Impulse Conduction

1. IMPULSE CONDUCTION
Dr. Hidaayah O. Jimoh-Abdulghaffaar
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2. INTRODUCTION
• Transmission of impulse along a neuron.
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3. NEURON CONT’D
• All neurons have the following major
components:
i. Dendrites
ii. Soma/ cell body
iii. Axon
iv. Presynaptic terminals
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4. Figure 1: A neuron
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5. NERVE IMPULSE
• A nerve impulse is the electrical message that
is transmitted down the axon of a neuron.
• Regenerated at points along the axon.
• The speed of nerve impulses: 1 m/s to
100m/s.
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6. CONDUCTION
• At rest, a neuron has a resting potential prior to
sending a nerve impulse.
• The membrane of a neuron maintains an
electrical gradient- difference between electrical
charge inside and outside the cell.
• This is known as electrical polarization- the
inside is slightly more negative than the outside
(about -70mV).
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7. CONDUCTION CONT’D
• The membrane is selectively permeable: Na+, K+,
Ca2+ & Cl- ions pass through channels in the
membrane.
• At rest, Na+ channels are closed, K+ channels are
partially closed.
• The Na+-K+ ATPase pump continually pumps 3 Na+
out of the cell and 2 K+ into the cell. This helps to
maintain the electrical gradient.
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8. Figure 2: Ion distribution & movement across the
nerve membrane
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9. Figure 3: The Na+-K+ ATPase Pump
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10. Figure 4: Conduction of impulse across a nerve membrane
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11. CONDUCTION CONT’D
• When a nerve is stimulated, there is
depolarization of the membrane.
• Voltage-activated Na channels are opened & Na
ions rush into the cell & a nerve impulse occurs-
action potential.
• After this, the neuron undergoes a refractory
period- time which a neuron resists another
action potential.
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12. CONDUCTION CONT’D
• Absolute refractory period:
– first part of the period in which the membrane
cannot produce an action potential.
• Relative refractory period:
– second part of the period in which a stronger than
usual stimulus can trigger action potential.
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13. CONDUCTION CONT’D
• In a neuron, action potential begins at the axon
hillock.
• There is propagation of action potential i.e.
transmission of action potential down the axon.
• The myelin sheath of axons are interrupted by
short unmyelinated sections called node of
Ranvier.
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14. Figure 5: Propagation of action potential across a nerve
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15. CONDUCTION CONT’D
• At each node of Ranvier, action potential is
regenerated by a chain of positively-charged ions
pushed along by the previous segment.
• The jumping of action potential from one node of
Ranvier to another is called SALTATORY
CONDUCTION.
• It provides rapid conduction of impulses and
saves energy for the cell.
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16. Figure 6: Saltatory Conduction
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17. Figure 7: Saltatory Conduction
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18. Figure 8: Movement of ions in saltatory conduction
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19. CLINICAL CORRELATES
• Demyelinating diseases
– Myelin sheath is destroyed
Multiple sclerosis
Optic neuritis
Transverse myelitis
Neuromyelitis optica spectrum disorder
Myelin oligodendrocyte glycoprotein antibody-
associated disease
Acute disseminated encephalomyelitis
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20. FURTHER READING
• https://youtu.be/b2ctEsGEpe0?si=zSa7A7UQ8
TOOKebZ
• https://youtu.be/A3pIk3cFOzI?si=dEDhwMuc
G7HTSioR
• https://youtu.be/w-
waXZ2LDRE?si=OWYfIrYwbozVZhRk
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