Resting potentials, Electrical Signals and Synapses

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What are the components in the typical anatomy of a neuron?: cell body
dendrites
axon
axon hillock
what occurs at the cell body? what does it contain? what does it do?: Input is recieved from other neurons here.

Cell body contains nucleus and organelles.

It synthesizes proteins and neurotransmitters.
What are dendrites? Why are they good?: processes designed to recieve input from other neurons.

they increase the surface area of the cell for recieving signals.
What does an Axon do?: an axon carries a signal away from a cell body to another neuron, muscle, or gland 1mm to 1 meter in length
Where is an Axon hillock located on a neuron? What's another name for it? What occurs here?: location: where the axon joins the cell body.

aka, initiating segment

it's the trigger zone where electrical signals called ACTION POTENTIALS generate
What is an axon terminal responsible for?: releasing neurotransmitters from the axon during action potential propogation from neuron to neuron.
what is myelin?: highly modified plasma membrane, wrapped around the axon 20 to 200 times by nearby support cells
2 types of myelinating cells?: oligodendrocytes = CNS

schwann's cells = PNS
spaces between myelin sheaths?: nodes of ranvier
What do the following neurons do? -Afferent -Efferent -Interneurons: Afferent - carry impulses from the tissues and organs INTO the CNS.

Efferent - carry impulses from CNS TO effectors: muscles, glands or neurons.

Interneurons - connect neurons within the CNS.
What is "excitable tissue"?: Nerves and muscle
How does excitable tissue transmit impulse?: by changes in membrane potential
how many kinds of changes in membrane potential are there, what are they?: 2: graded and action
5 kinds of Graded Potentials:: EPSP
ISPS
EPP
Generator Potential
Receptor potential
What is a Membrane Potential? How is it defined w/ re: to a cell?: seperation of charge across the cell membrane. The inside of a cell is negative compared to the outside.
Why is the membrane potential useful?: it can be used to do work on charged ions.
What is Potential? Units?: Voltage - a seperaton of charges, with the potential to do work. Measured in volts or mV
Waht is current: movement of charge
What is resistance? something with high R? something with low R?: hindrance to ion movement

-insulator - cell membranes
-conductor - salt solutions, ECF
waht is permeability: how easily a charge or something crosses a cell membrane.
what happens to the resistance of a cell membrane when you increase its permeability to an ion?: it becomes a better conductor.
How do you change the permeability of a cell?: by opening and closing channels.
whats the concentration and permeability in resting nerve cell of: Sodium Potassium Anions Chloride: Ion Extra Intra Rel. Perm
Na 150 15 1
K 5 150 50-75
Anions 0 65 None
Cl 125 10
what are the two factors that can cause ion movement across a membrane?: concentration gradients - ions will move down from high to low conc.

electrical potentials - opposite charges attract. Pos ion leaving high conc. increas charge where it goes and leaves a neg charge behind. so actually attracted BACK where started.
equilibrium potential: the membrane potential (difference in ions) where the concentration and electrical gradiens are balanced so the ion is at equilibrium, no flux in either direction across membrane.
How do you calculate the value of the membrane potntial that is the Equilibrium Potential?: By using the Nernst equation.
What is the Nernst Equation?: Equilibrium Potential
61 Conc outside
E = -- log (-----------)
z Conc inside
What is the real nernst equation?: RT Co
E = -- ln ---
zF Ci

R = ideal gas constant
T = absolute temp
z = valency of ion
F = faraday's constant
what do the constants in the nernst equation do?: allow for conversion of concentration to voltage
what are the units of the answer to the Nernst equation?: volts
how do you calculate the membrane potential for a membrane with more than one kind of ion channel?: by using the GOLDMAN EQUATION
What is the goldmann equation? what is it used for?: RT PK[K]o + PNa[Na+]o + PCl[Cl]o
Em= --ln ----------------------------
F PK[K}]i + PNa[Na+]i + PCl[Cl]i
What ion has the greatest permeability to a cell, and how does it affect the membrane equilibrium potential?: Potassium. Makes the memb. potential negative because its E=-90 mV.
What are the 2 ways you can change a cell's resting potential?: -Change its ion permeability

-Change its ion concentration gradient.
What is the Na+ Pump?: sodium potassium atpase
for every 3 Na+ it pumps out, 2 K+ enter the cell against their concentration gradient.
What two things would make Potassium move across the cell membrane?: -concentration difference
-electrical difference - membrane potential.
so what determines which WAY potassium will move?: electrochemical gradient - taking both factors into account. Calculating equil potential tells at what value potassium WON'T move, then making the cell more or less negative will cause a flux.
How is a high intracellular K and high extracellular Na concentration established?: via Na/K ATPase
How does Na/K Atpase work?: by hydrolyzing ATP to phosphorylate its intracellular side, changing conformation to allow binding of Na and K.
For every 3 Na out, 2 K in.
how many more times as many leaky K channels are there than Na?: 50-75x more.
What are equilibrium potentials for: -Potassium -Sodium -Resting cell: K = about -90 mV
Na = about +60 mV
Cell = -70 mV
WHY is the resting cell membrane so negative??: because of leak potassium channels - a lot of positive charge leaks out in the form of K ions, leaving behind negative charge.
Why isn't the resting potential -90, if K is the most influential ion on the membrane potential?: because some sodium leaks in, just a lot less. adds positive charge back to the memb. potential to make it less negative than -90.
Since K/Na ions are always fluxing down their concentrations, why don't they equilibrate?: because Na/K atpase keeps their concentrations constant.
What are the two roles of Na K ATPase?: -Maintaining ion conc. gradients,

