LO exam 1

LO: Describe the major neurotransmitters

(ACh, glutamate, and GABA) in terms of anatomy, function, receptors and drugs targeting the systems

Describe the main types of glial cells, including the main function of each

-Microglia have multiple functions in the developing CNS [8], as they contribute to (1) elimination of apoptotic cells and preventing oversupply of neurons, (2) support of neurogenesis, migration and differentiation of neurons, (3) axon growth and synaptogenesis - Microglia have phagocytic capabilities and are also known as the macrophages of the central nervous system. macrophages are phagocytic cells - They are important phagocytes and essential for the development of the CNS, as they eliminate apoptotic neurons, produce growth factors and contribute to function and structural organization of the nerve tissue -Microglia are attracted to and accumulate in locations of cell death where they engulf apoptotic cells during neurogenesis and migration, differentiation and positioning of the newly generated neurons. - Microglia often change shape upon activation and may even become migratory when injury is sensed

LO: Describe the major neurotransmitters (DA, NE, 5-HT, opioid peptides) in terms of anatomy, function, receptors and drugs targeting the systems LO: Identify drugs that target each system and the mechanism of action of each drug

5-HT

Identify how many neurons and glia are in the human brain

85 billion neurons 10,000 synapses per neuron (in cortex) 1 cm of myelinated axon / neuron (in cortex) 160,000 km is almost 100,000 miles (3,000 miles across the US- like running it 33 times) 2% of your body weight 10^14 synapses à 100 trillion!!!!

LO: Describe the major neurotransmitters (ACh, glutamate, and GABA) in terms of anatomy, function, receptors and drugs targeting the systems LO: Discuss methods for studying neurotransmitter systems including immunohistochemistry, in situ hybridization, neuropharmacological analysis (agonists, antagonists, etc) and ligand binding methods

ACh 1.Nicotine- nAChR agonist 2.Muscarine- mAChR agonist 3.Curare, alpha-bungarotoxin - nAChR antagonists Glutamate 1.MK-801, PCP, Ketamine - NMDAR antagonists ● GABA 1.Alcohol, benzodiazepines (like valium), non-BZD hypnotics (like Ambien), barbituates (sedatives, anticonvulsants): positive allosteric modulators 2.Muscimol: GABAa agonist 3.Picrotoxin, bicuculline: GABAa antagonists 4.Baclofen: GABAb agonist

What kind of technique could you use to label and visualize ACh, Glu, or GABA neurons to determine loss?

Answer : ALL of the above

Explain what Golgi and Cajal disagreed about

Cajal correctly argued that the brain is made up of individual cells we call neurons! (i.e. neuron doctrine) Golgi disagreed and thought it was a network of connected nerves that communicate by direct contact and continuity

Which neurotransmitter is the primary excitatory neurotransmitter in the brain?

Glutamate!

LO: Describe the term remyelination

Group TOD → 1- Remyelination - some new oligodendrocytes generating myelin 2- In multiple sclerosis, remyelination fails, leaving the axons and even the entire neuron vulnerable to degeneration that largely accounts for the progressive clinical decline 3- The myelin sheaths that are generated in remyelination are typically thinner and shorter than those that are generated during developmental myelination. Associated with recovery of function. 4- Blocking the damaging autoimmune response so myelin does not continue to be targeted and destroyed by the immune system (many MS drugs utilize this therapeutic route) and Blocking voltage gated potassium channels could help because now the repolarization doesn't happen and your depolarization way may last longer and travel from that one node to the next. Citation Franklin, R., ffrench-Constant, C. Remyelination in the CNS: from biology to therapy. Nat Rev Neurosci 9, 839-855 (2008). https://doi.org/10.1038/nrn2480 Figure legend a | Following demyelination in the CNS, a demyelinated axon has two possible fates. The normal response to demyelination, at least in most experimental models, is spontaneous remyelination involving the generation of new oligodendrocytes. The myelin sheaths that are generated in remyelination are typically thinner and shorter than those that are generated during developmental myelination. Nevertheless, they are associated with recovery of function. In some circumstances, however, and notably in multiple sclerosis, remyelination fails, leaving the axons and even the entire neuron vulnerable to degeneration that largely accounts for the progressive clinical decline that is associated with demyelinating diseases. For this reason, therapies that increase the chances of the regenerative outcome of demyelination are keenly sought. b | A well-established and effective means of identifying remyelination is to embed well-fixed tissue in resin and examine semi-thin sections by light microscopy. The images in this series are transverse sections from the adult rat cerebellar white matter, showing normally myelinated axons of various diameters in the left-hand panel, demyelinated axons (plus debris-filled macrophages) following injection of ethidium bromide in the middle panel and remyelinated axons with typically thin myelin sheaths four weeks after the induction of remyelination in the right-hand panel." #4. Therapies that promote re-myelination or prevent autoimmune demyelination are under investigation #4 way we could improve action potential by manipulating channels Voltage gated K+ and Voltage gated Na+ channels are responsible for the action potential. How could we target these channels to improve action potential conduction in a demyelinated axon? In a demyelinated axon, action potentials deteriorate because there are only VG K+ and VG Na+ channels at the nodes of Ranvier. The action potential is traveling in a region of axon that used to have myelin but doesn't so it travels more slowly and there are not VG channels to regenerate the AP so current is lost as it travels. How could you get that wave of depolarization to last longer and travel further to the next node? Blocking voltage gated sodium channels would only make the problem worse because its harder to generate Aps Blocking voltage gated potassium channels could help because now the repolarization doesn't happen and your depolarization way may last longer and travel from that one node to the next. This kind of treatment has been tried in the clinic, but remember this would be treating a symptom rather than the CAUSE of MS. Most therapeutics (as you saw on the previous table) try to modulate the immune response and prevent the immune system from damaging more myelin

Identify the stage when voltage-gated K+ Channels are open

Phase 4 - falling phase, (aka called repolarization phase) The voltage gated potassium channels are open resulting in potassium efflux (i.e. potassium flowing out of the neuron). Phase 5- potassium channels are still open and beginning to close (but this was not a choice in the clicker Q J

LO: Consider how sodium channel mutations can impact function and neuron excitability

Mutations can cause Inappropriate sodium channel inactivation for example. When sodium channels do not inactivate, then there is no absolute refractory period and neurons can fire another action potential immediately. You can get uncontrolled excitability and synchronized firing of neurons in the brain which causes a seizure. Epilepsy is a condition where an individual suffers from chronic, repeated seizures.

LO: Describe the major neurotransmitters (DA, NE, 5-HT, opioid peptides) in terms of anatomy, function, receptors and drugs targeting the systems LO: List the anatomical nuclei for each system à Locus Coeruleus LO: Draw the projection pathways for each system LO: Compare and contrast behaviors that each system modulates

Norepinephrine sites of origin (i.e. the norepinephrine cell bodies are in the...) Locus Coeruleus and other groups of NE neurons that are found in the brainstem. The axons of these neurons extend from the brainstem to different regions all over the brain to modulate a variety of functions. Some behaviors NE modulates... Your ability to pay attention to me in class (too little NE and you may be falling asleep; too much and you might be distracted and any noise or distraction in the room will capture your attention) You are walking outside late at night, you are frightened and staying vigilant. You see something out of the corner of your eye and turn your attention quickly to it. Its just a raccoon. NE can help you remain vigilant in your environment and turn your attention quickly to stimuli that could be a threat. From your text... The Noradrenergic Locus Coeruleus: Besides being a neurotransmitter in the peripheral ANS, NE is also used by neurons of the tiny locus coeruleusin the pons (from the Latin for "blue spot" because of the pigment in its cells). Each human locus coeruleus has about 12,000 neurons. We have two of them, one on each side. A major breakthrough occurred in the mid-1960s, when Nils-Åke Hillarp and Bengt Falck at the Karolinska Institute in Sweden developed a technique that enabled the catecholaminergic (noradrenergic and dopaminergic) neurons to be visualized selectively in histological sections prepared from the brain (Figure 15.11). This analysis revealed that axons leave the locus coeruleus in several tracts but then fan out to innervate just about every part of the brain: all of the cerebral cortex, the thalamus and the hypothalamus, the olfactory bulb, the cerebellum, the midbrain, and the spinal cord (Figure 15.12). The locus coeruleus makes some of the most diffuse connections in the brain, considering that just one of its neurons can make more than 250,000 synapses, and it can have one axon branch in the cerebral cortex and another in the cerebellar cortex! The organization of this circuitry is so different from what was then known about synaptic connections in the brain that it took many years of research before the mainstream neuroscience community could accept that NE was a neurotransmitter in the brain (Box 15.3). Lots of different functions, but the key part is that NE modulates these functions. Recordings from awake, behaving rats and monkeys show that locus coeruleus neurons are most strongly activated by new, unexpected, nonpainful sensory stimuli in the animal's environment. They are least active when the animals are not vigilant, just sitting around quietly, digesting a meal. The locus coeruleus may participate in a general arousal of the brain during interesting events in the outside world. Because NE can make neurons of the cerebral cortex more responsive to salient sensory stimuli, the locus coeruleus may function generally to increase brain responsiveness, speeding information processing by the point-to-point sensory and motor systems and making them more efficient

