Nervous system Sem 2.pptx (Brain structure) )

Nervous System
Presented By: Ms Shalini N Barad
Assistant Professor,
School of Pharmacy,
P. P. Savani University

 Index
1. Organization of nervous system
2. Neuron
3. Neuroglia
4. Classification and properties of nerve fibre
5. Electrophysiology
6. Action potential
7. Nerve impulse
8. Receptors
9. Synapse
10. Neurotransmitters.

Nervous system:
 The nervous system is very important in
helping to maintain the homeostasis
(balance) of the human body.

 The nervous system consists of extensive
neural networks.
 Communication between these networks
facilitates thinking, language, feeling, learning,
memory, motor function and sensation.
 Through the plasticity of our existing cells
and neural stem cells, our nervous system
can adapt to new situations and respond to
injury

 Basic functions of nervous system:-
 Sensory input: sensory receptors, present in
the skin and organs, respond to external and
internal stimuli by generating nerve impulses that
are sent to the central nervous system (CNS).
 Integration: the brain and spinal cord of the
CNS combine and sum up all the data received
from the body and send out nerve impulses.
 Motor output: the nerve impulses from the CNS
go to the effectors (muscles and glands). Muscle
contractions and gland secretions are responses
to stimuli received by sensory receptors.

Nervous system Sem 2.pptx (Brain structure) )

Nervous system divided into 2 parts:
 CNS is main system it consist of Brain & Spinal cord
 PNS consist of all nerves of the body which transmit
information from body brain & brain body
 Sensory Nervous system- in which
impulse/information goes to brain from PNS
 Motor Nervous system- it is the response of CNS
PNS
 Somatic Nervous system : It is under voluntary control
via skeletal muscles
 Ex- walking,
 Autonomic Nervous system- These are voluntary
responses of the body which can’t be control.
 Ex- breathing, heart rate etc

 Sympathetic Nervous system-
a. fight or flight system
b. The system activate when our body is in
panic, emergencies, vigorous exercise
situation
 Parasympathetic Nervous system-
a. rest & digest system
b. Reduces energy use
c. Promotes storage of energy
d. Waste Elimination
e. Homeostasis

 Nervous system is made of- nervous
tissue
Neuroglial
cell
Neurons
Nervous
tissue

 Neurons are the structural & functional unit of the nervous system and
are responsible for all neurological functions of the brain
 It transmit the information to other nerve cells, muscles or glands
 It consist of
 cell body:
 It is also called soma
 It contains the nucleus, mitochondria, and other organelles necessary for
neuronal functioning.
 These structures support the chemical processes of the neuron, most
notably the production of neurotransmitters.
 axons: it originate from the cell body at the axon hillock.
 It is single branch which conduct nerve impulses away from cell body
 It is also called nerve fiber
 Axon start at axom hillock & action potential is also generated here
 Plasma membrane of axon is called axolemma which is covered by
schwann cell (give protection to axon), second protection layer is myelin
sheath which is made of fatty material of schwann cell

 Axom terminal:
 At the end, axon end with axon
terminal which is also known as synaptic
nobe
 Axon terminal conduct vessicles inside
it, which contain neurotransmitter inside
it & neurotransmitter transfer
information from one neuron to another

 dendrites:
 Thin branch extension of cell body, comes out from the cell
body and receive afferent signals from other neurons.
 They conduct nerve impulses towards cell body
 A neuron may have a single dendrite or many dendrites
depending on its function and location in the nervous system.
 synapse:
 microscopic gaps found between neurons, typically between
the axon of one neuron and the dendrite of another.
 They are the site of chemical communication between
neurons.
 The neuron sharing information on one side of the synapse is
called the pre-synaptic neuron, while the neuron on the
receiving side of the synapse is called the post-synaptic
neuron.

