Basal Ganglia

Question 1

two basic functions of the basal ganglia

Answer 1

initiation of desired movement

suppress unwanted movement

Question 2

what are the major structures of the basal ganglia (nuclei)?

Answer 2

• striatum (largest)- contains caudate nucleus, nucleus accumbens, putamen
• external/internal globus pallidus
• subthalamic nucleus
• substantia nigra (compact and reticular)

Question 3

what makes up the so called lenticular nucleus of the basal ganglia, so called that because apparently it looked like a lens?

Answer 3

putamen (of striatum)

internal/ external segments of globus pallidus

Question 4

what are the parts of the basal ganglia striatum, and what separates two parts?

Answer 4

caudate nucleus and putamen separated by internal capsule (large fiber bundle)- histologically similar, but named differently because of separation (putamen way bigger)

and nucleus accumbens

Question 5

source of dopaminergic input to the basal ganglia?

Answer 5

nucleus accumbens

Question 6

situated just medial to the putamen in the basal ganglia are the __

Answer 6

internal and external segments of the globus pallidus

Question 7

parts of diencephalon. (hint- they all end the same)

Answer 7

thalamus, hypothalamus, subthalamic nuclei, epithalamus (all end in thalamus!)

Question 8

what are the two parts of the substantia nigra and what do they contain, respectively?

Answer 8

compact substantia nigra- dopaminergic neurons

reticular substantia nigra- GABA neurons

Question 9

the reticular substantia nigra and the internal segment of the globus pallidus have this in common (think output)

Answer 9

major population of GABA neurons

Question 10

this part of the substantia nigra projects back to the striatum, forming the nigrostriatal pathway, which influences basal ganglia function. What is _?

Answer 10

compact substantia nigra- dopaminergic neurons

Question 11

the location of the basal ganglia structures relative to the motor cortex?

Answer 11

subcortical (very close)

Question 12

what embryonic brain structure does the basal ganglia stem from?

Answer 12

telencephalon

Question 13

wide areas of motor cortex project into __ of the basal ganglia, which will then project down to ___, which activate neurons that project to the thalamus

Answer 13

motor cortex project to striatum (putamen and caudate nucleus), which projects to either internal or external globus pallidus

Question 14

both basal ganglia pathways (following projection to either internal or external globus pallidus) that are initiated at motor cortex level will utilize two ___ neurons in series to create ___, which will excite a third neuron

Answer 14

both basal ganglia pathways (following projection to either internal or external globus pallidus) that are initiated at motor cortex level will utilize two [GABA] neurons in series to create DISINHIBITION, which will excite a third neuron

Question 15

the basal ganglia is found lateral to a very large…?

Answer 15

lateral ventricle

Question 16

internal capsule

Answer 16

very large bundle of axons (V shaped on both sides or X shaped if put together) that carries all information into/out of all areas of cortex

separates caudate nucleus (bulging into lateral ventricle) from larger putamen

Question 17

location of thalamus in relation to internal capsule

Answer 17

just medial of the posterior limb of internal capsule

thalamus is destination of all outflow of basal ganglia

Question 18

all outflow of basal ganglia goes where?

Answer 18

thalamus (motor nuclei here)

Question 19

after receiving input from either the internal or external segments of the globus pallidus in the basal nuclei, the thalamus will project back where?

Answer 19

thalamus projects back to upper motor neurons (where input originated) and motor cortex, influence neurons there

Question 20

compare/contrast the direct and indirect pathways of basal ganglia projection

Answer 20

both begin with cortical excitation to GABA neurons in putamen and caudate nucleus (both in striatum)

direct pathway- GABA neurons of putamen project directly to/inhibit internal (medial) segment of globus pallidus where second population of GABA neurons is. Net excitatory effect- disinhibit thalamic neurons, promoting cortical excitation/ initiation of desired movement

indirect pathway- GABA neurons in putamen project to/inhibit external (lateral) globus pallidus, where second population of GABA neurons is. Net effect- excite neurons in subthalamic nucleus, which excite GABA neurons in internal (medial) globus pallidus, but this SUPRESSES thalamic activity, suppressing unwanted movement

Question 21

match:

• direct and indirect pathway of basal ganglia
• disinhibition and suppression of thalamic neurons
• suppress unwanted movement and initiation of desired movement

Answer 21

direct pathway- disinhibition of thalamic neurons- initiate desire movement
indirect pathway- suppression of thalamic neurons- suppress unwanted movement

Question 22

input from the basal ganglia is contralateral or ipsilateral?

