NERVOUS SYSTEM

1. NERVOUS SYSTEM NEURONS

2. ENDOCRINE VS. NERVOUS SYSTEM Speed endocrine -slow nervous - fast Energy endocrine - cheap nervous - expensive Control endocrine - all tissues nervous - muscle and glands

3. ORGANIZATION OF THE NERVOUS SYSTEM Central Nervous System brain and spinal cord completely encased in bone integrative and control center of the nervous system

4. ORGANIZATION OF THE NERVOUS SYSTEM Peripheral Nervous System (PNS) 31 pairs of spinal nerves leave neural canal thru intervertebral foramina 12 pairs of cranial nerves leave brain thru foramina in the skull two parts afferent or sensory division efferent or motor division

5. ORGANIZATION OF THE NERVOUS SYSTEM PNS - afferent division - sensory nervous system three parts 1. somatic sensory nerves from receptors in the skin, fascia, and around joints 2. visceral sensory nerves from receptors from organs, wall of vessels 3. special sensory nerves from receptors for smell, taste, vision and balance

6. ORGANIZATION OF THE NERVOUS SYSTEM PNS - efferent division - motor nervous system 2 parts 1. Somatic Nervous System voluntary nervous system carrying impulses to skeletal muscle 2. Autonomic Nervous System involuntary nervous system carrying impulses to smooth muscle, cardiac muscle and glands 2 divisions a. Sympathetic b. Parasympathetic

7. COMPONENTS OF THE NERVOUS SYSTEM 1. neurons carry impulses 2. supporting cells or neuroglia CNS astrocytes oligodendrocytes microglia ependymal cells PNS satellite cells schwann cells or neurolemmocytes

8. NEURON STRUCTURE a. cell body or soma contains the nucleus contains unique structures called ________ bodies dense staining, parallel layers of rough ER lack ________________ lysosomes, mitochondria, golgi, ribosomes neurofibrils and neurofilaments form cytoskeleton in CNS tend to cluster to form structures called _____________ in PNS cluster in groups called _________

9. NEURON STRUCTURE b. dendrite means tree process that picks up information contains _______________ regulated gates for Na and K

10. NEURON STRUCTURE c. axon makes up most of the length of a neuron has _______________ regulated gates 1 for Na and 1 for K carries information from the dendrites to the terminal branches arises from a cone-shaped process on the cell body called the __________________ may branch - called collaterals

11. NEURON STRUCTURE d. axon terminal, telodendrite, or terminal arborization passes information on to other neurons or effectors contain synaptic vesicles which release neurotransmitters

12. MYELINATED NEURONS (PNS) myelin sheath- Schwann cell (PNS) Schwann cells contain a fatty material called __________ great insulator- prevents flow of ions other Schwann cells may not contain myelin called ___________________ neurons neurilemma external to the myelin sheath contains nucleus and most of the cytoplasm external to neurilemma is the basement membrane and a thin sleeve of fibrous connective tissue called the ____________ neither neurilemma nor endoneurium are found in neurons in the CNS

13. MYELINATED NEURONS (PNS) nodes of Ranvier bare areas between myelin sheaths 500X more permeable as membranes than are unmyelinated neurons saltatory conduction increases velocity conserves energy

14. VELOCITY OF CONDUCTION 1. diameter - _____________ the diameter, the _____________ the resistance, the faster the conduction 2. myelin increases the speed of conduction

15. NEURONS BASED ON SPEED OF CONDUCTION C fibers slowest fibers, 1 meter per second (2 mph) _____________ diameter, _______________ located in visceral efferent nerves found in neurons constricting and dilating pupils in neurons increasing and decreasing heart rate

16. NEURONS BASED ON SPEED OF CONDUCTION A fibers fastest fibers, up to 140 meters per second (300 mph) ___________ diameter, ________________ large sensory neurons that relay information associated with touch, pressure, position of joints in all motor neurons carrying impulses to skeletal muscle

17. NEURONS BASED ON STRUCTURE 1.. Unipolar 2 processes are fused together and only a single process arises from the cell body 2. Bipolar 2 processes, one from each end of the cell body 3. Multipolar one long process arises from the cell body - axon many small processes make up the dendritic zone 4. Anaxonic no anatomical clues some found in retina and brain