 Tracts- Bundle of nerve fibers in CNS
 Nerves – Bundle of nerve fiber in PNS

 Types of neuron:
 A) On basis of function-

 Glial Cells
 Glial cells (also known as neuroglia) are the most abundant cell in the CNS.
 However, they are present in both the CNS and the peripheral nervous system (PNS).
 They are support cells to neurons.
 There are four main classes of glial cells within the CNS:
 astrocytes:
 important in maintaining cellular homeostasis.
 They perform tasks such as clearing excess neurotransmitters, maintaining the blood-
brain barrier, and promoting synapse formation
 oligodendrocytes:
 It is present in row along nerve fiber
 It is myelin-forming cells found in the CNS
 Myelin help to speed up transmission of electrical signal in neurons.
 ependymal cells:
 are found lining the ventricle and other fluid-filled spaces of the CNS.
 They are involved in the secretion of cerebrospinal fluid
 Protect brain & spinal cord both mechanically & immunologically
 microglial cells: it is smallest of neuroglial cell
 function as the macrophages of the CNS

 In the PNS:
 schwann Cell: myelin-forming cells found in
the PNS
 Satellite cell:- small glial cell that surrounds
the neurons sensory ganglia in ANS
 It is sensitive to injury & may excaberate
pathological pain.
 It gives protection to neuron cell.

 What is a Nerve Impulse?
 A nerve impulse is an electrochemical signal
generated by neurons that transmits
information.
 It is initiated by a stimulus that alters the
electrical state of the neuron’s membrane,
leading to the propagation of an action
potential.

 Electrophysiology:
 The electrophysiology of the nervous
system refers to the electrical processes
that help neurons to transmit signals across
the body.
 It refers to the study of electrical activity in
the brain, including how neurons generate,
transmit, and regulate electrical signals.
 These impulses are essential for
communication between neurons,
controlling bodily functions, thoughts,
emotions, and sensory perception.

 Neurons generate these impulses by
creating and maintaining voltage
differences across their membranes.
 This voltage difference is essential for
neuron communication and is influenced
by ion movement.

Resting Membrane Potential (RMP)
 The resting membrane potential is the
electrical charge across the neuron’s membrane
when it is not actively sending signals.
 Typical RMP: -70mV (inside is negative relative to
the outside).
 Maintained by:
◦ Sodium-Potassium Pump (Na /K ATPase):
⁺ ⁺
Continuously pumps 3 Na ions out
⁺ and 2 K ions in
⁺ ,
creating a net negative charge inside.
◦ Ion Channel Permeability: The cell membrane is
more permeable to potassium than sodium, allowing K⁺
to leak out more easily.

 4. Action Potential (Nerve Impulse)
 An action potential is a sudden, rapid electrical signal that
travels along the neuron. It is crucial for communication
between neurons.
 Phases of Action Potential:
A. Resting Phase (-70mV)
 Membrane potential maintained at -70mV.
 Na and K channels are closed.
⁺ ⁺
 The neuron is polarized, maintaining its resting potential.
B. Depolarization Phase (+30mV)
 When a stimulus exceeds the threshold potential (~-
55mV), voltage-gated Na channels open
⁺ . Called
predepolarization.
 Na ions
⁺ rapidly enter the neuron, making the membrane
potential positive (depolarization).
 Membrane potential peaks around +30mV.

C. Repolarization Phase
 At the peak of depolarization, Na channels close
⁺ , and K⁺
channels open.
 K ions
⁺ leave the neuron, restoring a negative charge inside.
D. Hyperpolarization Phase (Below -70mV)
 Excessive efflux of K causes a temporary dip below resting
⁺
potential (more negative than -70mV).
 This ensures the neuron cannot fire immediately again.
 The neuron gradually returns to resting potential through the
Na /K pump
⁺ ⁺ .
E. Refractory Period
 After hyperpolarization, the neuron enters a recovery phase where
it cannot generate another impulse until its membrane potential
stabilizes.
 After an action potential, the neuron temporarily becomes
unresponsive to new stimuli to ensure impulses move in one
direction only.

 The cycle of depolarisation &
repolarisation is called action potential.
 Action potential works 1000 times in 1
sec.

