PY460: Biological Bases of Behavior

1. PY460: Biological Bases of Behavior • Chapter 2: Nerve Cells & Nerve Impulses • The Cells of the Nervous System • The Nerve Impulse

2. Slide 2: The Cells of the Nervous System • 2 Basic cell types in the NS • Neurons- receive and transmit • electrical and chemical process of transmission • Glia- “glue” • multiple functions (discussed later in detail) • structural support, waste removal • Numbers • Cerebral Cortex 15 billion neurons • Cerebellum 70 billion neurons • Spinal Cord 1 billion neurons

3. Slide 3: Parts of the Neuron: On the Outside • Soma- the cell body (.005mm to 1 mm) • Cell Membrane (bi-lipid layer[2 fat molecules]) • “Protein Channels”control flow of ions in/out of cell • Dendrites- “tree”- receive incoming messages • Synapses- location at which info is received from other neurons • Dendritic Spines- short outgrowths on dendrites- increase dendrites surface area • Axon- long fiber (typically) down which electrical message (impulse) is sent. • Myelin Sheath- fatty insulating material around axon. • Presynaptic Terminal (End Bulb)-axon release of chemical that cross synapse excite next neuron.

4. Slide 4: Parts of the Neuron: On the Inside • Cytoplasm- viscous fluid in cell • Cell Nucleus- “the nut”- area containing genetic material • DNA- long strands of amino acids • Chromosomes- strands of DNA. Important in protein production- (genes are here) • Mitochondria-“powerhouse” to cell (aerobic energy) • Ribosomes- synthesis on newest building material (protein for cell) • Endoplasmic Reticulum- thin tubes that transport proteins • Lysosomes (recycler)- enzymes that break chemicals into their component parts to be recycled for later use. • Golgi Complex- homonal preparation for secretion

5. Slide 5: Parts of the Neuron: Exercise I 1 2 3 4 5 6 7 8

6. Slide 6: Sending & Receiving: Comparing Axons & Dendrites

7. Slide 7: Types of Neurons and their Axons • Sensory Neurons- highly sensitive and specialized to receive a particular stimulus (wavelength of sound, light, type of touch);sends msg. away from site for processing • soma usually of the trunk of the main axon • Afferent axons • Motor Neurons- excited by other neurons which results in excitation of muscle or glands cells • soma at one end of cell. Impulse moves from soma to axon hillock • Efferent axons • Interneruons- (Most numerous). In between sensory and motor processing • Intrinsic Neurons- neuron that exists only within a singular structure

8. Slide 8: Got to Get Me Some GLIA! • Glia- the other cell • size • volume • numbers • early theory • Types- • Astrocytes: chemical storage • star shaped • Oligodendrocytes: waste removal • brain and spinal cord • Schwann Cells: build myelin sheath around axons • Radial Glia: guiding neural and axon growth during embryonic development (also Schwann Cells)

9. Slide 9: Neural Exercise II 1 4 2 5 3 6 7

10. Slide 10: Changes in Neural Structure • Neuron Replacement- what happens when neurons die? • A few exceptions (olfactory receptors) • Brain Cancer- an abnormal proliferation of cells, but not neurons... • Plasticity- production of new neural connections • Changes in Cell Structures with Aging • dendrites • shrinkage • branching • more • wider • senility patterns

11. Slide 11: Blood-Brain Barrier

12. Slide 12: The Blood-Brain Barrier • Tightly packed endothelial cells • results- “little shall pass” • oxygen, CO2, fatty soluble molecules • active transport mechanism- pumps in necessary molecules (glucose=brain food) • Protection of the brain from “invaders” • viruses and natural killer cells (NKCs) • cell death • viruses in the nervous system • herpes • The price of protection.

