Flashcards in Axonal Transmission Deck (40)
What is the resting membrane potential? Give a value also.
When the inside of the cell is negatively charged with respect to outside.
How is the resting membrane potential maintained?
By the sodium-potassium pump. 3Na+ ions are pumped out of the membrane for every 2K+ ions pumped in.
Leaky K+ channels lead to K+ diffusing out of the axon, further increasing the negativity of the inside of the membrane.
Briefly outline the steps of an action potential.
1. Neurotransmitter binds to specific ligand-gated ion channels causing influx of Na+
2. Causes initial DEPOLARIZATION which stimulates opening of voltage gated Na+ channels resulting in further entry of Na+ ions
3. When the threshold potential (-55mV) is reached, a positive feedback loop is created
4. REPOLARIZATION occurs at +30mV. Na+ channels are inactivated. Sluggish voltage gated K+ channels open resulting in K+ diffusing out of the neurone and causing repolarization.
5. As the voltage gated K+ channels are slow to close, K+ continues to diffuse out resulting in HYPERPOLARIZATION - -75mV
6. Resting potential is restored. A second stimulus will not produce another action potential - the absolute refractory period.
7. In the relative refractory period, a second action potential can be induced if the stimulus strength is great
How is conduction achieved?
Action potential generates local currents that depolarize adjacent membranes.
How does fibre diameter and myelination effect propagation speed?
The larger the fibre diameter, the faster the action potential (less resistance).
Myelination increases propagation speed.
What is saltatory conduction?
Myelinated neurones have nodes of Ranvier. Action potentials jump from one node to the next as they propagate along a myelinated fibre.
What is multiple sclerosis? Give symptoms as well.
Degeneration of myelin which blocks neurotransmission.
Symptoms: Uncontrolled eye movements, slurred speech, tremor.
What occurs at an excitatory synapse?
The membrane potential of a postsynaptic neurone is depolarised.
What occurs at an inhibitory synapse?
The membrane potential of a postsynaptic neurone is hyperpolarised or stabilised.
What are the two types of synapse?
Electrical and chemical (majority)
Give the features of an electrical synapse.
1. Plasma membranes of the presynaptic and postsynaptic cells are joined by gap junctions
2. Very rapid communication
3. Synchronised transmission
4. Found in brainstem and hypothalamus neurones
Give the features of a chemical synapse.
1. Plasma membranes of presynaptic and postsynaptic neurones are joined by the synaptic cleft
2. Presynaptic neurone ends as axon terminal which contains neurotransmitter molecules
3. Covered by astrocytes which reuptake excess neurotransmitter
Outline the steps for neurotransmitter release.
1. Action potential arrives at pre synaptic neurone and cause calcium ion channels to open
2. Ca2+ ions cause vesicles containing neurotransmitter to fuse with the cell membrane
3. Neurotransmitter is released by exocytosis and diffuses across synaptic cleft
4. Neurotransmitter attaches to receptor sites on post synaptic membrane
What is temporal summation?
Signals arrive from the same presynaptic cell at different times. Potentials summate as there is a greater number of open ion channels.
What is spatial summation?
When two inputs occur at different locations in the postsynaptic neurone and combine.
Name 3 fast neurotransmitters (short lasting, rapid effect)
Name 3 neuromodulators (last longer, slow effect)
Which molecules make acetylcholine?
Acetyl coenzyme A and choline
Which enzyme breaks down acetylcholine? Which products are released?
Acetylcholinesterase. Produces choline and acetate.
Name the two types of acetylcholine receptor.
1. Nicotinic - found in neuromuscular junction. Respond to nicotine as well, and are found in reward pathways which explains why tobacco is so addictive.
2. Muscarinic - couple with G proteins.
What is noradrenaline affected by?
Antidepressants and stimulants. Imipramine and amphetamine blocks reuptake of noradrenaline.
What is dopamine affected by?
Antipsychotic drugs e.g. chlorpromazine blocks receptor
Anti-parkisons drug e.g. L-DOPA increases dopamine production
What is serotonin affected by?
Antidepressants. e.g. Prozac, increases serotonin
Which is the main excitatory neurotransmitter?
Which is the main inhibitory neurotransmitter?
How do local anaesthetics work?
They block sodium channels in the membrane , preventing depolarisation so no action potential is developed. Results in pain relief as no pain is transmitted.
Give the 4 parts of a neurone.
Which stain is used to see myelin?
Luxor fast blue
What three functional types of neurone are there?
Interneurons (CNS only)