Sensory and Cerebellar Defects

Question 1

Why does clasp-knife reflex happen in an upper motor neurone lesion?

Answer 1

Increased tone causes increases resistance

When sufficient force is supplied, resistance suddenly decreases

Question 2

Why does clonus happen in upper motor neurone lesions?

Answer 2

Loss of descending inhibition leads to self re-excitation of hyperactive reflexes

Question 3

How is a Babinski sign elicited?

Answer 3

Scrape along lateral edge of foot
Get dorsiflexion of hallux with extension/flex ion of toes

Due to loss of descending inhibition meaning the reflex is unable to be suppressed

Question 4

What are lower motor neurone signs?

Answer 4

Hypotonia/atonia
Hyporeflexia/areflexia
Denervation muscle atrophy 
Fasciculations 
Paralysis 
Muscle weakness
Muscle wasting

Question 5

What are fasciculations and why do they occur?

Answer 5

Spontaneous depolarisation in muscle
Happen because Ach receptors become hypersensitive to any neurotransmitter substance. Therefore any molecule vaguely similar to Ach can cause excitation and muscle contraction

Question 6

What are pyramidal upper motor neurone signs?

Answer 6

Reduction in motor tone
Loss of fractionation of finger movements
Similar to LMN signs but mor for same reasons

Question 7

Innervation of the detrusor muscle?

Answer 7

Parasympathetic

• pelvic nerve S2-4
• M3 receptors

Sympathetic

• hypogastric nerve T10-L2
• β3 receptors

Question 8

Innervation to internal urethral sphincter?

Answer 8

Sympathetic
-hypogastric T10-L2
-α-1 receptors
(Contraction)

Question 9

Innervation of external urethral sphincter?

Answer 9

Somatic

• pudendal nerve S2-4
• nicotinic receptor (Ach)
• causes contraction

Question 10

Spinal roots of afferent stretch receptors in bladder wall?

Answer 10

S2-S4

Question 11

What happens to bladder control if there is damage to S2-4?

Answer 11

Loss of parasympathetic efferents and sensory afferents

• loss of pelvic nerve (S2-4) so no contraction of detrusor
• loss of pudendal nerve (S2-4), external urethral sphincter
• loss of afferent stretch receptors

Therefore have unopposed action of SNS (hypogastric) so bladder capacity increased and cannot empty. Get overflow incontinence

Question 12

What happens if there is damage to the spinal cord above T10 to bladder control?

Answer 12

Loss of the pudendal nerve (S2-4)
Keep hypogastric
Keep pelvic

Bladder fills to a point and then, every 1-4 hours, afferent stretch receptors are activated stimulating voiding
Loss of voluntary control
Comparable to upper motor neurone lesion

Question 13

What hapless if there is damage to T12-L2 to bladder control?

Answer 13

Keep parasympathetic and afferent stretch receptors
Loss sympathetic and somatic
Loss of sympathetic outflow and failure of internal urethral sphincter to contract
Constant dribbling of urine because parasympathetic and afferent stretch receptor fibres still in tact. However do not become active because bladder does not fill enough

Question 14

Where is the most common site of damage to upper motor neurones?

Answer 14

Internal capsule

Cerebral cortex

Question 15

Why can repair of lower motor neurones not happen in poliomyelitis?

Answer 15

Causes damage to the cell body so axons cannot regenerate

Question 16

How can the internal capsule be damaged?

Answer 16

Supplied by the middle cerebral artery

-at risk from haemorrhagic stroke

Question 17

What are the upper motor neurone signs?

Answer 17

Due to loss of descending inhibition

• hypertonia
• hyperreflexia
• spastic paralysis

Clasp-knife reflex 
Clonus
Positive Babinski sign 
Choreoforms
Pronator drift

Question 18

Structure of the cerbellum?

Answer 18

Highly folded
Grey matter cortex
White matter periphery
Three peduncles which carry input and output fibres to and from the brainstem
Core has three pairs of deep nuclei that generate output projections to the brainstem

Question 19

What are the three functional zones of the cerebellum? Inputs and main function of each?

Answer 19

Vestibulocerebellum

• from vestibular system
• balance and ocular reflexes

Spinocerebellum

• spinocerebellar ascending tract
• unconscious proprioception, error correction

Cerebrocerebellum

• contralateral cerebral cortex
• fine motor control, movement planning, motor learning
• particularly visually guided movements and coordination of muscle activation

Question 20

Signs of cerebellar dysfunction?

Answer 20

DANISH PT
Dysdiadochokinesia
Ataxia 
Nystagmus 
Intention tremor
Slurred speech (ataxic and dysarthric)
Hypotonia 

Past-pointing (dysmetria)
Tremor

Question 21

Why does dysdiadochokinesia occur?

Answer 21

Unable to control agonist muscle groups

Question 22

How is dysmetria elicited and why does it happen?

Answer 22

Finger to nose test and heel-shin test

Inability to control smooth and accurate targeted movements - movements are jerky and overshoot target (past-pointing)

Question 23

When does an intention tremor occur?

Answer 23

In finger nose test

Occurs at the end of their movement path - tremor as they try to touch finger

Question 24

What is the speech like of someone with a cerebellar dysfunction?

Answer 24

Ataxic and dysarthric

• slow
• scanning (monotone and broken up into syllables)

Question 25

In which side is nystagmus maximal on in cerebellar dysfunction?

Answer 25

On the side of the lesion

Question 26

What is the rebound phenomenon in cerebellar dysfunction?

Answer 26

Examiner presses down on outstretched arms

Release pressure, arms rebound upwards much further than would be expected

Question 27

Causes of cerebellar dysfunction?

Answer 27

Tumours
Cerebrovascular disease
Genetic eg Fredrich’s ataxia