This presentation contains the basic information about nerve cells and action potential. This work is done for academic purpose only so if you are using give proper reference.

1. NERVE
PHYSIOLOGY
S.Sri Lakshman
BS/15/11/29

2. Contents
• Structure of Neuron
• Ion Channels
• Resting membrane potential
• Action potential
• Synaptic potential
• Absolute refractory and Relative refractory period
• IPSP and EPSP
• Summary
• Reference

3. Structure of Neuron
 Cell Body/Stoma
 Contains the nucleus
 Process the information
 Dendrites
 Receptive regions; transmit impulse to cell
body
 Short, often highly branched
 Axons
 Transmit impulses away from cell body
 Axon hillock; trigger zone
 Where action potentials first develop
 Presynaptic terminals (terminal buttons)
 Contain neurotransmitter substance (NT)
 Release of NT stimulates impulse in next
neuron
 Bundles of axons form nerves
• Neurons are the basic functional unit of a
nervous system.

4. Types of
Neuron(Structural)
1. Sensory neurons are
sensitive to various non-
neural stimuli. .
2. Motor neurons are able to
stimulate muscle cells
throughout the body,
including the muscles of the
heart, diaphragm, intestines,
bladder, and glands.
3. Interneurons are the
neurons that provide
connections between sensory
and motor neurons, as well as
between themselves.
Types of
Neuron(Functional)

5. Nongated (Leakage) channels
• Many more of these for K+ and Cl- than for Na+.
– So, at rest, more K+ and Cl- are moving than Na+.
• How are they moving?
– Protein repels Cl-, so Cl- moves out.
– K+ are in higher concentration on inside than out,
they diffuse out.
– Always open and responsible for permeability when
membrane is at rest.
– Specific for one type of ion.

6. Gated Channels

7. Gated Ion Channels
Ligand-gated: open or close in
response to ligand (a chemical)
such as ACh binding to receptor
protein.
Acetylcholine (ACh) binds to
acetylcholine receptor on a
Na+ channel. Channel opens,
Na+ enters the cell.
Ligand-gated channels most
abundant on dendrites and cell
body; areas where most
synaptic communication
occurs.

8. Resting Membrane Potential
 Nerve cell has an electrical potential of a –70 mV
 The potential is generated by different concentrations of Na+, K+, Cl,
and protein anions (A)
 But the ionic differences are the consequence of:
 Differential permeability of the axon membrane to these ions
 Operation of a membrane pump called the sodium-potassium pump
 Three sodium ions are removed from the axon for every two
potassium ions brought in.

9. Action potential
• Neurons communicate over long distances
by generating and sending an electrical
signal called action potential.
• The action potential is a large change from
-70mv to +30mv and back to normal value(-
70mv) which is a large change in membrane
potential.
• Action potentials are only generated if the
potential difference reaches a threshold
value of -55mv.

10. Phases of the Action Potential
• 1 – RESTING STATE
– RMP = -70 mV
• 2 – DEPOLARIZATION
– Increased Na+ influx
– MP becomes less negative
– If threshold is reached,
depolarization continues
– Peak reached at +30 mV
– Total amplitude = 100 mV
• 3 – REPOLARIZATION
– Decreased Na+ influx
– Increased K+ outflow
– MP becomes more negative
• 4 – HYPERPOLARIZATION
– Excess K+ outflow
Blue line = membrane potential
Yellow line = permeability of
membrane to sodium
Green line = permeability of
membrane to potassium

11. Positive feedback loop
This positive feedback loop
produce the rising phase of
action potential.
The raising phase of the action
potential ends when the positive
feedback loop is interrupted.
This can be done by two ways
as:
1.Inactivation of voltage-gated
Na+ channel
2.The opening of the voltage-
gated K+ channel

12. Action Potential-Resting Phase
• Na+ and K+ channels are closed
• Leakage accounts for small movements of Na+ and K+
• Each Na+ channel has two voltage-regulated gates
– Activation gates – closed in the resting state
– Inactivation gates – open in the resting state

