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Neuroanatomy > Motor control > Flashcards

Motor control Flashcards

1
Q

What is the main route via which the motor cortex communicates with muscles of the body?

A

Corticospinal tract

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2
Q

What is the main route by which the motor cortex communicates with muscles of the head and neck?

A

Corticobulbar tract

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3
Q

What types of cells project from the motor cortex into the corticospinal tract and from which layer?

A

Pyramidal cells (layer V)

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4
Q

What are the structures of the brain that fibres of the corticospinal tract run through before reaching the spinal cord?

A
  1. Internal capsule (forebrain)
  2. Cerebral peduncles (midbrain)
  3. Medullary pyramids (ventral medulla, hindbrain)
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5
Q

What happens to the fibres of the CST before they enter the spinal cord?

A
  • ~90% cross to contralateral side and descend in lateral corticospinal tract
  • ~10% don’t cross and remain on ipsilateral side to descend in the ventral corticospinal tract
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6
Q

What is the structure of the corticobulbar tract?

A

Fibres descend with the fibres of the corticospinal tract, but exit the brainstem at an appropriate level to innervate the motor nuclei of the cranial nerves (V, VII, IX, X, XI, XII).

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7
Q

What is the location of M1?

A
  • Frontal lobe
  • Anterior to central sulcus
  • Brodmann’s area 4
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8
Q

What are the location of the secondary motor areas?

A
  • Brodmann’s area 6
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9
Q

How can M1 be distinguished from other parts of the frontal lobe?

A

It contains very few granule cells, so is classified as agranular cortex.

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10
Q

What are the features of the upper midbrain?

A
  1. Cerebral peduncles: Contains descending motor fibres from the internal capsule.
  2. Substantia nigra
  3. Red nucleus
  4. Cerebral aqueduct
  5. Superior colliculus
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11
Q

What is the significance of the pons in terms of behaviour of motor neurones as they pass through?

A

Many fibres from the cerebral peduncles project into the cerebellum. Consequently, the medullary pyramids are narrower than the cerebral peduncles.

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12
Q

What is the nature of connectivity of CST with spinal cord neurones?

A
  • Indirect: CST neurones synapse onto spinal cord interneurones that the synapse onto motor neurones.
  • Direct: CST neurones synpase directly onto motor neurones (cortico-motoneuronal connections), especially those controlling intrinsic muscles of hands and feet (may explain manual dexterity).
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13
Q

What are the features of the mid-medulla?

A
  1. Medullary pyramids
  2. Dorsal column nuclei
  3. Trigeminal nuclei
  4. Medial lemniscus
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14
Q

What are the features of the lower medulla?

A
  1. Medullary pyramids
  2. Motor decussation
  3. Trigeminal nuclei
  4. Dorsal column
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15
Q

What are the locations of the ventral and lateral corticospinal tracts?

A
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16
Q

What are the additional descending pathways descending from the brain into spinal cord?

A
  1. Vestibulospinal tract: Arises from the vestibular nuclei and descend in the ventral spinal cord.
  2. Reticulospinal fibres: Arises from the reticular formation of the brainstem.
  3. Rubrospinal tract: Originates from the red nucleus (receives input form cerebral cortex and cerebellum) of the midbrain and projects mainly into the inferior olivary nucleus, from which cerebellar climbing fibres arise.
17
Q

What are the functions of the vestibulospinal tract?

A

Fibres control antigravity extensors of the lower limb and proximal muscles (trunk).

18
Q

What are the functions of the reticulospinal tract?

A

Fibres are involved with controlling stereotyped motor activity (e.g. walking, chewing) and other essential functions (e.g. breathing, heart rate).

19
Q

What are the functions of the rubrospinal tract?

A

May be involved in motor learning.

20
Q

What are the features of the cerebellum?

