2. 2007-2008 Nervous System

3. Evolution of the Nervous System 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. nerve net transverse nerves lateral nerve cords cerebral ganglia brain eyespot auricle nerve ventral nerve cord with ganglia a. Hydrab. Planarianc. Earthworm

4. Evolution of the Nervous System 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. brain tentacle brain eye thoracic ganglion giant nerve fiber cerebrum in forebrain hindbrain spinal cord f. Cate. Squidd. Crab

5. Evolution of the Nervous System Vertebrate Nervous-System Organization –Central nervous system Develops from an embryonic dorsal neural tube Cephalization and bilateral symmetry result in several paired sensory receptors –Eyes, ears, olfactory structures –Vertebrate brain is organized into three areas Hindbrain Midbrain Forebrain 4

6. Evolution of the Nervous System Division of Nervous System: –The Central nervous system (CNS) Includes the brain and spinal cord –The peripheral nervous system (PNS) Consists of all nerves and ganglia that lie outside the CNS Two divisions –Somatic nervous system »Sensory and motor functions that control skeletal muscle –Autonomic nervous system »Controls smooth muscle, cardiac, muscle, and gland »Divided into sympathetic and parasympathetic divisions 5

7. Organization of the Human Nervous System 6 radial nerve median nerve ulnar nerve a. sciatic nerve tibial nerve spinal cord cervical nerves brain cranial nerves common fibular nerve thoracic nerves lumbar nerves sacral nerves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8. Organization of the Human Nervous System 7 b. Central Nervous System brain and spinal cord Peripheral Nervous System autonomic motor fibers (to cardiac and smooth muscle, glands) sympathetic division parasympathetic division visceral sensory fibers (internal organs) somatic sensory fibers (skin, special senses) somatic motor fibers (to skeletal muscles) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9. 37.2 Nervous Tissue Neurons (nerve cells) –Cell body contains nucleus and organelles –Dendrites receive signals from sensory receptors or other neurons –Axon conducts nerve impulses to another neuron or to other cells Covered by myelin sheath Any long axon is also called a nerve fiber 8

10. Nervous Tissue Types of Neurons Motor (efferent) neurons –Accept nerve impulses from the CNS –Transmit them to muscles or glands Sensory (afferent) neurons –Accept impulses from sensory receptors –Transmit them to the CNS Interneurons –Convey nerve impulses between various parts of the CNS 9

11. Neuron Anatomy 10 node of Ranvier a. Motor neuron (multipolar) cell body dendrite axon muscle direction of conduction myelin sheath axon terminal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © M.B. Bunge/Biological Photo Service

12. 11 cell body b. Sensory neuron (unipolar) axon skin myelin sheath direction of conduction sensory receptor Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Anatomy

13. 12 c: © Manfred Kage/Peter Arnold, Inc. c. Interneuron (multipolar) axon cell body dendrite Neuron Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14. Nervous Tissue Transmission of Nerve Impulses –Resting Potential The membrane potential (voltage) when the axon is not conducting an impulse –The inside of a neuron is more negative than the outside, around -70 mV –Due in part to the activity of the sodium- potassium pump 13

15. Nervous Tissue An action potential is a rapid change in polarity across a portion of an axonal membrane An action potential is generated only after a stimulus larger than the threshold Gated channel proteins –One channel protein suddenly allows sodium to enter the cell –Another channel protein allows potassium to leave the cell 14

16. Cells: surrounded by charged ions Cells live in a sea of charged ions – anions (negative) more concentrated within the cell Cl -, charged amino acids (aa - ) – cations (positive) more concentrated in the extracellular fluid Na + K+K+ Cl - K+K+ K+K+ aa - K+K+ Cl - aa - K+K+ K+K+ channel leaks K + + –

17. Cells have voltage! Opposite charges on opposite sides of cell membrane – membrane is polarized negative inside; positive outside charge gradient stored energy (like a battery) +++++++++++++++ +++++++++++++++ –––––––––––––– ––––––––––––––

18. Measuring cell voltage unstimulated neuron = resting potential of -70mV

19. How does a nerve impulse travel? Stimulus: nerve is stimulated – reaches threshold potential open Na + channels in cell membrane Na + ions diffuse into cell – charges reverse at that point on neuron positive inside; negative outside cell becomes depolarized –++++++++++++++ –++++++++++++++ +–––––––––––––– +–––––––––––––– Na + The 1st domino goes down!

