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In The Name of Allah
The Most Beneficent The Most Merciful
ECE 4550:
Biomedical
Instrumentation
Lecture:
Neuro-Muscular
System
---Nerve
Engr. Ijlal Haider
University of Lahore, Lahore
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Basic Systems of Human
 Neuro-muscular
 Cardio
Vascular
 Respiratory
 Digestive
 Reproductory
 Endocrine
 Lymphatic
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Nervous System

Fast body controls

Majorly divided into



Central Nervous System (Brain and Spinal Cord)
Neuromuscular System (Peripheral Nerves,
come from the spinal cord to control the
muscles of the limbs)
The junction between the peripheral nerve and
the muscles is called the neuromuscular
junction.
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Neuro-muscular System
 Two
different types of nerves according to
their function:


Sensory nerves: that collect sensory
information and pass onto brain via spinal
cord
Motor nerves: controlling signals for muscles
are sent via motor nerves from brain via
spinal cord
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Reflex Arc
 Some
motor signals originate in Spinal
Cord itself, REFLEX ARC
 Muscles have reflex system
 If something happens suddenly, a signal is
sent from sensory nerves to spinal cord
 Spinal cord have reflex arc which will give
order to motor nerve and send
information to the brain
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 Nerves
are composed of bundles of
Nerve Fibers
 Nerve Fibers are made of Nervous Cells
called Neurons
 Brain contains about 1011 neurons
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Neurons
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Neurons
 At
birth the connection between Neurons
are not established
 Neurons are not regenerated
 Body has a cleaning system, all dead
Neurons are removed
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Nature of Pulses
 Control
signals travel along the nerves
called “impulses”
 All
nerves and muscle control signals are
ELECTRICAL
 All nerves and muscle control signals are
DIGITAL
 Due to their electrical nature they are also
called Nerve Potential
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Nerve Action Potential
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NAP
 The
peak-to-peak potential remains the
same whatever the conditions may be
 Strength of sensation is achieved through
frequency of nerve signal pulses
 Intensity of Stimulation vs. Pulse Frequency


Exhibits logarithmic behavior
Frequency may go 500 pps in very strong
sensations
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Nerve Conduction Velocity
 The
speed of nerve impulses varies
enormously in different types of neuron.
 Fastest travel at about 250 mph, faster
than a Formula 1 racing car.
 Visit this link for different results on Speed
of Impulse
http://www.painstudy.com/NonDrugRem
edies/Pain/p10.htm
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Nerve Conduction Velocity




For the impulse to travel quickly, the axon
needs to be thick and well insulated.
This uses a lot of space and energy, however,
and is found only in neurons that need to
transfer information urgently
Neurons that need to transmit electrical
signals quickly are sheathed by a fatty
substance called myelin (Schwann cells).
Myelin acts as an electrical insulator, and
signals travel 20 times faster when it is present.
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Generation of a NAP
A
Nerve Action Potential is generated
due to movement of ions across the
membrane of neurons
 Mainly due to movement of Na and K ions
 Inside the cell: more K and less Na
 Outside the cell: less K and more Na
 Inside of the cell is negative with respect
to outside of the cells due to larger size of
the K ions as compared Na ions
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Generation of NAP
 Semipermeable
membrane
 ATP (Atenosine Tri Phosphate): Na+/K+
pump
 Na+ channels
 K+ channels
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Generation of NAP
 Resting
potential: -70 mV
 Threshold: 5-15 mV
 Action potential:

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Depolarization: -55 mV to 30 mV
Repolarization: 30 mV to back at resting
potential
Hyper polarization: -90 mV
Resting potential: -70 mV
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Generation of NAP
 For
interactive simulations
 http://outreach.mcb.harvard.edu/animat
ions/actionpotential.swf
 http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter14/animation__the_nerve_impulse
.html
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RC Equivalent of Nerve Fiber
 NCV
of different
fibers varies
 Each fiber has its
own delay due to
RC nature of fibers
 Myelinated
neurons conduct
electrical impulses
more swiftly
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Saltatory Conduction

