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Chapter 5

PSYB65 chapter 5.docx

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Ted Petit

PSYB65 chapter 5 Sensorimotor system - Relies on somatosensory feedback from joints, tendons, muscles and skin - Brains organize movements in parallel and hierarchical system that relies heavily on functional segregation - We rely on feedback from somatic sensation. Eg. When tongue is numb at dentists you tend to make inaccurate movements and bite your tongue more. - Eg. G.O. a man with destruction of somatosensory nerves in both arms. Cant perform intricate motor skills because he doesnt know position of his own arms, how strong his grip is, and whether he was maintaining a constant level of muscle contraction. - These adjustments we make are automatic, dont need higher cortical areas Somatosensory receptors - Comes from skin. - 3 types of information o Nociception: pain and temperature o Hapsis: touch and pressure o Proprioception: awareness of body and its position is space - Most sensory receptors are mechanoreceptors: react to bending or stretching. They wrap arund hairs that cover our body so we can feel our hiar. It stretches or deforms follicle when hair is moved which then activates mechanoreceptors - Most mechanoreceptors have mechanosensitive ion channels. They are afferent axons that that enter spinal cord through dorsal roots - Spinal cord organized into o Dorsal root ganglia somatoesnsory o Ventral root ganlia for motor - There are 30 pairs of spinao nerves, each made up of dorsal and ventral roots that exit spinal cord - Spinal segments divided into 4 groups o 1-8 Cervical, thoracic 1-12, lumbar 1-5, sacral 1-5. - Dermatomes: the 30 dorsal roots that serve spinal nerve.if cut, spinal cord cant btain information from that nerve. But dermatomes overlap so you dont lose complete sensation. Somateosensory pathways in brain - 2 pathways o Dorsal spinothalamic tract: tranmits information about proprioception and hapsis. Enters spinal cord through dorsal root ganglion and synapses ipsilaterally in dorsal column nuclei of spinal cord. It goes up spinal cord until brainstem where hey go up medial lemniscus which synapse in the ventrolateral thalamus. o Ventral spinothalamic tract: nociceptive information. Enters through dorsal root ganglion, ascends spinal cord contralaterally. In brainstem, axons join medial lemniscus and ascend to ventrolateral thalamus - Damage to brainstem or thalamus resulst in equal loss of both hapsis and nociception - Damage to spinal cord results in loss of sensorimotor function below site of injury. - If damage spinal cord isnt completely cut through nociception is lost for side of body contralateral to injury while hapsis is lost for body ipsilateral to injury. Association cortex - 2 different areas of association cortex are top of hierarchy - Secondary and primary otor areas carry ommands independently - Basal ganglia and cerebellum modulate motor responses, - Critical feedback, both somatosensor and motor, is achieved through ascending sensorimotor pathways Posterior parietal association cortex - Parietallobeactive for interactions with space/spatial information - Helps determine original position of body and objects around body ins space - Receives inputfrom a variety of sensory systems:proprioception,hapsis and vision - Brodmanns area 5 (BA5) receivesinputs from primary somatosensory corticalarea. - BA3, BA1, BA2, BA7 receive higher order visual information - Damage to parietal lobes lead to difficulties with spatial relations and disturbances of body image. Eg. Fail to recognize parts of their body as belong to them - Posterior parietal lobes processes spatial relations of objects and the body to produce accurate movements - It also has extensive reciprocal connections with areas that are lower such as secondary and primary motor cortex Dorsolateral prefrontal cortex - Initiates voluntary movements - It directs lower areas in motor hierarchy sucha s secondary and primary motor cortex - Activation observed in dorsolateral prefrontal cortex (BA8) and secondary (BA6) and primary motor cortex (BA4) when moving fingers. similar activation when participants imagine moving their fingers EXCEPT for primary motor cortex - Information from parietalassociation cortex provided to dorsolateral prefrontal lobe to make decision of movement. - Also likely dorsolateral prefrontal lobe assesses likely outcome of planned movements o It sends projections to secondary and primary cortex. Specifys what movement and how movements will be made.Secondary motor cortex - Includes supplementary motor area, premotor cortex, and the cingulated motor areas - All connected together - Sends direct projects to brainstem nuclei. - Stimulation results in complex motor movements. Play a role in voluntary motor production - Bilaterally active before and during voluntary movements - Involved in planning and execution of motor movements, also imagined movements too? - Activation of supplementary motor associated with self-generated movements - Activation of premotor cortex associated with externally generated movements - Self generated movements controlled by internal feedback from supplementary motor area with somatosensory areas in parietal lobe\externally generated movements controlled by connections of premotor cortex with visual and auditory cortical areas - Cingulated activation active when there is conflivy about whether action should be taken Primary motor cortex - Controls movements of muscles, plans out coordinated activity of muscles - Directly in ftont of central fissure, next to primary somateosensory cortex - Heavy interconnectiosn with somatosensory cortex. Can modify motor prog
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