2. CONTENTS
Basic anatomy of brain and its function
Blood supply
Venous drainage
Cerebral blood flow
Cerebral perfusion pressure
Intracranial pressure
3.
4.
5. Brain is divided into supratentorial
and infratentorial compartment.
SUPRATENTORIAL COMPARTMENT
contains cerebral hemisphere and
diaencephalon
INFRATENTORIAL COMPARTMENT
contains brainstem and cerebellum
Cerebrum largest part of brain made
of two hemisphere , numerous folds
Based on functional differences
,divided into four lobes,frontal
,parietal ‘temporal’ occipital
6. LIMBIC system medial portion of
temporal lobe .
plays a vital role in forming memory ,
emotion and behaviour
Made of amygdala, hippocampus
fornix, mammalian bodies , cingulate
gyrus and para hippocampus
Basal ganglia made of caudate
nucleus, putamen , globus pallidus,
nucleus ambiguens , olfactory
tubercle , ventral pallidum,
subthalamic nuclei and substantia
nigra
7. Basal ganglia modulates voluntary
movement, procedural learning ,
routine behaviour
or habits
Diencephalon made of thalamus
,epithalamus, subthalamus, and
hypothalamus
Thalamus integrates sensory and
motor input and transmit the
information to the ipsilateral
cerebral cortex
It receives signal input from all the
senses except smell
10. INFRATENTORIAL COMPARTMENT is area under tentorial cerebelli. The primary
component is cerebellum
Cerebellum plays a major role in motor function ,coordination , posture ,and
balance
The most important cell in cerebellum are purkinjee cell ,and granule cell
11. BLOOD SUPPLY OF BRAIN
CBF is 15% of cardiac output
Brain is vulnerable to factors that acute
decrease blood flow
Autoregulation is a phenomenon of maintaining
a constant blood flow despite a change in
perfusion pressure
The arterial blood supply is divided into
anterior and posterior portion .
The anterior part is via left and right internal
carotid artery, while posterior is the vertebro
basilar artery. The anastomosis of the system
forms Circle of Willis
14. Venous Drainage of The Brain
features
-does not follow the arterial pattern.
- thin-walled due to absence of
muscular tissue in their walls.
no valves.
runs in the subarachnoid space.
- superficial and deep
DEPARTMENT OF MEDICINE, IMS BHU 14
15. It is made of two parts . The superficial
sinuses and deep sinuses . The superficial
system is composed of sagittal sinus and
cortical vein located on the surface of the
brain
The deep venous drainage system is
composed of lateral sinuses, sigmoid
sinuses ,straight sinus ,and deep cerebral
vein.
All the vein in deep venous drainage
system combine to form vein of Galen
both of these system combine to drain in
internal jugular vein
16. CEREBRAL BLOOD FLOW
Cerebral blood flow is tightly
regulated because brain lacks its own
glucose and oxygen storage
Normal cerebral blood flow is
50ml/100g/mim
In adult brain the CBF is 700ml/min
or 15% of CO
CBF is controlled by vasodilation or
vasoconstriction of arterioles.
Autoregulation of these vessel occur
in response to metabolic and
physiological parameters
PaCO2 : an acute 1mm decrease in
paco2 causes decrease in CBF by 4%
17. PaO2 CBF does not correlate with
pao2 when it exceeds 50 mm hg
Temperature CBF increases by 6 to
7% for each degree rise in
temperature
MAP : CBF is maintained across a
MAP of 50 to 150 mm hg
Blood viscocity :blood viscocity is
inversely proportional to CBF
CBF increases due to vasodilation
in response to decreasing
haemocrit
18. Cerebral perfusion pressure
CPP is the difference in the pressure
between the arterial and venous
circulation which dictates the blood flow
to the brain
CPP= MAP –ICP
normally CPP is 80 mm hg ( 70 to 90 )
Blood loss causing hypotension will reduce
MAP and CPP while an intracerebral
hematoma will increase ICP
CPP is regulated by four primary factors
1 Cerebral metabolism
2 CO2 and O2
19. CPP CONT…
3 Autoregulation
4 neurohumoral factors
Cerebral Metabolism : changes in
CBF and metabolism tend to follow
each other .local or global increase
in metabolic demand are met rapidly
by an increase in CBF and vice versa
these changes are controlled by
several vasoactive metabolic
mediators like hydrogen ions ,CO2
.adenosine.NO
2 carbon dioxide and oxygen
20. CPP CONT…
CBF is directly proportional to PaCO2 of 20 to 80 mm Hg
Blood flow changes to 1 to 2 ml/100g/min /mmhg change in Paco2
This effect is almost immediate to changes in the pH of CSF and cerebral
tissue
Hyperoxia is associated with only minimal decrease in CBF
3 Autoregulation : It is a myogenic mechanism .ie .vascular smooth muscle
constrict in response to increase in wall tension and relaxes in response to a
decrease in it
21. CPP CONT…
The autoregulation curve is shifted to
right in chronic hypertensive patient
4 Neurohumoral factors
: the
main action of sympathetic nerve is
vasoconstriction and hence it
protects the brain by shifting the
autoregulation to right in
hypertension
Parasympathetic nerve cause
vasodilation and may play a part in
hypotension and reperfusion injury
22. INTRACRANIAL PRESSURE
ICP is the pressure inside the
cranial vault relative to
atmospheric pressure
Normal ICP ranges between 5 to
15mmhg
ICP is a dynamic pressure
waveform with variation in
amplitude due to cardiac and
respiratory cycle
Within each wave there are three
distinct phase P1,P2,P3
23. ICP CONT….
The main intracranial vault volume in an adult male is 1473 ml and it consists
of three component brain parenchyma (85% of intracranial volume) ,cerebral
blood ,and CSF
Intracranial blood volume is 10% of intracranial volume (100 to 130ml )
Intracranial CSF accounts 75ml (5% of intracranial volume )
Since intracranial content are contained within the rigid skull vault ,an
increase in the volume of one compartment must be offset by reduction in
the volume of the other component if the pressure is to remain the same
29. REFRENCES
Maldonado KA, Alsayouri K. Physiology, Brain. [Updated 2023
Mar 17]. In: StatPearls [Internet]. Treasure Island (FL):
StatPearls Publishing; 2024 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK551718
TEXTBOOK OF NEUROANAESTHESIA AND NEUROCRITICAL
CARE/Springer/ 3rd ed
TEXTBOOK OF NEUROCRITICAL CARE/Mrek A Mirski
