The Nervous System

The brain contains near one hundred billion cells. Each neuron has one thousand synapses each. A neuron is around 10-100µm wide. The cell body of a neuron is surrounded by dendrites and has an elongated myelinated axon leading to the axon terminals. There are three types of nerve cell the multipolar neurone we have just described, the bipolar neuron where the dendrites are also on an extended vestige and the monopolar neuron both the cell body and axon and dendrite vestige are myelinated. Glial cells help to support, nourish and modulate neurons in the brain. Astrocytes are one type of glial cell. Astrocytes serve as a medium between the neurons and the capillary’s.

Resting potential is an uneven distribution of ions across the neural membrane. The difference in electrical potential causes electro-activity across the neuron. Information is conducted much faster along myelinated axons. Sodium-potassium pumps fire at intervals across the axon and serve to propel impulses to the axon terminals. Neural information travels from dendrite to the axon terminal. The surface of a neuron is rough because it is covered with boutons. Where an axon terminal meets and exchanges neurotransmission via synaptic vesicles to a dendrite is instrumental in information processing, this is known as a synapse.

Neural tissue helps organisms interact with their environment. Afferent sensory neurons carry information into the brain. Information may be electromagnetic e.g. visual by the optical nerve and the retina is part of the brain. The right hemisphere of the brain controls the left side of the body and visual field and vice versa.  Senses may be mechanical e.g. touch and hearing and chemical e.g. taste and smell. Afferent neurons act as thermo-receptors throughout the body. Nociception or pain is processed sensory cortex. Efferent motor neurons tell the body how to respond. Vestibular information, balance and motion are coordinated in the inner ear. Proprioceptive sensory information is the relative position of bodily parts.

At the age of one month the embryonic brain has specialises into three regions the forebrain, the midbrain and the hindbrain. In an adult human, the hindbrain develops into medulla, the pons and the cerebellum. The midbrain associates with the hindbrain to form the brainstem. The brain stem is responsible for automatic survival functions e.g. homeostasis. The medulla drives heart beat and breathing. The cerebellum orchestrates coordination and balance. The embryonic forebrain matures into the diencephalon and the cerebrum. The diencephalon consists of the thalamus, the hypothalamus and the epithalamiums. The thalamus relays messages and may be thought of the brains switch board for the cerebrum. The hypothalamus regulates the pituitary gland (therefore serves to regulate the sleep-wake cycle), hunger, thirst, and pleasure.

The cerebrum constitutes the cerebral cortex, white matter and basal nuclei; the cerebellum is made up of many lobes. The frontal lobe functions for decision making and speech. The partial lobe processes sensory information. The temporal lobe processes audio information and the occipital lobe, positioned at the posterior of the cerebrum, process visual information. The right and left hemispheres of the cerebrum are specialised. The left specialises in symbolic thinking, detailed learning and lateral thinking. The right side deals with spatial perception, context and metaphor.

Characteristics of mammals

Mammals are endotherms they produce body heat by internal means and possess body hair or fur. They have mammary glands to secrete milk for the nourishment of their young. Mammals typically have live births, high metabolic rate, epiglottises, four chamber heart and hypertonic urine

Latent Heat of Fusion

The energy released or absorbed by chemical substance during a change of state, without a change in mean squared velocity. Latent heat if fusion is literally, the enthalpy of a substance when is melted (converted from solid to liquid) without a change in temperature.

Specific Heat Capacity

Specific heat capacity is the joule energy required to heat one gram of substance by one Kelvin. Specific heat capacity changes with the state of matter of a substance.

Hamilton’s Rule rB > C

Quantified altruism, states relatedness multiplied by the potential number of children is greater than the risk taken. Known as kin selection.

The Baldwin Effect

A learnt behaviour that improves fitness for example will become easier learnt by natural selection (assuming those that fail to lean die). Iterated the behaviour becomes instinct.

The Relationship Between Structure And Function In The Liver by Caspar Zialor

The liver is an organ found in all vertebrates. The liver functions as an interface between the digestive tract and the blood. In humans the liver is a large organ that rests below the diaphragm in the abdominal cavity. The liver’s right lobe dominates the right anterior hypochondriac region, and the left lobe takes a fair dividend of the anterior epigastric region.

An organ is a group of tissues that work together to perform a specific function. The liver is a vital organ performing a great variety of different functions. The liver hosts a multitude of biochemical reaction pathways required for metabolisms- including carbohydrate and fat metabolisms. The liver also contributes to the breakdown of erythrocytes and the detoxification of drugs and toxicants in the blood. The liver functions on the deactivation of hormones which are substances secreted by an endocrine gland into the circulatory system. In the liver, enzymes remove the nitrogenous section of unanabolized proteins, catabolising them in a structured reaction pathway yielding urea destined for the kidneys, this process is called deaminiation.

