Kapitel 8: Det sensomotoriske system
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Questions and Answers

Hvad betyder det i konteksten af sensorimotorsystemet at være hierarkisk organiseret?

Det betyder, at sensorimotorsystemet er organiseret i niveauer, hvor højere niveauer styrer de lavere niveauer.

Hvad er den vigtigste rolle af sensorisk indgang for motor output?

Sensorisk indgang giver feedback om motor output, og hjælper dermed med at fine-tune bevægelser.

Hvad er den primære funktion af den posteriore parietal cortex i sensorimotorisk funktion?

Den posteriore parietal cortex integrerer sensorisk information af kroppen og omgivelserne, og den bidrager til at guide adfærd ved at levere spatial information.

Hvad er apraxia?

<p>Apraxia er en lidelse, hvor man har vanskeligt ved at udføre bevægelser, der er ikke forårsaget af simple motoriske underskud (f.eks. lammelse eller svaghed), og der ikke er et deficit i forståelse eller motivation.</p> Signup and view all the answers

Hvad er kontralateral neglect?

<p>Kontralateral neglect er en lidelse, hvor man har vanskeligt ved at reagere på stimuli på den side af kroppen, der er modsat (kontralateral) til den side af hjernen, hvor der er sket skade.</p> Signup and view all the answers

Hvad er den generelle rolle af områder i den sekundære motor cortex?

<p>Den sekundære motor cortex er involveret i planlægning og udførelse af specifikke bevægelses-mønstre.</p> Signup and view all the answers

Hvad der kendetegner spejlneuroner og hvorfor de har fået så stor opmærksomhed fra neurovidenskabsmænd?

<p>Spejlneuroner er neuroner, der aktiveres, når individet udfører en handling eller når individet observerer en lignende handling udføres af en anden. De har fået stor opmærksomhed, fordi de kan give et muligt mekanisme for social kognition.</p> Signup and view all the answers

Beskriv det konventionelle syn på funktionen af den primære motor cortex.

<p>Tidligere troede man, at den primære motor cortex var organiseret somatotopisk, med en separat neuronenhed for hver muskel.</p> Signup and view all the answers

Den nuværende opfattelse af den primære motor cortex er, at den er organiseret somatotopisk, dvs. hver muskel har en separat neuronenhed.

<p>False</p> Signup and view all the answers

Hvad er motorisk ækvivalens?

<p>Motorisk ækvivalens er evnen til at udføre den samme bevægelse på forskellige måder, ved at bruge forskellige muskler.</p> Signup and view all the answers

Hvordan lærer central sensorimotorisk system at udføre en kompleks opgave som f.eks. at skrive et ord?

<p>Læring af en kompleks opgave involverer to processer: Response chunking og forflytning af kontrol til lavere niveauer i hierarkiet.</p> Signup and view all the answers

Beskriv den generelle model af den sensorimotoriske funktion?

<p>Den generelle model af sensorimotorisk funktion er hierarkisk organiseret, med funktionel segregering og parallelle stier, der forbinder forskellige niveauer.</p> Signup and view all the answers

Hvad er den grundlæggende funktion af cerebellum i sensorimotorisk funktion?

<p>Cerebellum modtager input fra forskellige niveauer i hierarkiet og koordinerer og justerer bevægelser.</p> Signup and view all the answers

Hvordan er basal ganglia organiseret?

<p>Basal ganglia er en kompleks og heterogen samling af sammenkoblede kerner, og de er ikke organiseret systematisk som f.eks. cerebellum.</p> Signup and view all the answers

Hvad er den vigtigste rolle af motoriske motorunits?

<p>En motorisk enhed er den mindste funktionelle enhed i den motoriske kontrol, og den består af et enkelt motorneuron og alle de muskelfibre, som det innerverer.</p> Signup and view all the answers

Hvad er forskellen mellem hurtige muskelfibre og langsomme muskelfibre?

<p>Hurtige muskelfibre kontraherer og slapper af hurtigt men de bliver hurtigt trætte, mens langsomme muskelfibre kontraherer langsomt og er mere holdbare.</p> Signup and view all the answers

Hvilke receptorer er involveret i at overvåge muskelspænding?

<p>Golgi-seneorganer er ansvarlige for at overvåge muskelspænding.</p> Signup and view all the answers

Hvilke receptorer er involveret i at overvåge væksten af muskelfibre?

<p>Musclespindlet er ansvarlige for at overvåge ændringer i muskelens længde.</p> Signup and view all the answers

Hvad er strækrefleksen?

<p>Strækrefleksen er en refleks, der udløses af en pludselig ydre kraft, der strækker en muskelfiber. Det er en del af sensorimotorisk funktion, som hjælper med at holde lemmernes positioner når de udsættes for pludselige kræfter.</p> Signup and view all the answers

Beskriv mekanismen for strækrefleksen?

