physiology notes: neurotransmitters
- Acetylcholine: excitatory neurotransmitter in the CNS and neuromuscular junctions; can be excitatory or inhibitory in the autonomic system depending on the organ involved.
(1).ligand gated channels-nicotinic acetylcholine receptors: acetylcholine binds, Na+ enters, K+ leaves; more Na+ comes in producing EPSPs; in neuromuscular junctions.
(2).G-protein mediated channels- muscarinic acetylcholine receptors:
Acetylcholine binds, activating a G-protein; 1 type opens K+ channels
Letting K+ out causing an IPSP; others close K- channels causing EPSPs;
(3). Acetylcholinesterase: degrades acetylcholine; otherwise paralysis in muscle cells could result
- Monoamines: from amino groups; (similar in action to acetylcholine)
(1). Second messenger mediation: work through 2nd messengers; binding of neurotransmitter activates a cascade of enzymes generating cyclic AMP
(second messenger); cyclic AMP causes ion channels to open.
(2). Monoamine inactivation: monoamines reabsorbed by presynaptic cell and degraded by the enzyme monamine oxidase (MAO).
(3). Serotonin: involved in mood, behavior, appetite, cerebral circulation
(4). Dopamine: 2 separate systems; one involved in control of movements, one involved in behavior and reward
(5). Norepinephrine: general arousal
c.Amino acids: some are neurotransmitters, some create EPSPs, others generate IPSPs by opening voltage gated Cl- channels.
- polypeptides: small polypeptides used as that may act as analgesics, endogenous opioids
- nitric oxide: NO, a gas diffuses out of presynaptic cell and into postsynaptic cell; causes muscle relaxation; can produce engorgement of
spongy tissue with blood