Identify the stage when voltage-gated Na channels are open

Phase 3 - rising phase (aka called depolarization phase, rising phase and contributes to the overshoot phase

LO: Draw a typical action potential. Label the axes and each phase of the action potential LO: Describe the key molecular events that underlie each phase: Threshold; Rising phase; Overshoot phase; Falling phase; Undershoot phase; Refractory periodPhases of AP

Phases of AP 1-resting phase- RMP resting membrane potential (leaky K+ channels open- NOT voltage gated potassium channels) 2-threshold phase- EPSP depolarization to threshold (NT binding receptors at the dendrites resulting in EPSP) 3- rising phase Upshoot/depolarization/ (voltage gated Na channels open) Our book also includes an overshoot phase (this is where the membrane potential is greater than 0mv (between 3 and 4 in this image) 4- falling phase/re-polarization/ (voltage gated K+ channels open resulting in potassium efflux and Na channels are inactivated) 5- -undershoot phase hyperpolarization (VG K+ channels still open and Na channels inactived)

LO: Discuss how the resting membrane potential is maintained LO: Define the resting membrane potential

RMP (resting membrane potential) is the charge (voltage) difference across the cell membrane when the cell is at rest (i.e. not firing an action potential (AP) or receiving signals).

LO: Compare and contrast spatial summation and temporal summation

So you are more likely to get an action potential fired if... (1)You have many EPSPs adding together (2)You have few/less IPSPs (the IPSPs are inhibitory and decrease the potential of the membrane so when they sum with EPSPs it weakens the strength of the EPSP) (3)Channels are closed to increase membrane resistance (we will talk about this more with the dendritic length constant, but you don't want to lose your electrical signal across open channels in the membrane) (4)The more depolarized the membrane of the dendrites (if we have a bunch of potassium channels open and dendrites are very hyperpolarized, its harder to trigger an AP (you need more EPSPs)

LO: Draw a diagram to help you describe each of the steps in synaptic transmission

Steps in chemical synaptic transmission... Presynaptic Action Potential Depolarization of the Axon Terminal Voltage-Gated Calcium Channels Open Calcium Enters the Axon Terminal Fusion of "Docked" Synaptic Vesicles. (SNARE proteins coil to cause fusion) Exocytosis or Release of the Neurotransmitter Postsynaptic Receptors activated and change Vm

Discuss important histological procedures and how they contributed to the advancement of neuroscience (i.e. Golgi method, immunohistochemistry, in situ hybridization)

The common description of the target is quoted as "a limited number of cells at random in their entirety". This is the essence of Golgi staining: (1) Only single cells are stained, therefore there is no impediment from adjacent cell staining while deriving the morphological structure of the cells (very important for light microscopy where you have integrated input from different depths). (2)The cells are stained randomly, there is no known preference among neuronal cells for Golgi staining and I haven't seen any other types of cells in CNS stained with Golgi, therefore it is quite specific for neuronal cells (and leaving macro- and microglia, astrocytes etc. intact). (3) The cells are stained in their entirety, meaning that the complete cell is stained very nicely, showing detailed arborisation of dendritic tree, that was very important in studying of Purkinje cells in cerebellum. They shared the 1906 nobel prize Santiago Ramon y Cajal 1852- 1934 The father of modern neuroscience Spanish pathologist, histologist, neuroscientist, and Nobel laureate. His original pioneering investigations of the microscopic structure of the brain have led his being designated by many, as the father of modern neuroscience. Over the summer of 1868, Ramón y Cajal's father, hoping to interest his son in a medical career, took him to graveyards to find human remains for anatomical study. Sketching bones was a turning point for him and subsequently, he did pursue studies in medicine.‪[6]:207‬ Ramón y Cajal attended the medical school of the University of Zaragoza, where his father was an anatomy teacher It was not until he moved to the University of Barcelona in 1887, that he learned about Golgi's method, which uses potassium dichromate and silver nitrate to stain a few neurons at random dark black while leaving the rest transparent, thereby revealing the stained neurons' intricately branching structure without the confusing background of the others. This staining method, which Ramón y Cajal improved, was central to his work, allowing him to turn his attention to the central nervous system, whose neurons are densely intertwined in what would otherwise have been an unintelligible jumble. During this period he made extensive studies of neural material covering many species and most major regions of the brain, leaving behind a legacy of detailed drawings. Ramón y Cajal made several major contributions to neuroanatomy.[6] He discovered the axonal growth cone, and demonstrated experimentally that the relationship between nerve cells was not continuous, but contiguous.[6] This provided definitive evidence for what would later be known as "neuron doctrine", now widely considered the foundation of modern neuroscience.[6] In debating neural network theories (e.g. neuron theory, reticular theory), Ramón y Cajal was a fierce defender of the neuron theory. He provided detailed descriptions of cell types associated with neural structures, and produced excellent depictions of structures and their connectivity.

LO: Explain the purpose of synaptic integration

Their output is binary à fire or no fire à and this firing right is electrical in nature. A fast change in membrane potential that moves down the axon

Discuss the importance of animal research in the field of neuroscience Explain when animal research is needed

To study navigation at the single cell level like the Bat man did, we need animals. We simply cannot do this kind of experiment in a human (i.e. record from single neurons as we navigate around a room). While the bat brain is similar to the human brain it is NOT identical but it certainly can be a useful model. Even non-mammalian animal brains (like drosophila brains) can be incredibly valuable models even though they are not identical In other words,

LO: Explain why action potentials move away from the cell body LO: Describe the factors that enable salutatory conduction to occur

Voltage gated sodium channels that initiate the AP are clustered at nodes of Ranvier as well as the axon hillock. Experimentally, if you have a neuron in a dish that is at rest all of those voltage gated sodium channels are closed (NOT inactivated). So if you stimulate an AP in the middle of the axon at a node, what happens?? Remember, sodium channel inactivation is what prevents the AP from traveling backwards normally. But here the channels are at rest and closed (NOT inactivated) so the AP can travel down the axon towards the terminals BUT ALSO towards the axon hillock. Over course this is an experimental scenario, but it can be done by scientists with neurons in a dish!

What kind of signals cross the synaptic cleft?

depends on the synapse There are both electrical and chemical synapses in our nervous system. Chemical synapses are the predominant synapse so we will focus our discussion today on this synapse and discuss electrical synapses (i.e. gap junctions) only briefly

LO: Describe the main types of glial cells, including the main function of each LO: Glia easily match the number of neurons in the brain, yet neurons are the predominant focus of neuroscience textbooks. Explain why that might be the case.

research on glia has ramped up in the last decade and we are discovering all the fascinating ways glia contribute to brain function. The focus on neurons is simply historical and because for a long time glia were thought to be simply "by standers" "structural support" etc. This is what I learned as an undergraduate student, but thanks to lots of research (including scientists here at UNC). We know glia do a lot more in the brain than just support neurons. Astrocytes in particular, can providen neuronal support, nutrient support, repair damage, blood brain barrier, but they can also regulate communication between neurons! We will see this in our research story and in a few slides... Astrocytes often wrap themselves around synapses between neurons. They can take up released neurotransmitter, release transmitters of their own after increases in intracellular calcium. All of this can lead to alterations in synaptic activity (enhancement or inhibition)

LO: Explain why the action potential is referred to as all-or-none

you have to reach the voltage threshold that will cause the voltage sensor in the Na+ channel to move and to open Na+ channels. Once that happens the molecular machinery is there (all those VG Na channels) and they open. The wave of depolarization triggers opening of VG K channels and the rest of the AP ensues in its characteristic shape. In other words, an action potential occurs if the neuron reaches threshold. If the neuron does not reach threshold, an action potential will NOT occur. It is all or nothing! Remember action potentials are of fixed size and duration! Once you depolarize to threshold at the axon hillock, there are MANY voltage gated sodium channels there and their voltage sensitive gates move and open the pore for sodium to flow into the cell. This sets off the cascade of molecular events we just discussed and the characteristic AP ensues

LO: Compare and contrast neurotransmitter-gated ion channels and g-protein-coupled receptors

(1)LGIC- ligand gated ion channels. We call these ionotropic. In the learning outcome above they are called neurotransmitter-gated ion channels. They are channels and when neurotransmitter binds it opens the channel and ions flow into or out of the neuron depending on the receptor. Activation of these receptors results in FAST postsynaptic changes in membrane potential. ● (2)GPCR- g protein coupled receptors. We call these metabotropic. The receptor binds neurotransmitter which causes its associated g protein that is inside the neuron to activate and dissociate from the GPCR. The G protein can now work its magic inside the neuron and activate all kinds of different signaling pathways. In this image the g protein directly goes and binds to an ion channel causing it to open and ions to flow in causing a change in membrane potential. It takes longer for changes in membrane potential to occur with metabotropic receptors because they work through this g protein pathway rather than direct opening of a channel.