<p>Når en muskelfiber strækkes, aktiveres sensoriske receptorer i muskelfiberspindlet, som sender impulser til rygmarven via sensoriske neuroner. Disse impulser aktiverer motorneuroner i rygmarven, som sender impulser tilbage til den samme muskelfiber og får den til at kontrahere.</p> Signup and view all the answers

Hvad er tilbagetrækreaktionsrefleksen?

<p>Tilbagetrækreaktionsrefleksen er en kompleks refleks, der initieres af stimulering af smertereseptorer.</p> Signup and view all the answers

Tilbagetrækreaktionsrefleksen er monosynaptisk?

<p>False</p> Signup and view all the answers

Hvad er reciprok innervation?

<p>Reciprok innervation er et vigtigt princip i spinal rygmarvs-kredsløb, hvor antagonist-muskler styres af en synapse.</p> Signup and view all the answers

Hvad er recurrent collateral inhibition?

<p>Recurrent collateral inhibition er et mekanisme, hvor motorneuroner inhiberer sig selv kortvarigt, når de fyrer. Dette sikrer, at der er en konstant balance i aktivering af musklerne.</p> Signup and view all the answers

Beskriv kort fænomentet gang og i hvilken grad det styres af rygmarvsstier?

<p>Gang er en kompleks sensorimotorisk refleks, der kræver integration af mange forskellige typer af sensorisk information.</p> Signup and view all the answers

Hvad er et central sensorimotorisk program?

<p>Et central sensorimotorisk program er en sekvens af handlinger, der er programmeret til at udføre specifikke bevægelser.</p> Signup and view all the answers

Hvordan sker læring af komplekse bevægelse-sekvenser i et central sensorimotorisk system?

<p>Komplekse bevægelser læres ved at kombinere enkle handlinger i længere sekvenser (Response chunking), og ved at overføre kontrollen til lavere niveauer i hierarkiet (Shifting control to lower levels).</p> Signup and view all the answers

Hvordan illustrerer Jenkins og kollegaers PET-studie af simpel motorisk læring hovedpunkterne i dette kapitel?

<p>Studiet illustrerer, at de centrale sensorimotoriske områder er involveret i læring og at behovet for disse områder er afhængig af hvor kompleks handlingen er.</p> Signup and view all the answers

Hvad er neuroplasticitet?

<p>Neuroplasticitet er hjernens evne til at ændre sig som resultat af erfaring.</p> Signup and view all the answers

Nævn et eksempel på neuroplasticitet på kortikalt niveau og et på subkortikalt niveau.

<p>Et eksempel på neuroplasticitet på kortikalt niveau er forstærkning af signaler i den motoriske cortex, som modtages fra thalamus og fra andre motoriske områder. Et eksempel på neuroplasticitet på subkortikalt niveau er en forøgelse af antallet af oligodendrocytter, som danner myelin i den hvide substans i hjernen.</p> Signup and view all the answers

Study Notes

Chapter Overview and Learning Objectives

  • The sensorimotor system is hierarchically organized
  • Sensory input is crucial for motor output
  • Learning modifies sensorimotor control
  • A general model of sensorimotor function exists

Three Principles of Sensorimotor Function

  • The sensorimotor system is hierarchically organized, similar to a large efficient company, with commands flowing from high to low levels.
  • Motor output is guided by sensory input, allowing for continuous adjustments and fine-tuning of actions.
  • Learning alters sensorimotor control, transferring control from conscious to subconscious levels over time.

Motor Output is Guided by Sensory Input

  • Efficient systems continuously monitor and adjust their own actions, using sensory feedback to fine-tune their performance.
  • Sensory feedback in the sensorimotor system influences responses in most cases; ballistic movements are exceptions.
  • Sensorimotor feedback, for example from the somatosensory system, is crucial in adjusting ongoing responses.

Learning Changes the Nature and Locus of Sensorimotor Control

  • Initial tasks are carried out via conscious control and attention, involving the superior parts of the sensorimotor system.
  • With practice, actions are coordinated into continuous sequences, transferring control to lower levels of the hierarchy.
  • This relates to motor output for tasks such as typing, swimming, knitting, or playing basketball

General Model of Sensorimotor System Function

  • The sensorimotor system has a hierarchical structure (Figure 8.1)
  • Functional segregation is apparent; each part performs a specific function.
  • Parallel pathways allow for multiple ways of controlling lower levels
  • Feedback loops are crucial in the hierarchy

Posterior Parietal Association Cortex

  • The posterior parietal cortex integrates sensory information (visual, auditory, somatosensory) regarding location and position for directing behavior.
  • Damage to the posterior parietal cortex can cause apraxia or contralateral neglect.
  • Apraxia involves difficulty in carrying out planned movements, even if those movements are not physically impossible.
  • Contralateral neglect occurs when one side of the body or world is essentially ignored.

