Chapter 2
Controlling Behavior: The Role of the Central Nervous System
Modified: 2008-09-18 (spelling edits and addition of human reaction time datum)
Control and coordination are an essential component to animal behavior. In this chapter we will explore, briefly, the basics of the nervous system and how it controls FAPs, reflexes, prey capture, and escape behavior.
Key Points (adapted from text)
- Proximate causation is mainly controlled by the close coordination of the nervous system, sensory systems, and motor systems
- Reflexes are involuntary. Some are by highly specific stimuli, others by more general situations
- Animals gather information using a wide variety of strategies. Some strategies are more efficient than others
- The interaction between animals (and their nervous systems) and their environments is maximally important.
Stimulating a Behavior
- Fixed Action Patterns
(FAPs)
- First described by ethologists
- A stimulus will cause a stereotyped behavior
- Yawning
- Pecking at adult red spot in herring gulls
Components of the Nervous System
- Components
- Central Nervous System
- Autonomic Nervous System
- Sympathetic Branch
- Parasympathetic Branch
- Endocrine System
- Brain Comparison
- Neurons
- Basic unit of nervous system
- Thousands to billions, depending on species (~250k in a honey bee, ~100 billion in a human)
- Three types
- Afferent (sensory)
- Efferent (motor)
- Interneurons (multipolar)
- Resting Potential
- Polarized (like a battery) at rest
- ~ (-65 mv)
- Action Potential
- When neuron fires
- Depolarization occurs
- like a string of firecrackers
- Synapse
- Neurons do not touch (but come really close to each other)
- Space between neurons is the synapse
- Neural messages pass from one neuron to another via synapse
- Most synapses use chemical means to communicate from one neuron to next
- Neurotransmitters are the chemicals involved
- A small number of synapses communicate via electrical means
Controlling Prey Capture
- Bat Sonar*
- Nocturnal bats emit high frequency and detect the returning echoes
- Bats must turn off their ears while they emit the high frequency pulse
- Griffin demonstrated that there was a lower limit for prey detection
- Some prey, moths in particular, have evolved "bat detectors"
- The evolution of bat sonar and the subsequent evolution of pulse detection is an example of coevolution
- Coevolution refers to the evolutionary pressure exerted by species on each other
- Other species, thus, are part of the environment
- Plant poisons are another example of coevolution
- Dolphins, shrews, and cave swifts are other animals that have evolved echolocation
- Prey Capture by Toads
- How do toads identify a capture prey?
- Sequence
- Face potential prey
- Approach to striking distance
- Capture prey with tongue
- Swallow
- Wipe mouth
- Sequence is a reflex, innate, and stereotyped
- Flick first, eat later (or spit out)
- Large stimuli lead to escape behavior
- The Stimulus Filter
- Bipolar cells in toad brain decide
- Receptive field
- The Feature Detector
- Ewart's data
- Retinal cells involved in toad prey decisions
- Tectum cells are likely the feature detector
- More complex process than initially suspected
Controlling Escape Behavior
- Command Neurons
- Neuron or small set of neurons that elicit a specific behavior
- e.g., squid jetting response (see Case Study: Escape Jetting)
- Flipping Crayfish: A Rapid Escape Response
- Up to 10 ms latency (unprepared human reaction time is ~500ms)
- Stereotyped
- Adaptive
- Controlled by giant interneurons (GIs)
- Medial GI (MGI) connected to brain
- Lateral GI (LGI) connected to other neurons
- Crayfish reflexes
- LGI Circuit
- Does the LGI control the tail flip?
- LGI is connected to thousands of cuticle hairs
- LGI does cause tail flip
- Direct electrical stimulation
- No bypass mechanisms have yet been observed
- LGI inhibits contradictory behaviors
- (Note how discussion on pp. 38 to 40 address causation issues described in chapter 1)
- LGI Command-derived Inhibition
- Only one tail flip occurs per stimulus
- Post-flip Re-extension
- Sometimes tail flip is not stimulated by abdomen tap
- Further discussed in chapter 4
* Not covered in text
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