ACTION MEMBRANE POTENTIAL.

Action potential

Definition:

The action potential is a rapid and reversible reversal of the electrical potential difference across the plasma membrane of excitable cells such as neurons, muscle cells and some endocrine cells. 

In a neuronal action potential, the membrane potential rapidly changes from its resting level of approximately -70 mV to around +50 mV and, subsequently, rapidly returns to the resting level again. 

The neuronal action potential forms an important basis for information processing, propagation, and transmission. 

In muscle cells, the action potential precedes, and is necessary to bring about, muscle contraction.

 Some endocrine cells also exhibit action potentials, where the excitation leads to hormone secretion.

The action potential is also referred to as the electrical impulse or nervous impulse.

Resting potential across the membrane.

RESTING MEMBRANE POTENTIAL (RMP) : CURVE, GENERATION & MAINTENANCE

DEFINITION

• Resting Membrane Potential (RMP) is the voltage (charge) difference across the cell membrane when the cell is at rest.
• The resting membrane potential represents an equilibrium situation at which the driving force for the membrane-permeant ions down their concentration gradients across the membrane is equal and opposite to the driving force for these ions down their electrical gradients.
• When two electrodes are connected through a suitable amplifier and placed on the surface of a single axon, no potential difference is observed. However, if one electrode is inserted into the interior of the cell, a constant potential diff erence is observed, with the inside negative relative to the outside of the cell at rest.

GENERATION OF RMP

A membrane potential results from separation of positive and negative charges across the cell membrane.

In order for a potential difference to be present across a membrane lipid bilayer, two conditions must be met.

• First, there must be an unequal distribution of ions of one or more species across the membrane (i.e., a concentration gradient).
• Second, the membrane must be permeable to one or more of these ion species. The permeability is provided by the existence of channels or pores in the bilayer; these channels are usually permeable to a single species of ions.

The resting membrane potential represents an equilibrium situation at which the driving force for the membrane-permeant ions down their concentration gradients across the membrane is equal and opposite to the driving force for these ions down their electrical gradients.

In neurons, the resting membrane potential is usually about –70 mV, which is close to the equilibrium potential for K + .

Resting membrane potential is generated & maintained by following considerations :

1. Na-K ATPase (Na+-K+ Pump) – Active Transport of Sodium and Potassium Ions Through the Membrane

• In neurons, the concentration of K + is much higher inside than outside the cell, while the concentration of Na+ is much higher outside than inside the cell. This concentration difference is established by Na-K ATPase since this is an electrogenic pump because more positive charges are pumped to the outside than to the inside (three Na+ ions to the outside for each two K+ ions to the inside), leaving a net deficit of positive ions on the inside; this causes a negative potential inside the cell membrane.

2. Na+ & K+ Leak Channels – Leakage of Potassium Through the Nerve Membrane

• The outward K + concentration gradient results in passive movement of K + out of the cell when K + -selective channels are open. Similarly, the inward Na + concentration gradient results in passive movement of Na + into the cell when Na + -selective channels are open.
• Because there are more open K + channels than Na + channels at rest, the membrane permeability to K+ is greater. Consequently, the intracellular and extracellular K + concentrations are the prime determinants of the resting membrane potential, which is therefore close to the equilibrium potential for K+ .
• Steady ion leaks cannot continue forever without eventually dissipating the ion gradients. Th is is prevented by the Na , K ATPase, which actively moves Na + and K + against their electrochemical gradients.

SICLE CELL DISEASE (SICLE CELL ANAEMIA)

Sickle cell disease is a group of disorders that affects hemoglobin, the molecule in red blood cells that delivers oxygen to cells throughout the body. People with this disorder have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells into a sickle, or crescent, shape.

The term sickle cell disease (SCD) describes a group of inherited red blood cell disorders. People with SCD have abnormal hemoglobin, called hemoglobin S or sickle hemoglobin, in their red blood cells.

Hemoglobin is a protein in red blood cells that carries oxygen throughout the body.

“Inherited” means that the disease is passed by genes from parents to their children. SCD is not contagious. A person cannot catch it, like a cold or infection, from someone else.

People who have SCD inherit two abnormal hemoglobin genes, one from each parent. In all forms of SCD, at least one of the two abnormal genes causes a person’s body to make hemoglobin S. When a person has two hemoglobin S genes, Hemoglobin SS, the disease is called sickle cell anemia. This is the most common and often most severe kind of SCD.

