Brain and Behavior chapter 8
Brain and Behavior chapter 8 Nsci3300
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This 9 page Class Notes was uploaded by Caoimhe Notetaker on Wednesday October 28, 2015. The Class Notes belongs to Nsci3300 at Tulane University taught by Paul Colombo in Summer 2015. Since its upload, it has received 26 views. For similar materials see Brian and behavior in Psychlogy at Tulane University.
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Date Created: 10/28/15
Chapter 8 10282015 3 principles of sensorimotor control Sensorimotor system is hierarchically organized 0 Association cortex like company president specifies general goal rather than speci c plans of action 0 Main advantage to hierarchical organization is higher levels are left free to perform more complex functions 0 Signal ows between levels on multiple paths 0 Functional segregation each level composed of different units perform different functions information mainly ows down 0 Motor output is guided by sensory input 0 Monitor effects of activity in order to ne tune processes 0 Sensory feedback Only responses not in uenced by sensory feedback ballistic movements n Ballistic movements quick brief allor none high speed movements 0 Learning can change the nature locus of sensorimotor control 0 During initial stage of sensorimotor learning each individual response is performed under conscious control 0 Then after much practice individual processes are conducted without much conscious control by organizing individual response into continuous motor programs and transferring control to lower levels of neurons systems Insert graph Paralleled connection between levels and numerous feedback pathways Association Cortex Top of hierarchy 2 major areas O O Posterior parietal association cortex Dorsolateral prefrontal association cortex Posterior parietal O O 0 Position of body and external objects Plays role in directing behavior by providing spatial information and directing attention Receives info from 3 sensory systems visual auditory and somatosensory which help to localize body and external objects in space Most output goes to areas of motor cortex located in frontal cortex Dorsolateral prefrontal association cortex Secondary motor cortex Frontal eye eld controls eye movement Contains many small areas each specialized for guiding particular movements of eyes head arms or hand Consequences of damage Apraxia disorder of voluntary movement not attributable to a simple motor de cit or a de cit in comprehension or motivation I Cant perform tasks WHEN REQUESTED Bilateral symptoms but usually caused by unilateral damage to left posterior parietal lobe or its connections Contralateral neglect disturbance of ability to respond to stimuli on the side of the body opposite contralateral to the side of the brain lesion n Often behave as if left side of world does not exist and fail to realize they have a problem a Often associated with large lesions of right posterior parietal lobe n De cit in responding to stimuli left of body egocentric left n Evidence that object to left are still unconsciously perceived Dorsolateral prefrontal association cortex Receives projections from posterior parietal cortex Send projections to secondary motor cortex primary motor frontal eye eld 0 Decision to initiate voluntary movement may be made in this cortex but depend on interaction with posterior parietal and other areas of frontal cortex Secondary Motor Cortex Receive input from association cortex Send input to primary cortex 0 2 areas of sensorimotor cortex historically only two known 0 Supplementary motor cortex wraps over top of frontal lobe and extends down its medial surface into longitudinal ssure o Premotor cortex runs in a strip from supplementary to lateral ssure now know at least 8 3 different supplementary motor areas 2 premotor areas 3 small areas cingulate motor areas in cortex of cingulate gyrus o Stimulation of an area of secondary motor cortex typically elicits complex often involving both sides of body 0 Involved in programming of SPECIFIC patterns of movement after taking GENERAL direction from dorsolateral prefrontal cortex 0 Mirror neurons neurons that re when an individual performs a goaldirection hand movement OR when they observe some goal directed movement performed by another Might play a role in social cognition Primary Motor Located in precentral gyrus of frontal lobe Major point of convergence of cortical sensorimotor signals Major but not only point of departure of sensorimotor signals from cerebral cortex 0 Conventional view 0 Pen eld and Boldrey mapped primary motor cortex of conscious human patients during neurosurgery Applied brief stimulation to various points on surface noting what parts of body responded when Realized primary cortex is organized somatopically According to a map of the body referred to as motor huminculus Most dedicated to hand mouth 0 Current view 0 Recent mapping efforts used longer bursts of current more similar to motor response elicited more complex reactions involved several body parts rather than a singular muscle contractions 0 Target of movement is more important than direction which 0 was the convention view Sensorimotor system inherently plastic Damage to primary cortex 0 O O Disrupt ability to move one body part independently of others May produce astereognosia de cit in stereognosis process of identifying objects by touch May reduce speed accuracy and force of movement Cerebellum and Basal Ganglia Cerebellum O O 0 Contains gt 50 brains neurons Receives information from primary and secondary motor cortex Receive information about descending motor signals from brain stem nuclei Receive feedback from motor response via somatosensory and vestibular system o Comprises 3 courses and corrects ongoing movements that deviate from intended course 0 Plays major role in motor learning 0 Effects of damage Lose ability to contract direction force velocity amplitude of