5.3 Neuronal Communications Flashcards
Receptors
Detect a change
Sensory receptors examples
Light sensitive, pressure sensitive, heat sensitive, chemoreceptors
Light sensitive cells
in the retina receptors detect change in light intensity + convert it to an electrical signal
Pressure sensitive cells
- Change in pressure on skin = by pacinian corpuscles in the skin (receptor) converts movement to electrical
Temperature sensitive cells
Receptors in the skin are peripheral receptors
chemoreceptors
detect change in chemicals + ions
Transducer
Anything that converts one type of signal to another
Sensory neurone
detects the change = passes it from receptor to CNS
Motor neurone
passes info from CNS to the effector = part of body that performs the response + can be a muscle or a gland
Relay neurone
connects sensory and motor neurone
Dendrite
part of neurone that receives information (not in sensory neurones).
Difference between dendron and axon
Towards cell body = dendron, away from cell body = axon
Cell body
where organelles are found (end of motor neurone, not on end of sensory neurone)
Labelled motor neurone diagram
Labelled sensory neurone diagram
Labelled relay neurone diagram
Pacinian corpuscle stages
- when pacinian corpuscle’s stimulated, lamellae deformed + press on sensory ending
- causes stretch mediated sodium ion channels in sensory neurone’s membrane to become deformed
- sodium ion channels open, ions diffuse into cell, creating generator potential
- when the generator potential reaches the threshold it triggers an action potential
Action potential diagram
Stage 1
At rest, sodium + potassium pumps can pump sodium out + potassium in. 3 sodium’s out for every 2 potassium (requires ATP). Going to be negative inside compared to outside bc less protons come in for the amount that come out. Membrane quite permeable to potassium ions so they tend to leak out = very negative = -60 mV. Also have anions inside that contribute to this.
Neurone membrane charge at rest
- polarised (negatively charged)
- resting potential = -60mV
Stage 2
the membrane becomes depolarised (becomes less negative). Becomes less negative become sodium channels open so sodium enters so the membrane charge becomes less negative. This creates a generator potential (opening of sodium ion channels)
Stage 3
- Reached threshold. Some sodium ion channels are voltage gated (open at specific voltages)
Stage 4/5
eventually enough sodium ions enter to reach +40 mV. (2-5 = depolarisation) once you reach max point +40 mV the sodium ion channels close. (Positive feedback)
Stage 6
- Potassium ion channels open and potassium leaves so the membrane potential decreases. (Repolarised)
Stage 8
- Stage where too much potassium leaves = membrane is hyperpolarised (too negative). This is the refractory period = ions are all in the wrong places so another action potential can’t be generated = period that allows your cells to recover. Bc ions are in wrong order it allows action potential to move in one direction.
Stage 9
- Resting potential is restored using the sodium potassium pumps (polarised)
Can action potential differ depending on the stimulus?
Action potential will always be the same regardless of the stimulus if the threshold is reached (all or nothing)
Do all generator potentials lead to action potential
Not all generator potentials lead to action potential as the threshold -50 mV must be reached for action potential to occur. Has to be strong enough for enough sodium ions to enter to create an action potential. Combined effects can eventually reach threshold.
What are pacinian corpuscles
a pressure sensor. In the centre of the rings of connective tissue = sensory neurone
How do pacinian corpuscles function?
Pressure will dent the membrane so eventually it will go to the sensory fibre + push it. This will open (deform) sodium channels on the membrane. Sodium diffuses into the neurone bc of concentration gradient that was established while resting. Creates generator potential = creates a small change = becomes depolarised (sodium ions enter)
Myelin sheath
layer of fat = can’t conduct electricity (insulates axon)
- made up of Schwann cells
Myelin sheath function
- Ions can only pass along the neurone at the node of ranvier (saltatory conduction) = faster than moving across the whole axon = communication is faster than local current (going straight through axon)
How does action potential move alone a myelinated neurone?
Saltatory conduction
How does action potential move along a normal neurone
- sodium ions enter + build up at that channel = creates concentration gradient between sodium channels so sodium ions move sideways inside the neurone.
- When the sodium ions reach the next channel they create a change in voltage which open up the voltage gated sodium channels = sodium ions move in + they move sideways …..
- Action potential will always move in one direction it can’t move the other way bc it will only move in the direction where there are less sodium ions
How to differentiate between the strength of the stimulus in action potential:
- for a stronger stimulus the frequency of the action potential will increase.
Synapse
Junction between two neurones
Pre and post synaptic neurones
Pre synaptic neurone and post synaptic neurone + synapse in between. Always goes from pre to post use neurotransmitters to communicate. 100s of neurotransmitters.
