Unit 17: Neuronal Signalling🧠

What process explains how nervous tissue communicates within the nervous system?

neuronal signalling

What detects temperature in the skin?

thermoreceptors

What happens when the thermoreceptor detects a stimulus?

its membrane voltage changes

The amount of membrane voltage change in thermoreceptors depends on what?

the strength of the stimulus

What is the amount of change in neuronal signalling referred to as?

graded potential

What happens if the graded potential reaches the threshold?

an action potential is generated

The action potential is an electrical signal that travels ____ the axon

down

What is the travel pathway of an action potential? (3 locations)

axon hillock → axon terminals → synaptic end bulbs

What is the movement of the action potential along the axon called?

propagation

What causes the release of a neurotransmitter?

the action potential reaching the synaptic end bulbs

During neuronal signalling, a ____ diffuses across the synapse and binds to a ____ on the next neuron

neurotransmitter, receptor

A neurotransmitter diffusing across the synapse and binding to a receptor on the next neuron causes what to occur?

a change in the target neuron's membrane voltage, creating a new graded potential

During neuronal signalling, if the ____ ____ reaches threshold, the neuron generates an action potential at its ____ ____

graded potential, axon hillock

During neuronal signalling, the signal travels to the ____, where neurotransmitters are released at ____ synapse

thalamus, another

The thalamus relays sensory information to the ____ ____, where conscious perception of the stimulus begins

cerebral cortex

The cerebral cortex processes the information along with other sensory information, emotions, and memories to decide ____ ____ ____. Then it sends a ____ command to the body to produce a response

what to do, motor

Where are upper motor neurons located?

primary motor cortex

What do upper motor neurons do in the primary motor cortex?

send movement signals down the spinal cord

The upper motor neuron ____ with a ____ motor neuron in the spinal cord

synapses, lower

The upper motor neuron synapsing with a lower motor neuron in the spinal cord causes what to occur?

a graded potential in the lower motor neuron

If threshold is reached, an action potential travels down the lower motor neuron's axon into the ____

periphery

The axon reaches the muscle at the ____

NMJ

What causes an end plate potential and then a muscle action potential?

acetylcholine (ACh) being released at the NMJ

The muscle ____ ____ causes the muscle fibres to contract

action potential

Motor cortex → ____ ____ ____ → lower motor neuron → ____ → ACh → muscle action potential → muscle contraction

upper motor neuron, NMJ

What are the 3 main functions of the nervous system?

1. sensation

2. integration

3. response

Neurons communicate using ____ membranes, which can change their electrical state

excitable

The main electrical signal is the ____ ____, which occurs when ____ changes create a signal

action potential, membrane

What is used when signals involve more variable changes in the membrane?

graded potential

What do cells use to build up an electrical charge across the cell membrane?

ions

Why cant charged/hydrophilic ions cross the cell membrane directly?

because it is a phospholipid bilayer

How do ions cross the membrane? (2 ways)

1. channel proteins

2. active transport pumps

What are the pores called that allow specific ions to move across the membrane?

ion channels

Ion channels move channels ____ their concentration gradient

down

The sodium-potassium pump (Na⁺/K⁺ pump) uses ____ to move Na⁺ out of the cell and K⁺ into the cell

ATP

Why do sodium-potassium pumps require ATP?

because it moves ions against their concentration gradients

Ion channels do not always freely allow ions to diffuse across the membrane: some are opened by certain events, meaning the channels are ____

gated

What are the 4 types of ion channels called?

1. ligand-gated channels

2. mechanically gated channels

3. voltage-gated channels

4. leakage channels

How do ligand-gated channels open?

when a signaling molecule (ligand) binds to the channel

In the nervous system, the ligand is often a ____. These are also called ____ ____

neurotransmitter, ionotropic receptors

How do mechanically gated channels (mechanoceptors) open?

when the cell membrane is physically distorted, such as by pressure or touch

How do voltage-gated channels open and close?

in response to changes in the electrical voltage across the cell membrane

Normally, the inside of the membrane is ____

negative

When the inside of the membrane becomes less negative, ____ ____ begin allowing ions to cross

voltage-gated channels

How do leakage channels open and close?

randomly

Leakage channels help establish and maintain the ____ transmembrane voltage of an excitable membrane

resting

What is membrane potential?

the difference in electrical charge across the cell membrane

What is membrane potential measured in?

millivolts (mV)

What specifically does the membrane potential compare?

he inside of the cell to the outside, with the outside treated as 0

The fluids inside and outside the cell are mostly electrically ____ overall, but there is a small difference in charge right along the ____ ____

neutral, membrane surface

What does this small difference in charge along the membrane surface allow?

