from anesthetic point of view

1. ANATOMY AND PHYSIOLOGY OF
CENTRAL NERVOUS SYSTEM
Dr. aparna jayara (p.g. 1st year)

2. Organs
CNS:
• Brain
• Spinal Cord
PNS:
• Nerves

3. INTRODUCTION
Brain is a closed structure
Most of it is brain tissue
while some of it is blood
and CSF
Brain comprises 80%
Cerebral blood volume: 12%
CSF contribute to 8% of the space
inside the skull vault.
Any increase in 1 component
must be offset by equivalent
decrease in other to prevent
rise in ICT
Monro – Kellie doctrine

4. Brain
• It is one of the largest organs in the body, and
coordinates most body activities.
• It is the center for all thought, memory,
judgment, and emotion.
• Each part of the brain is responsible for
controlling different body functions, such as
temperature regulation and breathing.

5. Cerebrum
• It is the largest section of the brain
• It is located in the upper portion of the brain and
is the area that processes thoughts, judgment,
memory, problem solving, and language.
• The outer layer of the cerebrum is the cerebral
cortex, which is composed of folds of gray matter.
• The cerebrum is subdivided into the left and right
halves called cerebral hemispheres. Each
hemisphere has 4 lobes.

6. Lobes of Cerebrum

7. Lobes of Cerebrum
• 1. Frontal lobe: Most anterior portion of the
cerebrum, controls motor function,
personality, and speech
• 2. Parietal lobe: The most superior portion of
the cerebrum, receives and interprets nerve
impulses from sensory receptors and
interprets language.
• 3. Occipital lobe: The most posterior portion
of the cerebrum, controls vision.
• 4. Temporal lobe: The left and right lateral
portion of the cerebrum, controls hearing and

8. Cerebellum
• Second largest portion of the brain
• Located beneath the posterior part of the
cerebrum
• Aids in coordinating voluntary body
movements and maintaining balance and
equilibrium
• Refines the muscular movement that is
initiated in the cerebrum

9. Brain Stem
• Midbrain—acts as a pathway for impulses to
be conducted between the brain and the
spinal cord.
• Pons — means bridge—connects the
cerebellum to the rest of the brain.
• Medulla oblongata—most inferior positioned
portion of the brain; it connects the brain to
the spinal cord.

10. Spinal Cord
• Runs through the vertebral canal
• Extends from foramen magnum to 2nd
lumbar vertebra
• Regions
– Cervical
– Thoracic
– Lumbar
– Sacral
– Coccygeal
• Gives rise to 31 pairs of spinal nerves - all
are mixed nerves

11. Meninges
• Dura mater: outermost
layer; continuous with
epineurium of the spinal
nerves
• Arachnoid mater: thin and
wispy
• Pia mater: bound tightly to
surface

12. Blood Supply To The Brain

13. Arteries supplying the brain

14. 2 sources of blood:
ICA and VA

15. atlas
axis
Vertebro-basilar system CTA: CT angiography
C6
laterally
upward
backward

17. Circle of Willis

18. Circle of Willis

19. Circle of Willis
oculomotor n.
abducens n.
optic chiasm
mamillary
bodies
pituitary
stalk

20. 1. Circle of Willis encloses the optic chiasm, pituitary stalk and mamillary bodies.
2. Oculomotor nerve exits between the post. cerebral and sup. cerebellar arteries.
3. Vertebral arteries of the two sides unite to form the basilar artery at the ponto-
medullary junction. The root of the abducens nerve and initial segment of the ant. inf.
cerebellar artery can also be found here.

21. A1
A2

24. anterior cerebral
middle cerebral
posterior cerebral

26. Venous drainage
3 set of veins drain from
brain
1. Superficial cortical vein
2. Deep cortical veins
3. Dural sinuses
All ultimately drain into
right and left IJV

27. • Almost the total volume of venous blood collected from the
brain leaves the skull through the jugular foramen and the
internal jugular vein.
• If the jugular foramen and/or the internal jugular vein is
occluded, blood may escape through the diploic and emissary
veins connecting the dural sinuses with the veins of the scalp
skin.

