Neurology - voluntary motion

1. VOLUNTARY MOTION
Kazan State Medical University

2. Motor Cortex
• The motor cortex is located in the rear portion of the frontal lobe,
just before the central sulcus that separates the frontal lobe from
the parietal lobe.The motor cortex is divided into two main areas,
Area 4 and Area 6.Area 4, also known as the primary
motor cortex, forms a thin band along the central sulcus.

3. Primary Motor Cortex (Frontal Lobe)
Voluntary Movement
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4. Primary Motor Cortex
Our body is ‘mapped’ on the Primary Motor Cortex
(area on motor cortex related to amount of innervation)
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5. Central ‘butterfly’ shaped
grey matter contains the
cell bodies of motor
neurons and interneurons
Surrounding white matter
contains the axons of
ascending and
descending neurons
SpinalCord & Spinal Nerves
Dorsal roots (sensory) join with
ventral roots (motor) to form a
spinal nerve.
Spinal nerve contains sensory and
motor information.
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8. Descending Motor Pathways
Motor pathways to skeletal muscle arise from the primary
motor cortex and travel via two pathways
1. Pyramidal (also called Direct) pathways
OR
2. Indirect pathways.
(Indirect as there a pathways that involve the basal
ganglia, thalamus and cerebellum)

9. Two major descending pathways
Pyramidal vs. extrapyramidal
Striated muscles
Lower motor neurons
(brain stem and spinal cord)
Brain stem
centers
Motor cortex
Pyramidal
system Extrapyramidal
system
• Pathway for
voluntary movement
• Most fibers originate
in motor cortex (BA
4&6)
• Most fibers cross to
contralateral side at
the medulla
• Pathways for postural
control/certain reflex
movement
• Originates in brainstem
• Fibers do not cross
• Cortex can influence
this system via inputs to
brain stem

10. Voluntary Action
• Complex responses of the organism to external or internal variables
that seem to be flexible and the result of decisions or plans
• Knowledge of how (planning) and when (timing)?
• Requires monitoring of changes
• Is volition real?
• Is movement the goal (endpoint) of all brain systems?

12. Descending Motor Pathways: Pyramidal Pathway
Regulates fast fine voluntary
motor movement of
skeletal muscle
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13. Motor Unit
• A motor unit is a single α-motor neuron and all of the
corresponding muscle fibers it innervates.When a motor unit is activated,
all of its fibers contract. Groups of motor units often work together to
coordinate the contractions of a single muscle; all of the motor units that
subserve a single muscle are considered a motor unit pool.
• The number of muscle fibers within each unit can vary: thigh muscles can
have a thousand fibers in each unit, eye muscles might have ten. In
general, the number of muscle fibers innervated by a motor unit is a
function of a muscle's need for refined motion.The smaller the motor unit,
the more precise the action of the muscle. Muscles requiring more refined
motion are innervated by motor units that synapse with fewer muscle
fibers.
• Nerve cell axons are very thin, about 1 micrometer. However, they are
extraordinarily long. For many motor neurons the axon is over a meter
long, extending from the spinal column to a muscle cell.

14. Pyramidal Motor Pathway: Assesment
Babinski sign
Reflex manifest by the upturning of the big toe and also by
fanning of the other toes
Indicates Upper motor neuron damage in Pyramidal Pathway
The only clinical pyramidal sign with sensitivity >90%
Present in children up to 2 years.

15. Stretch Reflex :A simple motor pathway
Stretch of patellar
tendon stretches
muscle spindle.
Activates sensory
neuron
Synapses with alpha
motor neuron in
spinal cord
Contraction of
quadriceps muscle
Does not involve the brain
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