Embryonicly the liver is a gland derived from an outgrowth of the gut epithelium and performs both endocrine and exocrine functions. Structurally the liver is made up of countless lobules. Around the circumference of the lobules are arteries, veins and bile ducts - centripetal to their structure is their central vein. A complex of blood filled sinuids radiate from the central vein within the lobule. The fractal structure of the sinuids gives the liver a large surface area to maximize membrane transport and diffusion.

The liver undergoes three phases of depreciation of oxygen content in the blood as oxygen diffuses into the sinuid tissues; this is called the liver acinus. As blood channels from the hepatic artery into the central vein, the blood travels through three phases: preiportal- high oxygen content, intermediate and central venous drainage; the lowest oxygen content – plays a role in detoxification.

The size of the liver is controlled by metabolic requirements; mature differentiated hepatocytes may proliferate at any stage of their life. In rats transplanted or mutilated livers may grow to accommodate the specific organism very quickly potentially tripling in size within two weeks. Korkut Uygun has stripped the cells off the liver of a rat to its bear collagen structure and reconstituted cells over the old structure. The reformed liver was successfully transplanted into a genetically similar rat.

Hepatic macrophages float within the sinuids and are used for breaking down erythrocytes; this also occurs in the spleen and bone marrow. Heme, derived from heamaglobin, is broken down in the liver by enzymes. Heme oxygenase removes the iron from the heme to produce biliverdin, releasing an iron atom. Ferritin binds the iron atom in a cyclopentadienide anion complex on the catalase tetramer; these proteins are stored in the peroxisome. Preoxisomes are bountiful in the liver hepatocytes. Catalase tetramer has its role in the breakdown of methanol. The enzyme biliverdinase reduces biliverdin into bilirubin. Bilirubin is non-miscible however when conjugated with glucuronic acid - forming sterobilin - it is soluble enough to travel though the bile ducts into the intestines for defecation. Some bilirubin is also absorbed into the neighbouring kidney and synthesized into urobilinogen to be relieved in the urine.

A thin layer of squamous endothelial cells lines the sinuids, however hexagonal-cuboidal hepatocytes form the majority of dense matter in the liver. Between the endothelial cells and the hepatocityes is the space of disse formed from collagen. The hepatocytes apical domain forms a thin extracellular canal called the bile canaliculus.  The bile canaliculus leads into the bile ducts. Bile is the waste product of the hepatocytes metabolism; concentrated by the gall bladder. Bile facilitates the emulsification of lipids in the small intestine. The liver is associative with many other organs including the right kidney, oesophagus, gall bladder and adrenal gland. The falciform ligament separates the liver’s right and left lobes as can be seen in figure (1). The anterior superior right lateral region consists of three impressions: the colic, the duodenal and the right renal. Inferior to this is the right adrenal gland impression. The superior medial anterior of the liver is where the bile ducts, the portal vein and the hepatic artery affix illustrated in figure (1). The inferior medal region of the anterior liver appends the inferior vena cava; to the left is the caudate lobe. The liver is our largest and most metabolically active organ and thus produces the majority of our body heat. At the medial superior anterior is the quadrate lobe. At the inferior anterior of the left lobe is the gastric impression.

The liver receives nutrient rich blood originated from the small intestine from the portal vein leading though the left lobe; unmetabolized glucose carried up from the small intestine may be stockpiled as glycogen. The synthesis of glycogen from glucose monomers is a condensation reaction; this process is regulated by pancreatic hormonal signals received in the blood. Glycogen is a helical branched polymer stored in dense granules associated to the smooth endoplasmic reticulum of the hepatocytes. Glycogen is stored for when the body needs additional energy for catabolism. Glyocogen-debranching enzymes are encrusted in the plasma-cellular membrane of the hepatocytes. Glucose, also known as blood sugar, has a hydroxyl and an aldehyde functional group. Glycolysis is a stratified reaction pathway dictated by enzymes that produces ATP and occurs in the mitochondrion. In the liver, oxygenated blood is received through the right lobe’s hepatic artery to enable the preferable aerobic pathway Krebs cycle; each individual glucose molecule yields six carbon monoxide and thirty-four adenosine 5’-triphosphate molecules.

In hunter-gatherer communities, offal is valued over the animal’s meat. The liver is an extremely nutritious organ especially when eaten raw. The liver contains all the essential vitamins. As well as glycogen and iron, the liver stores fat-soluble vitamins: A, D, E and K, copper and some miscible vitamins, including vitamin B12. However the liver must be eaten quickly and cleaned thoroughly because bile taints the flesh.

