Motor pathways; cortical motor function

Question 1

Explain the different levels of the motor system heriachy

Answer 1

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

Question 2

What are the two side loops?

Answer 2

Basal ganglia and cerebellum

Question 3

What structures is the basal ganglia composed of?

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What is the function of the primary motor cortex?

Answer 6

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)

Question 7

What is the function of the lateral motor pathways?

Answer 7

Control distal and proximal muscles

Voluntary movements of arms and legs

Question 8

What is the function of the medial motor pathways?

Answer 8

Control axial muscles

Balance and posture

Question 9

Which descending motor pathways are classified as lateral and medial?

Answer 9

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

Question 10

Describe the pathway of the lateral corticospinal tract

Answer 10

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

Question 11

Describe the pathway of the anterior corticospinal tract

Answer 11

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

Question 12

Describe the pathway of the corticobulbar tracts

Answer 12

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

Question 13

Which neurotransmitters are used between

i) upper and lower motor neurones
ii) lower motor neurones and muscles

Answer 13

i) Glutamate

ii) ACh

Question 14

What is the function and location of the premotor cortex?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

What is the function of the posterior parietal cortex?

Answer 16

Ensures movements are directed accurately in space

Question 17

What is the function of the prefrontal cortex?

Answer 17

Involved in selection of movements for particular course of action

Question 18

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

Answer 18

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

Question 19

What are examples of upper motor neurone lesions?

Answer 19

Cerebral infarction

Damage to corticospinal tract

Question 20

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

Answer 20

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

Question 21

What is apraxia and what can cause it?

Answer 21

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.

Question 22

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

Answer 22

Weakness
Hypotonia
Hyporeflexia
Muscle atrophy
Fasciculations
Fibrillations

Question 23

What are examples of lower motor neurone lesions?

Answer 23

Damage to peripheral nerves

Lesion at the nerve root

Question 24

How are fibrillations tested and what are they?

Answer 24

Spontaneous twitching of individual muscle fibres.

Recorded using needle electromyography

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

What is the function of the rubrospinal tract?

Answer 27

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

Question 28

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

Answer 28

Involved in posture adjustments and head/eye movement

Question 29

What is the function of the reticulospinal tract?

Answer 29

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

Question 30

What is the function of the tectospinal tract?

Answer 30

Originates in the superior colliculus

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