18. NEURONS BASED ON FUNCTION 1. Motor or efferent neurons - 0.5 million to an effector away from the CNS muscle or gland all _____________ 2. Sensory or afferent neurons - 10 million from a receptor to the CNS most are ______________ bipolar - retina, inner ear, taste buds, olfactory neurons

19. NEURONS BASED ON FUNCTION 3. Interneurons, association neurons, internuncial neurons - 20 billion completely within the CNS distribution of sensory information and coordination of motor activity involved in higher brain functions all ____________________

20. Axonal Transport all of proteins made in the soma some are needed in the axon others are transported from axons terminals back to the soma two-way passage of protein, organelles and other materials along an axon is called axonal transport movement from soma to axon is called _______________ transport movement from axon to soma is called _______________ transport materials travel along microtubules

21. Axonal Transport Two types of axonal transport 1. Fast axonal transport, either direction moves organelles, enzymes, calcium ions and small molecules such as glucose and amino acids returns used synaptic vesicles and other materials to the soma some pathogens travel this pathway to invade neurons including tetanus toxin and herpes simplex, rabies, and polio viruses 2. Slow axonal transport or axoplasmic flow always a_____________________ moves enzymes and cytoskeletal components down axon, renews worn-out axoplasmic components in mature neurons, and supplies new axoplasm for developing or regenerating neurons

22. CONNECTIVE TISSUE COVERINGS A. Endoneurium around individual neurons B. Perineurium around fascicles of neurons C. Epineurium around entire nerve

23. REGENERATION - PNS about 6 months after birth all developing neurons lose ability to undergo mitosis Schwann cells - participate in repair Wallerian degeneration - axon distal to the injury degenerates and macrophages migrate into area to phagocytize debris Schwann cells do not degenerate _____________ and ______________ form a solid cellular cord, the regeneration tube, that follows path of original axon axon grows into the tube and the schwann cells wrap around the axon

24. REGENERATION - CNS Limited regeneration astrocytes produce scar tissue that prevents axon growth release chemicals that block the regrowth of axons some success grafts from PNS embryonic neurons

25. NEUROGLIA - CNS 1. Astrocytes outnumber neurons 50:1 two types A. protoplasmic astrocytes maintain blood brain barrier controls the interstitial environment Na, K, CO2; rapid transport; controls volume of blood flow; absorbs and recycles some B. fibrous astrocytes form supportive framework for the CNS form scar tissue when neurons are damaged

26. Astrocytes

27. NEUROGLIA - CNS 2. Oligodendrocytes forms _______________ sheaths tip of processes expand to form a pad that wraps around the axon, may have as many as 15 arm-like processes myelinated neurons = _________ matter unmyelinated neurons = __________ matter

28. Oligodendrocytes

29. NEUROGLIA - CNS 3. Microglia least numerous and smallest neuroglia capable of migrating thru neural tissue engulf cellular debris, waste products and pathogens small _________________ which develop from __________________

30. Microglia

31. NEUROGLIA - CNS 4. Ependymal cells line central canal and ventricles of the brain cuboidal cells but have no basement membrane have _____________ when lining the ventricles other areas - scattered ________________ specialized ependymal cells participate in the secretion of CSF (______________ plexus)

32. Ependymal cells

33. SYNAPSE 1. Electrical current can pass from one neuron to next via gap junctions may go both ways found in smooth and cardiac muscle rare in neurons and neuroglia

34. SYNAPSE 2. Chemical synaptic bulbs contain synaptic vesicles that contain a neurotransmitter neurotransmitter is released in the synaptic cleft causes excitation or inhibition of neuron or effector

35. CHEMICAL SYNAPSE - EXCITATORY Synaptic vesicles contain 3000 molecules of ACh or acetyl choline formation of Ach acetyl CoA + __________ ---> ACh uses enzyme acetyl transferase uses ATP from mitochondria ______________ leak from extracellular fluid causes synaptic vesicles to move to the membrane and dump ACh into synaptic cleft

36. CHEMICAL SYNAPSE - EXCITATORY Postsynaptic membrane receptors for ACh ACh binds to ligand-regulated gates on dendritic zone increases permeability to Na and K -- Na diffuses across (in) much faster opens chemical regulated gates EPSP - excitatory postsynaptic potential lasts up to 15-20 msec not an action potential carried to the axon by the cable properties of the dentritic membrane

