Topic 4: Synaptic Signalling Flashcards
what are the 3 type of neutrons and wha do they do?
motor (efferent) - from CNS to PNS
sensory (afferent) - from PNS TO CNS
interneurons - stays in CNS and connects sensory and motor
how does an action potential get generated?
by all or nothing signal when the cell gets depolarized, meaning the ions channels open allowing them to leave or enter the cell have making the membrane more positive, specifically the voltage gated Na+ channels
how does an action potential propagate?
unidirectionally, thanks to the inactivation of the sodium channels during the refractory period
when does the delayed K channel open?
after the peak at +50 mV
how can an action potential be measured?
The resting potential is -60mV, an action potential is determined when the membrane potential reaches +50mV.
what is the structure of voltage gated Na+ channels?
- voltage sensors: 4 alpha helixes and one of them is specially called the S4 helix, which is positive
- central channel: the 2 alpha helixes that will actually open and close, they contain selectively filter
- inactivation gate connected to he central channel and the voltage sensors
what are the states of the of the voltage Na+ channels?
- closed
- open
- inactive
describe the closed state of the Na channel (when is occurs and how)
in rest, the extracellular space side of the membrane is positive and the cytosolic is negative. The S4 voltage sensor holds the central channel closed.
describe the open state of the Na channel (when is occurs and how)
when the membrane is depolarized, the charges on each side of the membrane switch, this allows the negative charge now on the extracellular side to pull the S4 helix, which opens the central channel
describe the inactivated state of the Na channel (when is occurs and how)
when the membrane is in refractory, the sides of the membrane are still switched (ES negative, C positive) but inactivation gate plugs the central channel
how does Na+ channels contribute to the action potential
the rushing of the sodium into the cytosol makes it more positive and that causes the depolarization, the inactivation allows the K to come backing the cell to get repolarized
how are neurotransmitters released from and imported into synapses?
- an action potential propagates through the presynaptic nerve when it reaches the axon terminal, it imitates exocytosis of the neurotransmitter from the synaptic vesicles
- they then travel across the synaptic cleft into canal and receptors of the post synaptic cell
what is the role of calcium in synaptic signalling?
it opens calcium induced calcium channels in the sarcomere
why do nerves have mylein sheaths?
myelin does not conduct electricity so it allows the action potential to jump those sections and go faster, this is called saltatory conduction
where are neurotransmitters derived from?
amnio acids
what is an excitatory neurotransmitter?
they open cation channels to depolarize a cell (usually Na+ and Ca2+)
what is an inhibitory neurotransmitter?
opening of K+ or Cl- channels making the membrane hyperbolized so its harder to depolarize
what is the structure of a sarcomere? (4 minors)
titin- extends through the myosin bundle and attaches to the z line (helps prevent tearing)
nebulin- binds actin filament to z line
tropomodulin -caps the - end of actin and regulates the length of the actin filament
capz - caps the actin the plus end
what is the structure of a sarcomere (major)
actin - thin filament
myosin - thick filament
z disk - ends of the sarcomere
m line - middle of sarcomere
troponin- when activated by calcium, moves tropomyosin
tropomyosin - lies along the actin filament covering the binding spot
how does ca+ affect a sarcomere?
it binds to troponin complex, which changes its configuration for ti to move tropomyosin off the actin-myosin binding spot
describe the way a sarcomere contracts
1) ATP binds to myosin releasing it from the actin
2) ATP hydrolyzes giving the myosin head the energy for it to get in the cocked position
3) Ca2+ binds to the troponin allowing it to move tropomyosin off the myosin/actin binding site and powerstroke happens
4) another ATP comes & unbinds myosin from actin
what are 2 diseases that come from demylenation?
- multiple sclerosis: immune system attacks myelin in CNS
- gullian-barre syndrome- immune system attacks myelin in the PNS (temporary and virus caused)