A
  1. Vermis: Midline part of the cerebellum, between the 2 cerebellar hemispheres.
  2. Cerebellar hemispheres: Lateral to the vermis.
  3. Middle cerebellar peduncle: Connects the cerebellum to the pons of brainstem, containing fibres from pons projecting into cerebellum.
  4. Flocculus: Semi-detached part of the cerebellum located on the ventral aspects (cerebello-pontine angle). Concerned with vestibular function.
  5. Tonsils: Part of the cerebellum overhanging the dorsolateral aspects of the medulla.
21
Q

What are the deep cerebellar nuclei?

A
  1. Dentate nucleus
  2. Nucleus interpositus (globose + emboliform)
  3. Fastigial nucleus
22
Q

What is special about the output from the flocculus of the cerebellum?

A

Projects directly into the vestibular nuclei without synapsing in a deep cerebellar nuclei

23
Q

What are the cerebellar peduncles?

A
  1. Superior cerebellar peduncles: Output from deep nuclei of cerebellum to rest of the brain.
  2. Middle cerebellar peduncles: Input to cerebellum from pons.
  3. Inferior cerebellar peduncles: Input to cerebellum from medulla.
24
Q

What is the pathway associated with the cerebellar inputs from the cortex (via middle cerebellar peduncle)?

A

Crossed pathway

25
Q

What is the function of inputs into the cerebellum from the cortex?

A

Fibres originate form sensory/sensory association areas and relay information concerning vision, somatosensation, sound…). Probably allows integration of sensory input with motor output.

26
Q

What is the pathway associated with the cerebellar inputs from the body?

A

Uncrossed pathway

27
Q

What is the function of inputs into the cerebellum from the body?

A

Carries sensory information (mainly proprioception) from the body to the cerebellum.

28
Q

What is the pathway associated with the cerebellar inputs from the inferior olive?

A
29
Q

What is the function of inputs into the cerebellum from the inferior olive?

A

Important in motor learning and is thought to mediate plasticity in mossy fibre – granule cell – Purkinje cell pathway.

30
Q

What is the pathway associated with the cerebellar outputs?

A

Deep cerebellar nuclei

↓

Superior cerebellar peduncle

↓

Lower midbrain

↓

(decussation)

↓

Upper midbrain

↓

Red nucleus

↓

Thalamus:

  • Ventrolateral nucleus → M1
  • Ventromedial nucleus → Secondary motor areas
31
Q

What is the nature of cerebellar inputs and outputs into/from the cortex in terms of representation of body?

A
  • Cerebellar hemispheres represent ipsilateral sides of the body
  • Cortex respresents contralateral sides, so input fibres from the cortex into the cerebellum are crossed.
  • Outputs from the cerebellum to the cortex are also crossed.
32
Q

What are the layers of the cerebellum?

A
  1. Molecular layer: Low cell density. Composed of mostly granule cell axons, running parallel to each other. Perpendicular to these are the Purkinje cell axons. Also in this layer are basket and stellate cells.
  2. Purkinje cell layer: Composed of exactly 1 layer of Purkinje cell bodies.
  3. Granular layer: Contains large numbers (~ 50 billion) granule cells and a few golgi cells.
33
Q

What is the structure of the cerebellar network?

A
  1. As the parallel fibres of the granule cells run in the molecular layer, they contact the axons of the Purkinje cells, making contact with 1/3-5 they pass, making total of ~80 synaptic connections with Purkinje cells.
  2. Each Purkinje cell makes contact with ~250000 parallel fibres.
  3. All fibres synapsing onto granule cells are mossy fibres from the middle/inferior cerebellar peduncles.
  4. Granule cells synapse onto Purkinje cell dendrites via excitatory glutaminergic synapses.
  5. The Purkinje cells are the only cells that send fibres out of the cerebellar cortex. They synapse with neurones in the deep cerebellar nuclei via inhibitory GABAinergic synapses.
34
Q

What are the upper motor neurones?

A
  • Corticospinal tract
  • Corticobulbar tract
35
Q

What are the lower motor neurones?

A

Spinal cord motor neurones

36
Q

What is the functional significance of uncrossed fibres in ventral corticospinal tract?

A

They do not innervate muscles of ipsilateral limbs (fibres cross to innervate contralateral limb at level of spinal cord)

Neuroanatomy (7 decks)

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