13. Slide 13: The Action Potential • Electricity in a carbon-based being (that’s us) • decay of signal • need for specialized “wires” • need for specialized “transmitters” • eye • The concept of “potential energy”- “the capacity to be” • The Resting Potential (-70 mV): the polarized cell • at rest, the cell is more negative on the inside than the outside Microelectrode, see page 40 in Kalat

14. Slide 14: Forces Behind the Resting Potential • How does a cell maintain its resting potential • (i.e., how is it that the cell doesn’t become neutrally charged?) • CONCENTRATION GRADIENT: the difference in distribution of ions between inside and outside [balloon] • 20x more Na+ on Outside • 10x more K+ on Inside • more Cl- on inside of cell • Selective Permeability- the bilipid layer membrane -larger ions (Na+) cannot pass at all.. A few (Cl- and K+) pass through specialized “channels”. • Sodium Potassium Pump (3 NA+ out, 2 K+ in ) • active transport system- use of a lot of energy

15. Slide 15: Forces Behind the Resting Potential • ELECTRICAL GRADIENT (electrostatic pressure): differences in electrical charge between one ion and another. • Will attract positive ion into the cell, and negative ions out of the cell • excess Na+ on outside • Putting it together--- CLICK HERE • boardwork? • Why is it important that there be an action potential • what happens if membrane become more permeable? • “the poised bow & arrow”

16. Slide 16: The Action Potential- cell firing Hyperpolarization- increased polarization Depolarization- action potential moves toward a charge of zero mV (no longer polarized) Threshold- a certain level of depolarization in which an action potential (nerve impulse) will occur All or None Law- if threshold is met, nerve impulse is generate, if not (subthreshold stimulation).. cell will not fire. Think about flushing the toilet

17. Slide 17: The Action Potential: why the change? • Voltage Activated Channels- permeability to sodium changes if a certain (more depolarized) is reached. • Typically flow of sodium is balanced by exit of potassium. At a given level, “throw open the Na gates and shut the K+ gates” (figure 1) • Excess concentration of K+ drives K+ out, voltage channels close stopping more NA+ from coming in (Fig 2). • The sodium-potassium pump--back toward the incr. AP Figure 1 Figure 2

18. Slide 18:Anesthetics: Changing Nerve Permeability • What happens the flow of if K+ and Na+ is affected? • Scorpion Venom • Sodium Channels remain open/close Potassium • effect: prolonged depolarization.. • excess firing… nerve cell fatigue • Local Anesthetics- novacaine, xylocaine • prevent Na channels from opening • why.. Cell can’t depolarize • General Anesthetics- chloroform • open K channels • cell cant depolarize, b/c K+ leaving as fast as Na+ is coming in.

19. Slide 19: Propagation of the Action Potential • Refractory Periods- cell location cannot experience another AP • Absolute- cell incapable of generating another AP due to voltage gates being closed • Relative- cell must hyperpolarize to fire again as potassium gates channels remain open. • AP begins at Axon Hillock • Regeneration due to diffusion of Na in adjacent locations. • New AP runs down the axon. [rope demonstration] • Cant go backwards.. Why?

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21. Slide 21: The Action Potential: Regeneration • Myelin Sheath & Saltatory Conduction • Under the Myelin- no sodium channels • Between the Myelin (node)- many Na+ Channels • AP “jumps” between Nodes of Ranvier • the push of local current • periodic regeneration at nodes • [automobile analogy] • Multiple Sclerosis • destruction of myelin Nodes

22. Slide 22: Graded Potential: Intensity Matters • Local Neurons (also dendrites, somas) - don’t produce AP’s • Communicate by “graded potential” • membrane potentials that vary in intensity (magnitude) and don’t follow the all or none law. • Subsequent local neurons depolarize in proportion to the intensity of the incoming stimulus. • Signal will decay as it travels (unlike saltatory conduction).

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24. Concentration Gradient Slide 24: Electrical Gradient OUTSIDE THE CELL (NEURON) NA+ Cl- BACK K+ + + + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Cl- NA+ K (+) INSIDE THE CELL (NEURON)