BCS 240 Exam 2

Ohm's law

current= voltage * conductance (conductance = G =1/R)

Equilibrium

Wc=We ]solving eq potential (Eion) yields Nernst Equation

Nernst Equation

Eion=(2.3*RT/zF)log([out]/[in])

Reversal Potential

voltage at which suddenly current switches directions

EK+

-80mv

ENa+

+60mv

ECl-

-65mv

ECa2+

+120mv

Hydrated diameter

important factor limiting movement of ions through pores in membrane

Phospholipid bilayer (PLB)

Membranes are semipermeable: only somethings can flow through, ions flow through complex proteins (channels or pumps)

Ion channels

complex proteins composed of 4-6 subunits that span the PLB

Gated

transition from open to close (if there's conductance)

Selective

only let 1 or maybe a few things in (determined by chem properties of the channel and pore diameter)

Passive

ion flow doesn't directly expend energy

Leakage channels

open/close randomly, set resting potential

Voltage gate (VG)

open/close based on battery closed at rest, involved in AP propagation

Chemical channels

open/close by binding with a ligand/messenger

Mechanically gated/stretch channels

opened by membrane deformation

Diffusion

movement of substances down concentration gradient

Concentration gradient

established by a difference in ion concentration within a compartment or across a barrier/membrane

Electrical gradient

second force that makes ions move ] battery/voltage

Equilibrium potential

Wc=We (no net current)

Ion flux

When Vm=Eion, no net flux of ion through membrane

Capacitance

property of membrane that it stores electrical charge

Action Potential (AP)

Brief reversal of resting membrane potential: inside briefly becomes more pos than outside

AP Threshold

Threshold to open Nav channels is more positive/less negative than Vm

Rising phase

AP is terminated by Nav inactivation and net outward leakage current

Falling phase

Vm rapidly repolarizes to Vrest

Undershoot

outward currents activated by depolarization attributed to Kv channels

Refractory period

time during and after AP generation when membrane is unable or less able to generate another AP

Absolute refractory period

time during overshoot when all available Nav channels are either open or inactivated

Relative refractory period

follows absolute refractory period, associated with falling phase and undershoot

Stimulus strength and firing rate

Subthreshold inward currents are graded (proportional to stimulus strength)

Patch clamp technique

micropipette electrode forms a seal with a membrane, able to resolve minute currents carried by single ion channels

VG sodium channels

Nav closed at Vrest, opens when Vm>Nav threshold

VG K channels

Pore: selective for K ions, K is larger than Na but Na cannot flow through

AP propagation

current flows in through VG Na channels, depolarization spreads from site of AP initiation

Spike initiation zone

AP usually begins in the axon initial segment

Axon Hillock

Has the lowest threshold for action potential generation.

Electronic Flow

Describes the desired direction of action potential flow.

Cytoplasmic Conductance

Proportional to fiber diameter and limits flow along the membrane.

Membrane Conductance

Proportional to resting ion channel density and ion channel conductance, limits current flow across membrane.

Membrane Capacitance

Created by phospholipid bilayer which separates and stores charge, affects how fast membrane potential changes when ion channels open.

Length Constant (Lambda)

Distance over which a change in membrane potential falls to 37% of original magnitude.

Time Constant (r)

Time it takes membrane to reach 63% of new steady state potential in response to instantaneous change in membrane potential.

Conduction Velocity

Speed at which action potentials propagate down their axon.

Myelination

Restricts current flow across the membrane, increasing lambda and speeds membrane charging time.

Saltatory Conduction

Action potential propagates by jumping across nodes of Ranvier.

VG Channels in Myelinated Axons

Nav channels are restricted to nodes of Ranvier; AP cannot occur in internodal region.

Ephatic Communication

Occurs when two axons near each other cause one to fire due to intracellular current spread.

Nitric Oxide (NO)

A free-radical gaseous signaling molecule with a short half-life.

Electrical Synapses

Low resistance junctions that conduct electrical activity directly from one cell to another.

Gap Junction Structure

Composed of connexions which permit ions and other small polar molecules to pass from one cell to another.

Chemical Synapses

Involve presynaptic endings, synaptic vesicles, and receptors that mediate neurotransmitter release.

