Basal Ganglia

Question 1

Location of the nucleus accumbens

Answer 1

In the most rostral and ventral part of the corpus striatum

Question 2

Corpus striatum

Answer 2

=basal ganglia

basal nuclei

Caudate

Putamen

Globus pallidus

Question 3

Relationship between the basal ganglia and the amygdala

Answer 3

Similar embryological derivation but functionally different.

The nucleus accumbens also has close connections with the amygdala, thus providing an important link between the BG and the limbic system

Question 4

Answer 4

Question 5

Answer 5

Question 6

Nucleus accumbens function

Answer 6

Associated with reward and gratification.

It is an important site of action for addictive substances

Question 7

Lentiform nucleus=

Answer 7

Putamen and GP

Point lies against the genu of the internal capsule.

Question 8

With what is the putamen most closely associated on phylogenetic, connectional and functional grounds?

Answer 8

Caudate nucleus rather than GP

Question 9

Paleostriatum

Answer 9

=GP

Question 10

Neostriatum=

Answer 10

Caudate and putamen

Question 11

Striatum=

Answer 11

Putamen and caudate nucleus

Question 12

Answer 12

Question 13

What separates the putamen from the globus pallidus?

Answer 13

A thin lamina of nerve fibres- the lateral medullary lamina

Question 14

Layers of white matter and grey matter from insula to caudate

Answer 14

Insula

Extreme capsule

Clasutra

External capsule

Putamen

Lateral medullary lamina

GP

Question 15

Relationship of the caudate to the putamen

Answer 15

At the head of caudate it is almost completely separated from the putamen by the internal capsule

At its rostral extermity, it is continuous with the putamen through and beneath the anterior limb of the internal capsule.

At this anterior level, the most ventral and medial part of the striatum constitutes the nucleus accumbens.

Question 16

Relationship of the caudate nucleus to the ventricular system

Answer 16

Head of the caudate causes a prominent bulge in the lateral wall of the anterior horn of the lateral ventricle.

It also passes posteriorly, gradually tapering and following the curvature of the ventricle, descending into the temporal lobe where it lies in the roof of the inferior horn

Question 17

Anatomical arrangement of the globus pallidus

Answer 17

External

Medial medullary lamina

Internal

Question 18

Relationship of the GPi

Answer 18

Shares many similarities in cytology and connections with the pars reticulata of the SN in the midbrain.

Although the two are separated by the internal capsule, these are best regarded as a single entity in the functional sense.

Question 19

Substantita innominata

Answer 19

Refers to the basal part of the rostral forebrain that lies beneath the corpus stritatum.

This complex region contains several groups of neurones, one of them being the nucleus basalis of meynert that project widely to the cerebral cortex and utilise ACh as their neurotransmitter.

These neurones undergo degeneration in Alzheimer’s

Question 20

What are the three basal ganglia loops of the striatum

Answer 20

Putamen- voluntary motor

Caudate- volunatry eye movements, cognitive-executive

Ventral striatum- emotional affective

Question 21

Input portion of the basal ganglia

Answer 21

Striatum

Question 22

What are the three principle sources of striatal afferents?

Answer 22

Cerebral cortex

Thalamus

SN

Question 23

Corticostriatal fibres

Answer 23

Origin from widespread regions of the cerebral cortex, predominantly on the ipsilateral lobe.

Motor project mainly to the putamen

More anterior regions of the frontal lobe and other association cortices project mainly to the caudate.

Corticostriatal fibres are excitatory and use glutamic acid as their neurotransmitter

Question 24

Thalamostriatal projection

Answer 24

Come from intralaminar nuclei (centromedian and parafascicular nuclei) of the ipsilateral thalamus

Question 25

Nigrostriatal projection

Answer 25

From the pars compacta of the ipsilateral SN of the midbrain tegmentum Dopaminergic which has both excitatory and inhibitory effects.

Question 26

Pars compacta

Answer 26

Portion of the SN which contains the dark pigment neuromelanin which is a by-product of dopamine synthesis

Question 27

Whence does the nucleus accumbens receive its afferents?

Answer 27

From the ventral tegmental area, which lies medial to the SN. This projection is part of the mesolimbic pathway which also provides dopaminergic innervation of the amygdala.

