Neural conduction and synaptic transmission Flashcards
What is the resting membrane potential of a neuron
- 70 mv
What are the two processes that establish the resting membrane potential?
An active process and passive process
Describe the cell membrane at rest in the passive process
Largely impermeable to many ions except from K+. Other ions can cross the membrane via specialised channels that open under some circumstances
How is a membrane potential established in the passive process?
Through the selective diffusion of K+
What is the initial first stage of the passive process?
K+ flows down the chemical gradients from high concentration to a low concentration (comp 1 to comp 2)
What is the result of K+ leaving compartment 1? PP
Produces an electrical current
What does the production of the electrical current result in? PP
A separation of charge - solutions are no longer neutral. +ve charge in comp 2 and -ve charge in comp 1
What does the separation of charge lead to? PP
A potential difference/membrane potential
How does the system reach equilibrium? PP
Eventually, the number of K+ ions moving down the chemical gradient balances the number of ions moving down the electrical gradient
What is the mechanism used inn the active process?
Sodium potassium pump
What is the role of the active process to establish the resting potential?
To transport Na+ out of the neuron and K+ in
What is the ratio of Na+:K?
Three Na for every two K
What is the energy supplied by for the active process?
ATP
What is depolarisation?
When the membrane potential is made less negative
What is hyperpolarisation?
When the membrane potential is made more negative
What do the channels in the neurons do and when do they open?
They allow the passage of certain ions across the membrane and open when the cell is depolarised
What is the potential when the cell is depolarised to threshold?
-60mV
What happens when the cell membrane is depolarised to the threshold?
The Na+ channels open and polarity reverses to +30 inside. At this point voltage gated Na+channel closes and K+ opens, which restores the membrane potential.
How do action potentials travel down the axon?
The influx of sodium ions creates enough positivity for an action potential on the next part of the membrane
How is this process sped up by myelin?
The myelin allows the action potential to jump from node to node, rather than travelling the entire length of the nerve fibre.
What is a synapse
A point of specialised contact between two neurons
What is the structure of a synapse?
1)presynaptic element
2) synaptic cleft
3) Postsynaptic element
What is the most important feature of the presynaptic element?
The vesicles which contain neurotransmitters.
What could the postsynaptic element be?
A dendrite, a cell body, a terminal bouton
What is an action potential
Wave of depolarisation
What happens when the action potential reaches the presynaptic element?
The calcium channels are opened
What happens when the calcium channels are opened?
This allows for the binding of the vesicles to the presynaptic membrane, allowing them to open and neurotransmitters diffuse into the synaptic cleft.
What is the most important feature of the post synaptic element?
Receptors for the neurotransmitters. Once unlocked, the neurotransmitters open channels inside the cell
What happens when these channels are opened inside the cell?
Allows certain ions to flow through them. The flow of the charged ions through channels opened by these NTa produce the effects of these substances on the post-synaptic cell.
What are ionotropic receptors
Receptors made of usually 5 subunits
What are metabotropic receptors
Receptors indirectly associated with an ion channel
What happens when the neurotransmitters bind on the post synaptic element?
The opening of ion channels
What is produced when NTs bind to receptors?
Excitatory or inhibitory post synaptic potentials
What is an excitatory postsynaptic potential?
Makes the cell more likely to fire an action potential
What is an inhibitory postsynaptic potential?
Makes the cell less likely to fire an action potential
