Motor Systems at Universität Osnabrück

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Study with flashcards and summaries for the course Motor Systems at the Universität Osnabrück

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

Explain and contrast the concepts of feed-forward and feed-back control.

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

What is happening upon a lesion of the upper and lower motor neurons?

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

What are the mechanisms underlying the stretch reflex?

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

Which mechanisms limit recovery after spinal cord lesions?

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

What is a principled difference in functional organization of
cerebral cortex and cerbellar cortex?

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

General symptoms that occur after a cerebellar lesion?

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

Describe a classical conditioning experiment.

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

Describe the concept of a leaky integrate-and-fire-neuron.

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

Describe the current hypothesis on physiological effects of
classical conditioning on the cerebellum.

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

Explain the concept of a force field using the example of leg movements of a frog

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

In basal ganglia two major pathways of information conduction can be found. What happens if the direct or the indirect circuit is damaged?

Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

Which defect is thought to cause Parkinson? Explain the malfunction on the basis of the basal ganglia circuit

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Exemplary flashcards for Motor Systems at the Universität Osnabrück on StudySmarter:

Motor Systems

Explain and contrast the concepts of feed-forward and feed-back control.

  • Feedforward
    • we see smth which we want to interact with and we do so
    • for example want to catch smth then we move our arm and hand where it will land and catch it
    • control uses a prediction to generate proactive actions
    • fast and voluntary (sensory signals are too slow, think of saccades for
      instance)
    • error prone (no correction)
    • world model required

    • (open loop)

  • Feedback
    • same as before when want to catch smth but also get some information back
    • maybe because the thing we wanted to catch was heavier than expected 
    • we then need to move our arm again according to that such that we can still hold the thing
    • to do this a sensor needs to detect that the thing is heavier than expected and report that back such that we can adapt our grab
    • compares the actual state with a desired state
    • can correct movement errors due to noise and environmental
      perturbations
    • external control by changing reference state
    • gain control to adjust reaction to error magnitude
    • rather slow, can lead to oscillations
    • (closed loop)
  • so feedback is an extended version of feedforward which allows for back report and adjustment

Motor Systems

What is happening upon a lesion of the upper and lower motor neurons?

  • Lower motor neuron lesion
    • all excitation of muscle is lost
    • muscle paralyzed and flaccid (muscle tone decreases)
    • reflexes disappear
    • muscle eventually atrophies
  • Upper motor neuron lesion
    • paralysis
    • restricted to one side Hemiplegia results, if above point at which descending axons cross midline lesion is on contralateral side
    • if acute lesion get spinal shock eventually flaccidity lessens and limbs become spastic, tendon reflexes greatly exaggerated
    • reflxes are intact
    • Babinski reflex: sole of foot stroked, toes dorsiflex and spread instead of normal plantar flexion

Motor Systems

What are the mechanisms underlying the stretch reflex?

  • alpha motor neurons contact the muscles (partly over 1 meter length)
  • in muscle have musle spindles which are sensory organs (have muscle fibers inside) and those sensory fibers sense the length of the muscle and project back via 1a afferent fiber to the dorsal root ganglion where cell bodie resides,  axon continues and connect to alpha motor neuron
  • Stretching a muscle activates the muscle-spindle. A signal is sent by the Ia afferent via the dorsal horn to the alpha motor neurons. These active the muscle and synergistic muscles. This constitutes the mono-synaptic reflex arch.
  • also connections to antagonist muscles via inhibitory interneurons which then block these muscles

Motor Systems

Which mechanisms limit recovery after spinal cord lesions?

  • Lesions to the spinal cord often affect sensory and motor function in all bodily areas below the injury
  • Surgical Interventions are complex
  • Research is complex, too, because of accessibility
  • that in central nervous system neurons don't regrow due to the No-Go Protein but seemingly also other molecules

Motor Systems

What is a principled difference in functional organization of
cerebral cortex and cerbellar cortex?

  • Cerebrum
    • Excitatory input and output
    • Most areas (V1, V2, FFA, PPA,...) have excitatory connections with each nother
    • Backbone of recurrent excitation
    • The cerebrum is ‘mostly talking to itself’
  • Cerebellum
    • Excitatory input, inhibitory output

    • No recurrent activation

    • Request from outside, computation, output

    • No self-sustained activation over longer periods of
      time (on demand computations)

    • Without external input there is no activity. This is in marked contrast to the cerebral cortex.




Motor Systems

General symptoms that occur after a cerebellar lesion?

