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Unit 14 > Subcortical Motor Control > Flashcards

Subcortical Motor Control Flashcards

1
Q

What embryological structure do the basal ganglia develop from?

A

The telencephalon

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2
Q

What embryological structure does the thalamus develop from?

A

The diencephalon

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3
Q

Identify the tectum on the image
What it’s its function?

A

Label 7
Forms the roof over the cerebral aqueduct, contains the superior and inferior colliculi responsible for reflexes to auditory and visual stimuli

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4
Q

Identify the tonsils of the cerebellum on this image.
What is their function?

A

label 5
Found underneath each hemisphere of the cerebellum
Helps coordinate voluntary movement of distal parts of the limbs/

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5
Q

Identify the midbrain tegmentum in the image.
What is its function?

A

label 2
Meaning hood, makes up the main body of the midbrain
Contains the red nucleus (motor coordination), the PAG (pain processing) and reticular formation.
Between the cerebral peduncles and the substantial nigra.

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6
Q

Identify the basilar pons and the pontime tegmentum
What is the differentiation between these structures?

A

label 3
Basilar pons is the ventral pons, bulbous body
The pontine tegmental is continuous with the midbrain tegmentum, contains the vestibular nuclei.

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7
Q

What is the body of the fornix?
Identify it on this image

A

label 1
Is a white matter axon tract, the main outflow tract from the hippocampus, part of the limbic system.
Found superiorly to the thalamus, loops round from the hippocampus ins a C shape.

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8
Q

What term is used to describe the main body of the thalamus?

A

The dorsal thalamus

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9
Q

Identify the hypothalamus on this image
What is its function?

A

label 2
Below the thalamus and above the pituitary gland
Regulation of autonomic functions and bodily processes through the production of hormones.

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10
Q

What is the gross anatomy of the optic chiasm and the optic tract?

A

Loacted at the base of the brain, just inferior to the hypothalamus
See green ring on image

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11
Q

Identify the mammillary bodies on the image.
What is their function?

A

Bilateral
Small protrusions of the inferior hypothalamus, form part of the limbic system.
See purple label

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12
Q

Where does the oculomotor nerve leave the brain stem?

A

The junction between the midbrain and the pons.

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13
Q

Complete the labels on this image

A

1 - body of fornix
Hypothalamus
Oculomotor nerve
Basilar pons
Medulla
4th ventricle
Cerebral aqueduct
Inferior colliculi
Superior colliculi.

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14
Q

Where do the basal ganglia recieve inputs from?

A

Inputs from almost the entire cerebral cortex to the striatum.
Also inputs from dopaminergic nuclei in the midbrain, mainly the substantial nigra pars compact to the striatum.

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15
Q

What are the main outputs from the basal ganglia?

A

Main outputs are through the GP as an intermediate, which projects to the thalamus, then back to the cortex.
(complete a circle)

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16
Q

How do the basal ganglia influence eye movements?

A

Through communication with the superior colliculus

The dorsal striatum projects to the substantial nigra pars reticulata, this is an inhibitory synapse.
This disinhibits the superior colliculi, by reducing activity at the inhibitory synapse between the SN pars reticulata and the superior colliculus.
This enables reflexes to occur.

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17
Q

What is meant by the dorsal striatum?

A

The combined term for the caudate and the putamen.

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18
Q

What are the two different types of synapse present in the basal ganglia circuitry?

A

Excitatory synapse = glutaminergic synapse
Inhibitory synapse = GABAergic synapse.

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19
Q

What is meant by transient and tonic activity of the basil ganglia?

A

Refers to the level of activity along their axonal projectsions
Can by transient - quick burst of action potentials
Can be tonic - continuous stream of action potentials.

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20
Q

What receptor determines the effect of Glutamate in the basal ganglia circuitry?

A

The AMPA glutamate receptor
Is an excitatory receptor
Is an ionotropic receptor - allows cations to enter the cytoplasmic space - results in depolarisation of the cell.

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21
Q

What receptors determines the effect of GABA in the basal ganglia circuitry?

A

GABA A(subscript) receptor
Is an inhibitory recepotr
Is an inotropic receptor - allows Cl- to enter the cytoplasmic space, causes hyperpolarisation of the cell.

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22
Q

What is the role of the direct pathway in the basal ganglia?

A

Reinforces cortical activity

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23
Q

What is the role of the indirect pathway in the basal ganglia?

A

Inhibits cortical activity of neighbouring areas of the cortex.

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24
Q

What is the role of the hyperdirect pathway of the basal ganglia?

A

Prevents unwanted movement in advance
Inhibit movement just before it happens.

Note this pathway bypasses the striatum so is not regulated by the substantial nigra pars compact.

25
Q

What structure regulates both the direct and indirect basal ganglia pathway?

A

The substantia nigra pars compacta.

26
Q

What is the direct pathway within the basal ganglia?

