synapses and neurotransmitters

what is a synapse?

a very small gap between adjacent neurons

what messages are passed along the gap of the synapse?

neurotransmitters

where are neurotransmitters released from and why?

they are released from the axon terminals in response to action potential.

what do neurotransmitters do?

they diffuse across the synapse and will attach to receptors not he dendrite of the next neuron

what are some examples of neurotransmitters?

acetylcholine (ACh), noradrenalinę (norepinepherine), Adrenalinę (epinehrine), dopamine, histamine, adosine, serotonin

what is a neuromuscular junction

where an axon terminal meets muscle tissue instead of another neuron

what is the pathway of the neurotransmitters at a neuromuscular junction?

impulse is passed from axon terminals (the Nerve fibre) to muscles triggering a contraction

what is the process of a transmission across a synapse?

first an action potential (a nerve impulse ) reaches the axon terminal, activating the voltage gated cacium ion channels in the presynaptic neuron. As there is a high concentration go calcium in the extracellular fluid the calcium will move through the voltage gated calcium ion channels into the presynaptic neuron (at th axon terminal). the calcium triggers synaptic vesicles containing neurotransmitter to move through to the end of the terminal and fuse with the membrane, releasing the neurotransmitter by exocytosis. the neurotransmitter will then diffuse across the synaptic cleft and attaches to receptor sites on the membrane of the post synaptic neuron dendrite. this neurotransmitter/ receptor complex stimulates the ligand gated protein channels to open, alowing the influx of sodium ions and will trigger depolarisation. therfore initiating an action potential in the post synaptic neuron

what is the post synaptic neuron?

the one that receives the neurotransmitter

what is the presynaptic neuron?

the one that releases the neurotransmitter

how are neurotransmitters removed from the synapse?

by being reabsorbed by presynaptic membrane. or but being degraded by enzymes or by moving away by diffusion

what is the 1 direction neurotransmitters move

from an axon to a dendrite, or an axon to a cel body

whether or not the post synaptic neuron propagates the action potential depends on…

which neurotransmitter diffuses across the synaptic cleft, which receptor it binds to, which ions flow in and out the post synaptic neuron and whether or not depolarisation reaches the threshold

neurotransmitters can be…

excitatory or inhibitory

what does excitatory neurotransmitters do

the neurotransmitters cause depolarisation. the neurotransmitter will bind, the sodium channel will open and the sodium will rush in. the post synaptic membrane potential depolarises. therefore the action potential is propagated

what do inhibitory neurotransmitters do

the neurotransmitters cause hyperpolerisation. the neurotransmitter willl bind and potassium channels open and potassium rushes out or chlorine channels open and chlorine rushes in. therefore the membrane potential becomes more negative and hyper polarisation occurs.

what is the conciqunce of having an inhibitory neurotransmitter?

the membrane potential is further from the threshold and therefore an action potential is initiated more slowly or prevented entirely.c

can some neurotransmitters be excitatory and inhibitory?

yes, but at different synapses- is is dependant upon what receptors are on the post synaptic membrane

what are the similarites between a synapse and a neurotransmitter?

excitable cells are separated by the synaptic cleft. axon terminals store and release neurotransmitter. and binding of the neurotransmitter to receptors on the post synaptic membrane opens ion channels, altering membrane potential.

what are the differnces between a synapse and a neuromuscular junction?

synapse is a junction between 2 neurons whist a neuromuscular junction is a junction between neuron and skeletal muscle fibre. neurotransmitters in a synapse can be excitatory or inhibitory, while a neuromuscular junction can only be excitatory.

can the neurotransmitter in a neuromuscular junction be inhibitory

no only exitiatory

what are stimulants?

can stop inhibitory neurotransmitters from working and therefore the threshold is reached more readily having a stimulant effect. can increase the release of an exitatory neurotransmitter from the pre-synaptic neuron, causing increased neurotransmissions. Also it can prevent the reuptake of a neurotransmitter from the synapse left, meaning it hangs around longer, and continues to stimulate the post synaptic neuron. It also can increase the action of the post synaptic receptors meaning that transmission occurs more easily.

what is an example of a stimulant that can stop inhibitory neurotransmitters from and working and therefore the threshold is reached more easily, having a stimulated effect?

caffeine

what is an example of a stimulant that can increase the release of an exitatory neurotransmitter from the pre- synaptic neuron, causing increased neurotransmissions?

MDMA (extacy), amphetamines, ephedrine and pseudoepherdrine

what is an example of a stimulant which can prevent the reuptake of neurotransmitter from the synapse cleft, meaning that it hangs around longer, and continues to stimulate the post synaptic neuron?

SSRI’s (which is used to treat clinical anxiety or depression)

what is an example of a stimulant which can increase the action of post synaptic receptors, meaning that transmission occurs more easily?

nicotine

how do depressant chemicals have on transmission of nerve impulses?

they can increase the effects if inhibitory neurotransmitters, increasing hyperolarisation of the post synaptic neuron. they can block or inhibit an action potential by blocking ion chapels in the post synaptic neuron.

what is an example of a depressant that ca increase the effects of an inhibitory neurotransmitter, increasing hyperolarisation

alcohol and valium

what is an example of a depressant that can block of inhibit an action potential by blocking ion channes in the post synaptic neuron?

anaesthetics

what do neurotoxins do?

nerve agents that contain oragophosphates the prevent the breakdown of a neurotransmitter at a synapse (e.g acetyl chlorine) , causing persistent stimulation. and they increase the effiecent of post synaptic receptors.

what is an example of a neurotoxin that increase the effiencey of teh the post synaptic receptors?

alkaloids such as strychnine

what are nerve agents?

they are also called nerve gases, they contain organophosphates, whichcause the build up of Acetylcholine at neuromuscular junction.then all the mucles try and contract and the loss of muscle control prevents breathing.