Motor Systems

Spinal Cord:

  • Central gray matter – neuronal cell bodies and synapses
  • Peripheral white matter – ascending/descending fiber pathways (motor and sensory)

Muscle Unit:

  • A single motorneuron and all of its muscle fibers
  • Alpha motorneuron – largest cells of spinal cord and “final common pathway” from CNS to periphery. Each one usually innervates many muscle fibers – each muscle fiber innervated by only ONE alpha motorneuron

Spinal Reflex:

  • Stereotyped motor responses to stimuli
  • Afferents from periphery -> synapse(s) in spinal cord -> alpha motorneurons -> muscle fibers

General Info:

  • Motor (corticospinal) pathway extends from motor area of cortex through brain stem and crosses between brainstem and spinal cord
  • Fibers synapse in anterior horn (just prior to leaving cord)
  • Decorticate Posturing – Cerebral injury (e.g., CVA due to carotid occlusion) – flexion of wrist and elbow and extension of ankle and knee
  • Decerebrate Posturing – due to midbrain injury – posturing is similar, but elbow is extended
  • Upper Motor Neurons (i.e. first order neurons) – are neurons above the synapse in the anterior horn
  • Lower Motor Neurons (i.e., second order neurons) – peripheral motor neurons
  • Polio – attacks anterior horn cells – LMN disease
  • Gullian-Barre Syndrome – sensory and LMN loss due to peripheral nerve involvement

Abnormalities of Movement

  • Fasciculation – visible, continuous, and rapid twitching of a muscle or part of muscle without movement of a limb
  • Tremor – rhythmic involuntary back-and-forth movement that may be as rapid as trembling. It usually involves movement of a limb or body part. It may be represent only when the muscle is at rest, during a voluntary movement, or both.
    • In Parkinson’s tremor is present at rest
    • In Cerebellar disorder, tremor is intentional (i.e., occurs during intentional movements, such as drawing)
  • Tics – repetitive twitching of a muscle group such as, facial muscle twitching resulting in grimaces. They may be emotional or neurological origin
  • Chorea – obvious, rapid, sudden, involuntary, jerky movements that may involve the limbs, trunk, or face. They occur at irregular, unpredictable intervals and are not rhythmic or repetitive
  • Athetosis – differs from chorea primarily in that it is slow, writhing, and twisting, rather than rapid and jerky (may occur with cerebral palsey)
  • Myoclonus – sudden, rapid, unpredictable and involuntary jerking movements (e.g., a hiccup is a myoclonic movement of the diaphragm)

Upper Motor Neuron (UMN) Defects

  • Spastic paralysis
  • No significant muscle atrophy
  • No fasciculations/fibrillations
  • Hyperreflexia
  • Babinski may be present

Lower Motor Neuron (LMN) Defects

  • flaccid paralysis
  • significant atrophy
  • fasciculations/fibrillations
  • hyporeflexia
  • No Babinski

Ventromedial Tracts

Axial musculature involved in maintain posture (righting reflex and whole body orientation)

Dorsolateral Tracts

Distal musculature, initiation and control of voluntary movements.

Basal Ganglia

  • Subcortical telencephalic nuclei involved in initiation and control of movement
  • Extrapyramidal – mechanisms involving injury to the basal ganglia motor pathway outside of the corticospinal “pyramidal” system. Consists of:
    • Caudate nucleus
    • Putamen
    • Globus pallidus (pallidum)
    • Associate areas include substantia nigra, subthalamic, nucleus and projections from Basal ganglia to thalamic nuclei
  • Divisions:
    • Neostriatum or Striatum -> caudate -> putamen
    • Corpus Striatum -> striatum -> globus pallidus
    • Lentiform nucleus -> putamen -> globus pallidus
  • Symptoms of Impairment
    • Dyskinesia – involuntary movements
    • Bradykinesias – slowness in initiating or changing without significant weakness
    • Abnormal fixation – equilibrium and righting
    • Parkinson’s Disease – rigidity, bradykinesia, resting tremor, loss of postural reflexes
    • Ballism – sudden, forceful, flinging dyskinesia involving whole limb (contralateral arm to lesion in subthalamic nucleus)
    • Athetosis – slow, wormlike, writhing movements, usually in extremities
      • Lesion in striatum (usually putamen)
    • Torsion Dystonia – disorder of trunk and limb involving writhing movements which produce severe sustained contortion of neck, shoulder girdle, and pelvic girdle
      • Lesion in striatum (usually putamen)
    • Huntington’s Chorea – involuntary movements of limbs which are brisk and graceful and have appearance of fractions of purposeful movement
      • caudate
    • Choreoathetosis – combination of chorea and athetosis


  • Coordination of movement and posture, particular in adaption of movement to changing external and internal conditions
  • Lesions cause:
    • Ataxia
    • Hypotonia
    • Ipsilateral malfunctioning
    • Dysdiadochokinesia – failure of rapid alternating movements
    • Past pointing – inability to touch finger to nose or heel to shin

Gait Abnormalities

  • Spastic hemiparesis – the arm on the affected side is held flexed and immobile against the body, instead of swinging freely by the side. The affected leg is moved forward stiffly and in a semi-circle, sometimes with the toe dragging on the floor as the leg is moved forward
  • Scissors gait – steps are abnormally short and appear effortful. The knees remain in contact as if the patient were trying to hold an imaginary orange between the thighs as he walks – seen in MS
  • Ataxia – patient has difficulty in keeping his balance. Walks with feed wide apart
  • Parkinsonian – stooped posture, flexion at the hips, elbows, and knees. General mobility is decreased; steps are short and shuffling. Has difficulty both initiating and stopping

Muscle Tone

  • Flaccidity – when muscle tone is less than normal and the limb feels limp to the examiner
  • Posture retention – when a limb tends to remain in the position into which you move it or in which it was before you moved it
  • Rigidity – limb is abnormally resistant to movement in all directions
  • Cogwheel motion – limb yields in your attempt to move it, but with jerking rather than smooth movements (seen in Parkinson’s)
  • Spasticity – impairment of UMN – increase in muscle tension characterized by certain postural changes involving flexion of the finger, hand, arm, and legs