THE NERVOUS SYSTEM OF INVERTEBRATES AND VERTEBRATES
INVERTEBRATES
VERTEBRATES
Most invertebrate nerve cords are situated
ventrally. Invertebrates do not have a spinal
cord, and the connectives go from one
ganglion to the next in invertebrates
PORIFERA
CNIDARIA
PLATYHELMINTHES
NEMATODA
ANNELIDA
ARTHROPODA
MOLLUSCA
ECHINODERMATA
The spinal cords of vertebrates are situated
dorsally. In the spinal cord of vertebrates,
neurons and glial cells create a continuous
column of tissue. The typical nervous system
of vertebrates contains a central nervous
system where information is processed
quickly
NERVOUS SYSTEM OF INVERTEBRATES
No true nervous system
Presence of nerve net
Two anterior ganglia with a cephalized
nervous system
Ventral and dorsal nerve cord
Centralized brain, and small peripheral ganglia
Larger ganglia
3 pairs of ganglia
Presence of nerve net
NERVE NETS
CNIDARIA
ECHINODERMATA
Instead of a body concentrating neurons, A circumoral nerve ring and the outside
these phyla have a central nerve net. One or portion of the radial nerve cords are both
more nerve nets make up the nervous system, present
and the sensory ganglia is where information
is most likely to be integrated.
Ex: Starfish
Ex: Jellyfish
The nervous system contain diffuse nerve The majority of sensory information is
nets that transmits information bidirectionally absorbed peripherally
Both are invertebrates who has decentralized nervous systems which do not contain a
centralized concentration of neurons
MAMMAL
FISH
AMPHIBIANS
REPTILES
NERVOUS SYSTEM OF VERTEBRATES
OLFACTORY
CEREBRAL
RECEPTORS
HEMISPHERE
Well-developed,
When
removed,
situated in pits on the fish
can
still
snout
maintain normal
function
smaller than optic more
developed
nerve
than in fishes
Well-developed for
well-developed
vomeronasal system of cortex and basal
odor detection
ganglia
CEREBELLUM
Does not contain
deep
cerebellar
nuclei
less developed
formed by large
corpus cerebelli and
small flocculus
BIRDS
Small, majority have
approximately 50
receptors
Similar to
amphibians, and is
smooth
MAMMALS
well-developed
Dominates
the Large and trilobed
mammalian brain
Note: Amongst all the
vertebrates, mammals
have a large brain-tobody ratio
Trilobed
FISH
AMPHIBIANS
BRAIN IN VERTEBRATES
 Olfactory lobes are large
 Cerebral hemispheres are large
 Cerebellum is large