Question 28

Efferent projections of the striatum

Answer 28

Directed principally to the two segments of the globus pallidus and pars reticulata of the SN (striatopallidal and striagonigral fibres)

Question 29

Striatal efferent output

Answer 29

Inhibitory upon pallidal and nigral neurones with GABAergic neurotransmission. A number of neuropeptides are colocalised in these efferent neurones. The cells that porject to the internal segment of the globus pallidus and SN contain substance P and dynoprhin. The projection to the external segment of the GP contains met-enkephalin

Question 30

Ouput portion of the basal ganglia?

Answer 30

The internal pallidum and pars reticulata of the substantia nigra as they are the origin of the majority of basal ganglia efferent fibres

Question 31

Pallidal afferents

Answer 31

Arise principally from the striatum and subthalamic nucleus. Both utilise GABA as thier primary transmitter. Coefferents projecting to GPe contain enkephalin while those projecting to GPi contain substance P and dynorphin

Question 32

Subthalamopallidal projection

Answer 32

Originates in the STN of the caudal diencephalon Located beneath the thalamus against the medial border of the internal capsule. These fibres pass laterally through the internal capsule contributing to the subthalamic fasciculus, terminating in both segments of the globus pallidus

Question 33

Answer 33

Question 34

Answer 34

Question 35

Answer 35

Question 36

Answer 36

Question 37

Answer 37

Question 38

Output of subthalamopallidal pathway

Answer 38

Excitatory to pallidal neurones, using glutamic acid as its transmitter. The STN also sends similar fibres to the pars reticulata of the substantia nigra.

Question 39

GPe efferents

Answer 39

Principally on the STN Pallidosubthalamic fibres pass medially through the internal capsule to the subthalamic fasciculus. This projection is inhibitory, using GABA as its transmitter

Question 40

GPi efferents

Answer 40

Along with the pars reticulata of the SN projects primarily to the thalamus with a smaller projection to the brainstem tegmentum. These output neurones are all inhibitory and utilise GABA as their transmitter

Question 41

What are the two possible routes of palladothalamic fibres?

Answer 41

Ansa lenticularis (around the anterior marigin of the internal capsule) Lenticular fasciulus (through the internal capsule). These fibres course medially and then loop dorsally and latearlly as the thalamic fasciculus. In following this trajectory, the pallidothalamic fibres circumnavigate a cellular region of the subthalamus known as the zona incerta, which lies between the thalamus and the STN

Question 42

What are the main targets of pallidothalamic fibres?

Answer 42

Ventral anterior and ventral lateral thaalamic nuclei which project glutamatergic fibres to the motor regions of the frontal lobe A smaller contingent of medial pallidal efferent fibres pass caudally to termiante in the brainstem tegmentum in the nucleus tegmenti pedunculopontinus which lies at the boundary between the midbrain and the pons, near the lateral edge of the superior cerebellar peduncle. This area has been termed the mesencephalic locomotor region.

Question 43

Somatotropic organisaiton of striatal projections to the GP and SN

Answer 43

Pallidal neuroens are primarily involved in limb movements. Nigral cells control the axial muscualture including the EOM.

Question 44

Role of BG in movement

Answer 44

Cortical efferents to striatum causing ecxitation. Direct pathway- directly inihbiting internal pallidal or pars reticulata neurones. Causing disinhibition of target neurones and subsequent excitation of motor cortical neuroens. Indirect pathway- via the STN. Efferents terminate int he GPe inducing inihibtion of GPe inhibitory neurones disinhibiting the subthalamic neuroens. The resultant increase in discharge of STN causes activation of internal pallidal and nigral neuroens inihibting thalamic and cortical cells. Inhibiting unwanted movmenents.

Question 45

Draw the basal ganglia motor control pathway

Answer 45

Question 46

Action of dopamine on BG

Answer 46

Exerts an exciatory influence on the direct pathway i.e. disinihbiting movement. Inhibitory effect on indirect pathway.

Question 47

The ‘direct’ striatal output pathway: Projects to the external globus pallidus (gpe) Uses glutamate as its neurotransmitter Contains the neuropeptide enkephalin Inhibits the subthalamic nucleus Originates from ‘medium spiny’ striatal neurones

Answer 47

The ‘direct’ striatal output pathway originates from medium spiny neurones and projects to the internal globus pallidus (GPi). It uses GABA as its neurotransmitter and also contains dynorphin/substance P.