BASAL GANGLIA

Question 1

Striatum

Answer 1

AKA CORPUS STRIATUM

(caudate nucleus + putamen), located in telencephalon, utilize GABA and acetyl choline

Question 2

Globus pallidus

Answer 2

(external & internal), located in telencephalon, utilize GABA

Question 3

Subthalamic nucleus,

Answer 3

located in diencephalon, utilizes Glutamate

Question 4

Substantia nigra

Answer 4

(pars compacta [dopamine] & pars reticulata [GABA]), located in mesencephalon

Question 5

basal ganglia loops:

Answer 5

= Cortico-Basal ganglia
-Thalamo-Cortical loops
= two parallel pathways referred to as (1) direct and (2) indirect

Question 6

Basal ganglia nuclei:

Answer 6

• do not maintain direct connections with the spinal cord (input or output)
• have an input into extrapyramidal pathways (see fig. Above)
• work closely with supplementary motor cortex rather than premotor cortex
• by acting on supplementary cortex, basal ganglia indirectly modulate the function of pyramidal pathways

Question 7

Components of the basal ganglia

Answer 7

The basal ganglia consist of four major interconnected subcortical nuclei in the forebrain (1 & 2) and midbrain: (3 & 4)

1. Striatum (Caudate nucleus + putamen)
2. Globus pallidus [external (lateral) & internal (medial)] 3. Subthalamic nucleus
3. Substantia nigra (pars compacta & reticulata)

Question 8

Lenticular nucleus =

Answer 8

Putamen + Globus pallidus

Lenticular = lentil-shaped

Question 9

Functions of the basal ganglia

Answer 9

MODULATE CONTROL OF MVMTS
- INFLUENCES VOLUNTARY CONTROL AND EXTRAPYRAMIDAL PATHWAYS
§participate in control of voluntary movement, e.g. facilitate voluntary motor programs and suppress
unwanted motor programs
§modulate the functions of pyramidal and extrapyramidal pathways
§do not have direct connections with the spinal cord (input or output)
§receive major input from motor cortex and send their major output back to motor cortices via the thalamus (VL, VA subnuclei) (= Cortical-basal ganglia-(thalamo)cortical loop)
§Damage results in movement disorders (excessive involuntary movements, e.g. Huntington‘s disease, or reduced voluntary movement, e.g. Parkinson‘s disease)

Question 10

Topography of Striatum

Answer 10

§Caudate nucleus (c-shape) - body (1)
- head (2) - tail (3)
§Putamen (4)
§Internal & external pallidum (5)
The striatum is divided in caudate nucleus and putamen by the internal capsule.'
MOST IMPUT FROM FRONTAL LOBE

Question 11

Structure of caudate nucleus

Answer 11

• is located in the lateral wall of the lateral ventricle and bulges into this ventricle
• follows the lateral ventricle in a C-shaped course (posterior horn of lat. ventricle lacks caudate nucleus!) - is attached to the putamen with grey matter (cell) bridges
• has a big head in frontal lobe indicating that it gets most of its input from frontal lobe (motor cortex)

Question 12

Striatum (= dorsal striatum + ventral striatum)

Answer 12

tail of caudate is located in the temporal lobe & is small indicating that it gets less input from this lobe §anteriorly, the tail of caudate is almost continuous with the amygdala (in temporal lobe)
§Ventral parts of the caudate & putamen merge to form the nucleus accumbens (ventral striatum) §Only the dorsal striatum is part of the basal ganglia

Question 13

Basal ganglia (“defined as a functional unit”)

Answer 13

§The basal ganglia consist of four major interconnected subcortical nuclei in the forebrain
(cerebral hemispheres; STR, GPe, GPi), diencephalon (STN), and midbrain (SNc & SNr):
1. Striatum (STR = caudate nucleus + putamen)
2. Globus pallidus [external (lateral) = GPe; & internal (medial) = GPi] 3. Subthalamic nucleus (STN)
4. Substantia nigra (pars compacta = SNc; & pars reticulata = SNr)

Question 14

Note:

Answer 14

amygdala & claustrum are not part of the basal ganglia!!!

Question 15

Cortical-basal ganglia-(thalamo)cortical loop

Answer 15

is mostly simplified as represented by two parallel pathways: 1. direct pathway, 2. indirect pathway
§the striatum is the major recipient of inputs to the basal ganglia whereas the major output stations are considered the internal pallidum (GPi) and the pars reticularis of the substantia nigra (SNr)
§Direct & indirect pathways maintain a balance to achieve a smooth coordinated movement

Question 16

Cortical-basal ganglia-cortical loop (direct [fast] pathway)

GO Pathway ≈ accelerator of a car

Answer 16

In this pathway, all intrinsic connections of the basal ganglia are GABAergic and inhibitory
§Activation of the direct pathway disinhibits the thalamocortical tract, thereby increases thalamocortical activity to initiate & promote voluntary movements in accordance to cortical motor command
* INDIRECT AND DIRCET WORK TOGETHER TO GET SMOOTH, CO-ORDIANTED MOVEMENT.

Question 17

Cortical-basal ganglia-cortical loop (indirect pathway)

NOGO Pathway ≈ brake of a car

Answer 17

§In this pathway, the projection from subthalamic nucleus is the only excitatory (glutamatergic) intrinsic connection of the basal ganglia, all others are GABAergic and inhibitory
§The subthalamic nucleus acts as a brake of unwanted movements as it is disinhibited by GPe §indirect pathway inhibits thalamocortical neurons, thus suppresses unwanted motor plans
* SUPRESSES UNWANTED MOTOR PLANS

Question 18

Substantia nigra pars compacta (SNc)

Answer 18

modulates the cortical input into the striatum

§SNc maintains functional equilibrium of the direct and indirect pathways

Question 19

striatal neurones:

Answer 19

1) those that feed into direct pathway contain D1 dopamine receptors, whereas (2) those that project into the indirect pathway are regulated by D2 dopamine
receptor expressing cholinergic interneurons
(RECEPTORS THAT BIND TO DOPAMINE)
§Although their synaptic actions are different, the dopaminergic inputs to the two pathways lead to the same effect of both pathways, reducing inhibition of the thalamo-cortical neurons

Question 20

Cortical-basal ganglia-cortical loop (role of substantia nigra pars compacta)

Answer 20

D1: SNc activates medium spiny interneurons in the striatum. Thus the SNc acts to facilitate voluntary movements by promoting disinhibition of thalamocortical neurons
D2: SNc inhibits excitatory cholinergic neurons in the striatum. These interneurons normally excite the inhibitory medium spiny striatal interneurons. Therefore, the action of the SNc on the indirect pathway is to ultimately decrease tonic inhibition of the thalamus.

Question 21

Influence of SNc on the direct & indirect pathways

Answer 21

§SNc excites D1-receptor expressing neurons that facilitate voluntary movements initiated in the cortex (direct pathway)
§At the same time, SNc inhibts excitatory D2-receptor expressing cholinergic interneurons in the striatum (indirect pathway)
§No/less dopaminergic input, e.g. in Parkinson‘s disease leads to §reduced facilitation of voluntary movement (direct pathway) §increased suppression of unwanted motor plans (indirect pathway)