C2.2 Neural Signalling

Define Neurons

Cells within the nervous system that carry electrical impulses

What do electrical signals travel accross in nerves?

Nerve fibres

What are the two types of nerve fibres?

Dentrites and axons

Where are dentrites used?

Transmit signals between neurons in the brain or spinal cord

Where are axons used?

to transmit signals from toes or fingers to the spinal cord

How long are dentrites

Very short

How long are axons?

Very long

What does an imabalance of charge create?

A potential difference

What is the resting potential of the membrane potential?

-70mV

What is responsible for the movement of Na+ and K+ ions?

Sodium-potassium pump

What is needed for the sodium-potassium pump to work?

ATP

What kind of transport is the movement Na+ and K+ ions through the sodium potassium pump?

Active transport

What is pumped out of the sodium potassium pump?

3 Na+ ions

What is pumped into the sodium potassium pump?

2 K+ ions

What are two other factors that lead to a negative resting potential?

The presence of large negatively charged proteins and the permeability of the membrane to K+ ions.

What is an action potential?

The rapid change in charge when a neuron is firing

What is the potential difference during action potential?

+30mV

What triggers a change in action potential?

The opening of sodium and potassium channels along the axon

What happens to the sodium and potassium ions when the sodium and potassium channels are opened to trigger an action potential?

They move down the concentration gradient established during the resting potential by the sodium-potassium pumps

Where do the sodium ions move when the sodium channels open to trigger an action potential?

They move into the neuron

What is the result of Na+ ions entering the cell when the sodium channels open to trigger an action potential?

The membrane becomes positive

What is the name for a positive membrane potential when the sodium channels open to trigger an action potential?

Depolarization

Where do the potassium ions move when the potassium channels open after the cell has become depolarised?

Out of the cell

What happens to the cell when the K+ ions exit after the cell has become depolarised?

The membrane becomes negative

What is the name for a negative membrane potential when the potassium channels open to trigger an action potential?

Repolarisation

What type of channels are the sodium and potassium channels?

Voltage-gated ion channels

What causes the voltage gated sodium and potassium channels to open and close?

A change in potential

What does the sodium and potassium channels being voltage gated mean for the transmission of a nerve impulse?

It can be propagated in a unidirectional wave

What restores the resting potential after an action potential?

The sodium-potassium pumps

What is the name of the time between nerve impulses?

The refractory period

Define synapses?

Junctions between neurons and between neuron and effector cells

In what form is the signal brought to the synapse by the neuron?

a nerve impulse or action potential

What is the name of the neuron that brings the signal to the synapse?

The transmitting neuron

What is the name of the neuron which carries the signal away from the synapse?

The receiving neuron

What is the name of the membrane of the transmitting neuron?

The presynaptic membrane.

What is the name of the synapse on the receiving neuron?

The postsynaptic membrane.

What is the shape of the cross section of an axon?

Circular

What is the length of the diameter of an axon?

1 micrometer

How fast does the average impulse travel along the axon?

1 meter per second

What are the two ways of speeding up nerve impulses?

1. Larger axon diameters

2. Saltatory conduction

Why do larger axons have a faster nerve impulse speed?

Less resistance

Give an example of an animal with a large axon diameter?

Giant squid

How fast do giant squid’s nerve impulses travel?

25 meters per second

How large is the axon of a giant squid?

500 micrometers

Along which type of nerves does saltatory conduction occur?

Myelinated axons

Is the myelinated sheath continuous or discontinuous?

Discontinuous

What is the name of the gaps between the myelin sheath?

Nodes de Ranvier

How fast is a nerve impulse transmitted along a nerve using saltatory condunction?

100 micrometers per second

What is triggered when an action potential reaches an axon terminal?

The voltage gated calcium channels open

What does the diffusion of calcium ions into the cell promote?

The fusion of vesicles with the cell membrane

What do the vesicles which fuse with the membrane in the end of an axon contain?

Neurotransmitters

What does the fusion of the vesicles with the membrane at the end of an axon trigger?

The release of neurotransmitters

What do the neurotransmitters travel accross after being released from the axon terminal?

The synaptic cleft

What is the name of the process by which the neurotransmitters are released from the axon?

Exocytosis

What do neurotransmitters bind to once they have diffused across the synaptic cleft and what does this trigger?

They bind to specific receptors which open ligand-gated ion channels

Which ion enters the receiving neuron after the neurotransmitters triggered the opening of the ligand-gated ion channels?

Na+

What does the entrance of Na+ ions into the receiving neuron create in terms of potential?

An increase in membrane positivity

What is the potential of the membrane have to be to trigger an action potential?

-50mV

What is the name of a change in potential large enough to trigger an action potential?

An excitatory post-synaptic potential

What is the name of the neurotransmitter which is used at synapses between neurons and between neurons and muscle fibres?

Acetylcholine

What is acetylcholine broken down by?

Acetylcholinerase

Give an example of positive feedback in action potential?

If -50mV is reached by Na+ ions, then more Na+ ions come through

How long are Na+ channels open for?

1-2 milliseconds

How much does the entrance of Na+ raise the membrane potential?

+30 or +40 mV

What is the name of an action potential triggering a change in potential in another part of the axon?

Propagation

What are local currents?

The movement of Na+ ions by diffusion

Where are the sodium-potassium pumps and the sodium / potassium channels located on myelinated axons?

At Nodes de Ranviers

Where do action potentials only occur in myelinated axons?

At Nodes de Ranviers

Give two example of exogenous chemicals

Pesticides and drugs

What does exogenous chemicals affect?

Synaptic transmission

Give an example of a pesticide which affects synaptic transfer?

Neonicotenoid pesticides

How do neonicotenoid pesticides affect the synapse?

They irreversible bind the acetylcholine receptors

What is the impact of neonicotenoid pesticides irreversible binding to acetylcholine receptors?

Na+ channels stay open, the excess blocking normal synaptic transmission causing paralysis or death in insects

Give an example of a drug which which affects synapses?

Cocaine

What type of synapse does cocaine affect?

Synapses with dopamine as the neurotransmitter

Where does the cocaine bind to in the synapse?

Dopamine reuptake transporters

What is the role of dopamine reuptake transporters?

Pump dopamine back to the presynaptic neuron

What is the consequence of cocaine binding to dopamine reuptake transporters?

An excess of dopamine so the nerve is always excited

What type of drug is cocaine?

An excitatory or stimulant drug

What type of neurotransmitter make the membrane more negative when they bind to receptors?

Inhibitory neurotransmitters

What is the name for when a membrane is made more negative?

Hyperpolarisation

What is the consequence of inhibitory neurotransmitters on nerve impusles?

It is harder to reach the threshold potential so nerve impulses are inhibited

What is the lowering of the membrane potential caused by neurotransmitters known as?

Inhibitory postsynaptic potential

What are the two types of neurotransmitters?

Inhibitory and excitatory

Give an example of summation?

When an action potential is reached as a result of multiple excitatory neurotransmitters

What balance of inhibitory and excitatory neurotransmitters is needed to initiate an action potential?

When there is a predominance of excitatory neurotransmitters

What detects pain?

Free nerve endings

Give example of kinds of stimuli which opens positively charged ion channels as a response to pain

High temp, acid, certain chemicals (capsaicin in chili peppers)

What is consciousness an example of?

An emergent property

Define emergent property

the result of interactions between te elements of a system, where that system is more than the sum of its parts