A

The cerebral cortex projects to the dorsal striatum, this is an excitatory glutaminergic synapse that results in depolarisation of the striatum.
Striatum then projects to the globus pallidus internal segment, this is an inhibitory GABAergic synapse resulting in hyperpolarisation of the GPi.
This decreases GPi activity resulting in disinhibition of the thalamus. (as GPi norm has inhibitory effect on thalamus from GABAergiv synapse)
This enables the thalamus to communicate to the cerebral cortex via Gglutamineric synapses, to reinforce cortical activity.

27
Q

What is the indirect pathway of the basal ganglia?

A

The cerebral cortex projects to the dorsal striatum, this is a GLutaminergic excitatory synapse that results in depolarisation of the striatum.
This increase activity along the striatums projections to the GPe, this is an inhibitory GABAergic synapse, therefore results in hyperpolarisation of the GPe.
This disinhibits the subthalamic nucleus (as GPe normally has axonal projections to form an inhibitory synapse with ST nucleus.
Subthalamic nucleus axonal projection from an excitatory Glutaminergic synapse with the GPi, GPi depolarises.
This increases activity along GPi projections to the thalamus, these projection are GABAergic inhibitory so hyperpolarisae the thalamus, reduce efferent communication with the cerebral cortex, this suppresses cortical activity.

28
Q

What is the hyperdirect pathway of the basal ganglia?

A

The cerebral cortex has axonal projections to the subthalamic nucleus, these projects form a Glutaminergic excitatory synapse that result in depolarisation of the subthalamic nucleus.
The subthalamic nucleus then inc activity along is axonal projections to the GPi, these projections form a Glutaminergic excitaroy synapse resulting in depolarisation of the GPi.
As a result increases activity along its projections to the thalamus, these projects are GABAergic inhibotry so reduce efferent communication of the thalamus with the cerebral cortex.
This prevents unwanted movement in advance.

29
Q

How does centre surround functional organisation apply to the basal ganglia pathway?

A

Within a given functional area (M1) the cortex is organised into CSFO.
This means when the activity of one region of cortex is reinforced through the direct pathway the activity of the surrounding cortical areas are inhibited by the indirect pathway.
Eg contract biceps, relax triceps.

30
Q

What is the basic functional idea of the basal ganglia for all region of the crotex?

A

A feedback system for cortical function ensuring correct cortical functioning - only one output, the desired one.

31
Q

What is the general anatomy of the basal ganglia circuits?

A

Cortical input
Influences activity of the striatum
Influences activity of the palladium
Influences activity of the thalamus.

32
Q

What is the anatomy of the prefrontal loop of the basal ganglia?

A

The dorsolateral prefrontal cortex has projectsion to influence activity of the anterior caudate>
This influences that activity of the GPi, SNpR, this influences the mediodorsal and ventral anterior nuclei in the thalamus.
This feeds back to the dorsolateral prefrontal cortex.

33
Q

What is the anatomy of the limbic loop of the basal ganglia?

A

The limbic system, including amygdala and hippocampus, influence activity of the ventral striatum (the nucleus accumbens), this influences the activity of the ventral palladium.
This influences the activity of the mediodorsal nucleus in the thalamus.
This alters communication with the anterior cingulate and orbitofrontal cortex.

34
Q

What is the genetic cause of Huntington’s disease?

A

Is an autosomal dominant condition
Inc in CAG repeats on the region of chromosome 4 encoding the Huntington protein.
Number of repeats shows but polymorphism above 40 is an Huntington mutation.

35
Q

How does the genetic change alter the physiology to cause huntingtons disease?

A

In CAG repeats - inc PolyQ domain -
1. cause short mRNA production - after translation this leads to protein aggregation 2. HTT mRNA is produced, undergoes translation but then undergoes proteolysis, also producing toxic shortened fragments.
This leads to malfunction vesciel transport along neurons and progressive neuronal death, primary affects the dorsal striatum.

36
Q

How does Huntingtons disease normally present?

A

Present in middle age
Loss of striatal and cortical tissue results in disproportionate loss of indirect pthawt circuits, leading to hyperkineasia.
Choeriform movements (irregular and involuntary movements).
Tend to also have mental deterioration, grimacing, difficulty concentrating, difficult in speech.

37
Q

How does Huntingtons disease present on an MRI?

A

Diffuse Enlargement of the ventricles due to loss of white and grey matter, allow pressure of CSF to expand ventricular space.
Atrophy of caudate nuclei.

38
Q

How does the repeat length relate to Huntington severity and risk factors?

A

Genetic risk factor - inherit repeat length from parents.
Inc CAG repeats above 40 causes huntingtons, in number of repeats decreases the age of onset.
European population tends to have a longer CAG repeats than other ethnicities - more at risk of condition.

39
Q

Why does huntingtons also have non motor symptoms?

A

The striatum has projections throughout the cortex - these are known as median spiny neurons.
These are all vulnerable to neuronal death, resulting in loss of white matter throughout the cortex.
The motor symptoms are simply the easiest to spot, test and diagnose.

40
Q

Concerning the direct and indirect pathway in the basal ganglia, explain how Huntington disease affects movement.

