Electrical and synaptic signaling in neurons

dendrite function

receive signals from other neurons

axon function

transmits signals to other cells

synapse function

connection between two neurons

neuron function is based on the movement of _____

ions across the cell membrane

_____ use ATP to move ions against their concentration gradients

ion pumps

____ move ions along their concentration gradients

ion channels

the effect of ion channels of ion concentration depends on what?

the relative number of ion channels

membrane potential

the difference in electrical charge across the plasma membrane of every cell

resting potential

the membrane potential of a neuron not sending signals

changes in membrane potential act as ______

signals, transmitting and processing information

in a mammalian neuron at resting potential, where is the concentration of K+ highest?

inside the cell

in a mammalian neuron at resting potential, where is the concentration of Na+ highest?

outside of the cell

How are Na+ and K+ gradients maintained across the plasma membrane?

by sodium-potassium pumps which use ATP

What do the concentration gradients of Na and K at resting potential represent?

chemical potential energy

Voltage gated ion channels function

respond to changes in the voltage across a membrane, responsible for action potential

Ligand gated ion channels

open when a particular molecule binds the channel

action potentials

the signals conducted by axons, caused by a massive change in membrane voltage

Why do changes in membrane potential occur in neurons?

due to gated ion channels that open or close in response to stimuli

hyperpolarization

an increase in the magnitude of the membrane potential (inside of the cell becomes more negative)

What happens when gated K+ channels open?

K+ diffuses out, making the inside of the cell more negative (hyperpolarization)

depolarization

inside of the cell becomes less negative, decrease in membrane potential

What happens when gated Na+ channels are opened?

Na+ diffuses into the cell, causing depolarization

Graded potentials

changes in polarization where the magnitude of the change varies with the strength of the stimulus

How are graded potentials related to nerve signaling?

they themselves are not nerve signals but they have an effect on the generation of nerve signals

Action potentials have a ____ magnitude, are _____ and transmit signals over ____ distances.

constant; all or none; long

describe voltage gated Na+ and K+ channels are resting potential

most are closed

What is the first step of generating an action potential?

Voltage gated Na+ channels open and Na+ flows into the cell

describe the rising phase of axon potential generation

after Na+ channels open, the threshold is crossed and the membrane potential increases

describe the falling phase of the action potential

voltage gated Na+ channels become inactivated and K+ channels open, causing K+ to flow out of the cell

list the five stages of generating an action potential

1. resting state

2. depolarization

3. rising phase of AP

4. falling phase of AP

5. undershoot

describe the undershoot of an action potential

membrane permeability to K+ is higher at first than at rest, then voltage gated K+ channels close and resting potential is restored

where are action potentials usually generated?

at the axon hillock

Directionality of action potentials

one direction; towards the synaptic terminals

How are action potentials generated at an axon hillock?

an electrical current depolarizes the neighboring region of the axon membrane

What prevents action potentials from traveling backwards?

inactivated Na+ channels behind the zone of depolarization

Refractory period after an action potential

a second action potential cannot be initiated

What causes the refractory period after an action potential?

the temporary inactivation of the Na+ channels

How is the speed of an action potential related to the axons diameter?

speed increases with diameter

How are axons insulated in vertebrates?

by a myelin sheath

What effect does the myelin sheath have on an action potential’s speed?

it increases speed

generally, what produces myelin sheaths?

glia (either oligodendrocytes or schwann cells

What produces myelin sheaths in the CNS?

oligodentrocytes

What produces myelin sheaths in the PNS?

Schwann cells

Nodes of Ranvier

gaps in the myelin sheath where voltage gated Na+ channels are found

In vertebrates, where is the only place that action potentials are formed?

at nodes of ranvier

saltatory conduction

process by which action potentials in myelinated axons jump between the nodes of Ranvier

Where do neurons communicate with other cells?

at synapses

electrical synapses

the electrical current flows from one neuron to another

chemical synapses

a chemical neurotransmitter carries information across the synaptic cleft

most synapses are ___

chemical

How is electricity transferred at electrical synapses?

ions flow directly into the post synaptic cell through gap junctions

What causes the release of a neurotransmitter at a chemical synapse?

an action potential

What synthesizes and packages neurotransmitters and where?

the presynaptic neuron, in synaptic vesicles located in the synaptic terminal

How are postsynaptic potentials generated?

neurotransmitter binding causes ion channels to open

Direct synaptic transmission

involves the binding of NTs to ligand gated ion channels in the post synaptic cell

Excitatory postsynaptic potentials (EPSPs)

depolarizations that bring the membrane potential toward threshold

Inhibitory postsynaptic potentials (IPSPs)

hyperpolarizations that move the membrane potential farther from threshold

what happens when a nuerotransmitter binds a metabotropic receptor?

a signal transduction pathway is activated in the postsynaptic cell, involving a second messenger

metabotropic receptors

involved in regulating signaling at synapses; generation of a postsynaptic potential depends on one or more metabolic steps

compare metabotropic receptors to ligand gated (ionotropic receptors)

in comparison to ionotropic receptors the effects of second messenger systems have a slower onset but longer lasting effects