LO: Draw a diagram to help you describe each of the steps in synaptic transmission

(1)NT molecules are synthesized and packaged into synaptic vesicles. *NOTE this one was a bit of tricky question because, the packaging and synthesis is happening ALL the time and really doesn't have a place in this order because this is a continuous, on-going process** (2)An action potential arrives at the presyanptic nerve terminal (3)Depolarization opens voltage gated Calcium channels (VG Ca++ channels) which allows calcium to enter the presynaptic terminal (4)Increases in intracellular calcium via the VG Ca++ channels triggers the fusion of SV with the presynaptic membrane (5)The transmitter molecules diffuse across the synaptic cleft and bind receptors of the postsynaptic membrane (6)Binding of transmitters activates the receptors which initiates activation (depolarization/hyperpolarization ) of the post synaptic cell (7)Process is terminated by enzymatic breakdown of the transmitter and/or uptake of the tranimstter into cells and/or diffusion of the molecule away from the synapse

LO: Compare convergence and divergence of neurotransmitter systems

(a)Divergence (b)Convergence ● Most of the time the rule for Neurotransmitter systems is DIVERGENCE. Lots of different receptors for a single neurotransmitter. Here is an example of convergence... In the paper the authors show that DA and NE can bind to the same receptor to influence the same effector system

LO: Draw a diagram to help you describe each of the steps in synaptic transmission LO: Discuss three mechanisms for termination of synaptic transmission

1.Diffusion (some neurotransmitter will inevitably diffuse away from the post synaptic receptors) 2.Enzymatic degradation (not all synapses have enzymes that break down neurotransmitter in the synaptic cleft) 3.Reuptake through a neurotransmitter transporter (this is a primary way that neurotransmitter is removed from the synapse and recycled for future use) ● It depends on the type of synapse which method is most important for NT clearance

LO: Identify the criteria and experimental approaches used to determine if a substance in the brain is a neurotransmitter

1.The molecule must be synthesized and stored in the presynaptic neuron. 2.The molecule must be released by the presynaptic axon terminal upon stimulation. 3.The molecule, when experimentally applied, must produce a response in the postsynaptic cell that mimics the response produced by the release of neurotransmitter from the presynaptic neuron. The scientist often begins with little more than a hunch that a particular molecule may be a neurotransmitter. This idea may be based on observing that the molecule is concentrated in brain tissue or that the application of the molecule to certain neurons alters their action potential firing rate. Whatever the inspiration, the first step in confirming the hypothesis is to show that the molecule is, in fact, localized in, and synthesized by, particular neurons. Many methods have been used to satisfy this criterion for different neurotransmitters. Two of the most important techniques used today are immunocytochemistry and in situ hybridization

LO: Identify the criteria and experimental approaches used to determine if a substance in the brain is a neurotransmitter LO: Discuss methods for studying neurotransmitter systems including immunohistochemistry, in situ hybridization, neuropharmacological analysis (agonists, antagonists, etc) and ligand binding methods

1.The molecule must be synthesized and stored in the presynaptic neuron. Neurotransmitter "marker genes" include specific genes that are necessary for the synthesis, storage, degradation etc. of that particular neurotransmitter. Localizing transmitters and transmitter-synthesizing enzymes Immunocytochemistry—localize molecules to cells; Assesses Gene expression at the protein level Immunohistochemistry (IHC) (localizes molecules to cells in a brain slice). Assesses Gene expression at the protein level In situ hybridization (ISH) Localize expression of a molecule by detecting mRNA of that gene or genes required to synthesize the molecule In the left hand corner, I provided an example of a norepinephrine neuron. Let's imagine we are trying to prove that this neuron releases norepinephrine. Neurons that release norepinephrine as their neurotransmitter must express enzymes to make norepinephrine (like DBH). They also require proteins to accumulate norepinephrine into vesicles for release (i.e. VMAT2) and to re-uptake the neurotransmitter norepinephrine from the synapse for future release (i.e. NET, the norepinephrine transporter). They also often express enzymes to break that transmitter down. We can use ISH or IHC to detect the expression of any of these genes to build evidence that the neuron indeed releases norepinephrine as its transmitter! (this answers the poll on the next slide too J)

Diagram a neuron and label its components Describe the function of each component of the neuron

A = Axon hillock (axon) in this image. This region contains an abundance of voltage gated sodium channels which helps initiate the action potential B = Dendrites are the primary input structure (they receive information) C = Axon is usually insulated with myelin. BUT not all neurons are myelinated!! Myelin helps speed the propagation of the action potential. In the disease Multiple Sclerosis, myelin is lost and neurons lose their ability to adequately propagate action potential resulting in the loss of things like sensation (vision in one eye for example) D = Buttons in this image (aka axon terminal) are the primary output structures. This is where neurotransmitter is released from the neuron. The transmitter carrries signals from this neuron to other neurons.

LO: Explain the differences between agonists and antagonists

ANTAGONIST... Inhibitors of neurotransmitter receptors, called receptor antagonists, bind to the receptors and block (antagonize) the normal action of the transmitter. An example of a receptor antagonist is curare, an arrow-tip poison traditionally used by South American natives to paralyze their prey. Curare binds tightly to the Ach receptors on skeletal muscle cells and blocks the actions of ACh, thereby preventing muscle contraction. AGONIST... Other drugs bind to receptors, but instead of inhibiting them, they mimic the actions of the naturally occurring neurotransmitter. These drugs are called receptor agonists. An example of a receptor agonist is nicotine, derived from the tobacco plant. Nicotine binds to and activates the ACh receptors in skeletal muscle. In fact, the ACh-gated ion channels in muscle are also called nicotinic ACh receptors, to distinguish them from other types of ACh receptors, such as those in the heart, that are not activated by nicotine. There are also nicotinic ACh receptors in the CNS, and these are involved in the addictive effects of tobacco use.

LO: Describe how EPSPs and IPSPs contribute to the generation of an action potential in the post-synaptic cell (draw a diagram to illustrate this)

EPSP (excitatory post synaptic potentials)- occur when neurotransmitter (NT) binds a channel that opens and positive ions flow into the cell (depolarizations) IPSP (inhibitor post synaptic potentials)- occur when neurotransmitter (NT) binds a channel that opens and negative ions flow into the cell (hyperpolarization) EPSPs can sum together to depolarize the membrane to threshold at the axon hillock which will cause an AP IPSPs are inhibitory so they make an action potential (AP) less likely to fire EPSP summation Allows for neurons to perform sophisticated computations Integration: EPSPs added together to produce significant postsynaptic depolarization Spatial summation: EPSPs generated simultaneously at different sites Temporal summation: EPSPs generated at same synapse in rapid succession Not all synapses are excitatory. Action of inhibitory synapses—Take membrane potential away from action potential threshold. Inhibitory synapses exert powerful control over neuron output. Excitatory vs. inhibitory synapses: bind different neurotransmitters, allow different ions to pass through channels Membrane potential less negative than −65 mV = hyperpolarizing IPSP Shunting inhibition: Synapse inhibits current flow from soma to axon hillock.

