Invertebrate-Vertebrate NS Organization Flashcards
How do paramecium use calcium channels?
1) stretch receptors release calcium when they bump into an obstacle
2) calcium allows cilia to beat backwards
3) once the calcium is used the paramecium moves forward again
Describe the nervous system of a cnidarian.
they have a nerve net and neural “plexi”
they have little or no ganglia or anterior “brain”
What are ganglia?
collections of neurons
What are neural “plexi”?
loose collections of neurons similar to enteric ns in vertebrates
Describe the nervous system of a non-segmented flatworm.
with bilateral symmetry came cephalization (brain and nerve cord present)
What is cephalization?
concentration of neurons into ganglia at the anterior end
Describe the nervous system of a leech.
- with segmentation came segmental “ganglia”
- brain/head ganglia present
- processes of packet glia surrounding neural somata
What is segmental ganglia?
in each segment there is the same cells (number, position, type) connected by intersegmental connectives and with nerves to the periphery
Describe the nervous system of an arthropod.
- the fusion and specialization of segments accompanied the fusion and specialization of ganglia
- elaborate sensory functions = larger brains
- specialization of thoracic ganglia for locomotion
- “interior” neuropil
What is “interior” neuropil?
where input and output synapses intermix
Describe the nervous system of a gastropod (mollusk).
- large neuronal somata that can fire action potentials (up to 1 mm)
- supra and subesophogeal ganglia and pleural ganglia
- buccal ganglia
Are all of the gastropods neurons large?
no (ex. limax maximus has small neurons to process olfactory/olfacto-spatial information)
Describe the nervous system of a cephalopod.
- largest amount of cells and density in invertebrates
- largely visual processing
- retina - optic nerves - optic lobes
- cell bodieson outside with neuralpil inward
What is a central pattern generator?
network of cells oscillate (ex. nudibranch swimming, human walking, dog swimming)
How is a central pattern generator constructed?
1) the half-centre oscillator
2) neurogenic leech heart (rhythm generator)
If all are inhibitory synapses - where does the excitatory drive come from?
neurons within pattern generator are intrinsically active themselves so disinhibition leads to firing
What is important about the re-setting of the phase?
capacity to “reset” rhythm is a property of neurons that are controlling elements (hyperpolarize an HN)
What serves as evidence of autonomy of central pattern generators?
lobster stomatogastric ganglion - ~30 neurons in ganglion - controls many muscles and motor patterns
What is a polymorphic network?
concept that circuits can dynamically re-wire to generate alternative outputs
Where is the mammalian cycle of locomotion organized?
by central pattern generators in the spinal cord (cats on treadmill)
What modifications did the vertebrate brain undergo early on?
hindbrain became divided into ventral portion (medulla oblongata) and dorsal portion (cerebellum and anterior pons)
What is the medulla specialized for?
connecting tract between spinal cord and anterior brain that is the control center for autonomic pathways concerned with vital functions (heart rate, respiration, blood pressure)
Which part of the brain has changed much through vertebrate evolution and how?
in mammals and birds the cerebellum enlarged and became concerned with balance, equilibrium and muscular coordination/learning
In what ways did the midbrain become specialized?
optic lobes, visual centers associated with the optic nerves
In what ways did the forebrain change?
divided into anterior portion (cerebrum with prominent olfactory bulbs) and posterior portion (thalmus and hypothalamus)
Was the expansion of the forebrain equally distributed?
no, expansion mainly in “association” areas (not primary sensory or motor)
What determines the proportions of brain tissue?
amount of brain tissue devoted to processing information depends on amount of information that is needed to be processed
What are some examples of brain tissue proportions dependent on information processing?
1) star nose mole
2) weakly electric fish (larger cerebellum devoted to generating and interpreting electric field signals)
What change was seen in the cellular organization of the cerebrum with mammals?
multi-layered cerebrum (neocortex) and further extensive expansion and elaboration
What is the neocortex?
has 6 layers of cell bodies that appeared early in mammalian evolution (triassic jurassic)
Generally, what are the layers of the neocortex?
I/II: “principal” or projection neurons
III/IV: thalamic (sensory) input
VI: action potential output
What characteristics do interneurons possess?
they have short axons (mostly local connections/not projecting) and are mostly inhibitory)
How much does folding increase the area of the brain?
5 to 6 fold increase in area
What does a cubic mm of neocortex ontain?
- 90, 000 neurons
- 400 meters of dendrites
- 4 km of axons
- 7 x 10^8 synapses
What is the most cell dense part of the brain?
granule layer of the cerebellum
