Objectives: Define basal ganglia and describe the parts, describe the main connections and functions, describe the function and the disorders of basal ganglia
The main function of the basal ganglia is to provide a feedback mechanism for the selection and initiation of voluntary movement. They way it does that is it provides an input to the thalamus which acts as an inhibitory input to the lateral ventricle of the thalamus which then projects an excitaroty input to the motor cortex. Its motor input loop is essentially how voluntary movement is selected and initiated. So if anything affects this loop with either dampen or enhance voluntary movement (Parkinsons/Huntingson diseases).
The basal ganglia is a series of interconnected nuclei that composes of the caudate nuclei, putamen, globus pallidus and as well as the substantia nigra. These nuclei essentially form a feedback loop that connects to the cerebral cortex that allows for the selection of inhibitory and stimulating movements that may lead to a generation of purposeful movement.
Caudate is an egg-like structure and located laterally from the lateral ventricle. Putamen is next to the caudate which is separated by the internal capsule. The caudate is responsible for telling the brain that there is something wrong and something should be done to fix it. Caudate can be used in many ways but if its is overused you have conditions like Obsessive Compulsive Disorder. Putamen is involved with learning abilities such as playing the piano or riding a bike. Behind the putamen lays the globus pallidus which essentially acts as the output structure of the basal ganglia.
CAUDATE PUTAMEN (CPu)/Striatum
* Early anatomist have subdivided these two structures by the presence of the internal capsule * More recently with neurochemical and microscopical studies have shown that these structures are essentially similar in many regards based on their neurotransmitters as well as the receptors that are present * Therefore they made a recent subdivision that impinges on both the caudate and the putamen. It is subdivided rather than from the internal capsule, you have patches that are described as striosomes which are predominately D1 receptors abundant and the bulk of the matrix has D2 receptors. Essentially these receptors are different as D1 receptors are involved in direct pathways, pro-movement pathways and the D2 receptors are involved in inhibitory or anti-movement pathways * The bulk of the neurons are at least 95% of the neurons in the striatum (collectively known as the caudate putamen)
They are separated again into the external and internal segment. It sits in a close proximity to the thalamus and this is ideal because the globis pallidus sends its outputs greatly onto the thalamus to essentially summarise the information derived from the striatum.
It is essentially the external globis pallidus that acts as the output. The basal ganglia is made up direct and indirect pathways. Direct pathway being ‘pro-movement’ and this receives a direct movement from the striatum into the globis pallidus internal whereas the indirect pathway goes from the striatum to the globis pallidus external which then projects on the subthalamic nucleus and then projecting back to the globis pallidus internal. So essentially the GPi has the final say of the information that sends to the thalamus.
SUBTHALAMIC NUCLEUS (STM)
The subthalamic nucleus is an egg-like structure that is located just above the substantia nigra. It is considered the ‘engine’ of the basal ganglia. The reason why it is known as the ‘pacemaker’/’engine’ of the basal ganglia is because it is the only substructure that has glutamatergic neurons. The significance is because the neurons are excitatory, therefore it is able to cause an increase in action potential. These neurons are capable of exerting or stimulating on the GPi which balances out the negative influence...
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