The nervous system is a complex collection of nerves and specialized cells known as neurons that transmit signals between different parts of the body. The presentation provides a simplified overview of the nervous system and its functions
2. Contents
• Introduction to nervous system
• Neurons
• Neuron Structure
• Membrane Potential
• Resting Potential
• Action Potential and depolarization
• Positive Feedback Loop
• Repolarization and Hyper polarization
• Absolute and Relative Refractory Period
• Synaptic Potential
• EPSP & IPSP
• Summary
3. Nervous System controls and
regulates all the voluntary and
involuntary actions In the body.
The nervous system controls body
movement and coordination.
Units of nervous system known as
neurons influence most the actions.
They communicate with the muscles,
glands and neurons in the form of
impulses.
4. Neurons
Neurons have the same basic structure
There are three main types of neurons they are
bipolar, unipolar, multipolar
All neurons consist of three main components
• Cell Body(soma) – Largest part of the neuron.
Place where decision is made before signals go
on or stop.
• Dendrites – Branched from the cell body. Signal
receiving zone where the signals are obtained
and send towards the axon.
• Axon – This is where action potential is
generated and sent out as an outgoing signal
known as a nerve impulse.
6. The myelin sheath is formed by many Schwann cells
wrapping around them over and over again. Once the
myelin sheath is formed around the neuron the speed of
impulse transmission will become faster as the conductivity
is increased.
There are gaps in between the myelin sheath known as
Node of Ranvier this gap provides the pathway for the
impulses to pass through.
7. Ions Concentration
Inside cell
mm/l
Concentration
Outside cell
mm/L
Sodium 15 150
Potassium 150 5
Chlorine 10 125
Membrane Ion Concentration
There are two types of channels
1. Active – Chemically gated
Voltage Gated
2. Passive – Leakage Channels
8. Resting Potential
Resting potential is a phase where the neurons are at rest.
The voltage during this stage is around -70mV
During this stage both the sodium and potassium pumps are
closed.
9. Action Potential
Action potential is triggered when the neuron
needs to send a message in the form of
impulse
This is triggered at the axon hillock then
down towards axon.
It normally triggers at -70mV where the
action potential is generated
For this the threshold level must be
surpassed (-55mV) else wise action potential
cannot be triggered as a result its known as a
“all or none event”
During depolarization the sodium channels
open resulting in more sodium entering
inside causing the voltage to become more
positive
The peak of action potential is reached at
+30mV where the sodium channels are
inactive.
10. Positive Feedback Loop
The positive feedback system
gives rise to the action
potential. The positive
feedback system can be
interrupted as well when
1. When the voltage gated
sodium channels inactivates
2. And the potassium voltage
gated channels open.
11. For each time a sodium channel
takes in ions potassium need to
release out where 3 sodium
moves in and 2 potassium ions
move out.
After peak level of action
potential reached at +30mV
sodium channels begin to
inactivate and potassium
channels begin to open up
Then less sodium moves in and
more potassium moves out
increasing the negativity this
stage where the potassium
concentration is higher outside
is known as repolarization
phase
After this phase the negativity will
continue to decrease causing the
potential value to be lower than
the resting potential, at this point
both sodium and potassium
channels are closed and results in
a phase known as
hyperpolarization
12. Speed of Impulse Transmission
Action potential needs to be transmitted at a higher rate
flow so more impulses can pass through at a quicker rate.
Conduction velocity is the speed at which the action
potential is generated, to increase this velocity two main
factors can influence the changes.
1. The diameter of the axon – if the diameter is larger, the
resistance between walls and impulse flow is lower so at
higher speeds it can move through.
2. How well axon is insulated with myelin – when the axon is
myelinated the conductivity is higher and speed of
transmission between the nodes of Ranvier will be higher.
13. Absolute and Relative Refractory Period
After neuron has generated one action
potential another one cannot be
generated the sodium channels are
inactive and will not open even when
enough voltage is provided to open them
up
At this point the potassium channels are
opened up, this period is known as
absolute refractory period.
After the absolute refractory period
another action potential can be generated
if the value is higher than the threshold
during this period most the sodium
channels are inactive and some of the
potassium channels are active. This period
is known as relative refractory period.
,
14. Synaptic Potential
Action potential in the axon terminal causes the voltage gated
calcium channels to release calcium ions in the presynaptic
neuron.
The calcium ions causes the synaptic vesicles to fuse with the
calcium ion, this releases a fixed amount of neurotransmitter
into the synaptic cleft which diffuses across.
This neurotransmitter binds to a receptor on the postsynaptic
neuron, the chemically gated channels remain open until
neurotransmitter binds with receptor.
Current flows across the postsynaptic cell membrane.
The neurotransmitter breaks away from the receptor and
pumped away.
16. Excitatory and Inhibitory Post Synaptic Potentials
ESPS or excitatory synaptic potential increase the
possibilities of postsynaptic action potential by the
depolarization caused by the movement of positive ions
ISPS or inhibitory synaptic potential decrease the
possibilities of action potential being triggered or
produced
This response is influenced by the type of channel that
binds with a receptor and concentration of ions inside and
outside the cell.
17.
18. Summary
Neurons are important structures for the impulse
transmission.
The neuron structure doesn’t differ much in the neurons.
Myelination plays an important role in all neurons.
Resting potential is a constant.
Action potential is an all or none event which is similar to
the frequency change in a mobile transmission.
The positive feedback loop controls the setup of action
potential.
Impulse transmission differs for each neuron structure.
Synaptic Potential is essential for action potential to be
sent.
EPSP & IPSP makes the changes required for action
potential to be triggered further or prevented.
