Second Half Flashcards
What are the 3 types of movement?
Reflexive –> peripheral stimuli produces involuntary coordinated pattern of muscle contraction/relaxation (stretch reflex)Rhythmic –> can be spontaneous or due to peripheral stimuli; repetitive (chewing, scratching)Voluntary–> goal directed movement, improves with practice
How is the spinal cord nerves organized?
31 nerves: cervical, thoracic, lumbar, sacral, coccygealCervical: controls upper limb musclesThoracic: controls trunk and chest musculatureLumbar: controls lower back and leg musclesSacral: controls bowel and bladder muscles
What are the 4 types of spinal cord neurons
Local –> axons confined to adjacent spinal segmentsMotor –> axons innervate muscle fibres; organized in a distal (lateral) to proximal (medial) fashionPropriospinal –> axons connect distal spinal segmentsProjection –> axons reach higher brain centres
Describe motor units
One motor unit = motor neuron + all fibres it innervatesone motor neuron integrates multiple fibres, each fibre innervated by one neuronunits can be fast or slow twitchsize of motor units relates to amount of control needed (finer selection of motor fibres to contract if smaller units)Number of motor units recruited related to force generated
Describe how a muscle is innervated
Axons loses myelin sheath, branches into multiple extensions called synaptic boutons. It connects to a portion of the muscle membrane called the endplate. Boutons are positioned over junctional folds (deep depression in the post-synaptic muscle fiber) that have Ach receptors. Depolarization of axon causes Ca2+ to enter boutons, causes release of Ach. Ach crosses synaptic cleft, binds to the Ach receptors and depolarizes end plate to create potential. Ach receptors equally permeable to Na and K, but potential activates the voltage-gated Na+ receptors, which creates an action potential.
How is muscle force increased
recruit more motor unitsincrease frequency of action potentials, results in complete tetany (twitch–> summation–> incomplete tetany–> complete tetany)
What are spinal reflexes?
neuronal networks in spinal cord integrating responses to produce coordinated pattern of muscle contraction through divergent and convergent connections
Explain the withdrawal and crossed-extension reflex
Nocioceptor (in foot) senses painful stimulus, sensory neuron relays signal to spinal cord. Neuron diverges, one pathway goes up to higher brain centres, another activates flexion reflex (excites flexors in leg, inhibits extensors). Crossed-extension reflex also occurs (extensors excited) to shift weight onto that side to maintain balance
How does the spinal region control reflexes?
There is a resting membrane potential, and a threshold needed to produce action potential. Spinal cord changes resting membrane potential. Can have tonic excitatory input to raise resting potential, means that stimulus input will be more likely to generate potential. Can also be modulated to decrease reflex sensitivity.
How are postural reflexes organized?
SLR, MLR, LLR –> short, medium, long latency responseintegrates response at different regionsSLR=spinal cord, nonfunctionalMLR = cerebellum, brain stemLLR = cortex (functional) modulates response, knows more about body state
Describe task dependent reflexes
depends on task. Table vs. holding cup, amount of extensor activity changes
Describe 7 neonatal reflexes and why we don’t see them with age, and the study showing off the smart spinal cord
1) Babinski= touch bottom of foot, toes fan out, big toe raised. test for spinal cord injury2) STARtle reflex = star response due to sudden visual/auditory stimulus, arms/legs outwards, upwards, inwards, fists/feet open and clench3) Tonic neck reflex = head turned to side –> fencer’s pose, arm and leg to side that head faces is extended, other side flexes4) Grasp reflex = pressure on palm/fingers, results in grasping action5) Swimming reflex = belly touches water/ground = rhythmic alternating contraction/extension of arms/legs6) walking reflex = feet in contact with surface = lift and plant feet7) Righting reflex = when sit baby up, attempt to keep head uprightStop seeing because cortical regions develop, start to have descending pathway modulation, also start to have more control over movement so no need for reflexFrog experiment –> apply stimulus to one area, spinal cord cut, spinal cord can still control muscle to wipe that area –> shows spinal integration and control of movement
What is a CPG, how is it controlled
neuron network in the spinal cord that generates rhythmic pattern of reciprocal flexion and extension in absence of sensory inputInitiated by MLR (mesoencephalic locomotor region). walking initiated. see hip proprioception, hip flexor is stretched, causes burst of flexion (swing phase). when foot lands, GTO senses load, sends signal through 1b afferents to maintain extensor activity through positive feedback loop, creates flexor stretch in opposite leg.Proven through cat –> flexion/extension alternate, sudden stretch of hip flexor causes abortion of extension, flexion triggered early
How do neurons project to the spinal cord?
