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38 Cards in this Set

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What is the BASAL GANGLIA?
A group of nuclei in the brain interconnected with the cerebral cortex, thalamus and brainstem. Mammalian basal ganglia are associated with a variety of functions: motor control, cognition, emotions and learning.
MADE UP OF: CAUDATE, PUTAMEN, GLOBUS PALLIDUS
What three things does it interconnect?

What 5 functions is it associated with?

What 3 things is it made up of?
OVERVIEW: A) What parts of the brain control movement?
B) What part controls Movement modulation?
A)
1) Cortical areas
parietal, premotor, supplemental motor area
2) Descending tracts
pyramidal system
B)
Cerebellum and Basal Ganglia
Where does movement that requires significant planning start?
It starts in the parietal cortex, POSTERIOR to the postcentral gyrus.
You first see activity in the PREMOTOR CORTEX and then in the MOTOR CORTEX
A)In the INITIATION OF MOVEMENT, in what two places does activity of neurons take place and when?

B) When do you get the greatest amount of activity?
A)In all but the simplest movements, you get activity in the neurons of the basal ganglia and cerebellum (in lat hemisphere) even BEFORE the movement starts and BEFORE you get activity in the primary cortex.

B) You get the most activity when the movement is novel.
Why do we want to learn about the basal ganglia?
1) Want to understand basic movements
2) Want to understand circuitry of normal movement
3)und signs of pathological process
4)know current info
5) how patients with deficiencies respond to meds
What is the main hypothesis regarding basal ganglia activity?
"The model proposes that behaviors generated from the cerebral cortex are focused and facilitated by projections through the basal ganglia. These behaviors vary from species to species. Furthermore, the basal ganglia function to suppress other conflicting activities while reinforcing ongoing behaviors.”
KEY CONCCEPTS:
A) What is the basal ganglia?
B) What is the major INPUT/ OUTPUT of the basal ganglia? Where do its fibers go?
C)How does direct pathway facilitate movement?
D)Indirect?
E) What loop modulates ecpression of movements, behavior, and cognition?
F) What might lesions in basal ganglia cause?
A)a group of interconnected forebrain, diencephalon, and midbrain nuclei lying deep in the subcortical white matter, consisting of the striatum (caudate nucleus, putamen), globus pallidus, subthalamic nucleus and substantia nigra

B)Striatum (caudate and putamen) with widespread cortical input/ OUTPUT: Globus pallidus interna to frontal cortex via thalamic relay nuclei

C)Direct: releasing upper motor neurons form tonic inhibition

D)Indirect: modulates disinhibitory pathway of direct pathway

E) cortico-striato-pallidal-thalamo-cortical loop

F) Disorders in moevement, behavior, and cognition
A) What is EXTRAPYRAMIDAL?
B) What are the 4 nuclei of the BASAL GANGLIA?
a) It denote the basal ganglia as discussed in order to distinguished this from area of primary cortex and the pyramidal motor circuits. This from areas of primary and motor cortex function.

B)
1) Striatum (caudate, putamen)‏
2) globus pallidus (lateral and medial divisions)‏
3) substantia nigra (pars reticulata and pars compacta)‏
4) subthalamic nucleus (pars compacta and pars reticulata)
What can be found in the DORSAL and VENTRAL parts of the STRIATUM?
1) Dorsal: Caudate and putamen
2) Ventral: Nucleus accumbens
What are the AFFERENT and EFFERENT projections to and from the LATERAL GLOBUS PALLIDUS?
AFFERENT: input form striatum
EFFERENT: projects fot he subthalamic nucleus, inhibiting it
In efferent projections of LATERAL globus pallidus, where does SUBTHALAMIC NUCLEUS project to?
Medical globus pallidus
Where does the MEDIAL GLOBUS PALLIDUS receive AFFERENT projections?
Afferent:
EXCITATORY input: subthalamic nucleus
INHIBITORY input: (GABA) input from the striatum
Where does the MEDIAL globus pallidus send EFFERENT projections?
Efferent:
1) Lenticular fasciculus - arises from the medial globus pallidus and courses across the internal capsule to the VA-VL

2)Ansa lenticularis - arises from the medial globus pallidus and loops below the internal capsule to the VA-VL

3)Where the lenticular fasciculus and the ansa lenticularis join to enter the VA-VL they are termed the thalamic fasciculus
Where do teh VA-VL of the thalamus project to?
They project to the MOTOR CORTEX (precentral gyrus) and PREMOTOR CORTEX (in front of precentral gyrus- - all involved in planning of movement)

Why most of the basal ganglia have INDIRECT effect on movement by affectin OUTPUT of cerebral cortex
A) What does the SUBSTANTIA NIGRA do?