Hemoglobin SC disease and hemoglobin Sβ thalassemia (thal-uh-SEE-me-uh) are two other common forms of SCD.

Some Forms of Sickle Cell Disease

• Hemoglobin SS
• Hemoglobin SC
• Hemoglobin Sβ0 thalassemia
• Hemoglobin Sβ+ thalassemia
• Hemoglobin SD
• Hemoglobin SE

Overview

Cells in tissues need a steady supply of oxygen to work well. Normally, hemoglobin in red blood cells takes up oxygen in the lungs and carries it to all the tissues of the body.

Red blood cells that contain normal hemoglobin are disc shaped (like a doughnut without a hole). This shape allows the cells to be flexible so that they can move through large and small blood vessels to deliver oxygen.

Sickle hemoglobin is not like normal hemoglobin. It can form stiff rods within the red cell, changing it into a crescent, or sickle shape.

Sickle-shaped cells are not flexible and can stick to vessel walls, causing a blockage that slows or stops the flow of blood. When this happens, oxygen can’t reach nearby tissues.

HUMAN JOINT.

Joint: This is the point at which two or more bones meet.

This video explains different kinds and types of joints, I hope you enjoy it.

THE SKELETAL SYSTEM OF HUMAN!

The human skeleton is the internal framework of the body.

It is composed of around 300 bones at birth – this total decreases to 206 bones by adulthood after some bones have fused together.

The bone mass in the skeleton reaches maximum density around age 20.

 The human skeleton can be divided into the axial skeleton and the appendicular skeleton.

The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones.

The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs.

The human skeleton performs six major functions;

1:Support,
2: Movement,
3:Protection,
4:Production of blood cells,
5:Storage of minerals,
6:Endocrine regulation.

The human skeleton is not as sexually dimorphic as that of many other primate species, but subtle differences between sexes in the morphology of the skull,dentition, long bones, and pelvis exist.

 In general, female skeletal elements tend to be smaller and less robust than corresponding male elements within a given population. The human female pelvis is also different from that of males in order to facilitate child birth.
Unlike most primates, human males do not havepenile bones.

DivisionsEdit

Axial skeletonEdit

Main article: Axial skeleton

The axial skeleton (80 bones) is formed by the vertebral column (32–34 bones; the number of the vertebrae differs from human to human as the lower 2 parts, sacral and coccygeal bone may vary in length), a part of the rib cage (12 pairs ofribs and the sternum), and the skull (22 bones and 7 associated bones).

The upright posture of humans is maintained by the axial skeleton, which transmits the weight from the head, the trunk, and the upper extremities down to the lower extremities at the hip joints. The bones of the spine are supported by many ligaments. The erector spinae muscles are also supporting and are useful for balance.

Appendicular skeletonEdit

Main article: Appendicular skeleton

The appendicular skeleton (126 bones) is formed by the pectoral girdles, the upper limbs, the pelvic girdle or pelvis, and the lower limbs. Their functions are to make locomotion possible and to protect the major organs of digestion, excretion and reproduction.

Hypogeal germination.

• Hypogeal germination implies that the cotyledons stay below the ground. The epicotyl (part of the stem above the cotyledon) grows, while the hypocotyl (part of the stem below the cotyledon) stays the same length. In this way, the epicotyl pushes the plumule above the ground.

• Normally, the cotyledon is fleshy, and contains many nutrients that are used for germination. No photosynthesis takes place within the cotyledon.

• Because the cotyledon stays below the ground, it is much less vulnerable to for example night-frost [2] or grazing . The evolutionary strategy is that the plant produces a relatively low number of seeds, but each seed has a bigger chance of surviving.

• Plants that show hypogeal germination need relatively little in the way of external nutrients to grow, therefore they are more frequent on nutrient-poor soils. The plants also need less sunlight, so they can be found more often in the middle of forests, where there is much competition to reach the sunlight.

• Plants that show hypogeal germination grow relatively slow, especially in the first phase. In areas that are regularly flooded, they need more time between floodings to develop. On the other hand, they are more resistant when a flooding takes place. [1] After the slower first phase, the plant develops faster than plants that show epigeal germination.

Ecdysis is the process of moulting or shedding an outer cuticular layer.

This process enables the insects to grow again.

The video below is the video showing the ecdysis in cockroach.

MITOSIS AND GROWTH (SUMMARY)

GROWTH AND DEVELOPMENT (MITOSIS)

The world of cell division,this video try to explain the process of cell division by mitosis. I hope you enjoy it.