10 - Basal Ganglia: Structure, Circuitry, and Function Flashcards
Describe the embryonic developement of the basal ganglia? Where is it located?
Derived mainly from the telencephalon. Some components also derived from the diencephalon and mesencephalon.
Located beneath the cerebral cortex and lateral to the dorsal thalamus.
What is the function of the basal ganglia?
Monitors the amplitude and velocity of movement.
Also involved in the constant reinforcement of selective motor programs and suppression of interfering programs.
Refines movement and smooths it out.
What provides input to the basal ganglia? What does it send information to?
Input from the cerebral cortex, thalamus, and the brainstem.
Sends information to the thalamus and brainstem.
What are the components of the basal ganglia?
Caudate nucleus
Putamen
Globus Pallidus: GPe (external) and GPi (internal)
Subthalamic nucleus (Luys)
Substantia Nigra: pars compacta (SNc; dopaminergic) and pars reticulata (SNr; GABAergic)
Nucleus accumbens= ventral striatum
What makes up the lentiform or lenticular nucleus?
The globus pallidus and the putamen.
What makes up the striatum or neostriatum?
The caudate nucleus and the putamen.
________ and ________ are the major output nuclei of the basal ganglia? What do they have in common?
The internal globus pallidus (GPi) and the Substantia nigra pars reticulata (SNr)
Both are GABAnergic and therefor their output is INHIBITORY.
Where is the nucleus accumbens (ventral striatum) located? What is its function?
Below the head of the caudate nucleus.
Functions as a reward center.
What is the blood supply to the basal ganglia?
Anterior cerebral artery givse off the medial striate artery.
Middle cerebral artery gives off the lateral striate artery and the anterior choroidal artery.
Posterior communicating artery.
What is the direct (striatopallidal) pathway?
Cortex > glutamate excites the striatum > inhibitory (GABA) to globus pallidus internal segment and the pars reticulata of the substantia nigra > inhitbis (GABA) inhibition (excitation) of the thalamus > premotor and supplementary motor cortex.
What is the function of the direct (striatopallidal) pathway?
Thalamus is released from it’s inhibition - results in EXCITATION.
Movement is facilitated.
What is the indirect (striatopallidal) pathway?
Cortex > excites striatum > inhibitory output to globus pallidus external segment > inhibits subthalamic nucleus (only excitatory nucleus in the basal ganglia).
Subthalamic nuclei is also capable of excitatory input to the globus pallidus external segment and excites the output nuclei when it’s not inhibited.
What is the function of the indirect (striatopallidal) pathway?
Thalamus is inhibited because the subthalamic nucleus is inhibited.
Movement is inhibited.
What is the function of the Nigrostriatal pathway? What type of pathway is it? What is it composed of?
Dopaminergic.
Acts on both direct and indirect pathways to facilitate movement.
Striatum and Substantia Nigra pars compacta. (affected in parkinsons disease).
What are the effects of neurons with D1 dopamine receptors in the striatum? What are the effects of neurons with D2 dopamine receptors in the striatum?
D1 dopamine receptors: EXCITE the direct pathway and facilitate movement.
D2 dopamine receptors: inhibits indirect pathway (which inhibits movement) results in a release of inhibition and faciliates movement.
Thus, the effect of dopamine is to facilitate movement.
What is the effect of cholinergic neurons in the striatum? What effect does this have on in the direct and indirect pathway?
Inhibits striatal neurons of the direct pathway.
Excites striatal neurons of the indirect pathway.
Both cause INHIBITION of movement; which means Ach has the opposite effect as dopamine.
Do acetylcholine-containing interneurons project out of the striatum?
NO.
What are the major conections outside of the basal ganglia? Where do these terminate?
Extrinsic inputs terminate in the striatum.
- Cerebral cortex > corticostriatal pathway >caudate and putamen
- Intralaminar nuclei of thalamus > thalamostriate pathway > caudate and putamen
What sends inhibitory input to the motor nuclei of the thalamus?
The globus pallidus and the substantia nigra pars reticulata (via GABA).
The substantia nigra pars reticulata also sends inhibitory nts (GABA) to the superior colliculus.
What is the striatonigral pathway?
The striatum sending GABA (inhibitory) signals to the substantia nigra pars compacta.
Disorders of the basal ganglia are usually a disruption of ________?
Disruption in transmitter metabolism.
Abnormal movements are commonly caused by a release of the system from inhibition.
What are symptoms of basal ganglia dysfunction?
Involuntary movements
Tremor at rest
Athetosis: involuntary movements
Chorea: jerky movements
Ballism: flinging movements
Dystonia: distorted movements
Akinesia and bradykinesia: lack of movement or slowness of movement
Change in posture and muscle tone
Muscle rigidity
What is parkinson’s Disease (Paralysis agitans)? What are common symptoms?
Degeneration of dopaminergic cells in the substantia nigra pars compacta.
Tremor at rest, rigidity, and bradykinesia.
What is Huntington’s disease? What are common symptoms?
Degeneration of cholinergic and GABAergic neurons in the striatum.
Inherited; mutation in chrom 4 causing numerous CAG repeats (encodes glutamine).
Causes chorea (jerky movements), athetosis (involuntary movements), and dystonia (distorted movements).