LO: Explain how local anesthetics work LO: Diagram the structure of a voltage gated sodium channel LO: Identify where lidocaine interacts with VG sodium channels and how this impacts their function

Although you've tried to tough it out, you just can't take it anymore. You finally give in to the pain of the toothache and head for the dentist. Fortunately, the worst part of having a cavity filled is the pinprick in the gum caused by the injection needle. Then your mouth becomes numb and you daydream while the dentist drills and repairs your tooth. What was injected, and how did it work? Local anesthetics are drugs that temporarily block action potentials in axons. They are called "local" because they are injected directly into the tissue where anesthesia—the absence of sensation—is desired. Small axons, firing a lot of action potentials, are most sensitive to conduction block by local anesthetics. The first local anesthetic introduced into medical practice was cocaine. The chemical was isolated from the leaves of the coca plant in 1860 by the German physician Albert Niemann. According to the custom of the pharmacologists of his day, Niemann tasted the new compound and discovered that it caused his tongue to go numb. It was soon learned that cocaine also had toxic and addictive properties. (The mind-altering effect of cocaine was studied by another well-known physician of that era, Sigmund Freud. Cocaine alters mood by a mechanism distinct from its local anesthetic action, as we shall see in Chapter 15.) The search for a suitable synthetic anesthetic as a substitute for cocaine led to the development of lidocaine, which is now the most widely used local anesthetic. Lidocaine can be dissolved into a jelly and smeared onto the mucous membranes of the mouth (and elsewhere) to numb the nerve endings (called topical anesthesia); it can be injected directly into a tissue (infiltration anesthesia) or a nerve (nerve block); it can even be infused into the cerebrospinal fluid bathing the spinal cord (spinal anesthesia), where it can numb large parts of the body. Lidocaine and other local anesthetics prevent action potentials by binding to the voltage-gated sodium channels. The binding site for lidocaine has been identified as the S6 alpha helix of domain IV of the protein (Figure A). Lidocaine cannot gain access to this site from the outside. The anesthetic first must cross the axonal membrane and then pass through the open gate of the channel to find its binding site inside the pore. This explains why active nerves are blocked faster (the sodium channel gates are open more often). The bound lidocaine interferes with the flow of Na+ that normally results from depolarizing the channel. (PhD 102)

LO: Describe the major neurotransmitters (DA, NE, 5-HT, opioid peptides) in terms of anatomy, function, receptors and drugs targeting the systems LO: Identify drugs that target each system and the mechanism of action of each drug

Amphetamine causes the norepinephrine transporter (NET) to reverse and spill NE into the synapse rather than taking it up from the synapse (this results in increased levels of NE in the synaptic cleft) Cocaine blocks the uptake of norepinephrine from the synapse via NET, this results in increased levels of NE in the synaptic cleft

LO: Discuss how the resting membrane potential is maintained LO: Include discussion of the 3 major players: ions, the membrane, membrane proteins LO: Explain the importance of the sodium-potassium pump

Answer: Pumps 3 Na+ ions outside the cell and 2+ K+ ions inside Uses ATP to pump ions (by definition a pump requires energy, this pump uses ATP as its energy source) Helps maintain RMP

LO: Discuss how the resting membrane potential is maintained LO: Define the resting membrane potential

Answer: negatively ; -65mV

LO: Describe the structure and functional properties of the sodium channel LO: Discuss how sodium channel inactivation contributes to the refractory period LO: Describe the key molecular events that underlie each phase: Threshold; Rising phase; Overshoot phase; Falling phase; Undershoot phase; Refractory period

As VG sodium channels open they contribute to the rising phase and overshoot phase. They begin to inactivate at the overshoot phase and are fully inactivated during the refractory period, which prevents another action potential from firing! **Remember- sodium channel inactivation is different from sodium channel closing. At rest sodium channels are closed (1) in the bottom diagram. You can see how on the inside of the protein the pore is closed. (2) Depolarization causes the internal gates (green bars) to move and the channel to open, the pore is now open. (3) Sodium channel inactivation happens because the red ball and chain plugs up the pore Sodium channels are closed due to an internal gate (1) Sodium channels are inactivated due to the intracellular ball and chain portion of the protein (3) The absolute refractory period is due to VG sodium channel inactivation! At this point in time (when NA channels are inactivated) NO amount of depolarization is able to trigger another AP.

Describe the main types of glial cells, including the main function of each

Astrocytes are a part of the "Big 3". Astrocytes are the most abundant glial cell type in the CNS, which is a category of brain cells that are non-excitable. In recent years, studies have shown that astrocytes are more than brain glue and do not only passively support neurons. Previous literature in the last few decades have shown that astrocytes have a variety of roles in the CNS, including: Protecting and maintenance of the BBB: secreting factors that create more protection in terms of how substances/molecules are transferred into the CNS. Neurotransmitter uptake Glutamate and GLT-1 Synaptic plasticity through (NT uptake etc.) Metabolism and homeostasis: ion balance Injury/infection response to CNS: secrete cytokines/chemokines that help mediate neuroprotection Astrocytes use intracellular Ca2+ signals as one of their primary forms to engage in neural circuits, Along with their function in mainitaing a healthy CNS, they also have roles in drugs of abuse, specifically cocaine. -Astrocytes help form and maintain the BBB by secreting factors that maintain association of BBB-involved cells and tight junctions (help regulate travel of various molecules across tissues). -Endothelial cells form a single layer that lines all blood vessels and regulates exchanges between bloodstream and surrounding tissues. -brain only makes up 2% of body mass -Glucose is the main energy substrate in the adult brain -Astrocytes are the link between neuronal activity and brain energy consumption -Lactate is a part of the glycolysis (glucose broken down by cells) cycle and allows glucose breakdown, which enables energy production to continue. -Several neurodegenerative diseases linked to aging are characterized by a decrease in the consumption of energy by the brain in specific regions. These include Alzheimer's disease (AD), Parkinson's disease (PD), Frontotemporal dementia (FTD), depression and certain neurodevelopmental disorders. luminal surface of their endfeet that is in contact with vascular endothelium express glucose transporter

A drug causes potassium channels on a dendrite to open. Channel opening causes a/an

B - decrease in membrane resistance, Membrane resistance: The resistance to electrical current flow across a membrane; represented by the symbol rm. This resistance to ion flow is lower when channels are open. The membrane resistance, in contrast, depends on the number of open ion channels, which changes from moment to moment depending on what other synapses are active.

LO: Describe cre technology and how it can be used to identify the structure and function of neurons

CRE Technology Cre is an enzyme called a recombinase. Think of it like a tiny little pair of molecular scissors that is able to cut DNA. Cre recognizes DNA sequences called LoxP sites. When recognizes two LoxP sites in the DNA it will cut out the DNA in between those sites (the yellow region shown in the image below). This ability of Cre to recognize specific sites in the DNA and cut out anything in between is a geneticists dream! Now, scientists can use this molecule to manipulate the DNA of model organisms like mice to create genetically modified mice.

LO: Draw a typical action potential. Label the axes and each phase of the action potential LO: Describe the key molecular events that underlie each phase: Threshold; Rising phase; Overshoot phase; Falling phase; Undershoot phase; Refractory period LO: Discuss how sodium channel inactivation contributes to the refractory period THIS IS A CRITICAL SLIDE AND CONCEPT. Make sure you understand the molecular basis of the action potential. If you have questions seek help!

Depolarization above threshold triggers opening of Na+ channels which triggers the influx of na_ As the cell continues to depolarize you get the delayed opening of K+ channels and the flow of K+ out of the cell. Phases of AP 1-resting phase- RMP resting membrane potential (leaky K+ channels open- NOT voltage gated potassium channels) 2-threshold phase- EPSP depolarization to threshold (NT binding receptors at the dendrites resulting in EPSP) 3- rising phase Upshoot/depolarization/ (voltage gated Na channels open and sodium flows INTO the cell causing depolarization) Our book also includes an overshoot phase (this is where the membrane potential is greater than 0mv (between 2 and 3 in this image) 4- falling phase/re-polarization/ (voltage gated K+ channels open at the high membrane voltage resulting in potassium efflux (i.e. potassium flowing out of the neuron) and Na channels are inactivating which means Na is not flowing into the cell anymore so the voltage of the membrane begins to drop) 5- -undershoot phase hyperpolarization (VG K+ channels still open and Na channels are inactivated) **NOTE- sodium channel inactivation is different from sodium channel closing. At rest sodium channels are closed (1) in the right hand diagram. Depolarization causes the internal gate to move and the channel to open. Sodium channel inactivation happens because the red ball and chain plugs up the pore (3) in the right hand diagram. Sodium channels are closed due to an internal gate (blue in the diagram with little plus signs) Sodium channels are inactivated due to the intracellular ball and chain portion of the protein (red ball in the diagram) The absolute refractory period is due to VG sodium channel inactivation! At this point in time (when NA channels are inactivated) NO amount of depolarization is able to trigger another AP.

