Motor pathways; cortical motor function Flashcards Preview

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Flashcards in Motor pathways; cortical motor function Deck (30):
1

Explain the different levels of the motor system heriachy

Level 1: [lowest, no higher order function] Spinal cord for reflex movements
Level 2: Brainstem, integrates info from the vestibular, auditory and visual systems
Level 3: Primary motor cortex, Premotor and supplementary; program movements and voluntary actions
Level 4: Association cortices (Parietal and frontal), makes decisions in planning and executing movement

2

What are the two side loops?

Basal ganglia and cerebellum

3

What structures is the basal ganglia composed of?

Caudate nucleus, Putamen, Globus pallidus, Substantia nigra, Subthalamic nucleus

4

What are the two main parts of the pyramidal (descending system)?

Corticobulbar tract (innervates the face)
Corticospinal tract (innervates the body)

5

What are the three parts to the motor cortex and where are they found?

All found in the frontal lobe, anterior to the central sulcus
Primary motor cortex; Broadmann's area 4
Premotor cortex; Broadmann's area 6
Supplementary motor cortex; Broadmann's area 6

6

What is the function of the primary motor cortex?

Controls fine, precise, discrete voluntary movements
Betz/pyramidal cells are in the fifth layer of the grey matter
Corticospinal tracts originate from here (descending signals to execute movements)

7

What is the function of the lateral motor pathways?

Control distal and proximal muscles
Voluntary movements of arms and legs

8

What is the function of the medial motor pathways?

Control axial muscles
Balance and posture

9

Which descending motor pathways are classified as lateral and medial?

Lateral: lateral corticospinal, rubrospinal, lateral reticulospinal
Medial: ventral corticospinal, medial reticulospinal, tectospinal, vestibulospinal

10

Describe the pathway of the lateral corticospinal tract

Axon from first motor neurone originates in the primary motor cortex
Decussation at the medulla oblongata
Reaches anterior horn of the spinal cord and synapses with second motor neurone in the ventral horn

11

Describe the pathway of the anterior corticospinal tract

Axon from first motor neurone originates in the primary motor cortex
Remains ipsilateral descending into the spinal cord
Decussates and terminates in the cervical and upper thoracic levels
Innervates proximal limbs

12

Describe the pathway of the corticobulbar tracts

Axon originates from the lateral aspect of the primary motor cortex
Passes through the internal capsule to the brainstem
Terminates on the motor nuclei of the cranial nerves
Synapses with lower motor neurones to send signals to muscles of the tongue and face

13

Which neurotransmitters are used between
i) upper and lower motor neurones
ii) lower motor neurones and muscles

i) Glutamate
ii) ACh

14

What is the function and location of the premotor cortex?

Plans movements
Regulates externally cued movements
Anterior to primary motor cortex laterally

15

What is the function and location of the supplementary motor area?

Involved in planning complex movements and sequential actions
Regulates internally driven movements
Anterior to primary motor cortex medially

16

What is the function of the posterior parietal cortex?

Ensures movements are directed accurately in space

17

What is the function of the prefrontal cortex?

Involved in selection of movements for particular course of action

18

What are the symptoms of an upper motor neurone lesion and where are they seen?

Loss of function (negative signs):
-Paresis; graded weakness
-Paralysis

Increased abnormal motor function due to loss of descending inhibitory signals (positive signs):
-Spasicity
-Hyperreflexia
-Clonus
-Extensor plantar response/Babinski's sign

Seen on the contralateral side

19

What are examples of upper motor neurone lesions?

Cerebral infarction
Damage to corticospinal tract

20

Why is there no muscle atrophy in subjects with an upper motor neurone lesion?

No muscle atrophy as nutrients supplying the muscle is from lower motor neurones which are still intact

21

What is apraxia and what can cause it?

Upper motor neuron lesion; disorder of skilled movement not from weakness, abnormal tone, posture or movement disorders. Patients have lost ability to perform skilled movements, therefore are uncoordinated.
Lesion to inferior parietal lobe, frontal lobe (premotor, supplementary motor area).
Usually caused by stroke or dementia.

22

What are the symptoms of a lower motor neurone lesion and where are they seen?

Weakness
Hypotonia
Hyporeflexia
Muscle atrophy
Fasciculations
Fibrillations

23

What are examples of lower motor neurone lesions?

Damage to peripheral nerves
Lesion at the nerve root

24

How are fibrillations tested and what are they?

Spontaneous twitching of individual muscle fibres.
Recorded using needle electromyography

25

What is motor neurone disease caused when it affects both the upper and lower motor neurones?

Amyotrophic lateral sclerosis
(neurodegenerative disorder now affects lower and upper motor neurones). Patients will present with a combination of signs

26

What are the upper and lower motor neuron signs that a patient with MND will start to present with?

Upper motor neurone:
Babinski's sign
Increased muscle tone
Brisk limbs and jaw reflexes
Dysarthria
Dysphagia

Lower motor neurone:
Weakness
Muscle wasting
Tongue fasciculations and wasting
Dysphagia
Nasal speech

27

What is the function of the rubrospinal tract?

Still works even if there is a lesion to the primary motor cortex so descending signals can still arrive
Role is in movement velocity

28

What is the function of the lateral and medial vestibulospinal tracts?

Involved in posture adjustments and head/eye movement

29

What is the function of the reticulospinal tract?

Originate in the reticular formation of the brainstem and travel down the spinal cord
Involved in complex movements:
Orientating
Stretching
Maintaining a complex posture

30

What is the function of the tectospinal tract?

Originates in the superior colliculus
Most likely involved in reflexive turning of the head to visual stimuli