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BMS 249 - Developmental Neurobiology > Nervous system evolution > Flashcards

Nervous system evolution Flashcards

1
Q

Describe Euglena

A

A single cell organism which has a flagella and an eyespot- responds to light and moves away from it

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2
Q

What allows more complex behaviour and why?

A

Multicellular organisms - allows different cells to have different functions and allows a nervous system to develop

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3
Q

How is a sponge more developed that Euglena?

A

Has an epithelium which has different cell types - epithelial support cells and myocytes (muscles cells)

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4
Q

What are myocytes?

A

Mechanoreceptive cells that span the outer layer of the ectoderm (skin)

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5
Q

What can myocytes do in response to a signal? (daughter cells)

A

Proliferate to give:
- One daughter cell which ends up below the ectoderm (EFFECTOR CELL)

  • One daughter cell which stays in the ectoderm and has a more complex shape - forms connections with the other daughter cell (SENSORIMOTOR)

PRIMORIDAL NERVOUS SYSTEMS

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6
Q

What behaviours can single cell organisms have?

A

Receptive and responsive

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7
Q

What behaviours can multicellular organisms have?

A

Anticipatory and response

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8
Q

Where did the first sensory motor system evolve from?

A

Myocytes spanning the ectoderm proliferating to give a daughter cell which makes connections with the daughter cells below the ectoderm

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9
Q

How are hydra different to sponges?

A

Have a 2 layered nervous system - (sensory, motor to effectors)

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10
Q

Where do the motor neurons in a hydra come from?

A

Evolve from the sensory neurons spanning the epidermis, come to sit beneath the skin, above the effector cells

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11
Q

Where do motor neurons have an output too?

A

Other motor neurons or effector cells

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12
Q

How is it proved that Hydra are more complex than a one way flow nervous system?

A

They have neuropeptidergic cells which produce neurosecretory proteins which are regulatory

Secrete SOMATOSTATIN - regulates the myocytes by sensory neurons (FEEDBACK)

2-way flow of information between sensory and motor neurons

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13
Q

Which cells show proof of evolution of a primordial nervous system?

A

Sponges - sensory neurons

Hydra - sensory, motor and interneurons. Also have 2-way flow of information between the sensory and motor neurons

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14
Q

Apart from sensory and motor neurons, what other neurons do hydra have?

What does this allow?

A

Interneurons

More complex interactions and outputs

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15
Q

Where do interneurons lie in the hydra?

A

Lie between sensory and motor neurons

Lie between neurosecretory and motor neurons

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16
Q

What are the first neurons to develop in the body?

Which organism are these first evident?

A

Sensorimotor neurons - span the epidermis

Sponges

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17
Q

What do sensorimotor neurons develop into?

A

Sensory neurons (which span the skin)

Motor neurons which come to sit underneath the skin

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18
Q

What can interneurons be?

A

Excitatory or inhibitory

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19
Q

How are the nerves arranged in a hydra?

A

In a nerve net all overt the body - joined up and connected together in a diffuse system

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20
Q

What is the most primitive nervous system?

A

Nerve net (Hydra)

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21
Q

How is the nervous system of flatworms more complex than in the hydra?

What does this allow?

A

No diffuse nerve net, there is more organisation and clustering of nerves

Can predict position of major clusters of nerves

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22
Q

What clustering/organisation is present in the flatworm?

A
  • Gangliation
  • Cephalization
  • Bilateral symmetry of the nervous system
  • Fasciculation
  • Commissures
23
Q

What is gangliation in the nervous system?

A

Clustering of neuronal cell bodies

24
Q

What do ganglions/nuclei of the nervous system contain?

A

Cell bodies of the same neurons or cell bodies of different neurons

25
Q

What is cephalization of the nervous system?

What does this form during evolution?

A
  • Concentration of the sense organs and nervous control at the anterior end of the body
  • Forms the head and the brain
26
Q

How is there a clear anterior and posterior end of the flatworm?

A

More complex organisation of complex neurons near the head and specialise ganglia around the pharynx and mouth

27
Q

What is fasciculation?

