Action Potentials And Synapses Flashcards
What is involved in neurotransmission?
Two types of neurons: the pre and post synaptic cell. Pre sends an AP along the axon of the pre to the axon terminals which send a neurotransmitter to the post. Within a cell the intercellular transmission is electrical, between the cell the extra cellular transmission is chemical.
What is a resting membrane potential?
Lots of potassium inside and outside of a cell. If potassium channels open in membrane, this is because more potassium molecules inside than outside the cell (so would leave the cell). As cell becomes negative it will make potassium stay in the cell (potassium channels close). If sodium channels open, sodium will come into the cell. The mean of the two effects is -70mV.
What are the key concepts of ion channels?
Holes in membrane allow ions to enter the cell, these are selective for different ions. Can be open all the time, or opener by different stimuli, e.g. change in voltage. Ions flow down electrical &chemical gradients. Examples of channels that are not open all the time are voltage gates sodium and potassium channels. Other channels opened by the binding of specific molecules, which open protein channels.
What is an action potential?
Coveys a fast signal from one place to another in the body. Are generated by changes in the membrane permeability due to open and closing of voltage gated ion channels. It is a self-regenerating electrical wave. It is a transient change in membrane potential. Occurs only if a threshold membrane potential is achieved (-70mV).
What are the events in an action potential?
- Threshold potential is reached 2. Depolarisation due to opening of sodium channels 3. Repolarisation due to inactivation of sodium channels & opening of potassium channels 4. Hyperpolarisation as voltage-gated potassium channels are still open.
Depolarisation leads to opening of sodium channels. When threshold potential is reached get a depolarisation or the cell making membrane potential more positive (k+ channels open). Large increase of potassium leads to negative potential. Membrane potential dips below rest, then potassium channels close and resting membrane potential comes back to -70mV
Why are action potentials all or nothing?
To get an action potential must get a depolarisation at the threshold and then sodium channels open. Gives a positive feedback loop. If don’t reach this threshold then action potential doesn’t happen.
What is action potential propagation?
AP propagate (travel) along axons. As AP move it depolarises the next bit of membrane and opens sodium channels. If sodium channels open the membrane potential reaches threshold potential and action potential propagates along. AP only propagates in one direction because previous sodium channels are inactivated.
What are absolute refractory periods?
When all sodium channels are inactivated this is the absolute refractory period. Relative refractory period is when some sodium channels have been inactivated. ARP enforces a one-way transmission.
What is saltatory conduction and the function of the myelin sheath?
Axon packed with sodium & potassium = unmyelinated axon. Myelin wraps fatty sheaths around an axon. It is an electrical insulator - stops charge escaping. AP jumps between node of Ranvier (myelin sheath means AP can jump to next bit with no myelin). Process of conduction is called saltatory conduction. More efficient as it used less energy.
What happens at the synapse?
Is a chemical transmission in the synapse. At axon terminal, voltage gated calcium channels are opened. When calcium comes into the cell, it allows synaptic vesicles to fuse with the membrane & neurotransmitters to be released from the cell. These diffuse across synaptic cleft and hit ligand-gated ion channel (open when certain molecule binds to them). Causes electrical signal in post synaptic cell. Change is either excitatory or inhibitory depending on neurotransmitter released.
What happens at the postsynaptic membrane (excitatory)
Depolarisation of dendrites by ion flow through glutamate receptors generate an excitatory post-synaptic potential. Glutamate is the main way to depolarise a cell.
What happens at the postsynaptic membrane (inhibitory)?
GABA is the main inhibitory transmitter in the brain. It opens chloride channels allowing negative charge into the cell, generating an inhibitory post-synaptic potential. This hyperpolarises the membrane.
