Cellular Neuroscience Cheat Sheet PDF

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Cellular Neuroscience...

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Lecture 1 Central Dogma  DNA → RNA → Protein  DNA transcribed into mRNA in nucleus → mRNA exits nucleus via nuclear pores with cap leading + poly-A tail trailing  Ribosomal subunits outside of nucleus assemble into ribosome  mRNA runs through ribosome one codon at a time, connecting to its matching tRNA in the A section, adding to the growing polypeptide chain at the P section, and disconnecting from the tRNA at the E section. Mitosis  G0 → Cell cycle arrest  G1 → Growth and typical metabolic processes  S → DNA replication  G2 → Final growth  M → Mitosis Standard DNA Base-Pairing (Usual)  Thymine (keto) binds to Adenine (amino) via 2 Hydrogen bonding  Guanine (keto) binds to Cytosine (amino) via 3 Hydrogen bonding o Purines (double ring): A, G o Pyrimidines (single ring): C, T Anomalous DNA Base-pairing (mutation)  Thymine undergoes tautomerization into enol form (looks like C) and binds to Guanine (keto).  Cytosine undergoes a configuration change into imino form (looks like T) and binds to Adenine (amino). All living things are made of cells. In the past, mitochondria wanted to kill ancestor by secreting oxygen. Reproduction  Humans are diploids (2N).  Egg + Sperm are both Haploid (1N).  Egg: 20 cycles of mitosis throughout life, 15-40 years of epigenetic impact/mutations.  Sperm: 15-80 years of mitosis, 4x more mutations than eggs.  Fertilized eggs have 100-200 new mutations and are diploid (2N). Now a totipotent cell. Cell Development  future embryo (current cell mass) hooks in the wall of the uterus via the cytotrophoblast and syncytiotrophoblast, provided nutrition via the endometrial stoma.  Adults humans have 3x10^13 cells. Nervous System  Central Nervous System (CNS): Brain (cortex, hippocampus, etc.), spinal cord (five segments).  Peripheral Nervous System (PNS): o Somatic Nervous System (voluntary)  Motor: spinal cord → skeletal muscles  Sensory: Sensory receptors → spinal cord

o Autonomic Nervous System (involuntary)  Motor and sensory neuron to internal organs  Sympathetic, parasympathetic, enteric Neuron Doctrine  Neuron communicate with each other through synapse  Neuron 1 receives neurotransmitters from other neuron → Neuron 1 integrates the signals → Neuron 1 releases neurotransmitter onto other neurons Phospholipid Bilayers  Hydrophilic heads and hydrophobic tails made up of triacyl glyceride.  Carbohydrates makes sure proteins are assemble in correct way, deliver to cell surface. Lecture 2  Primary active transport = use ATP = Na+ and K+  Secondary active transport = use stored energy = Ca++ Cations (positive) → Cathode (negative) Anion (negative) → Anode (positive)

Nernst Equation = difference (gradient) across the membrane  = electrochemical potential, measured in J/mol x = electrochemical potential difference across the membrane for ion X R = Ideal gas constant T = absolute temperature ln = natural logarithm [X]i/[X] o = concentration difference across the membrane for ion “X” C = chemical potential difference across the membrane for ion “X” Z = charge on ion: Na +=+1, K+ = +1, Cl- = -1, Ca2+ = +2 F = Faraday’s constant Vm = electrical difference across the membrane, measured in V (or mV) E = electrical potential difference across the membrane for ion ‘X” Passive Transport  Movement of molecules across cell membrane with direction/driving force of electrochemical gradient Active Transport  Requires ATP.  Movement of molecules across the cell membrane against established electrochemical driving force.  Primary active transport couples the movement of molecules with the hydrolysis of ATP; Na+/K+ ATPase Ion Pump - 2 K+ inside and 3 Na+ outside against the gradient General Molecular Concentrations Regarding RMP  Na+ concentration high outside the cell; low inside  K+ concentration low outside the cell; high inside  Cl- concentration high outside the cell; low inside  Ca++ for signaling but high outside the cell; low inside

