The resting potential in most neurons has a value of approximately -70 mV.
The threshold potential is generally around -55 mV.
Initial depolarisation when there is Na+influx through ligand-gated Na+channels.
Action potential is an all or nothing response. The size of the action potential is constant and so, the intensity of the stimulus is coded by the frequency of firing of a neuron.
K+efflux is responsible for repolarisation.

Platelets are produced in the bone marrow by fragmentation of the cytoplasm of megakaryocytes, derived from the common myeloid progenitor cell. The time interval from differentiation of the human stem cell to the production of platelets averages 10 days. Thrombopoietin is the major regulator of platelet formation and 95% of this is produced by the liver. The normal platelet count is approximately 150 – 450 x 109/L and the normal platelet lifespan is 10 days. Under normal circumstances, about one-third of the marrow output of platelets may be trapped at any one time in the normal spleen.

Ion channels are pore-forming protein complexes that facilitate the flow of ions across the hydrophobic core of cell membranes. They are present in the plasma membrane and membranes of intracellular organelles of all cells, and perform essential physiological functions. They provide a charged, hydrophilic pore through which ions can move across the lipid bilayer. They are selective for particular ions and their pores may be opened or closed. Because of this ability to open and close, ion channels allow the cell to have the ability to closely control the movement of ions across the membrane. Gating refers to the transition between an open and closed ion channel state, and is brought about by a conformationational change in the protein subunits that open or close the ion-permeable pore.
Ion channels can be:
1. voltage-gated these are regulated according to the potential difference across the cell membrane or
2. ligand-gated – these are regulated by the presence of a specific signal molecule.

Haemoglobin is a 64.4 kd tetramer consisting of two pairs of globin polypeptide chains: one pair of alpha-like chains, and one pair of non-alpha chains. The chains are designated by Greek letters, which are used to describe the particular haemoglobin (e.g., Hb A is alpha2/beta2).

Two copies of the alpha-globin gene (HBA2, HBA1) are located on chromosome 16 along with the embryonic zeta genes (HBZ). There is no substitute for alpha globin in the formation of any of the normal haemoglobins (Hb) following birth (e.g., Hb A, Hb A2, and Hb F). Thus, absence any alpha globin, as seen when all 4 alpha-globin genes are inactive or deleted is incompatible with extrauterine life, except when extraordinary measures are taken.

A homotetramer of only alpha-globin chains is not thought to occur, but in the absence of alpha chains, beta and gamma homotetramers (HbH and Bart’s haemoglobin, respectively) can be found, although they lack cooperativity and function poorly in oxygen transport. The single beta-globin gene (HBB) resides on chromosome 11, within a gene cluster consisting of an embryonic beta-like gene, the epsilon gene (HBE1), the duplicated and nearly identical fetal, or gamma globin genes (HBG2, HBG1), and the poorly expressed delta-globin gene (HBD). A heme group, consisting of a single molecule of protoporphyrin IX co-ordinately bound to a single ferrous (Fe2+) ion, is linked covalently at a specific site to each globin chain. If the iron is oxidized to the ferric state (Fe3+), the protein is called methaemoglobin.

Alpha globin chains contain 141 amino acids (residues) while the beta-like chains contain 146 amino acids. Approximately 75 percent of haemoglobin is in the form of an alpha helix. The non helical stretches permit folding of the polypeptide upon itself. Individual residues can be assigned to one of eight helices (A-H) or to adjacent non helical stretches.

Heme iron is linked covalently to a histidine at the eighth residue of the F helix (His F8), at residue 87 of the alpha chain and residue 92 of the beta chain. Residues that have charged side groups, such as lysine, arginine, and glutamic acid, lie on the surface of the molecule in contact with the surrounding water solvent. Exposure of the hydrophilic (charged) amino acids to the aqueous milieu is an important determinant of the solubility of haemoglobin within the red blood cell and of the prevention of precipitation.

