Nervous systems Flashcards
What makes up the nervous system?
CNS and PNS
CNS = brain and nerve chord
PNS = sense organs and receptors
what are neuroid cells?
no neurons or discrte sense organs
contractile cells - myocyctes
- grouped concentrially around pores and major canals
- no synapses, many microtubules and filaments in cytoplasm., mechanical stimulation between adjacent cells.
Porifera
What are nerve nets/ diffuse networks?
Neurons arranged in networks, and synapse with each other - receive stimulus from all directions.
Cnidarians and Ctenophores.
what are Ganglia / Brain and multiple nerve chords? in the simplest form.
CNS 1
Plathelminthes.
Anteriorly - the concentration of nerve tissue forming ganglia (nerve bundle), with optic nerves, and auricles.
> contributed to the development of bilateral symmetry and forward movement.m
Multiple nerve cords running along the length - ladder-like nervous system
Brain and reduced number of nerve chords?
CNS 2
2 subdivisions
- protostome plan
- deuterostome plan
Protostome Plan - brain and reduced neeve chords?
CNS 2
Dorsal brain with ventral nerve chords = probs evolved from ladder-like systems.
Segmented taxa - Annelid and Arthropoda, with segmented ganglia. Increase functioning.
Non-segmented taxa - molluscs, additional ganglia scattered around body, cephalopods have fused ganglia to form a large brain, allows for associative learning.
polychetes are above ground and very active - more developed brain.
look at examples in slides lecture 1 NS slide 6
Deuterostome plan: Brain and nerve chord?
CNS 2
Echinoderms, have a central nerve ring and radial nerve chords
Chordates, have a brain (ganglia) with dorsal nerve chord, simple and somtime very reduced. - nerve chord and anterior swelling, neural gland and small cereba; ganglion.
Diffuse networks arw advantagous for radially symmetrical/ floating animals
Distinction between ganglia and brains is subjective - often depends on size and concentration of nerve tissue.
Size and complexity of brain is linked ot life style.
slide 8
What is PNS?
Tactile touch receptors.
- hair like or birstle strucutres
- linked to snesory nerves
- usaully all over the body but concentrated, on organs of feeding, moving anfd anterior.
- sesillia in arthropoda, hairs, bristles, pores or slits.
What are chemoreceptors?
used to find food, detect chemicals.
Speciallised cells with a receptor process extending through the cuticle or epidermal cells
- sensory nerve fibres extend from base of cell
- hollow, thin bristles with permable cuticle or pores (arhtropoda)
may be scatteredover whole body but concentrated at anterior.
Some unique receptors?
Rheoreceptors in Plathelminthes - detecting water movement
Proprioreceptors in Arhtropoda- stretch receptors, linked ot jointed appendages.
Vision and photoreceptors?
Eyes:
– “Photoreceptor shielded on one side by nearby
pigment which allows the detection of the
direction of a source of light”
* Can be single cell
– “an organ that can produce an image, however
crude, and not simply detect light.”
Orientation, navigation, predator avoidance, finding mates and prey, improved competitive ability diverification of sighted taxa.
interrelatedness between levels of acticvity and quality of vision.
What are pigment cells?
light sensitive, absorb light energy.
colour vision depends on different pigements.
from the retina.
What are photorecptors?
cilia or microvilli - dailiy break down and formation.
What is refraction?
beding of light waves.
occurs in the:
- cornea (treestrial)
- cornea and lens (aquatic)
What does the sharpness of the image depend on?
Refractive index fluid in eyes vs air or water.
Shape of the lens. [ flat, less refraction or round, more refraction ]
Distance between the lens and retina.
Mirrors in aquatic spp. ares of little light.
Vision can be split into 8 type according how light is bent.
Chambered eyes - light is bet by the lens, mirrors - reflect the light onto the retina.
Compound eyes
shadows, refraction and reflection.
How does vision in the sea work?
Change in visual scene with increasing depth has influenced evolution of vision in the sea.
Most light occurs in photic zone, but availability not consistent.
– Decreases with increase in depth
– Dark habitats (under rocks etc.)
– Most animals, including very active spp that rely on good
eyesight, occur in photic zone
- Most variable eye types are found among animals in photic zone.
- In deep environments, animals either have very large eyes or are blind
Simple pit eye
vision in water
Inactive speices live in the dark - no lens, cornea, can detect light direction and intensity.
Plathelminthes, Annelid, Gastropoda
Complex camera-type eye
vision in the sea
Active swimmers and predators.
Have an iris - controls light
cornea - modified cuticle section
true lens does most of the focusing = light detection and intensity, percieve images, discriminitae by size, shape and orientation.
Annelid, Cephalopod, Cnidaria
Single chambered eye with a single mirror?
Vision in the sea
actively swimming bivalvia
images are foremed using a concave mirror.
scallops
Basic compound eye
visionin the sea
sessile/ sedentary animals.
Each receptor is sheilded from neighbour by simple pigmne tube.
Burglar alarm eyes.
Clams
Chiton eyes
Vision in sea
refracting and reflecting superposition compound eye
in areas of poor light quality
krill, shrimp, lobsters