-Establishing ion conc. gradients.
Actually, in steady state, which ion has greater DIFFUSION, Na or K? Why?: Sodium. because it is much farther from its Epotential; -90 attracts +60.

Because Na/K ATPase pumps 3 Na out, 3 then diffuse back in. same goes for K.
what is depolarization?: a reduction in seperation of charge - membrane potential rises to 0 mV.
What is repolarization?: an increase in seperation of charge. membrane potent. decreases back toward negative resting potential
what is hyperpolarization?: continued repolarization after returning to resting membrane potential - K+ keeps on leaking out.
what is an excitatory synapse?: a synapse where a brief graded potential in the postsynaptic membrane brings the membrane potential closer to threshold.
what is an inhibitory synapse?: a synapse where the brief graded potential in the postsynaptic neuron drives its membrane potential farther from threshold, or stabilizes it at its present level.
what are Convergence and Divergence?: convergence of many synapses from different pre-synpt neurons on one post.

divergent branches of one synapse to many post-synaptic neurons.
what are synaptic vesicles?: pre-synaptic neuron vesicles that contain neurotransmitter
what is the role of the synaptic cleft?: it prevents DIRECT propagation of an action potential from neuron to neuron.
what are the 2 types of chemical synapses?: Excitatory - EPSPs
Inhibitory - IPSPs
what are chemical synapses?: synapses at which a chemical neurotransmitter is released.
What's the difference between an EPSP and ISPS?: the difference is in what NT is released, and by what mechanism it causes signal transduction and the type of channels that are opened as a result
What's the postsynaptic response to NT at: -Excitatory synapse? -Inhibitory synapse?: Excit: depolarization

Inhib: hyperpolarization
What is an EPSP?: Excitatory PostSynaptic Potential
-A graded potential
-Net flux of Na+ into the postsynaptic membrane and small flux of K+ out because the electrical gradient affects K movement more than its conc. gradient and the two are opposed.
what channels open during an EPSP?: all channels to small positively charged ions open, nonspecifically
what category of potential is an EPSP or IPSP? what is the purpose?: GRADED. spreads decrementally away.

purpose: to APPROACH threshold
what postsynaptic channels open during an IPSP? why?: chloride or potassium -- not sodium.

for cells that have Cl ATPase, Chloride's equil. potential is more negative than resting - -80 mV. opening channels makes it rush in and hyperpolarize the cell.

K+ rushes out, causes hyper-polarization as well.
how much is an EPSP worth?: about 0.5 mV
how much mVolts does it take to depolarize a neuronal membrane to threshold?: 15 mV
so does one synaptic event cause cell to reach threshold?: no
what is temporal summation?: when two or more inputs from successive firing of the same presynaptic neuron occur at different TIMES and are added together
what is spatial summation?: when two inputs to different SPACES on the postsynaptic neuron occur simultaneously
what does summing EPSPs and IPSPs do?: cancels each other out, with no net change of the cell membrane potential
how can EPSPs generate an action potential?: by having a lot of them input together, so that current from their summed membrane potential change is large enough to reach the initial segment.
why is the Initial Segment the place where an action potential is generated and propagated from down an axon?: because it has a lot of voltage gated Na channels. that means its THRESHOLD is much lower than other parts of the membrane. Thus, EPSPs will sum and cause a change in membrane potential, which the initial segment is very response to.
what are 4 examples of Graded Potentials?: EPSP
IPSP
EPP (endplate potential)
receptor potential in sensory neurons
how are Baroreceptors examples of graded potentials?: when B.P. increases, it causes the nerves to stretch and stimulte an EPSP. When the nerve cell depolarizes, it causes the nerve cell to stretch more, and depolarize more.
In summary, what are the 5 characteristics of Graded Potentials?: 1. Vary in Strength
2. Cause local Current Flow along the cell body membrane of the postsynaptic neuron.
3. Charge is conducted decrementally.
4. Membrane potential change can be Positive (depol) or Negative (hyperpol)
5. They can summate Temporally or Spatially
if you want to EXCITE a postsynapt. neuron, what channels would you open?: Sodium or Calcium - both are higher conc. outside and positively charged.
If you wanted to cause an INHIBITORY synapse on the postsynaptic neuron, what channels would you open?: Cl- or K+

