How do neurons communicate information? Flashcards
What are the main components of a neuron?
dendrites- receive info
cell body- processes/ integrates info
axon- carries info
axon terminal- transmits info to next cell
When is a neuron considered at rest?
It is considered at rest when it is not firing (not sending an action potential)
What is the electrical gradient?
This refers to the difference in charge across the membrane of the neuron
What is the chemical gradient?
This refers to the difference in number of ions inside and outside the neuron
What is the electrochemical gradient?
This is the collective term for the chemical and electrical gradient. it is caused by the difference in number and type of ions inside and outside the cell
What is the membrane potential?
This refers to the difference in total charge inside and outside the cell. At rest, the neuronal membrane has a resting potential of -70mV. The inside of the cell is around 70mV less positive than the outside meaning it is considered to be negative at rest.
What are ions channels?
These are proteins that facilitate movement of ions across the neuronal membrane
- Most ion channels are selectively permeable, meaning they only allow certain ions through
What are voltage-gated ion channels?
These are a type of ion channel that open when the membrane potential reaches a certain value
Why is the resting membrane -70mV?
1) At rest, the only ion channels that are open are the potassium (K) channels
2) There is a higher concentration of K inside the neuron, which pulls K out (diffusion)
3) However, inside of the neuron is negatively charged which pulls K in (electrical attraction)
4) The two forces of electrical concentration/ diffusion are in opposition, which reach an equilibrium of about -70mV
What is the sodium-potasium pump?
This pump transports ions across the membrane against the concentration gradient with the aim of returning the neuron back to its resting membrane potential
- One cycle of this pump transports 3Na ions outside the cell and brings in 2K ions inside. This will eventually restore chemical and electrical concentration to rest levels
When does a neuron fire (an action potential) ?
At rest, a neuron is negatively charged (-70mV)
- If negative current is injected, an inhibitory post-synaptic potential (IPSP) occurs because the neuron becomes less likely to fire an action potential (hyperpolarised)
- If positive current is injected, an excitary post-synaptic potential (EPSP) occurs because the neruon is more likely to fire (depolarised). If the neruon ESPS exceeds -50mV, an action potential occurs
Outline the full process of how neurons transfer information across the synapse
1) If a positive current is injected into the neuron, an ESPS occurs as it is more likely to fire
2) If this ESPS exceeds -50mV, an action potential is generated at the axon hillock to travel down the axon
3) Once this action potential arrives at the axon terminal, calcium ions (Ca) enter the axon terminal to stimulate the release of neurotransmitters from vesicles into the synapse
4) These neurotransmitters bind to receptors, which open to allow specific ions to move into the post-synaptic neuron, causing a change in potential
5) In response to neuron being depolarised and firing, voltage-gated ion channels open to return the membrane potential to resting levels. The Na ion channels open first, causing sodium Na ions to move into the cell, making it more positively charged (repolarisation). In response, the voltage-gated K ion channels open to allow K ions out of the cell, making the cell more negative again
6) Alongside this, the sodium-potassium pump is removing 3Na ions to outside the cell and 2k inside the cell
7) This will eventually lead to the restoration of the electrical and chemical concentrations to rest levels
8) The action of glutamate in the synapse is terminated by being taken up by glial cells, where it is recycled used again
