Psychology 210Psychology 210

Cellular Anatomy Cellular Anatomy

Lecture 2Lecture 2

Cells of the Nervous Cells of the Nervous SystemSystem

NeuronsNeurons Information processing and Information processing and

communicating nerve cellscommunicating nerve cells GliaGlia

Addressed laterAddressed later

What do you know about What do you know about neurons coming into this neurons coming into this

class?class? How does a neuron communicate How does a neuron communicate

with another neuron?with another neuron? What type of signal is processed in a What type of signal is processed in a

neuron?neuron? What are the parts of a neuron?What are the parts of a neuron?

Parts of a NeuronParts of a Neuron 3 main parts3 main parts

DendritesDendrites Receive Receive

informationinformation Soma (cell body)Soma (cell body)

Cellular Cellular maintenancemaintenance

AxonAxon Transmits Transmits

informationinformation

DendritesDendrites

Tree like processesTree like processes Receives information from other Receives information from other

neuronsneurons Dendritic spinesDendritic spines

Create more area for axons to transmit Create more area for axons to transmit informationinformation

Change depending on the amount of activityChange depending on the amount of activity This is one of the suggested bases for learning This is one of the suggested bases for learning

and memoryand memory A neuron can have multiple dendritesA neuron can have multiple dendrites

The somaThe soma

Nucleus- contains DNANucleus- contains DNA Nucleolus- constructs Nucleolus- constructs

ribosomesribosomes Endoplasmic reticulum- Endoplasmic reticulum-

contains ribosomes that contains ribosomes that construct proteinsconstruct proteins

Golgi apparatus- Golgi apparatus- “packages” proteins“packages” proteins

Mitochondria- produces Mitochondria- produces energyenergy

The AxonThe Axon Transmits information Transmits information

to other neuronsto other neurons Myelin sheath Myelin sheath

insulation that aids in insulation that aids in the speed of the neural the speed of the neural transmissiontransmission

Axon terminalAxon terminal End of the axon End of the axon Contains Contains

neurotransmittersneurotransmitters Also called terminal Also called terminal

buttonsbuttons

More on the AxonMore on the Axon

Axon hillockAxon hillock Where the Where the

action action potential potential beginsbegins

Nodes of Nodes of RanvierRanvier Segments of bare Segments of bare

axon not covered axon not covered by myelinby myelin

Giant SquidGiant Squid Used to study Used to study

axons in the axons in the 1930s-1940s1930s-1940s

Extra large Extra large axon visible axon visible to the eyeto the eye

Doesn’t have Doesn’t have myelin, so it myelin, so it is extra large is extra large to add to add conductanceconductance

Characterization of Characterization of neuronsneurons

Sensory neuronsSensory neurons Translates incoming sensory Translates incoming sensory

information into an electrical information into an electrical signalsignal

Afferent NeuronsAfferent Neurons Conduct information towards Conduct information towards

the brain from the muscles and the brain from the muscles and sensessenses

InterneuronsInterneurons Neurons in the spinal cord and Neurons in the spinal cord and

the brain that both the brain that both communicate a signal and communicate a signal and process that signal process that signal

Efferent NeuronsEfferent Neurons Conduct information away Conduct information away

from the brain to the muscles from the brain to the muscles and sensesand senses

Motor NeuronsMotor Neurons Translates electrical signal to Translates electrical signal to

the muscles and glandsthe muscles and glands

Not all neurons look the Not all neurons look the samesame

Named by the number Named by the number of extensions from the of extensions from the cell bodycell body

UnipolarUnipolar One extension that One extension that

branches into branches into dendrites and an axondendrites and an axon

BipolarBipolar Two extensions: one Two extensions: one

axon and one dendriteaxon and one dendrite MultipolarMultipolar

Many extensions: one Many extensions: one axon, many dendritesaxon, many dendrites

Unipolar NeuronsUnipolar Neurons

Found primarily in Found primarily in human embryos human embryos and invertebratesand invertebrates

Sensory neurons Sensory neurons that conduct that conduct impulses into the impulses into the brainbrain

Bipolar NeuronsBipolar Neurons

Found primarily as Found primarily as sensory neurons in sensory neurons in vision, audition vision, audition and olfactionand olfaction

Multipolar neuronsMultipolar neurons

Found everywhere Found everywhere elseelse BrainBrain Peripheral Peripheral

autonomic nervous autonomic nervous systemsystem

Spinal cordSpinal cord

What happens in a nerveWhat happens in a nerve

Neurons communicate information to Neurons communicate information to other neuronsother neurons