28. Blood-brain barrier (BBB)
The extracellular fluid of the CNS is separated from the blood by the
BBB ensuring strictly controlled and mainly carrier protein assisted
transport of macromolecules.
Is formed by endothelial cells attached to one other by tight junctions,
basement membrane, astrocytic endfeet.
Protects the CNS from possibly toxic agents.

29. the Circumventricular organs
“Circumventricular” = around the ventricles
Incomplete or missing BBB
Highly capillarized structures
Secretion of neurohormones or detection of hormones,
glucose, ions, etc.

31. Subfornical organ sensory fluid regulation
Organum
vasculosum
sensory,
secretory
detects peptides, fluid regulation
Median eminence secretory
regulates the anterior pituitary through the release
of neurohormones
Neurohypophysis secretory
store and secretes the hormones oxytocin and
ADH into the blood, but does not synthesize
either hormone
Subcommissural
organ
secretory
secretes certain proteins into the cerebrospinal
fluid, its specific function is as yet unknown.
Pineal gland secretory
stimulated by darkness to secrete melatonin and
is associated with circadian rhythms
Area postrema sensory
the vomiting centre of the brain (can detect
noxious substances in the blood and stimulate
vomiting in order to rid the body of these toxic
chemicals)

32. The cerebrospinal fluid (CSF)
• Provides mechanical protection for the brain and the spinal
cord.
• When floating in the CSF brain weighs only 50g (!) according to
the Archimedes’ principle.

33. • Cerebrospinal fluid (CSF) is a clear fluid
present in the ventricles of the brain, the
central canal of the spinal cord, and the
subarachnoid space.
• CSF is produced in the brain by
modified ependymal cells in the choroid
plexus (approx. 50-70%), and the remainder is
formed around blood vessels and along
ventricular walls.

35. Circulation of CSF
Lateral ventricles
interventricular foramen of Monroe
third ventricle
mesencephalic aqueduct
(aqueduct of Sylvius)
fourth ventricle
spinal cord central canal;
also, out the lateral apertures to the subarachnoid space to the venous
system

36. internal and external CSF
spaces
internal = ventricles external = subarachnoidal space

37. Site of CSF resorption: arachnoid granulations in the superior sagittal
sinus and lateral lacunae.

38. 20 ml of fluid produced every hr in choroids
plexus and reabsorbed by arachnoid villi
500ml/day, yet total csf volume is only about
150 ml

39. Brain Functions
• Vision
• Taste
• Cognition
• Emotion
• Speech
• Language
• Hearing
• Motor Cortex
• Sensory Cortex
• Autonomic Functions

40. Cerebellum
The cerebellum is connected to the
brainstem, and is the center for
body movement and balance.
Click image to play or pause video

41. Thalamus
Thalamus means “inner room” in Greek,
as it sits deep in the brain at the top of
the brainstem.
The thalamus is called the gateway to
the cerebral cortex, as nearly all
sensory inputs pass through it to the
higher levels of the brain.

42. Hypothalamus
The hypothalamus sits under the thalamus at
the top of the brainstem. Although the
hypothalamus is small, it controls many critical
bodily functions:
• Controls autonomic nervous system
• Center for emotional response and behavior
• Regulates body temperature
• Regulates food intake
• Regulates water balance and thirst
• Controls sleep-wake cycles
• Controls endocrine system
The hypothalamus is
shaded blue. The pituitary
gland extends from the
hypothalamus.

43. Cerebral blood supply:
Physiological considerations:
Brain accounts for 2% of body
weight yet requires 20% of
resting oxygen consumption
O2 requirement of brain is 3 – 3.5
ml/100gm/min
And in children it goes higher up to
5 ml/100gm/min
Brain has high metabolic rate
That’s why brain requires
higher blood supply
55ml/100gm/min is the rate
of blood supply
requires more
requires
more
substratete
substrate
requires
mlacks of
storage of
energy
substrate

44. Cerebral blood supply
Cortical grey matter
75 – 80 ml/100gm/min
Subcortical white matter
20ml/100gm/min
CMRO2 : 5.5 ml/100gm/min
Functional requirement is
3.3 ml/100gm/min
Integrity required 02 is
2.2 ml/100gm/min
60% functional
40 %
integrity

45. • High consumption bt low reserves responsible
for unconsciousness within 10 sec of
interruption of blood supply ( o2 tension
dropping below 30mmhg, if sustained for 3-8
min can cause irrev. Injury to brain (
hippocampmpus and cerebellum being most
sensitive)
• Main energy from glucose ( 5mg/100gm/min),
90% of which metabolized aerobically.