37. CHEMICAL SYNAPSE - EXCITATORY EPSP need 10 or more EPSPs to fire an action potential on the axon two ways to generate an action potential 1. ______________ summation all at the same time 2. ______________ summation over a short period of time

38. CHEMICAL SYNAPSE - EXCITATORY AChE or acetyl cholinesterase enzyme associated with the postsynaptic membrane breaks down ACh ACh ---> acetate + choline acetate - _____________ away choline - __________________ back into the synaptic bulb destroys ACh within 20 msec after its arrival

39. CHEMICAL SYNAPSE - INHIBITORY neurotransmitter -- GABA - gamma amino butyric acid increases permeability of the postsynaptic membrane to K and Cl ions opens chemical regulated gates causes IPSP - inhibitory postsynaptic potential drives the axon membrane away from threshold --hyperpolarization makes it harder for the voltage regulated gates to open

40. OTHER NEUROTRANSMITTERS 1. Biogenic amines norepinephrine (NE) epinephrine (EP) dopamine deficiency in brain can cause ________________ disease serotonin Prozac inhibits reabsorption LSD - activates serotonin receptors histamine

41. OTHER NEUROTRANSMITTERS 2. Acetyl choline formed from acetate and choline 3. Excitatory amino acids glutamate aspartate 4. Inhibitory amino acids GABA used to reduce anxiety glycine

42. OTHER NEUROTRANSMITTERS 5. Neuropeptides Substance P Opioids -- endorphins, enkephalins, dynorphins 6. Dissolved gases CO (carbon monoxide) NO (nitric oxide) 7. Others ATP, Prostaglandins, ADH, oxytocin, glucagon, insulin… and many other hormones

43. SYNAPTIC DELAY 0.2 - 0.5 msec time required to cross a chemical synapse and stimulate or inhibit postsynaptic membrane reflexes involved small number of synapses - less synaptic delay

44. SYNAPTIC FUNCTIONS Fatigue runs out of neurotransmitter enough for 10,000 transmissions can be exhausted in seconds only fatigue in the nervous system Acidosis -- below pH 7.4 ______________ neuronal activity below pH 7.0 -- acidosis coma

45. SYNAPTIC FUNCTIONS Alkalosis -- above pH 7.4 _________________ neuronal excitability above pH 7.8 -- alkalosis coma Chemicals Curare competes with ACh receptor on motor end plate Nerve gas (parathion, malathion) inactivates AChE for up to several weeks

46. SYNAPTIC FUNCTIONS Chemicals Atropine blocks ACh from binding dilates pupils antidote to nerve gas Botulism toxin inhibits release of ACh inhibits muscle contractions Caffeine reduces threshold

47. SYNAPTIC FUNCTIONS Chemicals Nicotine mimics ACh Venom of black widow spiders causes massive release of ACh Seafood neurotoxins (tetrodotoxin) blocks Na from entering voltage regulated gates Prostigmine inhibits AChE helps myasthenia gravis victims

48. MODIFICATION OF NEURONAL ACTIVITY Presynapse inhibition inactivates _______ channels examples: glycine, NE, GABA excitation or facilitation activates _________ channels example: serotonin

49. MODIFICATION OF NEURONAL ACTIVITY Neuromodulators chemical substances which alter neuronal activity indirectly either influence the release of neurotransmitter or the postsynaptic cell’s response to the neurotransmitter typically neuropeptides example - NO (nitric oxide) released by postsynaptic neurons in some areas of brain concerned with learning and memory diffuses into presynaptic neuron and stimulates it to release more neurotransmitter

50. NEURONAL CIRCUITS 1. Converging ciruit same source Pacinian corpuscles -- pressure different sources control of respiration

51. NEURONAL CIRCUITS 2. Divergening Circuit permits broad distribution of a specific input types A. amplification B. divergence into multiple tracts 3. Parallel after-charge circuit several neurons process same information at one time each chain has a different number of synapses, but eventually they all reconverge on a single output output neuron may go on firing for some time after input has ceased important in withdrawal reflexes longer-lasting output from small period of pain

52. NEURONAL CIRCUITS Reverberating Circuit axons extend back toward the sources of an impulse and further stimulate the presynaptic neuron helps maintain consciousness, muscular coordination, normal breathing, short term memory...