Nervous system evolution Flashcards by Karla Littleford

Describe Euglena

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

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What allows more complex behaviour and why?

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

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How is a sponge more developed that Euglena?

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

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What are myocytes?

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

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

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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What behaviours can single cell organisms have?

Receptive and responsive

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What behaviours can multicellular organisms have?

Anticipatory and response

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Where did the first sensory motor system evolve from?

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

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How are hydra different to sponges?

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

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Where do the motor neurons in a hydra come from?

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

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Where do motor neurons have an output too?

Other motor neurons or effector cells

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

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

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

What does this allow?

Interneurons

More complex interactions and outputs

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Where do interneurons lie in the hydra?

Lie between sensory and motor neurons

Lie between neurosecretory and motor neurons

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What are the first neurons to develop in the body?

Which organism are these first evident?

Sensorimotor neurons - span the epidermis

Sponges

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What do sensorimotor neurons develop into?

Sensory neurons (which span the skin)

Motor neurons which come to sit underneath the skin

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What can interneurons be?

Excitatory or inhibitory

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How are the nerves arranged in a hydra?

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

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What is the most primitive nervous system?

Nerve net (Hydra)

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

What does this allow?

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

Can predict position of major clusters of nerves

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What clustering/organisation is present in the flatworm?

Gangliation
Cephalization
Bilateral symmetry of the nervous system
Fasciculation
Commissures

What is gangliation in the nervous system?

Clustering of neuronal cell bodies

What do ganglions/nuclei of the nervous system contain?

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

What is cephalization of the nervous system? What does this form during evolution?

- Concentration of the sense organs and nervous control at the anterior end of the body - Forms the head and the brain

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

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

What is fasciculation?

Bundling of the axons of the nervous system

What are commisures?

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

What do commisures allow?

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

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

Around the pharynx - allow to catch food

What are suprapharyngeal ganglia?

Specialised ganglia piling up dorsally to the pharynx

What does the suprapharyngeal ganglia produce? What does this prove?

Neurotransmitters similar to that in the human brain Very primitive brain formed above the mouth

What was the primitive brain used for?

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

What is special about the c.elegans?

Well studied - entire nervous system has been mapped

What is a nerve ring?

Huge array of ganglia around the pharynx in c.elegans

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

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

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

Ventrally Shows: - Gangliation - Fasiculation - Cephalization

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

Clusters above the mouth/pharynx Complex array around the subosophageal region, extending dorsally Signs of protocerebrum (early brain) Eyes

In which organism is an early brain formed?

Drosophila (insect)

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

Through studies in drosophila

How does the nervous system develop in drosophila?

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

When is the nervous system set aside in development?

Very early

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

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

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

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

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

The hypothalamus Found in very close proximity to the pharynx

What does the hypothalamus do?

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

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

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

What is the neuroepithelium (neural plate)

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

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

Xenopus

What do all vertebrates share?

A common body plan

When does the neural plate appear in development?

2 weeks post fertilisation

What can be identified at 4.5 weeks post fertilisation?

Midbrain, forebrain, hindbrain and spinal cord

How does the neural tube develop?

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