The document discusses the differences between vertebrate and invertebrate nervous systems. It examines examples from various phyla of invertebrates including cnidarians, echinoderms, nematodes, platyhelminthes, annelids, molluscs, arthropods, and compares them to typical vertebrate systems. Key differences include the level of centralization, important neural structures like ganglia or the brain, and physiological properties. Invertebrates range from very decentralized nerve nets to centralized brains, while vertebrates have advanced centralized brains and spinal cords for rapid information processing.

1. Vertebrate and invertebrate nerve
physiology
Dr. Omony John Bosco

2. VERTEBRATE AND INVERTEBRATE NERVE PHYSIOLOGY
What are the major differences between vertebrates and invertebrates?

3. Typical examples of vertebrates and invertebrates
The differences mentioned above account for the nerve physiology in
the mentioned example of these categories given below

4. Differences between invertebrates and
vertebrates nervous system

8. Illustration of invertebrate nerves
• How are invertebrate able to be sentient (responsive, sensitive, feel,
emotions, perceptive)?. The answer to this question require an
understanding of their nerve structure and function.
• The most important is the organization of their nervous system
(centralization of their nervous systems and presence of structure that
enables sentience to arise) and the size of the nervous systems

9. Phylum: Cnidaria
Examples Jellyfish, sea anemones, coral
• The nervous system size may be of approximately 5,000-
20,000 nerve cells in a jellyfish. contain diffuse nerve nets,
which transmit information bi-directionally (signals can travel
in either direction through the network)
Centralization
• The nervous system consists of one or more nerve nets.
Information is likely to be integrated in the sensory ganglia.
• These animals possess a central nerve net rather than a body
concentrating neurons.
• Diffuse and/or through-conduction nerve nets.
Important structures
Sensory ganglia.
Comparative physiology
Seems that among invertebrates with nervous systems, these
have some of the most decentralized ones.

10. Phylum: Echinodermata
Examples
• Starfish, sea urchins, sea cucumbers
Centralization
• These animals have a circumoral nerve ring, which may be analogous
to a brain.
• However, it may be that most sensory input is integrated peripherally
and that there is no need for a central brain structure.
• Ectoneural subsystem, containing the circumoral nerve ring and outer
part of the radial nerve cords. Includes sensory and motor
components.
Important structures
• Hyponeural subsystem, a thinner, inner layer of the radial nerve cords
thought to control locomotion.
Comparative physiology
• As in cnidaria, these are very decentralized nervous systems that do
not contain a centralized concentration of neurons.

11. Phylum: Nematoda
Examples
• Roundworms
Centralization
• These animals have highly centralized nervous systems, with most
neurons concentrated in several anterior ganglia. There is a distinct
brain region which forms a ring shape.
Important structures
• Circumoral nerve ring. Anterior ganglia.
Comparative physiology
• The C. elegans connectome, like the brains of vertebrates such as
mammals, features highly connected hubs, which are themselves
interconnected in a central core structure.
• Thus, the macroscopic organization of the C. elegans nervous system
shows scale-invariant conservation with the brains of vertebrates
over many orders of magnitude of anatomical complexity.

12. Phylum: Platyhelminthes
Examples
• Flatworms
Centralization
• They have a centralized nervous system with a distinct brain
located in the head. This brain receives and integrates
information from sensory structures across the whole body.
Important structures
• Centralized brain structure located in the head.
Comparative physiology
• Continuous EEG waveforms have been recorded from the
planarian brain.
• The continuous waveforms suggest the existence of
feedback loop circuits in the neural network.
• This continuous waveform is similar to that recorded from
more developed brains.

13. Phylum: Annelida
Examples
• Earthworms, leeches
Centralization
• Some of these animals have a centralized nervous system with a
distinct brain. Some taxa contain higher brain structures such as
mushroom bodies (also found in arthropods). However, most
annelids lack these brain structures.
• The standard annelid brain is ring-shaped with two cerebral
ganglia.
Important structures
• Two cerebral ganglia forming a bilobed brain (in most annelids).
Mushroom bodies and glomerular neuropil (in some annelids).
Comparative physiology
• Some annelid brains can be divided into fore, mid and hind
sections (this mirrors the gross structure of advanced brains such
as the human brain).
• Some taxa contain mushroom bodies, which are considered
higher brain centers in insects.

