Neuronal Communication Flashcards
What is the function of the cell body?
Contains the nucleus, cytoplasm and other organelles. Vesicles contain neurotransmitters
What are dendrons?
Dendrons split into dendrites
Dendrons carry an action potential towards the cell body
What is an axon?
Axons are elongated nerve fibres which carry nerve impulses away from the cell body.
They can be short or long depending on the type or neurone.
Features of sensory neurons
Short dendrites
One long dendron
One short axon
Features of motor neurons
Many short dendrites
One long axon
Myelinated or non-myelinated
Features of relay neurones?
Short dendrites
One axon
What is the nervous communication pathway
Stimulus -> Receptor -> CNS -> Effector -> response
What is the role of sensory receptors?
Sensory receptors convert the energy of a stimulus into electrical energy (they are transducers).
The are specialised cells and each sensory receptor will respond to only one type of stimulus
Explain the processes of detecting a stimulus.
Once a stimulus is detected, the receptor cell changes the permeability of its cell membrane.
Ions move into and out of the cell via ion pumps and ion channels.
The charge on the ions create a potential difference. This is called the generator potential.
A generator potential is required in a sensory receptor for an action potential to be generated
How does a bigger stimulus affect the generator potential?
A bigger stimulus produces a bigger movement of ions across the membrane
This causes a bigger change in potential difference and thus a greater generator potential
What is an example of a sensory receptor?
The pacinian corpuscle.
It is found in the skin and detects pressure and vibration
The end of a sensory neurone is found within the centre of the corpuscle which is surrounded by many layers of connective tissue. Each layer is separated by a layer of viscous gel.
How do corpuscles only respond to changes in pressure and not when it’s constant?
They don’t respond when pressure is constant as the sodium ion channels remain open and thus a resting potential is not established
Why is it important that we don’t feel anything when pressure is constant?
So we don’t constantly receive unnecessary information - preventing cognitive overload
what is the synaptic cleft?
A gap between the dendrite of one neurone and axon terminal of another
what is the presynaptic neurone?
the neurone along which the impulse has arrived
what is the postsynaptic neurone?
the neurone that recieves the neurotransmitter
What is the refractory period?
After an action potential the neurone cell membrane cannot be excited again straight away. This is due to the ion channels recovering and can’t be made to open.
Why is the refractory period important?
Ensures action potentials don’t overlap (discrete)
Ensures action potentials are unidirectional (can’t travel backwards)
What are the 2 stages of the refractory period?
- The absolute refractory period (1ms), nothing happens
- The relative refractory period (5ms long), an action potential may occur only if the stimulus is more intense than the normal threshold.
what are myelin sheaths made up of?
they are made up of many layers of plasma membranes produced by Schwann cells
How does saltatory conduction occur in myelinated neurones?
K+ and Na+ ions cannot diffuse through the insulating myelin sheath. The myelinated neurone is only permeable to ions at the nodes of Ranvier.
between the nodes of Ranvier, sodium ions diffuse rapidly. This allows the wave of depolarisation to ‘jump’ from node to node, making the conduction faster.
How do non-myelinated neurones conduct action potentials?
In non-myelinated neurones, the impulse does not jump, but instead transmits along the nerve fibre.
Depolarisation occurs along the entire length of the neurone.
It takes more time for each region to be depolarised.
What is the speed of transmission in non-myelinated neurones?
up to 1m/s
What is the speed of transmission in myelinated neurones?
up to 100 m/s
How does axon diameter affect the speed of the impulse?
The bigger the axon diameter, the faster the impulse is transmitted.
This is due to less resistance to the diffusion of ions through the cytoplasm.
How does temperature affect the speed of the impulse?
The higher the temperature, the faster the speed of the impulse. This is because ions diffuse faster at higher temps. until approx. 40 degrees as the protein channels will start to denature.
What does the size of the stimulus determine?
The stronger/bigger the stimulus is, the frequency of action potentials increase.
How does the brain determine how intense a stimulus is?
from the frequency of the action potentials arriving in the sensory region of the brain.
What is the change in potential difference when the neurone goes from resting potential to action potential?
approx. -75mV to +35mV
Name 3 ways in which the resting potential is established.
–> Voltage-gated K+ ion
channels closing
–> Sodium-potassium
pump
–> K+ ion leak channels
A generator potential is caused by the movement of what ions?
Sodium ions (Na+)
What causes the voltage-gated sodium ion channels to open?
A stimulus with a potential difference that exceeds the threshold
How is the neurone repolarised?
–> Na+ V.G close
–> K+ V.G open
–> K+ ions leave
membrane
explain the process of synaptic transmission
When an action potential arrives at the end of the presynaptic neurone, it causes calcium ion channels to open.
Calcium ions flood into the the axon terminal and stimulates the synaptic vesicles to move toward the membrane of the
presynaptic neurone.
The vesicles fuse with the membrane, releasing acetyl choline (neurotransmitters) into the synaptic cleft via exocytosis.
Acetylcholine diffuses across the synaptic cleft and binds to receptors on sodium ion channels, openeing them. sodium ions flood into the postsynaptic neurone as a result.
The postsynaptic neurone depolarises, and if the threshold is reached an action potential is generated.
Acetycholinesterase in the synaptic cleft breaks down acetylcholine into ethanoic acid and choline.
Choline and ethanoic acid thendiffuse back into the presynaptic neurone where ATP from the mitochondria recombines them into acetylcholine and moves it back into the vesicles.
What is saltatory conduction?
When the action potential in a myelinated neurone jumps from node to node allowing it to travel faster as an action potential doesn’t need to be generated along the entire length (only at nodes of ranvier)
What is the all-or-nothing principle?
If depolarisation (caused by a stimulus) does not exceed -55mV, an action potential and impulse will not be produced (nothing).
After an action potential has been generated, the membrane enters a refractory period where it can’t be stimulated because Na+ channels are recovering and can’t be opened.
Give 3 reasons why this is important.
1) ensures discrete impulses (makes sure each impulse is separate)
2) ensures the action potentials travel in one direction, as if they travelled in two directions it would prevent a response
3) it limits the number of impulse transmission. This is important ti prevent over reaction to a stimulus
What is summation?
The rapid build-up of neurotransmitters in the synapse to help generate an action potential by two methods: spatial or temporal summation
What is spatial summation?
Many different neurones collectively trigger a new action potential by combining the neurotransmitter they release in order to exceed the threshold value
What is temporal summation?
One neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed the threshold value