LO: Discuss how the resting membrane potential is maintained LO: Identify two physical forces that determine a neuron's resting potential

Diffusion = ions flow from areas of high concentration to low concentration. So Na+ passively flows into the cell when channels open (because it is high outside and low inside) Electrical potential = ions flow towards oppositely charged ares. (opposites attract!). Electrical potential also drives Na+ into the cell when channels open because the inside of the cell is more negatively charged than the outside

LO: Describe the unconventional neurotransmitters, endocannabinoids, in terms of anatomy, function, receptors and drugs targeting the systems

Endocannabinoids •Small lipid molecules released from postsynaptic neurons retrograde signaling •Vigorous AP firing in the post synaptic neurons causes voltage gated calcium channels to open → calcium flows in → elevated calcium then stimulates synthesis of endocannabinoid synthesizing enzymes •Not packaged in vesicles! Manufactured rapidly and on demand •Small membrane permeable •Bind selectively to the CB1 type of cannabinoid receptor (presynaptic recptor mainly)--> reduce calcium channel opening so they inhibit release of NT •Receptors discovered BEFORE the NT (CB1 receptor mainly in the brain; CB2 immune tissue) More CB1 receptor than any other GPCR •Cannabis (active ingredient THC) at low doses - euphoria, feelings of calm, relaxation, altered sensations, reduced pain, increased laughter, talkativeness, hunger and light headedness along with decreased problem solving ability, short term memory and psychomotor performance (driving) •High doses -hallucinations •Treatment of nausea and vomiting and stimulate appetite in aids patients

LO: Explain what it means if K+ ions are at equilibrium

Equilibrium potential-Thus, an equilibrium state is reached when the diffusional and electrical forces are equal and opposite, and the net movement of K+ across the membrane ceases Be careful here, just because the NET movement of potassium across the membrane has ceased doesn't mean that K+ ions aren't flowing back and forth across open channels in the membrane. They are still flowing back and forth, there is just no NET flow. An impermeable membrane separates two regions: one of high salt concentration (inside) and the other of low salt concentration (outside). The relative concentrations of potassium (K+) and an impermeable anion (A−) are represented by the sizes of the letters. (b) Inserting a channel that is selectively permeable to K+ into the membrane initially results in a net movement of K+ down their concentration gradient, from left to right. (c) A net accumulation of positive charge on the outside and negative charge on the inside retards the movement of positively charged K+ from the inside to the outside. Equilibrium is established such that there is no net movement of ions across the membrane, leaving a charge difference between the two sides.(PhD 67) So when potassium ions are at equilibrium (Ek)... The concentration of potassium inside the cell is still greater diffusion and electrical forces are equal and opposite so that... There is no NET flow of K+ across the membrane (K+ ions are still moving back and forth)

LO: Identify factors that influence conduction velocity LO: Explain how the conduction velocity of a neuron varies with axonal diameter (draw a diagram to illustrate this)

Factors influencing conduction velocity Spread of action potential along membrane Dependent on (1) axon structure (2) Path of the positive charge Inside the axon (faster) Across the axonal membrane (slower) From your text... There are two paths that positive charge can take: down the inside of the axon, or across the axonal membrane. If the axon is narrow and there are many open membrane channels, most of the current will flow out across the membrane. If the axon is wide and there are few open membrane channels, most of the current will flow down inside the axon. The farther the current goes down the axon, the farther ahead of the action potential the membrane will be depolarized, and the faster the action potential will propagate. As a rule, therefore, action potential conduction velocity increases with increasing axonal diameter. (3) Axonal diameter (bigger diameter axon = faster AP conduction) Remember the squid giant axon is large in diameter for a reason. This axon is critical for mediating the squids escape response (propelling its body away from prey) which allows it to stay alive and escape prey in the wild. (4) Number of channels increasing the number of VG NA+ channels at the axon hillock would increase the neurons excitability and likelihood of firing an AP (5) Myelin: Layers of myelin sheath facilitate current flow and dramatically speed up AP conduction velocity Myelinated neurons = faster AP conduction Schwann cells in the PNS Oligodendroglia in CNS (6) Saltatory conduction at nodes of Ranvier Voltage-gated sodium channels concentrated at nodes

LO: Describe how a modulator can change length constant

GPCR Synaptic transmission that modifies effectiveness of EPSPs generated by other synapses with transmitter-gated ion channels Example: activating NE β receptor CLOSES K+ channel - increase Rm - EPSPs diminish less as they travel à easier to fire AP (neuron is more excitable) Also K+ channel contributes to low RMP so depolarization

LO: Assess the similarities and differences between electrical and chemical synapses

Gap junction Channel Connexon—formed by six connexins Cells said to be "electrically coupled" Flow of ions from cytoplasm of one cell to cytoplasm of another cell Unlike most chemical synapses, bidirectional Very fast transmission Postsynaptic potentials (PSPs) Synaptic integration: several PSPs occurring simultaneously to excite a neuron (causes AP) Studies in recent years have revealed that electrical synapses are common in every part of the mammalian CNS They are often found where normal function requires that the activity of neighboring neurons be highly synchronized. Left Figure legend: (a) Neurites of two cells connected by a gap junction. (b) The enlargement shows gap junction channels, which bridge the cytoplasm of the two cells. Ions and small molecules can pass in both directions through these channels. (c) Six connexin subunits comprise one connexon, two connexons comprise one gap junction channel, and many gap junction channels comprise one gap junction. Right Figure legend: (b) An action potential generated in one neuron causes a small amount of ionic current to flow through gap junction channels into a second neuron, inducing an electrical PSP. (Source: Part a from Sloper and Powell, 1978.)

LO: Describe what factors determine each neuron's unique physiology LO: Describe adaptation

Here the presence of a specific kind of K+ channel gives the neuron b it unique adaptation physiology!! The cerebral cortex has two major types of neurons as defined by morphology: aspinous stellate cells and spiny pyramidal cells. A stellate cell typically responds to a steady depolarizing current injected into its soma by firing action potentials at a relatively steady frequency throughout the stimulus (part a). However, most pyramidal cells cannot sustain a steady firing rate. Instead, they fire rapidly at the beginning of the stimulus and then slow down, even if the stimulus remains strong (part b). This slowing over time is called adaptation, a very common property among excitable cells. Another firing pattern is the burst, a rapid cluster of action potentials followed by a brief pause. Some cells, including a particular subtype of large pyramidal neuron in the cortex, respond to a steady input with rhythmic, repetitive bursts (part c). Variability of firing patterns is not unique in the cerebral cortex. Surveys of many areas of the brain suggest that neurons have as large an assortment of electrical behaviors as morphologies. What accounts for the diverse behavior of different types of neurons? Ultimately, each neuron's physiology is determined by the properties and numbers of ion channels in its membrane. There are many more types of ion channels than the few described in this chapter, and each has distinctive properties. For example, some potassium channels activate only very slowly. A neuron with a high density of these will show adaptation because during a prolonged stimulus, more and more of the slow potassium channels will open, and the outward currents they progressively generate will tend to hyperpolarize the membrane. When you realize that a single neuron may have more than a dozen types of ion channels, the source of diverse firing behavior becomes clear. It is the complex interactions among multiple ion channels that create the eclectic electric signature of each class of neuron.

Detail the ways in which neurons are specialized for communication

How does information flow in a neuron? Dendrite à soma (cell body) à axon hillock à axon à axon terminal where neurotransmitter is released! To answer this, next we look to the component of a synapse!

LO: Discuss important histological procedures and how they contributed to the advancement of neuroscience (i.e. Golgi method, immunohistochemistry, in situ hybridization) Learning Objective: Compare and contrast immunohistochemistry and in situ hybridization

IHC à measures protein levels

LO: Describe how an action potential is propagated along an axon

In an unmyelinated axon, the AP is regenerated constantly along the entire length of the axon. This requires a lot of energy and lots of VG K+ and VG Na+ channels! It requires energy because Na and K flow down their concentration gradients continually as the AP is regenerated over and over again. Na+/K+ ATP pumps have to do the hard work (requiring lots of ATP) to re- establish the concentration gradients and RMP (resting membrane potential).

LO: Describe the major neurotransmitters (ACh, glutamate, and GABA) in terms of anatomy, function, receptors and drugs targeting the systems LO: Compare and contrast neurotransmitter-gated ion channels and g-protein-coupled receptors

In example of a receptor agonist is nicotine, derived from the tobacco plant. Nicotine binds to and activates the ACh receptors in skeletal muscle. In fact, the ACh-gated ion channels in muscle are also called nicotinic ACh receptors, to distinguish them from other types of ACh receptors, such as those in the heart, that are not activated by nicotine. There are also nicotinic ACh receptors in the CNS, and these are involved in the addictive effects of tobacco use. The most thoroughly studied transmitter-gated ion channel is the nicotinic ACh receptor at the neuromuscular junction in skeletal muscle. It is a pentamer, an amalgam of five protein subunits arranged like the staves of a barrel to form a single pore through the membrane (Figure 6.18a). Four different types of polypeptides are used as subunits for the nicotinic receptor, designated α, β, γ, and δ. A complete mature channel is made from two α subunits, and one each of β, γ, and δ (abbreviated α2βγδ). There is one ACh binding site on each of the α subunits; the simultaneous binding of ACh to both sites is required for the channel to open (Figure 6.18b). The nicotinicACh receptor on neurons is also a pentamer, but, unlike the muscle receptor, most of these receptors are composed of α and β subunits only (in a ratio of α3β2).( The Neuromuscular Junction. Synaptic junctions also exist outside the CNS. For example, axons of the autonomic nervous system innervate glands, smooth muscle, and the heart. Chemical synapses also occur between the axons of motor neurons of the spinal cord and skeletal muscle. Such a synapse is called a neuromuscular junction, and it has many of the structural features of chemical synapses in the CNS (Figure 5.9). Neuromuscular synaptic transmission is fast and reliable (LGICs!). An action potential in the motor axon always causes an action potential in the muscle cell it innervates. This reliability is accounted for, in part, by structural specializations of the neuromuscular junction. Its most important specialization is its size—it is one of the largest synapses in the body. The presynaptic terminal also contains a large number of active zones. In addition, the postsynaptic membrane, also called the motor end-plate, contains a series of shallow folds. The presynaptic active zones are precisely aligned with these junctional folds, and the postsynaptic membrane of the folds is packed with neurotransmitter receptors. This structure ensures that many neurotransmitter molecules are focally released onto a large surface of chemically sensitive membrane. Because neuromuscular junctions are more accessible to researchers than CNS synapses, much of what we know about the mechanisms of synaptic transmission was first established here. Neuromuscular junctions are also of considerable clinical significance; diseases, drugs, and poisons that interfere with this chemical synapse have direct effects on vital bodily functions.

