Nervous System & Neural Integration

Objectives

At the end of this topic you will be able to answer:

Topic outline

Activities

 

minilecture image Minilecture:

The Nervous System: How it all comes together

presented 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?

Top

 

The insect nervous system

  • A brain (number 5)

  • The subesophageal ganglion (number 31)

  • Three thoracic ganglia (number 29) (the prothroacic, mesothoracic, and metathoracic ganglia)

  • A chain of abdominal ganglia (beads near 19)

  • All of these structures are connected by nerves called connectives (number 19)

  • Head: A

  • Thorax: B

  • Abdomen: C

 

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

Top

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:

Top

Neuromodulatory input is distributed throughout the brain