Chapter Three: The Biological Bases of Behavior

A. Communication and the Nervous System

Your nervous system is a complex communication network in which signals are constantly being received, integrated, and transmitted.

1. Nervous Tissue: The Basic Hardware
2. The Neural Impulse: Using Energy to Send Information
3. The Synapse: Where Neurons Meet
4. Neurotransmitters and Behavior

Contents

Nervous Tissue: The Basic Hardware

Synopsis: Information is received at the dendrites, is passed through the soma and along the axon, and is transmitted to the dendrites of other cells at meeting points called dendrites. (At least I think this is the way to the Emerald City, Dorothy).

Glia: The Support System


Neurons: The Communication Links

• Figure 3.1: Parts of the nueron
  
  
• Types of neurons
  
  
  • neuron
    
    
  • interneurons
    
    
  • sensory neurons
    
    
  • motor neurons
    
    
• Common features of neurons
  
  
  • soma
    
    
  • dendritic trees
    
    
  • dendrites
    
    
  • axons
    
    
  • myelin sheath
    
    
  • terminal buttons
    
    
  • synapse
    
    
  
  
  Building Blocks of the Brain
  
  A Rotating Neuron (movie requires 1.2 MB of RAM)

The Neural Impulse: Using Energy to Send Information

When the stimulation from another neuron is sufficient, the battery sends an action potential down the neuron.

Organization of nerve impulses

• Action potential

	HOT animation of an action potential in action (88k) By John Krantz Hanover College
HOT Backup in case Hanover College's server does not respond John Krantz Hanover College
	backup animation

• Absolute refractory period
  • 
  • This explains why Novocaine works so well at the dentist's office

All-or-None-Law

Synopsis: This law is based on two others that I'm sure you are familiar with: You can't be a "little" pregnant and you can't "half-fire" a gun.

Information about the strength of a stimulus is carried by the rate/frequency of action potentials -- the stronger the stimulus the more rapid the rate of firing action potentials.


Trivial pursuit facts about the neuron to wow your friends:

• Neural impulses travel over 200 miles per hour.
• Thick neurons conduct action potentials faster.
• Impulses travel even faster if neuron has myelin insulation.
• Moritmer Turnipseed has the largest neuron twine-ball in the midwest.

The Synapse: Where Neurons Meet

Synopsis: The neurons aren't physically connected to each other so the nerve impulse has to be converted to a chemical which ferries across the gap between the neurons.


Sending Signals: Chemicals as Couriers

Chemicals called neurotransmitters are the signal couriers that jump across the synaptic cleft

• Presynaptic neuron sends the signal.
• Postsynaptic neuron receives the signal.

Neurotransmitters

• 
• Synaptic vesicles store the neurotransmitters.
• Receptor sites are tuned to respond to specific neurotransmitters.

figure of the synapse (3.4)

Receiving Signals - Postsynaptic Potentials

When the neurotransmitter successfully crosses the gap, it doesn't automatically trigger another action-potential.

• Postsynaptic potential (PSP)
  
  
  • 
  • Does not follow all-or-none-law.
  • Graded in that PSP can increase or decrease the probability of an impulse in the receiving neuron.
  • Excitatory PSP
  • Inhibitory PSP
  • If there weren't any inhibitory PSP's, we could never stop the impulses.

Inactivation of neurotransmitters

• Reuptake is the recycling of the neurotransmitters back into the presynaptic neuron
  
  
• Would you like to see this process in action? figure 3.6

Integrating Signals: A Balancing Act

The neuron integrates the excitatory and inhibitory impulses -- if enough excitatory PSP's occur, the action-potential is fired off (as you can see in figure 3.5d.)

Neurotransmitters and Behavior

Specific neuotransmitters work at specific kinds of synapses and are associated with specific aspects of behavior.


Tracking Transmitters: Research Methods

Can you imagine how hard it is to measure neurotransmitter activity in the human brain?

• Humans: indirect measures.

  By-products in blood, urine, or in Cerebrospinal fluid (CSF)

• Animals: the blender approach.
  
  
• Chemical simulation studies.

Acetylcholines (Ach)

Every move you make, plus some aspects of attention, arousal and memory processes, can be attributed to Acetylcholines.

Low levels of Ach play a role in Alzheimer's disease.

Alzheimer's Association

Agonists

• 
• Explains why nicotine feels so good.

Antagonists

• 
• Watch out for arrows dipped with curare

Biogenic Amines

Dopamine, Norepinepherine, and Serotonin

Dopamine

• Controls voluntary behavior.
• Parkinsonism
  Information on Parkinsonism

Serotonin

• Regulates sleep and wakefulness

Norepinepherine

• Mediates arousal.

Psychological disorders affected by biogenic amines.

• Depression ( to disorders chapter.)
• Schizophrenia and the dopamine hypothesis ( to disorders chapter.)
  • Overactivity at the dopamine synapses
  • Figure 3.7

Drug Abuse and biogenic amines. (currently not active) Chapter 5

• Amphetamines
• Cocaine
• LSD

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