NERVOUS SYSTEM EVOLUTION

Question 1

What are the most basic properties of a nervous system?

Answer 1

Ability to be receptive and respond.

Question 2

What is an example f a single celled organism with a basic level nervous system?

Answer 2

Euglena
Responds to light photons transduced by pigment localised to an eye spot
Has a flagellum that propels

Question 3

What accompanies multicellularity?

Answer 3

Specialisation

Question 4

What does a more complex nervous system allow?

Answer 4

Anticipatory and responsive behaviours.

Question 5

What multicellular simple organism was studied in order to work out how nervous systems evolved?

Answer 5

Sponges

Question 6

What does the nervous system of a Sponge entail?

Answer 6

Water flows through the body wall and out via the osculum.

The flow of water is regulated by myocytes - specialised cells that respond to stretch.

Question 7

What is thought of stretch-receptive myocytes in terms of evolution?

Answer 7

It is thought stretch receptive myocytes evolved into primordial nervous systems.

Question 8

How are stretch receptive myocytes thought to have evolved into the primordial nervous system.

Answer 8

Myoctyes are mechanoreceptive cells that span the outer epithlial layer. Evolutionarily it is thought that a divison may have given rise to two different cells, one which stayed in the ectoderm and one which migrated. This is marked as the first neurons: sensorimotor cells that span from exterior to interior effector cells.

Question 9

What comprises the nervous system of a Hydra?

Answer 9

Consists of nerve nets of sensory, interneurons and motorneurons. New evidence suggests the potential to secrete regulatory peptides.

Question 10

Flat and segmented worms show features of higher organisation. What features are these.

Answer 10

Gangliation: lots of neruons coalesce
Cephalisation: clusters of brain like cells
Bilateral symmetry: axis formation
Fasciculation: nerve coming together
Commissures: axons crossing the midline

All are features of organisation.

Question 11

Where do ganglia seem to bundle in the segmented worm and why?

Answer 11

Around the mouth.

Survival is more likely to occur if you can feed in a controlled form ie control of food capture and digestion.

Question 12

In the human, where is the basal forebrain (hypothalamus) able to be palpated.

Answer 12

Near the soft palate.

Question 13

Why is the C Elegans an important model organism?

Answer 13

Its nervous system has been entirely mapped. This worm is the support for all theory of nervous system evolution.
302 neurons and 56 ganglia arrange in ventral, dorsal and lateral nerve cords.

Question 14

How can C Elegans be used as support for theory of nervous system evolution?

Answer 14

As C Elegans develops from a single cell, we can trace the progeny of cells as they divide and differentiate.

Question 15

What is the lineage of neural cells in C Elegans?

Answer 15

P0 gives rise to P1 and AB
P1 gives rise to body, muscles, gut aswell as the germ line
AB gives rise to the hypodermis and nervous system.

Question 16

What are the stages of the life cycle of a Drosophila?

Answer 16

Day 0 - Egg
Day 1 - Hatching into larva (3 larval stages)
Day 5 - Pupation (to become a pupa)
Day 9 - Metamorphosis into an adult fly

Question 17

What evidence of higher organisation is there in the Drosophila?

Answer 17

There is evidence of clusters of neurons above the mouth as well as a photocerebrum (basic brain) and eyes.

Question 18

What are the stages of the developing nervous system in Drosophila?

Answer 18

The region giving rise to the the nervous system lies next to the ectoderm.
The neurogenic region migrates downwards as the mesoderm involutes - this is gastrulation.
Individual neuroblasts delaminate and migrate inwards before coalescing - this is neurogenesis.

Question 19

What is the key difference between vertebrates and invertebrates?

Answer 19

The vertebrate nervous system arises from a sheet of cells called the neural plate which rolls up to give the neural tube after extending from the anterior to the posterior. This occurs on the dorsal side. In invertebrates, this is on the ventral side.