Download In The Name of Allah The Most Beneficent The

IN THE NAME OF ALLAH
THE MOST BENEFICENT THE MOST MERCIFUL
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ECE 4552:
MEDICAL ELECTRONICS
LECTURE:
NEURO-MUSCULAR
SYSTEM
---NERVES
Engr. Ijlal Haider
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Dept of . Electrical Engineering
University of Lahore, Lahore
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/NonDrugRemedies/Pai
n/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:

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/animations/actio
npotential.swf
 http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter
14/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





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





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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
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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




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


When neurons receive a stimulus and Na channels
are open they cannot be re stimulated until they are
closed once
Absolute Refractory Period


Period when another pulse cannot be generated (during
depolarization)
Relative Refractory Period

Period when another pulse can be generated but only in
presence of a very strong stimulation (during
repolarization)
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THANK YOU!
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