Driving Forces Regarding RMP Ions  Na+: Chemical potential drives inside the cell, same with electric potential  difference  K+: Chemical potential drives outside the cell, against the electric potential difference; largest contributor to RMP  Cl-: Chemical potential drives inside the cell, against the electric potential difference  Glucose: chemical potential drives inside the cell, no charge so no electric potential difference. Nernst Equilibrium Potential (E x)  When the electrochemical potential of ion X. T= 310K (in human) Zx = different number for different ion

There is no net movement of ion X At this condition, the membrane potential Vm is the Nernst Equilibrium Potential (Ex) of ion X.

Extracellular Concentration of K+ and its Impact on Excitable Cells  The normal range for [K+]o is: 3.6 - 5.0 mM and is controlled largely by kidneys. Normal: [K+]o = 4 mM, EK = -91 mV Hyperkalemia: [K+]o = 7 mM, E K = -80 mV Hypokalemia: [K+] o = 2 mM, E K = -109 mV

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Kidney failure causes hyperkalemia, which depolarizes the membrane and makes it easier for heart cells to initiate action potential. This causes cardiac arrhythmias and even cardiac arrest. • Lethal Injection: rapid infusion of high concentration KCl. • Diurectics may cause hypokalemia, which hyperpolarizes the membrane and makes it more difficult for heart cells to initiate action potential. This also causes cardiac arrhythmias and cardiac arrest. Resting Membrane Potential; the 𝑉m at which net current = 0  RMP's developed across cell membrane measured from inside of cell compared to outside.  All cells have RMPs 1. Neurons = -70mv 2. Skeletal muscle cells = -90mv 3. RBC = -10mv  RMP is depended on: 1. Concentration of ions inside and outside of cells 2. Relative permeability of cell membrane to the different ions 3. RMP is primarily determined by K+ because membrane is most permeable to it  Only very small number of ions need to cross a cell membrane to develop RMP Chord Conductance Equation  RMP is the weighted sum of 𝐸Na+ , 𝐸K+ , 𝐸Cl- based on the isolated contributions of conductance.

Fatty membrane is a great electrical conductor; hence the ability to hold charge. Most cells at rest, membrane has the highest conductance of K+; share of Gk in ΣG is the greatest  At rest, Vm is cloest to EK+ and is largely determined by K+ channels.  Depolarization corresponds to an increase in 𝑉m towards the 0 mark and 𝐸Na.  Repolarization corresponds to a decrease in 𝑉m up to the established RMP.  Hyperpolarization corresponds to a decrease in 𝑉 past the RMP, approaching E  RMP does not equate to the low bound of 𝐸& because at -90mV there is no 𝐾+flow in/out of the cell. ATP Dependent 𝑁𝑎2/ 𝐾2 Pump  

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Na+/K+ by pumping 3 Na+ for every 2K+ Active pump requires ATP.

Lecture 3/4 1. Voltage-gated channels: require a change in membrane potential for ion channel for ion channel to open/close (RMP & AP) Ligand-gated channels: requires a neurotransmitter to bind to receptor on the channel 2. before channel opens (EPP, ESEP, IPSP) Na+ Channel: Voltage-gated  Pseudotetramer (4 domains are linked together).  4 domains (6 transmembrane α regions) and 2 β transmembrane regions (regulate channel gating and surface presentation of protein.  Hydration radius distinguishable property between both +1 ions  Between domain 1 and 2 there are site cAMP-dependent protein phosphorylation.  Na+ can only go from outside to inside. K+ Channel: Voltage-gated  Tetramer (4 α subunits are not connected)  4 α subunits (monomers) with 6 transmembrane α regions) and 4 β subunits exist inside the cell membrane (help provide selectivity and regulation to the channel)  Pore regions allow only K+ to go from inside to outside  4th α region is where voltages sensors (positive) are (Lys and Arg rich)  1-4 α regions are voltage sensing and 5-6 are pore regions Generation of Action Potential (AP) 1. AP only occur in excitable cells (neurons and muscle cells) need Vm to reach or exceed threshold of cell membrane. 2. Membrane permeability/conductance to Na+ and K+ ions changes in response to stimulus via opening/closing of the VGCs to generate AP. 3. At rest, axon membrane is almost impermeable to Na+ (closed Na+ channel) and slightly permeable to K+ (partially open K+ channel) 4. RMP of -70mV is closer to EK than ENa

