General Concepts of the PNS and Neurotransmitters Flashcards
Synaptic transmission
When signaling factors (neurotransmitters) are released from one neuron and bind to the receptors of another neuron across a synaptic cleft.
What determines how many transmitters should be released?
The amplitude of the action potential determines the amount of transmitters released.
What role does Ca++ play in synaptic transmission?
When the presynaptic AP depolarizes the membrane, it opens the voltage-gated Ca++ channels. The influx of Ca++ causes vesicles in the axon terminal of the presynaptic neuron to empty quantum of transmitters into the synaptic cleft.
What determines the action of a neurotransmitter?
Its receptors. One neurotransmitter can have different actions depending on the different receptors that bind it.
What are the two types of cholinergic synapses?
Nicotinic - on neurons and skeletal muscle Muscarinic - on body tissues and CNS neurons
What is an agonist substance? Give some examples.
A substance that mimics a naturally occurring signaling factor and binds to the same receptors to stimulate an action E.g. nicotine and muscarine can mimic acetyl choline
Which neurotransmitters are released at adrenergic synapses? What are they classified as?
The catecholamines: norepinephrine, epinephrine, and dopamine.
Which neurotransmitters stimulate adrenergic receptors?
Norepinephrine and epinephrine.
Which catecholamine has its own receptor?
Dopamine.
Describe the metabolism of ACh.
Choline acetyltransferase synthesizes ACh from acetyl CoA and choline in the presynaptic terminal. Acetylcholine esterase (AChE) breaks it down into choline and acetate in the synaptic cleft.
What is the action (type of neurotransmission) of a nicotinic receptor?
Ionotropic transmission: it opens up a Na+/K+ channel
What is the action (type of neurotransmission) of a muscarinic receptor?
Metabotropic transmission: uses G-proteins for its actions
Compare the duration of the effects of muscarinic and nicotinic receptors.
Nicotinic receptors: short-term synaptic effects Muscarinic receptors: prolonged synaptic effects
Where are nicotinic receptors located?
Autonomous ganglion neurons and skeletal muscles.
Where are muscarinic receptors located?
Throughout the CNS and in tissues innervated by postganglionic parasympathetic and some sympathetic neurons.
How do epinephrine and norepinephrine get removed from the synaptic cleft?
Reuptake or destruction by monoamine oxidase (MAO) or catechol-O-methyl transferase
Describe the sequence of catecholamine synthesis from tyrosine.
Tyrosine –> L-DOPA –> Dopamine –> Norepinephrine –> Epinephrine
What do adrenergic α1-receptors regulate?
Ca++ and K+ channels
What do adrenergic β-receptors regulate?
Smooth muscle, the heart, and metabolism.
What is the effect of propanolol on adrenergic receptors?
Blocks β-receptors to decrease heart rate.
Rank these transmitters in terms of duration of effects (shortest to longest): neuropeptides, adrenergic, and cholinergic transmitters.
Cholinergic, adrenergic transmitters, and neuropeptides
How do cocaine and amphetamine change the pathway for transmitters?
By blocking reuptake, which prolongs the action of the neurotransmitter.
How can enzymes change the duration of the neuropeptide transmitter effect?
The slow breakdown of neuropeptides by enzymes extends the effect.
Compare small molecule and neuropeptide transmitters in terms of synthesis and vesiculation.
Small molecule transmitters are synthesized and packaged in the axon terminal (with help from transported enzymes). Neuropeptide transmitters are transported as pre-peptides in vesicles from the cell body and are modified (by transported enzymes) in the axon terminal.