Neurotransmitters Flashcards
About how many neurotransmitters are in the body?
100 chemical substances.
What are the 2 classes of neurotransmitters?
- Small molecules.
- Neuropeptides.
What are the characteristics of small molecules?
- Rapid acting.
- Acute responses of the nervous system.
ex: ACH, Dopamine.
What are the characteristics of neuropeptide molecules?
Slow/prolonged acting.
ex: CCK, GnRH.
Where are small molecules synthesized?
In the cytosol of presynaptic neurons.
What are small molecules absorbed by?
Active transport into vesicles.
What effect do small molecules normally have on post-synaptic neurons?
Increase or decrease conductance through ion channels.
What are the 2 types of neurons?
- Adrenergic.
- Cholinergic.
What 3 places are cholinergic neurons found?
- Sympathetic and parasympathetic preganglionic.
- Sympathetic postganglionic neurons that innervate sweat glands.
- All postganglionic parasympathetic glands.
What type of neurons secrete acetylcholine?
Cholinergic neurons.
What type of neuron are most postganglionic sympathetic neurons?
Adrenergic.
What are the 2 groups of neurons on the autonomic motor pathway?
- Preganglionic.
- Postganglionic.
Where are the cell bodies of preganglionic neurons?
In the brain or spinal cord.
How do the axons of preganglionic nerves exits the CNS?
Via cranial and spinal nerves.
What type of fibers compose preganglionic neurons?
Type B fibers.
Where to the synaptic end buttons of preganglionic neurons end?
Autonomic ganglia.
Where are the cell bodies of postganglionic neurons?
In the autonomic ganglion.
How many preganglionic axons is a postganglionic neuron cell body synapsing with?
1 or more.
What type of fibers compose postganglionic axons?
Type C fibers.
Where do the synaptic end bulbs of postganglionic neurons terminate?
In the visceral effector.
Where does the sympathetic division of the ANS originate?
The 12 thoracic segments and first 3 lumbar spinal segments.
*Thoracolumbar division.
Where does the parasympathetic division of the ANS originate?
The 4 cranial nerves and sacral segments 2-4.
*Craniosacral division.
What are the two types of cholinergic receptors?
- Nicotinic.
- Muscarinic.
Where are nicotinic receptors found?
- Dendrites and cell bodies of the sympathetic and parasympathetic postganglionic neurons.
- Motor end plate at neuromuscular junction.
What substance mimics the action of Ach by binding these receptors?
Nicotine.
Where are muscarinic receptors found?
- Effectors innervated by parasympathetic postganglionic neurons.
- Sweat glands.
What poison mimics the action of Ach binding?
Muscarine, a mushroom poison.
Are nicotinic receptors used for activation, inhibition, or both?
Activation.
What kind of action do nicotinic receptors stimulate in the nerve fiber?
Depolarization through increased Na+ permeability that leads to excitation of the postsynaptic cell.
Are muscarinic receptors used for activation, inhibition, or both?
Both.
What is an example of an excitatory muscarinic receptor?
Smooth, circular muscles of the iris to contract due to decreased K+ conductance.
What is an example of an inhibitory muscarinic receptor?
Inhibits/relaxes smooth muscles of GIT sphincters through increased K+ conductance.
Where is Ach synthesized?
In the presynaptic terminal.
What is Ach a combination of?
Acetyl-CoA and Choline.
What enzyme is key in the synthesis of Ach?
Choline acetyltransferase.
Where is norepinephrine released from?
Adrenergic neurons.
Where is norepinephrine synthesized and stored?
In synaptic vesicles.
What 2 neurotransmitters bind to adrenergic receptors?
- Epinephrine.
- Norepinephrine.
*Are both also hormones when released from the adrenal medulla.
What are the two main types of adrenergic receptors?
- a.
- B.
Where are adrenergic receptors found?
On visceral effectors.
What do a1 receptors stimulate?
Ca2+ release.
What do a2 receptors stimulate?
Decreased cAMP.
What do B1 and B2 receptors stimulate?
Increased cAMP.
Which type of receptor is stimulated more strongly by norepinephrine?
Alpha receptors.
What terminates norepinephrine activity?
- Reuptake by the axon that released it.
- Catechol-O-methyltransferase or Monoamine oxidase enzymatically degrades it.
What type of receptor is stimulated more strongly by epinephrine?
Both alpha and beta receptors are strongly stimulated.