medial or lateral pathwaysmedial=control basic posture, axial/proximal musclesreticulospinal, vestibulospinal, tectospinallateral = goal directed, voluntary movements, limb musclesrubrospinal, corticospinal
Describe 3 pathways
reticulospinal –> maintains posture and muscle tonevestibulospinal –> maintains balance, orientation of head/bodyrubrospinal –> excites neurons innervating proximal upper limb flexors
What is the function of the cerebellum?
Receives feedback, comparison of motor plan with actual responseInvolved in learning new motor skillsProduce smooth motion (timing)Coordinates groups of muscles with cerebral cortexMaintains equilibriumFine-tunes locomotor pattern by regulating timing/intensity of descending signals
How is the basal ganglia organized?
5 nuclei: substantia nigra, striatum caudate nucleus, putamen, subthalamic nuclei, globus pallidus No direct input to spinal cordReceives input to cerebral cortex, inputs to cerebral cortex through indirect pathways
List name and function of 4 basal loops
Occulomotor loop –> controls eye movementsMotor loop –> movement, links to primary motor cortex, premotor cortesxPrefrontal loop –> decision making, linked to DLPCLimbic loop –> related to emotions
What does the thalamus do?
connects regions
What is the function of the PPC?
Sensorimotor transformations –> integrate sensory input from different coordinate systems and convert to motor coordinates, reference frame suitable for motor centrePlanning, on-line control of movementSpatial maps/working memory
What are the different PPC regions and their function?
Parietal arm field –> retinotopic locations of spaces that can actually be reachedParietal eye field –> retinotopic location of objects, responds to auditory and visual inputparietal face field –> represents ultra near space of mouth/face through visual and tactile inputparietal grasp field –> shape information required to grasp objects
When are neurons in the PPC active?
During foreperiod –> planning movementMemory delay task –> PPC heavily active between cue and reach to plan movement
How does the cortex project to the motor neurons?
corticobulbar and corticospinal fibrescorticobulbar –> controls motor nuclei in brainstem for facial musclescorticospinal –> controls motor nuclei in spinal cord for voluntary control of trunk/distal limb muscles–> acts on spinal pathway or motoneuronsmost fibers cross at pyrimidal decussation for contralateral control
What is the function of the SMA?
supplementary motor area selects movement trajectories based on internal cuesinvolved with memoryimportant for bimanual movementsrole in learning sequences
What is the function of the premotor cortex
selects movement trajectories based on external cuesworks with basal gangliarole in decision makingSpatial choices experiment –> must plan for all trajectories, so heavily active before go signal, after go signal = burst to plan/select that trajectory. In one-target task, only has to plan for one trajectory, motor cortex neuron doesn’t fire until after go signal (no double hill)
What is the function of the motor cortex?
Provides somatotopic organizationexecutes and adapts movementsneurons in the same column activate synergistic muscles, therefore neurons in different columns can activate same muscle
How do individual motor cortex neurons affect force/direction of movement?
ex. neuron attached to flexor muscles.When flexor load applied, neuron fires to activate flexors and oppose movementwhen extensor load applied, neuron is silent b/c extension due to relaxation of antagonistNeurons fire different amount based on direction of movement, therefore movement is determined by resolution of vectors of the firing rate of groups of neurons
How does the cortex contribute to locomotion?
Motor cortex increased activity during step (enhanced muscle activity)PPC increase before step (motor planning, gait modification)
What does the DLPC do?
