Chapter 7 Neuronal Signaling

neurons are

excitable cells in the nervous system

What are glial cells

aka neuroglia, support cells in nervous system

components of a neuron

• contains nucleus and most organelles

soma

components of a neuron

• bring info into neuron

• input areas

dendrites

components of a neuron

• transmits electrical impulses called action potentials

• output arm of the neuron

  • signals leave the cell body

axon

components of neuron

• where axon originates and action potentials are generated

• located where axon & cell body join

axon hillock

components of a neuron

• releases neurotransmitter

axon terminal

Functional classes of neuron

• neural info flows into the CNS

afferent neurons

functional classes of neurons

• neural info flows away from CNS

• send info to effector organs like

  • muscles 💪

  • glands

efferent neurons

functional classes of neurons

• neural info remains within CNS

• communicated from neuron to neuron

• most are these

interneurons

What are a neuron’s integral membrane proteins?

signal receptors and ion channels

Ion channels: Neurons

• receptors receive signals and ________

• ion channels ________ ion flow to generate ________

transduce; control; electrical impulses

Ion channels in neurons are usually ______ to certain ion(s)

specific

Types of ion channels

• always open- don’t have a gate

• located throughout entire neuron

• allow one or more type of ion

• main job is to establish resting membrane potential (when neuron is not excited)

leak channels

Type of ion channels

• open or close in response to ligand binding

• found on dendrites and soma

• create synaptic potentials

ligand-gated channels

Type of ion channels

• open or close in response to changes in membrane potential

  • change in charge level across membrane

    • called membrane potential

voltage-gated channels

This type of voltage gated channel

• is found all around neuron

• more in the axon/ axon hillock

• generates action potentials

sodium and potassium channels

This type of voltage gated channel

• is located at the axon terminal

• help release neurotransmitters

calcium channels

Electrical potentials in neurons

• written as = E

• difference in voltage between two points

potential difference

Electrical potentials in neurons

• written as = Vn

• difference of charge across membrane at any place

membrane potential

Electrical potentials in neurons

• difference in membrane potential when cells is at rest

  • not receiving or sending signals

resting membrane potential

• when cell sis not excited it means that there is an electrochemical ___________ point of the cell

equilibrium

resting membrane potential (Vm) depends on ____________ of all ions that cross the membrane

equilibrium potentials

True or false all cells have a resting membrane potential

true

neurons maintain a resting membrane potential of approx ______

-70 mV

What are the 3 factors that help determine resting membrane potential

ion concentration gradients, membrane permeability, Na+/K+ pump

Which direction will Na+ go?

• will cross through a sodium leak ion channel

inside the cell

Which direction will K+ go?

• will cross through a potassium leak ion channel

outside the cell

main function of the Na+/K+ pump

pump 3 sodium out of cell and 2 potassium into cell using 1 ATP

energy source for the Na+/K+ pump

adenosine triphosphate (ATP)

net charge moved per pump cycle

net +1 charge removed from inside cell

direct effect of Na+/K+ pump on resting membrane potential

creates 20% charge difference by pumping out more positive ions than it brings in

The Na+/K+ pump moves from _____ to ______ gradient concentration

low to high

indirect effect of Na+/K+ pump on resting membrane potential

creates 80% charge difference by creating concentration gradients

What is the Sodium (Na+) concentration gradient?

higher outside, lower inside cell

What is the potassium (K+) concentration gradient

lower outside, higher inside cell

why potassium leaking out creates a negative charge inside

potassium carries positive charge out, leaving negative charged proteins inside

Step 1 of Na+/K+ pump cycle

3 sodium ions and 1 ATP molecule bind to pump from inside cell

Step 2 of Na+/K+ pump cycle

ATP splits and provides energy to change shape of channel so it opens to outside

Step 3 of Na+/K+ pump cycle

3 sodium ions are released outside, and 2 potassium ions bind from outside

Step 4 of Na+'/K+ pump cycle

phosphate releases, pump gets back to original shape, 2 potassium released inside

Location of higher Na+ concentration at rest

outside the cell

Location of higher K+ concentration at rest

inside the cell

Meaning of the suffix -ase in Na+/K+-ATPase

is an enzyme

what is the role of Na+/K+ pump in nerve cell signaling

maintains resting state so neurons can fire action potentials

number of Na+ ions moved per cycle

3

number of K+ ions moved per cycle

2

Equilibrium potential describes the

exact electrical voltage where 2 competing forces on an ion channel cancel each other out, so there is no net movement

What does sum of electrochemical forces = 0mV mean?

an equal number of ions are crossing in both directions

• made up cell

• initially has 0 mV membrane potential

• no electrical driving force

• membrane is only permeable to potassium

hypothetical cell

the ion distribution of both hypothetical cells is….

what ion concentrations are higher inside/ outside cell

higher concentration of sodium and chloride outside cell, higher concentration of potassium and organic anions inside cell

In a hypothetical cell the chemical driving force of potassium is driving it ?

outside the cell

In a hypothetical cell the electrical driving force of potassium is driving it ?

into the cell

In the hypothetical cell that is only permeable to potassium which driving force is higher?

electrical or chemical?

chemical, so potassium diffuses out of the cell

if the driving forces are in opposite directions which one wins?

the stronger force

Since the chemical force is diffusing potassium (K+) out the cell the inside of the cell becomes more_________?

negative

Now that there is a electrical gradient difference in the hypothetical cell that is only permeable to potassium

• inside cell is more negative

causing electrical force to do what with Potassium?

remember opposites attract

pull potassium back inside cell

when chemical and electrical forces are equal

cell reaches equilibrium

When hypothetical cell reaches equilibrium the equilibrium potential for potassium is?

