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Neuroscience > Motor pathways and higher motor control > Flashcards

Motor pathways and higher motor control Flashcards

1
Q

What is the role of the spinal cord and brainstem in motor control?

A

Execution

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2
Q

What is the role of the motor cortex in motor control?

A

Generation and initiation

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3
Q

What is the role of the basal ganglia in motor control?

A

Select and release based on learning

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4
Q

What is the role of the cerebellum in motor control?

A

Calibrate and adjust

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5
Q

What do more lateral tracts supply?

A

More distal muscles

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6
Q

What do more medial tracts supply?

A

More proximal muscles

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7
Q

Is the cortex needed for most motor functions?

A

No

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8
Q

What and where are Betz cells?

A

Layer IV large pyramidal cells, in the primary motor cortex, essential for certain movements - grasping grabbing/ dexterity

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9
Q

What are the three functional types of skeletal muscle fibres?

A

Slow-contracting (Type 1)
Fast-contracting fatigue Resistant (Type 2A)
Fast-contracting, easily Fatigued (Type 2B)

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10
Q

What innervates the three skeletal muscle fibres?

A

Innervation by alpha motor neurons is subtly different

Type 1 - smallest alpha neurons
Type 2A - medium sized alpha motor neurons
Type 2B - largest alpha motor neurons

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11
Q

Effects of LMN lesions

A 
Flaccid paralysis
Muscle weakness or paralysis
Hypotonia
Hyporeflexia 
Initially fasciculations 
Long term muscle wasting
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12
Q

Why are there fasciculations early in an LMN lesion?

A

Lack of ACh signalling, so upregulation of ACh receptors, increased sensitivity of muscle to acetylcholine

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13
Q

What are the medial descending tracts?

A

Anterior corticospinal , Vestibulospinal, pontine reticulospinal, Tectospinal

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14
Q

What are the lateral descending tracts?

A

Lateral corticospinal, Rubrospinal (magnocellular), Medullary reticulospinal

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15
Q

What do medial descending tracts mainly supply?

A

Axial/proximal muscles

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16
Q

What do medial descending tracts mainly supply?

A

Mainly axial and proximal muscles

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17
Q

What do medial descending tracts end on?

A

Interneurons

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18
Q

What do lateral descending tracts end on?

A

Alpha motor neurons

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19
Q

Where do corticospinal fibres arise?

A

Premotor (broadmann area 6), motor (broadmann area 4) and sensory cortex (broadmann area 3,2 and 1).

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20
Q

What are the principle inputs to the primary motor cortex?

A 
Primary somatosensory cortex (S1) area 3a for proprioception
Premotor cortex (area 6)

Contralateral cerebellar hemisphere via VL nucleus of thalamus

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21
Q

Where do the corticospinal fibres pass?

A

Through the internal capsule

Fibres bundle in the pons (pontine nuclei), then gather into pyramids in the medulla.

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22
Q

What happens at the pyramidal decussation?

A

At the lower medulla, at the pyramidal decussation, 85-90% of the fibres cross the midline to form the lateral corticospinal tracts and the remaining 10-15% form the ventral corticospinal tract.

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23
Q

What do the lateral and ventral corticospinal tract control?

A

Lateral tract controls distal limb motor neurons (especially fine hand movements) while ventral tract controls the axial motor movements.

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24
Q

What proportions of corticospinal neurons come from each area of the cortex?

A

40% from M1, 20% from premotor and 40% from post central S1

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25
Q

What is the internal capsule?

A

White matter structure situated in the inferomedial part of each cerebral hemisphere of the brain.

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26
Q

Where does the internal capsule pass through?

A

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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27
Q

What is the genu?

A

The bend in the V of the internal capsule

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28
Q

What is the anterior and posterior limb of the internal capsule?

A

The anterior limb is the part in front of the genu

The posterior limb is the part behind the genu between thalamus and lenticular nucleus

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29
Q

What is the retrolenticular portion of the internal capsule?

A

The retrolenticular portion is caudal to the lenticular nucleus and carries the optic radiation (from medial part of lateral geniculate nucleus) also known as the geniculocalcarine tract.

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30
Q

What is the sublenticular portion of the internal capsule?

