Motor Disorders

Question 1

Describe the structure of the cerebellum.

Answer 1

• Highly folded – grey matter cortex, white matter core
• 4 peduncles – carry input/output fibres from and to brainstem
• Core contains 3 pairs of deep nuclei – generate output projections to brainstem

Question 2

What are the functional zones of the cerebellar cortex and what are their functions?

Answer 2

o Vestibulocerebellum (archicerebellum)
• Main input from vestibular system
• Involved in balance and ocular reflexes - maintenance of balance
(flocculonodular lobe)

o	Spinocerebellum (paleocerebellum) - receives afferents from spinocerebellar pathways
•	Involved in error correction and maintenance of gait
(anterior lobe)

o Cerebrocerebellum (neocerebellum)
• Involved in movement planning and motor learning
• Particularly in relation to visually guided movement and coordination of muscle activation
Receives afferents from motor cortex/vestibular nuclei and basal ganglia
(posterior lobe)

Question 3

What are signs of cerebellar lesions

Answer 3

DANISH

• Dymetria & Dysarthria & Disequilibrium & Dysdiadochokinesia
• Ataxic gait
• Nystagmus
• Intention tremor
• Slurred Speech (dysarthria)
• Hypotonia

Question 4

What are demetria, dysarthria, disequilibrium and dysdiadokinesia?

Answer 4

o Dysmetria = past pointing during the finger nose test, hunting behaviour
o Dysarthria = scanning speech – spoken words may be broken up into separate syllables, unusual emphasis, may be slurred if facial muscle coordination is affected, monotonic
o Disequilibrium = poor balance
o Dysdiadochokinesia = inability to perform rapidly alternating movements

Question 5

What is ataxic gait?

Answer 5

o Fall over when you do the heel-toe test
o Wide based, rolling, unstable gait
o Patients fall towards the side of the lesion, typically.
o Arm swing may be increased

Question 6

Describe nystagmus in cerebellar lesion

Answer 6

Specifically coarse

Maximal on gaze towards lesion

Question 7

Describe intention tremor

Answer 7

o Movements are decomposed into a succession of separate movements rather than one smooth act.

Question 8

Describe hypotonia

Answer 8

o Hypotonia is common in cerebellar ataxia and is seen in defective posture maintenance, when patients may be unable to stand with the feet together. If the problems affect the vestibular centres of the cerebellum they may fall over if they close their eyes.
o The limbs are floppy and easily displaced by a relatively small force.
o Tendon tapping may lead to several oscillations of the limb (pendulous relfexes)

Question 9

What are causes of cerebellar dysfunction?

Answer 9

PASTRIES

• Posterior fossa tumour
• Alcohol
• (multiple) sclerosis
• Trauma
• Rare
• Inherited (Friedrich’s ataxia)
• Epilepsy medication (carbamazepine, phenytoin)
• Stroke

Question 10

What does the basal ganglia consist of?

Answer 10

• The caudate nucleus
• The putamen
o Caudate nucleus + Putamen = (Neo)striatum
• Globus Pallidus (external and internal)
o Putamen + Globus Pallidus = Lenticular nucleus
• Substantia Nigra (Pars Compacta and Pars Reticulata)
• Subthalamic Nucleus

Question 11

What is the output of the basal ganglia? Function of basal ganglia?

Answer 11

Thalamus which acts on the motor cortical areas to inhibit and initiate movement.

They regulate the amplitude and velocity of the planned movement, particularly in relation to the use of internal (e.g. proprioceptive) information.

Question 12

Describe the direct pathway

Answer 12

The substantia nigra sends dopaminergic input to the striatum, which act on excitatory D1 receptors and inhibitory D2 receptors.

The direct pathway: the striatum inhibits the Globus Pallidus Interna & Substantia Nigra pars reticularis, removing its inhibition on the thalamus which then stimulates the cortex.

Question 13

Describe the indirect pathway

Answer 13

The indirect pathway: The striatum inhibits the Globus Pallidus Externa, removing the inhibition on the subthalamic nucleus. This excites the Globus Pallidus Interna and the Substantia Nigra Pars Reticularis, and it inhibits the thalamus. This means the thalamus doesn’t excite the cortex, movement is inhibited.

Question 14

Describe the hyper direct pathway

Answer 14

The Hyper Direct Pathway: The cortex stimulates the subthalamic nucleus, which excites the GPI and SNr, this inhibits the thalamus and so reduces cortical excitation.

Question 15

Describe Parkinson’s disease pathophysiology

Answer 15

Parkinson’s disease occurs following degeneration of dopaminergic neurons in the substantia nigra (the nigro-striatal pathway). Both excitation via D1 receptors and inhibition via D2 receptors is diminished. Loss of inhibition via D2 means the striatum inhibits the GPE, which reduces inhibition of the subthalamic nucleus, meaning there is increased stimulation of the GPI and more tonic inhibition of the thalamus (meaning less output to the motor cortex). This is basically increasing the output of the INDIRECT pathway.

