Chapter 8: Action Flashcards
What is the role of prefrontal cortex and parietal cortex in movement?
Translate abstract intentions into movement patterns
What is the role of the primary motor cortex and supplementary cortex? (+cerebellum+basal ganglia)
Convert movement patterns into muscle commands
What is an effector? And an affector?
Part of the body that responds to a signal and can move.
Structure that sends signals to the brain (sensory)
How are muscles connected to the skeleton?
With eleastic fibers at joints
What does it mean that muscles are arranged in antagonist pairs?
That means one muscle is a flexor and the other one is an extensor. E.g. when the biceps contracts, the triceps gets a signal to relax
What is the main neurotransmitter of alpha motor neurons?
Acetylcholine
What are alpha motor neurons and what does the firing frequency say?
They are the final motor neuron to the muscle. The firing frequency tells you something about the force generated by the muscle
What are gamma motor neurons?
They are neurons of the proprioceptive system that are important for sensing and regulating the lengths of muscle fibers. They adjust muscle spindles so they can keep getting information from CNS
What are muscle spindles?
Bundle of receptors in a muscle that respond to stretch
What is the pathway of the alpha motor neurons via muscle spindles?
- Spinal cord
- Alpha motor neuron to muscle
- Muscle spindle responds to the amount of stretch
- Afferent nerve goes via dorsal root to spinal cord
- Synapse with interneurons
- Project to alpha neurons
What happens when there is an unexpected stretch? What is the function of a reflex?
Alpha neuron is activated with stretch reflex.
A reflex serves postural stability and protection without help of the cortex. They go via interneurons in spinal cord.
How does flexor/extensor coordination work when holding a cup whilst it’s being filled?
Muscle spindles register stretch and activate biceps and inhibit triceps
Name the 3 important structures of the brainstem for action
- Vestibular nuclei
- Reticular formation nuclei
- Substantia nigra: dopamine
What is the difference between an extrapyramidal tract and the pyramidal tract?
Extrapyramidal: only projections from brainstem to spinal cord. It’s important for control of posture, muscle tone and movement speed
Pyramidal: they come directly from the brain. The pyramidal tract (corticospinal tract (CST)) ends on spinal interneurons or monosynaptically to alpha motor neurons. They are important for fine motor control
What are corticomotoneurons and when do they fire the most?
They are neurons, part of the pyramidal tract, that stem directly from the brain. They fire more heavily when doing precision tasks
Are the extrapyramidal and pyramidal tract projecting contralaterally or ipsilaterally?
Extrapyramidal: both ipsi as contra
Pyramidal: only contra
What is the function of the cerebellum?
Fine adjustments of movements and error correction
What is ataxia?
Damage to cerebellum, which results in difficulty maintaining balance and do coordinated smooth movements
What are the 5 most importan nuclei of the basal ganglia and what is their function? What is the striatum?
Caudate nucleus, putamen, globus pallidus, subthalamic nucleus and substantia nigra.
Striatum = caudate nucleus + putamen
- Function: input
Part globus pallidus+part of SN
- Function: output
Remaining components (part SN, STN, part GP)
- Function: modulate activity in basal ganglia
What is the main role of the basal ganglia?
It’s a gating function for movement selection and initiation
What is the role of the M1 and specify the input and output?
- Motor initiation + activating lower levels
- Main output is pyramidal tract
- Input: all cortical areas involved in motor control
What is the somatotopic organization of M1? What is the difference between the two regions of M1?
Somatotopic: representation of effectors correspond to their importance of moving
Two regions:
- Caudal: manipulate tools
- Rostral: evolutionary old
What is hemiplegia?
M1 lesion, which results in loss of voluntary movement in contralateral side of the body
What is the main role of secondary motor areas and of what is the role of each of the two subareas?
Movement planning and control
- Premotor cortex: sensory guided movements (input from parietal cortex)
- Supplementary motor area:
- connection with MFC for informations about goals and preferences
- memory guided movements
What is the role of the two dorsal streams to the premotor cortex (PM)? What are the two disorders paired with
Dorso-dorsal: reaching for objects
- Optic ataxia: unable to reach for objects despite recognition
Ventro-dorsal: manipulating objects
- Apraxia: unable to coherently use objects and link gestures to meaningful actions despite object knowledge
Name three additional cortical regions for motor control
- Broca: producing speech
- Inf/sup parietal lobule
- MFC + frontal eyefields (eye movements and goals)
What are central pattern generators? What experiment indicated that?
Neurons in spinal cord can produce a sequence of motor actions without descending commands or external feedback signals
Experiment: disecting spinal cord in cats and let them walk on a threadmill. They do start walking
Why can we predict movement direction from M1 activity and what is it called?