Chlorine would go back into the cell, and Potassium would go out and leave neg charge behind --> hyperpolarization
What is an Action Potential?: a rapid, reversible change in membrane potential that passes down the length of the cell membrane and doesn't decay.
what is threshold potential?: the potential at which an action potential is generated when summed graded potentials reach this level.
What type of ion channels are opened when threshold is reached?: voltage-gated.
Compared to the Additive/degradative nature of graded potentials, what kind of response is seen in Action Potentials?: ALL OR NOTHING. If you reach threshold, you reach ACTION. If not, no action.
What are the Ionic Events of the Action Potential?: 1. At start, Permeability of Na increases from relatively IMPERMEABLE to 600x more permeable. Causes Depolariz, Overshoot.
2. At Peak, Permeability of K increases to 4x more, causes repolar/hyperpolariz.
3. Absolute and Relative Refractory periods.
What is the ABSOLUTE refractory period? Why does it occur?: That period in which you CANNOT generate an action potential in a postsynaptic neuron, no matter how hard you try, how strong the stimulus is.

The Na+ channels are still open, or they are inactivated.
What is a Relative refractory period? Why does it occur?: That period in which there is reduced excitability of the postsynaptic neuron - its difficult to stimulate it and requires a stronger stimulus.

Occurs because though Na+ channels are not closed, K+ channels are still open and more Na+ needs to rush in to cause depolarization.
What is the -Resting Membrane potential -Threshold Membrane Potential of a cell?: -Resting = -60 mV

-Threshold = -45 mV

(remember, resting plus 15)
whats the definition of a synapse?: an anatomically specialized site of interaction between nerve cells where on influences the electrical behavior of another.
2 ways a NT can affect excitation or inhibition of a postsynaptic cell:: -directly influence ion channels - neurotransmitters

-change metabolism with G proteins and 2nd messenger systems - neuromodulators
What is a Classical NT? How many can be released at one synapse?: a rapid, short-acting, small molecule.

only one is released
What is a nonclassical NT? How many are released at a synapse?: Neuropeptides - slow, long-acting, diffusable neuroMODULATORS.

multiple can be released, often along with a classical NT
what does ionotropic mean? what does metabotropic mean?: iono: that an NT acts directly on an ion channel.

metabo: that an NT acts indirectly on metabolism, via Gprotein/2nd messengers.
Glutamate: -what type of NT? -How many receptors? -Main role -modality of alteration?: Type: Amino Acid.
Has four receptors.
Main excitatory NT in the brain.
Ionotropic OR Metabotropic
Example of a Glutamate receptor:: NMDA - n methyl d aspartate.
what channels are altered by the main excitatory NT in the brain (what is it?): Glutamate.
Calcium channels to cause synaptic vesicle release.
What is the main inhibitory NT in the brain?: GABA - gamma amino butyric acid
What type of receptors are: GABAa GABAb: a = an ionotro NT that opens Cl- channels.

b = metabotro NT receptor that uses a Gprotein.
What types of ion channels are inhibited by -GABAa -GABAb: a = Cl- channels are opened
b = K+ channels are opened

both cause hyperpolarization
What is the main inhibitory NT in the spinal cord: Glycine
What are the FIVE things Monoamines alter?: -Mood
-Motivation
-Attention
-BP regulation
-Consciousness
what is a broad category of monoamines, what are three examples?: the Catecholamines
-Dopamine
-Norepinephrine
-Seratonin
Where do they act? -Norepinephrine -Dopamine -Seratonin: Norepine: SNS and Brain
Dopamine: Motor Control, Reward Pathways
Seratoni: Brain
how many types of Norepi receptors? what is its modality of alteration?: 4 types of receptors, and subtypes exist.

Metabotropic - alters metabolism via G protein...
What is Dopamine involved in? What if you have too much? What if you don't have enough?: Motor control

Too much causes Schizophrenia.
Not enough causes Parkinson's.

Treating Schizo with anti-DA drugs causes Parkinson's diseases symptoms.
What does Cocaine do?: Inhibits Dopamine and Norepinephrine reuptake in the brain. Their effects last longer and causes schizophrenia
how many receptors are there for Seratonin? Where are they?: takes the cake! 16.

in the brain
What is the action/affect of Seratonin?: inhibitory or excitatory to alter mood.
what are 3 drugs that inhibit seratonin reuptake?: -Zoloft
-Paxil
-Prozac

Alter mood.
What are the 2 types of receptors for Acetylcholine?: Muscarinic
Nicotinic
What is the modality, and effect site of -Nicotinic -Muscarinic? What NT are they receptors for?: Nico = Ionotropic - directly opens channels (Na) at NeuroMuscular junctions.

Musca = Metabotropic - acts via Gprotein in the Autonomic Nervous System.
what are the 3 amino acid NT?: glutamate
GABA
Glycine
what are the 3 monoamine NT?: -dopamine
-norepinephrine
-seratonin

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