LO: Describe how EPSPs and IPSPs contribute to the generation of an action potential in the post-synaptic cell (draw a diagram to illustrate this)

Integration of excitatory and inhibitory inputs •Example of 5 inputs, 3 excitatory and 2 inhibitory (overly simplified but allows us to think about how incoming synaptic information is integrated) •If all 3 excitatory → reach threshold → AP •If two excitatory & two inhibitory - don't reach threshold → no AP •3 excitatory & 2 inhibitory → reach threshold → AP

LO: Describe what factors determine each neuron's unique physiology

It's all about which molecular players on the membrane of that neuron!! (i.e. the properties and numbers of ion channels in its membrane.) Why do AP firing patterns look different? Each neuron's physiology is determined by the properties and numbers of ion channels in its membrane. This is why different neurons can have slightly different resting membrane potentials or thresholds for AP firing. In fact, Ion channels of excitable membranes was a whole book and COURSE in grad school → there are MANY different types of ion channels enough for a whole course!! Every neuron can have more than a dozen different types of ion channels. The unique combination of ion channels in that neuron gives it characteristic electrophysiological properties.

LO: Describe how an action potential is propagated along an axon

Move away from the cell body due to inactivation of voltage gated sodium channels Propagation of the action potential Orthodromic: action potential travels in one direction - down axon to the axon terminal Antidromic (experimental): backward propagation - if you start an AP in the middle of the axon experimentally, APs can travel in either direction because the sodium channels in front and behind are just closed (not inactivated) Typical conduction velocity: 10 m/sec Typical length of action potential: ~2 msec

LO: Discuss how the resting membrane potential is maintained LO: Define the resting membrane potential, how it is measured and its value in a "typical" neuron LO: Include discussion of the 3 major players: ions, the membrane, membrane proteins

Na/K Pump → moves 3 positive Na+ outside and 2 positive K+ inside cell (more positive ions leaving (helps keep membrane potential negative), Uses ATP and helps maintain the RMP The NA/K pump is CRITICAL for separating charge across the membrane and therefore is CRITICAL to RMP. If you commit to memory... Na is higher OUTSIDE the cell than inside K is higher INSIDE the cell than out The inside of the cell is more negative than the outside. You can figure almost any question about RMP out. For example, we know then that the NA/K pump needs to move more NA outside (3 ions) relative to the number of K ions it moves in (2)

LO: Differentiate when to use the nernst and goldman equations

Nernst = equilibrium potentials for individual ions Goldman = resting membrane potential of the neuron

Compare the the Neuron Doctrine and Reticular Theory

Neuron doctrine (Cajal) vs. reticular theory (Golgi) Over a six-year period, this led Ramón y Cajal to a major discovery: The brain itself is made of individual cells (neuron doctrine) . By the turn of the 20th century (1901-200), the cellular nature of the brain was fairly clear, and both scientists were awarded the Nobel Prize in Physiology and Medicine. They received it as a shared prize in 1906 for their work elucidating the structure of the nervous system. The revealed structure included specific features within nervous tissue, but also the cellular nature of that tissue, an idea that Golgi continued to reject even in his Nobel Prize acceptance speech.

LO: Compare and contrast neurotransmitter-gated ion channels and g-protein-coupled receptors

Neurotransmitter, acting on G-protein-coupled receptors, can also have slower, longer lasting, and much more diverse postsynaptic actions. This type of transmitter action involves three steps: 1.Neurotransmitter molecules bind to receptor proteins embedded in the postsynaptic membrane. 2.The receptor proteins activate small proteins, called G-proteins, which are free to move along the intracellular face of the postsynaptic membrane. 3.The activated G-proteins activate "effector" proteins. Effector proteins can be G-protein-gated ion channels in the membrane (Figure 5.17a), or they can be enzymes that synthesize molecules called second messengers that diffuse away in the cytosol (Figure 5.17b). Second messengers can activate additional enzymes in the cytosol that can regulate ion channel function and alter cellular metabolism. Because G-protein-coupled receptors can trigger widespread metabolic effects, they are often referred to as metabotropic receptors.

Describe the main types of glial cells, including the main function of each

Oligodendrocytes are another type of glial cell, who are known as the myelinating cells of the central nervous system. Their main function is to make myelin! Myelin-wraps around the axon like sheath to a sword but it is interrupted periodically by Nodes of Ranvier. The myelin helps to speed propagation of the AP (action potential) providing a sort of insulation Lactate is a part of the glycolysis (glucose broken down by cells) cycle and allows glucose breakdown, which enables energy production to continue. MS causes decreased ability to transmit signals in brain and body. In multiple sclerosis (MS) myelin is destroyed by the immune system which disrupts AP propagation. Progressively overtime this results in a loss of sensation and/or motor movement. Previously I mentioned that some glial cells have the same or similar function, but name differs based on the region. Oligodendrocytes and Schwann cells. Both of these cells main function is to create myelin, but the oligodendrocytes reside in the CNS, whereas the Schwann cells mainly reside in the PNS. (point out myelination differences) Oligodendroctyes -provide myelination in the CNS (central nervous system-brain & spinal cord)) - a single oligodendrocyte can myelinate several different axons Schwann cells -provide myelination in the PNS (peripheral nervous system) - a single schwann cell myelinates only a SINGLE axon. Typically there are many schwann cells on a single axon to provide the myelination

LO: Explain what it means if K+ ions are at equilibrium LO: Discuss why EK is relevant to the resting membrane potential (RMP)

Relative ion permeabilities of the membrane at rest—(cont.) Selective permeability of potassium channels—a key determinant of resting membrane potential Many types of potassium channels

Describe the methods used to classify neurons

Ways to categorize neurons Connectivity Anatomical location Structure # of neurites Dendrites Axon length Golgi type I -projection neurons (pyramidal neurons) Golgi type II- local circuit neurons (stellate cells, typically inhibitory interneurons) Gene expression function Motoneurons (motor neurons) stimulate muscles or glands; Sensory neurons respond to environmental stimuli, such as light, odor, or touch; Interneurons receive input from and send input to other neurons.

LO: Describe how vesicles fuse with the membrane

Remember V SNARE = synaptobrevin And T SNAREs = SNAP25 and Syntaxin The free ends of synaptobrevin, syntaxin, and SNAP25 begin to coil around each other and result in the Ternary complex, an extraordinarily stable rod shaped structure of alpha helices. SNARE COMPLEX As the energetically favorable coiling of the three SNAREs continues the vesicle membrane is pulled ever closer to the presynaptic membrane. Calcium enters through the voltage gated Ca channels triggers SNARE complex binding by synaptotagmin and displacement of complexin and opening of fusion pore

LO: Describe how EPSPs and IPSPs contribute to the generation of an action potential in the post-synaptic cell

Remember the action potential, starts in the axon hillock and is a signal of fixed size and duration due to the presence of voltage gated sodium channels and voltage gated potassium channels at the hillock and along the axon at nodes of ranvier These molecular components (i.e. VG Na+ channels and VG K+ channels) are not present in the same way/quantity in the dendrites Instead, in the dendrites, post-synaptic receptors receive signals from other neurons causing changes in depolarization (EPSP or IPSPs). These depolarizations and hyperpolarizations are NOT of a fixed size and duration. They can be big or small and they diminish in size as they travel along the dendrites toward the cell body and axon hillock.

LO: Discuss how the resting membrane potential is maintained LO: Include discussion of the 3 major players: ions, the membrane, membrane proteins LO: Explain the importance of the sodium-potassium pump

Resting membrane potential is the difference in voltage (i.e. charge) across the membrane of a cell. The NA/K pump is CRITICAL for separating charge across the membrane and therefore is CRITICAL to RMP. Thus the role of the sodium-potassium pump is create a concentration gradient (high potassium inside; high sodium outside). It creates this concentration gradient by using energy (ATP) to pump 3 sodiums out and 2 sodiums in.

