Neurotransmission Flashcards
Na+K+ depolarization and repolarization can be corrected ________.
Quickly
The Na+K+ pump accounts for __% of the ATP requirement of the nervous system
70%
Action potentials are propagated without _________ _______ and are _________.
Decreasing amplitude
Irreversible
When are voltage-controlled Na+K+ pump channels are closed?
During the resting stage
When the current is -70mV
What Na+K+ channels are always open?
Leakage channels
What is the propagation rate of an unmyelinated fiber?
Up to 2m/s
What kinds of responses are mediated by unmyelinated fibers?
Mediates slower, visceral responses
E.g. Secretion of stomach acid and the dilation of the pupils
What is the propagation rate of a myelinated fiber?
Up to 120 m/s
What kinds of responses are mediated by myelinated fibers?
Involved where speed is more important
E.g. motor to skeletal muscle, sensory signals for vision and balance
In the cell, neurotransmitters are contained in?
Synaptic vesicles
A synaptic vesicle contains how many molecules of this substance?
10,000 ACh (acetylcholine)
Hos does ACh “leave” a synaptic vesicle? And what do the released molecules do?
ACh quickly diffuses out by exocytosis and crosses the narrow gap and binds to the receptor proteins in the postsynaptic membrane
What is the refractory period?
A period of resistance to depolarization
What is the absolute refractory period?
A period of no stimulation
Why can’t the cell respond to stimulus during the refractory period?
The Na+ gates are open, so they cannot reopen as a response to a new stimulus
What is the relative refractory period?
A time when only an unusually strong stimulus can depolarize the membrane to provide a new action potential
“Maybe” a signal can be sent -Beachy
Why can signals be retransmitted during the relative refractory period?
The K+ gates are open, so an unusually strong stimulus can provide a new action potential
What is EPSP?
Excitatory postsynaptic potentials
Any voltage change in a positive direction which makes a neuron more likely to fire
These are graded, not all-or-nothing
What is summation?
A type of EPSP where the action potentials can be “added” together
Where does EPSP occur?
In the axon hillock or “trigger zone”
In EPSP what is “added up”?
Presynaptic potential
What is temporal summation?
The signal hits the same place, one after another
A single synapse generates many EPSP
What is spatial summation?
The signal hits different places at the same time
EPSP come from several different synapses at the same time
What is IPSP?
Inhibitory Postsynaptic Potentials
A hyperpolarizing of the postsynaptic membrane
What happens to the cell membrane in IPSP?
Membrane is more negative, so it’s less likely to fire
What molecules, and by what mechanism, does IPSP occur?
GABA and glycine both open chloride gates, so chloride ions flow in and hyperpolarize the postsynaptic membrane
What is presynaptic inhibition?
1 presynaptic neuron suppresses another presynaptic neuron
What is a neuromodulator?
Chemical messengers that have long-term effects on entire groups of neurons
What is substance P?
Facilitates transmission of pain signals to the brain
What is an endorphin?
Inhibits transmission of pain signals to the brain
What are the two categorizations of axonal transport?
Slow and fast
What is slow axonal transport?
0.5-10 mm/day, anterograde only
Transport from soma (cell body) to end bulb only
What is fast axonal transport?
200-400 mm/day, both anterograde and retrograde
What are two pathogens that attack humans via axonal transport?
tetanus: Bacterium, toxin from bacterium travels retrograde
rabies: virus, travels up axon (retrograde)
What is the difference between flaccid and spastic paralysis?
Flaccid paralysis: eg loose arm
Spastic paralysis: ex rigid arm
What is curare?
Arrowhead poison used in South America to hunt
How does curare affect the body?
Blocks ACh receptors in muscle (mirrors ACh)
Flaccid paralysis in resp muscles, then death
Is curare pre or postsynaptic?
Postsynaptic
What is botulism?
Food poising caused by the botulin bacterium
Is the most potent known microbial toxin
How does botulism affect the cell? And what kind of paralysis does it result in?
Blocks release of ACh @ presynaptic membrane
Flaccid paralysis
What is polio?
A virus destroys the motor neurons
Does polio result in flaccid or spastic paralysis?
Flaccid paralysis
What is tetrodotoxin?
Founnd in the skin and some organs of the puffer fish
What is the mechanism of tetrodotoxin?
A highly specific Na channel blocker.
Nerve fiber cannot generate and propagate an action potential
Is tetrodotoxin pre or postsynaptic? What kind of paralysis does it cause?
Postsynaptic
Flaccid paralysis
What is tetanus?
Toxin is tetanospasmin
What is the mechanism of tetanus?
Toxin blocks glycine release and this causes overstimulation (hyperpolarization)
What kind of paralysis comes from tetanus?
Spastic paralysis
What is MG?
Myasthenia gravis
Autoimmune disease of generalized muscle weakness
What is the mechanism of MG?
Muscle fibers become less and less susceptible to ACh
Is MG pre or postsynaptic?
Postsynaptic (the receptors on muscle fibers are destroyed)
What is used to treat MG and how does it work?
Use cholinesterase inhibitors to inhibit AChE, in the hope that more ACh can stimulate`
What is MS?
Multiple sclerosis
Degenerative disorder of myelin sheaths
Breakdown of myelin in CNS, replaced with hardened scar tissue
MS is a ________ disease which results in the loss of ______ function over time.
Progressive
Nerve
What are some symptoms of MS?
Doublevision, blindness, speech defects, tremors and numbness
What kind of synapse uses ACh?
Cholinergic
What kind of synapse uses NE?
Adrenogenic
