Mechanism of Generation and Propagation of Nerve Impulse.pptx

1. By Abhinav Baranwal
202110902120035
BSc. (H) Biotechnology 2nd Semester
Submitted to
Dr. Gurminder Kaur
Faculty of Biosciences,
Institute of Biosciences and Technology,
Shri Ramswaroop Memorial University

2. 2
Slide No.
I Neurons
1 Structure and Function 3 - 8
II Generation and Propagation of Nerve
Impulse
1 Nerve Impulse 9 - 10
2 Resting Membrane Potential 11
3 Action Potential 12
4 Propagation of Nerve Impulse 13
5 Repolarization 14
6 Refractory Period 14
7 Summary 15
References 16

3. • Neurons are cells specialized for carrying signals and the functional
units of the nervous system.
3

4. 4
• A neuron is a nerve cell with
all its branches.
• Neuron is formed from
neuroblast.
• It is the longest cell of the
body.

5. 5
A neuron consists of a
• Cell body
Two types of extensions
(fibres) that conduct
signals,
• Dendrites
• Axons

6. 6
• Nissl’s granules: A number of
small, basophilic granules
formed of rough ER with
ribosomes and are sites of
protein synthesis.
• Neuroplasm has large number
of mitochondria to provide
high energy for impulse
conduction.
• A mature neuron has no
centriole, so it cannot divide.

7. 7
• Dendrites are the tree-like
structures in neurons that
extend away from the cell body
to receive messages from other
neurons at synapses;
 They conduct nerve impulse
towards the cell body.
 Not all neurons have dendrites.

8. 8
Myelin sheaths
• Enclose axons,
• Form a cellular
insulation, and
• Speed up signal
transmission.

9. 9
NERVE IMPULSE
 Nerve function depends on charge differences across neuron membranes
 At rest, a neuron’s plasma membrane has potential energy the membrane potential, in which just inside the cell is
slightly negative and just outside the cell is slightly positive.
 The resting potential is the voltage across the plasma membrane of a resting neuron.

10. 10
NERVE IMPULSE
 The resting potential exists because of
differences in ion concentration of the fluids
inside and outside the neuron.
Inside the neuron
 K+ is high
 Na+ is low
Outside the neuron
 K+ is low
 Na+ is high

11. 11
Resting Membrane Potential
• Also known as Polarized State.
• In a resting nerve fiber, the cytoplasm just beneath its
membrane is electronegative relative to the layer of
extracellular fluid just outside the membrane. The inner side
of membrane is seen to possess a negative potential of about
70 millivolts relative to the outer side. This is called resting
membrane potential.
• The resting membrane has poor permeability for Na+
although it has a higher permeability for K+. Therefore, K+
can cross more easily while and Na+ have more difficulty in
crossing.
• This electrochemical gradients are maintained by the active
transport of ions involving Na+ - K+ ion transmembrane
pump. It shows Efflux of 3Na+ for Influx of every 2K+.

12. 12
Action Potential
• So the Resting Membrane Potential at -70mV is eligible to
receive a signal,
• Now when stimulated, voltage gated Na+ channel open
which causes a rapid, localized, temporary inflow of Na+
into the cell which causes development of net positive
charge on the inner side of membrane in that area. This is
called depolarization.
• It occurs at a particular region of neuron caller trigger zone.
Voltage gated ion channels are clustered in the area of
trigger zone. Stimulus of threshold value causes stoppage of
Na+ - K+ ATPase pump.
• Continued passage of Na+ ions into inside of neuron creates
a reverse potential of +20mV to +30mV.
• It creates a potential that sets in a wave of depolarization
through the nerve fiber. The membrane potential that sets in
a wave of depolarization is called action potential.

13. 13
• In the area of depolarization, the potential difference across
the membrane is small while nearby region has a large
difference in membrane potential. This produce a small local
current in the area. The local current becomes a stimulus and
causes the voltage gated Na+ channels of next region to
open and depolarize the area to produce fresh action
potential. This process will continue till the impulse reaches
the end of neuron.
Propagation of Nerve Impulse

14. 14
Repolarization
• As the Na+ channels close, the membrane becomes
extra permeable to K+ ions due to opening of K+
ions gates.
• With the pumping out of K+ ions, the interior of
neuron becomes negative and potential falls back to
resting potential. The phenomenon of change of
membrane potential from excited state to resting
state is called repolarization.
• However, K+ ion channels remain open for a bit
longer period so that the membrane potential
becomes more negative than -70mV. This is called
hyperpolarization.
Refractory Period
• The time period between two successive stimuli.

15. 15
Summary

16. 16
• https://www.biology4all.com/resources_library
• https://www.verywellmind.com/what-is-a-
neuron-2794890
• https://doi.org/10.3389/fncel.2019.00208
• Guyton, AC, and Hall, JE. 2006. Textbook of
Medical Physiology. 11th ed

17. 17
Thank You