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


Type of nerve impulse conduction that allows
action potentials to propagate faster and more
efficiently
Occurs in myelinated nerve fibers in the human
body
When an NAP travels via saltatory conduction, the
electrical signal jumps from one bare segment of
fiber to the next, as opposed to traversing the
entire length of the nerve's axon
Saltatory conduction gets its name from the
French word “saltare”, which means "to leap."
Saltation saves time and improves energy
efficiency in the nervous system
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Myelin Sheath






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Myelin a whitish, electrically insulating material composed of
lipids and proteins — sheathes the length of myelinated axons
Segments of unmyelinated axon, called Node of Ranvier,
interrupt the myelin sheath at intervals
Myelin sheaths wrap themselves around axons and squeeze
their myelin contents out to envelope the axon
Schwann cells serve the same function in the peripheral
nervous system
The Myelin sheath acts an insulator and prevents electrical
charges from leaking through the axon membrane
Virtually all the voltage-gated channels in a myelinated axon
concentrate at the nodes of Ranvier
These nodes are spaced approximately .04 inches (about 1
mm) apart
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Saltatory Conduction



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
Advantages of Saltatory Conduction:
Increased conduction velocity
Saltatory conduction is about 30-times faster than
continuous conduction
Improved energy efficiency
By limiting electrical currents to the nodes of
Ranvier, saltatory conduction allows fewer ions to leak
through the membrane
This ultimately saves metabolic energy — a significant
advantage since the human nervous system typically
uses about 20 percent of the body’s metabolic energy
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Saltatory Conduction
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Saltatory Conduction
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Myelin insulates the axon and allows the current to spread farther
before it runs out.
Knowing that it takes work on the neuron's part to make the gated
channel proteins, it would be a waste of energy for the neuron to
put gated channels underneath the myelin, since they could never
be used.
Myelinated axons only have gated channels at their nodes.
In a demyelinating disease, the myelin sheath decays... the
Schwann cells die selectively.
When myelin sheath is gone, the current from the initial action
potential cannot spread far enough to affect the region of the axon
where the gated channels are found.
Conductance of the action potential stops and the axon is never
able to send its output (the action potential) to its axonal terminals
If this axon innervated muscle, that muscle can no longer be
controlled
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Compound Action Potential


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Each nerve contains hundreds of axons with
different diameters, thresholds and the
degree of myelination.
These are categorized as Type A, further
subdivided into alpha, beta, gamma and
delta- These are myelinated and have larger
diameters
Type B- These are also myelinated and have
smaller diameters
Type C- These are unmyelinated and smaller
in size
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CAP
 When
a nerve is stimulated, the recorded
potential is sum of potential of all NAPs
 This potential is known as CAP
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CAP



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As stimulus strength increases, we recruit more
fibers, therefore more APs add up to produce
a larger curve.
Fast fibers will contribute APs that fall towards
the start of the CAP
slower fibers will contribute APs that fall
towards the tail section
As we gradually increase stimulus strength, we
recruit more and more fibers giving rise to a
wider CAP, with longer duration
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CAP Properties
 The
duration of the CAP
is the time from the
beginning of the
positive phase to the
end of the negative phase of the CAP.
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CAP Properties
 The
latency of the onset of the CAP is the
time from the onset of the stimulus artifact
to the onset of the CAP.
 The latency of the peak of the CAP is the
time from the onset of the stimulus artifact
to the peak of the CAP.
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CAP Properties
 The
latency of the beginning of the CAP
reflects how long it takes for the fastest
fibers to conduct action potentials from
the stimulus source to the recording
electrodes.
 When the latency is measured to the
peak of the CAP, we obtain the latency
of an average fiber in the nerve.
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Refractory Period

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When neurons receive a stimulus and Na
channels are open they cannot be re
stimulated until they are closed once
Absolute Refractory Period
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Period when another pulse cannot be
generated (during depolarization)
Relative Refractory Period
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Period when another pulse can be generated
but only in presence of a very strong stimulation
(during repolarization)
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Thank You!