PY460: Biological Bases of Behavior Chapter 2: Nerve Cells & Nerve Impulses The Cells of the Nervous...
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Transcript of PY460: Biological Bases of Behavior Chapter 2: Nerve Cells & Nerve Impulses The Cells of the Nervous...
PY460: Biological Bases of BehaviorPY460: Biological Bases of Behavior
Chapter 2:Chapter 2: Nerve Cells & Nerve ImpulsesNerve Cells & Nerve Impulses• The Cells of the Nervous SystemThe Cells of the Nervous System
• The Nerve ImpulseThe 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 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.
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
12
7
5
34
68
Slide 6: Sending & Receiving: Comparing Axons & Dendrites
Dendrites Axons
No. per cell Many One (or none)
Length Typically Short As long a 1meter
Myelin No Motor Neuron inVertebrates
Synapses Covered Only on theEnd Bulb
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
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)
Slide 9: Neural Exercise II
1
2
3
4
5
6
7
Slide Slide 1010: Changes in Neural Structure: 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 2).
The sodium-potassium pump--back toward the incr. AP
Figure 1 Figure 2
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
AP “jumps” between Nodes of Ranvier the push of local current periodic regeneration at nodes
– [automobile analogy]
Multiple Sclerosis destruction of myelin
Nodes
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:
Slide 24:
+ + + + + + + + + + + + + + + + + + + + + +- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
NA+
K (+)
K+
Cl-
Cl-NA+
Concentration Gradient
Electrical Gradient
INSIDE THE CELL (NEURON)
OUTSIDE THE CELL (NEURON)
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