How Nerves Work 3

Question 1

Examples of Graded Potentials
Where they occur
What their job is

Answer 1

Generator Potentials- at sensory receptors
Postsynaptic Potential- at synapses
Endplate Potential- at neuromuscular junction
Pacemaker Potential- in pacemaker tissues

Determine whether an action potential should be fired

Question 2

Four other Names for Graded Potentials

Answer 2

Electrotonic Potentials
Local Potentials
Decremental Potentials
Non-Propagated Potentials

Question 3

Describe Graded Potentials in Terms of the Decremental characteristic

Answer 3

The current released by the Graded potential weakens as it travels along the axon. This is due to he current leaking out (wasted current) so there is little to flow out the end. This means that Graded Potentials are only useful over very short distances.

Question 4

Describe Graded Potentials in terms of their Graded characteristic

Answer 4

Graded Potentials are called Graded because they can have different intensities of membrane potential (mV). A bigger stimulus will give a bigger response and vice versa. Therefore they can signal stimulus intensity in their amplitude.

Question 5

Describe two methods of hyperpolarising postsynaptic potentials and say if they are fast/slow and inhibitory/excitory postsynaptic Potentials

Answer 5

One way is to have a neurotransmitter bind to a receptor which opens the channel to let chloride ions into the cell which increases the internal negative charge, therefore hyperpolarising the cell. This triggers a fast IPSP.
When the channel and receptor are different proteins a G protein has to connect them and when this happens, K+ is released from the cell which increases the internal negative charge and hyperpolarises the cell. This triggers a slow IPSP.
These both stop the cell firing action Potentials.

Question 6

Describe two methods of depolarising postsynaptic potentials and say if they are fast/slow and inhibitory/excitory postsynaptic Potentials

Answer 6

A neurotransmitter binds to a receptor/ channel complex (non specific monovalent cation channel) and let’s sodium into the cell and potassium out of the cell. There is much more Na+ going in then K+ going out due to sodiums bigger equilibrium potential which creates a positive charge within the cell which depolarises it. This evokes a fast EPSP.

Receptor and channel coupled by G proteins close potassium channels so a positive charge remains in the cell so the cell depolarises. This evokes a slow EPSP

Question 7

Define Temporal Summation

Answer 7

A synapse is stimulated twice in order to add the Potential values together to reach the threshold to fire an action potential

Question 8

Define Spatial Summation

Answer 8

Two different synapses are stimulated and the depolarisation values from both are added together to reach the action potential threshold.

Note: Synapses closer to the axon Hillock will produce a larger response than those further away.