Muscle And Nerves Are Excitable Tissues Biology Essay

2 drops of hypertonic solution are added to the red blood cells (RBC) on the slide. Under the microscope, it is observed that the cells crenate. The crenated RBC changed its biconcave shape into spheres with short, sharp and a little bit round projections around it. The cells shrink as the cells have a lower concentration of non-penetrating solutes than the solution, causing a movement of the water out of the cells. Therefore, the solution is said to be hypertonic to RBC. 2 drops of hypotonic solution are added to the RBC on another slide. It is observed under the microscope that the cells swell. The concentration of non-penetrating solutes is lower in the solution compared to the cells. Therefore, there will be a movement of water into the cells through the process called osmosis, making the cells increase in volume. Thus, this solution is hypotonic to RBC. For the last slide, 2 drops of isotonic solution are added onto the RBC. There is no change to cells. This is because the concentration of non-penetrating solutes is the same in the solution and the cells. The penetrating solutes in the cells will diffuse out through diffusion and reaches equilibrium. There will be no movement of water and therefore the solution is isotonic.

The conical flask labelled A which contains 1g of yeast suspension, 25ml of sodium bicarbonate and 25ml of neutral red is being heated. The initial colour of the mixture is red. After heating, the colour changes from red to yellow. This is because the cell membrane likely to be permeable due to heating. High temperature might also kill the yeast cells. Thus, allowing the sodium bicarbonate to react with neutral red and results in a yellow-coloured solution. The conical flask labelled B contains 1g of yeast suspension, 25ml of sodium bicarbonate and 25ml of neutral red. Unlike conical flask A, conical flask be is not being heated. The initial colour of the solution is yellow-orange due to the reaction with sodium bicarbonate solution. Roughly after 15 minutes, the colour changes from yellow-orange to red. Neutral red turns red when the solution reacts with it is acidic. The intracellular fluid of the yeast cell is acidic. Therefore, it is said that the neutral red diffuses into the yeast cell and thus makes the solution red. The conical flask labelled C acts as a control. It contains only 25ml of sodium bicarbonate and 25ml of neutral red. Unlike conical flasks A and B, conical flask C does not contain yeast suspension. Therefore, only sodium bicarbonate will interact with the neutral red and the colour of the solution is yellow. The colour of neutral red in basic solution is yellow. Therefore, it can be concluded that sodium bicarbonate is a basic solution.

As a conclusion, when RBC is placed in hypotonic solution, it swells; in hypotonic solution, it shrinks; in isotonic solution, it remains unchanged.


Adding high potassium solution (50mM) to smooth muscle organs (uterus, stomach, bladder) results in a large contraction. Why?

High potassium depolarizes the smooth muscle cell membrane and opens the voltage-regulated calcium ion channels. As the depolarization of smooth muscle cell membrane is great, more extracellular Ca2+ will enter into the smooth muscle cell. More Ca2+ will bind with calmodulin, a kind of protein in the cytoplasm and form more calmodulin-Ca2+ complex which later combine with and activate the enzyme called myosin light-chain kinase (MLCK) that catalyzes the phosphorylation of myosin light chains. More cross bridge will become phosphorylated and able to bind to actin, leading to a stronger contraction.

Nifedipine (Adalat ®) may be used to effectively treat some patients who have hypertension. Systemic nifedipine may also be used to stop premature labour. What does nifedipine do? How does it reduce high blood pressure? How does it reduce contractions in the uterus?

Nifedipine belongs to the drug class called calcium channel blockers. It binds to the voltage-dependent calcium channels in the smooth muscle cells and thus blocking the extracellular Ca2+ from entering the cells through these channels. The reduction in calcium influx causes the smooth muscle cells to relax and the vessels to dilate. This effect is called vasodilation. It thus increases the blood flow as arteries dilated and decreases the peripheral vascular resistance, reducing blood pressure. The same situation applies to the uterus. The calcium channels are blocked by Nifedipine causing the muscles to relax as calmodulin dissociates from the MLCK, inactivating an enzyme. Dephosphorylation inhibits cross bridge from binding to actin. Thus, reduce the contraction in uterus.

Find an example of drug that interferes with channel activity and therefore alleviates the symptoms associated with a particular condition/ disease state.

Sotalol is a drug used in treatment and prevention of arrhythmias. It is a non-selective beta-blocker that also prolongs the refractory period of atria, ventricles and bypass tract. The binding of sotalol to beta-receptors prevents the binding of ligand to receptors. Therefore, the production of cyclic adenosine monophosphate cannot be activated and there will be a decrease in influx of calcium ions as calcium channel is less likely to be activated. A decrease in calcium influx meaning there will be less contraction on muscles like cardiac muscles. A decrease in cardiac muscles contraction allows time for the pacemaker to rectify arrhythmic contractions. Also, sotalol inhibits efflux of K+ ions by blocking the potassium channels. Thus, it prolongs repolarization, therefore creates a longer QT interval and decreasing automaticity (contracts without neural stimulation). It also slows atrioventricular (AV) nodal conduction.

Explain the relationship between membrane potential, the action potential and the equilibrium potentials (for Na+ and K+).

Describe the different phases of the action potential with respect to changes in membrane permeability.

Action potential occurs when voltage-gated ion channels open, altering the membrane permeability to ions such as Na+ and K+. The rising phase of action potential occurs due to a sudden increase in membrane permeability to Na+. The membrane depolarizes to above threshold voltage and stimulates an action potential to occur. As cell depolarizes, voltage-gated Na+ channel opens, allowing Na+ to enter the membrane. The rapid influx of the Na+ into the membrane depolarizes the cell even more.

Muscle and Nerves are EXCITABLE tissues. Discuss this statement.

Muscles and nerves are excitable tissues as they have the ability to propagate electrical signals rapidly in response to a stimulus. They are able to send a constant electrical signal over a long distance along the membrane. They response to depolarizing stimulus. An action potential begins to fire when the membrane depolarizes to above threshold voltage. The membranes contain several ion channels that may be opened or closed, allowing an influx or efflux of certain ions across the membrane, creating depolarization, repolarization or hyperpolarization of the membrane.