Cell Membrane, Action Potential, Neurotransmitters Flashcards
Difference between chemical transmission and electrical transmission of an action potential?
Chemical transmission: slower, uses chemical messengers called neurotransmitters to bind to receptors on postsynaptic neuron. Ions stimulated by chemical messengers–neurotransmitters
Electrical transmission: faster, more direct, uses direct flow of ions to cross the synapse without neurotransmitters. Use GAP JUNCTIONS. Ions directly moving.
Where are neurotransmitters synthesized and where are they stored?
Synthesized: in presynaptic neuron cell body or axon terminal
Stored: vesicles of presynaptic neuron (held by SNARE proteins)
Steps of chemical transmission
- Action potential comes down axon and causes PRESYNAPTIC membrane to DEPOLARIZE
- VOLTAGE-gated CALCIUM channels open
- Calcium flows into neuron
- Calcium concentration increases leading to PHOSPHORYLATION of SNARE complex proteins. Conformational change that releases them from being bound to the cytoskeleton
- Vesicles migrate to the presynaptic membrane
- Vesicles fuse with the cell membrane and release their neurotransmitter molecules into the synaptic cleft
- Neurotransmitters cross the synaptic cleft to BIND with POSTSYNAPTIC RECEPTORS
- Receptor binding opens LIGAND ion channels leading to ion flux and generation of postsynaptic potential for the next neuron
What are the usual methods for termination of neurotransmitters? Which neurotransmitter is the exception to this and what is its method of termination?
Usual method of termination is by reuptake of excess neurotransmitters by the presynaptic neuron OR glial reuptake (taken by other cells) OR simple diffusion
Acetylcholine is the exception in this case as it requires hydrolysis degradation by acetylcholinesterase to cleave it into acetate and choline and render it inactive.
Steps of electrical transmission
- Impulse arrives at presynaptic terminal and changes the charge/potential
- Change in potential causes ions to flow across GAP JUNCTION to next neuron
Note: these gap junctions contain GATED CHANNELS to allow for one-way traffic
Major monoamine neurotransmitters. What does “monoamine” mean?
Major monoamine neurotransmitters: dopamine, serotonin (5-HT), epinephrine, norepinephrine
Monoamines mean they are all derived from amino acids
Two divisions of monoamines?
Based on amino acid precursors:
(Synthesis of catecholamines) Phenylalanine –> tyrosine: dopamine, norepinephrine, epinephrine
Tryptophan precursor: serotonin
Order of transmitters synthesized in catecholamine synthesis
Phenylalanine –> tyrosine –> DOPA (offshoot: melanin) –> dopamine –> norepinephrine –> epinephrine
Note: with the exception of DOPA to melanin via tyrosinase, the enzymes describe the substrate making the product. Know what order the products are in and the enzyme names will be intuitive
What products can be derived from tryptophan?
Serotonin, then serotonin can be converted into melatonin
Acetylcholine responsible (in part) for which part of the nervous system. What is acetylcholine’s main function/role in the body?
Parasympathetic system. Responsible for skeletal muscle contraction.
How is acetylcholine activity stopped?
Taken out of the synaptic cleft through hydrolysis degradation. The enzyme acetylcholinesterase (AChE) hydrolyzes acetylcholine to acetate and choline.
What happens if there is a dysfunction of acetylcholine degradation?
Muscle remains in a state of constant contraction, cannot repolarize and relax
What neurotransmitter is nicotinic and muscarinic receptors associated with? What is the difference between the receptors?
Associated with ACh. Nicotinic and muscarinic receptors are the two main classes of ACh receptors.
Nicotinic receptors are IONOTROPIC–meaning they bind ACh or nicotine and the pore opens. Binding is directly responding for the channel opening and the flow of ions. Rapid action
Muscarinic receptors are METABOTROPIC–meaning an indirect mechanism of signal transduction via G-proteins to move ions. Slower
What happens when nicotinic receptor is impaired?
Acetylcholine cannot bind, acetylcholine responsible for muscle contraction, therefore muscle contraction cannot happen. Relaxation of skeletal muscle. Ion channel is closed
Dopamine responsible for which part of the nervous system. What is dopamine’s main function/role in the body?
Excitatory neurotransmitter of the central nervous system. Controls limbic system (emotional response/pleasure) and voluntary movement
What three pathways are associated with dopamine?
Mesocortical pathway: executive function/thinking
Mesolimbic pathway: behavior and mood
Nigrostriatal: normal movement
4 ways to affect neurotransmitter concentration?
- Rate of synthesis
- Rate of release
- Uptake to presynaptic cell
- Degradation
Tyrosine hydroxylase deficiency results in deficiency of what neurotransmitter? How can you get around this?
Dopamine. Supplement with DOPA. But remember excess dopamine is toxic to the body when in the bloodstream. To solve this, give an inhibitor that does not work in the brain. Transport to the brain and convert DOPA to dopamine. Keep DOPA in bloodstream
Glutamate responsible for which part of the nervous system. What is glutamate’s main function/role in the body?
Glutamate the most important excitatory neurotransmitter in the central nervous system. Acts on both ionotropic and metabotropic receptors.
Precursor for GABA?
Glutatmate
How is glutamate implicated in excitotoxicity?
Nerve cells are damaged by excess glutamate because excess glutamate causes activation of NMDA receptor and excessive spike in calcium intake. Excessive calcium and overstimulation causes apoptosis. Also NMDA produces nitric oxide
What part of the nervous system does GABA function and what is its primary role?
Central nervous system, main inhibitory transmitter.
Associated neurotransmitter to GABAa and GABAb receptors and what makes them different? What makes them the same?
Associated neurotransmitter: GABA
GABAa: ionotropic, GABA binds to GABAa and ion channel opens. CHLORIDE enters the cell. – decreases transmembrane potential and inhibits the generation of action potentials
GABAb: metabotropic, mediated by G-protein. opens POTASSIUM channels. Potassium leaves cell and transmembrane potential decreases and inhibits AP generation.
Same: inhibitory effect, lowers transmembrane potential
Difference: ionotropic/metabotropic, Cl enter/K exit
What part of the nervous system does norepinephrine play a role in? What is the main function of norepinephrine?
Major neurotransmitter of the sympathetic nervous system. Induces response known as the “fight-or-flight response”
What receptors does norepinephrine bind to? Where are these receptors? Where else does norepinephrine go to?
Noradrenergic receptors of the post synaptic membrane. Also circulated as a hormone. Dopamine also circulated as a hormone just fyi
Function of monoamine oxidase inhibitors?
MAO inhibitors prevent the catabolism of catecholamines (dopamine, norepinephrine, epinephrine) and serotonin. Leads to build up of these neurotransmitters in the vesicles and eventually when released increased concentration in the synapse.
Serotonin nervous system involvement and main function of serotonin
Also known as 5-HT. CNS. Excitatory neurotransmitter. Involved in mood, appetite, and sleep.
