C2.2 Neural signalling

Nerve impulse

Electrical signal passed between two cells, two types

Draw neuron and outline functions of dendrites, axon and cell body

• Dendrites → Receive data from another neuron

• Axon → Carries electrical impulses

• Cell body → Houses nucleus + organelles

Membrane potential

Voltage within membrane due to its distribution of ions

Resting potential

Electrical potential difference across the plasma membrane (-70mv)

Action potential

Rapid change in voltage across membrane

Depolarisation

Membrane potential goes from negative to positive

Repolarisation

Membrane potential goes from positive back to negative

Steps to action potential

1. Sodium-potassium pump maintains the electrochemical gradient of resting potential (-70mv) → 3 sodium, 2 potassium

2. Some potassium leaves the membrane

3. Some sodium voltage gate channels open

4. Some sodium ions leave the membrane through facilitated diffusion

5. Once threshold potential is reached, all sodium channels open and sodium continues to leave (-55mv)

6. Sodium channel gates close and potassium channel gates open

7. Potassium diffuses out of membrane

8. Sodium-potassium pump rests and goes back to its resting potential

Self-propagating

Depolarisation in one part triggers depolarisation in the next part

Saltatory conduction

Impulse jumping from node to node, increasing speed

Synapse

Gap between cells through which signals are passed

Steps for release of neurotransmitters from a presynaptic membrane

1. Action potential reaches the end of presynaptic neuron

2. Voltage-gated calcium ion channels open

3. Calcium ions enter the presynaptic neuron (facilitated diffusion)

4. Calcium ions force vesicles with neurotransmitters to fuse with the membrane

5. Neurotransmitters are released into the synapse (exocytosis)

6. Neurotransmitters diffuse across the synapse

7. Bind to receptors on the postsynaptic membrane

8. Ion channels open

9. If enough ions enter the post synaptic cell, that generates an action potential

10. Neurotransmitter is removed from the synapse → to stop this process

Threshold potential

Membrane potential that must be reached in order for voltage-gated ion channels to open

Local current

Movement of sodium ions between polarised and depolarised regions

Oscilloscope

Device that measures/visualises membrane potential

Exogenous chemical

Something that enters the body through an external source

Neonicotinoids

Blocks synaptic transmission by binding to acetylcholine receptors

Cocaine

Promotes synaptic transmission as it blocks the reuptake mechanism for dopamine

Summation

Multiple releases of an excitatory neurotransmitter

Consciousness

Simultaneous awareness of many things

Emergent property

Properties that are evident when components combine but are absent in the individual parts