1. 12-1 Nervous Tissue Chapter 12

2. 12-2 Nervous Tissue Overview of the nervous system Nerve cells (neurons) Supportive cells (neuroglia) Electrophysiology of neurons Synapses Neural integration

3. 12-3 Overview of Nervous System Master Control of the Body –Endocrine and nervous system maintain internal coordination endocrine = _____________________________ nervous –_______________________ receive information –brain and spinal cord determine responses –brain and spinal cord __________________________ _____________________________________________

4. 12-4 Subdivisions of Nervous System Two major subdivisions _________________________ –brain and spinal cord enclosed in bony coverings _________________________ –nerve = _________________ _______________________ –_____________ = swelling of ____________ in a nerve

5. 12-5 Sensory (____________) divisions (receptors to CNS) –visceral sensory and somatic sensory division Motor (_______________) division (CNS to effectors) –visceral motor division (ANS) effectors: cardiac, smooth muscle, glands sympathetic division (action) parasympathetic division (digestion) –somatic motor division effectors: skeletal muscle Functional Divisions of PNS

6. 12-6 Fundamental Types of Neurons Sensory (afferent) neurons –_________________________ _________________________ –Transmit info to brain/spinal cord ___________________________ –In between sensory and motor pathways in CNS –90% of neurons are interneurons –_________________________ _________________________ ___________________________ –send signals to muscles and glands –organs respond called effectors

7. 12-7 Properties of Neurons ____________________________ –ability to respond to changes (stimuli) in/out of body Conductivity –_______________________________ ____________________________ –____________________________________

8. 12-8 Structure of a Neuron _________________________ –single, central nucleus –cytoskeleton microtubules and neurofibrils (bundles of actin filaments) RER  Nissl bodies _________________________ –______________________ Singe axon (nerve fiber) arising from axon hillock for rapid conduction –_______________________ _______________________

9. 12-9 Variation in Neural Structure ____________________ –most common –many dendrites/one axon Bipolar neuron –______________________ ____________________ –sensory from skin and organs to spinal cord Anaxonic neuron –many dendrites/no axon –help in visual processes

10. 12-10 Types of Neuroglial Cells ___________________________________________ –wraps around nerve fibers ___________________________________________ –in areas of infection, trauma or stroke

11. 12-11 Types of Neuroglial Cells ________________________________ –_________________________________________________ –regulate composition of brain tissue fluid –convert glucose to lactate to feed neurons –secrete nerve growth factor promoting synapse formation –electrical influence on synaptic signaling –sclerosis – damaged neurons replace by hardened mass of astrocytes ________________________________________

12. 12-12 Myelin ________________________________________ –formed from wrappings of plasma membrane 20% protein and 80 % lipid (looks white) –all myelination completed by late adolescence In PNS, hundreds of layers wrap axon –____________________________________________ –covered by basal lamina and endoneurium Gaps between myelin segments = _________________

13. 12-13 Speed of Nerve Signal Diameter of fiber and presence of myelin ______________________________________________ Speeds –small, unmyelinated fibers = 0.5 - 2.0 m/sec –small, myelinated fibers = 3 - 15.0 m/sec –large, myelinated fibers = up to 120 m/sec Functions –slow signals supply the stomach and dilate pupil –fast signals supply skeletal muscles and transport sensory signals for vision and balance

14. 12-14 Regeneration of Peripheral Nerves Soma and neurilemmal tube intact Stranded end of axon and myelin sheath degenerate –cell soma swells, ER breaks up and some cells die Axon stump puts out several sprouts _____________________________ –schwann cells produce nerve growth factors

15. 12-15 Local Potentials Local disturbances in membrane potential –___________________ ___________________ –depolarization (opens gated Na + channels) decreases potential across cell membrane Na + rushes in Na + diffuses for short distance inside membrane producing a change in voltage called a local potential

16. 12-16 Local Potentials 2 ___________________________ –vary in magnitude with stimulus strength –get weaker the farther they spread –are reversible as K + diffuses out of cell –____________________________________ ____________________________________

17. 12-17 Action Potentials __________________________________________ If threshold potential (-55mV) is reached voltage- gated Na + channels open (Na + enters causing depolarization) Slow K + gates fully open K + exits repolarizing the cell __________________________________________ –excessive exiting of K +

18. 12-18 Action Potentials Called a spike Characteristics of AP –____________________ ____________________ voltage gates either open or don’t –irreversible (once started goes to completion and can not be stopped)

19. 12-19 The Refractory Period Resists stimulation ________________________ –as long as Na + gates are open –_________________________ ________________________ –as long as K + gates are open –__________________________ __________________________ Refractory period occurs to a small patch of membrane at one time (quickly recovers)

20. 12-20 Impulse Conduction - Unmyelinated Fibers

21. 12-21 _______________________________ Voltage-gated channels needed for APs –fewer than 25 per  m 2 in myelin-covered regions –up to 12,000 per  m 2 in nodes of Ranvier Fast Na + diffusion occurs between nodes

22. 12-22 Saltatory Conduction Notice how the action potentials jump from node of Ranvier to node of Ranvier.

23. 12-23 Synapses between Neurons First neuron releases neurotransmitter onto second neuron that responds to it –1st neuron is ________________________ –2nd neuron is ________________________ Number of synapses on postsynaptic cell variable –8000 on spinal motor neuron –100,000 on neuron in cerebellum

24. 12-24 Synaptic Relationships between Neurons

25. 12-25 Discovery of Neurotransmitters Histological observations revealed gap between neurons (synaptic cleft) _________________________________ –demonstrated function of neurotransmitters –“vagus substance” - later renamed acetylcholine Electrical synapses = gap junctions –cardiac and smooth muscle and some neurons

26. 12-26 Chemical Synapse Structure ______________________ have synaptic vesicles with neurotransmitter and ____________________ have receptors

27. 12-27 Types of Neurotransmitters _______________________________ –formed from acetic acid and choline Amino acid neurotransmitters _______________________________ –replace –COOH in amino acids with another functional group –______________________ (epi, NE and dopamine) –indolamines (serotonin and histamine) ________________

28. 12-28 _____________________ Chains of 2  40 amino acids Stored in axon terminal as secretory granules (called dense-core vesicles) Act at lower concentrations Longer lasting effects Some released from nonneural tissue –gut-brain peptides cause food cravings Some function as hormones –modify actions of neurotransmitters

29. 12-29 Synaptic Transmission 3 kinds of synapses with different actions _______________________________ = ACh Inhibitory GABA-ergic synapse = GABA ________________________________ = NE Synaptic delay (.5 msec) –time from arrival of nerve signal at synapse to start of AP in postsynaptic cell

30. 12-30 Neural Integration More synapses a neuron has the greater its information-processing capability –cerebral cortex  40,000 synapses estimated to contain 100 trillion synapses Chemical synapses are decision-making components –______________________________________

31. 12-31 Postsynaptic Potentials- EPSP __________________________________ _____________________ –a positive voltage change causing postsynaptic cell _____________________ result from Na + flowing into the cell –glutamate and aspartate are excitatory neurotransmitters ACh and norepinephrine may excite or inhibit depending on cell

32. 12-32 Postsynaptic Potentials- IPSP ___________________________________ postsynaptic cell to be less likely to fire (hyperpolarize) result of Cl - flowing into the cell or K + leaving the cell –glycine and GABA are inhibitory neurotransmitters ACh and norepinephrine may excite or inhibit depending upon cell