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Nervous Systems in Invertebrates and Vertebrates
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Covers the wide variety of nervous systems in both invertebrates and vertebrates.
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Comparative Anatomy and Physiology of AnimalsLecture 28 Invertebrate and Vertebrate nervous systems 26/02/21
Invertebrate neural networks
- With the exception of some multi-cellular animals have some form
of nervous tissue that link sensory receptors to a neural network
via sensory neurones and then to effectors via motor neurones.
Cnidarians
- Cnidarians have interconnected neurones that form complex two-
dimensional nerve nets.
- In sessile polyps, the entire nervous system is comprised of two
nets.
- One net lies at the base of the epidermis and the other at the base
of the gastrodermis.
- Neurones bridge at the mesoglea.
- Nerve impulses can move in any direction through the nets.
- Diffusion conduction means that a stimulus at one point on the net radiates outward like
ripples on a pond.
- There is no central control for coordinated responses.
Swimming medusa
- First indications of coordinated control are seen as nerve rings and ganglia are found around
the margin of the bell. These nerve rings are associated with the
swimming musculature and ocelli (light sensitive receptors.
- Ganglia are concentrations of neurones that serve as simple
integration centres.
- Each ganglion is associated with a sensory organ and can
generate motor output.
- Greatest output from ganglia controls muscular activity.
- Contraction of the musculature must be simultaneous so
neurones in the nerve ring couple with muscle cells electrically
with gap junctions.
, Platyhelminthes: Turbellaria
- There is a sub-epidermal ring-like brain connected to several nerve cords and multiple level
nerve nets that covet the whole body.
- More advanced species have a more concentrated bilateral brain and two ventrolateral,
longitudinal nerve cords.
- The nerve net is limited to the fringes of the body.
- Platyhelminthes also have basic sensory systems that detect light (ocellus and sensory pit) or
mechanical stimulation (statocysts and ciliary receptors).
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Nematoda and Annelida
- Nematodes have an intraepithelial nervous system.
- The brain is a collar-like and circumpharyngeal nerve ring.
- They also have two longitudinal nerve cords.
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