  • if lesion cerebellum in simulation after training
  • post-lesion non varying immeadiate response to conditioned stimulus
  • after lesion response has not the desired delay anymore but the response comes directly 
  • can also be observed in rabbits(not as clear but visible)
  • Delayed Movement Initiation
    • Asking subject with unilateral lesion of the cerebellum to clench both hands results in delayed initiation.
  • Dysmetry
    • loss of precision of movements, undershoot, overshoot
  • Decomposition
    • Coordination of multi joint movements is lost, e.g. shoulder moves before elbow, sequential instead of joint movements
  • Intentional tremor
    • jittering movements get stronger when target is approached.
  • Dysdiadochokinesia
    • inability to perform rapidly alternating antagonistic movements, e.g. pronation and supination of the lower arm.
  • Hypotonia
    • reduction of resistance on passive limb movements (low muscle tone)
  • Nystagmus
    • jittering eye movements
  • Deficits in motor learning
    • deficits in movement coordination & classical
      conditioning
  • Cerebellar lesions lead to multiple motor symptoms.

Motor Systems

Describe a classical conditioning experiment.

  • in a classical conditioning experiment an unconditioned stimulus is combined with a conditioned one
  • before the unconditioned stimulus is evoked a conditioning stimulus is given 
  • for example one can ring a bell before blowing air onto the eye of someone which leads to a closing of the eye
  • when doing this some times the subject is learning and reacts already to the conditioning stimulus, before the unconditioned stimulus occurs
  • if there is a certain delay between the unconditioned and conditioned stimulus this is also present

Motor Systems

Describe the concept of a leaky integrate-and-fire-neuron.

  • single-compartement leaky integrate and fire neuron mathematical model of neuron
  • Vm = membrane potential
  • single-compartment cauz Vm just one scalar value, as membrane potential in whole neuron
  • due to some input Vm goes up, no input Vm goes down again, therefor leaky, going to euqillibrium potential
  • integration of the synapse input, therefor integrate neuron
  • when Vm reaching threshold stop simulation, AP occured, reset Vm therefor fire
  • A leaky integrate and fire neuron is a 1-compartment with continuous and lossy integration of the input and a discontinuous dynamics when the threshold is reached

Motor Systems

Describe the current hypothesis on physiological effects of
classical conditioning on the cerebellum.

  • through classical conditioning the input of the parallel fibers to Purkinje cells is weakend through the unconditioned stimulus which comes over the climbing fibers
  • when a conditioned stimulus occurs always with the same delay before the unconditioned one the parallel fiber input is weakend always at the same time
  • so whenever a certain pattern of parallel fiber input occurs the input is weakend
  • the cerebellum notices this and like that the conditioning happens, through the notice of the same input pattern of the parallel fibers to the purkinje cell 
  • this activation is then weakend even without the unconditioned stimulus, so the purkinje cell doesn't communicate to the deep cerebellar nuclei


Motor Systems

Explain the concept of a force field using the example of leg movements of a frog

  • in force fields is a force created by the stimulation of the spinal cord at a certain position
  • when measuring that force it becomes clear that the force will always end at the same point of equillibrium(no force exerted anymore)
  • vectorfield indicates force exerted due to activation of spinal cord at a specific position as a function of the position of the leg
  • not homogeneous forece field (orientation and size vary)
  • equilibrium point no force exerted any more
    • all trajectories where ever leg starts will end up at equilibrium point
    • characterises an important aspect of effects of stimulation of spinal cord at a specific side cauz wherever leg starts if let move will end up at equillibrium point
  • The resulting force field is convergent and characterized by a single Equilibrium Point (EP):
    • amplitude of vectors are 0
    • represents the locus at which the leg would have been at steady state, if it was free to move

Motor Systems

In basal ganglia two major pathways of information conduction can be found. What happens if the direct or the indirect circuit is damaged?

  • If the direct circuit is damaged the cortex gets less excitatory input and through the still functioning indirect circuit the frontral cortex would be even further inhibited 
    • this would propably lead to similar symptoms as in parkinson's disease
  • If the indirect circuit would be damaged the cortex would be less inhibited 
    • this might lead to irrelevant activations and information overload
    • Huntington

Motor Systems

Which defect is thought to cause Parkinson? Explain the malfunction on the basis of the basal ganglia circuit

  • neurons in the substantia nigra degenerate through parkinson's disease, they normally would produce and release dopamine, which then is missing
  • through dopamine normally the direct pathway gets enhanced and the indirect pathway is inhibited
  • when this isn't happening the cerebral cortex isn't excitated through the direct pathway and gets more inhibited through the indirect pathway
  • (
  • if those neurons in substantia nigra degenerate have loss of excitation of direct pathway, so output to globus pallidus internal from direct pathway is reduced
  • the ouput to the globus pallidus external indirect pathway is increased, more inhibited less active, less inhibiting the subthalamic nucleus (more activated), more activity to globus pallidus internal segment
  • so neurons in globus pallidus internal segment are less inhibited and more activated leading to less activation in frontral cortex)
  • believe this causes all symptoms of Parkinson

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