Corpus Striatum

Question 1

what makes up the corpus striatum?

Answer 1

-caudate nucleus
-lentiform nucleus

Question 2

What is the striatum

Answer 2

-caudate and putamen

Question 3

what is the pallidum?

Answer 3

-globus pallidus

Question 4

what makes up the lentiform nucleus

Answer 4

-putamen and globus pallidus

Question 5

what makes up the basal ganglia?

Answer 5

-corpus striatum
-subthalamic nucleus
-substantia nigra

Question 6

describe the theories of the basal ganglia involved in initiation and sequencing of movements

Answer 6

–based on phenomenology of basal ganglia disorders, such as PD and HD -patients with PD have difficulty in initiating movement

-PD patients may be able to initiate a complex sequence of movements, but as the sequence proceeds movements gradually diminish in amplitude – e.g. micrographia and festinating gait

Question 7

describe the role of the basal ganglia in motor control

Answer 7

-Basal ganglia are required to set up the correct motor programs to execute complex simultaneous and sequential movements. Basal ganglia act on a readout of existing sensorimotor cortical activity to direct premotor cortical areas to select the correct parameters of motor programs required for a subsequent motor action

-In normal non-human primates neuron firing in putamen or globus pallidus is more strongly related to the second component of a composite motor response than to the first

Question 8

What is the scaling of movement hypothesis

Answer 8

–Convergence of disinhibitory (via direct pathway) and inhibitory (via indirect pathway) influences on key neurons of motor thalamus allows “scaling of movement”.

-balance between these two influences determines whether movement will be increased or decreased (e.g. in amplitude or speed)

Question 9

describe the focused selection hypothesis

Answer 9

–Focused selection and inhibition of competing motor programs.
Focusing of motor activity occurs via direct pathway allowing activation of “prime mover muscles” and via indirect pathway
inhibiting activation of “antagonist muscles”

Question 10

what are the striatal afferents

Answer 10

-cortex, thalamus, substantia nigra
-dopamine excitatory and inhibitory

Question 11

describe the corticostriate fibres

Answer 11

-all excitatory
-originate from all 4 lobes - mostly frontal and parietal

Question 12

describe the topographically organised parts of the striatum

Answer 12

-Somatosensory and motor – putamen
-Limbic (parahippocampal and cingulate) – nucleus accumbens
-Association cortical areas – caudate nucleus

Question 13

describe the thalamostriate fibres

Answer 13

-all excitatory
-originate from the intralaminar nuclei mostly centromedian nucleus (of thalamus)

Question 14

describe the nigrostriate fibres

Answer 14

-Substantia nigra pars compacta – putamen
-Ventral tegmental area – nucleus accumbens

Question 15

What are the striatal efferents

Answer 15

-globus pallidus, substantia nigra

Question 16

describe the striatopallidal fibres

Answer 16

-all inhibitory
-internal and external globus pallidus

Question 17

describe the striatonigral fibres

Answer 17

-All inhibitory
-Substantia nigra pars compacta
-Substantia nigra pars reticulata

Question 18

describe the pallidum connections

Answer 18

-pallidal efferents:
-Thalamus, pedunculopontine nucleus, habenula, superior
colliclus
- All inhibitory (GABA)

-pallidothalamic fibres:
-Internal globus pallidus:
–Ventral lateral nucleus – premotor cortex
–Ventral anterior nucleus – premotor (frontal eye field)
–Mediodorsal nucleus – prefrontal and cingulate

-External globus pallidus
–Subthalamic nucleus – internal globus pallidus

Question 19

what does activating the direct pathway do?

Answer 19

Stimulates the motor cortex to facilitate movements

Question 20

what does activation of the indirect pathway do?

Answer 20

reduced the motor cortex activity to suppress movement

Question 21

what do the direct and indirect pathways act as?

Answer 21

-acts as a balance
-In other words, the movements that need to be made are made and the movements that shouldn’t, are prevented.

Question 22

describe the role of dopamine in the direct pathway

Answer 22

-dopamine has excitatory effect on the neostriatum
-Through these receptors dopamine helps activate the direct pathway to facilitate movement.
-i.e., dopamine helps make movements the need to be made

Question 23

describe the role of dopamine in the indirect pathway

Answer 23

-In the indirect pathway dopamine binds to D2 receptors in the neostriatum.

-This is an inhibitory connection.

-So, through these receptors, dopamine helps inhibit the indirect pathway.

-As such, inhibition of the indirect pathway by dopamine also acts to facilitate movement

Question 24

What is the direct loop of the basal ganglia

Answer 24

(internal pallidum to thalamus always active to inhibit using GABA if not inhibited)

cerebral cortex —- (glutamate to excite) —->
striatum—- (GABA and SP to disinhibit) —->
internal pallidum —- (Turn off inhibition of GABA) —->
thalamus —- (glutamate to excite) —->
cerebral cortex (again)

Question 25

What is the indirect loop of the basal ganglia

Answer 25

(internal pallidum to thalamus always active to inhibit using GABA if not inhibited)
and
(from external pallidum to subthalamic nucleus neurons always active to inhibit using GABA if not influenced)

cerebral cortex —- (glutamate to excite) —>
striatum —- (GABA to disinhibit) —->
external pallidum —- (removes inhibition of subthalamic nucleus) —->
subthalamic nucleus —-(glutamate to excite) –>
internal pallidum —-(decrease activity in motor thalamus using GABA) —->
Thalamus —- (decrease glutaminergic neurons) —->
cerebral cortex