Upper and lower motor neurones

Question 1

What are the spinal tracts that coordinate movement? (x3)

Answer 1

Anterior and lateral corticospinal tracts. Corticobulbar pathway.

Question 2

What are the functions of the anterior and lateral corticospinal tracts?

Answer 2

ANTERIOR: supplies muscles of the trunk and proximal limbs; LATERAL: supplies skeletal muscles in distal parts of the limbs.

Question 3

What is the function of the corticobulbar pathway? Which nerves? (x4)

Answer 3

Supplies the muscles of the head, neck and face – carrying the motor cranial nerves V, VII, IX and XII.

Question 4

What is the course of the lateral corticospinal tract?

Answer 4

• UPPER MOTOR NEURONE emerges from primary motor cortex and travels through internal capsule (white matter structure in inferomedial part of each cerebral hemisphere past the basal ganglia).
• Upper motor neurone passes through cerebral peduncle of the midbrain, travelling through pons.
• UMN then undergoes pyramidal decussation in the medulla.
• Descends down contralateral lateral corticospinal tract to the correct spinal level.
• UMN synapses onto a LOWER MOTOR NEURONE in ventral horn of spinal cord.
• Lower motor neurone exits the spinal cord via the ventral root.

Question 5

What is the course of the anterior corticospinal tract?

Answer 5

• Upper motor neurone emerges from the primary motor cortex and travels through the internal capsule.
• Upper motor neurone passes through cerebral peduncle of the midbrain, travelling through the pons.
• UMN DOES NOT undergo pyramidal decussation in the medulla, remaining ipsilateral.
• UMN descends down ipsilateral half of anterior corticospinal tract to the correct spinal level.
• UMN synapses to LMN in contralateral ventral horn.
• LMN exits cord via the ventral root.

Question 6

What is the course of the corticobulbar pathway?

Answer 6

• Upper motor neurone emerges from head region of motor cortex.
• UMN passes through corticobulbar tract to the brainstem.
• UMN synapse to relevant cranial nerve in contralateral brainstem motor nuclei.
• Cranial nerve passes out of the brainstem to innervate muscles.

Question 7

What are lower motor neurones?

Answer 7

Neurones in the ventral horn of the spinal cord or cranial nerve nuclei of the brainstem with motor function.

Question 8

What are upper motor neurones?

Answer 8

Corticospinal and corticobulbar neurons – nerves projecting to the spinal cord and brainstem respectively.

Question 9

What does pyramidal and extrapyramidal refer to in neuroscience?

Answer 9

PYRAMIDAL refers to upper motor neurons that pass through medullary pyramids and part of the corticospinal/bulbar tracts; EXTRAPYRAMIDAL refers to basal ganglia and cerebellum, do not travel through medullary pyramids, and indirectly regulate involuntary movements.

Question 10

What are the two types of pathology seen in upper motor lesions?

Answer 10

Loss of function (negative signs) and increased abnormal motor function (positive signs).

Question 11

What are the negative signs associated with upper motor lesions? (x2)

Answer 11

LOSS OF FUNCTION (NEGATIVE SIGNS): results in PARESIS – graded weakness of movements; and PARALYSIS (aka plegia) – complete loss of muscle activity.

Question 12

What are the positive signs associated with upper motor lesions? (x3)

Answer 12

INCREASED ABNORMAL MOTOR FUNCTION (POSITIVE SIGNS): increased levels of abnormal muscle movement from loss of inhibitory descending inputs. For example:

• SPASTICITY – increased muscle tone (muscle tone refers to continuous contraction of muscles in the resting state – look at photo for abnormal muscle tone i.e. spasticity).
• HYPER-REFLEXIA – exaggerated reflexes.
• CLONUS – abnormal oscillatory muscle contraction

Question 13

What sign can be observed to test for upper motor lesions?

Answer 13

Babinski’s sign.

Question 14

What is apraxia?

Answer 14

A disorder in skilled movement i.e. patients have lost information about how to perform skilled movements e.g. doing up buttons, riding a bike etc.

Question 15

What lesions cause apraxia? (x2)

Answer 15

Lesion of the inferior parietal lobe or the frontal lobe (premotor cortex, supplementary motor area).

Question 16

What are common causes of apraxia? (x2)

Answer 16

Stroke causing infarction in motor areas of the brain affecting skilled movement, and dementia.

Question 17

What are the pathologies of lower motor neuron lesions? (x6) We Hate His Munted Facial Features

Answer 17

 Weakness

 Hypotonia (reduced muscle tone)

 Hyporeflexia (reduced reflexes)

 Muscle atrophy (decrease size)

 Fasciculations: uncontrolled twitch – caused because damaged motor units produce spontaneous action potentials.

 Fibrillations: spontaneous twitching of individual muscle fibres seen when a needle electromyography is being recorded.

Question 18

What is motor neuron disease? Disorders of MND?

Answer 18

A progressive neurodegenerative disorder, causing damage to upper and lower motor neurons. It can present as a variety of different disorders, though Amyotrophic Lateral Sclerosis (ALS) is the most common presenting disorder, characterised by stiff muscles, muscle twitching and muscle wasting (atrophy).

Question 19

What is the cause of death in patients with motor neuron disease?

Answer 19

When their respiratory musculature is no longer functional –> respiratory arrest.

Question 20

What are the signs of motor neuron disease?

Answer 20

 UPPER MOTOR NEURON SIGNS: increased muscle tone (spasticity of tongue and limbs), brisk limbs and jaw reflexes, Babinski’s sign, loss of dexterity (skill in performing task, especially hands), dysarthria (difficulty speaking) and dysphagia (breathing).

 LOWER MOTOR NEURON SIGNS: weakness, muscle wasting, tongue fasciculations and wasting, nasal speech and dysphagia.