13. Action Potential: Depolarization Phase
 Some stimulus opens Na+ gates and Na+ influx occurs
 K+ gates are closed
 Na+ influx causes a reversal of RMP
 Interior of membrane now less negative (from -70 mV  -55 mV)
 Threshold – a critical level of depolarization (-55 to -50 mV)
 At threshold, depolarization becomes self-generating
 Depolarization of one segment leads to depolarization in the next
 If threshold is not reached, no action potential develops

14. Action Potential: Repolarization Phase
• Sodium inactivation gates close
• Membrane permeability to Na+ declines to resting levels
• As sodium gates close, voltage-sensitive K+ gates open
• K+ exits the cell and internal negativity of the resting
neuron is restored

15. Action Potential: Hyperpolarization
• Potassium gates remain open, causing an excessive efflux of K+
• This efflux causes hyperpolarization of the membrane
(undershoot)
• The neuron is insensitive to stimulus and depolarization during
this time

16. Changes Occurring in the Channels
During the Action Potential
Potentials Na+ K+
Resting Close Close
Depolarization Open Close
Peak Inactive Start to open
Repolarization Inactive+Close Open
Hyperpolarization Close Open+Close

17. Synapse
Synaptic potential refers to the difference
in voltage between the inside and outside
of a postsynaptic neuron

18. Synaptic transmission involves,
Release of neurotransmitters from the presynaptic
cell.
Diffusion of neurotransmitter across the synaptic
cleft.
Binding of NT to receptors of postsynaptic cell.
It ends when the neurotransmitter dissociates from
the receptor and is removed from synaptic cleft.

19. Refractory Period
Absolute Refractory Period
• After the neuron has generated an
action potential, it cannot generate
another one.
• Many sodium channels are inactive and
will not open, no matter what voltage is
applied to the membrane.
• Most potassium channels are open.
This period is called the absolute
refractory period.
• Immediately after the absolute
refractory period, the cell can generate
an action potential, but only if it is
depolarized to a value more than the
normal threshold.
• This is because some sodium channels
are still inactive and some potassium
channels are still open.
• This is called the relative refractory
period.
Relative refractory period

20. Postsynaptic Potentials
Excitatory postsynaptic potential (EPSP)
• A depolarizing postsynaptic potential
is called an excitatory postsynaptic
potential. An EPSP is produced when
the movement of ions makes the
inside of the cell more positive. If the
neuron is depolarized to the
threshold, an action potential is
generated and more sodium ions
move into the cell.
Inhibitory postsynaptic potential (IPSP)
• A hyperpolarizing postsynaptic
potential is termed an inhibitory
postsynaptic potential. An IPSP is
produced when the movement of
ions make inside of the cell more
negative. It is known as the
breaking system of a neuron.

21. Summary
• Neuron is the basic functional unit of the nervous system.
• A typical neuron contains dendrites , stoma/cell body , axon,
myelin sheath and synaptic terminals.
• Resting membrane potential is -70mV and its maintained by
sodium-potassium pump.
• An action potential is only generated if the potential
differences reaches a threshold value that is -55mv.
• Synaptic potentials are smaller than action potentials.
• Synaptic potential comes in two forms; excitatory and
inhibitory.
• During the absolute refractory period, an action potential
cannot be generated.
• During the relative refractory period, an action potential can
be generated with a potential value more than the threshold
value.
• EPSP is produced when the inside of the cell becomes more
positive. As a result it depolarizes the neuron.
• IPSP is produced when the inside of the cell becomes more
negative.

22. References
 J. A. Freeman and D. M. Skapura, Neural Networks- Algorithms,
Applications and Programming Techniques, Pearson Education(
Singapore) Pvt. Ltd., 1991.
(Chapters 1 &2)
 psychology.about.com/od/biopsychology/f/neuron01.htm
 www.cell.com/neuron
 www.neurophys.com
 faculty.washington.edu/chudler/chnt1.html

23. Thank You
“Legends from the distant past are always exaggerated but; eventually,
someone outdoes them, that’s when new Legends are born.”