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BCMB 415 EXAM NOTES NERVOUS
SYSTEM EVOLUTION &
STRUCTURE OVERVIEW 2026
ACTUAL SIITING EXAM TIPS
1. The first organism where INV and VER diverged
a. Urbilateria : is the hypothetical last common ancestor of inv. & ver. having a bilateral symmetry
2. What kind of developments happened when INV and VER diverged
a. Protostome and Deuterostomes
i. Protostome(INV) has a ventral nervous system in comparison to the gastrointestinal
system
1. Protostomes encompass most of invertebrates (we are highly related to starfish)
2. Look at the head = Brian and mouth but as you go to the back of body this flips
3.
ii. Deuterostome(VER) is dorsal to the gastrointestinal.
1.
b. Head vs tail morphology
c. Segmentation of the body.
d. We are closely related to starfish than other stuff
3. What was Evolutionary trend or things noticed when the INV and VER diverged
a. Bilateral symmetry-left and right side symmetrical
b. Segmentation- most organisms have the same body organization (in larval stages, less so in
adults or visa versa)
c. Cephalization- increasing amount of nervous system is localized in the ‘front’ part of the
organism.
d. Specialization of ganglia : groups of neurons that are interconnected with each other and serve a
common function, for example we see it in parts of the nervous system and the complexity of the
interconnections become more specialized and we go through evolutionary trends.
e. Sensory receptors- early organisms have none specific/not specialized, and going through
,2
evolution brings more specialization and complexity.
f. Central pattern generators (CPG)- (Dr. Hall section) similar to ganglia, interconnected
neurons but are not all in one space and all functioning to control complex rhythmic
behaviors-prevalence increases in evolution.
i. Focused on a specific repetitive or rhythmic pattern
1. Laying, walking, chewing & need coordination
4. Describe the basic NS organization of cnidaria, annelids, arthropods and molluscs:
Annelids:
i. Segmented worms (earthworms and niches and leeches)
,3
NS includes ventral nerve cord
1. so the NS goes along midline of ventral side
iii. Primitive “brain”
1. @ front end of org
2. not very complex
3. Fusion of 2 segmented ganglia);
iv. Segmented with a ganglia (1000 group of neurons) in each segment
1. Each segment going down body—has ganglion that are pretty much id from one seg
to another
2. Cell body is on the outside of ganglia(Unipolar Neurons)
3. Each segmented ganglia receives sensory info from and controls muscles in local
region
4. Divide into 2 1⁄2's and connected by a group of axons called Commissure &
connect one ganglion set to another though Connectives
a. ConnectiVes (mneumonic: connect Vertically the hemiganglions together) :
nerve cords that go from one segment to another
b. Commissure( mneumonic: connect horizontally the hemiganglions
together) : nerve projection (or axon) that connects the left hemisphere to
the right hemisphere (where segments join together)
i. Not all ganglia have a commissure, and they are neuronal projections
that cross the midline.
c. Segmental nerves : Nerve roots that carry messages to the ganglion from
peripheral. Connect ganglion to muscles & sensory receptors.
i. Helps send signals out
d.
v. Invertebrates : have big cell bodies
vi. *here has 1st ventral gang (right after brain) slightly diff from the others
vii. Ganglion(the ball) as identical from one end to the other
1.
viii. Baseball analogy of ganglion
1. the cell bodies are localized on the outside of that ball.
, 4
2. axons are interconnected in the inside of the ‘ball’
ix. NOTES :
1. These are deterministic developments of the nervous system.
a. you can't have a one^ for one identical neuron working in the brain system.
2. There are glial cells in invertebrates in this, but they're not highly diverse, we don’t
really know what they do there actually (lol sucks)
x.
b. Arthropods I: Crustaceans (more prominent), Lobsters, Crawfish
i. Crustaceans
1.
ii. Ventral nerve cord
1. Runs length of organism
2. Segmental & Bilateral (run through Ventral side of Organism)
3. More cephalization(fusion of ganglia)
4. Extends to a series of paired segmental ganglia running through ventral side
a. usually identical from one segment to another
iii. Have identical ganglia
iv. Anterior ganglia have fused to form brain
1. Complex brain at the front end of the organism.
2. *The lobster brain is connected to a first ventral ganglion
3. Brain is larger than gang*see primary 1st ventral gang that is more complex than
gang
c. Arthropods II: Insects (more advanced than other arthropods)
i. Grasshopper
ii. Segmental ganglia(more fusion together)
1. First ventral ganglion (subesophageal) ganglion-stereotyped motor output and
regulation of all of the mouth parts.
