Transmission within a neuron (action potentials) Flashcards
What is a cell membrane made of and what is its function?
Lipid and protein, and it stops things from mixing.
Name 6 parts of a neuron.
Soma, dendrites, axon hillock, axon, bouton and synapse.
What’s inside the cell membrane?
Organic anions (-)
K+
Water
What’s outside the cell membrane?
Na+
Cl-
Water
Where are APs generated?
The axon hillock.
How are APs transmitted?
By changing electrical charges across the cell membrane.
If ions moved passively up and down electric and chemical gradients, which elements would move in and which out and what would this do?
Sodium in, potassium out, would change resting potential to 0mV.
What is the resting potential of a neuron?
-70mV - more anions inside and cations outside.
What are anions?
Negative ions.
What are cations?
Positive ions.
How is the resting potential maintained?
Through an active pump - the sodium-potassium pump.
What does the sodium-potassium pump do?
Uses energy to move 3 Na+ to the outside and 2 K+ to the inside.
What did Hodgkin and Huxley (1952) do?
Found action potentials in a giant squid axon (recorded voltage with electrodes) and developed a mathematical model - won Nobel prize.
How does an AP look on a voltage graph?
Resting potential, then goes up (depolarisation) to 40mV (spike), then falling (repolarisation) to -80mV, following which there is a gradual increase back up to -70mV (hyperpolarisation/recovery).
What is the firing threshold for an AP?
-55mV.
What happens to the cell membrane during depolarisation?
When the membrane reaches the threshold, voltage-gated sodium channels open and sodium rushes into the neuron, increasing the potential to 40mV.
What happens to the cell membrane during repolarisation?
Once the membrane reaches 40mV, the sodium channels close and voltage-gated potassium channels open. Potassium rushes out until the potential has decreased to -80mV.
What happens to the cell membrane during recovery/hyperpolarisation?
The membrane hyperpolarises - all channels close and the sodium-potassium pump works to restore normal ion balance (swaps 2 K- for 3 Na+). The potential returns to -70mV.
What does a Takifugu’s liver contain and how is it lethal?
Tetrodotoxin (TTX), it blocks sodium channels and prevents APs, meaning that about 70 micrograms can kill in 30 mins.
How fast does an AP in a regular neuron move?
2 m/s
What is myelin?
A fatty layer of insulation generated by Schwann cells and oligodendrocytes. Loss of myelin is seen in MS and it gets harder to produce with age.
What is saltatory conduction?
The way in which myelin covers axons with gaps (Nodes of Ranvier) and APs jump across nodes - it’s a fast, efficient method of transmission.
How fast can myelin and saltatory conduction make a neuron?
Up to 120 m/s
How does the AP encode information?
Spike frequency (firing rate)
