The motor system is hierarchically organized, with the highest level involving strategy in the neocortex and basal ganglia, the middle level involving tactics in the motor cortex and cerebellum, and the lowest level involving execution in the brainstem and spinal cord. Descending pathways in the lateral and ventromedial regions of the spinal cord control voluntary distal movements and posture/locomotion respectively. Key structures involved in motor control include the motor cortex, basal ganglia, and cerebellum.
2. THE MOTOR SYSTEM
The brain influences activity of the spinal cord in order to generate voluntary
movements
Hierarchy of controls
Highest level: Strategy, the goal of the movement and best way to achieve it.
Associated to neocortex and basal ganglia
Middle level: Tactics, the sequence of muscle contraction to achieve the goal.
Associate to motor cortex and cerebellum
Lowest level: Execution, activation of motor neurons that generate the
movement. Associated to brain stem and spinal cord
3. DESCENDING SPINAL TRACTS
Axons from brain descend along two major pathways
Lateral Pathways: involved in voluntary of distal musculature movement
under cortical control
Ventromedial Pathways: involved in control of posture and locomotion,
under brain stem control
4. THE LATERAL PATHWAYS
Base of midbrai
cerebral n
peducle
Right red
nucleus
Medullary
pyramid
pyramidal
decussation
Corticospinal Rubrospinal
tract tract
5. THE VENTROMEDIAL PATHWAYS
Vestibulospinal tract:
information from vestibular
system. Control neck and
back muscles. Guide head
movements
Vestibular nucleus
Vestibulospinal Tectospinal
tract tract
Spinal
cord
Tectospinal tract: information
from retina and visual
system. Guide control eye
movements.
7. THE MOTOR CORTEX
Area 4 = “Primary motor cortex” or “M1”
Area 6 = “Higher motor area”
Lateral region Premotor area (PMA), controls distal motor units
Medial region Supplementary motor area (SMA), controls proximal motor units
8. THE MOTOR CORTEX
The Contributions of Posterior Parietal and Prefrontal Cortex
Represent highest levels of motor control. Help in deciding about actions and their outcome, by integrating
many source of information
APs of PMA
Area 5: Inputs from areas 3, 1, and 2 neuron
Area 7: Inputs from higher-order visual cortical areas.
They both project to Area 6
Instruction
Trigger
9. THE BASAL GANGLIA
Basal ganglia
Project to the ventral lateral (VLo)
nucleus
Provides major input to area 6
Cortex
Projects back to basal ganglia
Forms a “loop” in order to select and
initiatiate willed movements
10. THE BASAL GANGLIA
Anatomy of the Basal Ganglia
Caudate nucleus, putamen, globus pallidus, subthalamic nucleus
Substantia nigra: Connected to basal ganglia
11. THE BASAL GANGLIA
The Motor Loop: Selection and initiation of willed movements
Excitatory connection from the cortex to cells in putamen
Cortical activation excites putamen neurons. Inhibits globus pallidus neurons.
Release cells in VLo from inhibition. Activity in VLo influences activity in SMA
12. THE BASAL GANGLIA
Basal Ganglia Disorders: Hypokinesia and hyperkinesia
Parkinson’s disease
Symptoms: Bradykinesia, akinesia, rigidity and tremors of hand and jaw
Organic basis: Degeneration of substantia nigra inputs to striatum
Dopa treatment: Facilitates production of dopamine to increase SMA activity
Huntington’s disease
Symptoms: Hyperkinesia, dyskinesia, dementia, impaired cognitive disability,
personality disorder
Hemiballismus
Violent, flinging movement on one side of the body
Some examples….
http://www.youtube.com/watch?v=ECkPVTZlfP8&feature=related PARKINSON
13. THE CEREBELLUM
Function: Sequence of muscle contractions
Lesion: Ataxia, characterized by uncoordinated and inaccurate movements.
Dysynergia, dysmetric
Anatomy: Folia and lobules, Deep cerebellar nuclei (relay cerebellar cortical output
to brain stem structures) Vermis (contributes to ventromedial pathways) Cerebellar
hemispheres (contributes to lateral pathways)
15. THE CEREBELLUM
The Motor Loop Through the Lateral Cerebellum
Axons from layer V pyramidal cells in the sensorimotor cortex form massive projections to pons
Corticopontocerebellar projection are 20 times larger than pyramidal tract
Function: Execution of planned, voluntary, multijoint movements