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CNS > Unit 6 - Basal Ganglia > Flashcards

Unit 6 - Basal Ganglia Flashcards

1
Q

Overview of co-ordination of movement

A
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2
Q

Function of basal ganglia

A

Role in shaping and refining movement

Facilitates a single target movement, while broadly inihibiting competing motor activities

Helps monitor and co-ordinate slow, sustained contractions related to posture and support

Inhibits muscle tone throughout the body

no direct connection to spinal cord (APs via pre and primary motor cortex)

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3
Q

What motor neurons are influenced by basal ganglia

A

Basal ganglia controlling motor output - influences firing of gamma motor neurons

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4
Q

Where are the medium spiny neurons found

A

In the striatum (input to BG)

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5
Q

What is the output of BG

A

Pallidum

  • Globus pallidus - internal
  • Substantia nigra pars reticulata (SNpr)
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6
Q

Other structures associated with BG

A

Subthalamic nucleus

Substantia nigra pars compacta - SNpc

Globus pallidus - external

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7
Q

Where does the striatum NOT receive input from

A

Auditory and visual are the only cortical areas not projecting to striatum

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8
Q

What is the corticostriatal pathway responsible for

A

Cortical input from most areas - particularly association areas

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9
Q

Caudate input from

A

Multimodal association area and motor areas that control the eye

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10
Q

Putamen input from

A

Somatic sensory cortices and premotor and motor cortex and visual and auditory association area

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11
Q

Overview of input to BG

A
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12
Q

What are the major output nuclei of BG

A

GPi

SNpr (from CAUDATE) - control of head movement

They connect to superior colliculus to control movement

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13
Q

What structure is responsible for head movement

A

Caudate → SNpr

Via superior colliculus

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14
Q

How do BG influence motor cortex

A

Via inhibition of tonic firing of thalamic nuclei

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15
Q

Inhibitory

A

GABA

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16
Q

Excitatory

A

Glutamate

17
Q

Overview of output

A
18
Q

What is the circuit within the basal ganglia

A

Cortex → striatum → GPi → Thalamus → cortex

Direct pathway

Thalamus is tonically active but under inhibitory control by BG

19
Q

Overall function of basal ganglia

A

BRAKE

Under normal circumstances the basal ganglia acts as an inhibitory control on the thalamus

slow down firing of the thalamus onto the premotor cortex so that movement is smooth, not jerky

Thalamus is tonically active and if left alone would continuously activate the cortex to carry out movement

Basal ganglia inhibits this tonic activity and dampen down activity to frontal cortex

20
Q

How is movement carried out via the direct pathway

A

Activate caudate and putamen

Inhibit BG output (specifically GPi)

Disinhibit thalamus

Enhanced signals to motor cortex

21
Q

What is the direct pathway responsible for

A

Excitatory signal that facilitates target movement

Cortex → striatum → GPi/SNpr → thalamus → cortex

DA (via D1 receptors) from SNpc facilitates direct pathway

22
Q

Where is the motor plan created

How is it executed

A

Created in pre motor cortex

This will excite and send glutaminergic projections to the caudate and putamen, activating neurons within this C/P brain region

Medium spiny neurons - gabanergic (inhibitory) - send more inhibiton to Gpi

Hence inhibit output of Gpi

Less APs to thalamus

Thalamus is free to fire, sending glutaminergic proejctions to the frontal cortex - MOVEMENT

23
Q

What does dopamine act on

A

D1 receptors (located on medium spiny neurons)

  • facilitates activity

Enhances activity of medium spiny neurons

24
Q

What facilitates the direct pathway

A

DA via D1 receptors

25
Q

What is the indirect pathway

A

Responsible for broad inhibition of other motor activity

Cortex → striatum → subthalamic nucleus → GPi/SNpr → thalamus → cortex

Overall enhances inhibitory output from BG

Dopamine (via D2 receptors) INHIBITS the indirect pathway

Balance between direct & indirect pathway - facilitates expression of intended movement

26
Q

Nature of neurons within GPi

A

Inhibitory

Dampen down activity in thalamus

Hence activation of GPi - we’ll increase inhibitory tone of thalamus and hence decrease movement

27
Q

How to increase activity of GPi

A

INDIRECT

Stimulation of caudate & putamen will in turn activate medium spinae neurons which act to inhibit Gpi segment

We decrease firing on internal segment - less inhibitory tone

Less inhibitory tone onto the subthalamic nucleus

As a result the subthalamic nucleus is DISINHIBITED - able to fire - sends GLUTAMINERGIC projections to internal segment

We stimulate the internal segment, inhibiting movement

28
Q

Relationship between direct and indirect pathway

A

Activate direct pathway

Disinhibit the thalamus, allow it to fire, carry out to movement

In order to inhibit competing motor movements - activate indirect pathway

Increase activity of internal segment, more gabergic tone, inhibiton of thalamus, less firing to frontal cortex and less movement

Dopamine modulates activity within striatum

Via 2 types of receptors

29
Q

MCQ

A
30
Q

How does dopamine modulate BG circuits

A

Substantia nigra pars compacta

Dopamine facilitates direct pathway (D1 - increase cAMP) and inhibits indirect pathway (D2 - decrease cAMP)

Modulates cortical input to striatum

Overall facilitates movement

31
Q

Difference in 2 types of MSNs

A

MSN that project to the direct pathway are those that contain D1 receptors

MSN that project to the INDIRECT pathway contain D2 receptors

32
Q

What effect does Parkinsons have on control of movement

A

Loss of nigrostriatal dopamine pathway

Results in imbalance within basal ganglia

Circuitry - increased inhibitory outflow of BG

Movement is difficult to initiate and difficult to terminate - hypokinetic

Dyskinesia - decreased voluntary and increased involuntary movement

Resting tremor

Diminished facial expressions

Reduced arm swing

33
Q

Overview of Parkinsons Disease

A
34
Q

Pathophysiology of Huntington’s Disease

A

Autosomal dominant - hyperkinetic

Degeneration of medium spiny neurons - in particular those that project to the GPe - the INDIRECT pathway associated with basal ganglia

GPe is overactive - decreased output from STN - inhibitory output is reduced - motor cortex is activated by inappropriate, jerky movements

35
Q

mHtt and neuroinflammation

A
36
Q

Overview of Huntingtons Disease

A

Less tonic inhibition

Thalamus fires more readily

37
Q

MCQ

A

CNS (36 decks)

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