THE NEURON :D “the basic working unit of the brain”

1. Neuroscience Society THE NEURON :D“the basic working unit of the brain”

2. Neurons • Transmit information to other nerve cells, muscle, or gland cells • between 1 billion and 100 billion neurons, depending on the species (humans = 100 billion)

3. Parts of a Neuron • Cell body • Cytoplasm • Nucleus • Dendrites • Receive messages • Axon • Transmit messages • End at nerve terminals • Synapse: contact points

4. Myelin Sheath • Axons are covered with myelin sheath • Speed transmissions of electrical signals along axons • Two types of cells: • Oligodendrocytes: brain • Schwann: peripheral nervous system

5. Action Potential • Ion channels:selectively permeable, water-filled molecular tunnels that pass through the cell membrane and allow ions — electrically charged atoms — or small molecules to enter or leave the cell. • Ability to generate electrical impulse: charge b/e inside and outside of cell • Nerve impulses  dramatic reversal in electrical potential (internal negative to positive) • Action potentials pass along axon at speeds up to several hundred miles per hour

6. Neurotransmitters • Brain’s “chemical messengers” • Voltage changes trigger release • Released at nerve terminals  diffuse across intrasynaptic space  bind to receptors • Neurotransmitter : receptor :: key : lock • triggers a response, such as the generation of an action potential, contraction of a muscle, stimulationofenzyme activity, or inhibition of neurotransmitter release from the target cell

7. Acetylcholine • First neurotransmitter. Identified 75 yrs ago • Released by neurons connected to voluntary muscles & muscles that control heartbeat • Formed at axon terminals • Action potential  calcium ion rushes in  ACh is released into synapse  attach to ACh receptors  broken down by acetylcholinesterase

8. Acetylcholine • Myasthenia gravis • Caused by antibodies that block ACh receptors • Fatigue and muscle weakness • Alzheimer’s • ACh-releasing neurons die • Drugs that inhibit acetylcholinesterase

9. Amino Acids • Building blocks of proteins • INHIBITORS: • Glycine • Gama-aminobutyric acid (GABA) • Activity increased by benzodiazephines (eg. Valium) & anticonvulsunt drugs • Huntington’s Disease: hereditary disorder (midlife). GABA-producing neurons in brain regions that coordinate movement degenerate  uncontrollable movements • ACTIVATORS: • Glutamate • Aspartate • Activate N-methyl-d-aspartate (NMDA)receptors

10. Catacholamines • Dopamine and Norepinephrine in brain and peripheral nervous system • Dopamine’s three circuits: • 1) control movement • 2) psychiatric symptoms (psychosis) • 3) regulate hormonal responses • Norepinephrine: • Defincies occur in patients with: Alzheimer’s, Parkinson’s, and Korsakoff’s Syndrome (cognitive disorder associated with chronic alcoholism) • Acute stress increases release from sympathetic nerves and the adrenal medulla

11. Catacholamines • 1) Dopamine deficits  Parkinson’s Disease • muscle tremors, rigidity, and difficulty in moving • Levodopa: a substance from which dopamine is synthesized • 2) Abnormalities  Schizophrenia • drugs that block certain dopamine receptors in the brain are helpful in diminishing psychotic symptoms • 3) regulate endocrine system • dopamine directs the hypothalamus to manufacture hormones and hold them in the pituitary gland for release into the bloodstream or to trigger the release of hormones held within cells in the pituitary

12. Serotonin • Present particularly in blood platelets and the lining of the digestive tract • Controls switches affecting various emotional states • Fluoxetine and other drugs that alter seretonin’s actions relieve symptoms of depression and OCD

13. Peptides • Chains of amino acids linked together • Enkephalin: opiate produced by brain and resembles morphine (opium derivative used to kill pain). Means: “in the head” • Endorphins: Act like opium or morphine to kill pain or cause sleepiness. Name comes from endogenous morphine • Opiod peptides may explain why injuries received during stress combat

14. Peptides • Activated by painful or tissue-damaging stimuli • Signals transmitted to central nervous system by special sensory neurons, small myelinated fibers, and tiny unmyelinated C fibers • Some C fibers contain peptide called substance P which causes sensation of burning pain • Active component of chili peppers (capsaicin) causes release of substance P

15. Trophic Factors • Small proteins in the brain • Necessary for the development, function, and survival of specific groups of neurons • Information about these proteins will be useful to design new therapies for degenerative diseases including Alzheimer’s and Parkinson’s

16. Hormones • Endocrine system = major communication system • SOURCES OF HORMONES: pancreas, kidneys, heart, adrenal glands, gonads, thyroid, parathyroid, thymus, and pituitary gland • Pituitary secretes hormones into blood • Endorphins are released from pituitary so they can be hormones too • System important for: basic behavioral activities and regulation of body functions

17. Hormones • Brain contains receptors for thryoid hormones and six classes of steroid hormones: androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, and vitamin D • Metabolic hormones: insulin (regulates glucose), insulinlike growth factor, ghrelin(stimulates hunger), and leptin(regulates energy intake)

18. Hormones • In response to stress and changes in our biological clocks, such as day and night cycles and jet lag, hormones enter the blood and travel to the brain and other organs • hormones alter production of gene products that participate in synaptic neurotransmission & the structure of brain cells • Circuitry of the brain can be altered in the course of a couple of hours to a day • Hormones are important for protection and adaptation • Stress hormones (Glucocorticoidcortisol) alter brain functions which is why SEVERE & PROLONGED STRESS CAN CAUSE PERMANENT BRAIN DAMAGE

19. Sex Hormones • Neurons in hypothalamus produce gonadotropin-releasing hormone (GnRH): acts on cells in the pituitary • GnRH causes two hormones in men & women to be released into bloodstream: • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH) • Men: FSH & LH bind to receptors in testes and release testosterone • Female: FSH & LH act on ovaries and release estrogen and progesterone • Increased levels of these  decreased levels of FSH & LH

20. Sex Differences • Size and shape of brain structures in the hypothalamus • Arrangement of neurons in the cortex and hippocampus • Actually more similar than they are different • Anatomical differences have also been reported between the brains of heterosexual and homosexual men • hormones and genes act early in life to shape the brain in terms of sex-related differences in structure and function

21. Gases • Nitric oxide and Carbon monoxide • Can be stored in any structure, not in synaptic storage structures • Made by enzymes when needed and released from neurons by diffusion • Don’t need receptors. They act on chemical targets (enzymes?) • Carbon monoxide: exact function is not known • Nitric Oxide • Erection • Intestine: Relaxation and normal movements of digestion • Brain: Major regulator of intracellular messenger molecule – Cyclic GMP • Neuronal damage after excess glutamate release (Stroke)

22. Second Messengers • Trigger biochemical communication after neurotransmitters at their receptor • Relay message of neurotransmitter from cell membrane to brain’s internal biochemical machinery • May endure from few milliseconds to up to several minutes • Before second messengers: ATP! • Norepinephrine activated receptor binds G protein on inside of membrane  causes enzyme adenylylcyclase to convert ATP to cyclic adenosine monophosophate(cAMP)