neurons and muscle cells to generate electrical signals, including action potentials

At rest, most ion channels are ____, except for leakage channels, which randomly open

closed

The ____ contains many negatively charged anions, including phosphate ions and negatively charged proteins

cytosol

These ion distributions create a resting membrane potential of about ____ mV. The exact value can vary between cells

-70

What is a stable, balanced state called?

resting membrane potential

What is the resting membrane potential maintained by?

ion leakage and ion pumping

To start an electrical signal, the membrane potential must ____

change

What are local changes in membrane potential called?

graded potential

What do graded potential sizes depend on?

the strength of the stimulus

Graded potentials can be what two things?

depolarizing or hyperpolarizing

What happens to the membrane in depolarization?

it becomes less negative

What happens to the membrane in hyperpolarization?

it becomes more negative

What is depolarization caused by?

Na⁺ or Ca²⁺ entering the cell

What is hyperpolarization caused by?

K⁺ leaving the cell or Cl⁻ entering the cell

What does it mean by action potentials being "all-or-none"?

they either occur completely or do not occur at all

Are action potentials graded?

no

Where does an action potential begin?

axon hillock

What is the first step of an action potential?

Na⁺ channels open, allowing Na⁺ to rush into the cell

What happens when Na⁺ is rushed into the cell?

it makes the inside of the cell less negative and causes depolarization (the membrane potential moves toward 0 mV)

What happens after the membrane potential moves toward 0 mV?

Na⁺ continues entering even after the membrane reaches 0 mV, causing the membrane potential to become positive

The membrane potential reaches approximately ____ mV during depolarization

+30

What 2 things happens when the membrane potential reaches +30 mV?

1. the Na⁺ channels become inactivated, stopping further Na⁺ entry

2. voltage-gated K⁺ channels open, allowing K⁺ to leave the cell

Voltage-gated K⁺ channels opening and allowing K⁺ to leave the cell, makes the inside of the cell more ____

negative

K⁺ leaving the cell, brings the membrane potential back toward ____ mV and is called ____

-70, repolarization

What does the K⁺ channels closing slightly late cause?

the membrane potential to briefly become more negative than −70 mV

The temporary overshoot in action potential signalling is called ____

hyperpolarization

What is the threshold for action potentials?

-55mV

What happens if the membrane does not reach −55 mV?

no action potential occurs

Every action potential is essentially the same ____

size

Does a stronger stimulus make a bigger action potential?

no

What does a strong stimulus cause instead of a bigger action potential?

more action potentials in a shorter amount of time

What are the 2 gates of the voltage-gated Na⁺ channel?

1. activation gate

2. inactivation gate

What happens at an activation gate?

it opens at −55 mV (threshold) and Na⁺ rushes into the cell causing depolarization

What happens at an inactivation gate?

closes shortly after and stops Na⁺ from entering

As the membrane returns below −55 mV, the ____ ____ closes and the ____ ____ reopens, resetting the channel

activation gate, inactivation gate

What happens at the singular voltage-gated K⁺ channel gate?

it opens at about −50 mV and K⁺ flows out of the cell causing repolarization

Voltage-gated K⁺ channel opens more ____ than the Na⁺ channel

slowly

The voltage-gated K⁺ channel closes with a slight ____, causing extra K⁺ to leave → ____

delay, hyperpolarization

How long does the entire action potential take?

2 milliseconds

What is the refractory period?

while an action potential is happening, another action potential cannot be initiated

The action potential starts at the ____ ____ of the axon, where there are many ____-gated Na⁺ channels

initial segment, voltage

Depolarization ____ along the inside of the membrane, causing more voltage-gated Na⁺ channels to open farther down the ____

spreads, axon

What does this create?: More Na⁺ enters → more depolarization → more Na⁺ channels open

a wave of depolarization moving toward the axon terminals

The Na⁺ channels that have already opened become ____, creating the absolute ____ ____

inactivated, refractory period

Na⁺ channels cannot immediately open again, so the signal does not ____ ____

travel backward

Behind the action potential, K⁺ channels open and K⁺ leaves the cell, ____ that section of the axon and ____ it for another action potential

repolarizing, resetting

What kind of conduction does an unmyelinated axon cause?

continuous conduction

What occurs in continuous conduction?

the action potential travels along every part of the axon, with voltage-gated Na⁺ channels opening continuously along the membrane

What is the speed of continuous conduction?

slow

What kind of conduction does a myelinated axon cause?

saltatory conduction