Motor control Flashcards
What is at the bottom of the motor control systems?
spinal cord
What does the spinal cord do
provides direct control of the muscles via motor neurons and interneurons. Motor neurons can have axons up to a metre in length
what is at the top of the motor control systems hierarchy?
the preomotor/SMA and parietal cortex which are responsible for actions plans and goals.
What is between the spinal cord and the preomotor
Between these two levels lie the primary motor cortex and subcortical brain regions which translate the motor plans and goals into specific actions
How is motor control carried out by muscles?
composed of elastic fibers that can change length and tension and act antagonistically – so when the biceps contracts, the triceps relaxes which enables flexion of the elbow, and if the triceps contracts and the biceps contracts this enables extension of the elbow.
Action potential in a motor neuron triggers the release of what?
acetylcholine, a neurotransmitter that makes muscle fibers contract
Where do motor neurons originate?
spinal cord
where do motor neurons exit
through the ventral root and terminate in the muscle fibers
How many cranial nerves control essential reflexes for keeping us alive
12
What are the 12 cranial nerves?
reflexes associated with eating, breathing, facial expressions
What are extrapyramidal tracts
Direct pathways from brainstem nuclei, including substantia nigra, down spinal cord to control posture, muscle tone, movement speed.
How many neurons does the cerebellum have
more neurons than rest of CNS combined
What does the cerebellum control
balance and eye/body coordination (but also does lots more!)
What do lesions result in
balance/gait problems, ataxia (fine coordination) as well as attentional, planning and language problems
Example of a subcortical motor structure
cerebellum
What are the basal ganglia
a key node in the subcortical motor control system.
What are the 5 nuclei in the basal ganglia?
caudate, putamen, globus pallidus, subthalamic nucleus and substantia nigra.
What does the primary motor cortex receive
input from almost all cortical motor regions
What does the motor cortex regulate
the activity of spinal motor neurons
Where does the corticospinal (pyramidal tract) have axons
project directly from the cortex to the spinal cord. Very long axons.
Each cerebral hemisphere controls movement on the opposite side of the body.
What is somatotopic organisation
different regions represent different body parts
What are the highest pats of the hierarchy
premotor and SMA
Lesions result in apraxia meaning …
affects movement of limbs and also speech.
What did Sherrington do?
He completely severed the spinal cord of cats and the placed them on a treadmill.
• Found that even without any descending commands from the cortex or subcortex, cats were able to produce the rhythmic alternating limb movements required to walk.
What are the neurons in the spinal cord called
central pattern generators
why do CPGs make a lot of evolutionary sense?
they enabled the fast generation of complex movements such as running away.
What did Bizzi et al do
trained deafferented monkeys to point to a target in a dark room. Deafferented means they had all the somatosensory feedback signals severed (the afferent signals from the nerve receptor back to the brain). An opposing torque was applied to arm to hold it in starting position for a short time. Crucially, because of the deafferentation the monkey didn’t know this force was being applied.
What did Bizzi find
Found that the monkey reached the target even when the opposing force was applied.
What did Georgopoulos find
require monkeys to move a lever to one of 8 targets, starting from the centre. Neurons preferred a direction.
Then he asked them to start from a different position and move the lever in the same direction.
The same neurons showed the same selectivity for this movement even though the target location was completely different.
What is a vector
direction of cell’s preferred direction combined with information about strength of firing.
What is a population vector
sum of individual neuron vectors
what does a population vector provide?
the most accurate estimate of the planned direction of movement
Direction of movement can be predicted from population vector how long before initiation of movement
300 ms
What did Chapin do
trained rats to press a lever for reward and measured multiple neuron responses in motor cortex.
What did Chapin find monkeys pressing a lever for reward did
This led to complex population vector responses such as this one, which shows the output of 40-odd neurons during the different stages of lever pressing.
Why did Mice stop presing the lever in Chapins study
- Mice eventually stopped pressing the lever as they learnt about the lack of precise correlation between force exerted and reward
- Mice continued to produce cortical signals necessary for moving the lever
• Patients with lesions in cerebellum, prefrontal cortex and parietal cortex have deficits in ….
earning to move in novel environments
What is tDCS
transcranial direct current stimulation
What did Galea et al inestigate
the different roles of the cerebellum and the primary motor cortex.
tDCS of the cerebellum led to a faster rate of adapation. tDCS of the motor cortex led to increased retention of adaptation (more error for a longer period of time after the end of adaptation).
Stimulation of the cerebellum means faster visuo-motor adaptation. Better performance on this task.
What happened in de-adaptation
The cerebellum stimulation makes little difference to the de-adaptation process. The motor cortex seems to affect it.
When is the primary motor cortex important
for consolidating newly learnt mapping
What did Miall do
They got subjects to move their arm to the right and then when a tone occurred to make a movement to a visual target. This task requires a prediction of where your hand will be in the future because there is a delay between hearing the tone and actually initiating the forward movement. If the subject just generated a motor command when they heard the tone they would miss the target because the motor command (trajectory) would be out of date and inaccurate by the time the motor command was actually initiated.
Using TMS, what can we disrupt?
neural activity
What is the role of basal ganglia in motor control
There is a complex network of inhibitory and excitatory connections within the basal ganglia and connecting the BG to other structures.
Input comes from the substantia nigra into the putamen and travels either via the direct route to the globus pallidus or via the indirect route via the substantia nigra.
what is mutual antagonism
activation of the direct pathway leads to excitation (input to thalamus is inhibitory, so if you inhibit that, the net effect is excitation).
does basal ganglia act in mutual antagonism
yes
What are the symptoms of Parkinsons
Hypokinesia,
bradykinesia,
tremor
What is hypokinesia?
reduction in voluntary movement
What is bradykinesia?
slow movement
What is Levodopa
treatment for parkinsons.
– Crosses the blood-brain barrier, enters the CNS and is converted into dopamine
Does the basal ganglia play a dual role in action and cogntiion
yes
