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 layer2 fat molecules)
• Protein Channelscontrol 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 (glucosebrain 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 (thats 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 doesnt 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 18Anesthetics 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 cant 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?

20
Slide 20
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) - dont
  produce APs
• Communicate by graded potential
• membrane potentials that vary in intensity
  (magnitude) and dont 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).

23
Slide 23
24
Slide 24
Concentration Gradient
Electrical Gradient
OUTSIDE THE CELL (NEURON)
NA
Cl-
BACK
K

- - - - - - - - - - - - - - - - - - - - - - - - -
- - - - -
Cl-
NA
K ()
INSIDE THE CELL (NEURON)