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Year 2 Neuro > Session 5: Motor pathways: Cortical motor function, basal ganglia and cerebellum > Flashcards

Session 5: Motor pathways: Cortical motor function, basal ganglia and cerebellum Flashcards

1
Q

Describe the hierarchical organisation in motor pathways

A

higher order areas = involved in more complex tasks
(programme and decide on movements, coordinate muscle activity)
lower level of the hierarchy = perform lower level tasks (execution movements - no planning and coordination involved)

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2
Q

What function does the motor cortex play in context to other areas of the CNS?

A

receives info from other cortisol areas and sends them to the brain and thalamus

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3
Q

What function do the cerebellum and basal ganglia play in context to other areas of the CNS?

A

adjust the commands received from other parts of the motor parts of the motor control system
(fine tune instruction before they reach the spinal chord)

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4
Q

What function does the brainstem play in context to other areas of the CNS?

A

passes commands from the cortex to the spinal chord

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5
Q

Where is the motor cortex located?

A

it is the pre-central gyrus (anterior to the central sulcus)

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6
Q

Where do axons from the motor cortex project down into the spinal chord?

A

they supply innervation to the muscles of the body via alpha motor neurones in the ventral horn of the spinal chord

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7
Q

Where do brainstem motor nuclei do?

A

they are responsible for the muscles of the face, head and neck
(facial and accessory nerves)

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8
Q

What are the extrapyramidal areas of the brain?

A

cerebellum and thalamus - they fine tune the output of the motor cortex

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9
Q

What is the function of the motor cortex?

A

to control fine, discrete, precise voluntary movement

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10
Q

In the fifth layer of the neocortex, why are the pyramidal cells very large?

A

they have to support an axon that can be up to a metre long

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11
Q

In short, describe the basic layout of the sensory homunculus

A

it is inverted

  • the lower limb is near the medial/longitudinal fissure
  • the upper limb and torso are lower
  • the face is the lowest
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12
Q

What will be the consequences of a stroke in/lack of blood supply involving the middle cerebral artery?

A

causes problems int he upper limbs

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13
Q

what will be the consequences of strokes affecting the anterior cerebral artery?

A

will impact the lower limbs

(also supplies subcortical areas - basal ganglia) so complete hemiparesis or hemiplegia

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14
Q

Motor neurones from the primary cortex project down through the _____

A

subcortical structures/pathways

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15
Q

What is the internal capsule?

A

the pathway through the subcortical structures

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16
Q

Describe the pathway depending motor pathways up until the end of the brainstem

A 
internal capsule
cerebral peduncles (emerge here)
pons (can't be seen externally here)
re-emerge at the medulla as the pyramids
pyramidal decussation (90-95% of fibres cross over here at the base of the medulla)
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17
Q

Describe how the tracts form after the pyramidal decussation and their pathways

A
  • the fibres that decussated at the pyramids descend in the spinal chord as the lateral corticospinal tract
  • at the appropriate level, fibres synapse with the alpha motor neurones in the ventral horns of the spinal chord
  • the 5-10% that don’t cross over carry on down and form the anterior coricospical tract
  • the neurones will cross over at the appropriate spinal level
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18
Q

What do the nerves fibres of the anterior corticospinal tract supply?

A

the axial musculature (muscles of the trunk and head)

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19
Q

What structures does the corticobulbar pathway connect?/Where does it start from and go to?

A

connecting the primary motor cortex to the motor (hypoglossal) nuclei within the (medulla) brainstem

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20
Q

What is the hypoglossal nucleus?

Where is it located?

A

a motor nucleus

near the midline of the medulla

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21
Q

Where does the hypoglossal nerve emerge?

What does it innervate?

A

between the pyramids and the side of the medulla (the olives)
innervates the muscles of the tongue

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22
Q

What are the (medullary) pyramids?

A

(they are paired white matter structures of the brainstem’s medulla oblongata)
they contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts.

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23
Q

What is meant by the internal capsule?

A

subcortical structures
The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus.

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24
Q

Where do CN IV, V and VI emerge?

