Nervous System.pptx

NERVOUS
SYSTEM
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Pabitra Thapa, Sr. Product Manager

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The nervous system is an organ system containing a network of
specialized cells called neurons that coordinate the actions of an
animal and transmit signals between different parts of its body
Three basic functions are performed by nervous systems:
Receive sensory input from internal and external environments
Integrate the input
Respond to stimuli
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Divided into Two Parts:
• Central (CNS)
• Peripheral (PNS)
http://www.morphonix.com
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CENTRAL NERVOUS SYSTEM
The Central Nervous System (CNS) is composed of the brain and spinal cord. The
CNS is surrounded by bone-skull and vertebrae. Fluid and tissue also insulate the
brain and spinal cord.
The central nervous system (CNS) is the largest part, and includes the brain and
spinal cord. The spinal cavity contains the spinal cord, while the head contains the
brain.
The CNS is enclosed and protected by meninges, a three-layered system of
membranes, including a tough, leathery outer layer called the dura mater.
The brain is also protected by the skull, and the spinal cord by the vertebrae.
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The Peripheral Nervous System (PNS)
• The Peripheral Nervous System (PNS) connects the CNS to
other parts of the body, and is composed of nerves (bundles of
neurons).
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Peripheral nervous system
• Somatic system
–12 pairs cranial nerves
–31 pairs spinal nerves
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There are 12 pairs of cranial nerves originating from the
brain. They are as follows:
Cranial nerves:
VII: Facial
VIII: Vestibulocochlear
IX: Glossopharyngeal
X: Vagus
XI: Accessory
XII: Hypoglossal
I: Olfactory
II: Optic
III: Occulomotor
IV: trochlear
V: Trigeminal
VI: Abducens
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Nervous tissue
• Nervous tissue is composed of two main cell types: neurons and
glial cells.
• The neuron is the functional unit of the nervous system that
transmit nerve messages
• Glial cells (named from the Greek for "glue") are non-neuronal
cells that provide support and nutrition, maintain homeostasis,
form myelin, and participate in signal transmission in the nervous
system
• . They are in direct contact with neurons and often surround them.
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Neurons
Nerve Cells
• Parts
– Soma (dendrites Branch off)
– Dendrites
– Axon
• Carry messages
– Called impulses
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Neuron- basic structural
unit of the nervous system
Dendrites- carry impulses
towards the cell
 Axon-carry impulses away
from the cell
Myelin sheath
Synaptic terminal
Epinephrine
Norepinephrine
Acetylcholine
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3 main types of nerve cells
sensory
neurone
relay neurone motor
neurone
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Sensory neurons
Carries impulses from receptors e.g pain receptors in skin to the CNS(
brain or spinal cord)
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Relay neuron
Carries impulses from sensory nerves to motor nerves.
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Motor neuron
Carries impulses from CNS to effector e.g. muscle to bring about
movement or gland to bring about secretion of hormone e.g ADH
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Stimulus-Response
•Stimulus (stimuli)
–Anything that the body can react or
respond to
•May be internal or external
•Response – the reaction to stimuli
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http://www.bbc.co.uk
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home.earthlink.net/~dayvdanls/IHP2.html
1.Stimuli comes into the
brain through the five
senses. The nerves that
bring stimuli into the
body are SENSORY
neurons.
2.The impulse travels
through
INTERNEURONS.
3.When the impulse
reaches the MOTOR
neuron, the response
occurs.
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Physiological anatomy of Neuron
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Synapses
The junction between a nerve cell and another cell is called
a synapse.
 Messages travel within the neuron as an electrical action
potential.
The space between two cells is known as the synaptic cleft.
To cross the synaptic cleft requires the actions of
neurotransmitters. Neurotransmitters are stored in small
synaptic vessicles clustered at the tip of the axon.
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SYNAPSES
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Neurotransmitter
• Neurotransmitter is the chemical substance which is used for
transfer of information through synapse”
Properties of neurotransmitter
• 1)It is synthesized in neuron
• 2)It is stored in presynaptic endings
• 3) It is released at the synapse
• 4)It has its specific receptors in the postsynaptic membrane
• 5)It is disposed quickly by suitable system as soon as action
is over
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Neurotransmitters are basically chemical messengers
the neurons (or nerve cells) use to communicate with
one another.
When one neuron wants to communicate to another,
it releases this chemical into the synapse (the space
between neurons), and the chemical finds its way
over to little receiving units on the other neuron (called
neuroreceptors), and binds to them, thus completing
the transmission
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• Some types of neurotransmitters are then 'recycled'
into the sending neuron, which is a process called
reuptake.
• This prevents the neurotransmitter from continuiing
to send the same message, as well as (from what I
understand) making them available again to be
transmitted as a new signal when needed
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Types of Neurotransmitters:-
Neurotransmitters are of two types that is inhibitory
and excitatory.
Inhibitory neurons are responsible for calming the
brain and create balance like balance in mood. They
can easily be replaced by excitatory neurotransmitters
when they are overactive. It is not necessary that
excitatory neurotransmitters are always exciting but
they also stimulate the brain.