Neurons have a preferred direction. Movement can be predicted by determining the population vector of many neurons together
What is a population vector and is this seen in people who are paralyzed?
Combined activity for many neurons that can predict the direction of movement. This also happens in people who are paralyzed. The population vectors happen before the actual movement
What is a center-out task and what does it measure?
Used to gather evidence for preference of movement direction. An animal has to move the lever to a specific target location
What is the affordance competition hypothesis? What is affordance and what is competition in this sense?
Explains how goals are transferred into action. Combination of sensory input and balancing reward
- Affordance = use sensory information to update potential actions
- Competition = expected rewards/costs provide information that can be used to assess the use of possible actions
How does action preparation in the premotor cortex work?
There is parallel preparation of action. Actions that are not executed, are inhibited
What is the difference in reference frame between action preparation in PM vs. parietal cortex? And what is the difference in movement intentions?
Parietal: vision centered
PM: proprioceptive, with no vision needed
Parietal: motor intention (desire to move)
PM: motor exectution without awareness
How do you become aware of making a movement?
Awareness emerges from intention and prediction, not from the movement itself.
Sometimes you perceive yourself moving, but there actually isn’t (parietal)
What’s the difference between the lateral and medial PM?
Lateral: stimulus guided movement
Medial: movement based on internal goals and skilled movements (with SMA)
What is the alien hand syndrome? For what statement gives this evidence?
Lesions to SMA
- Impairment of hands working together
- One limb has meaningful action, but person denies he did that
If lesions in corpus callosum, both hands may work in opposition to each other
So, this is evidence for competition in action planning between two limbs
What are mirror neurons and where are they located?
Respond to an action when you execute it or when someone else executes it.
- Located in premotor, parietal and temporal areas
What does excitability in the motor cortex say about someone’s expertise?
An elite basketball player show increase in motor cortex of arm muscles when watching basketball, but not when watching football.
What is a brain-machine interface (BMI)?
Technical device that connects neural signals from brain to f.e. a prosthetic device to be able to control them
Which two neurotransmitters does the basal ganglia mainly use?
GABA: inhibitory
Glutamate: excitatory
What is the direct pathway of the basal ganglia?
Activates cortex and initiates movement
- SN excites/inhibits striatum
- Striatum inhibits internal Globus Pallidus and substantia nigra
- inhibition of thalamus
- Excites cortex
What is the indirect pathway of the basal ganglia?
Inhibits cortex and stops movement
- SN excites/inhibits striatum
- Striatum inhibits external globus pallidus
- Less inhibition GPi or STN
- STN excites GPi
- Less inhibition in total of substantia nigra
- Stronger inhibition of thalamus
- Reduced excitation of cortex
What is the hyperdirect pathway of the basal ganglia?
It stops movement
- Direct connection motor cortex to STN that bypass striatum
- Excitation STN and GPi
- Stronger inhibition thalamus
- Reduced cortical excitation
What is Huntington disease and how do the symptoms relate to the basal ganglia pathways? What is hyperkinesia
There is reduced inhibition of indirect pathway, so increased inhibition of GPi, less inhibition thalamus which leads to cortex activation
Symptom: hyperkinesia: excessive involuntary movement
What is Parkinson disease and how do the symptoms relate to the basal ganglia pathways? What is hypokinesia and bradykinesia?
Reduced inhibition of direct path because of death dopamine cells in SN. It leads to less inhibition of GPi, more inhibition of thalamus and therefore less activation of cortex.
Hypokinesia: less voluntary movement
Bradykinesia: slower rate of movement
What is the function of the globus pallidus internal in the basal ganglia?
If it’s inhibited, it inhibits the thalamus and excites cortex (direct)
If it’s excited, it inhibits the thalamus enormously, which inhibits the cortex (indirect and hyperdirect)
What is the function of the subthalamic nucleus in the pathways of the basal ganglia?
If it’s less inhibited or excited, the STN will excite the GPi, which leads to the inhibition of cortex
What are forward models and what brain structure mainly generates them? What is an efference copy?
Motor system makes predictions of expected sensory consequences
Generated by cerebellum
Efference copy = copy of motor signal sent from cortex to muscles to generate predictions
What are sensory prediction errors used for?
If sensory feedback doesn’t match predictions made in forward model, these errors help adjust movements and learn from it
What happens with motor control of habits?
Motor control goes from cortex to subcortex after extensive learning.
Habits will stay when motor cortex is lesioned
What happens to the structure of your brain when you are better than average at bimanual coordination?
There is greater connectivity in corpus callosum between left/right SMA
Where in the brain will there be more connectivity if you’re better at juggling?
V5: motion perception
Intraparietal sulcus: movement planning based on sensory feedback
