CHAPTER 28 Nervous Systems

1. CHAPTER 28Nervous Systems Modules 28.1 – 28.9

2. NERVOUS SYSTEM STRUCTURE AND FUNCTION 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands • The nervous system has three interconnected functions • Sensory input • Integration • Motor output

3. SENSORY INPUT INTEGRATION Sensory receptor MOTOR OUTPUT Brain and spinal cord Effector Peripheral nervoussystem (PNS) Central nervoussystem (CNS) Figure 28.1A

4. The central nervous system (CNS) : the brain the spinal cord (in vertebrates) • The peripheral nervous system (PNS) : nerves ganglia (carry signals into/out of the CNS) • The nervous system can be divided into two main divisions

5. Sensory neurons convey signals from sensory receptors into the CNS • Interneurons integrate data and relay signals • Motor neurons convey signals to effectors • Three types of neurons correspond to the nervous system’s three main functions

6. 1 Sensoryreceptor 2 Sensory neuron Brain Ganglion 3 Motorneuron Spinalcord 4 Quadricepsmuscles Interneuron CNS Nerve Flexormuscles PNS Figure 28.1B

7. 28.2 Neurons are the functional units of nervous systems • Neurons are cells specialized to transmit nervous impulses • They consist of • a cell body • dendrites (highly branched fibers) • an axon (long fiber)

8. Dendrites Signal direction Cell body Cellbody Node of Ranvier Myelin sheath Signalpathway Axon Schwann cell Nucleus Nucleus Nodes ofRanvier Schwann cell Synaptic knobs Myelin sheath Figure 28.2

10. NERVE SIGNALS AND THEIR TRANSMISSION 28.3 A neuron maintains a membrane potential across its membrane • The resting potential of a neuron’s plasma membrane is caused by the cell membrane’s ability to maintain • a positive charge on its outer surface • a negative charge on its inner (cytoplasmic) surface Voltmeter Plasmamembrane Microelectrodeoutside cell –70 mV Microelectrodeinside cell Axon Neuron Figure 28.3A

11. These pump K+ into the cell and Na+ out of the cell • Resting potential is generated and maintained with help from sodium-potassium pumps OUTSIDE OF CELL K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ channel Na+ Plasmamembrane K+ Na+ - K+pump K+channel Na+ K+ K+ K+ Protein K+ K+ K+ K+ K+ K+ K+ INSIDE OF CELL Figure 28.3B

12. 28.4 A nerve signal begins as a change in the membrane potential • A stimulus alters the permeability of a portion of the plasma membrane • Ions pass through the plasma membrane, changing the membrane’s voltage • It causes a nerve signal to be generated

13. It is an electrical change in the plasma membrane voltage from the resting potential to a maximum level and back to the resting potential • An action potential is a nerve signal

14. Na+ K+ Na+ K+ Additional Na+ channels open, K+ channels are closed; interior ofcell becomes more positive. 3 Na+ channels close andinactivate. K+ channelsopen, and K+ rushesout; interior of cell morenegative than outside. 4 Na+ Actionpotential 3 4 2 The K+ channels closerelatively slowly, causinga brief undershoot. 5 Na+ Thresholdpotential A stimulus opens some Na+channels; if threshold is reached,action potential is triggered. 2 1 1 5 Resting potential Neuroninterior Neuroninterior Resting state: voltage gated Na+and K+ channels closed; restingpotential is maintained. 1 Return to resting state. 1 Figure 28.4

15. 28.5 The action potential propagates itself along the neuron Axon Action potential Axonsegment 1 Na+ Action potential K+ 2 Na+ K+ Action potential K+ 3 Na+ K+ Figure 28.5

16. Its size is not affected by the stimulus strength • However, the frequency changes with the strength of the stimulus • An action potential is an all-or-none event

18. 28.6 Neurons communicate at synapses • The synapse is a key element of nervous systems • It is a junction or relay point between two neurons or between a neuron and an effector cell • Synapses are either electrical or chemical • Action potentials pass between cells at electrical synapses • At chemical synapses, neurotransmitters cross the synaptic cleft to bind to receptors on the surface of the receiving cell

19. 1 SENDINGNEURON Actionpotentialarrives Axon ofsendingneuron Vesicles Synapticknob SYNAPSE 2 3 Vesicle fuses with plasma membrane Neurotransmitteris released intosynaptic cleft SYNAPTICCLEFT 4 Receivingneuron Neuro-transmitterbinds to receptor RECEIVINGNEURON Neurotransmittermolecules Ion channels Neurotransmitter brokendown and released Neurotransmitter Receptor Ions 5 6 Ion channel opens Ion channel closes Figure 28.6