14. Phylum: Mollusca, Class: Bivalvia
Examples
• Clams, oysters, mussels
Centralization
• These animals’ nervous systems have some level of
centralization, as they include 3 pairs of ganglia
connected by a nerve cord.
Important structures
• Cerebropleural ganglia, visceral ganglia, pedal ganglia.
Comparative physiology
• Unlike in other molluscs, there is no distinctive brain
structure, although there is centralization in ganglia.

15. Phylum: Mollusca, Class: Gastropoda
Examples
• Snails and slugs
Centralization
• Typically contain 5 pairs of ganglia, including the cerebral
ganglia, which are structurally and functionally
differentiated and receive and send signals across the
body.
Important structures
• Cerebral ganglia (in head). Procerebrum (in cerebral
ganglia), which may contain the learning mechanism.
• 5 paired ganglia throughout body (typically).
Comparative physiology
• These nervous systems are similar to those of bivalves,
although a bit bigger and with ganglia serving as a brain.

16. Phylum: Arthropoda, Class: Insecta
Examples
• Bees, fruit flies, grasshoppers
Centralization
• They have a centralized nervous system with a distinct brain.
The insect brain is segmented into three main regions.
• One of these regions, the protocerebrum, contains the
mushroom bodies which contain a large proportion of the
overall neurons in the central nervous system.
• There is some decentralization – for example the ventral nerve
cord is able to direct complex action even when the central
brain complex has been completely disconnected.
Important structures
• Mushroom bodies, which are important for learning, memory
and integrating information.

17. Phylum: Arthropoda, Subphylum: Crustacea
Examples
• Crabs, lobsters, woodlice
Centralization
• Contains a central nervous system. The largest
ganglion in it is found at the anterior end and
functions as the brain.
Important structures
• Anterior ganglion (the brain).
Comparative physiology
• Crustacean brains are somewhere between insects
and cephalopods in terms of size and complexity.

18. Phylum: Mollusca, Class: Cephalopoda
Examples
• Octopuses, squids
Centralization
• Have a centralized nervous system with a central brain structure. However, only approximately 1/10 of an
octopus’ neurons are found in this central structure.
• It should be noted that of the three main designs of cephalopod nervous system, the nautilus system is
simpler than the decapod and octopod (although still more complex than any non-cephalopod mollusc).
Important structures
• The central brain structure (approx. 40 million neurons in octopuses). Particularly the vertical lobe, which
contains around 25 million of these neurons and is involved in learning and memory.
• Optic lobes (approx. 120-180 million neurons in octopi).
• Tentacles (approx. 300 million neurons in octopi). Appear to retain a significant amount of function without
connection to central brain.
Comparative physiology
• Evidence of greater decentralization than in vertebrates, since individual tentacles appear to contain the
necessary neural circuitry for voluntary movement.
• The brains of octopuses produce similar EEG recordings to vertebrates.
• Analogies have been drawn between lobes in the cephalopod brain and the thalamus in vertebrates, which
likely plays a role in pain and consciousness.
• Analogies have been drawn between the vertical lobe in the octopus and mushroom bodies in insects.

19. Typical vertebrate nerve systems
Examples
Birds, amphibians, reptiles, mammals
Centralization
Contains a central nervous system.
Anterior brain, axial spinal cord and
system of well organised nerves.
Important structures
CNS (the brain and Spinal cord), Nerves
Comparative physiology
Vertebrates have advanced brains and
spinal cord where information is
process quickly
The complexity in terms of size and
processing make them advanced.

