L20 - Action Potentials Flashcards
What is a neuron?
A cell specialized to conduct electrochemical impulses called nerve impulses or action potentials
What does the neuron cell body consist of?
Soma (contains the nucleus)
Dendrites (receive information, the hairy projections of the soma)
Axon (fiber that extends from soma to connect signals to other neurons)
What is the Myelin sheath in the neuron responsible for?
Connect with other cells and membrane surfaces
Important for transmission of nerve impulses or action potentials
How do transmembrane proteins permeate the membrane?
Ion channels
What is the resting potential (homeostasis) of an ion?
-70 microvolts (MV)
True or false, any ion can permeate gated-ion channels
False
What are the key steps for the generation of an action potential?
- Chemical stimulus applies
- Membrane potential breaks threshold (goes from -70 to -60mV)
- When the voltage reaches the threshold ion channels enter, allowing positive ions to rush into the cell
- Once it reaches the peak it returns to normal.
What happens if the membrane potential doesn’t reach -60 mV when trying to generate an action potential?
It doesn’t reach the threshold and it returns to the resting membrane potential (-70mV)
Where along the neuron does the action potential travel to connect with another neuron?
The axon
What chemical rushes into a neuron when the action potential threshold is reached?
Sodium (Na+)
After an action potential, what is the term for the membrane potential returning to normal?
Hyperpolarization
What is the term for when Sodium enters and an action potential is rising (getting closer to 0)?
Depolarisation
What chemical enters once the action potential reaches its peak (30mV) to return the membrane potential to normal?
Potassium
Explain the steps of repolarisation
When does it happen exactly?
At 30mV voltage-gated potassium channels open
Potassium (+) move OUT of the cells (repolarization)
Membrane potential drops
During depolarisation, the membrane is within the absolute refractory period. What does this mean?
The membrane cannot respond to further simulation
During repolarization the membrane is in the relative refractory period, what does this mean?
The membrane can respond to larger than normal stimulus.
A stronger response requires a stronger action potential.
True or False
False
A stronger response has a quicker ‘rate’ at which action potentials occur.
Summarise the ion channels opening and closing during an action potential.
Sodium (Na) channel opens
Potassium (K) channel opens
Sodium channels inactive
Potassium channels inactive
What are the two properties that determine the velocity of propagation of an action potential?
Myelination (faster in myelinated axons than unmyelinated)
Diameter (faster in larger diameter axons than smaller diameter axons)
Where does the action potential occur?
Only at the nodes of Ranvier
What is the all-or-none law for action potentials?
The size of the action potential is unaffected by increases in the intensity of stimulation beyond the threshold level.
What is the refractory period?
A period during which further stimulation cannot cause another action potential.
How is the strength of a stimulus conveyed with action potentials?
Conveyed by the rate of neural firing (spikes/sec)
What is synapatic transmission?
Sending of action potential to other neurons so it can travel in the brain.
Where does synaptic transmission occur?
At the axon terminals which are at the tips of the axon’s branches
What does pre-synaptic and post-synaptic mean?
Pre-synaptic = where it’s coming from
Post-synaptic = where it’s going to
Is synaptic transmission chemical or electrical?
Chemical
It uses calcium (positive)
What are the steps of synaptic transmission?
- Arrival of action potential at axon terminal
- Voltage-gated Ca2+ (calcium) channels opsn and Ca2+ enters presynaptic neuron
- Neurotransmitter released into synaptic cleft (via exocytosis)
- Synaptic vesicle fuses to cell membrane
What part of the synaptic process determines the effect of the neurotransmitter?
The synaptic receptor
(not the neurotransmitter per se)
What are the 4 types of neurotransmittors than neurons can produce (biochemical classification)
amino acids (e.g. GABA)
monoamines (e.g. dopamine)
acetylcholine (own class)
neuropeptides (larger molecules, e.g. oxycocin)
What are Glial cells useful for?
They are a structural support cell (glial = glue)
Form things like the blood-brain barrier and help guide neurons during development.
(10x more of these than neurons)