At the same time decreases stimulation via D1 receptors of the striatum means there is diminished inhibition of the GPI, again causing increased inhibition of the thalamus and decreasing excitation of the motor cortex (Decreased output of the DIRECT pathway)

So… increasing inhibition from the indirect pathway and decreased stimulation from the direct pathway, causing inhibition of movement

Question 16

What are the classical symptoms of PD?

Answer 16

• Resting tremor, relieved by movement
• Increased tone (lead pipe or cog-wheel rigidity)
• Bradykinesia (pedestal turning, slower and smaller movements)

Question 17

Describe Huntingdon’s disease

Answer 17

Huntingdon’s chorea results from degeneration of inhibitory neurons in the striatum, this excessive activity means movement is not inhibited. It develops in the 3rd or 4th decade and affected patients die within five years.

Question 18

What are UMN lesions and LMN lesions?

Answer 18

• Damage to the motor tracts of the brain and spinal cord are termed UMN lesions, distinguishing them from LMN lesions consequent upon damage to cranial or spinal motor nuclei or peripheral nerves.

Question 19

What are pyramidal and extrapyramidal signs?

Answer 19

• Pyramidal signs are called upper motor neurone signs and arise from damage to the corticospinal tract. These tracts travel from the motor cortex to the ventral horn cells of the spinal cord and are sometimes referred to as ‘long tracts’.
• Extrapyramidal signs arise from damage to the extrapyramidal tracts (rubrospinal, tectospinal, vestibulospinal and reticulospinal tracts) and produce signs related to dysfunction of non-cortical motor systems such as the basal ganglia and cerebellum.

Question 20

Describe features of UMN lesion and LMN lesion

Answer 20

Hypertonia
Late disuse atrophy muscle wasting
Hyperreflexia
NO fasciculations
Positive Babinski's signs (dorsiflexion on applying sensation to sole of foot)

Hypotonia
Muscle wasting - early denervation atrophy
Hyporeflexia
Fasciculations
Negative Babinski’s sign (plantar flexion)

Question 21

What is a lower moron neurone? Where are cell bodies located? Where are axons?

Answer 21

• Lower motor neurone is the cell body and axon of an alpha-motor neurone.

o Cell bodies of all alpha-motor neurones are located within the CNS in either cranial nerve motor nuclei of the brainstem of the ventral horn of the spinal cord.

o Axons of alpha-motor neurones leave the CNS to course in the PNS as either motor divisions of cranial nerves or spinal segmental nerves and terminate on skeletal muscles through the neuromuscular junction.

Question 22

Describe the inhibition of lower motor neurones.

Answer 22

• Alpha motor neurones are under constant inhibition from upper motor neurones and in particular, the extra-pyramidal system.
• The intensity of the constant descending inhibition varies continuously.
• During deep sleep, descending inhibition paralyses virtually all skeletal muscles apart from those responsible for breathing or the extraocular muscles.
• Descending inhibition is temporarily lifted in order for us to carry out voluntary movements.

Question 23

What is tone?

Answer 23

• The minimal muscle power that allows us to maintain posture and minimal stiffness in our muscles is known as muscle tone.

Question 24

Describe the stretch reflex

Answer 24

• Muscle tone relies entirely on the operation of the muscle stretch reflex.
o When a muscle is stretched, its muscle spindle afferents detect the stretch, firing through muscle spindle afferents to inform the CNS of this.
o Muscle spindle afferents also make monosynaptic and oligosynaptic contacts with alpha-motor neurones.
o Thus continuous firing in muscle spindle afferents results in reflex contraction of muscles in which the muscle spindle itself resides.
o This on-going reflex contraction of the muscle gives it tone and thereby the ability to oppose passive displacements

Question 25

What does absence of tone suggest?

Answer 25

Pathology of LMNs - failure of communication between alpha-motorneurone, axons of alpha motorneurone, NMJ or muscle itself

Question 26

What signs can be elicited in LMN damage?

Answer 26

Flaccid paralysis - damage to LMN means that muscles become denervated - muscle cannot contract
Muscle atrophy due to denervation
Atonia and areflexia due to loss of innervation
Fasciculation - denervation to muscles mean that nAChR become hypersensitive for any neurotransmitter similar to ACh - this causes slight muscle contraction

Question 27

What happens if the cell body is damaged in LMN lesion? What if it is not?

Answer 27

Axons cannot regenerate so damage is permanent.

If it remains intact, then some Wallerian regeneration can occur and attempt to restore some fucntion

Question 28

What are autonomic consequences of LMN lesion?

Answer 28

An autonomous bladder is caused by LMN lesions, when there is damage to above S2-4 level. There is consequently a loss of parasympathetic and afferent neurones. This results in an individual with overflow incontinence and no ability to micturate.

Question 29

What are autonomic consequences of UMN lesion?

Answer 29

Any damage above the sacral region (i.e. T12 and above) can cause damage to the UMN and result in automatic reflex bladder. There is a loss of the descending inhibitory control, which results in loss of bladder control and involuntary leakage of urine, producing an urge urinary incontinence.