A depolarizing stimulus is applied to the membrane to produce a sub-threshold depolarization.  This stimulus produces a sub-threshold depolarization that is “Conducted with decrement”  Usually 15-20mV more positive than RMP  Sub-threshold depolarization is graded, non-regenerative potentials that decay in amplitude over time and distance.  Graded potential = increase in stimulus strength produce s an increase in amplitude of the depolarization. AP is generated once stimulus is strong enough to produce a supra=threshold depolarization. “All or none” response. Amplitude provides NO information on stimulus strength. Inject negative charge = Vm goes down

Inject positive charge = Vm goes up

If not enough to reach threshold, it will decay. Positive Feedback Loop Threshold = Na+ activation  When threshold is reach → feedback develops  Na+ activation happens when gNa increase and this lead to massive increase in depolarization = threshold is reach and Na+ rushes into cell  When membrane potential reverses and reach 50mV → Na+ inactivation (concentration of Na+ decrease to almost 0  Between domain 3 and 4 is the inactivation loop that close when membrane potential reaches 50mV (Na+ inactivation)  Increase Vm = more Na+ channel open = more Na+ entry Driving Forces for Na+ and K+ at Peak (50mV) of Action Potential  ΔE and ΔC for Na+ become opposite of each other  ΔE and ΔC for K+ both drive K+ out of cell  Membrane polarity is revered at the peak Na+ activation produce rapid outstroke (depolarization) of the AP and Na+ inactivation starts the rapid downstroke (repolarization) of AP gK+ help complete the rapid repolarization. STEPS FOR ACTION POTENTIAL 1. Depolarization of axon membrane to or above threshold potential; usually 15-20mV of RMP. 2. There is specific time sequence in opening ion channels 3. First: Na+ channels open for < 1 msec allowing Na+ to rapidly enter the axon down both its chemical and electrical gradients producing a reversal of the membrane polarity to + inside (Na+ activation and it results in a positive feedback loop). 4. Second: Na+ inactivation occurs before the E Na is reached preventing the further influx of Na+. 5. Third: K+ channels open allowing K+ to rapidly leave the axon down both its chemical and electrical gradients resulting in a repolarization followed by a after hyperpolarization. 6. The whole action potential lasts about 3-4 msec depending on the type of cell studied.

