Sensory Neurons – picks up the stimuli (nerve impulse) and carries it to the spinal cord and brain.Interneurons- Found within the brain and spinal cord. Relays the message between the sensory neurons and the motor neurons. Motor Neurons – transfers impulses away from the brain to the spinal cord

1. Impulse Conduction InImpulse Conduction In
NeuronsNeurons
By : Gaurav PandeyBy : Gaurav Pandey

3. NeuronNeuron
”Nerve Cell””Nerve Cell”
 Functional Unit of Nervous SystemFunctional Unit of Nervous System
1.1. Cell BodyCell Body – center part of the cell containing the– center part of the cell containing the
nucleusnucleus
2.2. DendritesDendrites
 Carries messagesCarries messages towardtoward the cell body.the cell body.
 Fingerlike projectionsFingerlike projections
1.1. AxonAxon
 Carries messagesCarries messages awayaway from the cell body.from the cell body.
 Elongated extension of the cell bodyElongated extension of the cell body
 End of the axon is divided into fingerlike projections calledEnd of the axon is divided into fingerlike projections called
axon terminalsaxon terminals..

4. Neuron ModelNeuron Model
 To check for understanding you will needTo check for understanding you will need
to construct a neuron model that containsto construct a neuron model that contains
dendrites, a cell body (soma), axon, anddendrites, a cell body (soma), axon, and
axon terminals.axon terminals.

6. Types of NeuronsTypes of Neurons
 Sensory NeuronsSensory Neurons – picks up the stimuli– picks up the stimuli
(nerve impulse) and carries it to the spinal(nerve impulse) and carries it to the spinal
cord and brain.cord and brain.
 Interneurons-Interneurons- Found within the brain andFound within the brain and
spinal cord. Relays the message betweenspinal cord. Relays the message between
the sensory neurons and the motorthe sensory neurons and the motor
neurons.neurons.
 Motor NeuronsMotor Neurons – transfers impulses– transfers impulses
away from the brain to the spinal cordaway from the brain to the spinal cord

7. How Neurons WorkHow Neurons Work
1.1. ReceptionReception
 Receptors in the skin sense stimuliReceptors in the skin sense stimuli
1.1. TransmissionTransmission
 Sensory neurons transmit the touch messageSensory neurons transmit the touch message
1.1. Data InterpretationData Interpretation
 Information is sorted and interpretedInformation is sorted and interpreted
1.1. TransmissionTransmission
 Motor Neurons transmit a response message to aMotor Neurons transmit a response message to a
musclemuscle
1.1. ResponseResponse
 Muscles are activated causing a responseMuscles are activated causing a response

8. Impulse TransmissionImpulse Transmission
 Start with a RESTING neuron – one NOTStart with a RESTING neuron – one NOT
transmitting an impulsetransmitting an impulse
 Plasma membrane controls [ ] of ionsPlasma membrane controls [ ] of ions
inside the cellinside the cell
 NaNa++
and Kand K++
on both sides of membraneon both sides of membrane
 NaNa++
Higher Conc OutsideHigher Conc Outside
 KK++
Higher Conc InsideHigher Conc Inside
 Remember NaRemember Na++
/K/K++
ATPase PumpATPase Pump

9. Sodium Potassium PumpSodium Potassium Pump

10. How an Impulse TravelsHow an Impulse Travels
 Stimulus excites a neuronStimulus excites a neuron
 Na+ channels open, Na+Na+ channels open, Na+
build up insidebuild up inside
 Inside more + that outsideInside more + that outside
 Change in chargeChange in charge
(depolarization)(depolarization)
 Membrane immediatelyMembrane immediately
behind depolarization returnsbehind depolarization returns
to RESTING STATEto RESTING STATE
 RESTING STATE – insideRESTING STATE – inside
negative, outside positivenegative, outside positive

11. 1. Resting State1. Resting State
 A neuron is not conducting an impulseA neuron is not conducting an impulse
 The K+ concentration is much higherThe K+ concentration is much higher
inside the cell than outinside the cell than out
 The Na+ concentration is much higherThe Na+ concentration is much higher
outside the cell than inoutside the cell than in

12. 2. Depolarization2. Depolarization
 A nerve cell is stimulatedA nerve cell is stimulated
 Membrane becomes permeable to Na+ forMembrane becomes permeable to Na+ for
an instant and they quickly move into thean instant and they quickly move into the
cellcell
 The inner surface of the cell membrane isThe inner surface of the cell membrane is
now more positively charged then thenow more positively charged then the
outside.outside.

13. 3. Repolarization3. Repolarization
 When the cell membrane becomesWhen the cell membrane becomes
depolarized, K+ automatically leaves thedepolarized, K+ automatically leaves the
cell until the cell is back to its resting state.cell until the cell is back to its resting state.

14. 4. The Impulse Travels4. The Impulse Travels
 ““Wave” of depolarization – transmission of anWave” of depolarization – transmission of an
impulse along length of axonimpulse along length of axon
 All or None PrincipleAll or None Principle – must reach a threshold– must reach a threshold
level or the impulse dieslevel or the impulse dies
 Covered by a white covering called aCovered by a white covering called a myelinmyelin
sheath (Schwann Cells)sheath (Schwann Cells), an insulator, an insulator
 Myelin sheath causes the ion exchange to occurMyelin sheath causes the ion exchange to occur
only at theonly at the nodesnodes which speeds up the processwhich speeds up the process
 For a short time after depolarization; the neuronFor a short time after depolarization; the neuron
cannot be stimulatedcannot be stimulated

15. 5. Transmission Across a Synapse5. Transmission Across a Synapse
 Neurons do not actually touch. This gapNeurons do not actually touch. This gap
between the two cells is call abetween the two cells is call a SYNAPSESYNAPSE
 Impulses are carried across a synapse byImpulses are carried across a synapse by
chemical messengers calledchemical messengers called
neurotransmitters.neurotransmitters.
 Approximately 30 different neurotransmitters;Approximately 30 different neurotransmitters;
do one of two things:do one of two things:
1.1. Stimulate the action potential in a second cellStimulate the action potential in a second cell
2.2. Inhibit the action potential in the next cellInhibit the action potential in the next cell

16. 6. Refractory Period6. Refractory Period
 The period of time it takes a neuron toThe period of time it takes a neuron to
return to its resting potential after beingreturn to its resting potential after being
stimulatedstimulated
 A neuron cannot be stimulated during thisA neuron cannot be stimulated during this
periodperiod
 This period of time is about 0.0004 of aThis period of time is about 0.0004 of a
secondsecond

18. ElaborationElaboration
 Neurotransmission:Neurotransmission:
Nifty Neurons and Muscle MessagesNifty Neurons and Muscle Messages

19. EvaluationEvaluation
Parts of Nervous SystemParts of Nervous System
 List the Four Major Parts of theList the Four Major Parts of the
Nervous SystemNervous System
 NeuronsNeurons
 NervesNerves
 BrainBrain
 Spinal CordSpinal Cord

20. THANK YOUTHANK YOU