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UVM NSCI 110 - The Motor Cortex
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Lecture 26 Outline of Last Lecture I. Music and language related tasks can be detected through PET scansa. Activate different regions surrounding Heschi’s gyrus II. There are various components that constitute expression of languagea. Phoneme, morphemeb. Semantics, syntax, lexiconc. Context, discourseIII. Different varieties of aphasia lead to deficits in speech and comprehension of languageIV. Information involving the somatosensory cortex involves a specific serial ordera. The amount you attend to a motor task depends on familiarity and complexityOutline of Current Lecture I. Control of motor activity exists in a hierarchya. Prefrontal cortex  premotor cortex  motor cortexII. Mirror neurons can be activated not just by carrying out a task, but by observing it and thinking about it as wellIII. Spatial representation of motor control is represented on a homunculusIV. The motor cortex involves several fundamental movement categories that may differ depending on the type of response requireda. Brainstem controls species-specific behaviorsb. Motor cortex involves complex series of movementsc. Spinal cord controls more instinctual movements such as walking or scratchingV. The cortex compensates action potential rates depending on anticipation of a taskVI. The cortex exhibits plasticitya. Rehabilitation can help lesioned areas regain motor controlVII. The corticospinal tract is the main efferent pathway leaving the motor cortexa. Lateral tracts relay information to the contralateral sidesb. Ventral tracts relay information to ipsilateral sidesCurrent Lecture- Hierarchy of movement controlo Prefrontal cortex plans  premotor cortex sequences  motor cortex executes actions - Monkey on slide: why is this behavior disrupted?o Can the joints assume the correct position?o Does the subject understand the use of the object?o Could movement sequence be enacted togetherThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. NSCI 110 1st Edition- Mirror neurons are neurons in the premotor cortex (and other areas) that can be active during action or observation of a specific tasko Active upon thinking about doing the task (not just doing it)o Less active if using a toolo The brain’s response to seeing different actions is influenced by the acquired motor skills of the individual observerMOTOR SYSTEM ORGANIZATION- Wilder Penfield mapped the cortices of patients who were about to undergo neurosurgeryo Confirmed motor cortex role in movement by asking different tasks of the patientso Stimulating electrode  movement of certain body parts- Homunculus is a topographical representation of the bodyo Spatial representation as perceived - The motor cortex does not represent muscle, but rather a repertoire of fundamental movement categorieso Monkey models revealed that longer stimulations give rise to more complex series of movements Defensive facial posture Hand-to-mouth Central body space Outward reach Climb/reacho Not the only site to elicit movement categories Brainstem gives rise to species-specific behaviors (swimming, grooming, nest-making, chewing, defensive behaviors) Spinal cord facilitates complex motor patterns that are common among a species (scratching, walking)- Activation in neurons occurs before motor activity takes placeo Anticipatory response before movement occurs Planning and executive movement discharged before/during  frontal cortexo The cortex is capable of code force of movement Rate/duration of firing compensates depending on weights of objects/complexity of tasko Simple coding of movement direction  Flexors/extensors- Is the motor cortex organization stable over time?o No, it changes! It is directly influenced on the daily tasks you participate in and lifestyle- Neuroplasticity of the motor systemo What occurs when a lesion is induced? Monkey experiment  lesioned a region responsible for digit/wrist/forearm movement Differences between no rehab and rehab? What happened to the cortical representation of the two subject groups?- The monkeys without rehab has less neurons devoted to the activity, but those with rehab regenerated the area to a larger extent- Corticospinal tract is the main efferent pathway that begins in the motor cortexo Corresponds to layer V of the cortex Axons descend into the brainstem, some go to the brainstem nuclei and emerge on the brainstem’s ventral surface as pyramidal tracts (bumps on each side  are seen in the lumps on the tegmentum)o Responsible for conscious control over skeletal muscles Internal capsule is the tract (of white matter) between the cortex and medulla From the medulla the tract can divide into the ventral (stays ipsilateral, smaller) or lateral (thicker) CS tract (know each of their functions) Decussation of Pyramids  looks like an “X”, where the lateral tracts cross over (the ventral tracts do not do this) All the tracts except those responsible for the face/neck descend down the CSo Corticobulbar tract gives us conscious control over eye/jaw/face muscles Descends to internal capsule but branches off near the brainstem Different output regions (midbrain, pons, medulla) depending on what movement is to be produced- Lateral CS tract branches at the medulla to cross to the contralateral sideo Moves digits and limbs- Ventral CS tract stays on the ipsilateral sideo Moves muscles of the midline/trunk- Organization in the spinal cord (ventral horn)o Lateral tract synapses with interneurons and motor neurons Interneurons synapse with motor neurons that innervate muscle More distal areas of the body correspond with more distal neurons in the spinal cordo The interneurons and motor neurons of the spinal cord are envisioned as a homunculus representing the types of muscles they innervateo Limb muscles are paired Extensors move limbs away from the trunk Flexors move limbs toward the trunko Connections between interneurons and motor neurons ensure coordination of extensor/flexor actionso Left upper motor neurons control: Trunk muscles along the midline Limbs on the body’s right


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UVM NSCI 110 - The Motor Cortex

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