What happens at the junction between a nerve and a muscle to initiate muscle contraction?

What we know as the motor plate or motor unit is the union between the nerve or rather the nerve terminal and muscle fiber.

When the nerve fiber enters a depolarization, thus generating an action potential in its membrane, conducting electrical energy along it triggers certain "communicators" to be released at the union with the muscle (motor unit) that will indicate the muscle to contracting, these "communicators" are called neurotransmitters and an example of them is acetylcholine or Ach, when released it binds to the specific receptor for the neurotransmitter of muscle tissue, thus generating it to contract the sarcoplasmic reticulum and increase intracellular calcification levels to carry out the shortening of the muscle fiber (muscle contraction).

Explanation:

Muscle fibers are classified into three large groups according to their function and physiology, we have smooth and striated muscle and, on the other hand, specialized or cardiac muscle that has a very particular characteristic, unlike the others, which is that it is autonomous. say that it has another mechanism to be induced to contraction and that it could control muscle contraction without the presence of a nerve or nerve terminal, this is because the cardiac muscle is essential for our life to contract to generate the pumping our blood and it is very risky to depend on a nerve terminal.

On the other hand, the nerves that have a myelin sheath envelope will drive their exciting stimulation to the muscle or muscle fiber more quickly since it is the saltatory method.

The nerve terminals act at the level of the intracellular concentrations of calcium of the muscular cells as we mentioned above, that is why a muscular cell when viewed under the microscope presents a REL (superplastic smooth endoplasmic reticulum) that acts as a calcium reserve for muscle contraction. Calcium is responsible for dislodging the topoisomerase from the active site where myosin and actin bind to generate the shortening of the Z lines.

transcription is a process in which information is rewritten. it is something our cells must do, in a more specialized and narrowly defined way. in biology, transcription is the process of copying out the dna sequence of a gene in the similar alphabet of rna. it needs to happen in the nucleus because that's where the dna is. dna is always inside the nucleus unless the cell is dividing.

transcription is the first step in gene expression, which involves copying a gene's dna sequence to make an rna molecule. transcription is performed by rna polymerases. it has three stages: initiation, elongation, and termination. rna molecules must be processed after transcription in eukaryotes.

explanation:

long version:

the protein synthesis consists two processes which are, transcription and translation. transcription takes place in the nucleus. it uses dna as a template to make an rna molecule. rna then leaves the nucleus and goes to a ribosome in the cytoplasm, where translation occurs. transcription is the first part of the central dogma of molecular biology: dna → rna. it is the transfer of genetic instructions in dna to messenger rna (mrna). during transcription, a strand of mrna is made that is complementary to a strand of dna.  

these three stages are:

  initiation: in which   is the beginning of transcription.occuring when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

    elongation: in which is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

    termination: in which is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

the correct answer is - d. china has a large and growing population.

the fact that china has a large (the biggest) population, and it is still growing, doesn't hinder the agriculture production in the country. in fact, it can for increased production in the agriculture, since there's more labor force, as well the sheer mass of people produces lots of scientists that come up with new inventions as to how to improve this sector. nice example is the inner mongolia region in china, in general dominated by the gobi desert, but few scientist came up with a nice idea as to how to make the region productive by using plants that are very resistant to droughts, so lots of people have been employed, and the region is becoming greener and greener each year, and the production of food in this region is also increasing.