B) What happens if you get degeneration of this?
A) It provides DOPAMINE to the STRIATUM

B) Parkinson's Disease
What are 4 functions of the STRIATUM?
1) Gets input from all areas of the cortex: glutamate and dopamine from SN

2) Striosome and matrix portions: input form limbic

3) Most are medium spiny neurosn: GABAergic and quiet unless have movement or stimulation

4) Some inhibitory interneurons: NO
What is the structure of the STRIATUM?
Convergence
1) Cortex
widespread input

2) Striatum
75 million neurons

3) Globus pallidus
0.7 million neurons
What is the CELLULAR organization of the striatum?
Medium Spiny Neuron (MSN)‏
1) Input:
Glutamate
Dopamine
2) Output:
GABA
A) Where does GLOBUS PALLIDUS PARSINTERNA receive inhibitory input from?


B) What is the major OUTPUT of the GPi/ SNr?
A) GABAergic/ striatum

B) Major output form GPi/ SNr is inhibitory to the thalamus

*NOTE: GPi and SNr are functionally the SAME
What is the CELLULAR organization of the GPi/ SNr?
1) Segregation:
Parallel circuits
Paucity of interneurons
Electrophysiology

and/or

2)Integration:
Convergent signals
What are FUNCTIONAL CONSIDERATIONS related to CONNECTIVITY?
1) Scaling:
Temporal interplay between the direct and indirect pathway
amplitude
velocity
comparator function

2)Focusing:
cortical selection of movements
center-surround mechanism
indirect pathway terminates broadly
direct pathway terminates narrowly
What are the functions of the GPi/ SNr?
1) Parkinson's Disease: rigid slow movements, trouble initiating movements, tremors

2) abnormal movements at rest: chorea, athetosis, dystonia
What is the DISINHIBITORY CIRCUIT?
*The permissive role of the basal ganglia in the initiation of movement is perhaps most clearly demonstrated by the observations of eye movement control.
A) What are the 2 pathways through the basal ganglia?

B) What is the DIRECT pathway involved in?
A) Direct and Indirect

B) Involved in facilitation movement and indirect inhibition of it as well
Describe the DIRECT and INDIRECT pathways
The striatal projections from the median spiny neurons of the caudate and putamen send out projections that terminate in another pair of nuclei and basal ganglia complex termed the globus pallidus and the substantia nigra pars reticulata nuclei are in turn the major sources of output from the basal ganglia. t the globus pallidus and subsection either partial allowed to have some output functions and in fact are actually part of the globus pallidus. The striatal projections to these think that resemble the cortical stride. Pathways and that they terminate in rostrocaudal bands locations of which very with implication of their sources in the stria a striking feature of the projections from them up needing spiny neurons to the globus pallidus and such an option I is the degree of convergence onto palatal particular to sell the be fared neurons of the internal globus pallidus and the substantia nigra together to price the major pathways at length the basal ganglia with upper motor neuron’s in the cortex and brain stem

the subdivision between the substantia nigra parser take a lot of and globus pallidus internal segment are superficial and are actually one functional unit. However, there are differences in their projections intact the substantia nigra parser take a lot a project directly to the superior clitoris by analogy be globus pallidus internal segment projects directly to the ventral anterior and ventral lateral thalamic nuclear complex. The upper motor neuron’s in the Spirit comatose command I movements without an intervening delay in the thalamus. However the particular to ask phones also project to the thalamus where they contact really neurons that project to the frontal eye fields of the premotor cortex.
Describe: Projections within the Basal Ganglia: Direct Pathway
The projections from the medium spiny neurons of the caudate and putamen to the internal segment of the globus pallidus and the substantia nigra pars reticulata are part of a direct pathway and serve to release the upper motor neuron’s from tonic inhibition. in the direct pathway, transiently inhibitory projections from the caudate and putamen project into tonically active inhibitory neurons in the internal segment of the globus pallidus. The neurons from the internal segment of the globus pallidus intern project to the ventral anterior and anterolateral complex of the thalamus. Transient excitatory inputs to the caudate and putamen from the cortex and substantial right or are also shown as is the transiently excitatory input from the thalamus back to the cortex

Let us imagine a scenario to help us illustrate how the basal ganglia facilitate movement. Note that the globus pallidus internal segment is tonically active inhibiting output from the thalamus to the frontal cortex. This tonic in addition serves as a way to prevent undesirable movements when they are not necessary. Imagine now the conscious act of raising and arm in order to push and elevator button. The cerebral cortex fires transiently excitatory input into the caudate and putamen. In addition to firing of axons to the upper and lower motor neuron units to raise the arm, a general program to release tonic in addition to allow the arm to move occurs. This transient excitation of the caudate and putamen results and transient suppression of the tonic in addition. Also it worked is the substantia nigra pars compact to wear dopamine helps facilitate this movement. This is not the only action of dopamine however.
Describe: Projections within the Basal Ganglia: Indirect Pathway
The direct pathway which facilitates movement is modulated by an additional pathway termed the indirect pathway. This circuit acts as a brake on the direct pathway. Let us revisit the scenario again where we are sending a program from the cortex to move the arm to push the elevator button. The excitatory cortical input to the indirect pathways activates medium spiny neurons of the striatum This transient inhibitory discharge, inhibits the tonically active GABAergic inhibitory output of the external globus pallidus. While it sends inhibitory output directly to the internal GP, the main effect is to transiently inhibit the tonic inhibition of the STN. This in turn transiently allows STN excitatory glutamatergic activity to the internal GP. This toactivated by the signals from the cortex, the medium spiny neurons discharge and inhibit the tonically active GABAergic neurons in the external globus pallidus. As a result the subthalamic cells become more active and by virtue of their excitatory glutamatergic synapses with the cells of the internal globus pallidus and reticulata, they increase the inhibitory outflow of the basal ganglia
A) What are the different types of neurons in the striatum?

