NS Clinical relevance and summary Flashcards
why do the body areas affected by shingles correspond to dermatomes?
virus within dorsal root ganglia, and usually restricted to 1 or 2 dorsal root ganglia so body areas reflect dermatomal distribution of those roots.
what are the contents of the spinal epidural space, and which is the most medically important and why?
blood vessels and AT
most important= vertebral venous plexus
plexus is valveless and communicates freely with veins of pelvic, abdom, thoracic and cranial cavities. So can provide route for spread of infections and cancer cells from viscera to brain.
* batson venous plexus receives drainage from prostatic veins, and plexus connects with vertebral venous plexus, allowing prostate cancer to metastasise to the VC, and so may present with back pain.
what will be the outcome of a lesion of the cuneate tract unilaterally at any level of the SC?
loss of tactile, pressure, vibration, light touch and conscious proprioception sensations in dermatomes of upper limb of ipsilateral side below level of lesion as tract ascends to brain without crossing (decussation in medulla.)
gracile tract= lower limb
Patient has sensory ataxia and +ve Romberg sign,what vitamin deficiency might this highlight and why are these symptoms important to pick up on for this disease?
Vit B12, causing degenerative changes in dorsal column
NS signs will be first to appear rather than those of anaemia- pernicious anaemia- megaloblastic, pallor, fatigue.
If signs detected early, can completely cure symptoms with vit B12 IM injections.
what tract damage is almost invariably associated with Babinski sign?
corticospinal tract
stroking of lateral aspect of sole of foot with hard, blunt instrument causes dorsiflexion/extension of large toe and fanning of other toes. Normal response= flexion of all toes- flexion plantar response.
signs and causes of cerebellar dysfunction?
Together= DANISH PASTRIES DANISH= signs= dysdiadochokinesis, dysmetria (past pointing) ataxia- broad-based gait nystagmus intention tremor scanning speech hypotonia- +ve heel to shin test- coordination lack, ataxia? PASTRIES=causes paraneoplastic syndromes Freidreich's ataxia stroke trauma raised intracranial pressure infection ethanol MS
What is it about the blood brain barrier in infants that allows kernicterus to occur?
the capillary endothelium is immature and fenestrated, allowing bilirubin to enter.
How can cerebral oedema occur with disruption of BB barrier?
e.g. with trauma or tumours- astrocytic foot processes of BB barrier disrupted, and as these requlate quantity of Na+ and H20 that can cross, disruption causes fluid leakage into the brain.
describe what is meant by the sacral sparing phenomenon
this is due to the somatotopic localisation in the long ascending and descending pathways. the more rostral spinal nerves (e.g. cervical and thoracic are represented internal to the more caudal, so with bilateral damage of the central part of the spinal cord, there is loss of sensations and voluntary motor control in area of peripheral distribution of the more rostral SC segments below the lesiom, but not the more caudal. **
what symptoms would a hemisection of the SC cause?
would damage lateral corticospinal tract, causing spastic paralysis ipsilaterally, and dorsal column, causing loss of tactile, vibration and proprioception senses ipsilaterally, and spinothalamic tract, causing loss of pain and temp senses contralaterally as decussation of these fibres at segmental level of SC, in anterior (ventral) white comissure.
=brown-sequard syndrome
what visceral afferent fibres supply the urinary bladder?
pain and temperature impulses from fundus travel with SNS nerves and reach SC via dorsal roots of T12 and L1
from mucosa at neck of bladder, pain and temp impulses travel with the sacral PNS nerve to S2, 3 and 4.
The spinothalamic tract then transmits impulses of both to higher centres.
how is fullness of bladder detected?
mechanoreceptors in bladder wall- send impulses to SC via sacral PNS route (S2-S4)
sensation that micturition is imminent arises from mechanoreceptors in trigone, impulses travel with sacral PNS nerves to S2-S4, and ascend in DC medial-lemniscal tract.
what is the uninhibited reflex bladder?
occurs with bilateral lesions of micturition centres in frontal lobe, so no conscious decision to void?
bladder is therefore incontinent but empties fully as reflex control of pontine micturition centres intact
what is the automatic reflex bladder?
results from bilateral SC lesions above sacral levels e.g. SC transection
bladder incontinent as cut ascending sensory and descending autonomic pathways creating UMN type lesion producing spastic reflex bladder, where patient insensitve to bladder filling. Stretching will activate intact spinal reflex producing incontinence, but bladder emptying will be incomplete due to interruption of spinal reflex pathways that trigger pontine micturition centres.
=urge urinary incontinence
what is the flaccid non reflex bladder?
results from bilateral lesions of sacral SC or spinal nerve roots in cauda equina. causes severe urinary retention and incontinence as PNS fibres lost necessary for detrusor contraction, so overflow incontinence results.
what syndrome does syringomyelia result in?
commissural syndrome= bilateral loss of pain and temp sensations in dermatomes at levels of the lesion.
lesion= pathologic cavitation of SC, cavity opens up around canal of SC.
what remains intact in anterior spinal artery syndrome?
the dorsal column, as this receives blood from the posterior spinal artery
therefore fine touch and conscious proprioception remain intact.
name given to condition in which syphilis (treponema pallidum) causes degeneration of dorsal columns?
tabes dorsalis
through what structure do fibres of the spinothalamic tracts conveying pain and temperature sensations decussate?
ventral (anterior) white commissure
why do fasciculations occur with lesions of lower motor neurones?
increased sensitivity of ACh receptors to circulating ACh, so only a very small amount of ACh will stimulate nerve APs to cause muscle contractions.
May be seen when patient asked to protrude their tongue in a cranial nerve examination.
what are upper motor neurones?
descending tracts of brain and SC, with cell bodies located in cerebral cortex or the brainstem, axons remain in CNS.
what are lower motor neurones?**
cell body located in SC (lamine IX) or cranial nerve motor nuclei.
what do lesions of the hypoglossal nucleus result in?
paralysis and atrophy of ipsilateral tongue muscles
what is the corticobulbar tract?
descends from cerebral cortex, through internal capsule, to brainstem cranial nerve motor nuclei (CL?), and control muscles of facial expression, extra-ocular muscles and neck muscles.
function of reticulospinal tracts?
automatic movements (locomotion) 2 neurone groups= pontine and medullary reticular neurones pontine= facilitate extensor movements, and inhibit flexor medullary do the opposite pontine extensor excitatory area is under inhibtory control from higher centres, whereas medullary areas is facilitated by higher centres.
so if brainstem impairment below level of red nucleus in midbrain, get decerebrate posturing= extension of U and LLs, as impair inhibition from cerebral cortex normally exerted on reticular formation (on pontine fibres.) to inhibit extensor reflexes mediated by reticular formation.
what is decorticate posturing and how does it occur?
impairment of brainstem activity above level of red nucleus, so red nucleus can cause flexion in upper limbs, so patients LLs extend but ULs flex.