Dorsolateral prefrontal cortex involved in spatial working memoryrole in decision making (how/when to move)sensorimotor transformation
Describe APAs
Anticipatory Postural Adjustmentspostural change before postural disturbance to offset movementmaintains equilibrium and stabilizes position (minimizes disturbance)Anticipates shift in centre of massHave a load–>unload tendency (kip-up) so COP has shift one way in order to shift the other way and thus make it easier for movement to occur (want to lift right leg, so shift onto right, then shift centre of mass to left to raise right leg. hip and shoulder shift to suport side, ankle shifts to moving side)APAs are context dependent. Voluntary movement generates APA, but having support negates APA. Similarly, if there is an external stimulus, action in stabilizers more as a reflexive movement, not a true APA. And if stability constraints help with movement (moving floor), APA is redundant and can create balance deficit
Describe reflex theory
Movements are due to reflex chaining (sequences of reflexes), reflexes are building blocks for behavioursstimulus-response
What are the limitations of reflex theory?
1) Reflex theory can’t account for voluntary movement - no external stimulus2) How does it describe very fast movements –> not enough time for sensory feedback to play role3) Can’t account for learning new movements –> perform different actions with different stimuli based on already learned rules4) Can’t account for different responses to same stimulus depending on context (overriding reflexes, scaling to meet task demand)
Describe motor program theory; define parameters, invariant features, and schema
Motor program theory says we don’t have stored motor commands for every action. Have generalized motor programs that generate motor commands. Motor programs are effector independent, can use sensory feedback to correct movement without affecting higher level program, errors reflected in movement can alter program and parameters. Motor program at lower level converts output from higher level to commands to motoneurons. Some programs govern discrete actions, complex movements then use programs to recruit these discrete programsMotor program controls class of actions (group of similar motor skills), performs same action in different circumstancesMotor program –> set of rules for generating motor commandsParameters –> features that change from one performance to another, change parameters = change behaviourInvariant features –> stay the same throughout class of actions regardless of parameters, defines motor programSchema = set of rules to provide basis for decision, representation of rules governing performance of skill in certain situation, facilitates selection of parameters
What is the evidence for motor program theory?
Typing keys = relatively equal percentage regardless of speedScaling movement of reaching = equal velocity curves regardless of distance –> shows extent of movement are preplanned
What is a limitation of motor program theory?
doesn’t account for complex movements
How can motor programs use sensory feedback?
If the movement duration is long enough, sensors can correct small perturbations without altering higher level motor program
How does motor program theory explain the walk-to-run transition?
Walk and running are two different classes of actions, with different invariant features. The transition equates to a change in the motor program. Person chooses to change motor programs
Describe Dynamic Action theory
Movement is self-organizing, based on interaction between individual and environment. New movements arise from a change in the control parameter that changes which attractor state is optimal
What are attractors, control parameters, and order parameters?
stable behavioural steady states –> minimal variation, optimal energyControl parameters are variables that increase or decrease and change the value of the order parameter (independent variable)Order parameters are values that are attached to attractor states that define the overall behaviour
Provide the evidence for dynamic action theory?
Bilateral finger movementsOrder parameter = the degrees (180 or 360)Attractor states = in phase or out of phase (defined by order parameter)Control parameter = speed of finger movementsAs control parameter increases, order parameter changes, and new stable behavioural state created
How does dynamic action theory discuss the walk-to-run transition?
speed is the control parameterrelative phase of legs (flexion/extension) is the order parameterattractor states = walking or runninggait change is the result of competition between the two attractor states
What is the role of sensory feedback and what are the issues of sensory feedback?
Inherent delays = takes time to receive and process and then act on sensory feedbackNoise –> information not perfectly accurate (going from 3D to 2D to 3D)Sensory feedback must be transformed into terms understood by motor systemsNeeds a reference signal, only indicates extent of movement deviation from intended performance
What are 3 types of noise, and 2 causes of noise, and the result of noise
sensor noise –> inaccurate sensory receptors, uncertainty in locationMotor noise –> noise in motor commands, variable movementsSensorimotor noise –> noise from combining sensory feedback and transformation to motor coordinatesCauses of noise: spontaneous action potentials generated by receptors/neurons, muscle fatigue = change in dischargeResults in lower accuracy and precision
What are the three types of internal models?
Cognitive model –> how objects work based on prior experienceInverse model –> calculates motor commands based on desired trajectory and knowledge of limb stateForward model –> calculates expected sensory feedback and limb state based on copy of motor command, predict behaviour of body, model causal relationship between actions and consequences
What are the two components of the inverse internal model?
Kinematic transformation –> Calculate limb trajectoriesDynamic transformation –> based on calculated trajectory, what are the joint trajectories (torques/muscle activations) required to perform the movement