movement And ability to adapt patterns of motor output to changing conditions Difficult to maintain posture Disturbances decrease balance gait stance control of eye movement Basal Ganglia o Organized in heterogeneous collection of interconnected nuclei 0 Perform modulatory function receive cortical input and transmit it back to cortex via thalamus o Participate in habit learning but not limited to habit learning Descending motor pathways 0 4 pathways descend o 2 in dorsoatera region of spinal cord 0 2 in ventromedia region of spinal cord 0 Signal conduct over these pathways act together in control of voluntary movement Dorsoatera o Corticospinal tract Descends primary cortex through meduary pyramids then cross and descend atera dorsoatera spina white matter a BETZ CELLS Axons synapse on small interneuron of spinal gray matter which synapses on motor neurons of distal muscles of wrist hands ngers and toes o Corticorubiospinal tract Descend from primary motor cortex synapses in red nucleus of midbrain cross and descend through medulla where some terminate in cranial nerve controls facial muscles rest descend to dorsolateral portion of spinal cord Axons synapse on interneurons that in turn synapse on motor neurons that project to distal muscles in arms andlegs Ventromedial o Corticospinal tract Direct axons descend ipsilaterally from primary directly to ventromedial areas of spinal white mater each axon descends and branches diffusely and innervates the interneurons circuit on both sides of spinal gray mater o Corticobrainstemspinal tract Axons feed into complex networks of brainstem structures some axons than descend bilaterally each side carries signals from both hemispheres controls proximal muscles of trunk and limbs interact with tectum auditory and visual info vestibular nucleus balance info from ear reticular formation info on walking jumping etc motor nuclei of cranial nerves face muscles 0 Differences o Ventromedial tracts are more diffuse 0 Motor neurons activated by ventromedial tracts project to proximal muscles of trunk limbs shoulder muscles motor neurons activated by dorsolateral tracts projects to distal muscles nger muscles 0 Ventro tracts involved in control of posture white body movements and can exert over limb movements 0 Dorso tracts control movement of limbs only coritcospinal division mediates independent movement of digits Sensorimotor spinal circuits Lowest level of hierarchy Capable of independent functioning Muscles 0 Motor units smallest units of motor activity 0 Tendon muscle to bone o Acetylcholine released by motor neurons at neuromuscular junctions activates the motor endplate on each muscle ber and causes the ber to contract 0 Contractions muscles way of generating force one direction Fast muscle bers contract and relax quickly poorly vascularized Slow muscle bers slowerweaker but capable of more sustained contraction richly vascularized Flexors bend of ex a joint Extenders straighten or extend o Synergic muscles two muscles whose contractions produce same movement Antagonistic those that act opposite bicep v tricep Muscles are elastic o Isometric contraction increase tension without shortening and pulling them together 0 Dynamic contraction with shortening and pulling together 0 Tension is increase by Increasing number of neurons in motor pool that are ring lncrease ring rate of those already ring Or combo Receptor organs of tendons and muscles 0 Activity of skeletal muscles is monitored by Golgi tendon organs and muscle spindles o Respond to different aspects of contraction Golgi embedded in tendons which connect each skeletal muscle to bone Respond to increase tension also protective when contraction is extreme in order to avoid damage excites inhibitory interneurons in spinal cord to release muscle Each muscle spinal ahs its own intrafusal muscle which is innervated by its own intrafusal motor neuron to keep muscle from falling slack CO CO Stretch re ex Elicited by a sudden external stretching force on a muscle Keeps external forces from altering intended position of body Withdrawal re ex Ex When you touch hot surface 0 Stimulus produces a burst of ring neurons in sensory neurons 0 Firing excites excitatory spinal interneurons that excite bicep motor neurons 0 At the same time ring excites inhibitory spinal interneurons that inhibit tricep motor neurons 0 The simultaneous contractions bicep and relaxation tricep cause a exion of elbow joint Reciprocal innervation o Antagonistic muscles are innervated in a way that permits a smooth unimpeded motor response 0 When one relaxes the other contracts 0 Movement produced by adjustment to level to relative contraction between antagonists Recurrent collateral inhibition 0 Each time a motor neuron res it momentarily inhibits itself and shifts the responsibility for the contraction of particular muscle to other members of muscles motor pool Walking a complex re ex 0 Must integrate info from many systems 0 Must be incredibly plastic 0 Walking can be controlled by circuits in spinal cord Central sensorimotor programs and learning Sensory motor system hierarchy of central sensorimotor programs 0 All but highest level of system have certain patterns of actually programmed into them Once activated each level is capable of operating on basis of current sensory feedback 0 Most of individual response you make are performed without direct cortical involvement and you are often barely aware of them Central sensorimotor programs are capable of motor equivalence 0 Some basic movement can be carried out in different ways involving different muscles Sensory info that controls central sensorimotor programs is not necessarily conscious Can develop without practice Practice can create central sensorimotor programs 0 Response chunking individual response become sequences of behavior 0 Shifting control to lower level lncrease speed lower levels act simultaneously Frees up higher level to deal with esoteric aspects of performance