20. Gate +– + + channel closed channel open How does a nerve impulse travel? Wave: nerve impulse travels down neuron – change in charge opens next Na + gates down the line “voltage-gated” channels – Na + ions continue to diffuse into cell – “wave” moves down neuron = action potential ––++++++–++++++ ––++++++–++++++ ++––––––+–––––– ++––––––+–––––– Na + wave  The rest of the dominoes fall!

21. How does a nerve impulse travel? Re-set: 2nd wave travels down neuron – K + channels open K + channels open up more slowly than Na + channels – K + ions diffuse out of cell – charges reverse back at that point negative inside; positive outside +––+++++––+++++ +––+++++––+++++ –++–––––++––––– –++–––––++––––– Na + K+K+ wave  Set dominoes back up quickly!

22. How does a nerve impulse travel? Combined waves travel down neuron – wave of opening ion channels moves down neuron – signal moves in one direction      flow of K + out of cell stops activation of Na + channels in wrong direction ++––+++++––++++ ++––+++++––++++ ––++–––––++–––– ––++–––––++–––– Na + wave  K+K+ Ready for next time!

23. How does a nerve impulse travel? Action potential propagates – wave = nerve impulse, or action potential – brain  finger tips in milliseconds! ++++––+++++––++ ++++––+++++––++ ––––++–––––++–– ––––++–––––++–– Na + K+K+ wave  In the blink of an eye!

24. Voltage-gated channels Ion channels open & close in response to changes in charge across membrane – Na + channels open quickly in response to depolarization & close slowly – K + channels open slowly in response to depolarization & close slowly +++++–++++++––+ +++++–++++++––+ –––––+––––––++– –––––+––––––++– Na + K+K+ wave  Structure & function!

25. How does the nerve re-set itself? After firing a neuron has to re-set itself – Na + needs to move back out – K + needs to move back in – both are moving against concentration gradients need a pump!! +++++––++++++–– +++++––++++++–– –––––++––––––++ –––––++––––––++ Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ wave  K+K+ Na + A lot of work to do here!

26. How does the nerve re-set itself? Sodium-Potassium pump – active transport protein in membrane requires ATP – 3 Na + pumped out – 2 K + pumped in – re-sets charge across membrane ATP That’s a lot of ATP ! Feed me some sugar quick!

27. Neuron is ready to fire again Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ aa - K+K+ K+K+ K+K+ +++++++++++++++ +++++++++++++++ ––––––––––––––– ––––––––––––––– resting potential

28. 1.Resting potential 2.Stimulus reaches threshold potential 3.Depolarization Na + channels open; K + channels closed 4.Na + channels close; K + channels open 5.Repolarization reset charge gradient 6.Undershoot K + channels close slowly Action potential graph –70 mV –60 mV –80 mV –50 mV –40 mV –30 mV –20 mV –10 mV 0 mV 10 mV Depolarization Na + flows in 20 mV 30 mV 40 mV Repolarization K + flows out Threshold Hyperpolarization (undershoot) Resting potential Resting 1 2 3 4 5 6 Membrane potential

29. 28 Resting and Action Potential of the Axonal Membrane d. An action potential can be visualized if voltage changes are graphed over time. resting potential threshold repolarization K + moves to outside axon Na + moves to inside axon action potential Voltage (mV) depolarization 0 0123456 Time (milliseconds) +60 –60 –40 –20 +20 +40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30. Myelin sheath signal direction  Axon coated with Schwann cells  insulates axon  speeds signal  signal hops from node to node  saltatory conduction  150 m/sec vs. 5 m/sec (330 mph vs. 11 mph) myelin sheath

31. myelin axon Na + + + +++ – – action potential saltatory conduction Multiple Sclerosis  immune system (T cells) attack myelin sheath  loss of signal Multiple Sclerosis  immune system (T cells) attack myelin sheath  loss of signal

32. Nervous Tissue Propagation of Action Potentials –In nonmyelinated axons, the action potential travels down an axon one small section at a time –In myelinated fibers, an action potential at one node causes an action potential at the next node Saltatory (jumping) Conduction –Conduction of a nerve impulse is an all-or-nothing event Intensity of signal is determined by how many impulses are generated within a given time span 31

