Week 3 - Nervous System (signalling) Flashcards
What is the typical RMP of a neuron?
-70mV
What is the function of a neuron?
Neuron are specialised cells that receive and transmit electrochemical signals.
What factors cause the resting membrane potential and what two transport mechanisms are invovled?
The resting membrane potential of -70mV is cause by the unequal distribution of Na+ and K+ ions across the plasma membrane. This is caused by:
• Na+ and K+ leak channels
• Na+ and K+ pump (3Na+ our 2 K+ in)
Why is the membrane more permeable to K+ when compared to Na+?
There are more K+ leak channels.
What prevents the Na+ and K+ gradients from dissipating considering the presence of leak channels which are always open?
The sodium potassium pump
What the major intracellular and extracellular ion?
- Intracellular: K+
* Extracellular: Na+
What is an action potential in terms of membrane potential?
Is the change in membrane potential from resting (-70mV) to a peak value of 30mV.
What channels are important for an action potential to initially occur?
Voltage gated Na+ channels
What is the threshold potential in terms of Na+ voltage gated channels?
Is the voltage at which the Na+ voltage gated channels open up to cause an influx of Na+ ions
What are graded membrane potentials?
Are membrane potentials that vary in size and direction
What causes changes in graded membrane potential?
The binding of neurotransmitter opens ligand gated channels.
What kind of ligand gated channels are bound by excitatory and inhibitory neurotransmitters?
- Excitatory - Na+ or Ca2+
* Inhibitory - K+ or Cl-
What is the difference between depolarisation and hyperpolarisation?
Depolarisation makes the membrane potential more positive, whereas hyperpolarisation makes the membrane potential more negative.
What role does calcium play at the pre synaptic axon terminal?
It is necessary for neurotransmitter release.
What is the threshold membrane potential?
-55mV
Where in the neuron is the action potential initiated?
At the axon hillock
Why is the axon potential initiated at the axon hillock?
That is where the density of the Na+ voltage gated channels is at there highest.
How does the action potential move along the axon?
Depolarization causes neighboring Na+ voltage gated channels to open which causes the action potential to travel down the length of the axon
What are the 5 stages of an action potential and what channels are open?
- Resting potential - Na+ and K+ leak channels are open
- Threshold - Some of the Na+ voltage gated channels are open
- Depolarisation - Na+ voltage gated channels open
- Reploarisation - K+ voltage gated channels open
- Hyperpolarisation - K+ voltage remain open which causes the membrane to become more negative that threshold.
What reestablishes the resting membrane potential after hyperpolarisation.
The sodium potassium pump and natural permeability of Na+ and K+ through their respective leak channels.
What is the absolute refractory period?
Is a period of an action potential in which a neuron cannot generate an action potential
What is the relative refractory period?
Is a period of an action potential in which a stronger than normal stimulus is required to generate an action potential.
What causes the absolute refractory period?
The inactivation of Na+ voltage gated channels whilst the K+ voltage gated channels remain open.
What causes the relative refractory period?
Not all Na+ voltage gated channels have recovered from inactivation and some of the K+ voltage gated channels remain open.
What are the three stages of activation of Na+ voltage gated channels?
- Open - can’t be stimulated
- Closed
- Inactivated - can’t be stimulated
Define conduction velocity
Is the speed that an action potential travels along an axon
When and why are fast neural signals important?
For fast conduction of neural pathways associated with things such as reflexes or motor movements.
When and why are slow neural signals used?
Used for things where fast responses are not essential such as the the stimulation of smooth muscles in the digestive tract.
What are the two factors that influence conduction velocity along a neuron?
- Axon diameter - larger axons have faster speed of transmission
- Myelination - myelinated axons have enhanced speed of neural transmission
How does the diameter of the axon affect conduction velocity?
Larger diameter axons have enhanced conduction speed as there is lees resistance to the flow of ions and thus adjacent areas of the membrane can be brought to threshold quicker.
What is the function of the myelin sheath?
To insulate the axon and enhance the speed of neural transmission.
How does the myelin sheath enhance the speed of neural transmission?
Prevents charge the leakage and charge only has to be generated at the nodes of ranvier
What type of conduction occurs in un-myelinated axons?
Continuous conduction
What type of conduction occurs in myelinated axons
Saltatory conduction
How is the intensity of a stimulus determined?
Based on the frequency of stimulation
• Low frequency is a small stimulus
• High frequency is a large stimulus
What are the three mechanisms that deactivate neurotransmitters after their release?
1) Re-uptake
2) Degradation
3) Diffusion
Define graded potential
Is the local changes in membrane potential that occur as a result of neurotransmitters binding to ligand gated ion channels.
Define excitatory postsynaptic potentials (EPSP)
The binding of neurotransmitters to ligand gated ion channels that causes the membrane potential to become more postively charged (depolarised) - increases the likelihood of an action potential occuring.
Define inhibitory postsynaptic potentials (IPSP)
The binding of neurotransmitters to ligand gated ion channels that causes the membrane potential to become more negatively charged (hyperpolarised) - decreases the likelihood of an action potential firing.
What ions become more permeable during an EPSP?
Na+ and Ca2+
What ions become more permeable during an IPSP?
K+ and Cl-
Define summation
Is the addition or combined effect of excitatory or inhibitory signals that results in changes in the post-synaptic membrane potential.
What is spatial summation?
Occurs when multiple synapses within close proximity are simultaneously stimulated
What is temporal summation?
Occurs when the same synapse is repeatedly stimulated
What are the different kinds of neuron summation?
- Spatial summation
* Temporal summation
At what voltage do the Na+ voltage gated channels become inactivated?
+30mV
