MOTOR SYSTEM
Consolidated by Kira Armstrong July 2002
Spinal Cord:
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Central gray matter – neuronal cell bodies and synapses
Peripheral white matter – ascending/descending fiber pathways (motor and sensory)
Muscle Unit:
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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:
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Stereotyped motor responses to stimuli
Afferents from periphery  synapse(s) in spinal cord  alpha motorneurons  muscle fibers
General Info:
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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
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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
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)
THE FINE PRINT: Caveat emptor! These study materials have helped many people who have successfully completed the ABCN board
certification process, but there is no guarantee that they will work for you. The notes’ authors, web site host, and everyon e else involved in the
creation and distribution of these study notes make no promises as to the complete accuracy of the material, and invite you to suggest chan ges.
Upper Motor Neuron (UMN) Defects
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Spastic paralysis
No significant muscle atrophy
No fasciculations/fibrillations
Hyperreflexia
Babinski may be present
Lower Motor Neuron (LMN) Defects
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flaccid paralysis
significant atrophy
fasciculations/fibrillations
hyporeflexia
No Babinski
Ventromedial Tracts
Axial musculature involved in maintain posture (righting reflex and whole body orientation)
See text notes for full details
Dorsolateral Tracts
Distal musculature, initiation and control of voluntary movements. See text notes…
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:
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Caudate nucleus
Putamen
Globus pallidus (pallidum)
Associate areas include substantia nigra, subthalamic, nucleus and projections from Basal
ganglia to thalamic nuclei
Divisions:
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Neostriatum or Striatum  caudate  putamen
Corpus Striatum  striatum  globus pallidus
Lentiform nucleus  putamen  globus pallidus
Symptoms of Impairment
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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
THE FINE PRINT: Caveat emptor! These study materials have helped many people who have successfully completed the ABCN board
certification process, but there is no guarantee that they will work for you. The notes’ authors, web site host, and everyon e else involved in the
creation and distribution of these study notes make no promises as to the complete accuracy of the material, and invite you to suggest chan ges.
Cerebellum
Coordination of movement and posture, particular in adaption of movement
to changing external and internal conditions
Lesions cause:
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Ataxia
Hypotonia
Ipsilateral malfunctioning
Dysdiadochokinesia – failure of rapid alternating movements
Past pointing – inability to touch finger to nose or heel to shin
Gait Abnormalities
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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
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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
THE FINE PRINT: Caveat emptor! These study materials have helped many people who have successfully completed the ABCN board
certification process, but there is no guarantee that they will work for you. The notes’ authors, web site host, and everyon e else involved in the
creation and distribution of these study notes make no promises as to the complete accuracy of the material, and invite you to suggest chan ges.