A

The sublenticular portion is beneath the lenticular nucleus are tracts involved in the auditory pathway from the medial geniculate nucleus to the primary auditory cortex (Broadmann areas 41 and 42)

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31
Q

What fibres make up the genu?

A

Originating in the motor part of the cerebral cortex

Pass through the base of the cerebral peduncle with the cerebrospinal fibers, undergo decussation and end in the motor nuclei of the cranial nerves of the opposite side.

It contains the corticobulbar tract, which carries upper motor neurons from the motor cortex to cranial nerve nuclei that mainly govern motion of striated muscle in the head and face.

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32
Q

What is the corticobulbar tract?

A

Carries upper motor neurons from the motor cortex to cranial nerve nuclei that mainly govern motion of striated muscle in the head and face.

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33
Q

What contains the corticobulbar tract?

A

Genu

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34
Q

Why does lesion in the IC affect the facial nerve?

A

Supranuclear lesion of facial nerve (corticobulbar tract)

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35
Q

Why is the top portion of the face spared in IC facial nerve lesion?

A

Supranuclear, upper face receives innervation from ipsilateral corticobulbar tract

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36
Q

What fibres make up the anterior limb of the IC?

A

Fibers running from the thalamus to the frontal lobe

Fibers connecting the lentiform and caudate nuclei

Fibers connecting the cortex with the corpus striatum

Fibers passing from the frontal lobe through the medial fifth of the base of the cerebral peduncle to the nuclei pontis

Thalami pontine fibers

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37
Q

What fibres make up the posterior limb of the IC?

A

The anterior two-thirds of the occipital part contains fibers of the corticospinal tract, which arise in the motor area of the cerebral cortex and, are continued into the pyramids of the medulla oblongata.

The posterior third of the occipital part contains:

Sensory fibers, largely derived from the thalamus, though some may be continued upward from the medial lemniscus

The fibers of optic radiation, from the lower visual centers to the cortex of the occipital lobe

Acoustic fibers, from the lateral lemniscus to the temporal lobe

Fibers that pass from the occipital and temporal lobes to the pontine nuclei

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38
Q

Blood supply to the IC Anterior limb

A

Lenticulostriate branches of middle cerebral artery (superior half) and recurrent artery of Heubner of the anterior cerebral artery (inferior half)

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39
Q

Blood supply to the IC Genu

A

Lenticulostriate branches of middle cerebral artery (Charcot)

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40
Q

Blood supply to the IC posterior limb

A

Lenticulostriate branches of middle cerebral artery (superior half) and anterior choroidal artery branch of the internal carotid artery (inferior half)

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41
Q

IC lesion symptoms

A

Contralateral spastic paralysis in upper and lower limbs

Asymmetrical hemiplegic gait

Contralateral lower face weakness: CNVII nuclei only receives contralateral innervation whereas the upper face receives bilateral innervation.

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42
Q

ACA lesion symptom

A

Lower limb contralateral UMN lesion

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43
Q

MCA lesion symptom

A

Upper limb contralateral UMN lesion

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44
Q

Paraplegia

A

Paralysis of lower half of body with involvement of both legs

45
Q

Hemiplegia

A

Paralysis of one side of the body

46
Q

Hemiparesis

A

Muscular weakness or partial paralysis restricted to one side of the body

47
Q

Spastic paraplegia

A

Paraplegia where paralysis is spastic, not flaccid.

48
Q

Tetraplegia or quadriplegia

A

All four limbs are affected by paralysis

49
Q

Monoplegia

A

Only one limb is affected

50
Q

Why is UMN resultant in spastic paralysis?

A

Removal of inhibitory signal on the lower motor neuron leads to spasticity.

Rigid also due to the reflex being maintained.

51
Q

What determines if a lesion produces a flexion/extension?

A

If above red nucleus then flexion response as rubrospinal is still intact - but abnormal.

If below red nucleus - pure extension response.

52
Q

Reticulospinal tract functions

A

Controls muscle tone, gain of spinal reflexes especially axial and proximal limb muscles

Recent evidence for direct reticulospinal input to distal limb muscles including hand in primates

53
Q

Origins of the reticulospinal tract

A

Medial reticulospinal tract from pontine, lateral reticulospinal tract from medullary reticular formation

54
Q

Inputs to the reticulospinal tract

A

From ascending tracts, motor/premotor cortex, vestibular apparatus, tectum

55
Q

Course of reticulospinal tract

A

Pontine RF projects ipsilaterally in ventral funiculus - medial reticulospinal tract.