Dorsolateral Prefrontal Association Cortex

  • The dorsolateral prefrontal cortex actively anticipates and plans movements.
  • Neurons in this area exhibit response properties related to intended target locations, rather than direction for movement.
  • Damage to this region can cause issues related to motor planning and voluntary movements.

Secondary Motor Cortex

  • It receives input from association cortex
  • It sends output to primary motor cortex
  • It is involved in planning and executing sequences of movements, also in species-typical behaviour.

Mirror Neurons

  • Mirror neurons fire both when performing an action and when observing another performing the same action.
  • Mirrors neurons are found in ventral premotor area and parietal cortex in monkeys.
  • Their role likely involves social cognition.

Primary Motor Cortex

  • It is a crucial area for coordinating and initiating movements.
  • The primary motor cortex has a somatotopic organization, or a map of the body.
  • Current studies suggest a broader function, responding to intended movement targets rather than just movement direction.

Cerebellum

  • The cerebellum plays a role in refining and coordinating movements.
  • It receives input from various parts of the nervous system and compares intended movements with actual movements to produce adjustments.

Basal Ganglia

  • The basal ganglia are involved in motor control and also related to motivation and cognition.
  • Its anatomy is more complex than the cerebellum, comprising a collection of interconnected nuclei. - It influences movement vigor and the suppression of unwanted actions.

Descending Motor Pathways

  • Neural signals travel from the primary motor cortex to spinal motor neurons via the dorsolateral and ventromedial pathways.
  • The pathways have differing functions - dorsolateral for distal muscles, and ventromedial for proximal muscles, posture, and locomotion.
  • These pathways are crucial for coordinating and controlling voluntary movements.

Sensorimotor Spinal Circuits

  • The spinal cord circuits are complex, and capable of controlling movement independent of cortical input.
  • They include a hierarchy of motor neurons associated with posture, movement patterns, reflexes, and other voluntary coordination functions.

Muscles

  • Motor units are the functional units of motor activity (motor neuron and associated muscle fibers)
  • Muscles differ in their properties, reflecting their roles in various tasks.
  • Fast muscle fibers support quick movements, while slow-twitch fibers allow for prolonged contractions.

Receptor Organs of Tendons and Muscles

  • Golgi tendon organs detect changes in muscle tension
  • Muscle spindles monitor changes in muscle length

Stretch Reflex

  • The stretch reflex rapidly adjusts for unexpected stretches, typically in response to sudden external force.
  • Feedback from muscle spindle and other receptors is essential in the reflex's rapid actions.

Reciprocal Innervation

  • Reciprocal innervation coordinates antagonistic muscle action by inhibiting the opposing muscle (e.g., biceps during extension)
  • This ensures a smooth and controlled motor activity.

Withdrawal Reflex

  • The withdrawal reflex triggers a rapid withdrawal of a limb from a noxious stimulus.
  • It integrates sensory information and motor output to protect from harm.

Recurrent Collateral Inhibition

  • Recurrent collateral inhibition ensures that each motor neuron is temporarily inhibited after firing, ensuring other motor neurons take over control, and allowing for rest.
  • This regulation ensures efficient use of motor neurons in a coordinated manner.

Walking: A complex Sensorimotor Reflex

  • Walking is a complex coordinated sequence of movements modulated by various sensory input and spinal circuits.
  • Control of posture and changes in terrain are examples of how the system adapts to complex and changing environments like walking and climbing.

Central Sensorimotor Programs and Learning

  • Sensorimotor programs are organised in hierarchies and encompass various levels in the hierarchy, from association cortex to spinal motoneurons.
  • The sensorimotor system demonstrates plasticity, adjusting itself by improving motor sequences from conscious to more automatic action plans and co-ordination.
  • Sensory feedback affects behaviour, which is important for smooth movement and learning.

Functional Brain Imaging of Sensorimotor Learning

  • The Jenkins study of motor learning used PET scans to observe brain activity during different motor tasks and found that association areas and cerebellum involvement decreased with practice.

Neuroplasticity Associated with Sensorimotor Learning

  • Sensorimotor learning leads to both cortical and subcortical changes.
  • The number of dendritic spines in motor cortex increase, suggesting enhanced synaptic strength with learning
  • Increased oligodendrocytes in subcortical pathways support myelination of new and existing axons, increasing their efficiency.

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Denne quiz giver en overordnet forståelse af sensorimotoriske funktioner og deres hierarkiske organisation. Du vil lære om, hvordan sensorisk input er afgørende for motorisk output, og hvordan læring kan ændre kontrol over disse systemer. Få indsigt i de tre grundlæggende principper for sensorimotorisk funktion og deres betydning.

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