Answer 22

contralateral. all basal ganglia connections are within same hemisphere, but corticospinal tract crosses–> contralateral input

Question 23

how does dopaminergic input from compact substantia nigra affect direct basal ganglia pathway

Answer 23

axons form nigrostriatal pathway- excites direct basal ganglia pathway by binding excitatory D1 receptors on GABA neurons in putamen

basically increases activity of putamen GABA neurons on GABA neurons in internal globus pallidus (inhibits these neurons more, net effect excitatory input to thalamus to initiate desired movement)

Question 24

how does dopaminergic input from compact substantia nigra affect indirect basal ganglia pathway?

Answer 24

inhibits indirect pathway by binding D2 [inhibitory] receptors on GABA neurons
(indirect pathway suppresses unwanted movement)

Question 25

what manifests from lesion (unilateral or bilateral) in direct pathway of basal ganglia?

Answer 25

Parkinson’s disease- underactive motor cortex. trouble initiating movement, generating velocity and amplitude

usually from degeneration of dopaminergic neurons in compact substantia nigra. Renders D1 receptors (on GABA neurons in putamen) inactive

indirect pathway will continue to suppress motor cortex

Question 26

patient presents with cogwheel or lead pipe rigidity of upper limbs, stooped posture and expressionless gait, writes tiny letters and doesn’t blink as frequently, and demonstrates pill rolling. what is it?

Answer 26

Parkinson’s

Question 27

indirect pathway of basal ganglia begins with excitatory motor cortex input to the GABA neurons in the striatum (mostly putamen). These project to external globus pallidus, inhibiting GABA neurons there.
external globus pallidus projects where?

Answer 27

external globus pallidus projects to subthalamic nucleus, so inhibition of external globus pallidus creates DISINHIBITION of subthalamic nucleus

Question 28

what does disinhibition of the subthalamic nucleus (by the indirect basal ganglia) allow to happen?

Answer 28

subthalamic nucleus is major population of glutamate (excitatory) neurons
these neurons project to GABA neurons in internal segment of globus pallidus–> suppresses thalamic cortical activity and motor cortex activity–> suppress unwanted movements

Question 29

the indirect pathway of the basal ganglia is enhanced by these neurons in the striatum

Answer 29

cholinergic neurons

contributes to suppression of unwanted movement by enhancing indirect pathway neurons (GABA neurons)

Question 30

degeneration of indirect basal ganglia pathway GABA neurons causes? (hint- mostly affects caudate nucleus neurons, rather than putamen)

Answer 30

Huntington’s

Question 31

cause and manifestation of Huntington’s

Answer 31

(usually bilateral) degeneration of indirect basal ganglia pathway
overactive motor cortex
involuntary movements- chorea (jerky movements superimposed on voluntary movements) and athetosis (slow, writhing limb movements)

autosomal dominant (chromosome 4)

Question 32

define chorea and athetosis

what neurodegenerative disease are they symptoms of

Answer 32

chorea- jerky involuntary movements, superimposed on voluntary movements
athetosis- slow, writhing limb movements (fingers and hands most obvious)
signs of Huntington’s

Question 33

what is the effect of an isolated lacunar stroke

Answer 33

lacunar stroke- lesions just one subthalamic nucleus
usually in hypertensive patient

overactive motor cortex by disabling subthalamic nucleus in indirect basal ganglia pathway

displays hemiballismus (violent ballistic movements of a limb), always contralateral to lesion (basal ganglia influences contralateral limbs)

Question 34

hemiballismus

Answer 34

violent ballistic movements of a limb

can occur from lacunar stroke (lesions just one subthalamic nucleus, affects indirect pathway, causing overactive motor cortex)