Propagation of Nerve Impulse
 The transmission of an action potential along the
axon occurs through two mechanisms:
A. Continuous Conduction (Unmyelinated
Fibers)
 The impulse travels steadily along the axon
without jumping.
 Slower compared to myelinated fibers.
B. Saltatory Conduction (Myelinated Fibers)
 The impulse "jumps" between Nodes of
Ranvier, accelerating the signal's movement.
 This method is faster and more energy-
efficient.

SynapticTransmission
 At the synapse, the electrical signal is converted into a
chemical signal to communicate with the next neuron or
effector cell.
 Steps in SynapticTransmission:
 Action Potential Arrival: The nerve impulse reaches the
axon terminal.
 Calcium Influx: Voltage-gated Ca² channels
⁺ open, allowing
calcium to enter the terminal.
 Neurotransmitter Release: Calcium triggers
neurotransmitter vesicles to fuse with the presynaptic
membrane, releasing neurotransmitters into the synaptic cleft.
 Receptor Binding: Neurotransmitters bind to receptors on
the postsynaptic cell, initiating a new action potential or
cellular response.

 Nerve Fiber:--
 BASIS OF CLASSIFICATION
 Nerve fibers are classified by six different methods.
1. DEPENDING UPON STRUCTURE
 Based on structure, nerve fibers are classified into
two types:
i. Myelinated Nerve Fibers :- Myelinated nerve
fibers are the nerve fibers that are covered by myelin
sheath.
ii. Non-myelinated Nerve Fibers :- Non
myelinated
nerve fibers are the nerve fibers which are not
covered by myelin sheath.

„2. DEPENDING UPON DISTRIBUTION
 Nerve fibers are classified into two types, on the basis of
distribution:
i. Somatic Nerve Fibers:- Somatic nerve fibers supply
the skeletal muscles of the body.
ii. Visceral or Autonomic Nerve Fibers :- Autonomic
nerve fibers supply the various internal organs of the
body. „
3. DEPENDING UPON ORIGIN
 On the basis of origin, nerve fibers are divided into two
types:
i. Cranial Nerve Fibers Nerve fibers arising from brain
are called cranial nerve fibers.
ii. Spinal Nerve Fibers Nerve fibers arising from spinal
cord are called spinal nerve fibers. „

4. DEPENDING UPON FUNCTION
Functionally, nerve fibers are classified into two
types:
i. Sensory Nerve Fibers :- Sensory nerve fibers
carry sensory impulses from different parts of
the body to the central nervous system.
 These nerve fibers are also known as afferent
nerve fibers.
ii. Motor Nerve Fibers :- Motor nerve fibers
carry motor impulses from central nervous
system to different parts of the body.
 These nerve fibers are also called efferent
nerve fibers. „

5. DEPENDING UPON SECRETION
OF NEUROTRANSMITTER
 Depending upon the neurotransmitter
substance secreted, nerve fibers are divided
into two types:
i. Adrenergic Nerve Fibers :- Adrenergic
nerve fibers secrete nor adrenaline.
ii. Cholinergic Nerve Fibers :- Cholinergic
nerve fibers secrete acetylcholine.

6. DEPENDING UPON DIAMETER AND
CONDUCTION OF IMPULSE
(ERLANGER-GASSER CLASSIFICATION)
 Erlanger and Gasser classified the nerve fibers into
three major types, on the basis of diameter (thickness)
of the fibers and velocity of conduction of impulses:
i)Type A nerve fibers
ii.Type B nerve fibers
iii.Type C nerve fibers.
 Among these fibers, type A nerve fibers are the
thickest fibers and type C nerve fibers are the thinnest
fibers.
 Type C fibers are also known asType IV fibers.
 Except type C fibers, all the nerve fibers are
myelinated.

 Type A nerve fibers are divided into four
types:
a.Type A alpha orType I nerve fibers
b.Type A beta orType II nerve fibers
c.Type A gamma nerve fibers
d.Type A delta orType III nerve fibers.

