Anatomy and Function of the Basal Ganglia

Question 1

The basal ganglia are a group of structures found … within the cerebral hemispheres. The structures generally included in the basal ganglia are the …, …, and … … in the cerebrum, the … nigra in the midbrain, and the … nucleus in the diencephalon.

Answer 1

The basal ganglia are a group of structures found deep within the cerebral hemispheres. The structures generally included in the basal ganglia are the caudate, putamen, and globus pallidus in the cerebrum, the substantia nigra in the midbrain, and the subthalamic nucleus in the diencephalon.

Question 2

Hierarchy of motor control

Answer 2

Question 3

The basal ganglia: the filter of the brain

• … control - filter all of the various movement options available
• Sitting within wider … network - wider set of interactions amongst the cortex, cerebellum, brainstem, spinal cord

Answer 3

• Motor control - filter all of the various movement options available
• Sitting within wider motor network - wider set of interactions amongst the cortex, cerebellum, brainstem, spinal cord

Question 4

Basal ganglia anatomy

label

Answer 4

• Caudate nucleus - most superior part of basal ganglia - head and tail
• Inferiorly - putamen - nucleus
• Behind putamen - medial edge - globus pallidus nucleus
• = Make up functional unit of basal ganglia
  
  • Behind globus pallidus - thalamus
  • Not technically part of basal ganglia

Question 5

Is the thalamus part of the basal ganglia?

Answer 5

not technically - sits behind

Question 6

Basal ganglia - cross section of brain

Answer 6

Question 7

where is the subthalamic nucleus located?

Answer 7

The subthalamic nucleus is a small collection of neurons situated ventral to the thalamus (i.e., below the thalamus)

Question 8

Where is the substantia nigra located?

Answer 8

The substantia nigra (SN) is a basal ganglia structure located in the midbrain that plays an important role in reward and movement. - below the subthalamic nucleus

Question 9

Terms - basal ganglia:

• Globus pallidus is split into pars externa and pars interna
• Pallidum = globus pallidus internal + external
• … nucleus = putamen + globus pallidus
• … striatum = caudate + putamen + pallidum
  
  • Divided by … CAPSULE: white matter of ascending and descending tracts
• Neostriatum = dorsal striatum (motor striatum) = caudate + putamen

Answer 9

• Globus pallidus is split into pars externa and pars interna
• Pallidum = globus pallidus internal + external
• Lentiform nucleus = putamen + globus pallidus
• Corpus striatum = caudate + putamen + pallidum
  
  • Divided by INTERNAL CAPSULE: white matter of ascending and descending tracts
• Neostriatum = dorsal striatum (motor striatum) = caudate + putamen

Question 10

Terms - basal ganglia:

• Globus pallidus is split into pars externa and pars interna
• Pallidum = globus pallidus internal + external
• Lentiform nucleus = … + … …
• Corpus striatum = … + … + …
  
  • Divided by INTERNAL CAPSULE: … matter of ascending and descending tracts
• Neostriatum = dorsal striatum (motor striatum) = caudate + putamen

Answer 10

• Globus pallidus is split into pars externa and pars interna
• Pallidum = globus pallidus internal + external
• Lentiform nucleus = putamen + globus pallidus
• Corpus striatum = caudate + putamen + pallidum
  
  • Divided by INTERNAL CAPSULE: white matter of ascending and descending tracts
• Neostriatum = dorsal striatum (motor striatum) = caudate + putamen

Question 11

Basal Ganglia - anatomy

Answer 11

Question 12

Which one is a T1 image? Which is T2? (Basal ganglia focus)

Answer 12

• T1 on left, T2 on right
• Different contrasts - clinical practice
• T1 left - white matter white
• T2 - white matter dark - useful for swelling, oedema, tumours
• BASAL GANGLIA IS GREY MATTER

Question 13

The basal ganglia are a group of … matter nuclei in the deep aspects of the brain that is interconnected with the cerebral cortex, … and brainstem.

Answer 13

The basal ganglia are a group of grey matter nuclei in the deep aspects of the brain that is interconnected with the cerebral cortex, thalami and brainstem.