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Excitatory neurotransmitters
· Dopamine
· Histamine
· Norepinephrine
· Epinephrine
· Glutamate
· Acetylcholine
Inhibitory neurotransmitters
· GABA
· Dopamine
· Serotonin
· Acetylcholine
· Taurine
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Neurotransmitter Overview
Acetylchloine helps with memory and learning.
Dopamine is primarily responsible for sex drive, mood, alertness, and
movement.
Norepinephrine and epinephrine influence alertness, arousal, and mood.
Dopamine Noradrenaline Adrenaline
Serotonin is involved in mood, appetite control, emotional balance, and impulse
control.
GABA helps with relaxation and sedation.
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Classification of neurotransmitter
Biogenic amines Peptides Aminoacid others
1)Catecholamines
a) Epinephrine
b) Norepinephrine
c) Dopamine
2)Histamine
3)5-HT(Serotonin)
1)Opoid Peptides
a) Enkephalins
b) Endorphin
c) Dynorphin
2)Substance P
3)Neurotenmin
4)Somatostatin
1)GABA
2)Glycine
3)Glutamate
4)Aspartate
1)Acetylcholine
2)Adenosine
3)ATP
4)NO
5)CO
6)Prostaglandi
n
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Acetylecholine
The first neurotransmitter discovered is acetylcholine. It was
discovered by a German scientist Otto Loewi, winner of Nobel
Prize.
Many functions of the body are associated with this
neurotransmitter.
For example, it is responsible for the stimulation of muscles like
the muscles of gastro intestinal system. It is also present in the
sensory neurons of the nervous system and controls the dreams a
person has during his sleep.
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ACETYLCHOLINE
• Transmitter used by all motor axon arising from spinal cord
• Ach acts on two types of receptor
1)Muscarinic cholinergic receptor: In smooth muscle and glands,
C.N.S
2)Nicotonic cholinergic receptor: In autonomic ganglia, C.N.S
and N.M.J
Note: Deficits in pathway involving Ach in brain have been
implicated in some form of senile dementia (Alzheimer's
disease)
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Dopamine
• This neurotransmitter is most commonly
known for its relationship to feelings of
'pleasure' or 'desire', but is also involved
in body movement, memory, attention,
and so on
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Dopamine
It is part of the brain’s reward system and creates feelings of
satisfaction or pleasure when we do things we enjoy, such as eating
or having sex.
Eating foods that taste good and having sex also stimulate an
increase in dopamine levels.
 For this reason, many surmise that a deficient level of dopamine
in the brain may be behind peoples’ tendencies to use drugs, drink
alcohol, smoke cigarettes, be promiscuous, gamble or overeat.
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Dopamine
Dopamine’s functions are diverse, affecting memory, motor
control, and pleasure. It allows us to be alert and motivated and to
feel satisfied.
Dopamine is associated with positive stress states such as being in
love, exercising, listening to music, and sex.
 Once produced, dopamine can, in turn, convert into the brain
chemicals norepinephrine and epinephrine.
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High Dopamine
• However, too much of a good thing can be bad for you. An
increased level of dopamine in the frontal lobe of the brain
contributes to the incoherent and disrupted thought
processes that are characteristic of schizophrenia.
• High dopamine levels have been observed in patients with
poor gastrointestinal function, autism, mood swings,
aggression, psychosis, anxiety, hyperactivity, and children
with attention disorders.
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Dopamine
Neurons containing high level of dopamine are found in
mid brain region (substantia nigra). Axon of these neuron
end in corpus striatum.
In Parkinson's disease there is degeneration of
dopaminergic synapse in corpus striatum, which causes
muscular tremor and rigidity.
Receptors: D1, D2, D3, D4
Number of D4 receptor increase very much in
schizophrenia. So drugs used in treatment of schizophrenia
block this receptor.
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Low level of Dopamine
Too little dopamine in the motor areas of the brain are responsible
for Parkinson's disease, which involves uncontrollable muscle
tremors.
A decline in dopamine levels in the thinking areas of the brain is
linked to cognitive problems (learning and memory deficits), poor
concentration, difficulty initiating or completing tasks, impaired
ability to “lock onto” tasks, activities, or conversations, lack of
energy, lack of motivation, inability to “feel alive”, addictions,
cravings, compulsions, a loss of satisfaction in activities which
previously pleased you, and slowed motor movements.
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Epinephrine and Norepinephrine
 Primary transmitter for postganglionic
 Epinephrine and norepinephrine act on two types of
receptor
 α:- α1, α2
 β :- β1, β2, β3
 Both the neurotransmitter are also secreted by adrenal
medulla
 Norepinephrine has greater affinity for α adrenergic
receptor whereas epinephrine ha greater affinity for β
adrenergic receptor 43

Epinephrine (adrenaline)
Epinephrine, also known as adrenaline, is an excitatory neurotransmitter.
It is derived from norepinephrine and is secreted along with norepinephrine in
response to fear or anger.
This reaction, referred to as the “fight or flight” response, prepares the body for
strenuous activity.
Epinephrine regulates attentiveness, arousal, cognition, sexual arousal, and
mental focus. It is also responsible for regulating the metabolism.
