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PSYCH 261 Chapter 8

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Deltcho Valtchanov

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Control of Movement Chapter 8 Muscles, motor neurons *Effectors – e.g., the hands (distal) or neck (proximal); somethin that allows you intearact with your environment *Eyes – effectors for vision *Muscles arranged in agonist / antagonist pairs – e.g., biceps and triceps (facilitating vs. preventing function) *Primary site of interaction between muscles and the CNS is via alpha motor neurons (nicotinic ACh receptors) *Extrafusal Muscle Fibers – responsible for force exerted by contraction of skeletal muscle; RESP FOR PHYSICALACTION *Alpha Motor Neuron – neuron whose axon synapses with extrafusal muscle fibers; MUSCLE SENSORS; attched to extrafusal *Intrafusal Muscle Fibers – functions as a stretch receptor; HAVE SENSORY PROPERTIES *Gamma Motor Neuron – neuron whose axons synapse with intrafusal muscle fibers; SENSING THE STRECTHING OF INTRAFUSAL FIBERS *Alpha motor neurons originate in the spinal cord, exit via the ventral root and terminate at extrafusal muscle fibres *Acetylcholine (nicotinic receptors) is the neurotransmitter released by action potentials in alpha motor neurons; primary neurotransmitter for the muscles Stretch reflex *Monosynaptic stretch reflex – knee jerk *Patella stretches quads which contract kicking your foot out *Time from tap to jerk is ~ 50 msec – too short to involve the brain Stretch reflex *Monosynaptic *Sensory neuron *Dorsal root of spinal cord *Motor neuron *Ventral root of spinal cord Polysynaptic reflexes *Agonist – muscle whose contraction produces or facilitates a particular movement. *Antagonist – muscle whose contraction resists or reverses a particular movement. Secondary reflexes Primary Motor Cortex *Somatotopic Organization *Topographical organization/mapping of parts of the body represented in particular brain regions. *Motor Homunculus – man within the man. Phantom Limb Remapping somatosensory representations. *IN PHANTOM LIMB INTERNEURONS STOPS SO CELLS STARTS FIRING RANDOMNLY Mirror therapies for phantom limb pain. Action specific pathways Corticospinal Tract – MOVES ARMS AND LEG MOVEMENT AND LOCOMOTION *Lateral tract – controls distal muscles (arms, fingers, lower legs, feet) *Completely crosses at medulla (i.e., completely contralateral) *Ventral tract – posture, locomotion *Projects ipsilaterally and contralaterally Corticobulbar Tract – facial and tongue movement *Face, tongue control *Crosses at pons *Synapses with cranial nerves *V (trigeminal) *chewing, pain & touch for face and mouth *VII (facial) *facial expression *IX (glossopharyngeal) *tongue movement *X (vagus) *digestion, taste *XII (hypoglossal) *tongue movements Corticobulbar Tract *Upper part of face represented bilaterally *After unilateral brain damage both eyebrows and eyelids can still be controlled *Lower part of face is exclusively contralateral *Unilateral brain damage causes facial droop Rubrospinal Tract - main purpose is to coordinate movement; where fine motor controls come in *Originates in the red nucleus of midbrain *Receives input from motor cortex and cerebellum *Projects mainly to the cerebellum *Modulates motor control and co-ordination Planning Movements *Complex network of cortical and subcortical structures Supplementary Motor Area *Supplementary Motor Area – plays a critical role in planning and initiation of movements and in behavioral sequences (also active for imagined movements). *Pre-SMA – involved in control of spontaneous movements. *SMA has topographic connection with motor cortex *Premotor Cortex – involved in learning and executing complex movements guided by sensory information; can stimulate movements before you do them Internally vs. Externally Guided Movements *Rely on different neural networks *Parietal, cerebellar and lateral premotor regions – spatially directed movements (novel situations) *SMA, basal ganglia, temporal lobe (hippocampus) – internally driven, familiar sequences of movements Cortical Movement Disorders *Hemiplegia – paralysis arising from motor strip lesions (or thalamic lesions); unable to perform motor actions in the one side of the body *Apraxia – constellation of disorders arising from left inferior parietal lesions – sequential and gestural movement control impaired; still has motor functions but have severe troubles executing plan movements (e.. Playing piano) *Optic ataxia – from bilateral superior parietal injury – poor control of movements in the periphery; sensory disorder – individuals lack sensory information coming in *Alien hand syndrome – anarchic control of contralateral hand; their hand move by itself w/o the individual wanting it to move; lesions to the corpus collosum Apraxia (different from Ataxia!) *Limb-kinetic – clumsiness of hand control associated with pyramidal motor system lesions (not an impairment to learned motor plans); disconnects motor neurons to everything else *Ideomotor – disconnection between the idea and execution (actual motor movement) *E.g. Motor plan is not connected to the idea; if you wanted to do something you can’t perform the action *Inability to perform gestures on command but can imitate successfully *Can imitate motor movements *Ideational – inability to form the motor plan and execute it *Can’t perform gestures due to a loss of the motor plan (or idea) C
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