Question 14

Basal ganglia: interface with cortex

• Inputs from cortex from … (caudate and putamen together) from that - into pallidum - (globus pallidus - internal and external segments)- from that the signals come to … - filtering occurred through basal ganglia
• … releases movement signals back out to cortex again
• Loop system - basal ganglia is performing filtering function - to more precise action plan in line with goals

Answer 14

• Inputs from cortex from striatum (caudate and putamen together) from that - into pallidum - (globus pallidus - internal and external segments)- from that the signals come to thalamus - filtering occurred through basal ganglia
• Thalamus releases movement signals back out to cortex again
• Loop system - basal ganglia is performing filtering function - to more precise action plan in line with goals

Question 15

Basal Ganglia loops

• Focus = motor loop, but there are others:
  
  • … loop = helping coordinate eye movements - light flash - move eyes towards stimulus - inputs from cortical regions - to basal ganglia - filtered - towards thalamas - back to cortex
  • … loop = inputs from lateral aspect of prefrontal cortex - high level cognitive functions, working memory and planning - hold plan in mind to coordinate actions through the day - prefrontal loop helps to engage in these and filter through basal ganglia
  • … loop = medial aspect of prefrontal cortex - relevant for dysfunctional behaviours - addiction. Anterior cingulate to more ventral aspects of striatum - loop strongly associated with things like reward processing and motivational behaviour - key loop involved in conditions such as addiction

Answer 15

• Focus = motor loop, but there are others:
  
  • Oculomotor loop = helping coordinate eye movements - light flash - move eyes towards stimulus - inputs from cortical regions - to basal ganglia - filtered - towards thalamas - back to cortex
  • Prefrontal loop = inputs from lateral aspect of prefrontal cortex - high level cognitive functions, working memory and planning - hold plan in mind to coordinate actions through the day - prefrontal loop helps to engage in these and filter through basal ganglia
  • Limbic loop = medial aspect of prefrontal cortex - relevant for dysfunctional behaviours - addiction. Anterior cingulate to more ventral aspects of striatum - loop strongly associated with things like reward processing and motivational behaviour - key loop involved in conditions such as addiction

Question 16

Basal Ganglia loops

Answer 16

Question 17

Motor loop: movement filter

• Example - make a plan to catch ball - narrow down options - sometimes alter actions … launching - send ball to another area - in this situation, stop original, reassess, re-…, new motor plan
• Processes become tricky and … in quite a number of conditions
• Important for … lives

Answer 17

• Example - make a plan to catch ball - narrow down options - sometimes alter actions after launching - send ball to another area - in this situation, stop original, reassess, re-engage, new motor plan
• Processes become tricky and dysfunctional in quite a number of conditions
• Important for everyday lives

Question 18

The Direct Pathway - Basal Ganglia

Answer 18

Question 19

The Direct Pathway - Basal Ganglia

• ‘Go’ pathway - Facilitates movement
• Pathway depends on neurotransmitter balance
• Glutamate - primary … NT
• GABA = primary … NT
  
  • 1) Plan comes from cortex - striatum - via glutamatergic … connection
  • 2) Striatum to Globus pallidus - (internal segment) via GABA … connection
  • 3) Internal segment to thalamus - output inhibitory (2 inhibitory - double inhibition - striatum is active - excitatory - sending AP to internal globus pallidus - because those AP use GABA - internal globus pallidus is inhibited - because inhbited by striatum -> link from internal to thalamus can no longer be exerted) overall the thalamus is not inhibited and becomes excited - sends a signal back to cortex (Excitatory)
  • Overall - … inhibition - direct pathway promotes movement

Answer 19

• ‘Go’ pathway - Facilitates movement
• Pathway depends on neurotransmitter balance
• Glutamate - primary excitatory NT
• GABA = primary inhibitory NT
  
  • 1) Plan comes from cortex - striatum - via glutamatergic excitatory connection
  • 2) Striatum to Globus pallidus - (internal segment) via GABA inhibitory connection
  • 3) Internal segment to thalamus - output inhibitory (2 inhibitory - double inhibition - striatum is active - excitatory - sending AP to internal globus pallidus - because those AP use GABA - internal globus pallidus is inhibited - because inhbited by striatum -> link from internal to thalamus can no longer be exerted) overall the thalamus is not inhibited and becomes excited - sends a signal back to cortex (Excitatory)
  • Overall - double inhibition - direct pathway promotes movement

Question 20

The Direct Pathway - Basal Ganglia

• ‘Go’ pathway - … movement
• Pathway depends on neurotransmitter balance
• Glutamate - primary excitatory NT
• GABA = primary inhibitory NT
  
  • 1) Plan comes from cortex - … - via glutamatergic excitatory connection
  • 2) … to … … - (internal segment) via GABA inhibitory connection
  • 3) Internal segment to thalamus - output inhibitory (2 inhibitory - double inhibition - striatum is active - excitatory - sending AP to internal globus pallidus - because those AP use GABA - internal globus pallidus is inhibited - because inhbited by striatum -> link from internal to thalamus can no longer be exerted) overall the thalamus is not inhibited and becomes excited - sends a signal back to cortex (Excitatory)
  • Overall - double inhibition - direct pathway … movement

