Full-text Article. Add your Article s to Indexes. ScopeMed Web Sites. Home Journals Articles by Year. Follow on Twitter. Signals come into the basal nuclei and signals leave the basal nuclei, the striatum is the part of the basal nuclei which has incoming signals from the entire cortex motor, sensory, visual etc.
These input and output components are common to both direct and indirect pathways. When a decision is taken to perform an action, multiple competing motor programs are sent to the striatum. The basal nuclei ensure the correct program is selected using the direct and indirect pathways. Thus initiation of movement begins in the cortex, but the selection of the appropriate pathway occurs in the basal nuclei.
When trying to remember which neurotransmitters are involved, a basic fact to remember is that axons from the cortex, thalamus and subthalamic nucleus are glutamatergic neurotransmitter: glutamate , glutamatergic axons are excitatory when they synapse.
Axons travelling from the striatum to the globus pallidus and all axons from the globus pallidus are GABAergic axons neurotransmitter: GABA , which are inhibitory when they synapse. At the end of each pathway section, I have summarised the effect of each pathway mathematically, using the number 1 to represent the positive effect of glutamate and the number -1 to represent the effect of GABA.
See Figure 6. Glutamatergic axons from the cortex synapse on medium spiny neurones in the striatum caudate and putamen , these cortical axons are part of the corticostriate tract and have an excitatory effect on spiny neurones in the striatum causing them to fire more, these neurons are GABAergic, and they synapse on neurones in the globus pallidus internal GPi and substantia nigra pars reticularis SNr.
The increased inhibition of these GPi and SNr neurones, means they fire less. Therefore the net effect is that the inhibitory effect of the GPi and SNr on the thalamus is reduced, so that glutamatergic neurones in the thalamus increase firing, they have an excitatory effect on the motor cortex, promoting movement. So to summarise, the direct pathway promotes movement and is an example of a positive feedback loop.
Think of this literally as an indirect version of the direct pathway, the beginning and end destinations are the same, but a detour is involved hence indirect and the consequence of the detour is that instead of promoting movement like the direct pathway , it inhibits movement. So once again we start off in the cortex, corticostriate axons synapse on neurones in the striatum, from here the striatal neurone axons travel towards the globus pallidus external GPe , not the internal as in the direct pathway.
If you recall, the cortex has an excitatory effect, causing the striatal neurone to increase firing, the striatal neurone itself is GABAergic. Therefore its effect is to increase inhibition on the neurone in the GPe. Therefore the GPe neurone, which is also a GABAergic neurone fires less now, thereby reducing its inhibition on the neurone it synapses within the subthalamic nucleus.
The subthalamic neurone is a glutamatergic neurone, it is now less inhibited by the neurone in the GPe, therefore increases firing. This GPi neurone increase firing, and is a GABAergic neurone and increases the level of inhibition on the neurones it synapses within the thalamic nuclei. The end results are decreased firing of the glutamatergic neurones in the thalamic nuclei and therefore reduced stimulation of the motor cortex. The basal ganglia, however, continuously inhibit the thalamic neurons, which stops them from communicating with the motor cortex—inhibiting movement in the process.
Then, the signal follows a circuit in the basal ganglia known as the direct pathway , which leads to the silencing of neurons in the globus pallidus and substantia nigra. This frees the thalamus from the inhibitory effects of the basal ganglia and allows movement to occur. There is also a circuit within the basal ganglia called the indirect pathway , which involves the subthalamic nucleus and leads to the increased suppression of unwanted movements.
It is thought that a balance between activity in these two pathways may facilitate smooth movement. Again, this is just one perspective on basal ganglia function, and despite the importance the basal ganglia are thought to have in movement, there is still much we need to learn to fully understand their contribution to it.
We can see the importance of the basal ganglia to movement, however, when we look at cases where the basal ganglia have been damaged. In Parkinson's disease , for example, dopaminergic neurons of the substantia nigra degenerate.
When this happens, the ability of the basal ganglia to inhibit contradictory movements is affected. This may cause individuals with Parkinson's disease to have difficulty initiating movements, resulting in some of the symptoms associated with Parkinson's disease like rigidity and slow movement. About Recent Edits Go ad-free. Edit article.
View revision history Report problem with Article. Citation, DOI and article data. Jones, J. Basal ganglia. Reference article, Radiopaedia. Central Nervous System. URL of Article. In a strict anatomical sense, it contains three paired nuclei that together comprise the corpus striatum : caudate nucleus lentiform nucleus putamen globus pallidus Functionally, two additional nuclei are also part of the basal ganglia: subthalamic nuclei substantia nigra On this page:.
Quiz questions.
0コメント