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47 Cards in this Set

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What are the three principles of sensorimotor function?

1) The sensorimotor system is hierarchically organized




2) Motor output is guided by sensory input




3) Learning changes the nature and locus of sensorimotor control

How does hierarchical organization work for the sensorimotor system?

The higher up levels of control do not manage the details of action - they control the more complex functions




(Functional segregation occurs)




Information flows down (Sensory systems, it flows up)

How does sensory input guide motor output

Via sensory feedback - the effects of one's activities are fine-tuned based on continuous monitoring

What types of movements DO NOT involve sensory feedback?

Ballistic movements: Brief all-or-none high-speed movements




(Controlled by lower levels of sensorimotor hierarchy, and occur way faster because the impulse has to travel less)

How does sensorimotor control differ during motor movement from learning to learnt performance?

Initially, each stage is performed under conscious control




Eventually the responses become integrated -- a series of actions that flow properly

What is the general flow of information for the sensorimotor system?

Association cortex --> Secondary motor cortex --> Primary motor cortex --> Brain stem motor nuclei --> Spinal motor circuits --> Muscle




Feedback goes from muscle back to:


a) Spinal motor circuits


b) Association cortex

What are the two areas of the sensorimotor association cortex?

1) Posterior parietal association cortex




2) Dorsolateral prefrontal association cortex

What is the function of the posterior parietal association cortex?

Integrates the original position of the body part (that is going to move), and the position of any external objects the body will need to interact with




(I.e. Directs behaviour based on spatial information)

What 3 sensory systems does the sensorimotor association cortex receive information from?

1) Visual system


2) Auditory system


3) Somatosensory system

Where are the main areas the sensorimotor association cortex outputs to?

- Motor cortex


- Dorsolateral prefrontal cortex


- Secondary motor cortex (some areas)


- Frontal eye field (Area of prefrontal cortex that controls eye movements)

What are the 2 major consequences of posterior parietal cortex damage?

1) Apraxia: Voluntary movement disorder (same movement can be made with unconscious thought)


- Unilateral damage to left posterior parietal lobe area (Bilateral symptoms)




2) Contralateral neglect: Inability to consciously respond to a stimuli on the body opposite a brain region


- Typically damage to right posterior parietal lobe area --> Results in damage to the egocentric left

What is the dorsolateral prefrontal association cortex important for?

Sends information to motor cortex (primary and secondary), and frontal eye field




IMPORTANT FOR: Evaluation of external stimuli, initiation of voluntary action

What are the 2 large areas of the secondary motor cortex (Old theory)?

Supplementary motor area: Wraps over top, extends into the longitudinal fissure




Premotor cortex: Runs from supplementary motor area, to the lateral fissure

What do we (now) think are the 8 different areas of the secondary cortex?




What seems to be the function?

3 Supplementary motor areas (SMA, preSMA, supplementary eye field)




2 Premotor areas (Dorsal and ventral)




3 Small areas (cingulate motor areas - the cingulate gyrus)




- Seem to be involved in programming patterns of movement, after getting the general instructions from dorsolateral prefrontal cortex

What are mirror neurons? What does it showcase?




Do humans have them?

Fire when you either perform a particular goal-directed hand movement, or watch someone perform the same movement




Evidence for social cognition (I.e. Presence of perception)




We haven't found them in humans, but areas of the motor cortex are active when we watch certain actions

Where is the primary motor cortex?

Located in the precentral gyrus

How is the primary motor cortex laid out?

Somatotopically - according to a map of the body (I.e. The "Motor Homunculus" - greatest dedication to the areas requiring the most intricate movements)

How does the primary motor cortex of monkeys differ from everyone else?




Why?

They have 2 different hand areas - one for muscle/joint reception, and the other for receptive input from the skin




Allows for greater levels of stereognosis

What is the original and current view of primary motor cortex function?




What does the new notion prove?

Original: Each neuron is responsible for the direction of movement of a body part




Current: Certain neurons are responsible for the target of the movement (not direction)


- We can therefore get to result A from any position


- Supports the notion of sensorimotor system plasticity***

What are the effects of primary motor cortex lesions?

Potential for asteronosia (inability to recognize objects by touch)




Movement may be slowed, or slightly inaccurate - not eliminated completely because we have plenty of motor pathways that descend directly from the secondary motor cortex

What is the general purpose of the cerebellum and basal ganglia in the sensorimotor system?

To coordinate and modulate the activities of the sensorimotor system (They are "organizers")

Main function of the cerebellum in motor control?

It compares the input sources of:


- Primary/secondary motor cortex


- Descending motor signals from brain stem motor nuclei


- Feedback from motor responses (via somatosensory and vestibular systems)




Compares these and corrects ongoing movements - CRITICAL for motor learning

What happens if the cerebellum is damaged?

Learning NEW motor sequences is very difficult, and ability to fine-tune and control movements is lost - you even tremor from maintaining posture

What is the function of the basal ganglia?

Modulatory function - Contributes fibers to descending motor pathways




Involved in motor output AND cognitive function modulation




Basically, learns how to receive awards and avoid punishment

What are the 4 pathways through which neural signals are conducted from the primary motor cortex to the motor neurons of the spinal cord?

