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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