The haemoglobin tetramer is a globular molecule (5.0 x 5.4 x 6.4 nm) with a single axis of symmetry. The polypeptide chains are folded such that the four heme groups lie in clefts on the surface of the molecule equidistant from one another.

Synthesis of platelets occurs in the bone marrow by fragmentation of megakaryocytes cytoplasm, derived from the common myeloid progenitor cell. The average time for differentiation of the human stem cell to the production of platelets is about 10 days. The major regulator of platelet formation is thrombopoietin and 95% of this is produced by the liver. Normal platelet count is 150 – 450 x 109/L and the normal lifespan of a platelet is about 10 days. Usually about one-third of the marrow output of platelets may be trapped at any one time in the normal spleen.

Haemoglobin is composed of four polypeptide globin chains each with its own iron containing haem molecule. Haem synthesis occurs largely in the mitochondria by a series of biochemical reactions commencing with the condensation of glycine and succinyl coenzyme A under the action of the key rate-limiting enzyme delta-aminolevulinic acid (ALA) synthase. The globin chains are synthesised by ribosomes in the cytosol. Haemoglobin synthesis only occurs in immature red blood cells.
There are three types of haemoglobin in normal adult blood: haemoglobin A, A2 and F:
– Normal adult haemoglobin (HbA) makes up about 96 – 98 % of total adult haemoglobin, and consists of two alpha (α) and two beta (β) globin chains. 
– Haemoglobin A2 (HbA2), a normal variant of adult haemoglobin, makes up about 1.5 – 3.5 % of total adult haemoglobin and consists of two α and two delta (δ) globin chains.
– Foetal haemoglobin is the main Hb in the later two-thirds of foetal life and in the newborn until approximately 12 weeks of age. Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin. 
Red cells are destroyed by macrophages in the liver and spleen after , 120 days. The haem group is split from the haemoglobin and converted to biliverdin and then bilirubin. The iron is conserved and recycled to plasma via transferrin or stored in macrophages as ferritin and haemosiderin. An increased rate of haemoglobin breakdown results in excess bilirubin and jaundice.

The extrinsic pathway for initiating the formation of prothrombin activator begins with a traumatized vascular wall or traumatized extravascular tissues that come in contact with the blood. Exposed and activated by vascular injury, with plasma factor VII. The extrinsic tenase complex, factor VIIa-tissue factor complex, activates factor X to factor Xa.

Protein and phosphate are the primary intracellular anions, while chloride (Cl-) and bicarbonate are the predominant extracellular anions (HCO3-).

Mitochondria are membrane-bound organelles that are responsible for the production of the cell’s supply of chemical energy. This is achieved by using molecular oxygen to utilise sugar and small fatty acid molecules to generate adenosine triphosphate (ATP). This process is known as oxidative phosphorylation and requires an enzyme called ATP synthase. ATP acts as an energy-carrying molecule and releases the energy in situations when it is required to fuel cellular processes. Mitochondria are also involved in other cellular processes, including Ca2+homeostasis and signalling. Mitochondria contain a small amount of maternal DNA.
Mitochondria have two phospholipid bilayers, an outer membrane and an inner membrane. The inner membrane is intricately folded inwards to form numerous layers called cristae. The cristae contain specialised membrane proteins that enable the mitochondria to synthesise ATP. Between the two membranes lies the intermembrane space, which stores large proteins that are required for cellular respiration. Within the inner membrane is the perimitochondrial space, which contains a jelly-like matrix. This matrix contains a large quantity of ATP synthase.
Mitochondrial disease, or mitochondrial disorder, refers to a group of disorders that affect the mitochondria. When the number or function of mitochondria in the cell are disrupted, less energy is produced and organ dysfunction results.

A membrane potential is a property of all cell membranes, but the ability to generate an action potential is only a property of excitable tissues. The resting membrane is more permeable to K+and Cl-than to other ions (and relatively impermeable to Na+); therefore the resting membrane potential is primarily determined by the K+equilibrium potential. At rest the inside of the cell is negative relative to the outside. In most neurones the resting potential has a value of approximately -70 mV.