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Y2 - NMH > Cortical motor function, basal ganglia and cerebellum > Flashcards

Cortical motor function, basal ganglia and cerebellum Flashcards

1
Q

What are the 2 tiers of the hierarchical organisation of motor function and what is their generalised involvement in motor function?

A
  1. Higher orders - more complex tasks, planning and coordinating muscle activity
  2. Lower orders - less complex, execution of movement
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2
Q

Which muscles are brainstem motor nuclei responsible for?

A

Muscles of the head, neck and face

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3
Q

1) Which areas of the brain constitute extrapyramidal areas?
2) What determines pyramidal and extrapyramidal classifications?
2) What is the generalised function of these areas?

A

1)

  • Thalamus
  • Cerebellum

2)

  • Pyramidal = via the main corticospinal (lateral / medial) tracts
  • Extra-pyramidal = not via the corticospinal tracts

3)

  • Fine tune output of the motor cortex
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4
Q

Describe the anatomical location of the primary motor cortex (M1)

A
  • Precentral gyrus anterior to the central sulcus
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5
Q

Where in the hierarchy of motor control does the primary motor cortex fall?

A
  • Lower order - execution of movement
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6
Q

What is the function of the primary motor cortex in movement and how is it carried out?

A
  • Upper motor neurones descend from primary motor cortex and provide information to lower motor neurones in the brainstem and spinal cord - via alpha motor neurones in ventral horn for spinal cord
  • Information for precise, fine, voluntary motor output
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7
Q

How many layers are there in the neocortex?

A

6

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8
Q

What type of cells can we find in layer 5 of the neocortex of the primary motor cortex, and give one structural adaptation to their function

A
  • Pyramidal cells
  • Very large because they have to support axons that may be > 1m
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9
Q

Describe the somatotopic mapping of the motor homunculus in the primary motor cortex, with mention of the lower and upper limbs, the torso and the face

A
  • The homunculus is inverted
  • The lower limbs are mapped closer to the median / longitudinal fissure
  • The upper limbs are more lateral and low (medial)
  • The torso and face are evel more lateral / low
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10
Q

In regards to the somatotopic mapping of the motor homunculus in the primary somatotopic cortex and the perfusion fields of the cerebral arteries, describe the pathological consequences of stroke at the following sites:

1) Anterior cerebral artery
2) Middle cerebral artery
3) Posterior cerebral artery

A

1)

  • Anterior cerebral artery’s perfusion field is more medial and superficial / cortical
  • Stroke here would affect the structures closer to the median / longitudinal fissure so the lower limbs will be greatly affected

2)

  • Middle cerebral artery’s perfusion field is more deep / inferior, including sobcortical structures
  • Therefore stroke here would affect the lower parts of the primary motor cortex as well as subcortical structures such as the basal ganglia, causing pathology in regards the lower limbs and general motor function. Specifically, you would suffer hemiparesis and hemiplegia

3)

  • The posterior cerebral artery’s perfusion field located very posteriorly
  • Therefore it does not cover the primary motor cortical areas whatsoever which is very anterior (at precentral gyrus)
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11
Q

Describe the route of the descending motor pathways of the lateral and anterior corticospinal tracts and then say what the fibres eventually innervate

A
  • Both start at the primary motor cortex
  • Then descend past subcortical structures through the internal capsule (which bisects the basal ganglia) and then down to the brainstem
  • Descends through the cerebral peduncles at the midbrain
  • Descends through the transverse fibres at the pons
  • Descends to the pyramids of the medulla. At this point there is pyramidal decussation of the fibres of the lateral corticospinal tract (90-95%), however the fibres of the anterior corticospinal tract do not yet decussate (5-10%)
  • THEN EITHER..
  • After pyramidal decussation, the fibres travel via the lateral corticospinal tract in the spinal cord and then terminate to innervate the muscles in the distal parts of limbs
  • OR
  • For fibres that did not decussate here, they continue down along the anterior spinal tracts of the spinal cord and decussate at the appropriate level before terminating to innervate axial muscles (in the trunk and proximal parts of the limbs)
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12
Q

Outline the corticobulbar pathway and what the eventual innervation is

A
  • From primary motor cortex to motor nuclei of the brainstem - through the hypoglossal nucleus
  • Hypoglossal nucleus → hypoglossal nerve root fibres along brainstem and emerging to eventually innervate the muscles of the tongue such as the genioglossus / geniohyoid / intrinsic muscles
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13
Q

Describe the anatomical location of the premotor cortex

A
  • Frontal lobe anterior to the primary motor cortex
  • Note: ignore the red circle
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14
Q

1) Where in the hierarchy of motor function does the function of the premotor cortex fall?
2) Outline the motor function of the premotor cortex

A

1)

  • Higher order - executive function

2)

  • Executive function and control to regulate externally cued movement - intra- and extra-personal movement (i.e in relation to other body parts and in relation to the environment)
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15
Q

Describe the anatomical location of the supplementary motor area (SMA)

A
  • Frontal lobe anterior to the primary motor cortex, but medial
  • Note: ignore the red circle
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16
Q

1) Where in the hierarchy of motor control does the function of the supplementary motor area fall?
2) Outline the general function of the supplementary motor area

A

1)

  • Higher order - executive motor function

2)

  • Planning complex movements
  • Regulates internally driven movements such as planning the mechanics of speech
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17
Q

Define association cortices

A

Cortical areas that do not have direct impact on the activity of a different primary cortical area but do have indirect impacts

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18
Q

What are 2 motor association cortices and how do they impact motor function?

