C13 - Nerve nets

Question 1

Do animals in the phyla that appear very early in the fossil record have nervous systems?

e.g. Phyla Porifera, which include sponges

Answer 1

No

Question 2

Additional side

Evolution…

Answer 2

1. Phylum porifera e.g. Sponges (No nervous system)
2. Phylum Cridaria e.g. Jelly Fish, have radial symetry and a Nervous network
3. Phylum Chordates e.g. humans have bilateral symetry and a central nervous system

Question 3

What is a nerve net?

Answer 3

• The simplest type of nervous system.
• It is A diffuse network of cells that group into ganglia but do not form a brain.
• There are two types

1. Ganglion cells provide connections in several directions
2. Sensory cells detect stimuli e.g. light, sound, touch

Question 4

what are the 2 types of cell in a nerve net

Answer 4

1. Ganglion cells provide connections in several directions
2. Sensory cells detect stimuli, e.g. light, sound, touch or temperature

Question 5

What is a common example that i will see of a creature with a nerve net

or

What is the model organism for studying nerve nets?

Answer 5

A Hydra

Question 6

what are the 3 reasons why a hydra is the model organism for studying nerve nets

Answer 6

A nerve net has

1. A simple pattern
2. Its easy to manipulate in experiments
3. Regenerates rapidly i.e. when replacing a lost tentacle

Question 7

Where is a hydra’s nerve net found?

Answer 7

• The nerve net is found in its ectoderm…
  
  • The outer layer… of the two layers of cells… of its body wall.

Question 8

What does the nerve net allow the hydra to do?

Answer 8

The nerve net…

Allows the hydra to sense light, physical contact and chemicals.

In response, it can contract to perform locomotion hunt and feed so even without a brain, it shows complex movements and behaviours.

Question 9

Additionl Slide

What are the limitations of a nerve net?

Answer 9

• A nerve net cannot detect the direction of a stimulus
• However…
• A larger stimulus stijulates more cells and triggers a larger response

Question 10

What are the major differences between a hyrdras nerve net and the central nervous system of a human?

Answer 10

Hydra Human

System Nerve net CNS

Cell types 2 Many

Regeneration. Rapid Very slow

Myelin Sheath. Absent Present

Conduction speed. Slow ~5m/s^-1 Fast ~120m/s^-1

Ability to generate neurones. Present Absent