ATP dependent Na+, K+ pump in AXON (ΔC never change) 1. Na+, K+-ATPase maintains the ion concentrations by pumping 3 Na+ out for every 2K+ into the cell. 2. It is electrogenic and contributes about 5 mV to the RMP. 3. It is an active pump that requires ATP to generate energy. Refractory Periods 1. Absolute Refractory Periods:  Last about 1 msec  No AP can be produced no matter how strong stimulus is.  Parallel time course for Na+ activation and inactivation. 2. Relative Refractory Period:  Parallels the time course for changes in gK+  Last about 3-4 msec in axon  A second AP can be produced if the stimulus strength is stronger than normal 3. The refractory period limits the maximum frequency of AP that can be generated in a neuron. If the RF period = 4 msec then the maximum frequency of AP is 250Hz. Na+ Channel Blockers  Local anesthetics: synthetic analog derive from cocaine, that lack the addictive properties of cocaine (addictive part is blocked by dopamine). o They block Na+ channel from outside of membrane and prevent Na+ entry during depolarization above threshold. Thus, they block the generation of AP’s in sensory neurons that send pain signals to the brain. However, they can block the generation of AP’s in all neurons (both sensory and motor).  Skin biopsies + superficial skin surgery (Lidocaine + Tetracaine)  Dental (Novocaine, Procaine)  Poisons o Tetrodotoxin (TTX): Japanese puffer fish that is eaten raw or cooked. o Saxitoxin (STX): marine bacteria (dinoflagellate = red tide) that are eaten by shellfish. The toxin is resistant to cooking so you can be become ill if you eat contaminated shellfish.  They block Na+ channels from outside and prevent the generation of AP’s in neurons and skeletal muscle cells. The Na+ channels in the heart have a one amino acid sequence change in the pore region that prevents these toxins from blocking AP’s in this organ.  Symptoms: Tingling of the lips and tongue, nausea, vomiting, muscle cramps, muscle weakness and paralysis.  Treatment: Gastric lavage and emetics if detected early enough and mechanical ventilation until body metabolizes the toxin. Propagation of AP Down an Axon  AP initiates at axon hillock (initial region of axon of neuron that connects to neural soma) o Axon hillock contains largest segment of neurol excitability + is why AP selectivity  Excitability across neuron

o Dendritic + neurosomantic threshold are very high due to lower/absence of expression of Na+ channel o When the threshold of a section of neuronal cell exceeds the synaptic potential, AP's will not fire - this is the case with Dendrites and the soma but quickly changes at the Axon Hillock o Threshold in neuron for AP quickly decrease in Axon Hillock which allow constant unchanged synaptic potential to be able to meet threshold activating AP  Na+ channel express density dictates excitability across neuron o Axon hillock + node of Ranvier contains high density of Na+ channels o Myelin sheath have same density of Na+ channels as dendrites and the neurosoma do: Practically none due to decreased expression by the cell in these regions. Conductions of AP  Regions of membrane with high density of Na+ channels + conduct action potential (axon hillock + node of Ranvier) depolarize during AP process o Negative charged regions do not conduct AP o Unmyelinated axons depolarize for short distance o Local current flow to depolarize adjacent area of membrane + allow conduction of depolarization down axon  Passive/Electrotonic conduction carried with decrement o Electrical stimulus with constant current applied to axon, membrane increase by 4.5mV at 0mm o Vm decrease with distance Length Constant (λ)  Also called space constant as passive conduction is two dimensional on membrane  Decays 1\e pr 37% of its original Determination of Axonal Length Constant 1. Radius of axon: larger the axon, longer the LC 2. Specific membrane resistance: myelination increase LC 3. Unmyelinated axons: AP regenerate small section, it takes time so CV is slow. It is inefficient + use lots of energy 4. In larger unmyelinated axon: CV higher due to longer length constant + AP regenerated fewer times Conduction Velocity      

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Schwann Cells in peripheral neurons Oligodendrocytes in central nervous system neurons CV in unmyelinated correlate to axon diameter CV in myelinated increase as linear function of axon diameter range 15-130m/sec 1-300 myelin → increase Rm → increase LC → AP jumps between one node to next (Saltatory Conduction) CV for large myelinated axons (> 10mm) can reach 130 m/sec. Only a few neurons including alpha motor neurons to skeletal muscles and 1a muscle spindle sensory neurons attain this speed of conduction. From the cerebral cortex to the muscles that move your toes is about 15 msec for myelinated fibers. It would take 2 seconds if you had to rely on unmyelinated axons

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Myelinated fibers are more efficient than unmyelinated fibers because only small sections of the axon undergo AP’s. Fewer ions cross the membrane in unmyelinated that produce more AP for same length. Na+, K+-ATPase has to pump much fewer ions across the membrane in myelinated fibers and uses less energy.

