• Brainstem- motor tracts (UMN axons) decuss.
• ? reflex centres for balance and ANS

3
NORMAL MOTOR CONTROL

• ?
• Motor tracts in spinal cord - ventral white
• ?
  matter
• LMNs in spinal cord - axons in ventral root of
• ?
  spinal nerve
• Neuromuscular junction - ACh released onto
• ?
  nicotinic receptors
• Muscle fibres - organised in motor units

4
NEUROMUSCULAR UNIT

• Motor unit one motor neuron (LMN or ? motor
  neuron) group of skeletal muscle cells it
  innervates
• Disorders of skeletal muscle
• - Atrophy ? cell size due to disuse, nerve
• injury or disease
• - Dystrophy genetic disorder of muscle tissue
  (eg Duchenne musc. dyst.- X-linked)

5
NEUROMUSCULAR UNIT

• Disorders of the neuromuscular junction
• ACh action affected by
• - botulinum toxin
• - some insecticides
• - autoimmune receptor destruction
• (myasthenia gravis)
• May ? paralysis of diaphragm ?
• 
  ventilatory failure

6
PERIPHERAL NERVE DISORDERS

• Herniated intervertebral disc may press on spinal
  nerve root ? pain, ? function
• Polyneuropathies ANS or somatic
• - symmetric
• - demyelination or axonal degeneration
• - causes alcohol, diabetes, immune (eg acute
  Guillain-Barré syndrome)
• LMN lesions - eg trauma, polio

7
UMNs - MULTIPLE SCLEROSIS

• Demyelination of white matter in brain, spinal
  cord
• ? slow or blocked action potential
• Onset young adults
• Autoimmune (macrophages, T-cells) ? ?
  oligodendrocytes
• MRI shows lesions (scarring)

8
UMNs - MULTIPLE SCLEROSIS

• Symptoms optic nerves, parasthesias, motor
  weakness, mood swings, fatigue
• Wide range of severity
• Attacks and remissions, ? IgG in CSF
• Treat acutely with corticosteroids
• (? inflammation)

9
SPINAL CORD ORGANISATION

• Spinal reflexes are hard-wired but are
  modulated and integrated into complex movements
• Somatic reflexes - for posture, balance, tone
• Stretch reflexes used for diagnosis
• - hypotonia ? function (damage to reflex arc
• or electrolyte imbalance
• -hypertonia ?inhibition of LMNs (damage
  to upper motor circuits)

10
SPINAL CORD INJURIES

• Most frequently lower cervical (C4-C6)
• upper thoracic
• Common mechanism hyperextension or
• 
  hyperflexion
• Primary injury (compression or shearing ?
  irreversible damage to mainly grey matter)
• Secondary injury (swelling, ischemia)
• Spinal shock post-injury areflexia (time?)

11
SPINAL CORD INJURIES

• Partial (some function below injury - anal
  sphincter) vs complete (no sensation, motor
  function below)
• Level of injury and functional loss
• High cervical (above C4) tetraplegia
• requires
  ventilation
• Thoracic- paraplegia (some leg function T12)
• Lumbar - incomplete foot control