Answer 20

• ‘Go’ pathway - Facilitates movement
• Pathway depends on neurotransmitter balance
• Glutamate - primary excitatory NT
• GABA = primary inhibitory NT
  
  • 1) Plan comes from cortex - striatum - via glutamatergic excitatory connection
  • 2) Striatum to Globus pallidus - (internal segment) via GABA inhibitory connection
  • 3) Internal segment to thalamus - output inhibitory (2 inhibitory - double inhibition - striatum is active - excitatory - sending AP to internal globus pallidus - because those AP use GABA - internal globus pallidus is inhibited - because inhbited by striatum -> link from internal to thalamus can no longer be exerted) overall the thalamus is not inhibited and becomes excited - sends a signal back to cortex (Excitatory)
  • Overall - double inhibition - direct pathway promotes movement

Question 21

The Indirect Pathway - Basal Ganglia

• … from Cortex to striatum - this synapses on to … globus pallidus (inhibitory using GABA) - output link from … to subthalamic nucleus is inhibitory also - double inhibition (Can’t exert inhibition over subthalamic nucleus) - subthalamic nucleus is exctited - synapse onto … globus pallidus - inhibitory to thalamus (goes down) - no influence to cortex = no …

Answer 21

• Excitatory from Cortex to striatum - this synapses on to external globus pallidus (inhibitory using GABA) - output link from external to subthalamic nucleus is inhibitory also - double inhibition (Can’t exert inhibition over subthalamic nucleus) - subthalamic nucleus is exctited - synapse onto internal globus pallidus - inhibitory to thalamus (goes down) - no influence to cortex = no movement

Question 22

The Indirect Pathway - Basal Ganglia

• Excitatory from Cortex to striatum - this synapses on to external globus pallidus (inhibitory using GABA) - output link from external to subthalamic nucleus is inhibitory also - … inhibition (Can’t exert inhibition over subthalamic nucleus) - subthalamic nucleus is exctited - synapse onto internal globus pallidus - inhibitory to … (goes down) - no influence to … = no …

Answer 22

• Excitatory from Cortex to striatum - this synapses on to external globus pallidus (inhibitory using GABA) - output link from external to subthalamic nucleus is inhibitory also - double inhibition (Can’t exert inhibition over subthalamic nucleus) - subthalamic nucleus is exctited - synapse onto internal globus pallidus - inhibitory to thalamus (goes down) - no influence to cortex = no movement

Question 23

The Hyperdirect Pathway - Basal Ganglia

• Rapidly stop action plan - Entirely … normal route to basal ganglia
• Straight to … nucleus via excitatory link - Rapidly activates STN
• STN activates Gpi - very high activity - inhibitory over thalamus - thalamus - no excitatory outflow to cortex - … movement
• Useful in … - about to cross - slam own brakes on = quickly

Answer 23

• Rapidly stop action plan - Entirely bypasses normal route to basal ganglia
• Straight to subthalamic nucleus via excitatory link - Rapidly activates STN
• STN activates Gpi - very high activity - inhibitory over thalamus - thalamus - no excitatory outflow to cortex - pause movement
• Useful in emergency - about to cross - slam own brakes on = quickly

Question 24

The Hyperdirect Pathway - Basal Ganglia

• Rapidly stop action plan - Entirely bypasses normal route to basal ganglia
• Straight to subthalamic nucleus via … link - Rapidly … STN
• STN activates Gpi - very high activity - … over thalamus - thalamus - no … outflow to cortex - … movement
• Useful in emergency - about to cross - slam own brakes on = quickly

Answer 24

• Rapidly stop action plan - Entirely bypasses normal route to basal ganglia
• Straight to subthalamic nucleus via excitatory link - Rapidly activates STN
• STN activates Gpi - very high activity - inhibitory over thalamus - thalamus - no excitatory outflow to cortex - pause movement
• Useful in emergency - about to cross - slam own brakes on = quickly

Question 25

_Pathways Summary (basal ganglia)_ * Cortex -\> striatum ... * Striatum outputs -\> ... * Thalamus -\> cortex ... * The ... of thalamus prevents movement * Reducing ... of thalamus facilitates movement

Answer 25

* Cortex -\> striatum excitatory * Striatum outputs -\> inhibitory * Thalamus -\> cortex excitatory * The inhibition of thalamus prevents movement * Reducing inhibition of thalamus facilitates movement