Multiple Sclerosis 1. Slowly progressive CNS disease characterized by disseminated white patches of demylelination in the brain and spinal cord. 2. Both sensory and motor deficits with exacerbations and remissions. 3. Signs and symptoms are caused by interference with AP production and propagation in myelinated neurons. (LC, saltatory conduction) 4. Both genetic and environmental (slow or latent virus) factors may influence susceptibility to this disease. 5. Females are affected more often than males. 6. Onset is between 20-40 years of age. 7. More common in temperate climates (1:2,000) than in the tropics (1:10,000). About 500 individuals have this disease in WNY. 8. Where you spend the first 15 years of life seems to be a factor. Relocating after age 15 does not alter risk. Frequency of AP 1. Amplitude of the APs in a train is the same and does not provide any information about the strength of the stimulus. (All-or -none response) 2. AP frequency provides information on the strength of the stimulus. 3. As the strength of the stimulus applied to the axon increases, it produces a greater depolarization above threshold and the frequency of AP’s increases. 4. AP frequency can range from 0-400 AP/sec (0-400 Hz). 5. The refractory period limits the maximum frequency of AP’s in a neuron. 6. If the total refractory period (absolute + relative) is 4 msec, then the maximum frequency of AP’s in that neuron is 250 AP/sec (1000 msec/4 msec = 250 AP/sec) 7. Most large, myelinated neurons discharge at a maximum frequency of about 100 AP/sec Lecture 5 Neuromuscular Junction: Special Synapse between Motor and Skeletal Neuron  Afferent motor neurons (located in grey matter of spinal cord) → extend a synapse onto skeletal muscle cell.  Inner spinal cord: contains white matter filled with Schwann Cells to form protective and conductive outer layer to spinal cord.  NMJ is the junction between axon terminal of α motor neuron and a skeletal muscle cell 1. Function: transmit information from neuron to the muscle cell by releasing Ach (excitatory neurotransmitter) 2. Ach produce EPP in skeletal muscle cells → contraction  Synaptic vesicles in active zone are aligned with Ach receptors on end plate to maximize response.

Nicotinic Type Acetylcholine Receptor: ligand-gated channel  Alpha subunits of Ach receptors compose of 4 transmembrane regions (M1, M2, M3, M4)  ACHR is a Ach-gated non-selective cationic channel  Need 2 Ach to bind to the receptor (α γ and α δ ) in order for the channel to open → K+, Na+, Ca++ is let through but not Clo Very little Ca++ go through, mostly K+ and Na+ o When it is open, Vm will try to bring on 0mV → depolarize end plate  Curare prevents Ach from binding to Ach receptors on postsynaptic membrane  In a healthy person, EPP is always a supra-threshold potential that produce an AP in the skeletal muscle cell (all or none) o EPP above threshold always elicits AP o Ca++ entry cause muscles to contract Properties of End-Plate Potential a. Depolarization produced by a non-specific increase in gNa+ and gK+ in the AchR in the end plate (EP) region. b. Graded potential: (amplitude (mv) depends on the amount of Ach released and the number of AchR activated ; NOT an all-or -none potential like the AP)

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Propagated outside the EP region by local current flow (amplitude of EPP decreases as it moves away from the EP region) d. Very large (40 mv) synaptic potential that is always suprathreshold in a healthy person. e. 1  MNAP → 1 EPP → 1AP in skeletal muscle cell Sequence of Events at NMJ (How does AP in α-MN lead to muscle contraction?) 1. ONLY 1 NMJ for each skeletal muscle cell (near center of cell) 2. Neurotransmitter vesicles are made of cell body and transport to axon terminal via axon 3. In Axon terminal, choline- acetyltransferase (ChAT) catalyzes the production of acetylcholine (Ach) from choline and acetyl-CoA. 4. Ach is actively transported into vesicles. 5. AP in αMN depolarize axon terminal + open Calcium Channel (voltage-gated) 6. Entry of Ca++ into axon terminal trigger fusion of Ach vesicles with presynaptic membrane around dense bars in active region. 7. Ach is released and diffuse across synaptic cleft to activate Ach recep...