THE MOTOR SYSTEM, part II
THE MOTOR SYSTEM, part II
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
DESCENDING SPINAL TRACTS
Axons from brain descend along two major pathways Lateral Pathways: involved in voluntary of distal musculature movement under cortical controlVentromedial Pathways: involved in control of posture and locomotion, under brain stem control
THE LATERAL PATHWAYS
Base of cerebral peducle
Medullarypyramid
Corticospinaltract
Rubrospinaltract
pyramidal decussation
midbrain
Right red nucleus
THE VENTROMEDIAL PATHWAYS
Vestibular nucleus
Spinal cord
Vestibulospinaltract
Tectospinaltract
Vestibulospinal tract: information from vestibular system. Control neck and back muscles. Guide head movements
Tectospinal tract: information from retina and visual system. Guide control eye movements.
THE VENTROMEDIAL PATHWAYS
Cerebellum
Spinal cord
Reticulospinaltract
pons
Medullaryreticular formation
Pontine reticular formation
Pontine reticulospinal tract: enhance antigravity reflexs, helps maintaining a standing posture
Medullary reticulospinal tract: opposite function
THE MOTOR CORTEXArea 4 = “Primary motor cortex” or “M1”Area 6 = “Higher motor area”Lateral region Premotor area (PMA), controls distal motor unitsMedial region Supplementary motor area (SMA), controls proximal motor units
THE MOTOR CORTEXThe Contributions of Posterior Parietal and Prefrontal CortexRepresent highest levels of motor control. Help in deciding about actions and their outcome, by integrating many source of informationArea 5: Inputs from areas 3, 1, and 2Area 7: Inputs from higher-order visual cortical areas. They both project to Area 6
Instruction
Trigger
APs of PMA neuron
THE BASAL GANGLIA
Basal ganglia Project to the ventral lateral (VLo) nucleusProvides major input to area 6
Cortex Projects back to basal gangliaForms a “loop” in order to select and initiatiate willed movements
THE BASAL GANGLIAAnatomy of the Basal GangliaCaudate nucleus, putamen, globus pallidus, subthalamic nucleusSubstantia nigra: Connected to basal ganglia
THE BASAL GANGLIA
The Motor Loop: Selection and initiation of willed movementsExcitatory connection from the cortex to cells in putamenCortical activation excites putamen neurons. Inhibits globus pallidus neurons.Release cells in VLo from inhibition. Activity in VLo influences activity in SMA
THE BASAL GANGLIA
Basal Ganglia Disorders: Hypokinesia and hyperkinesia
Parkinson’s diseaseSymptoms: Bradykinesia, akinesia, rigidity and tremors of hand and jawOrganic basis: Degeneration of substantia nigra inputs to striatumDopa treatment: Facilitates production of dopamine to increase SMA activity
Huntington’s diseaseSymptoms: Hyperkinesia, dyskinesia, dementia, impaired cognitive disability, personality disorder
HemiballismusViolent, flinging movement on one side of the body
Some examples….
http://www.youtube.com/watch?v=ECkPVTZlfP8&feature=related PARKINSON
THE CEREBELLUM
Function: Sequence of muscle contractionsLesion: Ataxia, characterized by uncoordinated and inaccurate movements. Dysynergia, dysmetricAnatomy: Folia and lobules, Deep cerebellar nuclei (relay cerebellar cortical output to brain stem structures) Vermis (contributes to ventromedial pathways) Cerebellarhemispheres (contributes to lateral pathways)
THE CEREBELLUM
THE CEREBELLUMThe Motor Loop Through the Lateral CerebellumAxons from layer V pyramidal cells in the sensorimotor cortex form massive projections to ponsCorticopontocerebellar projection are 20 times larger than pyramidal tractFunction: Execution of planned, voluntary, multijoint movements