DescendingMotorSystems - Descending Somatic Motor Systems...

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Unformatted text preview: Descending Somatic Motor Systems Overview Numerous separate descending pathways influence skeletal (somatic system) motor activity Hierarchy of structures significantly influencing motor system Cortex Basal ganglia Diencephalon Brainstem Cerebellum Spinal Cord Descending Somatic Motor Systems Overview of pathways Spinal Pathways (via spinal nerves) 1. Pyramidal Tracts Corticospinal: arise from pyramidal cells (largest are Betz cells) in motor cortex and surrounding areas Lateral Corticospinal concerned with voluntary, discrete, skilled movement Anterior Corticospinal regulates precision of axial and girdle muscle movements Pyramidal cells in motor cortex Descending Somatic Motor Systems Overview of pathways More Spinal Pathways (via spinal nerves) 2. Extrapyramidal Tracts Reticulospinal facilitates or inhibits voluntary movement or reflex activity (originates in the pons & medulla) Tectospinal concerned with reflex postural movement in response to visual & auditory stimuli (originates in superior colliculus) Rubrospinal regulates muscles tone for limb extension (originates in red nucleus) Vestibulospinal facilitates activity of the extensor muscles, inhibits activity of the flexor muscles and is concerned with postural activity associated with balance (originates in vestibular nucleus, incorporates projections from the inner ear and cerebellum) Descending Somatic Motor Systems Overview of pathways Cranial Pathways (via cranial nerves) Corticobulbar- pathway from cortex to voluntary muscles of the head Will be focusing on corticospinal & corticobulbar Descending Somatic Motor Systems Corticospinal/Corticobulbar Organization Descending pathways from cortex follow the two or the three neuron organization: Firstorder neuron or Upper Motor Neuron (UMN) cell body in cortex Second order neuron (interneuron) interneurons in corticospinal tract, but not corticobulbar Third order neuron or Lower Motor Neuron (LMN) (also called final common pathway ) cell body in spinal cord for corticospinal tract; cell body in brainstem nuclei for corticobulbar tract Descending Somatic Motor Systems Corticospinal/Corticobulbar Organization Laterality pattern Cortex is contralateral to motor output and sensory input points for corticospinal, most output and input crosses at the pyramidal decussations in the caudal medulla for corticobulbar, it crosses in the pons and medulla) LMNs in spinal cord and in brainstem extend to innervate muscles ipsilaterally Descending Somatic Motor Systems Corticospinal/Corticobulbar Organization Organization of motor cortex Rostral to central sulcus Somatotopic representation of the body (motor homunculus) Somatosensory and Motor Homunculi web.odu.edu/webroot/instr/sci/kcarson.nsf/ files/Chapter 6 .ppt/$FILE/Chapter 6 .ppt Descending Somatic Motor Systems Corticospinal/Corticobulbar Organization...
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DescendingMotorSystems - Descending Somatic Motor Systems...

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