2 Cells of the Nervous System NeuronsInformation processing and communicating nerve cellsGliaAddressed later
3 What do you know about neurons coming into this class? How does a neuron communicate with another neuron?What type of signal is processed in a neuron?What are the parts of a neuron?
4 Parts of a Neuron 3 main parts Dendrites Soma (cell body) Axon Receive informationSoma (cell body)Cellular maintenanceAxonTransmits information
5 Dendrites Tree like processes Receives information from other neurons Dendritic spinesCreate more area for axons to transmit informationChange depending on the amount of activityThis is one of the suggested bases for learning and memoryA neuron can have multiple dendrites
6 The soma Nucleus- contains DNA Nucleolus- constructs ribosomes Endoplasmic reticulum- contains ribosomes that construct proteinsGolgi apparatus- “packages” proteinsMitochondria- produces energy
7 The Axon Transmits information to other neurons Myelin sheath insulation that aids in the speed of the neural transmissionAxon terminalEnd of the axonContains neurotransmittersAlso called terminal buttons
8 More on the Axon Axon hillock Nodes of Ranvier Where the action potential beginsNodes of RanvierSegments of bare axon not covered by myelin
9 Giant Squid Used to study axons in the 1930s-1940s Extra large axon visible to the eyeDoesn’t have myelin, so it is extra large to add conductance
10 Characterization of neurons Sensory neuronsTranslates incoming sensory information into an electrical signalAfferent NeuronsConduct information towards the brain from the muscles and sensesInterneuronsNeurons in the spinal cord and the brain that both communicate a signal and process that signalEfferent NeuronsConduct information away from the brain to the muscles and sensesMotor NeuronsTranslates electrical signal to the muscles and glands
11 Not all neurons look the same Named by the number of extensions from the cell bodyUnipolarOne extension that branches into dendrites and an axonBipolarTwo extensions: one axon and one dendriteMultipolarMany extensions: one axon, many dendrites
12 Unipolar Neurons Found primarily in human embryos and invertebrates Sensory neurons that conduct impulses into the brain
13 Bipolar NeuronsFound primarily as sensory neurons in vision, audition and olfaction
15 What happens in a nerveNeurons communicate information to other neuronsThe signal itself is an electrical signal within the neuronAction PotentialFrom neuron to neuron, communication is chemical
16 The Resting Potential Two forces at work in a neuron Potassium IonsTwo forces at work in a neuronForce 1: Equilibrium: the idea that the concentration of a molecule tries to remain constant throughout the medium (substance)
17 The Resting PotentialEx. Smells: the garbage begins to smell in one spot, but the smell slowly expands throughout the houseThe smell gets lighter and lighter as it expands throughout the houseIt tries to spread out as evenly as possible
18 Status of the main players (ions) Sodium (Na+): more of it outside of the neuronPotassium (K+): more of it inside of the neuronChloride (Cl-): more of it outside of the neuron
19 Based on equilibrium…What does Na+, K+, and Cl- want to do? Are they “happy” where they are?What direction will they move if allowed?
20 Due to equilibrium… Na+ wants to move inside the neuron K+ wants to move outside the neuronCl- wants to move inside the neuron
21 What about charge? Does charge play a role in things? According to charge, how might the ions react?
22 How do charges react to each other? Opposites attractLike charges repel
23 One more piece to the puzzle There are large molecules inside the neuron with negative charges
24 Now which way do the ions want to go? Potassium:Which way does equilibrium push?What about the charge?
25 Now which way do the ions want to go? Chloride:Which way does equilibrium push?What about the charge?
26 Now which way do the ions want to go? Sodium:Which way does equilibrium push?What about the charge?
27 At rest Resting potential -70mV Potassium can cross the membrane Sodium and Chloride cannot cross the membraneWhat will potassium want to do at rest?
28 StimulationWhen stimulated by another neuron, some Na+ channels are openedK+ channels close
29 The action potentialIf the signal is strong enough, it makes it to the axon hillockIf strong enough, an action potential is generatedThresholdBegins an action potential
30 The action potentialDepolarization: occurs when Na+ flows into the cellDue to Na+ channels opening
31 The action potentialNow, 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 APAt the beginning of the AP, Na channels open and Na enters the cell
32 How’s potassium feeling now? Sodium moving inside the cell made the inside of the cell more positiveThis repels potassium to move outside
33 The action potentialK+ channels open at the peak and K+ flows out of the cellThis repolarizes the cell and even overshoots the resting potential of beforeCalled hyperpolarizationThen the Na/K pump brings the K back inside the cell and the Na back outside the cell2 K for every 3 NaUses energy (ATP)
34 The action potentialAt the peak, K+ channels open and K+ exits the cellConditions are now back where they started in terms of potential and charge, but the ions are in opposite positions
35 The action potentialThe Sodium Potassium pump restores the original environment of the resting potential so that the neuron can fire yet againThis is known as the refractory period
36 Graded Potentials Action Potentials are referred to as “all-or-none” Either get an action potential or notInputs that don’t reach threshold: Graded PotentialsCan add up across synapses/inputs to reach threshold
37 Saltatory Conduction Insulation is not perfect Signal loses strength down the axonRegeneration of the Action Potential occurs at each break in the myelin
38 At the Axon Terminal Vesicles containing neurotransmitters are present When an action potential reaches the axon terminal, Ca2+ channels open up and this causes the fusing of the vesicles to the membrane and the release of the neurotransmitters into the synaptic cleft
39 In the Synaptic CleftNeurotransmitters cross the membrane and bind to receptors on the receiving neuronDepending on the neurotransmitter, it can either excite or inhibit the post-synaptic neuronExcitatory Postsynaptic Potential (EPSP)- the excitation of the receiving neuronInhibitory Postsynaptic Potential (IPSP)- the inhibition of the receiving neuron
40 Neurotransmitters Various chemicals Can either excite the receiving neuron or inhibit itAcetylcholine- an excitatory NT typically found in the musclesGABA- an inhibitory NT typically found elsewhere in the nervous system
41 How transmission occurs Multiple synapses on each neuronal dendriteSome can excite while others inhibitAxon potentials can be created by multiple EPSPs from multiple neuronsCalled Spatial Summation
42 How transmission occurs One synapse can fire repeatedly on the same dendrite within a short temporal window (time period)Axon potentials can be created by multiple EPSPs from a single neuronCalled Temporal Summation
43 Summary: One last thing Transmission within the neuron is electricVia action potentialsTransmission between neurons is chemicalVia neurotransmitters
44 Glial cells Astrocytes- structural support and blood brain barrier Oligodendrocytes- myelination of axons CNSSchwann cells- myelination of axons PNSMicroglia- clean up