The answer is B. Geology has shown a thin layer of iridium (a rare mineral on earth but found on asteroids and meteors) in the rock layers between the Cretaceous and Paleogene periods. Below this layer are numerous fossils of pterosaurs and dinosaurs, but above the layer are drastically few. The aftermath of asteroid impact is believed to have smothered most vegetation from earth which dinosaurs depended on as a source of food.
Answer:
A dermatome represents the unilateral area of skin on the body that is innervated by fibers from the sensory portion of a single spinal nerve coming from the spinal cord. Each spinal nerve contains spinal roots (anterior and posterior) that come together to form the spinal nerve.
Explanation:
The phylum Echinodermata , which contains about 6000 species, gets its name from the Greek, literally meaning "spiny skin." Many echinoderms actually do have "spiny" skin, but others do not. This phylum exists exclusively in the sea, and cannot be found on land or in fresh water.
Answer:
1. Inhibiting IP3 channels, leading to decreased Ca2 in the sarcoplasm and reduced contraction.
2. Increasing the relative activity of MLCP, leading to a decrease in tension.
3. Activating K channels, increasing K leaking out of the cell which hyperpolarizes it and decreases the likelihood of Ca2 entry.
Explanation
In smooth muscle, cyclic AMP (cAMP) mediates relaxation because cAMP inhibits a specific kinase required for myosin light chain protein (MLCP) phosphorylation, thereby triggering contraction in the smooth muscles. It has been shown that cAMP inhibits 1,4,5-trisphosphate (IP3)-dependent calcium ions (Ca 2+) release by activation of the cGMP-dependent protein kinase (PKG). PKG proteins act to modulate Ca2+ oscillations by stimulating sarcoplasmic Ca2+-ATPase membrane proteins, increasing Ca2+ in the sarcoplasmic reticulum stores and Ca2+ efflux from the cells, and activate voltage-gated potassium (K) channels, thereby leading to membrane hyperpolarization and reducing Ca2+ entry through Ca2+ channels.
