Motor pathways
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General organization of motor systems
•
•
•
Cerebral cortex contains numerous circuits for motor control
Cerebellum and basal ganglia also participate in important feedback
loops in which they project back to cerebral cortex via thalamus
Sensory inputs also plays an essential role in motor circuits and
feedback loops
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• The circuits within the cerebral cortex involve the primary
cortex and the association cortices regions like Premotor
cortex, supplementary motor area and parietal
association cortex which are crucial to the planning and
formulation of motor activities
– Lesion of the association cortices regions can lead to apraxia
which is loss of ability to execute or carry out learned purposeful
movements, despite having the desire and the physical ability to
perform the movements
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Cortical areas involved in motor function
• Primary motor area
(Broadmann’s area 4)
is the major area
involved
– execution of
movements
– determining force and
direction of movements
– adapting movements to
changes in sensory
feedback
– Lesion of this area
leads to motor deficit
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• Premotor & Supplementary
motor areas are also
involved in higher-order
motor planning and project
to primary motor cortex
– Planning of complex
movements
– Mental rehearsal of
movements
– Learning movement
sequence
– Lesions in these areas do not
produce severe movement
deficit but rather deficit in
motor planning
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Cortical areas involved in motor function
• Posterior parietal cortex
(sensory association area)
Posterior parietal cortex
– Provides information to
premotor cortex about
environment
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Cortical areas involved in motor function
• Prefrontal association
cortex
Prefrontal association
cortex
– Planning of behavior
– Major input to premotor
areas
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The motor homunculus
• Functional mapping
and lesion studies
have demonstrated
that primary motor
area is somatotopically
organized
• Thus adjacent regions
of the cortex
correspond to adjacent
areas on the body
surface
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Descending tracts
• Descending motor pathways
arise from the cerebral cortex and
brainstem
• Divided into 2 based on their
location in the spinal cord
– Lateral motor systems travel
in lateral column of spinal
cord and synapse in the more
lateral groups of ventral horn
neurons
• Control movements of the
extremities
– Medial motor systems travel
in anteromedial spinal cord
columns to synapse on medial
ventral horn motor neurons
• Control the proximal axial and
girdle muscles involved in
postural tone, balance, orienting
movements of the head and neck
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to body
to face
Rubrospinal tract
(to face)
(to mouth)
Modified from Purves et al., 2004
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• At cervicomedullary
junction (level of foramen
magnum), 75-85% of
pyramidal tract fibres
cross over in the
pyramidal decussation to
enter lateral white column
of spinal cord forming the
lateral corticospinal tract
to
body
to
face
Rubrospin
al tract
(to face)
• The remaining (approx
15%) of corticospinal
fibres continue into the
spinal cord ipsilaterally,
without crossing, and
enter anterior white
matter column to form
anterior corticospinal
tract that occupy anterior
white column at cervical
and upper thoracic levels
to supply deep muscles
of the neck
(to
mouth)
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Modified from Purves et
al., 2004
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• During its descent through the brainstem, the corticospinal tract gives off
fibres that activate motor cranial nerves nuclei (Corticobulbar/
Corticonuclear), notably those serving the muscles of the face, jaw and
tongue
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Unilateral face, arm, leg paralysis
(Hemiplegia) Without sensory loss
Unilateral face, arm, leg paralysis
(Hemiplegia) With sensory loss
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Paraplegia
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Lower motor neurons
• Lower motor neuron
– Motor neurons in the
anterior gray horns of
spinal cord & their axons
that innervate skeletal
muscles
• Upper motor neuron
– Carry motor output from
cerebral cortex and
brainstem to lower motor
neuron in spinal cord &
brainstem which in turn,
project to muscles in the
periphery
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Consequences of injury to the motor system
•
Lower motor neuron lesion e.g.
nerve transection or motor
neuron disease
– Paralysis/weaknes
– Decreased stretch reflexes
including:
• decreased muscle tone
(flaccidity/hypotonea)
• decreased resistance to
stretch
– Muscle fasciculations
and atrophy
X
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Consequences of injury to the motor system
• Upper motor neuron injury e.g.
stroke or brain trauma, spinal
cord injury
– Paralysis/weakness for fine
movements
– Increased stretch reflexes
including:
• Increased muscle tone
(hypertonia)
• Increased resistance to stretch
(spasticity)
• Clonus (rhythmic contraction
of flexor muscles in response
to passive dorsiflexion)
– Positive Babinski sign (extensor
plantar response  withdrawa 
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X
X
X
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Babinski sign
From Blumenfeld, 2002
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Paraplegia
• Paraplegia is an impairment in
motor or sensory function of the
lower extremities.
• The area of the spinal canal that
is affected in paraplegia is either
the thoracic, lumbar, or sacral
regions. If all four limbs are
affected by paralysis, tetraplegia
or quadriplegia is the correct
term. If only one limb is affected,
the correct term is monoplegia.
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Unilateral face, arm, leg paralysis
(Hemiplegia) Without sensory loss
Unilateral face, arm, leg paralysis
(Hemiplegia) With sensory loss
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Test yourself
• A 53-year-old widower was admitted to HKMU hospital
complaining of a burning pain over his right shoulder region and
the upper part of his right arm. The pain had started 3 weeks
previously and, since that time, had progressively worsened. The
pain was accentuated when the patient moved his neck or
coughed. Two years previously, he had been treated for
osteoarthritis of his vertebral column. The patient stated that he
had been a football player at college, and since that time, he
continued to take an active part in the game until he was 42 years
old. Physical examination revealed weakness, wasting, and
fasciculation of the right deltoid and biceps brachii muscles. The
right biceps tendon reflex was absent. Radiologic examination
revealed extensive spur formation on the bodies of the fourth,
fifth, and sixth cervical vertebrae. The patient demonstrated
hyperesthesia and partial analgesia in the skin over the lower part
of the right deltoid and down the lateral side of the arm. Using
your knowledge of neuroanatomy, make the diagnosis. How is
the pain produced? Why is the pain made worse by coughing?
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