Flashcards in Sensory and Cerebellar Defects Deck (27):
Why does clasp-knife reflex happen in an upper motor neurone lesion?
Increased tone causes increases resistance
When sufficient force is supplied, resistance suddenly decreases
Why does clonus happen in upper motor neurone lesions?
Loss of descending inhibition leads to self re-excitation of hyperactive reflexes
How is a Babinski sign elicited?
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
What are lower motor neurone signs?
Denervation muscle atrophy
What are fasciculations and why do they occur?
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
What are pyramidal upper motor neurone signs?
Reduction in motor tone
Loss of fractionation of finger movements
Similar to LMN signs but mor for same reasons
Innervation of the detrusor muscle?
-pelvic nerve S2-4
-hypogastric nerve T10-L2
Innervation to internal urethral sphincter?
Innervation of external urethral sphincter?
-pudendal nerve S2-4
-nicotinic receptor (Ach)
Spinal roots of afferent stretch receptors in bladder wall?
What happens to bladder control if there is damage to S2-4?
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
What happens if there is damage to the spinal cord above T10 to bladder control?
Loss of the pudendal nerve (S2-4)
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
What hapless if there is damage to T12-L2 to bladder control?
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
Where is the most common site of damage to upper motor neurones?
Why can repair of lower motor neurones not happen in poliomyelitis?
Causes damage to the cell body so axons cannot regenerate
How can the internal capsule be damaged?
Supplied by the middle cerebral artery
-at risk from haemorrhagic stroke
What are the upper motor neurone signs?
Due to loss of descending inhibition
Positive Babinski sign
Structure of the cerbellum?
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
What are the three functional zones of the cerebellum? Inputs and main function of each?
-from vestibular system
-balance and ocular reflexes
-spinocerebellar ascending tract
-unconscious proprioception, error correction
-contralateral cerebral cortex
-fine motor control, movement planning, motor learning
-particularly visually guided movements and coordination of muscle activation
Signs of cerebellar dysfunction?
Slurred speech (ataxic and dysarthric)
Why does dysdiadochokinesia occur?
Unable to control agonist muscle groups
How is dysmetria elicited and why does it happen?
Finger to nose test and heel-shin test
Inability to control smooth and accurate targeted movements - movements are jerky and overshoot target (past-pointing)
When does an intention tremor occur?
In finger nose test
Occurs at the end of their movement path - tremor as they try to touch finger
What is the speech like of someone with a cerebellar dysfunction?
Ataxic and dysarthric
-scanning (monotone and broken up into syllables)
In which side is nystagmus maximal on in cerebellar dysfunction?
On the side of the lesion
What is the rebound phenomenon in cerebellar dysfunction?
Examiner presses down on outstretched arms
Release pressure, arms rebound upwards much further than would be expected