 „Properties Of Nerve Fiber:
1. EXCITABILITY „
a) Action potential or nerve impulse „
b) Electrotonic potential or local potential „
c) Voltage clamping „
2. CONDUCTIVITY „
d) Mechanism of conduction of action potential „
e) Conduction through myelinated nerve fiber – saltatory
conduction
3. REFRACTORY PERIOD
„ „
 Types of refractory period „
4. SUMMATION „
5.ADAPTATION „
6. INFATIGABILITY „
7.ALL-OR-NONE LAW

1. Excitability: it is defined as the physiochemical change
that occurs in a tissue when stimulus is applied.
A) Action Potential Phases
 The action potential is a rapid, transient electrical signal
characterized by distinct phases:
1. Resting Phase
 Membrane potential is stable at ~ -70 mV.
 Dominated by K leak channels
⁺ with Na /K pump
⁺ ⁺
maintaining ionic gradients.
2. Depolarization Phase
 Stimulus triggers voltage-gated Na channels
⁺ to open.
 Na influx
⁺ causes membrane potential to become less
negative (depolarize).
 Once the threshold (~ -55 mV) is reached, an action
potential becomes self-propagating.

3. Peak Phase
 The membrane potential spikes to around +30 mV.
 At this point, Na channels inactivate
⁺ and K channels
⁺
open.
4. Repolarization Phase
 K efflux
⁺ (outward flow of potassium ions) returns the
membrane potential back toward the resting level.
5. Hyperpolarization Phase
 Due to the delayed closure of K channels, the membrane
⁺
potential becomes more negative than the resting state (e.g., ~ -
80 mV).
 This hyperpolarization ensures unidirectional conduction of
impulses.
6. Return to Resting State
 The Na /K pump
⁺ ⁺ restores ionic balance, returning the cell to
its resting membrane potential.

B) ELECTROTONIC POTENTIAL OR
LOCAL POTENTIAL:
 Electrotonic potential is a non-propagated
local response in nerve fibers, resulting from a
subliminal stimulus altering the resting
membrane potential and producing a slight
depolarization of 7 mV.
 The firing level is reached when depolarization
reaches 15 mV, allowing only action potential
to develop.

C) VOLTAGE CLAMPING
„ :
 Voltage clamping is an experimental
technique used to study the ionic currents
that flow through nerve membranes by
controlling the membrane potential.
 It has been crucial in understanding the
electrical properties of nerve fibers,
particularly the behavior of voltage-gated
ion channels during an action potential.

2. CONDUCTIVITY
„
 Conductivity refers to the ability of nerve fibers to transmit
impulses from one area of stimulation to another.
 In the body, action potential is typically transmitted in one direction.
 However, in experimental conditions, the action potential can travel
in either direction.
A) Mechanism of conduction :
 Depolarization occurs first at the stimulation site, causing
depolarization of neighboring areas.This depolarization travels
throughout the nerve fiber, followed by repolarization.
B) Mechanism of Saltatory Conduction:-
 Saltatory conduction occurs when the impulse jumps from one
node to another, making it about 50 times faster than
nonmyelinated fibers.
 The myelin sheath is not permeable to ions, causing depolarization
only in the node of Ranvier, where the myelin sheath is absent.

3. REFRACTORY PERIOD
 Refractory period is the period at which the nerve
does not give any response to a stimulus. „
 TYPES OF REFRACTORY PERIOD
 Refractory period is of two types:
1. Absolute Refractory Period -- Absolute
refractory period is the period during which the
nerve does not show any response at all,
whatever may be the strength of stimulus.
2. Relative Refractory Period It is the period,
during which the nerve fiber shows response, if the
strength of stimulus is increased to maximum

4. Summation:
 It is a phenomenon where two or more
subliminal stimuli are applied within a short
interval of about 0.5 milliseconds, resulting in
a strong response in the nerve fiber, as the
subliminal stimuli are combined to produce
the response.

5. Adaptation:- Adaptation occurs when a
nerve fiber experiences increased excitability
initially, gradually decreasing until it ceases to
respond, known as accommodation.
 Cause: Continuous stimulation of nerve
fibers leads to depolarization, which
inactivates the sodium pump and increases
potassium ion flux.