46. Regulation of cerebral blood flow
• CEREBRAL PERFUSION PRESSURE
• CPP=MAP-ICP(CVP if it is greater than ICP)
• Normally its is 80-100 mmhg, icp is normally
less than 10 mmhg, cpp is primarily
dependent on MAP.
• CPP less tha 50 mmhg show slowing of EEG,
those with CPP between 25 and 40 mmhg hav
a flat EEG. Sustained <25 mmhg lead to irrev.
Brain damage.

47. Regulation of cerebral blood flow

49. Autoregulation
• Cerebral vasculature rapidly (10-60s) adapts to
change in CPP( decrease in cpp causes
vasodilatation and vice versa)
• CBF remains const b/w MAP of 60-160 mmhg.
• Beyond these limits , blood flow becomes
pressure dependent.

50. Factors regulating cerebral blood flow
• Hemodynamic autoregulation
• Metabolic mediators and chemoregulation
• Neural control
• Circulatory peptides

51. Cerebral blood flow regulation
Arteriolar diameter as
well as cerebral vascular
resistance both vary with
CPP but CBF remains
constant in this range.

52. Cerebral blood flow regulation
2. Venous physiology:
Venous system contains
most of the cerebral
blood volume
Slight change in vessel
diameter has profound
effect on intracranial
blood volume
But evidence of their role
is less
Less smooth
muscle content
Less innervations
than arterial
system

53. Cerebral blood flow regulation
Pulsatile perfusion:
Fast and slow components of myogenic
response bring a change in perfusion pressure
Cardiac output:
Cardiac output may be responsible for improved
cerebral blood flow
They are indirectly related via central
venous pressure and large cerebral vessel
tone.

54. Cerebral blood flow regulation
Rheological factors:
Related with blood viscosity.
Hematocrit has main influence on blood
viscosity.
Flow is inversely related with hematocrit.
In small vessels cells move faster than plasma.
This reduces microvascular hematocrit and
viscosity FAHRAEUS LINDQVIST EFFECT

55. Metabolic and chemical regulation
1. Carbon dioxide
coupler between flow
and metabolism
At normal conditions CBF
has linear relationship
with CO2 between 20 –
80 mm Hg
For every mm Hg change
of PaCO2 CBF changes
by 2 – 4 %

56. Metabolic and chemical regulation
Oxygen:
Within physiological range PaO2 has no effect on
CBF
Hypoxia is a potent stimulus for arteriolar
dilatation
At PaO2 50 mmHg CBF starts to increase and at
PaO2 30 mm Hg it doubles

57. CO2 and Oxygen

58. Metabolic and chemical regulation
Temperature:
Like other organs cerebral metabolism
decreases with temperature
For every 1˚C fall in core body temperature
CMRO2 decreases by 7 %
At temperature < 18 ˚C EEG activity ceases

59. Temperature

60. Pharmacology and autoregulation
Anaesthetic drugs can alter autoregulatory
responses as seen with blood pressure and
CO2 drug
CBF CMR
Preserve
response to
CO2
Preserve
autoregulation
barbiturates ↓ ↓ yes yes
propofol ↓ ↓ yes yes
etomidate ↓ ↓ yes ….
morphine ± ↓ …. yes
fentanyl ± ± yes yes
benzodiazepines ↓ ↓ yes …
ketamine ↑ ↑ yes yes
lignocaine ↓ ↓ … …
response