A

Huntingtons disease causes degenration of the striaum - disproportionately affects the indirect pathway, causes a shift where the direct pathway is the dominant circuit, meaning that inappropriate activation occurs, resulting in hyperkinesia due to loss of inhibition (from indirect pathway)

41
Q

How is the indirect pathway affected by huntingtons disease?

A

Cerebral cortex projects to the dorsal striatum.
The striatum is dengeneration in huntingtons disease.
Loss of projections from the striatum to the GPe, these would have been an inhibitory GABAergic synapse, loss of this means the GPe is more likey to be depolarised.
Increase activity along projections to the GPinternal segment (including indirectly via the subthalamic nucleus).
Results in increased inhibition of the GPi (GABAergic synapse), this reduced the tonic inhibition of the GPi on the thalamus.
Increases activity of the thalamus, resulting in involuntary movement.

42
Q

What are some proposed treatments for Huntingtons disease?

A

Use of anti-sense aligonucleotides and CRISP to alter genetics.
Suppress expression of CAG repeated.

43
Q

What are the key structural subdivision of the cerebellum?

A

The vermis - seperates the left and right hemispheres.
Flocculus and nodulus (midline) form the flooculonodular lobe - responsible for maintaining balance

44
Q

What are the three different functional division of the cerebellum?**

A

The vestibulocerebellum
The cerebrocerebellum
The spinocerebellum
These are all efferent pathways

45
Q

What are the peduncles of the cerebellum?

A

Contain the axon tracts that link the cerebellum and the rest of the brain
Superior, middle and inferior.

46
Q

What are the deep cerebellar nuclei?

A

Contain the output projection neurons of the cerebellum.

47
Q

What are the different input systems into the cerebellum?

A

Lower inputs from the vestibular system and the cerebellar system (Clarkes nucleus and the external cuneate nucleus). Both via the inferior cerebellar peduncle.

Higher inputs arrive from the frontal/parietal cortex CIA the pontine nuclei (middle cerebellar peduncle) or the red nucleus then inferior olive (inferior cerebellar peduncle).

48
Q

What is the role of the vestibulocerebellum?**

A

Receives inputs from the vestibular system, role in the unconscious vestibular ciruitry in order to regulate movements involving posture and equilibrium.
Includes the flocculus and the modulus.

49
Q

What are the two sites of cerebellar efferent projections?**

A

To the brainstem motor centres, or to the thalamus then the cerebral cortex motor system indirectly - the spinocerebellar
To the vestibulo nuclei to control the cestibulospinal reflexes - the vestibulocerebellum.

50
Q

What is the function of the cerebrocerebellum?**

A

Efferent pathway
Projections from the cerebellum to the VL nucleus in the thalamus to the frontal cortex, including the premotor area.

51
Q

What is the function of the spinocerebellum?**

A

Efferent pathway
Cerebellum cortex
Cerebellum deep nuclei (fastagial)
Projections via the inferior cerebellar peduncles
1. Brainstem motor nuclei including the reticular formation, then to LMN in the ventral horn of the spinal cord.
2. VL nucleus of the thalamus via superior cerebellar peduncles, to M1, then the corticospinal tract.

52
Q

What is the function of the vestibulocerebellum?**

A

Efferent projections from the cerebellum
1.Cerebellum (floculonodular lobe)
2. Deep cerebellar nuclei project to
3. Vestibular nuclei in the brainstem (project back and forth with the cerebellum) via inferior cerebellar peduncle
4. Control vestibulospinal reflexes via projections down the spinal cord, destination in the anterior white commisure and synpasis with a LMN in the ventral horn in the spinal cord
5. Control vestibulocular reflex via projection from the denate/interposed nuclei to the superior colliculi via the superior cerebellar peduncles and then oculomotor nuclei. (and other extra-ocular muscle nuclei)

53
Q

What is the function of the cerebellum?

A

Motor learning and control.
Associated with cognition and sophisticated cortical function.
Emotion.
Examples - divided attention, word comprehension, balance and posture.

54
Q

How does the cerebellum development compare to that of the cerebral cortex?

A

Development of cerebellum aligned with development of the prefrontal cortex
Mate sophisticated primates with larger prefrontal cortex tend to have a larger cerebellum.

55
Q

What are the three different ways that cerebellar diseases can present?

A

Cerebellar motor syndrome - ataxia, errors in metrics of vulntary movement and coordination
Vestibulocerebellum syndrome = periodic vertigo, dipolopia and sporadic eye movements
Schmahmann syndrome or cerebellar congitive/affective syndrome = language deficits, personality changes and poor executive functioning.

56
Q

What part of the cerebellum is responsible for balance?

A

The flocculonodular lobe

57
Q

What part of the brain is responsible for the sense of proprioception?

A

The anterior lobe of cerebellum- combines proprioception inputs with visual and auditory information to fine-tune body movement

58
Q

What is the posterior lobe of the cerebellum responsible for?

A

Co-ordination of movement
Influence the initiation, planning and co-ordination of movement and determine the next movement required based on constantly changing external stimuli and sense of proprioception.
Dentate nucleus - cerebrocerebellum

Unit 14 (17 decks)

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