Which proteins mediate synaptic vesicle docking and fusion?

SNAREs

LO: Describe the factors that enable salutatory conduction to occur

Saltatory conduction requires two things.. (1) Myelin (2) Nodes of ranvier - concentration of voltage gated sodium channels and other molecular components required to generate an AP "Jumping" of APs from one node to the next Saltatory conduction makes for FAST action potential conduction, which means we can react faster and think faster. It also means the neurons save energy! Think about unmyelinated axons and all those VG Na+ and VG K+ channels opening and closing. Na+ and K+ are constantly flowing down their concentration gradients along the entire axon rather than just at the nodes of ranvier. Myelinated neurons get to spend less energy on Na+/K+ pumps for re-establishing concentrations gradients after an AP (not as much Na+ and K+ is going to be displaced in an myelinated axon) The good thing about fat axons is that they conduct action potentials faster; the bad thing about them is that they take up a lot of space. If all the axons in your brain were the diameter of a squid giant axon, your head would be too big to fit through a barn door. Fortunately, vertebrates evolved another solution for increasing action potential conduction velocity: wrapping the axon with insulation called myelin

LO: Describe the major neurotransmitters (DA, NE, 5-HT, opioid peptides) in terms of anatomy, function, receptors and drugs targeting the systems LO: List the anatomical nuclei for each systemà Raphe Nuclei LO: Draw the projection pathways for each system LO: Compare and contrast behaviors that each system modulates LO: Identify drugs that target each system and the mechanism of action of each drug

Serotonin sites of origin (i.e. the serotonin cell bodies are in the...) Raphe nuclei that are found in the brainstem. The axons of these neurons extend from the brainstem to different regions all over the brain to modulate a variety of functions. The Serotonergic Raphe Nuclei. Serotonin-containing neurons are mostly clustered within the nine raphe nuclei. Raphe means "ridge" or "seam" in Greek, and, indeed, the raphe nuclei lie to either side of the midline of the brain stem. Each nucleus projects to different regions of the CNS (Figure 15.13). Those more caudal, in the medulla, innervate the spinal cord, where they modulate pain-related sensory signals (see Chapter 12). Those more rostral, in the pons and midbrain, innervate most of the brain in much the same diffuse way as do the locus coeruleus neurons. Raphe neurons fire most rapidly during wakefulness, when an animal is aroused and active. Raphe neurons are the most quiet during sleep. The locus coeruleus and the raphe nuclei are part of a venerable concept called the ascending reticular activating system, which implicates the reticular "core" of the brain stem in processes that arouse and awaken the forebrain. This simple idea has been refined and redefined in countless ways since it was introduced in the 1950s, but its basic sense remains. Raphe neurons seem to be intimately involved in the control of sleep-wake cycles, as well as the different stages of sleep. It is important to note that several other transmitter systems are involved in a coordinated way as well. We will discuss the involvement of the diffuse modulatory systems in sleep and wakefulness in Chapter 19.

discuss how the resting membrane potential is maintained Define the resting membrane potential, how it is measured and its value in a "typical" neuron

To measure resting membrane potential, you need a few things... (1)Neuron (2)Reference electrode- this is the electrode that sits in the bath and tells you the potential OUTSIDE your neuron (3)Recording electrode- this is the electrode that you pierce the neuron with. Once it is inside it tells you the potential difference between the external solution and inside your neuron. ● In the example above, the resting membrane potential of the neuron is -60 mV. That means the inside of the neurons is 60mV MORE NEGATIVE than the external bath solution. There are lots of proteins (among other things like ions, etc) inside the neuron that are negatively charged, making the inside of the neuron more negative than the solution outside.

Compare different levels of analysis in neuroscience research (molecular, cellular, systems, behavioral, and cognitive neuroscience)

So just broadly what are some of the ways that we decode the brain. What are all the levels that we can look at the brain! Levels of analysis: molecular, cellular, systems, behavior, cognitive From the text "Neuroscience: Exploring the Brain" Molecular Neuroscience The brain has been called the most complex piece of matter in the universe. Brain matter consists of a fantastic variety of molecules, many of which are unique to the nervous system. These different molecules play many different roles that are crucial for brain function: messengers that allow neurons to communicate with one another, sentries that control what materials can enter or leave neurons, conductors that orchestrate neuron growth, archivists of past experiences. The study of the brain at this most elementary level is called molecular neuroscience. Dr. Robertson's Example: I consider myself a molecular neuroscientist because my PhD dissertation focused on the study of a single protein, the norepinephrine transporter and how its function/dysfunction can influence behavior. Cellular Neuroscience The next level of analysis is cellular neuroscience, which focuses on studying how all those molecules work together to give neurons their special properties. Among the questions asked at this level are: How many different types of neurons are there, and how do they differ in function? How do neurons influence other neurons? How do neurons become "wired together" during fetal development? How do neurons perform computations? Dr. Robertson's Example: I consider myself a cellular neuroscientist because my post doctoral research focused on studying the developmental origins of norepinephrine neuron diversity. Systems Neuroscience Constellations of neurons form complex circuits that perform a common function, such as vision or voluntary movement. Thus, we can speak of the "visual system" and the "motor system," each of which has its own distinct circuitry within the brain. At this level of analysis, called systems neuroscience, neuroscientists study how different neural circuits analyze sensory information, form perceptions of the external world, make decisions, and execute movements. Behavioral Neuroscience How do neural systems work together to produce integrated behaviors? For example, are different forms of memory accounted for by different systems? Where in the brain do "mind-altering" drugs act, and what is the normal contribution of these systems to the regulation of mood and behavior? What neural systems account for gender-specific behaviors? Where are dreams created and what do they reveal? These questions are studied in behavioral neuroscience. Cognitive Neuroscience: Perhaps the greatest challenge of neuroscience is understanding the neural mechanisms responsible for the higher levels of human mental activity, such as self-awareness, imagination, and language. Research at this level, called cognitive neuroscience, studies how the activity of the brain creates the mind.

List and Describe the four essential steps in the scientific process with examples

The Bat Man Summary Question- because he wanted to find out how a mammalian brain navigates a more natural environment. In particular, he wanted to know how brains deal with a third dimension. He's discovered new aspects of the complex encoding of navigation, cell type responsible for the bat's 3D compass He's revealed the 3D territory of a typical bat-nav neuron- spherical place cell fields Also discovered another cell- long sought vector cell- tracks angle and distance to a particular goal This is an important field of research and the 2014 Nobel prize in physiology was awarded to navigation researchers The "bat man" Had to develop new technology- wireless GPS and electrophysiology devices that were small enough for the bat to carry ID levels of analysis: The Bat Man's research would be considered à cellular neuroscience, systems neuroscience and behavioral neuroscience Scientific process 1. Observation - observe how bats navigate 3D space (because humans operate upright) 2. Replication - repeating the same experiment in different subjects/animals in the same lab 3. Interpretation - his new work put to rest once popular theory from rat studies that proposed a certain type of brain oscillation creates grid-like neural maps (oscillation absent in bats) 4. Verification- need to be done by other scientists, a different research group (find these cells in other mammals or in bats)

LO: Analyze how stress can modulate EPSPs in the brain

The aim of this study was to determine whether rats subjected to chronic stress in adolescence show changes in learned fear, anxiety, and synaptic transmission in the prelimbic cortex during adulthood. Male Sprague Dawley rats were subjected to seven days of restraint stress on postnatal day forty-two (PND 42, adolescence). The field excitatory postsynaptic potentials of stressed adolescent rats had significantly lower amplitudes than those of controls, although the amplitudes were higher in adulthood. Our results demonstrate that short-term stress in adolescence induces strong effects on excitatory synaptic transmission in the prelimbic cortex Anxiety-like behavior was measured one day (PND 50) and twenty-one days (PND 70, adulthood) after stress using the elevated-plus maze and dark-light box tests, respectively. Rats that had been stressed during adolescence and adulthood had higher anxiety-like behavior levels than did controls 1.EPSP are smaller in adolescent animals that experienced stress 2.In adolescence, stress reduced EPSP size but this effect is no longer present in adulthood (the EPSPs do not differ between the stressed & control conditions) 3.We see that stress can reduce EPSPs in adolescent rats in a similar region of cortex to the impairment seen in humans. Both studies in the frontal cortex suggest that EPSP effects (Rats) and function impairment (humans) is reversable after stress.

