Very comprehensive and complete summary of the seventh task of the block GGZ2025, with many images and figures (original from the basic book). Summary contains material from the basic book (Kolb & Whishaw) and schemes from YouTube videos. Now available as bundle!
The basal ganglia are a collection of
nuclei that make movements and prevents
unwanted movements. The caudate
nucleus (body and tail) together with the
putamen form the striatum. To
important components are 1) making a
movement (the direct pathway) and 2)
not making a movement (the indirect
pathway).
Normally, activity of the thalamus is inhibited. The aim of the direct pathway is to lessen
this inhibition, to allow thalamus to be more active because the thalamus connects to cortex.
Excitatory glutamate +
Motor cortex Muscles
Striatum
Inhibitory
GABA
Less inhibition
Globus Pallidus
of thalamus Thalamus
(internal)
Substantia nigra
Subthalamic nucleus
1) When the motor cortex ‘starts’ to make a movement, it excites the striatum (putamen
and caudate nucleus) by the release of glutamate.
2) The excitatory neurons connect to inhibitory neurons in the striatum, that inhibit the
activity of the globus pallidus internal. Normally, the globus pallidus inhibits the
thalamus, but because of the GABA, this inhibition becomes less.
3) The thalamus then excites the motor cortex, which stimulates muscle movements.
4) The substantia nigra has dopamine-neurons which connect to the inhibitory neurons in
the striatum. The dopamine from the substantia nigra binds to D1-receptors in the
striatum. This further strengthens the inhibitory effect of GABA on the globus
pallidus, which makes it possible for the thalamus to become more active.
5) The subthalamic nucleus sends excitatory neurons to the substantia nigra, which
further increases release of dopamine. The substantia nigra can in turn also inhibit the
subthalamic nucleus.
Indirect pathway; inhibiting unwanted movements. If the thalamus would not be inhibited, it
would send tons of excitatory messages to the motor cortex (“the thalamus is a very excited
puppy, and has to be held on a leash to prevent it from being too excited”). The ‘leash’ for the
thalamus is the globus pallidus internal.
If the basal ganglia want to prevent us from making unwanted movements, they make the
thalamus even less active. They send a massage to the globus pallidus internal to make it send
more inhibitory messages.
Motor cortex
+ Thalamus
Striatum Subthalamic nucleus
- Inhibitory
+ +
+ Less
Substantia nigra inhibitory
effect on
Globus Pallidus Internal
- Globus Pallidus External
Less inhibition
Red arrows; if we want to inhibit a movement, the motor cortex sends excitatory signals to the
striatum. The striatum in turn inhibits the activity of the globus pallidus external. Normally,
the globus pallidus external has an inhibitory effect on the subthalamic nucleus. When the
globus pallidus external is inhibited, there is less inhibition of the subthalamic nucleus. This
in turn excites the globus pallidus internal, which inhibits activity of the thalamus (green).
Blue arrows; the substantia nigra is the ‘adjustment of the leash’, it allows us to perform some
movements. The subthalamic nucleus sends excitatory signals to the substantia nigra, which
in turn sends dopamine (excitatory) to the striatum. Dopamine neurons connect to receptors
(D2-receptors) on excitatory neurons in the striatum, which in turn connect to inhibitory
neurons that connect to the globus pallidus external. Because of this, the inhibitory neurons
are less active in inhibiting the globus pallidus external.
2
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