Neuroscience of Communication: Chapter 3

Basics of Neural Signaling and Synaptic Function

electrical gradients are created by movement of charged particles. what are they? what are the dring forces that place ions in motion

This “movement” is accomplished through the development of driving forces that can place particles such as ions (electrically charged atoms) and other chemicals into motion.

the driving forces would be concentration gradients or CURRENTS

kinetic vs potential

kinetic - drive the motion of a substance from its high to low concentration region.

potential - “potential” or “capacity” or “ability” to place that substance into motion

mvmt of charged particles creates

electricty

movement within a neuron requires no metabolic energy

voltage is

magnitiude of potential energy

current is

the number of charged particles passing a given point in a given amount of time r

resistance refers to forces that

The theorem states that voltage is the product of current and resistance, written symbolically as V = I × R,

impede currents

unit is : ohm (Ω)

fluid environment of the neuron

The four principal ionic players are sodium (Na+), chloride (Cl−), potassium (K+), and calcium (Ca2+).

usually intracelluarly there is high amount of anions (inside cell is neg charged) and K+ ions

ion channels have structural features that

restrict the type of ion allowed to pass and controls the rate of ion passage

what are the passive and active features of a cell membrane ?

Because of both types of features what would you call this membrane ?

passive transport - osmosis & diffusion

vs

active transport - sodium potass pump

the membrane would be considered semipermeable

3 ways ion channels can “gate” ionic currents

1. ligand - chemical process allowing the passage ofneurotransmitters during synapse

2. voltage - gating occurs in the axon during the transmission of the signal (action potential)

3. mechanical- gating occurs with certain types of sensory receptors

why does a neuron need an ion pump

because an ion pump is an active mechanism to counteract the leakage of the cell membrane and ensure the electrical stability of the cell.

how do neuorns maintain separation of charges ?

impermeable nature of phospholipid bilayer

what creates membrane potential?

The positive and negative ions on each side of the cell membrane creates the membrane potential. The two sides of the membrane are said to be polarized.

resting membrane potential is the

baseline or resting condition of the neuron

-60 to -70mV

this is maintained by flow of K+ and Na+ (by the specific ion pump)

at rest the resting membrane potential can…

send messages. but that does not mean it is necessarily READY to send messages.

describe the importance of an action potential

neurons need to create an electrical signal that arrives at its destination without weakening.

an action potential is a rapid change in membrane potential at a specific location on the axon that is propagated down

action potentials are initiated in the

axon hillock

difference between Na+ and K+ channels

explain the drivng forces that causes sodium to rush into cells when Na+ channels are open

three Na+ ions are removed from the inside of the cell for every two K+ ions brought back into the cell.

this requires ATP

what are the 4 phases of an action potential

1. neuron is a rmp (resting membrane potential)

2. influx of Na+ results in depolarization, THEN Na+ gate closes

3. outward flow of K+ results in repolarization

4. hyperpolarization (absolute refractory period) restores to rmp

all or none principle

An action potential occurs when it is stimulated to its threshold. Once the threshold occurs, depolarization will occur to its full strength.

propagation of action potential along an axon differs depending on 2 things:

1. diameter of axon

2. distance the action potential needs to travel to

speed of conduction depends on two things :

1. diameter of axon

2. distance in front of action potential that the current can spread

the synpase is the

point of communication btwn neuronsthe g

the gap btwn presynaptic neuron and postsynaptic neuron is called the

synaptic cleft

2 types of synapses

1. chemical - presynaptic then cleft then postsynaptic terminal, transmission (depolariz.) reception phade

2. electrical - fast transmission but no flexibility or nuance

explain transmission phase

depolarization in the terminal bouton opens calcium channels resulting in an influx of calicium.

this causes the synaptic vesicles to mvoe and bind to the membrane, releasing neurotransmitters into the cleft.

explain the recption phase of a chemical gradiant

neurotransmitters move across the synpatic cleft and generate postsynaptic potentials in the postsynaptic membrane

positive ions move in resulting excitatory postsynaptic potential

neg ions move in or postiive ions move out, resulting in inhibiotry postsynaptic potential

ending chemical synpatic transmission options (3)

neurotransmitters must be removed or deactivated to prevent stray stimulation

1. diffusion

2. enxymatic degration

3. re-uptake

amino acid neurotransmitters

1. glutamate

2. gaba

3. glycine

amine neurotransmitters

• acetylcholine

• dopamine

• norepinephrine

• epinephrine

  • seotonin

how does a neuron reach a firing threshold

Depolarizing inputs in the form of EPSPs (“yea” votes) are related to driving a neuron toward the firing threshold,

what is spatial summation

Spatial summation occurs when two or more closely adjacent synapses are simultaneously activated, allowing for their individual postsynaptic potentials to combine to influence the overall membrane potential of the neuron.

temporal summation

firing a very rapid succession of APs to create several synaptic potentials at one synaptic location

neural integration is ..

and caused by ..

is the process where a postsynaptic neuron combines all incoming synaptic potentials (EPSPs and IPSPs) to generate an action potential of its own

caused by spatial summation

temporal summation

in what three ways can summation be complicated

1. typical postsynaptic potentials are very small (need 100s for summation to work)

2. the dissipation of electrical energy in fluid and as a function of distance (ex: sound gets softer the further u go)

3. excitatory versus inhibitory synapses are not uniformly distributed across a neuron. excitatory are too far!