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PY460: Biological Bases of Behavior Chapter 2: Nerve Cells & Nerve Impulses • The Cells of the Nervous System • The Nerve Impulse 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 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 dendritesincrease 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. 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 Slide 5: Parts of the Neuron: Exercise I 1 2 3 4 5 7 6 8 Slide 6: Sending & Receiving: Comparing Axons & Dendrites Dendrites No. per cell Axons Many One (or none) Length Typically Short Myelin No As long a 1 meter Motor Neuron in Vertebrates Only on the End Bulb Synapses Covered 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 Slide 8: Got to Get Me Some GLIA! Glia- the other cell size volume numbers early theory TypesAstrocytes: 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) Slide 9: Neural Exercise II 1 2 3 4 5 6 7 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 Slide 11: Blood-Brain Barrier 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. 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 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 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” 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 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 Figure 1 2). Figure 2 The sodium-potassium pump--back toward the incr. AP 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. 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? Slide 20: Slide 21: The Action Potential: Regeneration Myelin Sheath & Saltatory Conduction Under the Myelin- no sodium channels Between the Myelin (node)- many Na+ Channels Nodes AP “jumps” between Nodes of Ranvier the push of local current periodic regeneration at nodes – [automobile analogy] Multiple Sclerosis destruction of myelin 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). Slide 23: Concentration Gradient Slide 24: Electrical Gradient OUTSIDE THE CELL (NEURON) BACK NA+ Cl- K+ ++++++++++++++++++++++ -----------------------------Cl- NA+ K (+) INSIDE THE CELL (NEURON)