lec6- Animal nervous system part 2 Flashcards
why do action potentials not get smaller over time?
Action potentials propagate down the axon without getting smaller, because new action potentials are continuously generated along the axon membrane
what are the three steps to action potential propagation?
- Na+ enters the axon attracting negative charges and repelling positive charges
- Positive charges spread downstream, so the membrane downstream depolarizes
- More Na+ channels open in response to depolarization when the adjacent membrane reaches threshold, resulting in new action potential
why are action potentials unidirectional?
Action potentials are unidirectional due to the relative refractory period where hyperpolarization is making the membrane more negative than the resting potential meaning a stronger stimulus is required to raise membrane potential, and the absolute refractory period has inactivated Na+ channels that wont open for a while again, hence why action potentials can only go in one direction
how is information in the nervous system encoded?
by the frequency of action potentials
why do large diameter neurons transmit action potentials more frequently?
because they experience less resistance
what is wrapped around neurons in the peripheral nervous system?
schwann cells
what is wrapped around neurons in the central nervous system?
oligodendrocytes
what do the cells that wrap around neurons form?
myelin sheaths
what do myelin sheaths do?
act as insulation, preventing ion leaks
what are the Nodes of Ranvier?
the gap between the myelination that has a cluster of sodium and potassium channels
how does distance affect the amplitude of depolarization?
the longer the distance, the more the amplitude of depolarization decreases
are action potentials regenerated at each node?
Yes
what is saltatory action potential conduction?
action potentials being able to jump node to node due to the myelinated axons
why are action potentials quicker in myelinated axons?
- The myelination prevents ion leaks
- Action potentials regenerate at the next node of ranvier
- Signals continue to jump this way which is faster than an unmyelinated axon
what is multiple sclerosis (MS)?
it is a disease that destroys the oligodendrocytes that make myelin sheaths in the CNS, resulting in slow electrical signals
what is the synaptic cleft?
The gap between the Axon terminals and the dendrites
what do synaptic vesicles contain?
neurotransmitters
what is the presynaptic neuron?
The presynaptic neuron is the neuron with the axon terminal at the synapse
what is a postsynaptic neuron?
The postsynaptic neuron is the neuron on the other side of the synaptic cleft, has the dendrites
why are neural signals from neurotransmitters so fast?
because the neurotransmitters have to travel a short distance from presynaptic neuron to postsynaptic neuron
how is information transferred at the synapse?
- Action potential arrives at the end of the axon
- Depolarization causes voltage gated calcium channels to open
- In response to influx of calcium, vesicles fuse to presynaptic membrane and release neurotransmitters into synaptic cleft
- Neurotransmitters bind to receptors on postsynaptic membrane causing change in membrane and chance for triggering action potential
- Response ends when all neurotransmitters in synaptic cleft are either diffused away, digested, or taken up by presynaptic cell
what do neurotransmitters bind to?
ligand-gated ion channels or G-protein coupled receptors
what is EPSP (Excitatory postsynaptic potential)?
when the postsynaptic membrane is depolarized
what is IPSP (inhibitory postsynaptic potential)?
when the postsynaptic membrane is hyperpolarized
what do EPSP, IPSP, and both at the same time do?
EPSP make action potential likely, IPSP make action potential less likely, and both at the same time cancel out
what does SSRI drug do?
SSRI is an antidepressant drug that inhibits serotonin (neurotransmitter) reuptake to make it last longer in the synaptic cleft and have more activity
how are EPSPs and IPSPs graded?
in magnitude
what happens when multiple EPSPs occur close together?
higher chance for action potential
what is it called when EPSPs occur closely?
summation
how do neurons integrate information from many synapses?
via the axon hillock that receives IPSPs and EPSPs allowing integration from a wide array