Primarily controls the mouth
BCMB 415 EXAM NOTES NERVOUS
SYSTEM EVOLUTION &
STRUCTURE OVERVIEW 2026
ACTUAL SIITING EXAM TIPS
1. The first organism where INV and VER diverged
a. Urbilateria : is the hypothetical last common ancestor of inv. & ver. having a bilateral symmetry
2. What kind of developments happened when INV and VER diverged
a. Protostome and Deuterostomes
i. Protostome(INV) has a ventral nervous system in comparison to the gastrointestinal
system
1. Protostomes encompass most of invertebrates (we are highly related to starfish)
2. Look at the head = Brian and mouth but as you go to the back of body this flips
3.
ii. Deuterostome(VER) is dorsal to the gastrointestinal.
1.
b. Head vs tail morphology
c. Segmentation of the body.
d. We are closely related to starfish than other stuff
3. What was Evolutionary trend or things noticed when the INV and VER diverged
a. Bilateral symmetry-left and right side symmetrical
b. Segmentation- most organisms have the same body organization (in larval stages, less so in
adults or visa versa)
c. Cephalization- increasing amount of nervous system is localized in the ‘front’ part of the
organism.
d. Specialization of ganglia : groups of neurons that are interconnected with each other and serve a
common function, for example we see it in parts of the nervous system and the complexity of the
interconnections become more specialized and we go through evolutionary trends.
e. Sensory receptors- early organisms have none specific/not specialized, and going through
,2
evolution brings more specialization and complexity.
f. Central pattern generators (CPG)- (Dr. Hall section) similar to ganglia, interconnected
neurons but are not all in one space and all functioning to control complex rhythmic
behaviors-prevalence increases in evolution.
i. Focused on a specific repetitive or rhythmic pattern
1. Laying, walking, chewing & need coordination
4. Describe the basic NS organization of cnidaria, annelids, arthropods and molluscs:
Annelids:
i. Segmented worms (earthworms and niches and leeches)
,3
NS includes ventral nerve cord
1. so the NS goes along midline of ventral side
iii. Primitive “brain”
1. @ front end of org
2. not very complex
3. Fusion of 2 segmented ganglia);
iv. Segmented with a ganglia (1000 group of neurons) in each segment
1. Each segment going down body—has ganglion that are pretty much id from one seg
to another
2. Cell body is on the outside of ganglia(Unipolar Neurons)
3. Each segmented ganglia receives sensory info from and controls muscles in local
region
4. Divide into 2 1⁄2's and connected by a group of axons called Commissure &
connect one ganglion set to another though Connectives
a. ConnectiVes (mneumonic: connect Vertically the hemiganglions together) :
nerve cords that go from one segment to another
b. Commissure( mneumonic: connect horizontally the hemiganglions
together) : nerve projection (or axon) that connects the left hemisphere to
the right hemisphere (where segments join together)
i. Not all ganglia have a commissure, and they are neuronal projections
that cross the midline.
c. Segmental nerves : Nerve roots that carry messages to the ganglion from
peripheral. Connect ganglion to muscles & sensory receptors.
i. Helps send signals out
d.
v. Invertebrates : have big cell bodies
vi. *here has 1st ventral gang (right after brain) slightly diff from the others
vii. Ganglion(the ball) as identical from one end to the other
1.
viii. Baseball analogy of ganglion
1. the cell bodies are localized on the outside of that ball.
, 4
2. axons are interconnected in the inside of the ‘ball’
ix. NOTES :
1. These are deterministic developments of the nervous system.
a. you can't have a one^ for one identical neuron working in the brain system.
2. There are glial cells in invertebrates in this, but they're not highly diverse, we don’t
really know what they do there actually (lol sucks)
x.
b. Arthropods I: Crustaceans (more prominent), Lobsters, Crawfish
i. Crustaceans
1.
ii. Ventral nerve cord
1. Runs length of organism
2. Segmental & Bilateral (run through Ventral side of Organism)
3. More cephalization(fusion of ganglia)
4. Extends to a series of paired segmental ganglia running through ventral side
a. usually identical from one segment to another
iii. Have identical ganglia
iv. Anterior ganglia have fused to form brain
1. Complex brain at the front end of the organism.
2. *The lobster brain is connected to a first ventral ganglion
3. Brain is larger than gang*see primary 1st ventral gang that is more complex than
gang
c. Arthropods II: Insects (more advanced than other arthropods)
i. Grasshopper
ii. Segmental ganglia(more fusion together)
1. First ventral ganglion (subesophageal) ganglion-stereotyped motor output and
regulation of all of the mouth parts.
Primarily controls the mouth
