Neurology

Question 1

Components of Nervous system?

Answer 1

The nervous system is composed of two components:
central
peripheral: sensory and motor.

The nervous system can also be divided into somatic
and autonomic:
somatic: supplies the skin and muscles
autonomic: supplies glands, sphincters and
smooth muscles within blood vessels etc.

Question 2

What are the different types and functions of neuroglia?

Answer 2

astrocytes: form the ‘blood–brain barrier’
microglia: perform a phagocytic role in the CNS
oligodendroglia: produce myelin.

Question 3

How is cerebral blood flow regulated?

Answer 3

Cerebral blood flowis controlledby threemechanisms:
Autoregulation: myogenic or metabolic

Cerebral perfusion pressure = MAP - ICP

• Myogenic autoregulation occurs when the cerebral
  blood vessels constrict or dilate to maintain
  adequate cerebral perfusion.
  Flow is maintained by changes in
  the cerebrovascular resistance (CVR) with increasing
  vasoconstriction at high CPP and vasodilatation at
  low CPP. The effect of CVR can also be seen to affect
  cerebral blood volume (CBV): vasodilatation
  increasing CBV and vasoconstriction decreasing it.

Myogenic autoregulation can be impaired by a
number of factors, such as:
hypoxia
ischaemia
trauma
cerebral haemorrhage
tumour
infection.

Metabolic
The activity of certain areas of the brain will differ
depending on the task being performed; as a consequence
these areas will require additional blood
flow.
The increased activity results in a decrease in PaO2
and increase in PaCO2 and H+
- local vasodilatation of cerebral blood vessels
and thus increased perfusion.

Local
PaCO2 are associated with an increase
in CBF due to marked cerebral vasodilatation; however,
just as hypercapnia results in vasodilatation
then a fall in PaCO2 (hypocapnia) results in cerebral
vasoconstriction.
CO2 control is important in Head injury patients
low–normal CO2 prevents increases in ICP
due to cerebral vasodilatation. Equally it must be remembered that overzealous ventilation to low CO2
levels can be equally detrimental due to vasoconstriction and consequent cerebral ischaemia.

Question 4

What are the functions of CSF

Answer 4

1) Protective liquid shock absorber

2) Appropriate Ionic environment

Question 5

Blood–brain barrier is not continuous and in
some areas consists of fenestrated capillaries.
These areas lie in the midline and include:

Answer 5

• third and fourth ventricles: allows drugs and
  noxious chemicals to trigger the chemoreceptor
  area in the floor of the fourth ventricle; this
  in turn triggers the vomiting centre. In addition
  angiotensin II passes to the vasomotor centre in
  this region to increase sympathetic outflow and
  causes vasoconstriction of peripheral vessels
• posterior lobe of pituitary: allows the release of
  oxytocin and antidiuretic hormone (ADH) into
  the circulation
• hypothalamus: this allows the release of releasing
  or inhibitory hormones into the portal–
  hypophyseal tract.

Question 6

Preconditions for the diagnosis

of brainstem death

Answer 6

1) the patient must be in a coma
2) there must be a known cause for the patient’s
coma
3) this cause must be known to be irreversible
4) the patient must be dependent on a ventilator.

Question 7

Exclusion criteria for the diagnosis

of brainstem death

Answer 7

1 )no residual drug effects from narcotics, hypnotics,
tranquillisers, muscle relaxants, alcohol
and illicit drugs
2) core body temperature must be > 35C
3) no circulatory, metabolic or endocrine abnormality
disturbance that may contribute to the coma.