Question 30

Describe upper motor neurones. Where are they located? What are their function?

Answer 30

Upper motor neurones are made from cell bodies and axons of descending or motor fibres.
They are located within higher centres of the nervous system and all their processes remain within the confiners of the CNS.
The upper motor neurones provide the descending inhibition to the lower motor neurones and run from the higher regions of the brain to the spinal cord.

Question 31

What is the pyramidal system made of? What are the rest of the descending fibres?

Answer 31

The pyramidal system is made from upper motor neurones originating in the motor cerebral cortex with axons descending as either the lateral or ventral corticospinal tracts, making only 1 synaptic contact with motor neurones of distal limb muscles (i.e. the hand and fingers).
The rest of the descending fibres descend together as the extra-pyramidal system.

Question 32

What is the corticospinal system responsible for making it special?

Answer 32

The corticospinal system is special in that it is responsible for fractionation (ability to move individual muscles) of finger movements.

Question 33

What is the extra-pyramidal system responsible for?

Answer 33

The extra-pyramidal system is responsible for the constant descending inhibition of lower motorneurones however this is titrated to allow some tone in muscles.
Descending inhibition from the extra-pyramidal system inhibits the operations of most stretch reflexes (that give rise to muscle tone) whilst a random few escape it at any given time for short periods.

Question 34

What do UMN lesions lead to?

Answer 34

If abnormalities of UMNs develop, these will lead to reduction of descending inhibition to muscle stretch reflexes leading to a rise in motor tone.

Question 35

What is the most common site of UMN damage?

Answer 35

Typically, the most common site of damage is the internal capsule or the cerebral cortex. Resulting damage to these upper motor neurone tracts will result in reduction in descending inhibition.

Question 36

What is spinal shock and how does it present?

Answer 36

• Occurs after severe damage of the descending tracts.
• Can last weeks to months.
• Flaccid paralysis and areflexia even though the ventral roots may be in tact. Eventually becomes spastic and hypereflexic, typical of an UMN.
• Reason of loss of reflex activity is thought to involve the loss of motor influences exerted by descending fibres from the reticular formation.
• As these fibres degenerate, the intact connections in the reflex circuits become dominant and show themselves as upper motor neurone signs.

Question 37

What are UMN lesion signs?

Answer 37

Hyperreflexia - due to loss of the descending inhibitory neurone action, thus loss of the inhibition of the spinal reflexes resulting in excessive action fo the muscle reflexes.

Hypertonia - loss of inhibition to LMN resulting in increased tone as reflex circuit is no longer inhibited

Spastic paralysis - continuation of the increased muscle tone, whereby the muscle tone becomes so high that the individual’s limbs enter a state of spastic paralysis. In upper limbs, the flexors are stronger than the extensors so results in an overall flexion of the limb, whereas in the lower limb, the extensors are stronger than the flexors so results in overall extension of the limb. Obviously, this has a significant effect on gait.

Babinski’s sign (extensor plantar reflex)
A blunted instrument is taken and run along the sole of the foot laterally from heel to toe, a normal individual will show flexion of the toes yet an affected individual will show abduction of the toes and excessive dorsiflexion of the big toe.

Myoclonus - spasmodic involuntary contractions of muscles

Choreas - additional spasmodic muscle movmeents

Question 38

Describe Babinski’s reflex, it’s purpose

Answer 38

o The purpose of the reflex is to cause the withdrawal of the area of the skin from the stimulus. This reflex is mediated by the spinal cord, but influenced by higher centers. The area of skin from which the reflex can be obtained is known as the receptive field of the reflex. To be more specific, a noxious stimulus to the sole of the foot, which is the receptive field, causes immediate flexion of the toes, ankle, knee, and hip joints with attendant withdrawal of the foot from the stimulus.

o The abnormal plantar reflex, or Babinski reflex, is the elicitation of toe extension from the “wrong” receptive field, that is, the sole of the foot. Thus a noxious stimulus to the sole of the foot produces extension of the great toe instead of the normal flexion response. The essential phenomenon appears to be recruitment of the extensor hallucus longus, with consequent overpowering of the toe flexors The movements of the other joints remain the same.

Question 39

Describe myoclonus.

Answer 39

• Myoclonus – spasmodic involuntary contractions of muscles
o Due to alternate stretching and unloading of the muscle spindles in a spastic muscle.
o Can be demonstrated in the flexor muscles of the leg by pushing on the sole of the patient’s foot to dorsiflex the ankle.
o If there is damage to descending UMN pathways, holding the ankle loosely in this position generates rhythmic contractions of both the gastrocnemius and soleus muscles.

Question 40

What is the main sign seen in pyramidal lesions?

Answer 40

the loss of the finer movements of the distal muscles (i.e. loss of dexterity) as the corticospinal tract is involved in fractionation of finger movements.

Though rare alone - UMN lesion usually involve extrapyramidal and pyramidal or just eactrapyramidal