A
  1. Posterior parietal cortex - involved in 3D space perception to facilitate motor function
  2. Prefrontal cortex - involved in selection of appropriate movements for a particular course of action
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19
Q

Where are the following motor neurones found:

1) Upper motor neurones
2) Lower motor neurones

A

1)

  • Found in the primary motor cortex - corticospinal and corticobulbar

2)

  • Motor neurones of the ventral horn projecting to the musculature
20
Q

What are the 2 types of pathological signs of upper motor neurones dysfunction what causes one of them, and what are the precise signs within the subcategories (6 total)?

A
  1. Loss of function (negative signs):
  • Paresis = graded weakness of movements
  • Paralysis (plegia) = complete loss of muscle activity
  1. Increased abnormal motor function (positive signs) due to loss of inhibitory descending inputs (think HSBC acronym):
  • Hyperreflexia = exaggerated reflexes
  • Spasticity = increased muscle tone
  • Babinski’s sign
  • Clonus = abnormal oscillatory muscle contraction
21
Q

What are the 6 symptoms of lower motor neurone disease and where applicable, explain why these occur or how to measure them or both

A
  1. Weakness
  2. Hypotonia
  3. Hyporeflexia
  4. Muscle atrophy
  5. Fasciculations - damaged motor units produce spontaneous action potentials - resulting in a visible twitch
  6. Fibrillation - spontaneous twitching of individual muscle fibres - can be recorded by needle electromyography
22
Q

1) What is apraxia?
2) What are the 2 main common causes of apraxia and what are the areas affected?

A

1)

Disorder of skilled movement

2)

  • Stroke
  • Dementia
  • Affecting mostly the inferior parietal lobe (posterior parietal cortex) and also the frontal lobe including the premotor cortex and the supplementary motor area
  • Remember that the posterior parietal cortex is involved 3D visual perception so defect here impacts this
  • Remember also the motor function roles of the premotor cortex and SMA as motor association cortices
23
Q

What is another name for Motor Neurone Disease?

A

Amyotrophic Lateral Sclerosis (ALS)

24
Q

What causes motor neurone disease?

A

Many genetic causes

25
Q

What are the 6 upper motor neurone and 5 lower motor neurone signs indicative of motor neurone disease?

A

Upper - think HSBC but affecting the limbs and jaw and think of the mouth and swallowing

  1. Hyperreflexia of limbs and jaw
  2. Spasticity of limbs and tongue (increased muscle tone of limbs and jaw)
  3. Babinski’s sign
  4. Loss of dexterity
  5. Dysarthria
  6. Dysphagia

Lower

  1. Weakness
  2. Muscular atrophy
  3. Tongue fasciculations (twitch) and wasting
  4. Nasal speech
  5. Dysphagia
26
Q

What are the 8 component parts of the basal ganglia?

A
  1. Caudal Nucleus
  2. Lentiform Nucleus (putamen + external globus pallidus)
  3. Subthalamic Nucleus
  4. Substantia Nigra
  5. Ventral Pallidum
  6. Claustrum
  7. Nucleus Accumbens
  8. Nucleus basalis of Meynert
27
Q

What 2 components of the basal ganglia are known as the striatum collectively?

A
  • Caudal nucleus
  • Putamen
28
Q

What are the 2 parts making up the lentiform nucleus of the basal ganglia?

A
  1. Putamen
  2. External Globus Pallidus
29
Q

What is one of the main functions of the Nucleus Accumbens of the basal ganglia?

A
  • Involved in the limbic reward system
30
Q

1) Describe the anatomical location of the caudate nucleus of the basal ganglia in relation to the ventricular system
2) Describe the anatomical location of the putamen of the lentiform nucleus in relation to the caudate nucleus
3) Describe the anatomical location of the nucleus accumbens in relation to the caudate nucleus
4) What bisects the basal ganglia?

A

1)

  • Lateral to the walls of the anterior horns of the lateral ventricle

2)

  • Inferior and lateral to the caudate nucleus

3)

  • Further inferior to the putamen within the basal ganglia still though

4)

  • The internal capsule
31
Q

What is one of the main functions of the Nucleus Basalis of Meynert (part of the basal ganglia)?

