. There are many diseases that affect signal transmission along neural pathways. These includemultiple sclerosis (MS), myasthenia gravis, and amyotrophic lateral sclerosis (ALS or 'LouGehrig's Disease). Often, a component of these afflictions is a malformation or degenerationof the myelin sheath. MS is a demyelinating disease, which means that the axons of neuronsare intact but the myelin sheaths are damaged. Why would loss or damage to the myelinsheath be a problem for signal transmission, even if the axon was intact

In neurons that are enveloped by myelin sheath, the nerve stimulus or neuronal action potential is transmitted in a saltatory way, that is, this action potential jumps in the spaces not surrounded by the myelin sheath and it is in this way that it is transmits much more efficient and faster.

Explanation:

Myelin neurons are those that are covered by myelin sheaths, this sheath is formed mainly by fatty acids, these fatty acids generate an alternate isolation along the axon so that the stimulus diffuses through the bare areas where they will have ionic channels premises in order to generate the potential for action.

If this myelin sheath disappears, not only is the response slower, but it is rendered incapable because an axon that does not have ion channels to spread the signal is discovered in the external environment.

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?