Medullary RF projects contralaterally in anterolateral funiculus - lateral reticulospinal tract

56
Q

What are the funiculi of the spinal cord?

A

Lateral, ventral, posterior white matter regions

57
Q

Effects and importance of the reticulospinal tract

A

Modulates reflex action during ongoing movements (postural readjustment)

Pontine facilitate axial and proximal reflexes

Medullary end on both α and γ motorneurons - inhibit proximal limb muscles

Cortical input to reticular formation important to suppress reflexes during voluntary movements

58
Q

Vestibulospinal tract functions

A

Antigravity actions

59
Q

Vestibulospinal tract origin

A

From lateral and medial & inferior vestibular nuclei

60
Q

Vestibulospinal tract inputs

A

From otoliths and cerebellum to lateral vestibular nucleus

Semicircular canals and neck proprioceptors to medial vestibular nucleus

61
Q

Vestibulospinal tract course

A

Both medial and lateral tracts run ipsilaterally in ventral funiculus of the spinal cord

62
Q

Lateral vestibulospinal tract effects and importance

A

Lateral vestibulospinal tract facilitates antigravity (extensor) motor neurones (especially axial) for posture

63
Q

What inputs to the lateral vestibular nucleus?

A

Otoliths and cerebellum

64
Q

What inputs to the medial vestibular nucleus?

A

Semicircular canals and neck proprioceptors

65
Q

Medial vestibulospinal tract effects and importance

A

Medial (continuous with MLF) to axial muscles of neck/trunk and propriospinal neurons

66
Q

Tectospinal tract functions

A

Control of neck/eye coordination

67
Q

Tectospinal tract origin

A

Superior colliculus (tectum)

68
Q

Tectospinal tract inputs

A

Retina via optic nerve, from visual cortex, from auditory inputs

69
Q

Tectospinal tract course

A

Fibres cross and descend in contralateral ventral funiculus of upper spinal cord

70
Q

Tectospinal tract acts on

A

Axial muscles of neck/upper thorax – moves the neck and thus the direction of gaze

71
Q

Rubrospinal tract origin

A

Large neurones of red nucleus, topgraphically arranged

72
Q

Rubrospinal tract inputs

A

Motor cerebral cortex, cerebellum, globus pallidus, reticular formation, ascending from cord.

73
Q

Rubrospinal tract course

A

Cross in midbrain, descend through pons, medulla, lateral funiculus of cord

74
Q

Rubrospinal tract actions

A

Inter neurones controlling distal limb muscles.

Facilitates flexors.

75
Q

What are all the cranial nerve motor nuclei

A

(III, IV, VI, V3, VII, IX, X, XI, XII).

76
Q

Examples of diffuse descending tracts

A

Locus coeruleus

Raphe nuclei

77
Q

What NT does the locus coeruleus supply and what is its role?

A

Locus coeruleus (noradrenaline) facilitates locomotor and sympathetic activity and inhibits nociception

78
Q

What NT does the raphe nuclei supply and what is its role?

A

Raphe nuclei (5-HT/serotonin) inhibits spinal neuronal activity, promotes sleep and inhibits nociception.

79
Q

What element of the reflex can be modified by the cortex?

A

Long latency M2 component of the reflex

80
Q

Inputs to the PFC

A

Limbic system (via dorsomedial & anterior thalamic nuclei)

Parietal & occipital cortex: visuo-spatial signals (magnocellular-dominated dorsal visual stream)

Inferotemporal cortex (ventral stream object recognition)

81
Q

Outputs from the PFC

A

Frontal eye fields

Pre- & supplementary motor cortex

Back to posterior parietal cortex

Caudate & cerebellum

82
Q

What can PFC neurons encode

A

PFC neurons can encode delay, short-term memory, necessary for subsequent motor response.