5. INFATIGABILITY:-
 Nerve fibers cannot be fatigued due to their
ability to conduct only one action potential at
a time.
6.ALL-OR-NONE LAW:--The all-or-none
law states that when stimulated, a nerve gives
maximum response or does not respond at
all.

Receptors :
 Receptors are sensory nerve endings that
produce impulses when stimulated, which are
transmitted through afferent nerves.
 receptors are often defined as the biological
transducers, which convert (transducer)
various forms of energy (stimuli) in the
environment into action potentials in nerve
fiber.

 CLASSIFICATION OF RECEPTORS
 Generally, receptors are classified into
two types:
 A. Exteroceptors
 B. Interoceptors.

 EXTEROCEPTORS
 Exteroceptors are the receptors, which give
response to stimuli arising from outside the
body
 Exteroceptors are divided into three groups:
1. Cutaneous Receptors or
Mechanoreceptors: Cutaneous receptors, also
known as mechanoreceptors, are located in the
skin and respond to mechanical stimuli like
touch, pressure, and pain, as well as vibration.

 2. Chemoreceptors Receptors,:- which
give response to chemical stimuli, are
called the chemoreceptors.
 3.Telereceptors:- Telereceptors, also
known as distance receptors, are
receptors that respond to stimuli arising
away from the body.

 „ INTEROCEPTORS
 Interoceptors are the receptors, which give
response to stimuli arising from within the body.
 Interoceptors are of two types which are as
follows:
1. Visceroceptors Receptors:- situated in the
viscera are called visceroceptors.
2. Proprioceptors:- Proprioceptors are the
receptors, which give response to change in the
position of different parts of the body.
Proprioceptors

 „Receptors PROPERTIES „
1. Specificity of response „
2. Adaptation – sensory adaptation „
3. Response to increase in the strength of
stimulus „
4. Sensory transduction
5. Receptor potential
„ „
6. law of projection

1. Specificity of response
 Specificity of response or Müller law refers to
the response given by a particular type of
receptor to a specific sensation.
 In addition, each type of sensation depends upon
the part of the brain in which its fibers terminate.
 For example, pain receptors give response only
to pain sensation.
 Similarly, temperature receptors give
response only to temperature sensation.

2. adaptation :
 Sensory adaptation, also known as
desensitization, occurs when a receptor's
discharge of sensory impulses decreases due to
continuous stimulation.
 Receptors are divided into phasic and tonic types
i. Phasic receptors, which get adapted rapidly.
Touch and pressure receptors are the phasic
receptors
ii. Tonic receptors, which adapt slowly.
Muscle spindle, pain receptors and cold
receptors are the tonic receptors.

 3. RESPONSETO INCREASE IN
STRENGTH OF STIMULUS – WEBER
FECHNER LAW
 The Weber-Fechner law states that to double
a receptor's response, the stimulus
intensity must be increased 100 times,
directly proportional to the logarithmic
increase in stimulus intensity.

 4. SENSORYTRANSDUCTION:
 Sensory transduction in a receptor is a process by
which the energy (stimulus) in the environment is
converted into electrical impulses (action
potentials) in nerve fiber
(transduction = conversion of one form of energy into
another).
 It involves events like receptor potential development
and action potential development in the sensory nerve.
 The type of receptor varies, such as chemoreceptors
converting chemical energy into action potentials or
touch receptors converting mechanical energy.

 5. RECEPTOR POTENTIAL:
 Receptor potential is a non
propagated
transmembrane potential difference that develops
when a receptor is stimulated.
 It is also called generator potential.
 Receptor potential is short lived and hence, it is called
transient receptor potential.
 potential difference developed when a receptor is
stimulated, similar to
i. excitatory postsynaptic potential in synapse,
ii. endplate potential in neuromuscular junction, and
iii. electrotonic potential in nerve fiber.

 It is crucial for the development of action
potential in sensory nerves when strong
enough.
 Pacinian corpuscles are used to study
receptor potential due to their large size and
anatomical configuration.
 When pressure is applied, the corpuscle
compresses, causing elongation and
deformation of the core fiber, opening sodium
channels and producing mild depolarization.

