Electrical Neural Communications

What is the formula for Ohms law?

V=IR current times resistance = voltage

What are moving particles with a charge (ions)?

current

Where does movement stem from?

sodium ions

What causes sodium to slow down causing resistance?

intra and extracellular fluid

What is the term for negative resting potential?

hyperpolarized

What is the term for positive resting potential?

depolarized

How many sodium ions do human cells have inside them, and how many sodium ion cells surround them?

20, 600

What connects the semi-permeable membrane to ions outside the cell?

ion channels

When sodium flows into the cell the voltage

increases

Resistance in the channels means they are blocked by an _______ which means the signal is conducted more ______

antagonist, slowly

The resting membrane potential is the

difference in electrical charge inside and outside of the neuron

What are ions?

attoms that have lost or gained electrons

When a neuron is at rest sodium ions are more concentrated _________ of the neuron.

outside

What are negatively charged ions called?

anions

What is the resting energy of a neuron?

-70 mv

What is the resting membrane potential maintained by?

the sodium potassium pump and the semi-permeable membrane

What does the sodium potassium pump use to transport proteins?

ATP from mitochondria

How many sodium are pumped out of the cell and how many potassium are taken into the cell through the sodium potassium pump?

3 sodium out of the cell, take 2 potassium in.

Does sodium or potassium move more easily through ion channels?

potassium

Diffusion and electrostatic pressure prodcue

action potential

Define diffusion

moving from an area of high concentration to an area of low concentration

Define electrostatic pressure

opposites attract, charges repel each other

What are the two forces that act on ions once the channel is open?

chemical gradient and electrical gradient

Define the electrical gradient

electrical forces act on charged molecules, pulling opposite charges together and pushing some charges away from eachother.

What causes ions to be attracted to the inside of the cell?

electrical gradient

Define the chemical gradient

given time a high concentration of substance will diffuse to a lower concentration and settle evenly over space.

What is the action potential?

Short-lasting, temporary change in membrane potential which travels down the length of the axon. This then triggers the release of neurotransmitters at the axon terminal buttons of the synapse.

What is the characteristic shape of the action potential?

Rapid depolarization to prolonged hyperpolarization then repolarization to resting membrane potential.

Describe where the action potential starts and ends.

It starts at the axon hillock, then axon, then ends at the terminal buttons.

What needs to happen to trigger an action potential?

Inputs must be very depolarizing to bring the voltage more positive and reach the action potential threshold of about -55 mv.

What do presynaptic neurons do?

Release neurotransmitters onto dendrites which causes a small amount of ion movement.

What are small deviations in membrane voltage?

Post Synaptic Potentials

What is spatial summation?

Two small excitatory post synaptic potentials from two adjacent inputs, multiple signals add up to cause an action potential. These signals are separated by space.

What is temporal summation?

Multiple EPSPs from the same input occur close together in time.

What are graded potentials?

EPSPs and IPSPs

What do EPSPs do?

Add up to stimulate sodium channels to open up.

What is an example of a neurotransmitter that is excitatory?

Glutamate

What is an IPSP?

Inhibits neuron from firing an action potential.

What is an example of a neurotransmitter that is inhibitory?

GABA

Since glutamate is excitatory, what happens when it's released into the synapse?

Must bind to glutamate receptors, then this causes sodium channels to open, as positivity increases the neuron depolarizes causing an action potential.

What are ligand-gated ion channels?

Specialized membrane proteins that open a physical pore to let specific ions pass through.

EPSPs and IPSPs have graded nature meaning,

they don't have a single fixed size, it depends on how many neurotransmitters are released and how many receptors activated.

What is the size, travel length and speed of EPSPs and IPSPs?

they are typically small, about 0.5-2 mv, tracel 1-2 mm before dying, go about 0.1-1 meter per second.

How is the action potential propagated down an unmylenated neuron?

continuous conduction

How do neurons signal stimuli of different intensities?

by changing their firing frequency (rate law) and recruiting varying numbers of neurons (population coding)

Why does the action potential stop at the terminal button?

Reaches the physical end of the axon and does not reverse the other way.

What is a absolute refractory period?

voltage gated ion channels are inactivated

What is a post synaptic cell?

it has synapsed with another neuron

What happens to the size of graded potentials as they travel through the neuron?

they decrease

What is capacitance?

the physical ability to separate and store charge.

If something has low capacitance what does it mean?

It is leaky, like the neuron's membrane.

Are action potentials slow compared to graded potentials?

yes

What is neural summation (or integration)

graded potentials add up

Remember that inhibitions from synapses can cancel out

excitatory

When an axon is having max firing rate, how many action potentials can happen in a second?

1,000

How long are APs, what size, and where do they occur?

they are a constant fixed size, last 1 1/2 - 2 1/2 milliseconds long (but can also be affected by how long NTs are docked on a receptor), and happen from the axon hillock down to the terminal buttons.

When channels open why does sodium enter the cell?

Diffusion and electrostatic pressure

What leaves and enters the cell during an action potential?

sodium comes in, potassium leaves

As potassium continues to leave the cell, the cell

repolarizes

Why does the action potential only go one way and the stop?

the absolute refractory period drives it in once direction

How many neurons are there in the brain?

86 million

What neurotransmitters causes muscles to contract?

acetylcholine

What is saltatory conduction (myelnated neuron)?

the action potential travels underneath the myelin, appears to decrease each time it touches myelin then reaches full strength again when it touches nodes of ranvier.

What is continuous conduction? (unmylenated neuron)

AP travels straight down with no interruptions

Do myelinated or unmyelinated neurons have faster signals?

myelinated