T3 (Fys) Varför så slapp?/Elektrochemistry Flashcards
What are the differences in responses of neurons when stimulated by a a) hyperpolarizing current b) depolarizing current?
a) passive response, shifting according to electrochemical grafient
b) active response, opening of ion channels
Describe the three different types of neuronal electrical signals/potentials which can be measured.
Receptor potential: eg. when microelectrode touches skin, potential difference +7mV over 25 ms, stepwise repolarization
Synaptic potential: eg. when microelectrode stimulates presynaptic contact to hippocampal pyramidal neuron, potential difference +5mV over 20 ms, uniform repolarization, all sensory neurons
Action potential: “Stimulation of spinal reflex causes action pitential in spinal lotor neuron”, 2 ms depolarization/repolarization
What happens with the membrane potential of a neurone when stimulated with a sub-threshold current?
Passive movement of current along the neuron (both ways?).
What is the basis for the all-or-none fashion of the action potential?
The following of Na influx by K efflux (hyperpolarization) since the change in membrane potential when Na-ions rish in induces K-ion channel activation.
Describe the Na- and K-channel during depolarization.
Na: Closed - open - inactivated (refractory period) - closed (uninactivated) (fast activation/inactivation)
K: Closed - closed - open - closed (slow activation/no specific inactivation)
How does the scorpions α-toxin and β-toxin work?
α-toxin: prolongs opening (slows the inactivation) of Na-channels but decreases change in potential
β-toxin: decreases threshold value closer to -80mV (vs. -50-(-40) mV)
What different voltage-gated ion channels are there in neurons? What are their functions?
Na-channel: different types help regulate the action potential persistency (rapidly inactivating, voltage sensitive etc.)
Ca-channel: mediate cell processes, most importantly release of neurotransmitter in synapse
K-channel: most numerous (nearly 100 known), inward rectifier, delayed rectifier, A channels
Cl-channels: control excitability, contribute to resting membrane potential, help regulate cell volume
Name the different types of ligand-gated ion channels and their functions.
Neurotransmitter receptor: reacts to for example glutamate
Ca-activated K-channel: responds to intracellular Ca, translates into electrical signal
Cyclic nucleotide-gated channel: responds to e.g. cAMP ans cGMP
What other stimulus can ion channels be dependent of?
Stretch (hair cells in concha) and heat.
What ATPase pumps, ion exchangers and co-transporters are found in neurons?
ATPase: Na/K pump, Ca pump
Ion exchanger: Na/Ca exchanger, Na/H exchangers
Co-transporter: Na/K/Cl co-transporters, K/Cl co-transporter, Na/neurotransmitter co-transporter
Describe the physiology and function of electrical synapses.
Electrical synapses are based on gap junctions formed by connexons. The joining of the itracellular space between the pre- and postsynaptic cell allows for charge propagation from the one to the other, and synchronized firing. Used in extensive networks in the brains gliacells and also found in hypothalamus (endocrine secreting).
Describe the physiology and function of the chemical synapse.
Based on the release of chemicals (neurotransmitters) into the synaptic cleft, the chemical synapse requires a pre-synaptic action potential that causes influx of Ca, and receptor-gated ion channels on the post-synaptic membrane. This allows for charge propagation from one cell to the next.
What is a co-transmitter. What could its function be?
Some neurons produce two or more neurotransmitters these are called co-transmitters. As different neurotransmitters are packaged separately the nerve response can change with increased firing intensity through release of different quantities and ratios of different neurotrandmitters.
Compare synthesis, transportation to nerve terminal, packaging and TEM graphing if small-molecule transmitters (SMT) and peptide transmitters (PT).
Synthesis: SMT enzymes are synthesized in the soma and transported by slow axonal transport (0.5-5.0 mm/day) to the nerve terminal where SMT precursors have been transported in, whilst PT enzymes AND precursors are synthesized in the soma and transported in vesicles by fast axonal transport (e.g. kinesin) down microtubules at up to 400m/day.
Packaging: SMTs are packaged into small 40-60 nm clear-core vesicles at the terminal whilst PTs are packaged in the soma into 90-250 nm large dense-core vesicles.
What three criteria define a neurotransmitter?
- The substance nust be present in the presynaptic neuron.
- The substance must be released in response to presynaptic depolarization and the release must be Ca-dependant.
- Specific receptors for the substance must be present on the postsynaptic cell.
EPPs are made up of multiple…
…MEPPs.
What is the duration and the reason for existence of the vesicle cycle.
1 minute. Vesicles are recycled due to transpirtstion from the golgi apparatus in the soma taking so long.
What are the steps of the vesicle cycle.
Endosome - budding - docking - priming - fusion (release of transmitter) - budding - endosome- …
What type of stimulation favours small-molecule neurotransmitters and what type of stimulation favours both?
Low-frequency stimulation induces the rekease of only small-molecule neurotransmitters while high-frequency stimulation induces the release of both small-molecule and peptide transmitters.
List some causes of myasthenic diseases.
Auto-immune decreasing of calcium ions (LEMS, Lambert-Eaton myastenic syndrome), AChase in congenital myasthenic syndrome and
What connects Latrodectism with schizophrenia?
In both conditions neurexin is thought to play a vital role. In latrodectism α-laterotoxin binds to neurexin on synaptotagmin (receptor part of Ca) whilst mutations in the neurexin gene is found in people suffering from schizophrenia.
Differentiate between ionotropic and metabotropic receptors.
Ionotropic receptors have transmitter binding sites connected directly to the ion channel and are fast, whilst metabotropic receptors aren’t connected to an ion channel but instead induce channel functions via G proteins (these are GPCRs) and are slower.
The action potential feedback cycle…
…
The conductance of the different ions in a neuron can be considered the same as what in physiological conditions?
The membrane permeability.