6. LAW OF PROJECTION
The law of projection states that when a
sensory pathway from receptor to cerebral
cortex is stimulated at a specific site, the
sensation is always felt at that site.

 The law of projection states that sensations in the
right cerebral cortex are felt in the left hand, not
the head.
 Amputated patients often experience phantom limb
pain, where the cut ends of nerve fibers merge
within the scar.This sensation, triggered during thigh
movement, makes the patient feel as if the sensation
is from a nonexistent leg, a phenomenon known as
phantom limb pain.
 If somesthetic area in right cerebral cortex, which
receives sensation from left hand is stimulated,
sensations are felt in left hand and not in head.

 SYNAPSE
 DEFINITION
 Synapse is the junction between two neurons.
 CLASSIFICATION OF SYNAPSE
 Synapse is classified by two methods:
A.Anatomical classification
B. Functional classification.

1.ANATOMICAL CLASSIFICATION
 Depending upon ending of axon, synapse is
classified into three types:
1. Axoaxonic synapse:-- in which axon of
one neuron terminates on axon of another
neuron
2. Axodendritic synapse:-- in which the
axon of one neuron terminates on dendrite of
another neuron
3. Axosomatic synapse:- in which axon of
one neuron ends on soma (cell body) of
another neuron

2. „ FUNCTIONAL CLASSIFICATION
 Functional classification of synapse is on the
basis of mode of impulse transmission.
 According to this, synapse is classified into
two categories:
1. Electrical synapse
2. Chemical synapse.
1. Electrical Synapse
 Electrical synapse is the synapse in which the
physiological continuity between the
presynaptic and the pos

1.Electrical Synapse
 Electrical synapse is the synapse in which the physiological
continuity between the presynaptic and the post synaptic
neurons is provided by gap junction between the
presynaptic and the post synaptic neurons
 The gap junction between two synaptic neurons provides
direct ion exchange, allowing action potentials to enter
the terminal portion of the presynaptic neuron and the
postsynaptic neuron.
 This type of impulse transmission occurs in tissues like
cardiac muscle fibers, smooth muscle fibers of the
intestine, and epithelial cells of the lens in the eye,
resulting in minimal synaptic delay and impulse
transmission in either direction.

2. Chemical synapse
 is a junction between nerve fibers and muscle
fibers, where signals are transmitted through
chemical transmitters.
 There's no continuity between neurons due
to synaptic cleft.
 Action potentials reach presynaptic terminal,
releasing neurotransmitter substance, and
producing potential change.

 FUNCTIONAL ANATOMY
 OF CHEMICAL SYNAPSE
 Functional anatomy of a chemical synapse is shown in figure
Neuron from which the axon arises is called the
presynaptic neuron and the neuron on which the
axon ends is called postsynaptic neuron.
 Axon of the presynaptic neuron divides into many small
branches before forming the synapse.These branches are
known as presynaptic axon terminals.
 Types of AxonTerminals
1. Terminal knobs
 Some of the terminals are enlarged slightly like knobs called
terminal knobs.
 Terminal knobs are concerned with excitatory
function of the synapse

2. Terminal coils or free endings
 Other terminals are wavy or coiled with free ending with out
the knob.
 These terminals are concerned with inhibitory function.
 Structures of AxonTerminals and Presynaptic Membrane
 Presynaptic axon terminal has a definite intact membrane
known as presynaptic membrane.
 Axon terminal has two important structures:
i. Mitochondria, of which help in the synthesis
neurotransmitter substance
ii. Synaptic vesicles, which store neurotransmitter substance.

 On the basis of functions, synapses are
divided into two types:
1. Excitatory synapses, which transmit the
impulses (excitatory function)
2. Inhibitory synapses, which inhibit the
transmission of impulses (inhibitory
function).

 Excitatory postsynaptic potential (EPSP):--
 It is a nonpropagated electrical potential
created during synaptic transmission.
 It occurs when calcium ions enter the
presynaptic axon terminal, releasing
neurotransmitter substance.
 The neurotransmitter binds with a receptor
protein in the postsynaptic membrane,
forming a neurotransmitter-receptor complex.
 Common excitatory neurotransmitter in a
synapse is acetylcholine.

