<span>If the production of saliva is increased by the symphatetic nervous system (SNS) then, the parasymphathetic nervous system (PNS) does almost exactly the opposite of the action of the SNS. Therefore, for this item what is done by the parasymphatetic nervous system is to decrease the production. </span>
Answer:
Certain mutations in the repressor gene or operator sequence make the operon constitutive.
Explanation:
Lac operon is not expressed in the absence of lactose sugar. The repressor gene codes for the repressor protein which in turn binds to the operator region. The operator region of lac operon serves as a binding site for the repressor protein. Binding of repressor to the operator region of lac operon does not allow the RNA polymerase to transcribe the genes and the expression of operon is prevented.
Certain mutations in the repressor gene or operator sequence make the operon transcriptionally active even in the absence of lactose. A mutation in the repressor gene that results in the synthesis of non-functional repressor protein or no repressor protein would make the operon constitute. Similarly, a mutation in the operator sequence that does not allow an otherwise functional repressor protein to bind it would also result in the expression of the operon in the absence of lactose.
<h2>Action potential </h2>
Explanation:
Brief sequential change in the membrane potential of excitable cells after stimulus is called action potential
Phases of action potential includes:
- Depolarization: Starts when a threshold stimulus applied on a neuron via Na+ mechanically operated channels that trigger action potential
- Depolarization of membrane potential is due to influx of Na+ via voltage gated Na+ channels
- Fast opening of voltage gated Na+ channels shift membrane potential from -70mV to +50mV at which voltage gated Na+ channels becomes inactive, thus influx of Na+ abruptly stops
- Repolarization: Starts with the efflux of K+ by the opening of voltage gated K+ channels
- Voltage gated K+ channels starts to open when voltage gated Na+ channels becomes inactive
- Hyperpolarization: Occurs due to excessive efflux of K+ by voltage gated K+ channels
- Additional efflux of K+ occurs due to slow inactivation of voltage gated K+ channels
- In a typical neuron cell, membrane potential of cytoplasm is negative (-70mV) at rest hence called resting membrane potential
- Resting membrane potential of excitable cells is established by Na+ K+ pump and maintained by K+ leaky channels at rest
C. theory is the answer to your question
