Motor function and dysfunction

Question 1

Upper motor neurones can be excitatory or inhibitory of lower motor neurones (via inhibitory inter neurones), what is the net effect of UMN on LMNs?

Answer 1

Net effect is inhibitory

Question 2

Describe the path of motor neurones from motor homunculus to muscle

Answer 2

• fibres come together at corona radiata and converge and go through internal capsule (between thalamus and lenticulate nucleus)
• fibres pass though cerebral peduncle of midbrain (mickey mouses ears)
• fibres decussate at medullary pyramids
• fibres travel down lateral corticospinal tract
• UMN Fibres synapse with LMN in the ventral horn
• LMN fibres exit the ventral root and enter the spinal nerve and go to the muscle

Question 3

What is the function of the pontine reticulospinal tract, rubrospinal tract , lateral vestibulospinal and ventral corticospinal tracts?

Answer 3

potine reticulospinal= paralysis in sleep
rubrospinal= not functional in adults, only animals and babys
ventral corticospinal= undecussated fibred involved in posture & trunk muscles
lateral vestibulospinal tract= postual control, balance etc

Question 4

give 5 features of LMN lesions

Answer 4

• weakness
• areflexia
• muscle wasting (normally LMN provide trophic factors (growth factors), also loss of use)
• fasciculation (uncoordinated contractions, dont need to know why)
• hypotonia (floppy)

Question 5

Give and explain 5 features of UMN lesions

Answer 5

• weakness (no excitation of LMN)
• hypertonia (net effect of UMN is inhibition, loss of UMN= more excitation= more rigid muscles)
• hyperreflexia (loss of descending inhibition= muscle spindles can excite LMN more easily)
• extensor- planter reflex (and increased flexor activity as these muscles are generally more powerful)

Question 6

Describe the path of motor neurones for cranial nerves

Answer 6

From homunculus, down to relevant cranial nerve nucleus via corticotubular tract- found next to internal capsule

Question 7

Why do lesions of UMN to facial nerves (eg strokes) tend to be forehead sparing?

Answer 7

Because UMN fibres to the upperface split and go to both ipsilateral and contralateral CNVII nucleus, whereas UMN fibres to the lower face only go to the contralateral nucleus. This means in a right sided stroke, the left upper face can still get innervated by the left side of the brain, but the lower face cannot.

Question 8

Which parts of the cerebellum control which parts of the body?

Answer 8

Vermis regulates trunk musculature
Hemisphere regulate limbs
Tracts are ipsilateral in cerebellum.

Question 9

Why may cerebellar tumours lead to hydroencephalus?

Answer 9

The 4th ventricle is just infront of the cerebellum, behind the pons. Blockage of this= CSF build up

Question 10

Give 6 signs of cerebellar pathology?

Answer 10

• Disdidochokinesis
• Ataxia
• Intention tremour
• slurred speech
• Hypotonia

Question 11

What is the role of the basal ganglia and of the cerebellum?

Answer 11

Basal ganglia takes an idea/ motor plan from prefrontal cortex and determines the most appropriate set of movements, also kick starts and and fine tunes movement by stimulating appropriate (direct pathway)and inhibiting inappropriate movements (indirect pathway) .
Cerebellum looks at current position of limbs and determines appropriate sequence. It is also involved in muscle memory.

Question 12

What structures make up the basal ganglia? (5)

Answer 12

• lentiform nucleus (putamen, globus pallidus interna and externa)
• striatum (putamen, caudate nucleus)
• substantia nigra
• subthalamic nucleus

Question 13

What is the general effect of the direct and indirect pathway?

Answer 13

Direct= stimulatory (stimulate putamen, more  inhibit GPi, less inhibits thalamus, more stimulate cortex)
Indirect= inhibitory (inhibit GPe, less inhibit STN, more stimulate GPi,  more inhibits thalamus, less stimulate cortex)

Question 14

Why does dopamine release lead to more stimulation of cortex? (2)

Answer 14

dopamine stimulates putamen to activate direct pathway and also inhibits the indirect pathway

Question 15

Does the basal ganglia communicate with the ipsi or contralateral cortex?

Answer 15

ipsilateral cortex, so coordinates contralateral movement

Question 16

What is the pathophysiology behind parkinsons disease?

Answer 16

Destruction of substantia nigra and so less dopamine release, so less inhibition of indirect pathway and less activation of indirect pathway

Question 17

What are the 3 cardinal signs of parkinsons?

Answer 17

• resting tremour
• bradykinesia
• hypertonia

Question 18

Give 3 non cardinal signs (but still signs) of parkinsons?

Answer 18

• hypophonia
• reduced facial expression
• micrographia
• dementia
• depression
• shuffling gait

Question 19

What is the pathophysiology behind huntingons?

Answer 19

loss of cells within the striatum so loss of indirect pathway so less inhibition so more movement

Question 20

Give 3 symptoms of huntingdons?

Answer 20

• chorea (involuntary jerky movements)
• dystonia (sustained repetitive muscle contractions resulting in twisting and repetitive movements)
• poor coordination
• cognitive decline and behaviour dificulties

Question 21

What is hemiballismus?

Answer 21

Subthamic nucleus damage, so less excitation of GPi by indirect pathway so less inhibition of the thalamus. This means more movement

Question 22

How can hemiballismus present?

Answer 22

unilateral, explosive, involuntary movements often secondary to subcortical stroke

Question 23

What is motor neurone disease? how will it present?

Answer 23

Destruction of motor neurones- both upper and lower. They will present with weakness, poor coordination, fasiculation, hypo or hypertonia areflexia, hyperreflexia- they may have upper and lower motor neurone signs. the SOD genes have been implicated.

Question 24

Which parts of the internal capsule correspond to which structures?

Answer 24

Genu= face (corticobulbar tract)
posterior limb, from medial to lateral:
- upper limb
- trunk
- lower limb