A

from the lateral medulla

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25
Q

Where is the premotor cortex situated and what is its function?

A

located anterior to the motor cortex

involved in the planning of movements - much more of an executive function

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26
Q

Where is the supplementary motor area located and what is its function?

A

located on the frontal lobe anterior to M1, medial

involved in planning complex movements and programming sequencing of movements e.g. mechanics of speech

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27
Q

What are the 2 speech areas of the of the supplementary motor area?

A

Wernicke’s (posterior) and Broca’s (inferior frontal) on the left hand side
the supplementary motor area is involved in the actual mechanics of speech

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28
Q

What are association cortices?

A

there is no direct correlation between activity in these areas and motor activity, but they do impact other areas that are involved in motor activity

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29
Q

Which of the association cortices of the brain contributes towards motor function?

A

posterior parietal cortex - 3D spatial perception

prefrontal cortex - involved in planning

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30
Q

What are the three parts of the motor cortex?

A

Primary Motor Cortex
Premotor Cortex
Supplementary Motor Area

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31
Q

What makes up the association cortex?

A

Frontal Cortex
Parietal Cortex
NOTE: this is not exactly part of the motor pathway but it influences the planning and execution of movements

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32
Q

Define lower motor neurone

A

motor neurone in the ventral horn

projects to musculature

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33
Q

Define upper motor neurone

A

neurones in the primary motor cortex

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34
Q

Define pyramidal

A

refers to the main corticospinal tract (i.e. lateral corticospinal tract)

35
Q

Define extrapyramidal

A

anything outside of the lateral corticolspinal tract (i.e. the basal ganglia and cerebellum)

36
Q

Describe the signs and symptoms that result when an upper motor neurone lesion occurs

A

loss of function (negative signs):

  • paresis
  • paralysis/plegia

Increased abnormal motor function (positive signs) (due to loss of inhibitory descending inputs):

  • spasticity
  • hyperflexia
  • clonus
  • babinski’s sign
37
Q

What is apraxia?
What part of the brain is it usually related to?
Where do lesions causing apraxia usually occur?
What condition/diseases can cause apraxia?

A

a disorder of skilled movement - not to do with muscle weakness, but with actually performing the movement.

usually related to problems of the parietal lobe (and frontal lobe)
lesions of the inferior parietal lobe and frontal lobe (premotor cortex and supplementary motor area)

any diseases of these areas can cause apraxia, most common causes = stroke and dementia

38
Q

Describe the signs and symptoms of lower motor neurone disease

A
  • Weakness
  • Hypotonia
  • Hypoflexia
  • Muscle atrophy (due to lack of innervation to the musculature)
  • Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
  • Fibrillations: spontaneous twitching of individual muscle fibres
39
Q

What is Motor Neurone Disease (MND)?

A
  • A disease of both upper and lower motor neurones
  • Progressive neurodegenerative disorder of the motor system
  • Spectrum of disorders with similar clinical presentations
40
Q

What is another name for Motor Neurone Disease (MND)?

A

Amyotrophic Lateral Sclerosis (ALS)

41
Q

What are the upper motor neuron signs in Motor Neurone Disease (MND)/ALS?

A
  • Increased muscle tone (spasticity of limbs and tongue)
  • Brisk limbs and jaw reflexes
  • Babinski’s sign
  • Loss of dexterity
  • Dysarthria
  • Dysphagia
42
Q

State the lower motor neuron signs in Motor Neurone Disease (MND)

A
  • Weakness
  • Muscle wasting
  • Tongue fasciculations and wasting
  • Nasal speech
  • Dysphagia
43
Q

What is the basal ganglia?

A

a group of (subcortical) structures/nuclei found deep within the cerebral hemispheres and the brainstem, that are responsible primarily for motor control, as well as other roles such as motor learning, executive functions and behaviors, and emotions.
Although there are a variety of nonmotor functions associated with the basal ganglia, they are best known for their role in facilitating movement.

The globus pallidus and substantia nigra are each made up of multiple nuclei.