33. 32 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Animation

34. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

35. Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

36. Nervous Tissue Transmission Across a Synapse –A synapse is a region where neurons nearly touch –Small gap between neurons is the synaptic cleft –Transmission across a synapse is carried out by neurotransmitters Sudden rise in calcium in the axon terminal of one neuron Calcium stimulates synaptic vesicles to merge with the presynaptic membrane Neurotransmitter molecules are released into the synaptic cleft 35

37. Synapse Structure and Function 36 path of action potential synaptic cleft receptor neurotransmitter Na + Ca 2+ 1. After an action potential arrives at an axon terminal, Ca 2+ enters, and synaptic vesicles fuse with the presynaptic membrane. cell body of postsynaptic neuron axon terminal synaptic vesicles enclose neuro- transmitter 2. Neuro- transmitter molecules are released and bind to receptors on the postsynaptic membrane. presynaptic membrane postsynaptic membrane 3. When an excitatory neuro- transmitter binds to a receptor, Na + diffuses into the postsynaptic neuron, and an action potential begins. neuro- transmitter postsynaptic neuron Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

38. Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

39. Synapse Impulse has to jump the synapse! – junction between neurons – has to jump quickly from one cell to next What happens at the end of the axon? How does the wave jump the gap?

40. axon terminal synaptic vesicles muscle cell (fiber) neurotransmitter acetylcholine (ACh) receptor protein Ca ++ synapse action potential Chemical synapse  Events at synapse  action potential depolarizes membrane  opens Ca ++ channels  neurotransmitter vesicles fuse with membrane  release neurotransmitter to synapse  diffusion  neurotransmitter binds with protein receptor  ion-gated channels open  neurotransmitter degraded or reabsorbed We switched… from an electrical signal to a chemical signal

41. Nerve impulse in next neuron Post-synaptic neuron – triggers nerve impulse in next nerve cell chemical signal opens ion-gated channels Na + diffuses into cell K + diffuses out of cell – switch back to voltage-gated channel –++++++++++++++ –++++++++++++++ +–––––––––––––– +–––––––––––––– Na + K+K+ K+K+ K+K+ ion channel binding site ACh Here we go again!

42. Nervous Tissue Synaptic Integration –A single neuron is on the receiving end of Many excitatory signals, and Many inhibitory signals –Integration The summing of excitatory and inhibitory signals 41

43. Synaptic Integration 42 (a): Courtesy Dr. E.R. Lewis, University of California Berkeley a. b. threshold resting potential axon terminalscell body of the neuron excitatory signal integration inhibitory signal Time (milliseconds) +20 –20 –40 –70 –80 0 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

44. 37.3 The Central Nervous System The Central Nervous System –Consists of the brain and spinal cord –Three specific functions: Receives sensory input Performs integration Generates motor output 43

45. The Central Nervous System –Consists of the brain and spinal cord –Spinal cord and brain are wrapped in three protective membranes called meninges Spaces between meninges are filled with cerebrospinal fluid Fluid is continuous with that of central canal of spinal cord and the ventricles of the brain 44

46. The Central Nervous System The Spinal Cord –Two main functions Center for many reflex actions Means of communication between the brain and spinal nerves –Composed of grey matter and white matter Cell bodies and short unmyelinated fibers give the gray mater its color Myelinated long fibers of interneurons running in tracts give white mater its color 45

47. The Central Nervous System The Brain –The cerebrum is the largest portion of the brain in humans Communicates with, and coordinates the activities of, the other parts of the brain Longitudinal fissure divides the cerebrum into left and right cerebral hemispheres 46

48. The Human Brain 47 skull meninges third ventricle pituitary gland pineal gland fourth ventricle spinal cord Diencephalon Cerebellum hypothalamus midbrain pons Brain stem b. Cerebral hemispheresa. Parts of brain Cerebrum (telencephalon) corpus callosum medulla oblongata opening to lateral ventricle thalamus (surrounds the third ventricle) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

