1. © 2013 Pearson Education, Inc. Chapter 18, Section 6 4/13/2013 Chemical Messengers Neurotransmitters Hormones Supplemental

2. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Chemical Messengers: for coordination of biological processes within an organism  Terms and Definitions:  neuron:  neuron: a nerve cell.  neurotransmitter  neurotransmitter: a chemical messenger between a neuron and another target cell; neuron, muscle cell or cell of a gland. - the molecule acts over a short distance (across a synapse, ~ 0.1 µm) Eg, Acetylcholine  hormone:  hormone: a chemical messenger released by an endocrine gland (secretary organ) into the bloodstream and transported there to reach its target cell (its site of action). over a long distance (~ 20cm). Eg, Insulin

3. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Chemical Messengers  Five Classes: :  Cholinergic Messengers: Acetylcholine, and likes  Amino acid Messengers: Glutamate, GABA, etc.  Adrenergic Messengers: Monoamines  Peptidergic Messengers: Insulin, Glucagon, etc.  Steroid Messengers: Androgen, Estrogen, etc.  Messengers are also classified by how they work;  activate enzymes.  affect the synthesis of enzymes.  affect the permeability of membranes.  act directly or through a secondary messenger.

4. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Chemical Communication  Many drugs used in medicine influence chemical communication  Antagonist:  Antagonist: a molecule that blocks a natural receptor and prevents its stimulation.  Agonist:  Agonist: a molecule that competes with a natural messenger for a receptor site; it binds to the receptor site and elicits the same response as the natural messenger.  A drug may decrease or increase the effective concentration of messenger.

5. © 2013 Pearson Education, Inc. Chapter 18, Section 6  A neurotransmitter 5

6. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Amine (Quaternary) as well as Esther the first neurotransmitter found (1914) by Henry Dale & Otto Loewi (NP, 1936)  communicate between the nervous system and the muscle.  When stimulated, it releases into the synapse where it binds to muscle cell receptors causing the muscles to contract. 6 Acetylcholine (ACh): the main cholinergic messenger

7. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Acetylcholine  The main cholinergic messenger is acetylcholine.  Cholinergic receptors  There are two kinds of receptors for acetylcholine.  We look at the one that exists in motor end plates of skeletal muscles or in sympathetic ganglia.

8. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Acetylcholine  Storage and release of acetylcholine (ACh).  The nerve cells that bring messages contain ACh stored in vesicles.  The receptors on muscle neurons are called nicotinic receptors because nicotine inhibits them.  The message is initiated by calcium ions, Ca 2+.  When Ca 2+ concentration becomes more than about 0.1  M, the vesicles that contain ACh fuse with the presynaptic membrane of nerve cells and empty ACh into the synapse.  ACh travels across the synapse and is absorbed on specific receptor sites.

9. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Acetylcholine  Action of the acetylcholine (cont’d)  The presence of ACh on the postsynaptic receptor triggers a conformational change in the receptor protein.  This change opens an ion channel and allows ions to cross membranes freely.  Na + ions have higher concentration outside the neuron and pass into the cell.  K + ions have higher concentration inside the neuron and leave the cell  This change of Na + and K + ion concentrations is translated into a nerve signal.  After a few milliseconds, the ion channel closes.

10. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Acetylcholine in Action

11. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Acetylcholine  Removal of ACh  ACh is removed from the receptor site by hydrolysis catalyzed by the enzyme acetylcholinesterase.  This rapid removal allows nerves to transmit more than 100 signals per second.

12. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Acetylcholine is linked to Alzheimer’s disease  In Alzheimer’s disease, ACh levels may decrease by 90%.  Aricept, an Alzheimer’s medication, slows the breakdown of ACh in order to elevate the acetylcholine levels in the brain. Acetylcholine 12

13. © 2013 Pearson Education, Inc. Chapter 18, Section 6  Include dopamine, norepinephrine, and epinephrine  All of these are closely related in structure and all are synthesized from the amino acid tyrosine. Catecholamines 13

14. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Dopamine  produced in the nerve cells of the midbrain and acts as a natural stimulant to give us energy and feelings of enjoyment.  Control muscle movement, improve, cognition, memory, & learning  Cocaine and amphetamine block the reuptake of dopamine resulting in a longer lifetime in synapse. 14

15. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Norepinephrine and Epinephrine  Norepinephrine (noradrenaline) and epinephrine (adrenaline) are hormonal neurotransmitters that play a role in sleep, attention and focus, and alertness.  Epinephrine is synthesized from Norepinephrine.  Both are normally produced in the adrenal glands.  Both are highly produced during the fight-or-flight response, increasing blood pressure, heartv rate, constrict blood vessel, dilate airways, stimulating breakdown of glycogen.  Administered during cardiac arrest.broncodialator.  Low level leads to Attention Deficit Disorder(ADD) 15

16. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Serotonin (5-Hydroxytryptamine)  Serotonin helps us relax, sleep deeply and peacefully, think rationally, and it provides us a feeling of well-being and calmness.  Serotonin is synthesized from the amino acid tryptophan.  Psychedelic drugs stimulate the action of serotonin at its receptors.  Low serotonin levels may be associated with depression, anxiety disorders, etc.  Prozac and Paxil (antidepressant drugs) are selective serotonin reuptake inhibitors (SSRIs). 16

17. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Prozac and Paxil 17

18. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Histamine 18  synthesized in the nerve cells in the hypothalamus from the amino acid, histidine.  is produced by the immune system in response to pathogens and invaders, or injury.  When it combines with histamine receptors, it produces allergic reactions – inflammation, watery eyes, itchy skin,.etc.

19. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Amino Acid Neurotransmitters Glutamate  the most abundant neurotransmitters in the nervous system.  stimulates the synthesis of nitrogen monoxide (NO). Both Glutamate & NO involved in learning and memory  Too much glutamate in the spinal cord causes degeneration of nerve cells (Lou Gehrig’s disease of Muscular atrophy).  Too rapid uptake of glutamate may results in schizophrenia: 19

20. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Gamma(  )-Aminobutyric Acid (GABA)  the most common inhibitory neurotransmitter in the brain.  produces a calming effect by inhibiting the ability of nerve cells to send electrical signals to nearby nerve cells.  Alcohol, & sedatives increases the inhibitory effects.  Caffeine decreases the GABA levels in the synapses causing opposite effects. 20

21. © 2013 Pearson Education, Inc. Chapter 18, Section 6 Gamma(  )-Aminobutyric Acid (GABA) GABA  the most common inhibitory neurotransmitter in the brain.  produces a calming effect by inhibiting the ability of nerve cells to send electrical signals to nearby nerve cells.  Alcohol, & sedatives increases the inhibitory effects.  Caffeine decreases the GABA levels in the synapses causing opposite effects. 21

22. © 2013 Pearson Education, Inc. Chapter 18, Section 6