83
Q

Lateral prefrontal cortex roles

A

Inhibitory control, executive function, task switching, working memory

84
Q

Orbitofrontal PFC roles

A

Motivated decision, emotional & autonomic responses: taste, smell, reward (medial), loss chasing behaviour (lateral).

85
Q

What is the role of the posterior parietal cortex?

A

Integration of visual, proprioceptive, auditory, motor and motivational signals

Active touch - sensorimotor integration for the representation of the body image (morpho-synthesis)

Active sight - representation of peripersonal and teleceptive space

Coordinate conversions: e.g. from retinotopic (visual map) to egocentric by direction of attention, e.g. for preparation of eye movements.

86
Q

Connections of the posterior parietal cortex

A

Prefrontal & supplementary motor cortex

87
Q

What do lesions of the PPC cause?

A

rhs Lesions cause neglect, misdirection of movement, lack of body image, dressing apraxia, anosagnosia
lhs languange focused

88
Q

Pre motor cortex Inputs

A

Prefrontal, posterior parietal, cerebellum (via VL thalamus)

89
Q

Pre motor cortex outputs

A

Motor cortex, prefrontal cortex, posterior parietal cortex, cerebellum, corticospinal tract

90
Q

Pre motor cortex function

A

Sensory guidance of movement e.g. directing reach

91
Q

When does the pre motor cortex fire?

A

In advance of movement, can show direction selective firing - shows ‘planning’ function

92
Q

What are the two distinct parieto-premotor channels?

A

Dorsal pathway for reaching (direction and extent)

Ventral for grasping (shape dimension of object)

93
Q

Where are mirror neurons?

A

Lateral ventral premotor area

94
Q

What are mirror neurons?

A

Neuron fires when other monkey/human performs action (i.e precision grip)

Does not fire when pliers used for picking up food

95
Q

What is the role of mirror neurons? How does this work? And what is their importance?

A

Mirror neurones might help us to imitate and learn new movements, such as speaking. Encode abstract representation of motor task.

When monkey observes an action, he starts automatically to prepare the same action. In this way he becomes able to perform it fast, thus prevailing on possible competitors

96
Q

What are mirror neurons importantly NOT associated with?

A

Motor preparation

Mirror neurons cease firing when the food is moved toward the animal and becomes available to him. If the firing of mirror neurons were related to motor preparation, the neuron activity should have increased and not decreased in the phase that precedes movement execution

97
Q

What is the supplementary motor area function?

A

Used for internally generated movements, mental rehearsal sequential movements - readiness potential

98
Q

SMA Inputs

A

Prefrontal cortex, basal ganglia

99
Q

SMA outputs

A

Motor cortex, corticospinal tract

100
Q

Primary motor cortex inputs

A

Cortico-cortical: sensory cortex behind (3a particularly), supplementary (medial 6) and premotor (lateral 6) cortex

Thalamic: dorsal columns via (VPL), cerebellum (VL)

Non-specific: from intralaminar thalamus & ascending aminergic systems (NA, 5-HT, DA)

101
Q

Primary motor cortex outputs

A

Provide 40% of the corticospinal (pyramidal) tract axons, 20% of these monosynaptic to distal muscle motoneurones

Putamen (input to neostriatum of basal ganglia)

Pons (corticopontine tract: input to intermediate cerebellum)

Cranial nerve nuclei (corticobulbar)

Red nucleus (input to rubrospinal tract)

Brainstem reticular formation (descending control of reflex activity)

102
Q

What is the role of M1 revealed by stimulation?

A

Not about specific muscle but about coordinated behaviour - initiation of these movements

103
Q

What do populations of M1 neurons code for?

A

Direction and force

104
Q

Which areas would you NOT expect to be active when subjects mentally rehearse the movement without moving the fingers?

A

Motor cortex (area 4) and somatosensory motor cortex (area 1)

Supplementary motor cortex - area 6 - to be active only

105
Q

The area where a cortical lesion would paralyse the right arm

A

Left hemisphere, medial M1

106
Q

The principal relay site from cerebral cortex to cerebellar cortex

A

Thalamus

107
Q

The area where a cortical lesion would paralyse the left leg

A

Right hemisphere, most medial M1 along the longitudinal fissure

108
Q

The area responsible for planning spontaneous movement

A

PMA

Neuroscience (19 decks)

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