Question

Nervous System: How does being "cephalized" relate to this? Choose 3 animal phyla that each have a different nervous system organization and explain their differences. If asked, could you describe or answer questions about an action potential (resting membrane potential, threshold, depolarize, repolarize, hyperpolarize)? Body Support: • What supports the shape/structure of Poriferans, Cnidarians, Arthropods, and Chordates? Muscles: • What does it mean to say a muscle has voluntary control? Give an example. What does it mean to say a muscle has involuntary control? Give an example. If asked, could you describe or answer questions about the sliding filament contraction process (actin, myosin, ATP, Ca2+, troponin, tropomyosin, power stroke)?

Answer 1

Nervous system

1) Cephalization is a evolutionary trend toward nervous system centralization in which there is development of a head and brain at center part of body.... Sense organs or tissues are mostly concentrated or located on or near the head, which is at the front of the animal as it moves forward.The brain is organization of nervous tissue which coordinates and controls sensory information and nervous activity. It is important a it allows for the organism to make quick movements. Due to cephalization it allow  organism to have an axis of symmetry, thus help in making quick movements possible as the organism can either find prey or avoid being prey.

2)

Coelentra- do not have Ny brain or cephalization. They contain nerve net in form of interconnected neurons. Thus is simplest type of nervous system found in multicellular organisms.

Platyhelminthese- for the first time nervous system appear in these organism, have ladder like nervous system .longitudinal nerve cord appears in flatworm. Along with longitudinal nerve cord they have anterior collection of nerve cells that can be called a brain. Apart if these structures, they have well-defined sensory and motor pathways as well as coordinating interneurons.

Molluscan- Their nervous system referred as tetraneural nervous system, because they has four main neural strands:

Two pairs of connectives that connect the cerebral ganglia to the pedal ganglia on the ventral side.

Secpnd visceral ganglia and parietal ganglia passing the pleural ganglia on the dorsal side.

3)

RMP - RMP is the difference in the voltage across the cell membrane when the cell is at rest. It is due to the  distribution of charged particles (ions) across the membrane at resting conditions.

Threshold -  threshold potential is critical level to which a membrane potential must be reduced or depolarized to initiate an action potential. Any stimulus which fail to reach threshold potential will fail in to generate action potential.

At RMP , membrane is in polarized state ( outer is positive and inside is more negative) due to continuous operating of Na-K pump of K channels.

As action potential reach, this leads to opening of Na channels and allow entry of Na in to cell. So the  inward flow of Na increases the concentration of positively charged cations in the cell and causes depolarization decrease of potential to - 70 to -40 or -30 .

After over of action potential, Na K pump again tranport Na ions outsidevtje cell. This sllow again re establishing of membrane potential to - 70mv . This is known as repolarization.

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