Transcript PY460: Physiological Psychology

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
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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
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Numbers
Cerebral Cortex
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15 billion neurons
Cerebellum
70 billion neurons
Spinal Cord
1 billion neurons
Slide 3: Parts of the Neuron: On the Outside
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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
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Dendrites- “tree”- receive incoming messages
 Synapses- location at which info is received from other
neurons
 Dendritic Spines- short outgrowths on dendritesincrease dendrites surface area
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Axon- long fiber (typically) down which electrical
message (impulse) is sent.
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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
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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
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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
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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!
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Glia- the other cell
 size
 volume
 numbers
 early theory
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TypesAstrocytes: chemical storage
 star shaped
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Oligodendrocytes: waste removal
 brain and spinal cord
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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
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Slide 10: Changes in Neural Structure
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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
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Tightly packed endothelial cells
results- “little shall pass”
oxygen, CO2, fatty soluble molecules
active transport mechanism- pumps in necessary
molecules (glucose=brain food)
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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
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Electricity in a carbon-based being (that’s us)
 decay of signal
 need for specialized “wires”
 need for specialized “transmitters”
 eye
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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
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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
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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
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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?
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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?
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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
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2).
Figure 2
The sodium-potassium pump--back toward the incr. AP
Slide 18:Anesthetics: Changing Nerve Permeability
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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
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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
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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
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Myelin Sheath & Saltatory Conduction
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Under the Myelin- no sodium channels
Between the Myelin (node)- many Na+ Channels
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Nodes
AP “jumps” between Nodes of Ranvier
 the push of local current
 periodic regeneration at nodes
– [automobile analogy]
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Multiple Sclerosis
 destruction of myelin
Slide 22: Graded Potential: Intensity Matters
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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)