1. Nervous System Oranismal S&F Tony Serino. Ph.D. Biology Dept. Misericordia University

2. Nervous System Controls and/or modifies all other systems Rapid response time Usually short duration General anatomy and physiology of neurons Lecture Outline:

3. Functional Areas

4. Divisions of the Nervous System

5. Nervous Tissue Non-excitable Tissue (Supportive cells) –Neuroglia –present in CNS –Schwann and Satellite cells –present in PNS –Create myelin, protect and nurture neurons Neurons (excitable tissue) –Initiate and conduct electrical signals (action potentials)

6. Neuron Anatomy Axonal terminal Nerve ending Synaptic boutons Synaptic knobs

7. Functional Zones of a Neuron Receptor Zone Initial segment of Axon (trigger zone) Axon Nerve endings

8. Node of Ranvier: gaps in myelin sheath

9. Synapses Areas where neurons communicate with other cells Can be chemical (with neurotransmitters) or electrical (gap junctions)

10. Anatomy of Synapse (chemical) Neurotransmission ends when NT diffuses away, re-absorbed by presynaptic neuron, or NT metabolized (degraded) by enzymes in cleft

11. Membrane Potentials Produced by the unequal distribution of ions across a selectively permeable membrane The inside of the cell is called negative by convention The intensity of the ion difference is expressed as voltage (measured in millivolts (mV))

12. Measuring Membrane Potentials

13. Resting Membrane Potential A semi-permeable membrane Distribution of ions across membrane Presence of large non-diffusible anions in interior Na-K pump (3 Na + out for every 2 K + in) Parameters necessary to create a resting membrane potential:

14. Gated Channel Proteins Opening gate allows ions to travel into or out of the cell thereby changing the membrane potential Can be controlled chemically or electrically

15. Chemically Gated Channel Protein

16. Voltage (electrically) Gated Channel Protein

17. Graded Potentials Depolarization Hyperpolarization Transient Decremental Due to chemically gated channels opening Can be summated May be excitatory or inhibitory Will only trigger AP if the threshold of the neuron is reached. Inside of cell becomes less negative Inside of cell becomes more negative

18. Graded potentials magnitude vary with stimulus strength

19. Action Potentials Wave-like, massive depolarization with rapid repolarization Propagated down entire length of axon or muscle cell membrane All or none No summation possible Due to opening of voltage gated channels and corresponding positive feedback cycle established

20. Endocrine System Controls and modifies the internal environment by releasing chemicals (hormones) into the blood Slower response time but longer duration of action compared to nervous system

21. Chemical Messengers (hormones) Hormone –secreted by cell into blood and acts on another cell some distance away Neurohormone –secreted by neuron into blood to affect a target cell some distance away Local hormones –secreted by cell into interstitial fluid to affects cells nearby –Paracrines –affect neighboring cells –Autocrines –affect the secreting cell Pheromones –secreted by cell onto body surface to affect cells of another individual

22. Hormones Chemical Classification –Amines –single or few amino acids, most water soluble Epinephrine, Thyroxine (but water insoluble), Melatonin –Proteins –short to long chains of amino acids; water soluble GH, FSH, LH, Insulin, Glucagon, ADH, etc. –Steroids –derivatives of cholesterol; water insoluble Estrogen, Testosterone, Progesterone, Cortisol, Aldosterone

23. Steroid Hormones

24. Characteristics Common to all Hormones Must have target cell with appropriate receptor molecules Receptor-hormone complex must trigger events in target cell that changes its physiology Mechanisms for deactivating the hormone response must be present

25. Controlling Hormone Response Half-life of the hormone Physiological range Modifying target cell response –Up and down regulation Turning off secretion –Negative feedback –Control by other hormones, neurons and metabolites

26. Control of Hormone Secretion

27. Mechanisms of Hormone Action Water Soluble Water Insoluble Carrier protein 2 nd messengers

28. 2 nd Messengers: cAMP

29. 2 nd Messengers: IP 3 and Ca ++ -Calmodulin

30. Steroid Hormone Transduction

31. Different Styles of Secretion Prohormone –a hormone that is made as a larger (inactive form) that must be changed prior to secretion (allows for storage of hormone in secreting cell) Ex.: proinsulin, pro-opiomelanocortin Prehormone –a hormone that is secreted in an inactive form that must be changed near or in the target cell Ex.: Thyroxine, Angiotensinogen

32. Proinsulin

33. Types of Endocrine Disorders Hypersecretion –Too much secretion of the hormone Hyposecretion –Too little secretion of hormone Hyporesponsiveness –Normal secretion, but little to no response by target cells

34. Endocrine Glands