Basal Ganglia: Structure, Circuitry and Function Flashcards
Basal ganglia is embryonically developed from
telencephalon mainly
and also the diencephalon and the mesencephalon
What makes up the striatum
caudate nucleus and putamen
What makes up the lenticular n. or the lentiform n.
putamen and globus pallidus (external/lateral segment and internal/medial segment)
what makes up the basal ganglia
- caudate nucleus
- globus pallidus (internal and external segment)
- Subthalamic nucleus
- Substantia nigra: pars compacta and pars reticula
- Nucleus accumbens=ventral striatum
The basal banglia is supplied by
- anterior cerebral artery branch: medial striate artery
- Middle cerebral artery branches: Lateral striate artery and anterior choroidal artery
- Posterior communicating artery
What is the effect of the indirect pathway
- thalamus is inhibited
- movement is inhibited
What is the effect of the direct pathway
- thalamus is disinhibited
- movement is facilitated
Describe the direct pathway
- Cortex excites Striatum (Caudate and Putamen)
- Striatum inhibits Globus Pallidus and Substantia nigra
- Substantia Nigra (pars reticula) and Globus pallidus (internal segment) inhibit Thalamus. BUT bc they were inhibited they don’t really inhibit the thalamus so the thalamus is disinhibited
- The disinhibited thalamus excites the supplementary motor area and premotor cortex
Describe the Indirect Pathway
- Cortex excites Striatum (Caudate and putamen)
- Striatum inhibits Globus pallidus (external segment)
- Globus pallidus (external segment) inhibits Subthalamic nucleus
- Subthalamic nucleus excites Globus pallidus (internal segment) and Substanstia nigra (pars reticulata)
- Bc globus pallidus (internal segments) and substantia nigra (pars reticulata) were activated they are now able to fully inhibit the thalamus so the thalamus is inhibited and movement is inhibited
What are the two components of the circuits that are the main output for the basal ganglia
- Globus pallidus (internal segment) and Substantia Nigra (pars reticulata)
- They are inhibitory
In general is the basal ganglia excitatory or inhibitory
inhibitory
is the cerebellum excitatory or inhibitory
excitatory
Describe the Nigrostriatal pathway
- substantia nigra pars compacta releases dopamine which works on the striatum.
- works on both the direct and indirect pathways to facilitate movement
- involed in parkinsons
what are the two types of output neurons in the striatum that dopamine affects
Neurons with D1 dopamine receptors
Neurons with D2 dopamine receptors
Neurons with D1 dopamine receptors
-excite the direct pathway (which facilitates movement)
Neurons with D2 dopamine receptors
Inhibits indirect pathway (which inhibits movement) which leads to disinhibition and facilitates movement!
you are inhibiting the pathway that inhibits movement, so movement is not inhibited, it is facilitated
Thus what is the effect of dopamine
to facilitate movement
Effect of Ach on the striatal neurons
- Inhibit striatal neurons of the Direct pathway
- Excite striatal neurons of the indirect pathway
- Both result in inhibition of movement
- these effects are opposite of dopamine which facilitates movement by exciting the direct and inhibiting the indirect
Extrinsic inputs to the basal ganglia terminate mainly
in the striatum
Extrinsic inputs to basal ganglia terminate mostly in the striatum (caudate and putamen) they are from:
-Cerebral cortex (motor, sensory,
association, and limbic): topographical
projections (corticostriatal pathway)
-Intralaminar nuclei of the thalamus: also
topographically organized
(Thalamostriatal pathway
Extrinsic output from the basal ganglia arises
mainly from
the globus pallidus and substantia
nigra, pars reticulata. which are both GABAergic
where do the output signals from the globus pallidus and substantia nigra (pars reticulata) project to
- motor nucleus of the thalamus
- superior colliculus of the midbrain
How does the Striatum connect within the basal ganglia
-Projects to globus pallidus, both internal (direct) and external (indirect) segments (striatopallidal
pathway)
-Projects to substantia nigra, both reticulata (direct) and compacta (Striatonigral)
-Reciprocally connected with substantia nigra, pars compacta (nigrostriatal and
striatonigral pathways)
How does the Subthalamic nucleus (glutamatergic) make connections within the basal ganlgia
- Receives input from the motor and premotor cortices
- Reciprocally connected with the globus pallidus, external segment
- • Projects to globus pallidus, internal segment and substantia nigra, pars reticulata
How does the substantia nigra make connections within the basal ganglia
Receives from and projects to the striatum
Striatonigral and Nigrostriatal
General Functional significance of the basal ganglia
- involved in the regulation of movement: through direct and indirect connections with the cerebral cortex, the basal ganglia influence descending motor systems (e.g. corticospinal and corticobulbar tracts)
- involved in habit learning and skill acquistion
- forms the major component of the extrapyramidal system: however there are extensive interconnections and cooperation between the extrapyramidal and the pyramidal system n the control of movement
- involved in the control of eye movements and the memory of orientation in space
- contributes to cognition
- related to limbic functions
Dysfunctions of the basal ganglia
- disorders of the basal ganglia are usually a disruption of transmitter metabolism
- abnormal movements are commonly caused by a release of the system from inhibition
symptoms of basal ganglia disfunction
-involuntary movements:
*tremor at rest
*athetosis
*chorea
*ballism
*dystonia
-akinesia and bradykinesia
changes in posture and muscle tone
-muscle rigidity
Parkinson’s Disease (Paralysis agitans)
- degeneration of dopaminergic cells in SNc
- tremor at rest, rigidity, bradykinesia
Huntington’s Disease
- degeneration of cholinergic and GABAergic neurons in the striatum
- inherited; mutations in chromosome 4 causes numerous CAG repeats (encodes for glutamine)
-choreas, athetosis, dystonia
Tardive dyskinesia
- results from long-term use of antipsychotic agents, which block DA transmission
- involuntary movements especially of the tongue and face
Hemiballismus
- lesion of the subthalamic nucleus
- violent “ball-throwing” movements of contralateral arm
Similarities between cerebellum and Basal Ganglia
- no direct output to the spinal cord
- connections with the brainstem
- projections via thalamus to cortex
Differences between the cerebellum and the basal ganglia
- cerebellum has direct input from the spinal cord, and the basal ganglia has no input from the spinal cord
- cerebellum has INDIRECT input from the cortex, and basal ganglia has DIRECT input from the cortex
- cerebellar output is excitatory and basal ganglia output is inhibitory
- cerebellum coordinates the execution of movements and compares them with intended movements, the basal ganglia PLANS and executes complex motor strategies: amplitude and velocity of movement
-Cerebellar lesion=ipsilateral symptoms
and
basal ganglia lesion=often contralateral but sometime can be bilateral
-cerebellar lesions cause ataxia, impaired balance, and intentional tremor,
and
basal ganglia lesions cause too much or too little movements, and tremor at rest