A

Bundling of the axons of the nervous system

28
Q

What are commisures?

A

Neurons crossing the midline to synapse on the contralateral side of the body

29
Q

What do commisures allow?

A

Communication between the left and right side of the body and direction of movment

30
Q

In annelids (segmented worms) where is the biggest clustering of ganglia found and why?

A

Around the pharynx - allow to catch food

31
Q

What are suprapharyngeal ganglia?

A

Specialised ganglia piling up dorsally to the pharynx

32
Q

What does the suprapharyngeal ganglia produce?

What does this prove?

A

Neurotransmitters similar to that in the human brain

Very primitive brain formed above the mouth

33
Q

What was the primitive brain used for?

A

Originally for the organism to be the best at eating and surviving

34
Q

What is special about the c.elegans?

A

Well studied - entire nervous system has been mapped

35
Q

What is a nerve ring?

A

Huge array of ganglia around the pharynx in c.elegans

36
Q

What proves that skin and nervous system have an early lineage relationship?

A

Through the study of c.elegans:

  • All cells develop from a single cell (P cell)
  • Divides into P and AB cell
  • Hypodermis and other cells of the body derive from the AB cells
37
Q

Where does the nervous system lie in the drosophila and what does it show?

A

Ventrally

Shows:

  • Gangliation
  • Fasiculation
  • Cephalization
38
Q

How are the neurons in the head of the drosophila arranged?

A

Clusters above the mouth/pharynx

Complex array around the subosophageal region, extending dorsally

Signs of protocerebrum (early brain)

Eyes

39
Q

In which organism is an early brain formed?

A

Drosophila (insect)

40
Q

How do we know how the nervous system in humans develop?

A

Through studies in drosophila

41
Q

How does the nervous system develop in drosophila?

A

1) Migration of neurogenic region ventrally as gastrulation occurs (ectoderm moves into the embryo, 2 areas of neurogenic region are brought together)
2) Individual cells delaminate and become neuroblasts (dividing progenitors)
3) Neuroblasts divide and give: 2nd neuroblast and a ganglion mother cell
4) GMC form neurons and ganglia
5) Neuroblast are retained as a multipotent cell

42
Q

When is the nervous system set aside in development?

A

Very early

43
Q

How is the development of the vertebrate nervous system different to invertebrates?

A
  • Nervous system located on the dorsal side of the body (fascicles)
  • NS also develops from the ectoderm as well as the neurogenic region
44
Q

What are the commonalities of the nervous system between vertebrates and lower order animals?

A

1) Sensory and motor nerves (in something even as simple as hydra)
2) Specialised set of neurons around the mouth and pharynx, which overtime has progressed to be a part of the ventral forebrain

45
Q

What is the most ancient part of the CNS and where is it found?

A

The hypothalamus

Found in very close proximity to the pharynx

46
Q

What does the hypothalamus do?

A

Coordinates activities and behaviours in the ABSENCE of conscious higher order mechanisms (autonomous manner)

47
Q

What are the key differences between the development of the nervous system between vertebrates and lower order animals?

A

1) Neurogenic region doesn’t delaminate - maintains cell-cell contacts and increased cohesion with neighbours
2) Neural cells stay as a layer called the NEUROEPITHELIUM (or neural plate)
3) Ectodermal layers are brought together and fuse over the neural tube

48
Q

What is the neuroepithelium (neural plate)

A

A flat, single-cell layered plate-like structure of neural cells

49
Q

Which organism allowed us to understand how the nervous system was set aside?

A

Xenopus

50
Q

What do all vertebrates share?

A

A common body plan

51
Q

When does the neural plate appear in development?

A

2 weeks post fertilisation

52
Q

What can be identified at 4.5 weeks post fertilisation?

A

Midbrain, forebrain, hindbrain and spinal cord

53
Q

How does the neural tube develop?

A

Neural plate gets longer and then rolls up and elongates along the AP axis

BMS 249 - Developmental Neurobiology (16 decks)

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