20. Nerve physiology
• Ionic Equilibrium and Resting of Membrane Potential
ELECTROCHEMICAL POTENTIAL
Membrane Conductance
Definition
• Membrane conductance refers to the number of channels that are
open in a membrane. For example, Na + conductance is proportional
to the number of open channels that will allow the Na + to pass
through the membrane.
• It does not indicate if there will be a net diffusion of ions through the
channels.

21. General Properties
• If conductance is increasing, channels are opening, and if conductance is
decreasing, channels are closing
• The rate at which ions move across a membrane depends on the number of
open channels and the net force.
• When ions flow through channels, the cell's membrane potential changes.
• However, under physiological conditions, too few ions flow to produce a
significant effect on the ion's extracellular concentration or the concentration
gradient across the membrane.
• Channels are classified into three main groups:
• Ungated channels: Because these channels have no gates, they are always
open. For example, all cells possess ungated potassium channels.
• This means there will be a net flux of potassium ions through these channels
unless potassium is at equilibrium.

22. • Voltage-gated channels: In these channels, the gates open and/or
close in response to a membrane voltage change. For example, many
excitable cells possess voltage-gated sodium channels.
• The channels are dosed under resting conditions, but membrane
depolarization causes them to quickly open and then quickly close.
• Ligand-gated channels: The channel complex includes a receptor to a
specific substance (ligand).
• It is the interaction of the ligand with the receptor that regulates the
opening and dosing of the channel.
• For example, post-junctional membranes of chemical synapses possess
ligand-gated channels, and transmission depends on the interaction of
the transmitter and the ligand-gated channel

23. Net Force
• The net force acting on an ion across a membrane is the sum of two
independent forces.
Concentration Force
• Determined by the concentration difference across the membrane. The
greater the concentration difference, the greater the concentration force.
Electrical Force
• The size of this force is determined by the electrical difference across the
membrane (usually measured in millivolts [mV]).
• The in vivo magnitude is determined by the membrane potential (Em), which
is a value that must be measured or given.
• The direction of the force is based on the fact that like charges repel and
opposite charges attract. For example, if the membrane potential is -70 mV,
this represents a force of 70 mV that attracts all positive ions and repels all
negative ions.

25. Important Points Regarding CI-
• Because the measured membrane potential and the calculated equilibrium
potential are the same in magnitude and charge, the chloride ions are at
equilibrium.
• No matter what the membrane conductance to chloride is, there will not be a
net diffusion of chloride ions, nor will a change in the conductance of chloride
in a steady-state situation alter the cell's membrane potential.
Important Points Regarding K +
• The potassium ion is not at equilibrium. The net force on the potassium ions is
15 mV. Because this is a small force, the potassium ions can be considered dose
to but not quite at equilibrium.
• Because all cells at all times have open potassium channels (ungated), there
must be a net flux of potassium ions across the membrane.
• Also, because the ion will always diffuse to bring the membrane potential closer
to the ion's equilibrium potential, the flux must be an efflux from the cell.

26. • Increasing potassium conductance will accelerate the efflux of potassium ions and
hyperpolarize the cell.
• Increased extracellular potassium ions will reduce the efflux of the potassium ions
or even create an influx of potassium ions, the net result of which will be
depolarization.
• Decreased extracellular potassium ions will accelerate the efflux of the potassium
ions, the net result of which will be hyperpolarization.
• Thus, a cell's resting membrane potential is very sensitive to changes in the
extracellular potassium ion concentration.
Important Points Regarding Na +
• The sodium ion is not at equilibrium. The net force on the sodium ions is 135 mV.
This is considered a large force; therefore, the sodium ions are a long way from
equilibrium.
• In most cells, including excitable cells under resting conditions, there is not a
significant number of open sodium channels (conductance dose to zero). Thus,
even though there is a large net force, flux is minimal.
• An increase in membrane conductance to sodium ions will produce an influx of
sodium ions and depolarization.

27. • Because sodium channels are dosed under resting conditions, changes
in extra cellular sodium will not affect the resting membrane potential.
• Thus, a cell's resting membrane potential is not sensitive to changes in
extra cellular sodium.