the basal ganglia also known as the basal nucleus or the extrapyramidal nuclei are a collection of subcortical structures located deep within the white matter of the brain it forms part of the extrapyramidal motor system which has functions such as regulation of involuntary movements so movements not under conscious control the fine-tuning of voluntary movements and the maintenance of posture the basal ganglia is made up of five pairs of nuclei the chordae nucleus the putamen the globus pallidus the subthalamic nucleus and the substantia grouped into broader clusters these nuclei are known as the striatum the globus pallidus the subthalamic nuclei and the substantia let's talk about each of these nuclei in a bit more detail and their function the striatum is found inside the insular lobe and is made up of the dorsal striatum and the ventral striatum however the ventral striatum is actually considered part of the limbic system rather than the basal ganglia it is the dorsal striatum which is part of the basal ganglia the dorsal striatum is made up of the chordae nucleus and the putamen during development the chordae nucleus is separated from the putamen by descending white matter fibers which at this level are known as the internal capsule the striatum is the primary input unit of the basal ganglia it receives input from the cerebral cortex it receives excitatory glutamatergic neurons from the cerebral cortex glutamatergic neurons release glutamate a stimulatory neurotransmitter the substance of the striatum itself is mainly composed of projection neurons and interneurons functionally they are inhibitory neurons called gabaergic neurons that release inhibitory neurotransmitters called gaba the axons of these neurons form the direct and indirect pathways of the basal ganglia which project into the globus pallidus and the subthalamic nuclei the next nuclei to talk about is the globus pallidus which is made up of an internal segment gpi and an external segment gpe the globus pallidus is composed mainly of inhibitory gabaergic projection neurons which fire spontaneously and irregularly at high frequencies gabaergic neurons inhibit things they release the neurotransmitter gaba neurons that project from the striatum to the internal part of the globus pallidus are part of what's called the direct pathway of the motor loop meanwhile neurons that project from the striatum to the external part of the globus pallidus are part of the indirect pathway the direct pathway basically means it goes from the striatum straight to thalamus both of these segments play an essential role to the modulation of motor pathways in particular the creation of smooth and precise motor actions and also inhibitory actions to balance the excitatory component coming from the cerebral cortex next we have the subthalamic nuclei which are bi-concave paired structures found within the subthalamus they are not an anatomical part of the basal ganglia however due to their functional connection they are considered part of the basal ganglia the function of the subthalamic nucleus is not well known however some theory suggests it has a crucial role related to modulation of planned motor movements they receive input and also give output to the globus pallidus and the nuclei contains glutamatergic neurons which are the excitatory neurons lastly we have the substantia which is a small motor nucleus found in the anterior part of the midbrain even though it is located in the midbrain which is part of the brainstem functionally the substantia is considered part of the basal ganglia the substantia is made up of the pars compactor and the parse reticulata the pars compacta supplies the striatum with dopamine a neurotransmitter acting as an input to the basal ganglia area the striatum the pars reticulata serves as an output as it conveys signals from the basal ganglia to the thalamus so putting all these different nuclei of the basal ganglia together all these connections allow for a regulation of involuntary movements it allows for the fine-tuning of voluntary movements and the maintenance of posture via skeletal muscles the main efferent nerve fibers or output of the basal ganglia are made up of neurons that are directed towards the thalamus and the brain stem these originate from the internal part of the globus pallidus and the reticular part of the substantia there are many afferents or inputs to the basal ganglia and these include the cerebral cortex through the corticostriatal pathway this is the largest afferent connection to the basal ganglia the second input to the basal ganglia is from the substantia because there are fibers here that play an important role specifically from the compacta as they supply the striatum with dopamine enabling the regulation of movement initiation termination and modulation the third input to the basal ganglia is from the thalamus these fibers are glutamatergic and are responsible for excitatory effects on the cerebral cortex and brain stem and then it sort of loops back around to the striatum this is what we call the thalamostriatal pathway the functions of the basal ganglia are not fully understood however its known primary function is to fine-tune voluntary movements it receives impulses for the upcoming movement from the cerebral cortex processes these impulses and then conveys instructions to the thalamus which then sends this information back to the cortex the instructions of the fine-tuned movements is then sent to the skeletal muscle via the pyramidal motor system much of this involves preventing unwanted movements to start and reducing the excitatory input from the cerebral cortex preventing excessive and exaggerated movements other functions that have been established include the reward processing and motivation decision making working memory and eye movements some clinical anatomy now parkinson's disease is the most well-known disease of the basal ganglia classic signs and symptoms of parkinson's disease include bradykinesia which is slowness of movement arresting tremor postural instability which is the inability to basically stand upright and shuffling gait this disease is a result of neurodegeneration of dopaminergic neurons specifically dopaminergic neurons which are found in the substantia pass compacta degeneration of the substantia results in decreased dopaminergic input to the striatum resulting in the classic features of parkinson's disease bradykinesia resting tremor rigidity and postural instability basically it is a hypokinetic movement disorder next is huntington's disease unlike parkinson's disease which is a hypokinetic movement disorder huntington's disease is a hyper kinetic movement disorder meaning it is characterized by excessive abnormal and involuntary movements classic signs and symptoms include involuntary movements cognitive degeneration and psychiatric dysfunction the cause of huntington's disease is a genetic error specifically it is caused by a cag repeat sequence on chromosome 4p on the htt gene the huntington's the gene the resultant abnormally long huntington gene leads to neuronal death in the chordate and putamen of the basal ganglia there is no cure for huntington's disease however a drug called tetrabinazine helps reduce disease symptoms tetrabinizine inhibits uptake of monoamines such as serotonin dopamine and adrenaline in two synaptic vessels resulting in reduced stimulation of the striatum the next case we will discuss is hemibolism which is derived from the greek to throw hemi ballism is used to describe hyperkinetic involuntary forceful movements of the ipsilateral arm and leg the most common cause of hemobolism is a lesion in the contralateral subthalamic nuclei such as from a stroke traumatic brain injury neoplasm vascular malformation amongst many other causes the last clinical case we will discuss is tourette's syndrome which presents as sudden repetitive uncontrolled movements and vocalization called ticks these ticks are associated with dysfunction of projection from the striatum and results in increased dopaminergic activity similar to huntington's disease and hemobolism so in summary in this video we talked about the basal ganglia which is a collection of subcortical structures located deep within the white matter of the brain we discussed the five pairs of nuclear that make up the basal ganglia the chordae nucleus the putamen the globus pallidus the subthalamic nucleus and the substantia and the fact that they can be grouped into broader clusters we then talked about the function of each nuclei and the function of the basal ganglia broadly we finished off discussing four relevant clinical anatomy cases which were parkinson's disease huntington's disease hemi ballism and tourette syndrome thank you you