49. The Lobes of a Cerebral Hemisphere 48 Frontal lobe Occipital lobe Parietal lobe premotor area trunk arm hand face tongue leg primary motor area motor speech (Broca’s) area prefrontal area central sulcus primary somatosensory area somatosensory association area primary taste area general interpretation area primary visual area visual association area lateral sulcus Temporal lobe auditory association area primary auditory area sensory speech (Wernicke’s) area Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

50. The Central Nervous System Cerebral Cortex A thin but highly convoluted outer layer of gray matter Covers the cerebral hemispheres Contains motor areas and sensory areas as well as association areas –Primary motor area is in the frontal lobe, just ventral to the central sulcus –Primary somatosensory area is in the parietal lobe, just dorsal to the central sulcus 49

51. The Central Nervous System Other Parts of the Brain Diencephalon A region encircling the third ventricle Includes three structures –Hypothalamus Forms the floor of the third ventricle Integrating center that maintains homeostasis Controls the pituitary gland 50

52. The Central Nervous System Other Parts of the Brain Diencephalon (continued) Thalamus Consists of two masses of gray matter located in the sides and roof of the third ventricle Receives all sensory input except smell Integrates sensory information and sends it to the cerebrum Pineal gland Secretes melatonin 51

53. The Central Nervous System Other Parts of the Brain Cerebellum Separated from the brain stem by the fourth ventricle Largest portion of the brainstem Receives sensory input from the eyes, ears, joints, and muscles Sends motor impulses out the brain stem to the skeletal muscles 52

54. The Central Nervous System Other Parts of the Brain Brain Stem Contains the midbrain, pons, and the medulla oblongata Midbrain Acts as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum Pons Contains axons that form a bridge between the cerebellum and the rest of the central nervous system Medulla Oblongata Contains reflex centers for vomiting, coughing, sneezing, hiccupping, and swallowing 53

55. 37.4 The Peripheral Nervous System Somatic system –Includes cranial nerves and spinal nerves Gather information from sensors and conduct decisions to effectors Controls the skeletal muscles –Voluntary Autonomic system –Controls the smooth muscles, cardiac muscles, and glands –Innervates all internal organs –Usually involuntary –Divided into two divisions Sympathetic division Parasympathetic division –Utilizes two neurons and one ganglion for each impulse 54

56. Cranial and Spinal Nerves 55 dorsal root ventral root vertebra spinal cord white matter central canal gray matter frontal lobe olfactory bulb olfactory tract optic chiasma temporal lobe optic nerve cerebellum medulla gray matter white matter vertebra b. c. a. dorsal root ganglion spinal nerve Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. c: © Karl E. Deckart/Phototake

57. The Peripheral Nervous System Reflex Arc Sensory receptors generate a nerve impulse that moves along sensory axons through a dorsal root ganglion toward the spinal cord Sensory neurons pass signals on to many interneurons in the gray matter of the spinal cord Nerve pulses travel along motor axons to an effector, which brings about a response to the stimulus 56

58. A Reflex Arc Showing the Path of a Spinal Reflex 57 white matter ventral root axon of motor neuron axon of sensory neuron pin dorsal root ganglion interneuron dendrites Dorsal gray matter central canal ventral horn sensory receptor (in skin) cell body of sensory neuron cell body of motor neuron effector (muscle) Ventral dorsal horn Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

59. The Peripheral Nervous System Sympathetic division –Especially important during fight or flight responses –Accelerates heartbeat and dilates bronchi Parasympathetic division –Promotes all internal responses associated with a relaxed state –Promotes digestion and retards heartbeat 58

60. Autonomic System Structure and Function 59 inhibits tearsstimulates tears constricts pupils ganglion dilates pupils Sympathetic Division inhibits salivation stimulates salivation cranial nerves Parasympathetic Division slows heart speeds heart dilates air passages cervical nerves thoracic nerves lumbar nerves constricts bronchioles stimulates liver to release glucose stimulates adrenal secretion vagus nerve inhibits activity of kidneys, stomach, and pancreas increases intestinal activity decreases intestinal activity ganglion inhibits urination stimulates urination sacral nerves stimulates gallbladder to release bile increases activity of stomach and pancreas sympathetic ganglia causes orgasmic contractions causes erection of genitals Acetylcholine is neurotransmitter. Norepinephrine is neurotransmitter. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

61. Comparison of Somatic Motor and Autonomic Motor Pathways 60