B) What are the patchwork of neurotransmitters?

C) What happens with the constituitive firing activity?
A)
1)Mesium spiny neurons
2)Cholinergic interneurons
3)Enkehalinergic interneurons
4)Projection neurons all contain GABA

B) -

C)
1)It's an intrinsic pacemaker of membranes
2)Input affects firing rate and type
What is the PROJECTION PATTERN?
The projection pattern is highly topographic
1) Sensorimotor areas - central & caudal putamen
2) Frontal eye fields - body of caudate
3) Association areas - caudate and rostral putamen
4) Limbic areas - ventral striatum and olfactory tubercle
*3) What are the AFFERENT and EFFERENT nuclei/ projections of the SNr?
Afferent:
Caudate and Putamen

Efferent:
The substantia nigra pars reticulata projects to the mediodorsal thalamic nucleus and the brain stem reticular formation and superior colliculus
Therefore, it can feed back on the cerebral cortex or may influence motor function more directly through tectospinal or reticulospinal tracts
What are functional observations regarding the function of teh basal ganglia?
The predominant theories for function of the basal ganglia include a role in establishment of motor patterns (probably stored in the cerebral cortex) and then a role in accessing these motor programs
What are 3 characteristics of Parkinson's Disease?
1) Akinesia, resting tremor, rigidity, delayed postural corrections

2) Caused by degeneration of the substantia nigra pars compacta (loss of dopamine to the striatum)

3) The net result is less tonic dopamine effect on the output of the striatum
a) Less excitation of the direct pathway and less inhibition of the indirect pathway
b) The net result is less excitatory feedback to the cerebral cortex from the VA/VL of the thalamus
How would you treat PD?
1) Treatment
Dopamine replacement by use of precursors (L-dopa) or stimulators
May use anticholinergic medicines
2) Pallidotomy
Carefully placed lesions of the medial globus pallidus may reduce akinesia by reducing inhibitory pressure on the VA-VL, thereby facilitating cortical movement
3) DBS
STN
GPi
What is Hyperkinesias?
A)Chorea:
1) Quick, jerky, random involuntary movements
2) Can be caused by striatal degeneration (such as Huntington's disease)
3) May be caused by excess of dopamine function
What are Other hyperkinesias?
B)Athetosis:
Slow writing, snakelike movements caused by many lesions, primarily of the striatum
C) Dystonia
Twisting of the limbs, trunk or neck due to structural or functional abnormality of the basal ganglia
D)Hemiballism
Due to lesion
s of the subthalamic nucleus (usually strokes)‏
A)What are the Basal ganglia loops and Nonmotor functions?

B)What are teh 4 Parallel Circuits?

C)What are the segrated functions?
A)

B)
Parallel Circuits
Cortical regions
Striatal regions
Pallidal nucleus
Thalamic nucleus

C)

Traditionally, the basal ganglia have been regarded as motor structure that regulate the inition of movemnet. However,the basal ganliga ar also central strucures in antomical cicuits or loops that ar involve din mdulationg non-motor aspects of behavior. These parallel loops orginate in broad regions of the cortex, engage specific subdivisions of the basal galnglia and thalamus, and ultimately terminate in areas of the frontal lobe outside the primary motor and premotor cortices. These non motor loops include a prefreontal loop involving the dorsolateral prefrontal cortex an dpart of the caudate. A limbic loopinvolving the cingulate cortex and the ventral striatum, and an oculomotor loop that modulates the activity of the frontal eye fields. The anatomical smilarity of these loops to the traditional motor loop suggests that the non-motor regulatory functions of the basal ganalgia may be gnerally the same as what the basal ganglia do in regulating the initiation of movement. For example, the prefrontal loop may regulate the initiation and termination of cognitive processes such as planning, working memory, and attention. By the same token, the limbic loop may regulate emotional behavior and motivation. This is important because we deal with diseases and treatments that potentially alter these nonmotor loops and their manifestation of cognitive and emotional deterioration can be seen in HD and PD.
What is the VENTRAL STRIATAL SYSTEM?

A) Where is it located?

B) What does it consist of?

C) Where do AFFERENTS arise?
A) Located ventral to the striatum

B) Nucleus accumbens and ol' factory tubercle

C) AFFERENTS arise from limbic cortex including the hippocampus, amygdala, piriform cortex, cingulate cortex and entorhinal cortex
What is the ventral pallidum? What does it also regulate?
1) This projects to the mediodorsal nucleus of the thalamus which in turn projects to the prefrontal and anterior cingulate cortex
2) This is also involved in regulating head and eye movements (attention) and visceral reactions (emotions)‏