Although the basal ganglia are a distinct part of the motor system, they appear to work with the pyramidal motor pathway—the path that conducts signals for action directly along nerve tracts that descend from the cerebral cortex to the motor neurons that activate skeletal muscles. The basal ganglia refine action signals from the cortex, thereby ensuring that an appropriate motor plan is communicated to the muscles. Unlike the pyramidal pathway, the basal ganglia process information indirectly in a set of loops, whereby they receive input from the cortex and return it to the cortex via the thalamus. In that way the basal ganglia modify the timing and amount of activity that leaves the cortex and travels down the pyramidal pathway, amplifying activity that leads to a positive outcome and suppressing activity that leads to a deleterious outcome in a particular situation.

44
Q

What are the structures of the basal ganglia?

A
  • caudate
  • putamen
  • globus pallidus
  • substantia nigra
  • subthalamic nucleus
  • Ventral pallidum
  • Claustrum
  • Nucleus accumbens
  • Nucleus basalis of Meynert
45
Q

What is meant by the striatum?

A

caudate and putamen (+external globes pallidus)
OR
caudate and lentiform nucleus

46
Q

What is meant by the lentiform nucleus?

A

putamen +external globes pallidus

47
Q

What is meant by the lentiform nucleus?

A

putamen +external globus pallidus

48
Q

What 2 important motor disorders arise as a result of problems in the basal ganglia?

A

Parkinson’s

Huntington’s

49
Q

What is unusual about the location of the substantial nigra?

A

only competent of the basal ganglia that is not with the rest of the cortex in the subcortical areas
(in the midbrain)

50
Q

Where is the caudate nucleus located?

A

the lateral wall of the anterior horn of the lateral ventricle
(a more medial competent of the BG)

51
Q

Where is the putamen located?

A

more laterally and slightly inferior to ventricles

52
Q

Where is the nucleus accumbens located relative to the other structures making up the BG.

A

inferiorly

53
Q

Name the fibre pathway that bisects the BG

A

internal capsule (pathway through subcortical structures)

54
Q

State the functions of the basal ganglia

A
  • Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions)
  • Moderating and coordinating movement (suppressing unwanted movements)
  • execution of movements
55
Q

State the functions of the basal ganglia

A
  • Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions)
  • Moderating and coordinating movement (suppressing unwanted movements)
  • execution of movements
56
Q

Where is the circuitry of the basal ganglia damaged in Parkinson’s?

A

there is a breakdown in the nigrostriatal connectivity (connection from striatum to substantial nigra). Dopaminergic cells project to the striatum and are very important in initiation and planning of movement.

57
Q

Where is the circuitry of the basal ganglia damaged in Huntington’s?

A

affects neurones within the striatum, and affects local circuitry within the striatum.

58
Q

Where is the circuitry of the basal ganglia damaged in Ballism (uncontrolled movement of the arm)?

A

due to problems in the subthalamic area

59
Q

Describe the posture and walking of someone with Parkinson’s

A

slightly stooped

walking gait and shuffling in movement

60
Q

Describe the neuropathology of Parkinson’s

A

Loss of substantia nigra neurons and presence of Lewy body inclusions in some of the remaining neurons

neurodegeneration of the dopaminergic neurones
- These dopaminergic neurones originate in the substantia nigra and project to the striatum

at microscopic level, there is Lewy body pathology, which sit in the pigmented cells of the substantial nigra

61
Q

State the main motor signs of Parkinson’s

A

Bradykinesia:
• Slowness of (small) movements
• Micrographia (writing gets very small)

Hypomimic face:
• Expressionless

Akinesia:
• Difficulty in the initiation of movements because cannot initiate movements internally

Rigidity
Tremor at rest

62
Q

Describe the neuropathology of Huntington’s disease

A

Degeneration of GABAergic inhibitory neurons in the striatum (caudate then putamen)

63
Q

What type of disease is Huntington’s?

