Central Nervous system

1. CENTRAL NERVOUS SYSTEM
Unit 1: Function of CSF, Intracranial pressure
Unit 2: Metabolic requirements of the brain, Cerebral
autoregulation
Unit 3: Consciousness
Unit 4: Basic function of the eyes: light reflex, movements
Unit 5: Cough and gag reflex
By Mr. Sujoy Tontubay
Assistant Professor, iLEAD,Kolkata.
B.Sc(C.U), M.Sc(V.U), Post graduate diploma in Epidemiology and Public health.
Biomedical Laboratory Science and Management(M.Sc)

2. 1.Cerebrospinal fluid (CSF) is a colorless, watery fluid found in
the meninges surrounding the central nervous system: the brain
and spinal cord.
2.This fluid is produced by the choroid plexus.

3. • CSF performs vital functions including: Support; Shock absorber; Homeostasis; Nutrition;
Immune function.
• Adult CSF volume is estimated to be 150 ml with a distribution of 125 ml within the
subarachnoid spaces and 25 ml within the ventricles

4. Functions:
• Shock absorber - It protects the brain from damage during head
trauma.
• It also helps transport nutrients to the central nervous system
(brain and spinal cord) and removes waste.
• Nutrition - The CSF contains glucose, proteins, lipids, and
electrolytes, providing essential CNS nutrition.
• Immune function - The CSF contains immunoglobulins and
mononuclear cells.
• Support - The CSF supports the weight of the brain estimated at
1500 gm and suspends it in neutral buoyancy to a net weight of
about 25 gm. Hence, the entire brain density is cushioned,
protecting it from crushing into the bony cranium.

5. Intracranial pressure (ICP)
• Intracranial pressure (ICP) is the pressure exerted by fluids such
as cerebrospinal fluid (CSF) inside the skull and on the brain tissue.
ICP is measured in millimeters of mercury (mmHg) and at rest, is
normally 7–15 mmHg for a supine adult.
• Intracranial hypertension (IH), also called increased ICP (IICP)
or raised intracranial pressure (RICP), is elevation of the pressure
in the cranium. ICP is normally 7–15 mm Hg; at 20–25 mm Hg, the
upper limit of normal, treatment to reduce ICP may be needed.
• A brain injury or another medical condition can cause growing pressure
inside your skull. This dangerous condition is called increased intracranial
pressure (ICP) and can lead to a headache. The pressure also further injure
your brain or spinal cord.
• This kind of headache is an emergency and requires immediate medical
attention.

6. What causes ICP?
• Causes of ICP:
• Too much cerebrospinal fluid (the fluid around your brain and spinal cord)
• Bleeding into the brain
• Swelling in the brain
• Aneurysm
• Blood pooling in some part of the brain
• Brain or head injury
• Brain tumor
• Infections such as encephalitis or meningitis
• Hydrocephalus
• High blood pressure
• Stroke

7. What are the symptoms of ICP
• These are the most common symptoms of an ICP:
• Headache
• Blurred vision
• Feeling less alert than usual
• Vomiting
• Changes in your behaviour
• Weakness or problems with moving or talking
• Lack of energy or sleepiness

8. How is ICP diagnosed?
• To diagnose ICP, your doctor may do the
following:
• Medical history and physical exam including
a neurological exam to test senses, balance
and mental status
• Spinal tap (also called lumbar puncture),
which measures the pressure of
cerebrospinal fluid
• Computed tomography (CT) scan, the gold
standard imaging test, creates a series of
cross-sectional X-ray images of the head and
brain

9. How is ICP treated?
• Increased intracranial pressure is an emergency. Treatment might
include:
• Medicine to reduce swelling
• Draining extra cerebrospinal fluid or bleeding around the brain
• Removing part of the skull (craniotomy) to ease swelling (though this
is rare)

10. What are the complications of ICP?
• ICP has serious complications, such as:
• Seizures
• Stroke
• Neurological damage
• Death

11. Energy metabolism of the CNS
• Although brain constitutes only 2 % of the total body weight its metabolic demands are
extremely high. It utilizes around 20 % of the total oxygen and 20 % of the total glucose
consumption. The biggest share of its consumption is used to maintain the membrane potential
through Na+/K+–ATPase and other processes involved in transport of ions across the membrane.
• Brain is at the same time the most sensitive organ to oxygen or glucose deficit. Shortage of
oxygen causes unconsciousness within few tenths of seconds and
the damage to neurons becomes irreversible after about 5 minutes. The rate of neuronal death
depends on many factors, for example temperature. People with hypothermia have
significantly reduced cellular metabolism and thus the demands for oxygen and nutrients
supply decrease leading to a longer survival in their absence.
• the brain metabolism utilizes almost exclusively saccharide sources, particularly glucose. Its daily
consumption is about 120 g.
• Regarding other energy sources, our brain (unlike most of the other peripheral tissues) does not
utilize fatty acids. Transported in bloodstream bound to the albumin, fatty acids are unable to cross
the hematoencephalic barrier. However, during a long-term starvation brain metabolism adapts to
the consumption of ketone bodies (synthesized from the excess of acetyl-CoA). A full adaptation
develops approximately within three weeks of starvation. After this period, the brain is able to cover
up to 50% of its energy expenditure from the oxidation of ketone bodies.

12. Cerebral autoregulation
• Cerebral autoregulation is a process in mammals, which aims to maintain
adequate and stable cerebral blood flow. While most systems of the body
show some degree of autoregulation,the brain is very sensitive to over-
and underperfusion. Cerebral autoregulation plays an important role in
maintaining an appropriate blood flow to that region. Brain perfusion is
essential for life since the brain has a high metabolic demand. By means of
cerebral autoregulation the body is able to deliver sufficient blood
containing oxygen and nutrients to the brain tissue for this metabolic need,
and remove CO2 and other waste products.
• This regulation of cerebral blood flow is achieved primarily by small
arteries, arterioles, which either dilate or contract under the influence of
multiple complex physiological control systems. Impairment of these
systems may occur e.g. following stroke, trauma or anaesthesia, in
premature babies and has been implicated in the development of
subsequent brain injury. The non-invasive measurement of relevant
physiological signals like cerebral blood flow, intracranial pressure, blood
pressure, CO2 levels, cerebral oxygen consumption

13. Consciousness
• Consciousness defines an individual’s awareness of themselves and their
surroundings together with their own mind – including a person’s own
thoughts and dreams. The conscious experience relies on the integration of
multiple parts of the nervous system.
• Neurologically speaking, the consciousness system is a series of cortical
and subcortical brain networks that work in synergy to maintain attention,
alertness, and awareness.
• Sleep is a physiological state of reduced consciousness. However,
consciousness can be also impaired or completely lost as a consequence of
pathology. A person can have different degrees of consciousness and in
turn awareness.
• By