REPTILES




BIRDS



MAMMALS





Olfactory nerves are smaller
than optic nerve
Cerebral hemispheres are
more developed than in fishes
Cerebellum is less developed
Telencephalon is the largest
region of the brain
Olfactory lobes are well
developed
A pair of auditory lobes is
posterior to the optic lobes
Olfactory nerves are small
Optic nerves are welldeveloped
Cerebral hemispheres, optic
lobes, and cerebellum are
large
Cerebellum is trilobed
Olfactory lobes are welldeveloped
Cerebellum is large and
trilobed (lobes have gyri and
sulci)
The mammalian brain is
dominated by cerebral
hemisphere
Amongst all the vertebrates,
mammals have a larger brainto-body ratio
Trivia: The tree shrew has the highest brain-to-body ratio of any mammal despite its size.
NERVOUS SYSTEM OF OCTOPUS COMPARED TO HUMANS
HUMAN (MAMMAL)
OCTOPUS (CEPHALOPODS)
“Smartest animal”
“Smartest Invertebrate”
Their neurons are located in a network of
specialized structures that are located
throughout the body of the octopus. Each arm
has its own cluster of nerve cells that allows
the octopus to independently control their
arms to process information in their
Nerve cells are located in the brain and spinal
environment. The distribution of neurons
cord. The brain is responsible for processing
allows the octopus to have a high-level
information, and the spinal cord transmits
dexterity and adaptability
information between the body and the brain
Type of Nervous System: Decentralized
Type of Nervous System: Centralized nervous
nervous system
system
Both have complex neural systems and centralized brain that can integrate sensory information
and also allows them to perceive visual and auditory information with great accuracy.
PALLIUM
Lungfish and amphibian (frog)
⁃
presence of dorsal, lateral, and medial pallial division
Reptiles (Lizard)
⁃
Presence of dorsal ventricular ridge (dorsal, lateral, medial, and hypertrophies region)
⁃
dominates the central region of the cerebral hemisphere
⁃
derivative of the lateral pallium
⁃
receive visual, auditory, and sensory stimuli
Birds (pigeon)
⁃
accounts for the relative increase in size of the cerebral hemispheres and growds the
lateral ventricle into a slit
⁃
⁃
The dorsal Hypertrophies region is called the WULST
highly organized visual information for stereoscopic vision
Mammals (mouse)
⁃
Dorsal pallium is enlarged (neocortex)
⁃
Unlike reptiles and birds, they have enlarged cerebral hemispheres due to the DVR
⁃
The mammalian neocortex (NC) comprises two moieties, one dorsal (NCd, receiving
lemnothalamic somatosensory and visual inputs), and one lateral (NCl, receiving auditory and
visual collothalamic inputs)
AXON REGENERATION IN ZEBRAFISH AND AXOLOTL
Unlike other vertebrates, zebrafish and axolotls are capable of axon regeneration. Meaning,
they have the ability to regenerate any part of their nervous system, including the central
nervous system. The nervous system responds to the damage through:
1. When the axon is damaged, the reactive glial cells releases growth factors to promote
regeneration of axon
2. Growth factors released by glial cells signal nearby neurons to form new connections
and pathways, and to stimulate the migration of neural stem cells to the injury
3. Process of cell signaling happens for the coordination of the regeneration.
4. After the injury has been regulated, neural stem cells migrate to the injury to form
connections with other neurons and establishing pathways, causing an axon growth
5. Axons grow in a specific direction with the help of attractive and repulsive signals
Uninjured spinal cord
Loss of axonal connections
Reconstruction
Regenerated axon
Axonal regrowth
Time course of axonal regeneration in adult zebrafish stained with acetylated-tubulin (green)
and DAPI (blue). (A) Uninjured adult spinal cord. (B) 3-day post transected spinal cord showing
complete loss of axonal connections (green) in the injury epicenter (yellow star). (C) 15-day post
transected spinal cord showing some regenerated axons passing through the injury epicenter
(yellow star). (D) A 30-day post transected spinal cord showing significant numbers of
regenerated axons passing through the injury epicenter (yellow star). Significant axonal
regrowth can be observed compared to uninjured cord.
THE SENSE ORGANS OF INVERTEBRATES AND VERTEBRATES
INVERTEBRATES
VERTEBRATES
The sense organs in invertebrates are less
specialized and complex. They have multiple
sensory structures that are basic, such as the
antennae of insects that serve as multiple
sense organ
Sense organs, like eyes for detecting visual
stimuli, ears for detecting auditory stimuli,
and nose for detecting olfactory stimuli, are
specialized, organized, and interconnected
structures that work together to provide a
comprehensive sensory experience for the
vertebrates
Both vertebrates and invertebrates retreat in response to unpleasant stimuli to lessen the
chance of being harmed with the help of neural processing where the sense organs of both
invertebrates and vertebrates have the ability to transmit signals that was detected by the
sensory receptors to the nervous system to be interpreted.
SENSE ORGANS BETWEEN TWO INVERTEBRATES
INSECTS (ARTHROPODS)
SNAILS (MOLLUSCA)
Insects have compound eyes (ommatidia)
Snails have simple eyes (ocellus) made up of
with high amounts of photoreceptor cells.
one photoreceptor cell, therefore is only
These compound eyes can detect motion,
helpful for registration of the presence of
colors, and patterns. Insects have sensillum
light. Snails have antennae as
as chemoreceptors, mechanoreceptors,
chemoreceptors.
thermoreceptors.
Both have olfactory systems that can detect chemical signals, such as pheromones and odors
to find potential mates and locate food respectively.
SENSE ORGANS BETWEEN VERTEBRATES
ECHOLOCATION
MARINE MAMMALS
CAVE-DWELLING MAMMALS
TOOTHED WHALES
BATS
These marine mammals can identify objects Bats uses echolocation to navigate while flying
underwater by producing short sound pulses and locating their pray in the dark caves. They
and listening for their echoes in the muddy produce sound pulses by tongue-clicking
ocean depths. They use sound waves by
contraction of pharyngeal muscles to release Types of echolocations: Frequencyhigh-pressure of air and water.
modulated calls and constant-frequency calls
Animals who uses echolocation involves self-producing short and high-frequency sounds, then
listening for the returning echoes
Trivia: Visually impaired humans utilize both active and passive echolocation
Reference:
Antczak, James., & Udvadia, Ava. (2023). Axon Regeneration: Methods and Protocols. Humana
Press.
G.S., Peter. (2016, December 6). Other Minds: The Octopus, The Sea, and the Deep Origins of
Consciousness. Macmillan Publishers.
Thomas, J., Moss, C., & Vater, M. (2004). Echolocation in Bats and Dolphins. University of Chicago
Press.