A

GENETIC DISEASE: Gene on chromosome 4 (codes for Huntingtin protein), autosomal dominant
• TRIPLET REPEAT PROBLEM: CAG repeat

64
Q

State the main motor signs of Huntington’s disease

A
  • Choreic movements (Chorea)
  • —-> Rapid jerky involuntary movements
  • —-> Hands and face affected first; then legs and rest of body
  • Speech impairment
  • Difficulty swallowing
  • Unsteady gait
  • Later stages, cognitive decline and dementia

(all due to uncontrolled motor movements)

65
Q

What is the fold of the dura called that covers the cerebellum?

A

tentorium cerebelli

66
Q

Where is the 4th ventricle, relative to the cerebellum?

A

just inferior to it

67
Q

Name the 3 main pathways to the cerebellum

A 
Cerebellar Peduncles (CP)
Three main fibre bundles that allow communication between the cerebellum and other regions of the CNS
  • The inferior cerebellar peduncle
  • The middle cerebellar peduncle
  • The superior cerebellar peduncle
68
Q

Describe the 3 main pathways of the cerebellum

A

The inferior cerebellar peduncle is input from the spinal cord to the spino-cerebellar tracts.

The middle cerebellar peduncle (largest) is transverse fibres that connect the two halves of the cerebellum.

The superior cerebellar peduncle is the main output pathway from the cerebellum going up to the basal ganglia and thalamus etc.

69
Q

What does ‘peduncle’ mean, and how does this relate to the cerebellar peduncles?

A

Peduncle is the name for a fibre tract, which also has a structural role.

In this case, the peduncles have a structural role to keep the cerebellum on the back of the brainstem.

70
Q

How does the cortex of the cerebellum differ from the neocortex?

A

3 layers, not 6

71
Q

Name the 3 layers of the cortex of the cerebellum and what types of cells are contained within these layers

A
  • outer-molecular layer (not many neurones, lots of glial cells)
  • piriform layer has lots of Purkinje cells
  • granular layer - there are granule cells (neuronal as well)
72
Q

Describe the afferent/input system of the cerebellum

A
  • Inferior olive (nucleus in the rostral medulla) projects to Purkinje cells via climbing fibres. The climbing fibres terminate in the molecular layer where the dendritic tree of the purkinje cell is found
  • All other inputs go to the granule cells via mossy fibres, and then onwards via parallel fibres. Parallel fibres innervate the purkinje cells
73
Q

Describe the efferent/output system of the cerebellum

A

all output from Purkinje cells is via deep nuclei

74
Q

State the divisions of the cerebellum

A

vestibulocerebellum
spinocerebellum
cerebrocerebellum

75
Q

What functions take place in the vestibulocerebellum, and where does it have connections to?

A
  • Regulation of gait, posture and equilibrium
  • Coordination of head movements with eye movements
  • Connections with the superior colliculus
76
Q

What functions take place in the spinocerebellum,?

A
  • Coordination of speech
  • Adjustment of muscle tone
  • Coordination of limb movements
  • Fine control of the main corticospinal output
  • It modulates and refines output to the musculature
77
Q

What functions take place in the cerebrocerebellum,?

A
  • Coordination of skilled movements – motor learning
  • Cognitive function, attention, processing of language
  • Emotional control
78
Q

Describe Vestibulocerebellar Syndrome

A

Damage (tumor) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open).

79
Q

Describe Spinocerebellar syndrome

A

Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based).

80
Q

Describe Cerebrocerebellar or Lateral Cerebellar Syndrome

A

Damage affects mainly arms/skilled coordinated movements (tremor) and speech. Results in skilled movement loss.

81
Q

Main motor signs of cerebellar problems

NOTE: Deficits apparent ONLY upon movement

A
  • Ataxia: General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
  • Dysmetria: Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
  • Intention tremor: Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
  • Dysdiadochokinesia: Inability to perform rapidly alternating movements, (rapidly pronating and supinating hands and forearms)
  • Scanning speech: Staccato, due to impaired coordination of speech muscles
82
Q

State the main changes that you would see in the basal ganglia as you move posteriorly through the brain

A
  • start to see the thalamus as you move posteriorly - not seen anteriorly
  • caudate nucleus starts off larger and becomes diminished
83
Q

Draw the Basal Ganglia Circuitry

A

(OneNote)

Year 2 Neuro (16 decks)

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