A
  • Cholinergic transmission to the cortex involved in memory
32
Q

Give 3 functions of the basal ganglia including some examples where applicable

A
  1. Elaborating associated movements e.g. swinging arms while walking, matching facial expressions to emotions
  2. Moderating and coordinating movement
  3. Chronology of movement (performing movements in order)
33
Q

Where in the basal ganglia circuitry do the following diseases exert their pathology?

1) Parkinson’s
2) Huntington’s

A

1)

  • Nigrostriatal connectivity - i.e. in dopaminergic neurones connecting the substantia nigra to the striatum (caudate+lentiform nuclei)
  • Also in the subthalamic nucleus

2)

  • Within local circuitry of the striatum
34
Q

1) What causes the ballistic motor movements in Parkinson’s e.g. uncontrollable arm movement?
2) What causes the uncoordinated movement / the loss of associated movement in Parkinson’s disease?

A

1)

  • Defect in the subthalamic nucleus of the basal ganglia

2)

  • Neurodegeneration in the dopaminergic nigrostriatal neurone connectivity
35
Q

What external pathological sign is observable in the brain of a patient with Parkinson’s disease?

A
  • Pale substantia nigra - due to less neuromelanin accumulation (appear black) in dopaminergic neurones due to lack of these dopaminergic neurones that constitute the substantia nigra
36
Q

List and describe the 5 main motor signs indicative of Parkinson’s disease

A
  1. Bradykinesia - slow movement in basic movements and also micrographia (small writing)
  2. Akinesia - difficulty in initiating movement
  3. Hypomimic face - expressionless face due to difficulty in associated motor function established by basal ganglia
  4. Pill-rolling tremor - 4-7Hz, usually unilateral
  5. Rigidity - increased resistance to externally imposed joint movement
37
Q

What microscopic pathological sign can be detected in the brain of people with Parkinson’s disease and where?

A
  • Lewy Body pathology
  • In pigmented cells of the substantia nigra
38
Q

1) Describe the pathophysiology behind the cause of why you develop huntington’s disease
2) Under what condition are you likely to develop Huntington’s in later life?

A

1)

  • Unstable CAG repeats on chromosome 4 - encoding Huntingtin proteins which causes degeneration of the GABAergic inhibitory neurones in the striatum

2)

  • If >35 unstable CAG repeats
39
Q

5 clinical signs of Huntington’s disease?

A
  1. Choreic movements (jerky, involuntary)
  2. Speech impairment
  3. Difficulty swallowing
  4. Unsteady gait
  5. Cognitive decline including dementia in later life
40
Q

Where does the cerebellum sit and what dural fold covers it?

A
  • Sits in the posterior cranial fossa
  • Tentorium cerebelli dural fold covers it, keeping it in place
41
Q

Describe the anatomical location of the 4th ventricle in relation to the cerebellum

A

Inferior to it

42
Q

1) What are the 3 cerebellar peduncles and what are each of their individual functions?
2) What is an overall function of all of the cerebellar peduncles collectively?

A

1)

  1. Superior cerebellar peduncle - main output pathway from the cerebellum up to the basal ganglia and thalamus
  2. Middle cerebellar peduncle - transverse fibres that connnect the 2 halves of the cerebellum and transmit to pons
  3. Inferior cerebellar peduncle - input from the spinal cord to the spino-cerebellar tracts

2)

  • Keep the cerebellum in place on the back of the brainstem
43
Q

How does the laminar structure of the cerebellum differ to that of the neocortex?

A
  • 3 layers as opposed to 6 in the neocortex
  • Different cell types within the laminar layers
44
Q

How many layers are there to the laminar structure of the cerebellum - list and name them in order from outer to inner and mention what type of cells you find in each layer

A
  1. Molecular layer - not many neurones, more glial cells
  2. Piriform layer - many purkinje cells
  3. Granular layer - granule cells
45
Q

Outline the 2 routes for medullary-cerebellar communication in terms of the medulla and cerebellum and in terms of the layers of the cerebellar laminar structure and the cells involved

A

Either:

  1. Climbing fibres originate in the inferior olive of the rostral medulla and terminate in the molecular layer where the dendritic tree of the Purkinje cells are found - hence there is cellular communication here

Or:

  1. Mossy fibres project to the granular layer of the cerebellum where they communicate with granular cells and then parallel fibres from these granular cells project up and innervate the Purkinje cells
46
Q

List the 3 divisions of the cerebellum (note: not layers)

A
  1. Vestibulocerebellum
  2. Spinocerebellum
  3. Cerebrocerebellum
47
Q

1) What are the functions of the vestibulocerebellum?
2) What causes vestibulocerebellar syndrome and what are the signs?

A

1)

  • Gait
  • Posture
  • Equilibrium
  • Coordination of head and eye movements
  • Connections w/ superior colliculus

2)

  • Vestibulocerebellar syndrome - gait ataxia and tendency to fall

Y2 - NMH (12 decks)

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