 INHIBITORY FUNCTION:-
 Postsynaptic inhibition occurs when an inhibitory
neurotransmitter, such as GABA, dopamine, and glycine,
is released from the presynaptic terminal instead of an
excitatory neurotransmitter.
 This leads to the development of an inhibitory
postsynaptic potential (IPSP), which is an electrical
potential in the form of hyperpolarization.
 This hyperpolarized state inhibits synaptic transmission.
 Presynaptic inhibition occurs when the presynaptic
axon terminal fails to release sufficient excitatory
neurotransmitter substances.

 Neurotransmitter :-
 A neurotransmitter is a chemical substance that
facilitates the transfer of nerve impulses
between neurons via a synapse.
 CRITERIA FOR NEUROTRANSMITTER
1. It must be found in a neuron
2. It must be produced by a neuron
3. It must be released by a neuron
4. After release, it must act on a target area and
produce some biological effect
5.After the action, it must be inactivated.

 CLASSIFICATION OF
NEUROTRANSMITTERS
A)DEPENDING UPON CHEMICAL NATURE
 Depending upon their chemical nature,
neurotransmitters are classified into three
groups.
1. Amino Acids
 Neurotransmitters of this group are involved
in fast synaptic transmission and are
inhibitory and excitatory in action.
 GABA, glycine, glutamate (glutamic acid) and
aspartate (aspartic acid) belong to this group.

2. Amines
 Amines are the modified amino acids. These
neurotransmitters involve in slow synaptic
transmission.
 These neurotransmitters are also inhibitory
and excitatory in action.
 Noradrenaline, adrenaline, dopamine,
serotonin and histamine belong to this group.
3. Others
 Acetylcholine, formed from choline and
acetyl coenzyme A, and nitric oxide (NO),
both neurotransmitters, are not classified
into specific categories.

 DEPENDING UPON FUNCTION
 Some of the neurotransmitters cause
excitation of postsynapticn neuron
while others cause inhibition.
 Thus, neurotransmitters are classified
into two types:
1. Excitatory neurotransmitters
2. Inhibitory neurotransmitters.

 1. Excitatory Neurotransmitters :
 Excitatory neurotransmitter is a chemical
substance responsible for impulse transmission
from presynaptic to postsynaptic neurons.
 Released from the presynaptic axon terminal, it
causes slight depolarization in the resting
membrane potential, excitatory postsynaptic
potential (EPSP), leading to action potential
development.
 Common excitatory neurotransmitters are
acetylcholine and noradrenaline.

2. Inhibitory Neurotransmitters:-
 Inhibitory neurotransmitters, such as GABA
and dopamine, prevent impulse conduction
from the presynaptic neuron to the
postsynaptic neuron.
 They cause potassium channels to open,
leading to hyperpolarization and the inhibitory
postsynaptic potential (IPSP).

 TRANSPORT AND RELEASE OF
NEUROTRANSMITTER :
 Neurotransmitter, produced in neurons, is
transported through axons and stored in
vesicles.
 Under the influence of a stimulus, these
vesicles open and release the
neurotransmitter into synaptic cleft.
 It binds to specific receptors on the surface
of the postsynaptic cell.

 INACTIVATION OF
NEUROTRANSMITTER
 After the execution of the action, neurotransmitter
is inactivated by four different mechanisms:
1. It diffuses out of synaptic cleft to the area where it
has no action
2. It is destroyed or disintegrated by specific enzymes
3. It is engulfed and removed by astrocytes
(macrophages)
4. It is removed by means of reuptake into the axon
terminal.

 REUPTAKE OF
NEUROTRANSMITTER
 Reuptake is a process by which the
neurotransmitter is taken back from synaptic
cleft into the axon terminal after execution of
its action.
 Reuptake process involves a specific carrier
protein for each neurotransmitter.

Nervous system Sem 2.pptx (Brain structure) )

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Nervous system Sem 2.pptx (Brain structure) )