THE NERVOUS SYSTEM

1. THE NERVOUS SYSTEM

2. I. Introduction • Functions of N.S. • Sensory input • Integration • Homeostasis • Mental activity • Control of skeletal muscles

3. I. Introduction • Divisions of the N.S. Central N.S. Peripheral N.S. Efferent Afferent Brain Spinal Cord Autonomic Somatic Parasympathetic Sympathetic

4. Sympathetic NS Fight or Flight • Dilates pupils • Reduces saliva, mucus, peristalsis, intestinal motility, urine secretion • Increases heart rate, glycogen to glucose conversion

5. Parasympathetic NS Digest & Rest • Constricts pupils • Reduces heart rate • Increases mucus production, gastric juice production, digestion, urine production, intestinal tract motility, peristalsis

6. II. Histology of the N.S. • Neurons – 1. Basics • nerve cells • functional unit of n.s. Neurons are not nerves!

7. A. Neurons 2. Structure. a. Cell body b. Dendrites receive incoming signals towards cell body

8. A. Neurons 2. Structure c. Axons transmit signals away from cell body

10. 2. Structure c. Axons • Myelin Sheath - membrane "insulation" around axons • Nodes of Ranvier - gaps between myelin

11. 2. Structure c. Axons • Nissil bodies - rough endoplasmic reticulum... Lots of protein synthesis • Synaptic vesicles - stores neurotransmitter at axon terminal

13. Structural Classification of Neurons

14. II. Histology of the N.S. • Neuroglia – nonexcitable;help & support neurons OF THE CNS • Astrocytes - "nurse" cells; nourish & protect neurons; form blood brain barrier • Oligodendrocytes - form myelin in CNS

15. II. Histology of the N.S. • Neuroglia – nonexcitable;help & support neurons OF THE CNS • Microglia - provide immune protection in CNS. • Ependymal cells –circulate cerebrospinal fluid

16. II. Histology of the N.S. • Neuroglia – OF THE PNS • Schwann Cells - form myelin in peripheral nerves • Satellite Cells – surround and support neurons of the ganglia

17. C. Nerves and Ganglia • Nerves • bundles of nerve cell axons and/or dendrites in periphery of body. • Functional classification • Sensory (afferent) nervescarry incoming signals from sense receptors towards CNS.

18. C. Nerves and Ganglia • Nerves b. Functional classification • Motor (efferent) nerves – carry outgoing (away from CNS) signals to muscle & glands. • Interneurons nerves – connect motor and sensory neurons

19. C. Nerves and Ganglia • Ganglia. Ganglia are bundles of nerve cell bodies in periphery of body.

20. II. Histology of the N.S. • Gray & White Matter • White Matter • Made of mylinated processes • Gray Matter • Unmylinated processes and cell bodies

21. II. Histology of the N.S. • Spinal cord gray matter forms H in center surrounded by white matter • Gray & White Matter 3. Location

22. II. Histology of the N.S. • Gray & White Matter 3. Location • Brain central white matter with a superficial gray matter covering

23. III. Neurophysiology • Membrane Properties • When at rest, the neuron has more + charges outside than inside • This electric imbalance called the restingmembrane potential

24. Resting Potential

25. A. Membrane Properties 3. Resting Potential ion distribution • Lg # Na+ outside; K+ inside

26. A. Membrane Properties • Changes in ion distribution • Stimulation of membrane opens ion channels (pores) • When this occurs it is called an Action Potential

28. III. Neurophysiology • Action Potentials • Are a specialized kind of electric signal generated only by neurons and muscle cells • are self-propagating • are all-or-none events.

29. III. Neurophysiology • Action Potentials have 3 Phases • Depolarization • Rapid (1 msec) • sodium channels open, Na+ rush in

30. III. Neurophysiology • Action Potentials have 3 Phases • Depolarization • Ends in an overshoot (i.e. brief period of time inside of cell is more positive than outside)

31. III. Neurophysiology • Action Potentials have 3 Phases • Repolarization • Na+ channels close • K+ channels open and K+ rushes out

32. III. Neurophysiology • Action Potentials have 3 Phases • Repolarization • overshoots the resting point

33. III. Neurophysiology • Action Potentials have 3 Phases • Undershoot Phase • Membrane is hyperpolarized back to the resting potential • K+ channels close • Na+/K+ pump reestablishes the resting potential • 3 Na+ movedfor 2 K+

34. Na+ / K+ Pump Reestablishes Resting Potential

36. III. Neurophysiology • Nerve Impulse • Impulse conduction • Unmyelinated fibers conduct impulse over entire membrane surface. • Myelinated fibers conduct impulse from node to node • Action potential spreads down the fiber to adjacent areas of membrane

39. III. Neurophysiology • All or None Response • If the nerve fiber responds to the impulse, it responds completely • Greater intensity of stimulation triggers more impulses per second, not stronger impulses

40. IV. The Synapse • Defined The junction (cleft) between 2 neurons

41. IV. The Synapse • Synaptic Transmission • The process by which the impulse is transmitted across the synaptic cleft

42. IV. The Synapse • Synaptic Transmission • Steps • Impulse reaches the synaptic knobs of axon • synaptic vesicles release neurotransmitter into the cleft

43. IV. The Synapse • Kinds of Neurotransmitters • Acetylcholine (ACh) • Made from acetic acid • Biogenic Amines • Made from amino acids • Include: dopamine, epinephrine (adrenaline), norepinephrine (noradrenaline), Serotonin and histamine

44. C. Kinds of Neurotransmitters • Amino Acids • Peptides (includes endorphins) • ATP • Nitric Oxide (NO) • Carbon monoxide (CO)

45. Nicotine mimics acetylcholine but can block function by producing sustained depolarization

46. V. The Reflex Arc • The Pathway • Receptors • Sensory Neuron • CNS Integration Center • Motor Neuron • Effector • Reflexes • Are rapid, automatic responses to stimuli • A specific stimulus produces the same motor response

48. VI. The Brain • The Cerebrum • Function • Thinking and consciousness • Willed movements • Memory • Vision • Hearing • Sensory perception • Emotions • Speech

49. A. The Cerebrum 2. General Comments • 83% of total weight of brain • Paired cerebral hemispheres

50. A. The Cerebrum 3. Anatomy • Lobes Named for bones over them • Frontal • Temporal • Parietal • Occipital • Insula (limbic) –inside lateral sulcus