Page 458 - Fundamentals of anatomy physiology

Chapter 12 Neural Tissue 445

Table 12–4 (continued)

Class and Mechanism Location(s) Comments
Neurotransmitter Chemical Structure of Action

Neuropeptides Arg Pro Lys Pro Glu Glu Phe Phe Indirect: G proteins and CNS: Synapses of pain receptors within Important in pain pathway,
Substance P second messengers spinal cord, hypothalamus, and other regulation of pituitary gland
Gly areas of the brain function, control of digestive tract
Met Leu PNS: Enteric nervous system (network reflexes
of neurons along the digestive tract)

Neuropeptide Y 36-amino-acid peptide Indirect: G proteins and CNS: hypothalamus Stimulates appetite and food
Opioids 31-amino-acid peptide second messengers PNS: sympathetic neurons intake
Indirect: G proteins and
Endorphins second messengers CNS: Thalamus, hypothalamus, brain Pain control; emotional and
Enkephalins stem, retina behavioral effects poorly
understood
Endomorphin
Tyr Gly Gly Phe Indirect: G proteins and CNS: Basal nuclei, hypothalamus, Pain control; emotional and
Dynorphin second messengers midbrain, pons, medulla oblongata, behavioral effects poorly
Met Indirect: G proteins and spinal cord understood
second messengers
9- or 10-amino-acid peptide CNS: Thalamus, hypothalamus, basal Pain control; emotional and
nuclei behavioral effects poorly
understood

Tyr Gly Gly Phe Leu Arg Arg Ile Indirect: G proteins and CNS: Hypothalamus, midbrain, medulla Pain control; emotional and
second messengers oblongata behavioral effects poorly
understood 12
Arg
Gln Asn Asp Trp Lys Leu Lys Pro

Purines (see Figure 2–25) Direct or indirect (G CNS: Spinal cord
ATP, GTP (see Figure 2–25) proteins), depending on PNS: Autonomic ganglia Produces drowsiness; stimulatory
type of receptor CNS: Cerebral cortex, hippocampus, effect of caffeine is due to
Adenosine Peptide containing fewer Indirect: G proteins and cerebellum inhibition of adenosine activity
than 200 amino acids second messengers
Hormones
ADH, oxytocin, Typically indirect: G proteins CNS: Brain (widespread) Numerous, complex, and
insulin, glucagon, and second messengers incompletely understood
secretin, CCK, GIP,
VIP, inhibins, ANP, CO Indirect: By diffusion to CNS: Brain Localization and function poorly
BNP, and many NO enzymes activating second PNS: Some neuromuscular and understood
others messengers neuroglandular junctions
Gases Indirect: By diffusion to CNS: Brain, especially at blood vessels
Carbon monoxide enzymes activating second PNS: Some sympathetic
(CO) messengers neuromuscular and neuroglandular
junctions
Nitric oxide (NO)
O Indirect: G proteins and CNS: cerebral cortex, hippocampus, Euphoria, drowsiness, appetite;
Lipids NH OH second messengers
Anandamide cerebellum receptors are targeted by the

CH3 active ingredient in marijuana