In The Name of Allah The Most Beneficent The Most Merciful 1

ECE 4550: Biomedical Instrumentation Lecture: Neuro-Muscular System ---Nerve Engr. Ijlal Haider University of Lahore, Lahore 2

Basic Systems of Human  Neuro-muscular  Cardio Vascular  Respiratory  Digestive  Reproductory  Endocrine  Lymphatic 3

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. 4

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 5

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 6

 Nerves are composed of bundles of Nerve Fibers  Nerve Fibers are made of Nervous Cells called Neurons  Brain contains about neurons 7

Neurons 8

 At birth the connection between Neurons are not established  Neurons are not regenerated  Body has a cleaning system, all dead Neurons are removed 9

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 10

Nerve Action Potential 11

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 12

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 edies/Pain/p10.htm edies/Pain/p10.htm 13

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. 14

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 15

Generation of NAP  Semipermeable membrane  ATP (Atenosine Tri Phosphate): Na+/K+ pump  Na+ channels  K+ channels 16

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 17

Generation of NAP  For interactive simulations  ions/actionpotential.swf ions/actionpotential.swf  hill.com/sites/ /student_view0/ chapter14/animation__the_nerve_impulse.html hill.com/sites/ /student_view0/ chapter14/animation__the_nerve_impulse.html 18

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 19

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 20

Myelin Sheath  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 21

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 22

Saltatory Conduction 23

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Saltatory Conduction  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 25

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 26

CAP  When a nerve is stimulated, the recorded potential is sum of potential of all NAPs  This potential is known as CAP 27

CAP  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 28

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. 29

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. 30

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. 31

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) 32

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Thank You! 34