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8/19/2019 1. Nerve and Aksi Potensial
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Nerve and action Potentials
Irfan Idris
Physiology DepartmentMedical Faculty, UNHAS
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lassification of Neurons and
Nerves
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Supporting ells
! "here are four types of supporting cells, calledneuroglial #or glial$ cells, in the central nervoussystem
% oligodendrocytes, &hich form myelin sheathsaround a'ons of the NS(
% microglia, &hich migrate through the NS andphagocytose foreign and degenerated material
% astrocytes, &hich help to regulate the e'ternal
environment of neurons in the NS( % ependymal cells, &hich line the ventricles #cavities$
of the )rain and the central canal of the spinal cord
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! "here are t&o types of supporting cells in
the peripheral nervous system*
% Schwann cells, &hich form myelin sheaths
around peripheral a'ons( and
% Satellite cells, or ganglionic gliocytes,
&hich support neuron cells )odies &ithin the
ganglia of the PNS+
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Resting Membrane Potential
of Nerves
! Active "ransport of Sodium and Potassium
Ions "hrough the Mem)rane"he
Sodium-Potassium #Na.-/.$
! 0ea1age of Potassium and Sodium
"hrough the Nerve Mem)rane
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Origin of the Normal Resting
Membrane Potential
! Contribution of the Potassium DiffusionPotential 2ecause of the high ratio ofpotassium ions inside to outside, 34*5, theNernst potential corresponding to this ratio is %
67 millivolts "herefore, if potassium ions&erethe only factor causing the resting potential
! Contribution of Sodium Diffusion !hroughthe Nerve Membrane diffusion of sodium ions
through the /.-Na. lea1 channels+ "he ratio ofsodium ions from inside to outside themem)rane is 8+5
! Contribution of the Na."#. Pump
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Nerve $ction
Potential
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%nitiation of the $ction Potential
! $ Positive"&eedbac' (icious Cycle Opens theSodium Channels % if any event causes enough initial rise in the mem)rane potential
from %68 millivolts to&ard the 9ero level, the rising voltage itselfcauses many voltage-gated sodium channels to )egin opening+"his allo&s rapid inflo& of sodium ions, &hich causes a furtherrise in the mem)rane potential
! !hreshold for %nitiation of the $ction Potential % A sudden rise in mem)rane potential of 54 to 38 millivolts usually
is re:uired+ "herefore, a sudden increase in the mem)ranepotential in a large nerve fi)er from %68 millivolts up to a)out %;4millivolts usually causes the e'plosive development of an actionpotential+ "his level of %;4 millivolts is said to )e the thresholdfor stimulation
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TRANSMISI SINAPTIK
ELEKTRIK
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Nerve fi)er types in mammalian nerve+
&iber !ype &unction
&iber Diameter
)*m+
Conduction(elocity
)ms+
Spi'eDuration
)ms+
$bsoluteRefractoryPeriod )ms+
$
< Proprioception( somaticmotor
5=-=8 >8-5=8
? "ouch, pressure 4-5= 38->8 8+7-8+4 8+7-5
@ Motor to musclespindles
3-; 54-38
Pain, cold, touch =-4 5=-38
- Preganglionicautonomic
B3 3-54 5+= 5+=
C
Dorsal root Pain, temperature,some mechano-reception, refle'
responses
8+7-5+= 8+4-= = =
Sympathetic Postganglionicsympathetics
8+3-5+3 8+>-=+3 = =
5 A and 2 fi)ers are myelinated( fi)ers are unmyelinated+
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Numerical classification sometimes used for sensoryneurons+
Number Origin &iber !ype
Ia Muscle spindle, annulospinal ending+ A <
I) Colgi tendon organ+ A <
II Muscle spindle, flo&er-spray ending( touch, pressure+ A ?
III Pain and cold receptors( some touch receptors+ A
I Pain, temperature, and other receptors+ Dorsal root