Epinephrine is used medicinally as a stimulant in cardiac arrest, as a
vasoconstrictor in shock, as a bronchodilator and antispasmodic in bronchial
asthma, and anaphylaxis.
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High levels
Epinephrine levels which are too high can result in restlessness,
anxiety, sleep problems, acute stress, and ADHD. Excess amounts
of epinephrine can also raise the blood pressure, increase the heart
rate, cause irritability and insomnia.
Low levels
Low levels of epinephrine can also contribute to weight gain,
fatigue, lack of focus, decreased sexual arousal, and poor
concentration.
Stress tends to deplete our store of adrenalin (epinephrine), while
exercise tends to increase it.
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NOREPINEPHRINE
•is an excitatory neurotransmitter that is
responsible for stimulatory processes in
the body
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NOREPINEPHRINE
High levels
Elevated norepinephrine activity is a contributor to anxiety.
 Also, brain norepinephrine turnover is increased in conditions of stress.
Increased levels of norepinephrine will lead to alertness and mood elevation and
increased sexual interest. However, high amounts raise blood pressure, increase
heart rate, and cause anxiety, fear, panic, stress, hyperactivity, an overwhelming
sense of dread, irritability, and insomnia.
Low levels
Low levels of norepinephrine are linked to lack of energy, focus, and motivation.
Insufficient norepinephrine levels also contribute to depression, loss of alertness,
and poor memory.
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Serotonin(5-Hydroxytryptamine)
Present in high concentration in certain nuclei located in
brain stem
Also present in blood platelets and GI tract (Myenteric
plexus)
Receptors:-
 5HT1 , 5HT2 , 5HT3 , 5HT4 , 5HT5 , 5HT6 , 5HT7
 5HT6 receptor have high affinity for antidepressant drugs
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• Serotonin is an inhibitory neurotransmitter
and plays a pivotal role in maintaining a
balance between the excitatory and
inhibitory neurotransmitters.
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Low levels of serotonin
• Low levels of serotonin can result in depressed mood,
anxiety, panic attacks, low energy, migraines, sleeping
problems, obsessions or compulsions, feeling tense and
irritable, craving sweets or loss of appetite, impaired
memory and concentration, angry or aggressive behavior,
slowed muscle movement, slowed speech, altered sleep
patterns, and having a reduced interest in sex, chronic
fatigue, premenstrual complaints, impulsivity,
hypoglycemia, and insulin resistance.
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High levels
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Excess amounts of serotonin cause sedation, a
decrease in sexual drive, a sense of well-being, bliss,
and of being one with the universe. However, if
serotonin levels become too high they can result in
Serotonin Syndrome, which can be fatal.
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Serotonin Syndrome
Extremely high levels of serotonin can be toxic and possibly fatal, causing a
condition known as “Serotonin Syndrome”.
It is very difficult to reach these high levels by overdosing on a single
antidepressant, but combining different agents known to increase levels of
Serotonin, such as an SSRI and an MAOI, can result in this condition.
Serotonin Syndrome produces violent trembling, profuse sweating,
insomnia, nausea, teeth chattering, chilling, shivering, aggressiveness, over-
confidence, agitation, and malignant hyperthermia.
 Emergency medical treatment is required, utilizing medications that
neutralize or block the action of serotonin.
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Histamine
• Found in brain, gastric mucosa and in
heparin containing cell called mast cell.
• Receptors: H1 , H2 , H3
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Glutamate
It is the main excitatory transmitter in brain and
spinal cord.
It is responsible for 75% of excitatory transmission
in brain.
Receptors:
 Metabotropic:- G protein coupled
 Inotropic:- Kainate, AMPA and NMDA
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Gamma- Aminobutyric acid(GABA)
Gamma- Aminobutyric acid is the major inhibitory mediator in brain.
Receptors: GABAA , GABAB , GABAC
GABA has a calming effect on the brain and helps the brain filter out
“background noise”.
It improves mental focus while calming the nerves.
GABA acts like a brake to the excitatory neurotransmitters which can cause
anxiety if the system is overstimulated.
It regulates norepinephrine, adrenaline, dopamine, and serotonin and is a
significant mood modulator.
The primary function of GABA is to prevent overstimulation.
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• High levels
Excessive GABA levels result in excessive relaxation and
sedation, to the point that normal reactions are impaired
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Low levels
Insufficient GABA results in the brain being
overstimulated.
People with too little GABA tend to suffer from anxiety
disorders and may have a predisposition to alcoholism.
Low levels of GABA are associated with bipolar disorder,
mania, poor impulse control, epilepsy, and seizure
disorders.
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Glycine
Inhibitory aminoacid
When act through NMDA receptor produces excitatory effect.
Glycine mediated inhibitory synapses predominate in the spinal cord
whereas GABA-ergic synapses are most numerous in brain
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The Brain and Drugs
• Some neurotransmitters are excitory, such as acetylcholine, norepinephrine,
serotonin, and dopamine.
• Some are associated with relaxation, such as dopamine and serotonin.
Dopamine release seems related to sensations of pleasure.
• Endorphins are natural opioids that produce elation and reduction of pain,
as do artificial chemicals such as opium and heroin.
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