Movement L7 Flashcards
Essentially, the PARAMETERS of movement (force, speed and timing) are computed by the ________.
Essentially, the PARAMETERS of movement (force, speed and timing) are computed by the cerebellum.
what part of motion are basal ganglia involved in?
action selection
basal ganglia
D: basal ganglia
the basal ganglia are a collection of large subcortical forebrain nuclei.
what are the main basal ganglia
The main nuclei are the Putamen & Caudate and the globus pallidus.
what are the 2 mid brain basal ganglia
(substantia nigra & subthalamic nucleus
inouts and outputs to the basal ganglia
Major inputs to the basal ganglia arise from the cerebral cortex (all lobes): the outputs are directed to the parts of the thalamus that supply the frontal lobes.
The ultimate output is inhibitory to the thalamus
The nuclei in the basal ganglia are mainly interconnected by what type of neuronal connections?
The nuclei in the basal ganglia are mainly interconnected by sequential inhibitory connections (GABA)
describe basal ganglia output to the thalamus
Basal ganglia output neurons (e.g.. internal globus pallidus) fire continuously, inhibiting the thalamus and therefore preventing movement.
In turn, Inhibition of these inhibitory neurons will ‘release’ the thalamus from inhibition (disinhibition) allowing it to respond to excitatory inputs and activate motor cortex.
Picture for your aid
describe the dirwect basal ganglia circuit
A ‘direct’ circuit:
- corticostriate fibres activate neurons in the caudate or putamen nuclei.
- These inhibit neurons in the internal globus pallidus, which tonically inhibit neurons in the thalamus. Increased activity in this pathway generates disinhibition in the thalamus, allowing movement.
describe an indirect pathway dfor the basal ganglia
An ‘indirect’ pathway:
Corticostriate inputs activate different caudate or putamen neurons that in turn inhibit neurons in the external globus pallidus,
which inhibits the subthalamic nucleus.
Subthalamic neurons excite the internal globus pallidus.
Increased activity in this pathway disinhibits the subthalamic nucleus allowing it to increase activity in internal globus pallidus, increasing inhibition in the thalamus and preventing movemenT
describe the hyper direct pathway for basal ganglia
- A “hyper- direct” pathway.
Connections from the motor cortex directly excite the subthalamic nucleus,
which in turn excites the internal globus pallidus.
Activity in this pathway will abruptly inhibit the thalamus, to stop movement (an emergency brake).
The internal globus pallidus can thus be seen as a ‘______’ on movement
The internal globus pallidus can thus be seen as a ‘brake’ on movement
describe the role the substantia nigra plays
A critical role in the activity of these circuits provided by the substantia nigra, which provides dopaminergic projections to the caudate and putamen.
This connection differentially modulates the direct pathway (facilitating its activity) and the indirect pathway (depressing its activity).
The substantia nigra is therefore in a controlling position to either permit or forbid activity in the motor cortex which generates movement.
describe basal ganglia movement problems
Basal ganglia dysfunction leads to characteristic problems with either an excess or a paucity of movement.
In hyperkinesia movements are produced not as random twitches, but often well coordinated – but are produced at inappropriate times
do you understand the basal ganglia model for parkinsionism?
i hope so!
role of dopamine in basal gangia movement pathway
Dopamine:
- i) activates the inhibitory direct pathway to the internal globus pallidus via D1 receptors and
- ii) suppresses the inhibitory projections to external globus pallidus (part of the indirect pathway) via D2 receptors.
Loss of dopamine therefore leads to _____ activity in the direct pathway and ____ activity in the indirect path,
Loss of dopamine therefore leads to reduced activity in the direct pathway and more activity in the indirect path,
in parkinsonism - internal globus pallidus -
more or less active?
more active! = increased inhibition
2 treatments for parkinism
controlled lesions of the Globus Pallidus (pallidotomy) or, more common nowadays, deep brain stimulation in the subthalamic nucleus. These both disrupt the excessive inhibition of the thalamic neurons, alleviating the symptoms.
The real physiological role of the basal ganglia is more complex and appears to be related to ….
The real physiological role of the basal ganglia is more complex and appears to be related to decision making.
if all visual stimuli always drove saccades it would be bad. To prevent this, the superior colliculus is tonically inhibited by ….
tonically inhibited by basal ganglia output (substantia nigra/globus pallidus).
fat
mamba
