Term
| what can incoming signals from sensory stimulus or other neurons do to the cell membrane? |
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Definition
they can depolarise it causing the membrane potential to rise from -70mV. for example, the opening of Na+ channels causing an influx of sodium ion and makes the cell inside more positive.
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Term
| what is the critical threshold level than a cell membrane must be depolarised beyond to trigger an action potential (nerve impuls) in the axon? |
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Definition
-55mV
other incoming signals can do the reverse and hyperpolarise the membrane ie cause the membrane potential to decrease thus making an action potential less likely. |
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Term
| in relation to axon hillock and trigger zone, where is an action potential initiated? |
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Definition
initiated at the trigger zone of the axon hillock.
stages of an action potential.
resting state, threshold potential, depolarisation phase, repolarisation phase, undershoot aka refractory phase then back to resting state until next action potential is triggered. |
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Term
| how is the forward direction of an action potential ensured? |
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Definition
| it is ensured in the way that if an action potential were to travel in the opposite direction it would bump in to the refactory (undershoot) phase where the membrane is not depolarised enough. |
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Term
true or false?
action potentials are self-propagating with no loss of signal intensity as it moves down the axon |
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Definition
true.
they move along the axon activating voltage gated sodium, potassium and calcium channels.
an action potential is an all or nothing event. if the cell membrane isn't depolarised beyon the threshold it will not result in an action potential. |
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Term
| what is saltatory conduction? |
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Definition
| where impulses jump between nodes of ranvier in the myelinated axon at speeds of 150m/sec |
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Term
| the intensity of a signal is conveyed by f.......... of nerve impulses. there is a short r.............. period during which another action potential can be s.......... this explains the u.............................. movement AKA undershoot. |
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Definition
frequency
refractory
stimulated
unidirectional |
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Term
synapses can be e......... gap junction but usually are c........
transmitters are stored in membrane bound synaptic v.....
the amount in one vesicle is called a q......
the arrival of AP causes i..... of Ca2+ then fusion of vesicles with p........ membranse and release of transmitter into synaptic cleft. |
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Definition
electrical, chemical, vesicles, influx, pre-synaptic
the transmitter then binds to receptors on the post-synaptic membrane and the effect of the transmitter can EXCITATORY or INHIBITORY |
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Term
| which two mechanisms are used to terminate transmitter activity? |
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Definition
- catabolism (degradation)
- uptake of transmitter into axon terminal or glial cells.
some synapses also have regulatory mechanisms in the form of autoreceptors these are often inhibitory so stop transmitter relase. |
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Term
| the synaptic cleft is 100nm and the post-synaptic site has considerable membrane thickness and contains what else? |
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Definition
post-synaptic receptors where transmitter bind to.
the enzymes required for synthesis of transmitter molecules found in cytoplasm and in synaptic vesicles. mitochondria are transported to the axon terminal to provide energy. |
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Term
| name the 4 criteria for transmitter substances such as acetylcholine |
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Definition
- synthesised in the neuron
- present at presynaptic terminals, within synaptic vesicles
- endogennous substance (dug) at reasonable conc mimics same action of endogenously released transmitter
- specific mechanism exists for removing transmitter from synaptic cleft
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Term
| ACh is synthesised by choline acetyl transferase where is it found and what is it involved in? |
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Definition
found in the brain at the neuromuscular junction and in autonomic ganglia.
involved in learning and memory.
Brain ACh is deficient in Alzheimer's disease |
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Term
ACh receptors can be nicotinic or muscarinic. what does this mean?
what stops the action of ACh and where is this found? |
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Definition
- nicotinic = these receptors can not only be opened by ACh but also by nictoine (neuromuscular junction, brain, autonomic nerves)
- muscarinic = these receptors are more sensitive to muscarine than nictoine ( smooth muscle, exocrine glands, brain)
ACh action is stopped by acetylcholinesterase attached to the EC side of synaptic membranes (neuronal and glial) |
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Term
| if i am substance that binds to a receptor and stimulate it mimicking a transmitter what am i? an agonist or an antagonist? |
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Definition
an agonist -
eg nicotinic agonist is nicotine from tobacco
eg muscarinic agonist is muscarine from toadstool Amanita muscarina |
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Term
| if i bind to a receptor but i doNOT stimulate it thus blocking the transmitter, am i an agonist or an antagonist? |
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Definition
antagonist
eg cuare, dart poisin is a nicotinic antagonist
eg Atrpin from (deadly nightshade) Atropa belladonna is a muscarinic antagonist |
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Term
| neuromuscular junction (NMJ) - this junction between the a..... terminal of a m..... neuron and striated muscle fibre is responsible for initiation of m......... contraction. |
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Definition
axon, motor, muscle
in vertebrates, numberous nicotinic acetylcholine receptors are found at NMJ |
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Term
| which two starting products does choline acetyl transferase use to make ACh? |
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Definition
choline and acetyl CoA
The enzyme acetylcholinesterase breaks ACh down into acetate and choline to be reused.
inhibitors of acetylcholinesterase are used to treat Alzheimer's disease. |
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Term
| Alzheimer's disease was first described by Alois Alzheimer in 1907. it is characterised by p.......... loss of s..... term memory until the patient is completely d......... |
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Definition
progressive, short, demented
neuropathological changes include loss of brain weight, enlargement of ventricles, numberous senile plaques found outside the nerve cell and neurofibrillary tangles in the brain. for a histological diagnosis of Alzheimer's, a combination of plaques and tangles must be found. |
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Term
also associated with alzheimers is degeneration of cholinergic nerve cells and loss of cholinergenic marker enzymes.
senile plaques are found outside the nerve cell but where are neurofibrillary tangles NFT found? |
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Definition
NFT found inside nerve cells - tau a microtubule associated axonal protein accumulates in the cell bodies and dendrites
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