Question 26

_Pathways Summary (basal ganglia)_ * ... -\> striatum excitatory * Striatum outputs -\> inhibitory * Thalamus -\> ... excitatory * The inhibition of thalamus ... movement * Reducing inhibition of thalamus ... movement

Answer 26

* Cortex -\> striatum excitatory * Striatum outputs -\> inhibitory * Thalamus -\> cortex excitatory * The inhibition of thalamus prevents movement * Reducing inhibition of thalamus facilitates movement

Question 27

_Pathways Conundrum (basal ganglia)_ * How does striatum ‘know’ if a motor plan is to be promoted (... pathway) or prevented (... pathway?) * We have a lot of options, always changing, so movement plans are NOISY. How do the basal ganglia achieve their filter?

Answer 27

* How does striatum ‘know’ if a motor plan is to be promoted (direct pathway) or prevented (indirect pathway?) * We have a lot of options, always changing, so movement plans are NOISY. How do the basal ganglia achieve their filter? * The inputs from cortex in relation to your AP - cortex to striatum with **weights/flags** - actions may **override** - **one response much more active than other active**

Question 28

_Pathways Conundrum (basal ganglia) - transmitters_ * How does striatum ‘know’ if a motor plan is to be promoted (direct pathway) or prevented (indirect pathway?) * We have a lot of options, always changing, so movement plans are NOISY. How do the basal ganglia achieve their filter?

Answer 28

* 2 different populations of striatum neurons - direct / indirect entry for pathways * Medium spiny neurons - really big dendritic arbres - much bigger than cell bodies - large way - lots of spines * 2 types of spiny neurons - different dopamine receptors

Question 29

_Substantia nigra_ * Most inferior nucleus underneath subthalamic nucleus * Key region to release **...** to release to striatum * 1 issue wrong in ... disease

Answer 29

* Most inferior nucleus underneath subthalamic nucleus * Key region to release **dopamine** to release to striatum * 1 issue wrong in parkinson's disease

Question 30

What is this pointing to ?

Answer 30

it releases dopamine

Question 31

_Striatum neurons & dopamine_ * D1 type of receptor - direct pathway - ... effect on postsynaptic neuron - Receive ... * Indirect - D2 type - ... - dopamine from nigra - ... its activity

Answer 31

* D1 type of receptor - direct pathway - excitatory effect on postsynaptic neuron - Receive dopamine - AP generated - ramp up activity in direct pathway * Indirect - D2 type - inhibitory - dopamine from nigra - inhibits its activity

Question 33

_D1 vs D2 receptors_ * Of the two major classes of DA receptors, D1 and D2, it is generally accepted that D1receptors function in the ... pathway in the basal ganglia whereas the D2 receptors function in a parallel ... pathway. Thus, D1 receptor activation ... movement whereas D2 receptor activation ... movement.

Answer 33

Of the two major classes of DA receptors, D1 and D2, it is generally accepted that D1receptors function in the direct pathway in the basal ganglia whereas the D2 receptors function in a parallel indirect pathway. Thus, D1 receptor activation facilitates movement whereas D2 receptor activation inhibits movement.

Question 34

release of DA tips pathway towards ... of movement

Answer 34

promotion of movement

Question 35

_Striatum neurons and acetylcholine_ * Small population of interneurons within striatum (Interneurons - live within striatum - never project out) * Role of interneurons - tune up and modulate within area * ACH release - opposes effect of ... - increasing ACH - tips other way and balance towards more activity flow in indirect pathway - ... movement

Answer 35

* Small population of interneurons within striatum (Interneurons - live within striatum - never project out) * Role of interneurons - tune up and modulate within area * ACH release - opposes effect of **dopamine** - increasing ACH - tips other way and balance towards more activity flow in indirect - **preventing** movement

Question 36

_Pathway balance - basal ganglia:_ * The ‘balance’ of activity between the 2 medium spiny neuron populations determines the likelihood of movement taking place through the direct & indirect pathways * This balance is regulated by ...- favour direct, promote movement & ... - more indirect, inhibit movement * And influenced by the cortical inputs to the ...

Answer 36

* The ‘balance’ of activity between the 2 medium spiny neuron populations determines the likelihood of movement taking place through the direct & indirect pathways * This balance is regulated by dopamine- favour direct, promote movement & acetylcholine - more indirect, inhibit movement * And influenced by the cortical inputs to the striatum

Question 37

_Overview of pathway balance_

Answer 37