• Ek=

-94 mV

In the hypothetical cell that is only permeable to potassium the chemical and electrical driving forces are at equilibrium but

• opposite in ________

• equal in _________

direction; magnitude

• made up cell

• initial membrane potential of 0 mV

• permeable only to sodium ions

hypothetical cell

in the hypothetical cell that is only permeable to sodium the chemical driving force is driving it at which direction?

into the cell

in the hypothetical cell that is only only permeable to sodium the electrical force is driving it at which direction?

into the cell

Since the chemical and electrical driving forces are in the same direction in the hypothetical cell that is only permeable to sodium → Na+ diffuses _________

into the cell

In the hypothetical cell that is only permeable to sodium

• as it diffuses into cell the inside of the cell becomes?

less negative

In the hypothetical cell that is only permeable to sodium

• now that the inside of the cell is more positive

• the electrical driving force begins to push Na+ ________ of cell

remember like charges repel each other

out

When hypothetical cell reaches equilibrium the equilibrium potential for sodium is?

• ENa=

+60 mV

When the hypothetical cell that is only permeable to sodium reaches equilibrium the chemical and electrical driving force are:

• opposite in ________

• equal in ________

opposite; magnitude

Membrane is 25x more permeable to ____ than _____

K+; Na

the membrane is more permeable to potassium because?

there are more potassium leak channels than sodium leak channels

In resting potential more positives are leaving cell so inside of the cell becomes _______

negatively charged

Since the cell during resting potential is negatively charged the electrical driving forces are

• driving Na+ ____ cell

• driving K+ _____ cell

into

As the electrical force grows the chemical force is affected causing

• the K+ outflow to _____

• the Na+ inflow to ______

slow down; speed up

Resting potential: neuron

What is this state called

• equilibrium develops

• membrane potential stops changing/ ions still flow equally

• inflow of Na+ is balanced by outflow of K+

steady state

during the resting potential of a neuron the ____________ equal the __________

outflow of potassium; inflow of sodium

resting membrane potential: Neuron

what is the resting membrane potential?

-70mV

the resting membrane potential is closer to the ___________ equilibrium potential

• resting Vm = -70mV

potassium

the strength of the force trying to move the ion _____ as the membrane potential moves __________ from the equilibrium potential

grows; away

the resting potential of a cell Vm is ____ mV less negative than Ek

24

During resting membrane potential of a cell, the ___________ drives K+ into the cell therefore, _________ membrane potential

• remember cell is negative inside

electrical force; raising

During resting membrane potential of a cell, the __________ drives K+ out of the cell therefore, __________ membrane potential

• remember concentration is higher inside than outside

chemical; lowering

During resting potential of a cell, the net force is ________

• chemical and electrical force are almost equal

weak

the resting potential of a cell Vm is ____ mV less negative than ENa

130

V, is 130 mV less negative than ENA

• Electrical force is ______ the cell

• Chemical force is _______ the cell

• net force is _________

into; into; strong

The net force is strong because Na+ flows into the cell, but the resting membrane has _________ to Na+, so influx of Na+ is _______

low permeability; slow

The net force is weak because K+ flows out of the cell, but the resting membrane is __________ to K+

highly permeable

there is a _____ Na+ leak when a neuron is at rest

• a high force but a _____ permeability

small; low

there is a ______ K+ when a neuron is at rest

• a low force but a _________ permeability

small; high

the _______ helps to maintain the resting potential

Na+/K+ pump

The Na+/K+ pump

• pumps Na+ back ________

• pumps K+ back _________

out of cell; into cell; against

The Na+/K+ pump uses _____________

• Na+ and K+ pumps _______ their concentration using ATP

primary active transport; against

the Na+/K+ pump is an example of?

homeostasis

State the relative “leak permeabilities” of K+ and Na+ in neurons at rest & why they cause a -70mV membrane potential

the membrane is x25 more permeable to K+ than Na+, high leakage makes the inside more negative driving it towards equilibrium but a slight trickle of incoming Na+ makes the membrane more positive

The membrane does ‘t reach Ek because _____ is flowing in through its leak channels

sodium

membrane potential changes Δ V happen because of?

gated ion channels that open or close in response to stimulus

The opening and closing of gated ion channels affects _________

movement of ions

The movement of ions through opened or closes gated channels creates an ________

• ex: sodium rushing in when gate is open

• hint: can become more positive or negative

electrical signal

What does gated mean?

able to be opened/closed by some stimulus

what are the 3 types of gated channels

voltage gated, ligand gated, mechanically gated