21. 28.7 Chemical synapses make complex information processing possible • Excitatory neurotransmitters trigger action potentials in the receiving cell • Inhibitory neurotransmitters decrease the cell’s ability to develop action potentials • The summation of excitation and inhibition determines whether or not the cell will transmit a nerve signal

22. Dendrites Synaptic knobs • A neuron may receive input from hundreds of other neurons via thousands of synaptic knobs Myelinsheath Receivingcell body Axon Synapticknobs Figure 28.7

23. 28.8 A variety of small molecules function as neurotransmitters • Most neurotransmitters are small, nitrogen-containing organic molecules • Acetylcholine • Biogenic amines (epinephrine, norepinephrine, serotonin, dopamine) • Amino acids (aspartate, glutamate, glycine, GABA) • Peptides (substance P and endorphins) • Dissolved gases (nitric oxide)

24. NERVOUS SYSTEMS 28.10 Nervous system organization usually correlates with body symmetry • Radially symmetrical animals have a nervous system arranged in a nerve net • Example: Hydras Nervenet Neuron A. Hydra (cnidarian) Figure 28.10A

25. cephalization, the concentration of the nervous system in the head end • centralization, the presence of a central nervous system • Most bilaterally symmetrical animals exhibit Eye Brain Brain Brain Brain Ventralnervecord Ventralnervecord Nervecord Giantaxon Transversenerve Ganglia Segmentalganglion B. Planarian (flatworm) C. Leech (annelid) D. Insect (arthropod) E. Squid (mollusk) Figure 28.10B-E

26. 28.11 Vertebrate nervous systems are highly centralized and cephalized CENTRAL NERVOUSSYSTEM (CNS) PERIPHERALNERVOUSSYSTEM (PNS) Brain Cranialnerve Spinal cord GangliaoutsideCNS Spinalnerves Figure 28.11A

27. The brain and spinal cord contain fluid-filled spaces Dorsal rootganglion(part of PNS) Gray matter Meninges BRAIN White matter Central canal Spinal nerve(part of PNS) Ventricles Central canalof spinal cord SPINAL CORD(cross section) Spinal cord Figure 28.11B

28. 28.12 The peripheral nervous system of vertebrates is a functional hierarchy Peripheralnervous system Sensorydivision Motordivision Sensingexternalenvironment Sensinginternalenvironment Autonomicnervous system(involuntary) Somaticnervous system(voluntary) Sympatheticdivision Parasympatheticdivision Figure 28.12A

29. This happens because neurons carrying information from the skin and those carrying information from the internal organs synapse with the same neurons in the CNS • Referred pain is when we feel pain from an internal organ on the body surface Heart Lungs and diaphragm Lungs and diaphragm Liver Gallbladder Heart Stomach Liver Pancreas Small intestine Appendix Ovaries Kidney Colon Urinarybladder Ureters Figure 28.12B

30. The autonomic nervous system exerts involuntary control over the internal organs • The somatic nervous system exerts voluntary control over skeletal muscles • The motor division of the PNS

31. 28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment • The autonomic nervous system consists of two sets of neurons that function antagonistically on most body organs • The parasympathetic division primes the body for activities that gain and conserve energy • The sympathetic division prepares the body for intense, energy-consuming activities

32. PARASYMPATHETIC DIVISION SYMPATHETIC DIVISION Eye Brain Constrictspupil Dilatespupil Salivaryglands Stimulatessalivaproduction Inhibitssalivaproduction Lung Relaxesbronchi Constrictsbronchi Acceleratesheart Slowsheart Adrenalgland Heart Stimulatesepinephrineand norepi-nephrine release Liver Spinalcord Stomach Stimulatesstomach,pancreas,and intestines Stimulatesglucoserelease Pancreas Inhibitsstomach,pancreas,and intestines Intestines Bladder Stimulatesurination Inhibitsurination Promoteserection ofgenitals Promotes ejacu-lation and vaginalcontractions Genitals Figure 28.13

33. 28.20 The cellular changes underlying memory and learning probably occur at synapses • Memory and learning involve structural and chemical changes at synapses • Long-term depression (LTD) • Long-term potentiation (LTP)

34. 1 Repeatedactionpotentials Sendingneuron Sendingneuron Synapticcleft 2 2 4 Ca2+ Cascade ofchemical changes 3 3 Ca2+ Receiving neuron LTP Figure 28.20