Synaptic Transmission

Front 1

what is a synapse

Back 1

-a synapse is a junction between a neurone and another neurone.

-or between a neurone and an effector cell e.g a muscle or gland.

Front 2

what is a synaptic cleft

Back 2

the tiny gap between the cells at a synapse is called the synaptic cleft

Front 3

what is a synaptic knob

Back 3

a swelling on the presynaptic neurone

Front 4

what does the synaptic knob contain

Back 4

it contains synaptic vesicles filled with chemicals called neurotransmitters

Front 5

what happens when the action potential reaches the end of a neurone

Back 5

when a neuro transmitter reaches the end of a neurone it causes neuro transmitters tobe released into the synaptic cleft they diffuse across the postsynaptic membrane and bind to specific receptors

Front 6

what happens when neurotransmiters bind to receptors

Back 6

when neurotransmitters bind to receptors they might :

-trigger an action potential in a neuron,

-cause muscle contraction in a muscle cell or

-cause a hormone to be secreted from a gland cell.

Front 7

why is it important for impulses to be unidirectional

Back 7

because the receptors are only on the postsynaptic membranes therefore impulses have to be unidirectional and can only travel in one direction

Front 8

why are neurotransmitters removed from the cleft

Back 8

so the response doesnt keep happening e.g theyre taken back into the presynaptic neurone or theyre broken down by enzymes and the products are taken into the neurones.

Front 9

describe the process of a nerve impulse being transmitted across a cholinergic synapse

Back 9

1) an action potential arrives at the synaptic knob of the presynaptic neurone

2)the action potential stimulates voltage gated calcium ion channels in the presynaptic neurone to open

3)calcium ions diffuse into the syaptic knob

4)the influx of calcium ions into the synaptic knob causes the synaptic vesicles to fuse with the presynaptic membrane

5)the vesicles release the neurotransmitter acetylcholine(ACh) into the synaptic cleft = exocytosis

6)ACH diffuses across the synaptic cleft and binds to specific choloinergic receptors on the postsynaptic membrane

7)this causes sodium ion channels in the postsynaptic neurone to open

8)the influx of sodium ions into the postsynaptic membrane causes an action potential on the postsynaptic membrane - if the threshold is reached.

9)ACh is removed from the synaptic cleft so the response doesn't keep happening.

Front 10

what is ACh broken down by

Back 10

its broken down by an enzyme called acetylcholinesterase and the products are re absorbed by the presynaptic neurone and used to make more ACh.

Front 11

what is a neuro muscular junction

Back 11

a neuromuscular junction is a synapse between a motor neurone and a muscle cell

Front 12

how do neuromuscular junctions work

Back 12

neuromuscular junctions use the neurotransmitter ACh which binds to cholinergic receptors called nicotinic cholinegic receptors

Front 13

what are the differences between the way that meuromuscular junctions and cholinergic work

Back 13

1) the possynaptic membrane has lots of fols which forms clefts - thses clefts store the enzyme that breaks down ACh - called acetylcholinesterase - AChE

2) the postsynaptic membrane has more receptors than other synapses

3)when a motor neurone fires an action potential it always triggers a response in a muscle cell - this isnt always the case for a synapse between two neurones.

Front 14

what do excitatory neurotransmitters do

Back 14

they depolarise the postsynaptic membrane - making it fire an action potential if the threshold is reached e.g acetylcholine is an excitatory neurotransmitter - it binds to cholinergic receptors to cause an action potential in the postsynaptic membrane.

Front 15

what do inhibitory neurotransmitters do

Back 15

they hyperlpolarise the postsynaptic membrane - make the potential difference more negative - preventing it from firing an action potential.

e.g GABA is an inhibitory neuro transmitter

-when it binds to its receptors it causes potassium ion chanels to open on the postsynaptic membrane, hyperpolarising the nerone.

Front 16

if a stimulus is weak how does this affect whether an action potential happens or not.

Back 16

if a stimulus is weak only a small amount of neurotransmitter will be released from a neurone into the synaptic cleft = might not be enough to excite the postsynaptic membrane to the threshold level and stimulate an action potential

Front 17

hat is summation

Back 17

summation is where the effect of neurotransmitter released from many neurones is added together

Front 18

what are the two types of summation

Back 18

spatial summation

temporal summation

Front 19

how does spatial summation work an what effect does it have on producing an action poential

Back 19

spatial summation is when many neurones connect to a singular neurone

-the small amount of neurotransmitter released from each of these neurones can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an action potential

Front 20

what happens in spatial summtion if neurones release an inhibitory neurotransmitter

Back 20

then the total effect of all the neurotransmitters might be no action potential

Front 21

what is temporal summation and how does it affect action potential.

Back 21

emporl summation is where two or more nerve impulses arrive in quick succession from the same presynaptic neurone = makes the action potential more likely because more neurotransmitter is released into the synaptic cleft

Front 22

how can a drug of the same shape as neurotransmitters affect synaptic transmissions

Back 22

drugs that are the same shape as neurotransmitter mimic their action at receptors =more receptors are activated. e.g nicoting mimics acetylchline so binds to nicotinic cholinergic receptors

Front 23

how do drugs that block receptors affect synaptic transmission

Back 23

some drugs block receptors so they cant be activated by neurotransmitters = fewer receptors can be activated.

Front 24

how can a muscle be paralysed by using block receptors

Back 24

block effectors block the efects of acetylcholine by blocking nicotinic cholinergic receptors at neuromuscular junctions so muscle cells cant be stimulated = paralysed.

Front 25

how do drugs that inhibit the enzymes that break down neurotransmitters affect synaptic transmission

Back 25

inhibiting the enzymes that break down neurotransmitters means that there are more neurotransmitters in the synaptic cleft to bind to receptors and theyre there for longer.

Front 26

how do drugs that stimulate the release of neurotransmitters affect synaptic transmission

Back 26

they stimulate the release of neurotransmitters from the presynaptic neurone so more receptors are activated

Front 27

How do drugs that inhibit the release of neurotransmitters from the presynaptic neurone affect synaptic transmission

Back 27

drugs that inhibit the release of neurotransmitrs mean that less receptors are activated.