LO: Discuss the demyelinating disease multiple sclerosis and ways to alleviate failed AP propagation in the disease

The critical importance of myelin for the normal transfer of information in the human nervous system is revealed by the neurological disorder known as multiple sclerosis (MS). Victims of MS often complain of weakness, lack of coordination, and impaired vision and speech. The disease is capricious, usually marked by remissions and relapses that occur over a period of many years. Although the precise cause of MS is still poorly understood, the cause of the sensory and motor disturbances is now quite clear. MS attacks the myelin sheaths of bundles of axons in the brain, spinal cord, and optic nerves. The word sclerosis is derived from the Greek word for "hardening," which describes the lesions that develop around bundles of axons, and the sclerosis is multiple because the disease attacks many sites in the nervous system at the same time. Lesions in the brain can now be viewed noninvasively using new methods such as magnetic resonance imaging (MRI). However, neurologists have been able to diagnose MS for many years by taking advantage of the fact that myelin serves the nervous system by increasing the velocity of axonal conduction. One simple test involves stimulating the eye with a checkerboard pattern and measuring the elapsed time until an electrical response is noted at the scalp over the part of the brain that is a target of the optic nerve. People who have MS characteristically have a marked slowing of the conduction velocity of their optic nerve.

LO: Explain the dendritic length constant (draw a diagram to illustrate this) LO: Compare membrane resistance and internal resistance

The length constant is an index of how far depolarization can spread down a dendrite or axon Higher the length constant the further depolarization will travel In ideal scenario two factors : (1) the resistance to current flowing longitudinally down the dendrite, called the internal resistance (ri); and (2) the resistance to current flowing across the membrane, called the membrane resistance (rm). Most current will take the path of least resistance; therefore, the value of λ will increase as membrane resistance increases because more depolarizing current will flow down the inside of the dendrite rather than "leaking" out the membrane. The membrane resistance, in contrast, depends on the number of open ion channels, which changes from moment to moment depending on what other synapses are active. The dendritic length constant, therefore, is not constant at all!( Why do we care about dendritic length constants?? Dendritic length constants can be measured experimentally to help us create computational models of information processing in dendrites!! "The length constant is unique for an individual neuron can predict how EPSPs may cause action potentials (fire/no fire) based on the properties of that neuron"

LO: Identify factors that influence conduction velocity

The location and number of VG sodium channels influences where APs are initiated and how quickly they can propagate. Remember, positive charge moves faster down the axon if it is traveling inside the axon rather than across the membrane.

LO: Assess the similarities and differences between electrical and chemical synapses

The physical nature of synaptic transmission was debated for almost a century. One attractive hypothesis, which nicely explained the speed of synaptic transmission, was that it was simply electrical current flowing from one neuron to the next. An alternative hypothesis about the nature of synaptic transmission, also dating back to the 1800s, was that chemical neurotransmitters transfer information from one neuron to another at the synapse.

Explain why resting membrane potential is essential to how neurons signal one another

The resting membrane potential (RMP) is the voltage difference between the outside and inside of the neuron at rest (i.e. when no action potentials are being fired). Changes in the RMP (i.e electrical signals) are the basis for how neurons communicate. In the image above the sensory neuron is at rest in step 1, then you step on a tack and that changes the voltage of the membrane triggering an action potential and that signal (change in membrane potential) is carried up your body to your brain so that you perceive the pain and yank your foot up! 5%5

LO: Explain why resting membrane potential is essential to how neurons signal one another

The resting membrane potential (RMP) is the voltage difference between the outside and inside of the neuron at rest (i.e. when no action potentials are being fired). Changes in the RMP (i.e electrical signals) are the basis for how neurons communicate. Neurons receive information across the synapse through chemicals (i.e. neuortransmitters). They take all of this information from thousands of synapses à integrate the information by changes in the membrane potential à and then either fire or don't fire (i.e. generation of an action potential)

LO: Describe how vesicles fuse with the membrane

The specific binding and fusion of membranes seem to depend on the SNARE family of proteins, which were first found in yeast cells. SNARE is an acronym too convoluted to define here, but the name perfectly defines the function of these proteins: SNAREs allow one membrane to snare another. Each SNARE peptide has a lipid-loving end that embeds itself within the membrane and a longer tail that projects into the cytosol. Vesicles have "v-SNAREs," and the outer membrane has "t-SNAREs" (for target membrane). The cytosolic ends of these two complementary types of SNAREs can bind very tightly to one another, allowing a vesicle to "dock" very close to a presynaptic membrane and nowhere else. (the next slide provides an image of this)

LO: Imagine experimental ways to reduce how many action potentials a given neuron can fire - propose a way to do this

There are lots of possibilities here and the grasshopper mouse & scorpion venom case give us one example in nature. You can block VG Na channels with venom. Here are some other ways to REDUCE the number of APs a neuron will fire... 1.You could also increase the opening of K+ channels à (potassium flows out, cell gets more negative) result in less APs 2.You could increase inhibitory input to the neuron (activate GABA receptors and increase the number of IPSPs) à this lowers the chance of depolarization to threshold and will result in less Aps 3.You could prolong the duration of Na channel inactivation à remember and AP can't occur while VG Na channels are inactivated so if they stay inactived for longer this will result in less APS

Detail the ways in which neurons are specialized for communication

They propagate current in one direction! From the presynaptic cell that releases the transmitter to the postsynaptic cell that contains receptors that recognize and bind the transmitter Despite this, the postsynaptic cells still have the power to regulate presyanptic cells (retrograde signaling) nitric oxide. Receptors at the presynaptic membrane at some syanpse contains receptors that may either inhibit or facilitate release of transmitter by biochemical mechanisim

LO: Identify factors that influence conduction velocity LO: Explain how the conduction velocity of a neuron varies with axonal diameter (draw a diagram to illustrate this)

Think how you often feel itch slower than pain Itch fiber is unmyelinated and small Pain fiber is myelinated and thickerà this leads to faster AP conduction

Summarize how the grasshopper mouse is resistant to scorpion venom

We will walk through the data collected by the scientists that discovered why the grasshopper mouse is resistant to scorpion venom. This is their first experiment to demonstrate the resistance of the grasshopper mouse to venom. Paw licking is a sign of pain, so when you inject with scorpion venom you expect a "normal" house mouse to feel that pain and lick their paw like crazy. We would suspect from the video we watched that the grasshopper mouse won't lick like crazy and is somehow resistant to the pain from the scorpion venom

LO: Discuss how diffuse modulatory systems are similar

We'll focus on the modulatory systems of the brain that use either norepinephrine (NE), serotonin (5-HT), dopamine (DA), or acetylcholine (ACh) as a neurotransmitter. Recall from Chapter 6 that all of these transmitters activate specific metabotropic (G-protein-coupled) receptors, and these receptors mediate most of their effects; for example, the brain has 10-100 times more metabotropic ACh receptors than ionotropic nicotinic ACh receptors. Because neuroscientists are still working hard to determine the exact functions of these systems in behavior, our explanations here will necessarily be general. It is clear, however, that the functions of the diffuse modulatory systems depend on how electrically active they are, individually and in combination, and on how much neurotransmitter is available for release (Box 15.2).

LO: Explain what it means if K+ ions are at equilibrium LO: Discuss why EK is relevant to the resting membrane potential (RMP)

Which ion is RMP closest to and why? At rest, neurons are selectively permeable to K+ because K+ channels are open. This contributes to RMP Why isn't the RMP -80mV exactly? → Because the membrane is also somewhat permeable to Na+ (a few sodium channels are open at rest) SO, if you memorize the equilibrium potential of the key ions in a neuron AND you know the RMP of the neuron (-65mV), you can ALWAYS predict which direction the ion will flow. Each ion will always move in the direction that moves the RMP closer and closer to equilibrium potential. Let's think about Na ions. The equilibrium potential of sodium is 62mV. REALLY positive compared to the -65mV RMP. So, when sodium channels open, they are going to flow into the cell as that will raise the voltage of the membrane (making it more positive) and positive until you reach 62mV. When the net flow of Na ions cease

LO: Describe the major neurotransmitters (ACh, glutamate, and GABA) in terms of anatomy, function, receptors and drugs targeting the systems

While glutamate is the major excitatory neurotransmitter in the nervous system, GABA is a major inhibitory neurotransmitter in the nervous sytem. The transmitter-gated channels of most inhibitory synapses are permeable to only one natural ion, Cl−. Opening of the chloride channel allows Cl− to cross the membrane in a direction that brings the membrane potential toward the chloride equilibrium potential, ECl, about -65 mV. Notice that if the resting membrane potential were already -65 mV, no IPSP would be visible after chloride channel activation because the value of the membrane potential would already equal ECl (i.e., the reversal potential for that synapse; see Box 5.4). If there is no visible IPSP, is the neuron really inhibited? The answer is yes.

LO: Describe the major neurotransmitters (DA, NE, 5-HT, opioid peptides) in terms of anatomy, function, receptors and drugs targeting the systems LO: Review what kind of receptors (LGIC, GPCR) are targeted by each neurotransmitter

•ALL NE receptors are GPCRs!!! •Human genome has 800 different GPCRs! •>70% of drugs target GPCRs