61. Pharmacology and autoregulation
Inhalational agents affecting CBF
volatile
anaesthetic CBF CMR
Preserve
response to
CO2
Preserve
autoragulation
Xenon ↓ ↓ yes yes
desflurane ↑ ↓ yes yes
sevoflurane ↑ ↓ yes yes
isoflurane ↑ ↓ yes yes
enflurane ↑ ↓ yes yes
halothane ↑↑↑ ↓ yes yes
nitrous oxide ↑ ↑ … …

62. EFFECTS @ DIFFERENT MACs
D o s e b e y o n d 1 M A C
CMR reduced; but vasodilatory effect
predominates
CBF increases
@ 1 M A C
CMR suppression = vasodilation CBF unchanged
@ 0 . 5 M A C
CMR suppression predominates So net CBF decreases

63. Pharmacology and autoregulation
Vasoactive agents:
Drugs that do not cross blood brain barrier do not affect CBF

64. Pharmacology and autoregulation
Dexmedetomidine:
Causes 25% reduction in CBF primarily by
reducing CMR
ACE inhibitors, Angiotensin receptor
antagonists, β blockers…….. Do not reduce CBF
or alter autoregulation

65. Metabolic mediators and
chemoregulation
Control CBF by acting as local vasodilators
Ions and chemicals
H+, K+,
adenosine and phospholipid metabolites
Final common pathway is via NO

66. Neurogenic effects
Neurogenic effects: sympathetic tone shift
the curve to right

67. Circulatory peptides:
Vasoactive peptides like angiotensin II do affect
CBF.
Reactive oxygen molecules
Alteration to vasomotor function
Vascular remodeling
De silva et al: effects of angiotensin II on cerebral circulation: role of oxidative
stress; review article – front physiology ; jan 2013

68. To summarize

69. Clinical considerations
Hypertensive patients:
Autoregulatory curve shifts to right
Protection from breakthrough but at the cost of
risk of ischemia
May suffer cerebral ischaemia during
hemorrhage, shock or hypotension

70. Clinical considerations
Elderly patients:
With age CBF decreases
Younger people have increased blood flow in
frontal areas…. Frontal hyperaemia
But with age this increased flow reduces
Flow in other areas are well maintained hence
blood is more uniformly distributed
Autoregulatory failure occurs in morel elderly

71. Auto regulatory failure
For auto regulatory failure to occur vasomotor
paralysis is the end point
• Acute ischemia
• Mass lesions all lead to
• Inflammation vasomotor
• Prematurity paralysis
• Neonatal asphyxia
• Diabetes mellitus

72. Autoregulatory failure
Two stages before infarction:
a. Penlucida at flow 18 – 23 ml/100gm/min
brain becomes inactive but function can be
restored at any time by reperfusion
b. Penumbra at lower flow rates brain
function can be restored by reperfusion but
only within a time limit

73. Hemodynamic considerations
Cerebral steal: it means blood is diverted from
one area to another if pressure gradient exists
between the two circulatory beds
Vasodilatation in non ischemic brain takes blood
from ischemic areas to normal areas causing
more ischemia
Vasoconstriction results in redistribution of
blood from normal to ischemic areas leading
to inverse steal or ROBIN HOOD EFFECT

74. Hemodynamic considerations
Vessel length and viscosity
At breakthrough point flow depends on vessel
length and viscosity
Autoregulation has failed and it behaves like
fluid in a rigid tube
Pressure gradient across the ends are now same
so distal area have the lowest flow
This makes watershed areas more vulnerable to
ischemic changes

75. Considerations for ischemia
Consideration relevant to
global ischemia
Prevent and treat
hypotension as well as
vasogenic & cytotoxic
edema
Induction of mild
hypothermia for 24 hrs
Consideration relevant to
focal ischemia
Barbiturate coma, volatile
anesthetics (xenon),
calcium channel
antagonists
PaCO2 and temperature

76. Therapies for enhancing perfusion
• Induced hypertension
• Inverse steal
• Hypocapnea
• Hemodilution
• Pharmacological agents
• Barbiturates, propofol
• Intra arterial delivery of drugs. Like mannitol
and vasodilators

77. Thank You !!!