1) Dorsolateral corticospinal tract (Direct)


2) Dorsolateral corticorubrospinal tract (Indirect)




3) Ventromedial corticospinal tract


4) Ventromedial cortico-brainstem-spinal tract

Which of the dorsolateral tracts synapses on the red nucleus of the midbrain?




Hint: Also control muscles of the face

Dorsolateral corticorubrospinal tract

Where do the 2 dorsolateral tracts end up in the body? (I.e. What part do they control?)

Dorsolateral corticospinal tract: Distal muscles of the wrists, hands, fingers, toes




Dorsolateral corticorubrospinal tract: Distal muscles of arms/legs

What are betz cell neurons?

Extremely large pyramidal neurons (of the primary motor cortex), found in the dorsolateral corticospinal tract

What muscles do the ventromedial cortico-brainstem-spinal tract control?

Proximal muscles of trunk and limbs

What 4 brainstem structures interact with the ventromedial cortico-brainstem-spinal tract?




Function of interaction of each?

Tectum: Receive auditory/visul information about spatial location




Vestibular nucleus: Receives balance information from inner ear




Reticular formation: Motor programs like walking, swimming, jumping, etc.




Motor nuclei (of cranial nerves): Controls muscles of face

Branching patterns of the ventromedial corticospinal tract vs. ventromedial cortico-brainstem-spinal tract?

Ventromedial corticospinal: Branch diffusely (Connected like a bridge in both sides)




Ventromedial cortico-brainstem-spinal: Branch bilaterally (Think separate on each sides)

Difference between the ventromedial and dorsolateral tracts?

Ventromedial are much more diffuse than DL




VM goes to proximal muscles, DL projects to distal muscles

What are the 2 types of contraction?

Isometric: No change in length




Dynamic contraction: Muscle shortens, is pulled together

Difference between fast and slow twitch muscle fibers?

Fast: Poorly vascularized, slow recovery, pale




Slow: Well vascularized, fast recovery red colour

What are the two receptor types that monitor muscle activity?

Golgi tendon organ: Respond to increases in muscle tension




Muscle spindles: Respond to changes in muscle length

What is the muscle-spindle feedback circuit?

Each muscle spindle receptor has an intrafusal muscle - monitors the contraction of the extrafusal muscle (the skeletal muscle) - so that there is no slack in the spindle when the muscle contracts, and tension is maintained

What two important sensorimotor principles are demonstrated by a "reflex"?

1) Role of sensory feedback in regulating motor output


- Body feels "stretching force" on a muscle, and so it elicits a kickback response




2) Ability of lower-level circuits to modulate "finer details" without higher level involvement

Which is monosynaptic, the stretch reflex or withdrawal reflex?

Stretch reflex




- Withdrawal reflex crosses 2 synapses, takes 1.6ms

What is reciprocal innervation?

The way that antagonistic muscles are innervated to result in a smooth motor respone


E.g. Pull the hand away by excite bicep, inhibit tricep




Varied levels of cocontraction (Smooth movements, we can stop them very precisely by just activating the antagonistic muscles slightly)

What is recurrent collateral inhibition? What are they mediated by?

Inhibition on local circuits of motor neurons - gives them an "occasional break" - momentarily inhibited to shift responsibility of contraction to other muscles in the motor pool




- Mediated by renshaw cells

What is the central sensorimotor program theory?

Suggests the highest levels of the system have patterns of activity programmed into them


I.e. Complex movements are produced by "activating the program"




When engaged, the basal ganglia and cerebellum work to coordinate the movements and ensure their effectiveness



What is motor equivalence?

Ability to perform a basic movement (e.g. Writing your name) in different ways with different muscles (e.g. Hand, foot)




- Illustrates sensorimotor system plasticity - the function is stored far higher up in the hierarchy than just the muscle....and adapted to the situation when needed

What does the Ebbinghaus illusion demonstrate? (Big and little circles, reach for it with same-sized pinch)

There is evidence for unconscious interpretation of sensory information that controls a motor program

Proof of sensorimotor program development WITHOUT practice?

Mice without forelimbs still moved their shoulders when the behaviour of "grooming themselves" was elicited, even though they never had arms to move the shoulders....they simply "learnt the response"

What are the 2 important principles of learning a sensorimotor program (I.e. motor pattern)

1) Response chunking individual parts of a movement (The chunks can then be "chunked")




2) Shifting control to lower levels of the system


- Permits greater speed, and frees up higher levels of the system

Which sensorimotor areas are active during performance of a NEWLY-learnt sequence?




From PET Jenkins study - key press sequence learning brain activity

- Dorsolateral prefrontal cortex


- Premotor cortex


- Primary motor/somatosensory cortexes


- Posterior parietal cortex


- Cerebellum




Less, but active: Supplementary motor area

Which sensorimotor areas are active during performance of a TRAINED sequence?




From PET Jenkins study - key press sequence learning brain activity

- Primary motor and somatosensory cortexes


- Supplementary motor area




Less, but active:


- Cerebellum


- Posterior parietal cortex


- Premotor cortex