Lecture 3 Flashcards
Incoming signals can do two things to the polarity of the nerve cell membrane. What are they?
Depolarise it - causing membrane potential to rise from resting potential (-70mV).
Hyper-polarise it - lowering the membrane potential further, reducing the chance of an action potential occurring.
What is a threshold potential? (both value and description)
The critical level of depolarisation of the cell membrane, whereby any additional depolarisation causes an action potential to be triggered in the axon.
-55mV.
Where is an action potential initiated in a nerve cell?
Trigger zone of the axon hillock.
5 stages of an action potential in a nerve cell? (1 being at initial resting state)
- ) Initial resting state - retention of K+ in the cell.
- ) Threshold - Na+ flows in through voltage-gated ion channels.
- ) Depolarisation phase - large influx of Na+.
- ) Repolarisation phase - inactivation gate closes, preventing influx of more Na+, K+ ion channel opens, allowing flux of K+.
- ) Undershoot - membrane potential temporarily goes below expected.
What phrase describes an action potential’s longevity, and why?
Self-propagating, as there is no loss in signal intensity as it travels down the axon.
What does ‘all or none’ refer to?
Each stimulus produces either a full action potential, or none at all.
What is saltatory conduction, and how fast is it?
Impulses jumping between Nodes of Ranvier due to myelinated axons.
Up to 150m/sec.
How is the intensity of a signal conveyed?
By the frequency of nerve impulses.
What is a refractory period?
What does it explain?
A short time after an action potential has occurred when another cannot be stimulated.
(Explains unidirectional movement.)
2 types of synapse, and which is more common?
Electrical (gap junctions)
Chemical - more common.
What are transmitters stored in?
Membrane bound synaptic vesicles.
What is the amount of transmitter in one vesicle known as?
Quantum.
What an action potential arrives at a synapse, what happens?
Influx of Ca2+, fusion of vesicles with pre-synaptic membrane, release of transmitter into synaptic cleft.
Transmitter binds to receptor on post-synaptic membrane.
What two effects can transmitters have?
Excitatory.
Inhibitory.
There must be a mechanism to terminate transmitter activity. What 2 methods are capable of doing this?
Catabolism.
Uptake of neurotransmitter into axon terminal or glial cells.
What effect do auto receptors typically exhibit?
Inhibition - stopping transmitter release.
Where are enzymes required for synthesis of transmitter molecules typically found?
In cytoplasm and synaptic vesicles.
4 criteria for transmitter substances?
- Synthesised in neurone.
- Present at presynaptic terminals and packaged in vesicles.
- Endogenous substance at reasonable concentration mimics action of endogenously released transmitter.
- Specific mechanism exists for removing transmitter from synaptic cleft.
Four well known biogenic amines? Their functional class? Secretion sites?
- Noradrenaline, Excitatory or inhibitory, CNS and PNS.
- Adrenaline, Excitatory or inhibitory, CNS and PNS.
- Dopamine, Usually excitatory, sometimes inhibitory, CNS and PNS.
- Serotonin, Typically inhibitory, CNS.
Four well known amino acids? Their functional class? Secretion sites?
- GABA, inhibitory, CNS and invertebrate neuromuscular junction.
- Glycine, inhibitory, CNS.
- Glutamate, excitatory, CNS and invertebrate neuromuscular junction.
- Aspartate, excitatory, CNS.
Two well known neuropeptides? Their functional class? Secretion sites?
- Substance P, excitatory, CNS and PNS.
- Met-enkephalin, typically inhibitory, CNS.
Where is acetylcholine (ACh) found, and what is it involved in?
The brain, at neuromuscular junction and in autonomic ganglia.
Involved in learning and memory.
In what disease is there a deficiency of brain ACh?
Alzheimer’s disease.
What is acetylcholine synthesised by?
Choline acetyl transferase.
What are the 2 types of receptors for acetylcholine? (and where are they found?)
Nicotinic (neuromuscular junction, brain, autonomic nerves).
Muscarinic (smooth muscle, exocrine glands, brain).
What enzyme stops acetylcholine transmitter? And where is it found?
Acetylcholinesterase.
Attached to extracellular side of synaptic membranes.
What is an agonist?
Substance that binds to a receptor and stimulates it (mimicking transmitter).
What is an antagonist?
Substance that binds to a receptor but doesn’t stimulate it (blocking transmitter).
One example of a nicotinic agonist?
Nicotine.
One example of a nicotinic antagonist?
Curare.
One example of a muscarinic agonist?
Muscarine.
One example of a muscarinic antagonist?
Atropine.
What is the neuromuscular junction responsible for the initiation of?
Muscle contraction.
Where are nicotinic acetylcholine receptors found in vertebrates?
Neuromuscular junction.
What enzyme combines Acetyl-CoA and Choline?
Choline acetyl transferase.
What are inhibitors of acetylcholinesterase often used to treat?
Alzheimer’s disease.
When was Alzheimer’s first discovered, and by whom?
- Alois Alzheimer.
What characterises Alzheimer’s?
Progressive loss of short term memory, until patient is left completely demented.
Neuropathological changes involved in Alzheimer’s?
Loss of brain weight, enlargement of ventricles, numerous senile plaques, neurofibrillary tangles (NFTs) in the brain, degeneration of cholinergic nerve cels and loss of cholinergic marker enzymes.
What do NFTs consist of, and where are they found?
Consist of tau (microtubule associated axonal protein), accumulate in cell bodies and dendrites.