ACH
Neurotransmitter
Neurons that uses ACH as a neurotransmitter
cholinergic neurone
How synapse works (step 1)
- in pre synaptic neurone the neurotransmitters are packed into vesicles so when an action potential arrives at the synaptic bulb it causes a change in voltage and allows bolted gated calcium ion channels to open and calcium ions enter the presynaptic bulb
How synapse works (step 2)
- Calcium ions cause the vesicles containing the neurotransmitters to move and fuse with the presynaptic membrane, so neurotransmitters are released through Exocytosis = bc fibrous proteins attach vesicles to membrane + when calcium ions come along they attach and shorten the protein causing the neurotransmitter to be brought to the membrane
How synapse works (step 3)
- Neurotransmitters diffuse across the synaptic cleft and bind to complementary receptors on sodium ion channels. Sodium ion channels open and sodium ion diffuses across the post synaptic neurone and creates an excitatory post synaptic potential (voltage increases). Action potential created in post synaptic neurone = generator potential DOESNT always lead to action potential, it’s only if it reaches the threshold.
How synapse works (step 4)
- If Acetylcholine (ACH) is present then it binds to the receptors on sodium ions channels = allows sodium ions to enter post synaptic membrane = enough sodium ions then action potential is reached. If this reaction lead to a muscle being contracted, if you don’t clean it up (remove ACH) then the muscle stays contracted because ACH will keep on binding to the sodium channels so they stay open so the post synaptic neurone stays depolarise. In the synaptic cleft there’s an enzyme called acetylcholinesterase = breaks down acetylcholine into an acetyl group and choline group. These two are recycled back into the presynaptic neurone = made into acetylcholine using ATP.
How synapse works.
- in pre synaptic neurone the neurotransmitters are packed into vesicles so when an action potential arrives at the synaptic bulb it causes a change in voltage and allows bolted gated calcium ion channels to open and calcium ions enter the presynaptic bulb
- Calcium ions cause the vesicles containing the neurotransmitters to move and fuse with the presynaptic membrane, so neurotransmitters are released through Exocytosis = bc fibrous proteins attach vesicles to membrane + when calcium ions come along they attach and shorten the protein causing the neurotransmitter to be brought to the membrane
- Neurotransmitters diffuse across the synaptic cleft and bind to complementary receptors on sodium ion channels. Sodium ion channels open and sodium ion diffuses across the post synaptic neurone and creates an excitatory post synaptic potential (voltage increases). Action potential created in post synaptic neurone = generator potential DOESNT always lead to action potential, it’s only if it reaches the threshold.
- If Acetylcholine (ACH) is present then it binds to the receptors on sodium ions channels = allows sodium ions to enter post synaptic membrane = enough sodium ions then action potential is reached. If this reaction lead to a muscle being contracted, if you don’t clean it up (remove ACH) then the muscle stays contracted because ACH will keep on binding to the sodium channels so they stay open so the post synaptic neurone stays depolarise. In the synaptic cleft there’s an enzyme called acetylcholinesterase = breaks down acetylcholine into an acetyl group and choline group. These two are recycled back into the presynaptic neurone = made into acetylcholine using ATP.
Presynaptic bulb
- contains lots of mitochondria
- Lots of SERs to package the neurotransmitters into vesicles
- Lots of vesicles containing acetylcholine
- Voltage gated calcium ion channels
Post synaptic membrane
- Contains sodium ion channels
Why is movement only in one direction from pre to post synaptic neurone
because only the presynaptic neurone contains the neurotransmitters and only the post synaptic neurone contains the receptors.
Summation
Combined affect of anything
Temporal summation
In order to reach the threshold for action potential = allow one neurone to have multiple action potentials which lead to multiple small excitatory post synaptic potential = to reach threshold potential.
Spatial summation
Different neurones combine together = allows post synaptic neurone to reach the threshold
This can allows action potentials from diff parts of the nervous system can converge to generate an action potential.
Inhibitory post synaptic potential
some presynaptic neurones can be inhibitory neurones and release neurotransmitters which promotes the decrease of the membranes potential. This is known as the inhibitory post synaptic potential. It makes it harder to reach the threshold potential so they reduce the effect of summation (involves chloride)
Excitatory synapse
promotes depolarisation which allows the threshold to eventually be released (involves sodium)
Control communication
- One presynaptic neurone can speak to multiple post synaptic neurones
- Synapse can filter out unwanted low level signals = bc it’s low there wouldn’t be an action potential so it wouldn’t be transmitted further
- Low level action potentials can be amplified by summation.
- After repeated stimulus, the synapse involved may run out of neurotransmitters which means the person becomes habituated to the stimulus
- Synapse allows the creation of memory and strengthen pathways in our brain.
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Detect movement