The signal itself is an electrical signal The signal itself is an electrical signal within the neuron within the neuron Action PotentialAction Potential

From neuron to neuron, communication From neuron to neuron, communication is chemicalis chemical

The Resting PotentialThe Resting Potential Two forces at work Two forces at work

in a neuronin a neuron Force 1: Force 1:

Equilibrium: the Equilibrium: the idea that the idea that the concentration of a concentration of a molecule tries to molecule tries to remain constant remain constant throughout the throughout the medium medium (substance)(substance)

Potassium Ions

The Resting PotentialThe Resting Potential

Ex. Smells: the garbage begins to Ex. Smells: the garbage begins to smell in one spot, but the smell smell in one spot, but the smell slowly expands throughout the slowly expands throughout the househouse The smell gets lighter and lighter as it The smell gets lighter and lighter as it

expands throughout the houseexpands throughout the house It tries to spread out as evenly as It tries to spread out as evenly as

possiblepossible

Status of the main Status of the main players (ions)players (ions)

Sodium (NaSodium (Na++): more of it outside of ): more of it outside of the neuronthe neuron

Potassium (KPotassium (K++): more of it inside of ): more of it inside of the neuronthe neuron

Chloride (ClChloride (Cl--): more of it outside of ): more of it outside of the neuronthe neuron

Based on equilibrium…Based on equilibrium…

What does NaWhat does Na++, K, K++, and Cl, and Cl-- want to want to do? Are they “happy” where they do? Are they “happy” where they are?are?

What direction will they move if What direction will they move if allowed?allowed?

Due to equilibrium…Due to equilibrium… NaNa++ wants to move inside the neuron wants to move inside the neuron KK++ wants to move outside the neuron wants to move outside the neuron ClCl-- wants to move inside the neuron wants to move inside the neuron

What about charge?What about charge?

Does charge play a role in things?Does charge play a role in things? According to charge, how might the According to charge, how might the

ions react?ions react?

How do charges react to How do charges react to each other?each other?

Opposites attractOpposites attract Like charges repelLike charges repel

One more piece to the One more piece to the puzzlepuzzle

There are large molecules inside the There are large molecules inside the neuron with negative chargesneuron with negative charges

Now which way do the ions Now which way do the ions want to go?want to go?

Potassium:Potassium: Which way does equilibrium push?Which way does equilibrium push? What about the charge?What about the charge?

Now which way do the ions Now which way do the ions want to go?want to go?

Chloride:Chloride: Which way does equilibrium push?Which way does equilibrium push? What about the charge?What about the charge?

Now which way do the ions Now which way do the ions want to go?want to go?

Sodium:Sodium: Which way does equilibrium push?Which way does equilibrium push? What about the charge?What about the charge?

At restAt rest Resting potentialResting potential

-70mV-70mV Potassium can cross the membranePotassium can cross the membrane Sodium and Chloride cannot cross the Sodium and Chloride cannot cross the

membranemembrane

What will potassium want to do at rest?

StimulationStimulation

When When stimulated stimulated by another by another neuron, neuron, some Nasome Na++ channels channels are openedare opened

KK++ channels channels closeclose

The action potentialThe action potential

If the signal is If the signal is strong enough, strong enough, it makes it to it makes it to the axon hillock the axon hillock

If strong If strong enough, an enough, an action potential action potential is generatedis generated ThresholdThreshold Begins an action Begins an action

potentialpotential

The action potentialThe action potential

DepolarizationDepolarization: occurs when : occurs when NaNa++ flows into flows into the cellthe cell Due to NaDue to Na++

channels channels openingopening

The action potentialThe action potentialAt the beginning of the AP, Na channels open and Na enters the cell

Now, there is more of a positive charge inside than outside (the Na stops coming in for the same reasons the K did originally, a balance of two forces) this represents the peak of the AP

How’s potassium feeling How’s potassium feeling now?now?

