Nervous System & Neural Integration
Objectives
At the end of this topic you will be able to answer:
- What is the basic layout of the nervous system?
- How is it all integrated?
- Understanding how the nervous system can integrate everything
Topic outline
- Part 1: the nervous system: layout and circuitry, and effects on behaviour
- Part 2: Neurons: how they work, communicate and produce behaviours
- Part 3: Neural integration: wiring the eyes and antennae
Activities
- Part 1: Minilecture: The Nervous System, How it all comes together
- Part 2: Minilecture: What are Neurons?
- Part 3: Minilecture: Wiring Eyes and Antennae
Minilecture:The Nervous System: How it all comes togetherpresented by A. Paulk |
The ‘black box’
The insect brain is comprised of inputs (sensory input), outputs (motor outputs), and incorporates the physiological state of the insect.
All of this information is integrated by the insect nervous system.
Research in understanding how this ‘black box’ of the insect nervous system operates to produce behaviour has highlighted the importance of connectivity, of functional circuits, and of the system as a whole.
Considering the numerous connections between the sensory input, the motor output, and the internal physiological state: How do we unravel the mechanisms in the ‘black box’ of the insect nervous system?
Sensory input: the different types
The nervous system has to integrate all of this information to allow the insect to produce behaviour.
Motor output: where behaviour is produced
The motor output can produce a variety of different types of behavior depending on the sensory input and the physiological state of the animal .
Internal physiological state
In addition to the sensory input and the motor output, the physiological state of the insect can play a major role in how the nervous system works.
The ‘black box’: How is the nervous system wired?
The insect nervous system
- The insect nervous system is composed of a series of bundles of nerve fibers, called ganglia, which are composed of brain cells, or neurons.
- Evolutionarily, a fusion of many of these ganglia led to the formation of the brain, located in the head, and enlarged thoracic ganglia (reference)
- The basal condition in the insect nervous system is:
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The insect nervous system: different designs
Like any system in insects, there have been various modifications to this design, which includes fusion of all the ganglia (1) to clear separation of the ganglia (2) (which is the basal condition)
Within the nervous system: the thoracic and abdominal ganglia
The layout of the thoracic and abdominal ganglia do follow a certain pattern:
Sensory input is often separated from motor output
The thoracic ganglia (or fused into a single thoracic ganglion) tends to be more developed compared to the abdominal ganglion because control of the wings (11,12) and legs ( is in the thorax
There is an orientation in the thorax: the more distal the sensory input to the thoracic ganglion, the more lateral and posterior the projections
The thoracic ganglion: sensory input includes mechanosensory, auditory, and gustatory input (from the tarsi)
Abdominal ganglia: sensory input is generally mechanosensory input
Within the nervous system: the subesophageal ganglion
The subesophageal ganglion (arrow) is closely associated with the brain and lies underneath the gut .
The brain is then connected via nerves to wrapping around the gut, with the brain above (dorsal to) the gut
The subesophageal ganglion contains key structures for neurohormones and is a major interface between the rest of the body and the brain.
Within the nervous system: the brain
The brain (arrow) has a large amount of sensory input from the eyes, the antenna, the mouthparts, and input from the thoracic ganglion via the cervical connective
The brain is one of the major integrators of information in insects.
However, if you cut it off, many insects can live for days.
Why? Because the thoracic and subesophageal ganglia contain the motor centers and much of the circuitry for living, except for feeding.
In other words, the insect has two brains: the ‘brain’ and the thoracic ganglia!
The functions and brain areas involved are:
Protocerebrum: visual input from the eyes and the ocelli, pars intercerebralis, and major central brain structures called the mushroom bodies and central complex, which are discussed in another mini-lecture.
Deutocerebrum: Antennal inputs and processing area (olfaction and mechanosensation) and antennal motor center
Tritocerebrum: nerve connections to the labrum of the insect and gustatory inputs
The nervous system: layout and function
The insect nervous system contains numerous inputs and outputs, though their wiring and connectivity depend on the functional role of the circuit.
There are numerous connections throughout the brain:
- In the central brain, information from the sensory systems as well as information from the internal state of the insect is integrated.
- The central brain includes the central complex, the mushroom bodies, and the protocerebrum.
- Additional input indicating the internal physiological state of the insect enters via the median bundle (a central tract from the thoracic ganglion) and from the cervical connective from the thorax.
- Neuromodulatory input also can change the dynamics of the system.
Neuromodulatory input is distributed throughout the brain
- Neuromodulatory input is differentially distributed throughout the brain
- Neuromodulatory input can indicate the arousal state of the insect (such as octopamine) or correlate with the circadian rhythm (such as serotonin)
Brain integration
The insect system is even more complicated than these basic connection schemes.
Check out the following websites which display the layout of the fly brain (1), the Drosophila adult and larval brains (2), and the layout of the honeybee brain (3):
http://flybrain.neurobio.arizona.edu/
http://www.neuraldevelopment.com/content/2/1/9
http://www.neurobiologie.fu-berlin.de/beebrain/Default.html
TOPIC REVIEWDo you know…?What brain areas do what for the insect?
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