Synaptic Transmission

A chemical messenger or neurotransmitter is released by presynaptic terminal in response to depolarization.

EPSP

Net inward current that depolarizes and pushes toward threshold.

IPSP

Net outward current that hyperpolarizes and pushes away from threshold.

Shunting PSP

Synaptic response that prevents or reduces changes in membrane potential by clamping it near Eion.

Unitary PSP

Relatively constant amplitude PSP in response to a single PSP, releasing a fixed number of vesicles.

Calcium's Role in NT Release

Calcium binds to synaptotagmin proteins on vesicles which triggers fusion with the membrane.

Ionotropic Receptors

Associated with ligand-activated ion channels, allowing fast and short-acting responses.

Metabotropic Receptors

Associated with G proteins, leading to slower and longer-lasting effects.

Reuptake

Process where free neurotransmitters are taken back into the terminal to be repackaged or destroyed.

Enzymatic Degradation

Process where neurotransmitters are broken down in the synapse and then resynthesized.

Synaptic Mimicry

When an NT produces the same effect as in vivo during experimental application.

Neurotransmitter Types

Includes small neurotransmitters like acetylcholine, glutamate, and GABA, and large neuropeptides.

Coexistence of NTs

Many neurons contain two neurotransmitters: one small and one large, but never two of the same size.

Transmitter Release Mechanism

Involves exocytosis triggered by action potential depolarizing the presynaptic membrane.

Graded PSP

Amplitude of PSP is proportional to the strength of the stimulus.

Temporal Summation

Summation of PSPs over time at one synapse.

Spatial Summation

Summation of PSPs at different synapses at the same time.

Neurotransmitter Criteria

Must be synthesized and stored in presynaptic neuron, released by presynaptic axon terminal, and produce a postsynaptic effect.

GABA

Dominates in the cortex and works by allowing Cl- to flow in, causing hyperpolarization.

Glycine

Dominates in the spinal cord and works similarly to GABA.

Microiontophoresis

A precise but expensive method for applying neurotransmitters.

Pressure ejection

A less precise and cheaper method for applying neurotransmitters.

Neurotransmitter removal

Can occur through degradation, reuptake, or diffusion with glial help.

Acetylcholine (Ach)

Used in CNS and PNS, activating motor ganglion and parasympathetic end organs.

Glutamate

Primary excitatory neurotransmitter with a primary function from thalamus to cerebral cortex.

Dopamine

A catecholamine neurotransmitter involved in motor selection and reward, sourced from substantia nigra and VTA.

Norepinephrine (NE)

A catecholamine neurotransmitter that keeps you alert in the CNS and is used in sympathetic end organs in the PNS.

Epinephrine

A catecholamine neurotransmitter used in the PNS for the fight or flight response.

Serotonin

An indolamine neurotransmitter sourced from the raphe nucleus and involved in the emotional system.

Melatonin

An indolamine neurotransmitter that allows sleep to continue, sourced from the pineal gland.

Histamine

Involved in allergic reactions, sourced from the hypothalamus and targets the thalamus.

Neuropeptides

Made in the soma and released in large vesicles, involved in appetite control and pain.

G proteins

Composed of alpha, beta, and gamma subunits, involved in signaling pathways when activated.

Second messengers

Molecules like cAMP and calcium that are activated by G proteins to initiate cellular responses.

NT lifecycle

Includes synthesis, packaging, release, binding to receptors, and inactivation.

AchE enzyme

Degrades acetylcholine in the synaptic cleft.

GAD enzyme

Converts glutamate into GABA.

Dopamine synthesis

Derived from tyrosine and can be converted into norepinephrine and epinephrine.

Substance P

A pain signal that responds with inflammation through the PKC pathway.

AgRP

A neuropeptide in the hypothalamus that promotes hunger.

POMC/CART

Neuropeptides in the hypothalamus that promote satiety.

EC50

The concentration of a drug that produces 50% of its maximum response.

IC50

The concentration of an antagonist that produces 50% of its maximum inhibitory response.

Fast excitation

Associated with AMPA ionotropic receptors for glutamate.

Fast inhibition

Associated with GABAA ionotropic receptors for GABA.

Autoreceptors

Receptors located on the presynaptic neuron that respond to the neurotransmitter released by that neuron.