Sodium moving Sodium moving inside the cell inside the cell made the inside made the inside of the cell more of the cell more positivepositive

This repels This repels potassium to potassium to move outsidemove outside

The action potentialThe action potential

K+ channels open at the peak and K+ K+ channels open at the peak and K+ flows out of the cellflows out of the cell

This repolarizes the cell and even This repolarizes the cell and even overshoots the resting potential of beforeovershoots the resting potential of before Called hyperpolarizationCalled hyperpolarization

Then the Na/K pump brings the K back Then the Na/K pump brings the K back inside the cell and the Na back outside inside the cell and the Na back outside the cellthe cell 2 K for every 3 Na2 K for every 3 Na Uses energy (ATP)Uses energy (ATP)

The action potentialThe action potentialAt the peak, K+ channels open and K+ exits the cell

Conditions are now back where they started in terms of potential and charge, but the ions are in opposite positions

The action potentialThe action potential The Sodium The Sodium

Potassium pump Potassium pump restores the restores the original original environment of environment of the resting the resting potential so that potential so that the neuron can the neuron can fire yet againfire yet again

This is known as This is known as the refractory the refractory periodperiod

Graded PotentialsGraded Potentials Action Potentials are Action Potentials are

referred to as “all-or-none”referred to as “all-or-none” Either get an action potential Either get an action potential

or notor not Inputs that don’t reach Inputs that don’t reach

threshold: Graded Potentialsthreshold: Graded Potentials Can add up across Can add up across

synapses/inputs to reach synapses/inputs to reach thresholdthreshold

Saltatory ConductionSaltatory Conduction Insulation is not perfectInsulation is not perfect

Signal loses strength down the axonSignal loses strength down the axon Regeneration of the Action Potential occurs at Regeneration of the Action Potential occurs at

each break in the myelineach break in the myelin

At the Axon TerminalAt the Axon Terminal Vesicles containing Vesicles containing

neurotransmitters are neurotransmitters are presentpresent

When an action When an action potential reaches the potential reaches the axon terminal, Caaxon terminal, Ca2+2+ channels open up and channels open up and this causes the fusing of this causes the fusing of the vesicles to the the vesicles to the membrane and the membrane and the release of the release of the neurotransmitters into neurotransmitters into the synaptic cleftthe synaptic cleft

In the Synaptic CleftIn the Synaptic Cleft Neurotransmitters cross the Neurotransmitters cross the

membrane and bind to membrane and bind to receptors on the receiving receptors on the receiving neuronneuron

Depending on the Depending on the neurotransmitter, it can neurotransmitter, it can either excite or inhibit the either excite or inhibit the post-synaptic neuronpost-synaptic neuron

Excitatory Postsynaptic Excitatory Postsynaptic Potential (EPSP)- the Potential (EPSP)- the excitation of the receiving excitation of the receiving neuronneuron

Inhibitory Postsynaptic Inhibitory Postsynaptic Potential (IPSP)- the Potential (IPSP)- the inhibition of the receiving inhibition of the receiving neuronneuron

NeurotransmittersNeurotransmitters

Various chemicalsVarious chemicals Can either excite the receiving Can either excite the receiving

neuron or inhibit itneuron or inhibit it Acetylcholine- an excitatory NT Acetylcholine- an excitatory NT

typically found in the musclestypically found in the muscles GABA- an inhibitory NT typically GABA- an inhibitory NT typically

found elsewhere in the nervous found elsewhere in the nervous systemsystem

How transmission occursHow transmission occurs

Multiple synapses on each neuronal Multiple synapses on each neuronal dendritedendrite

Some can excite while others inhibitSome can excite while others inhibit Axon potentials can be created by Axon potentials can be created by

multiple EPSPs from multiple multiple EPSPs from multiple neuronsneurons

Called Spatial SummationCalled Spatial Summation

How transmission occursHow transmission occurs

One synapse can fire repeatedly on One synapse can fire repeatedly on the same dendrite within a short the same dendrite within a short temporal window (time period)temporal window (time period)

Axon potentials can be created by Axon potentials can be created by multiple EPSPs from a single neuronmultiple EPSPs from a single neuron

Called Temporal SummationCalled Temporal Summation

Summary: One last thingSummary: One last thing

Transmission within the neuron is Transmission within the neuron is electricelectric Via action potentialsVia action potentials

Transmission between neurons is Transmission between neurons is chemicalchemical Via neurotransmittersVia neurotransmitters

Glial cellsGlial cells Astrocytes- Astrocytes-

structural support structural support and blood brain and blood brain barrierbarrier

Oligodendrocytes- Oligodendrocytes- myelination of myelination of axons CNSaxons CNS

Schwann cells- Schwann cells- myelination of myelination of axons PNSaxons PNS

Microglia- clean upMicroglia- clean up