Figure 1 posterior and anterior veiws of their liver by Caspar Zialor

Abraham L. Kierszenbsum, M.D., Ph.D. Histology and Cell Biology An Introduction to Pathology 2^nd edition (Mosby, Inc., an affiliate if Elsevier 2002, 2007)

David Hames & Nigel Hooper Bios Instant Notes Biochemistry 3^rd edition (Taylor & Francis Group 1997, 2005)

Neil A. Campbell & Jane B. Reece Biology 8^th edition (Pearson International, Benjamin Cummings 2008)

Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter Molecular Biology Of the Cell 4^th edition (Garland Science, a member of the Taylor & Francis Group 2002)

Anne Waugh & Allison Grant Ross and Wilson Anatomy and Physiology in Health and Illness 11^th edition (Churchill Livingstone and affiliate of Elsevier 2006, 2010)

A. William Johnson Invitation to Organic Chemistry (Jones and Bartlett Publishers ,Inc. 1999)

Brian and Deborah Charleworth Evolution A Very Short Introduction (Oxford University Press 2003)

John Wiseman The SAS Survival Handbook (Guild Publishing London 1988)

Pg. 17 (New Scientist 19^th of June 2010)

Brownian Motion

Robert brown first observed though a microscope the jerky movement of pollen particles in water. This jostling can also be observed in an airborne smoke particle, the average speed of air molecule is 1000mph. Although an atom cannot be seen the existence of atoms can be inferred empirically. The force acted onto the pollen or smoke particle by the atom is tiny however, movement occurs because of imbalances in the acting kinetic forces, knocking the particle in jerky movements. The seemingly uniform pattern of Brownian motion is a fractal. Temperature is the mean squared velocity therefore if the temperature is increased a greater activity of motion is observed. Einstein popularised Robert browns 19^th century idea and thwarted atomic theory sceptics of the early 20^th century.

Kinetic Theory & Pressure law

In 1859 James Klerk Maxwell speculated on the properties of air based on almost prophetic postulates. J. C. Maxwell visualised air particles as tiny solid spheres travelling distances that are much greater than their diameters. Maxwell presumed all particles in a gas volume are initially at random positions. Maxwell devised as though experiment in which the law of entropy may be breached if the particle in given volume could be spontaneously organised, dubbed by lord kelvin as Maxwell’s dæmon.

The average speed of an air molecule is 1000mph. Maxwell postulated molecules travel between collisions at a constant speed. Interactions between particles conserve energy but still some will deviate from average greatly, traveling much faster or slower than average velocity. Maxwell prophesised the properties of the ‘at the time’ undiscovered Nobel gases in his ideal gas model which overlooked the influence of intermolecular forces.

Maxwell’s insights into the properties of gases allowed him to create a new definition of temperature. Temperature is now understood as the mean squared velocity, because temperature is directly proportional to pressure (at constant volume and mass). Pressure is the force per unit area exerted on the inside of a container. Therefore Maxwell’s ideal gas laws describe the relationship between pressure per unit area and the frequency of collisions in a given volume. Pressure is the kinetic energy of gas particles colliding with the inside of a container.

Principles of Atomic Bonding

Covalent Bonding & Ionic Bonding

Atoms are constantly striving for eight electrons in their outer shell; this is called the octet rule. In order achieve an outer shell of eight they must be willing to share or receive different amounts of electrons; valence is an atoms capacity to from bonds. Interaction between unpaired electrons and vacancies in energy shells are the cause of all atomic bonding. Ionic and covalent bonds are opposing ends of a spectrum of electrostatic interaction between atoms or ions. In reality there is a gradient from one to another.

Figure 1; triple covalent bond in nitrogen

Electrons interact in pairs– electrons negotiate their repelling charges via spin pair repulsion. Negatively charged covalence electrons may also reel electro-positive nuclei together. All bonds between any non-metallic substances will be covalent. A covalent bond is when neither atom has the strength of attraction to fully remove an electron from the other and orbiting electron pairs can be shared between two atoms. Nitrogen is not naturally found as an individual atom but is diatomic and occurs as an N2 molecule. Nitrogen has three valence electrons and five electrons in its outermost P-orbital. Nitrogen requires three in its outer shell to complete its octet. By sharing three electrons each. They now have six in their P-orbital  - each nitrogen is allowed a temporary octet, including their inner 1s2 orbits. A dative covalent bond occurs when an electron pair is donated to an acceptor atom - dative covalent bonds are weaker.

Many simple covalent molecules have low boiling points e.g. nitrogen, ethanol, carbon dioxide and ammonia are all gasses at room temperature. N2 shares three pairs of electrons therefore N2 has three covalent bonds; each bond is named successively as s, p, and d. Three is the maximum amount of covalent bonds two atoms can share. It’s common for covalent substances to be water-insoluble; polymers and oils are covalent substances.

Figure 2; Ionic bonding in sodium chloride

Although covalent bonding is stronger – having a greater bond enthalpy than ionic bonding; ionic compounds are crystalline solids often with very high boiling points. An ionic bond forms when an electron is permanently removed and attached to another atom to form two oppositely charged ions. Oppositely charged ions are attracted to one another by electrostatic. Ionic bonds typically occur between metals and non-metals. Metals are very ready to pass on electrons; they are conductive and reduction agents. Non-metals are often oxidising agents and have a tight nuclear radius and therefore high electronegativity. When you react sodium and chlorine – sodium oxidizes to become a positively charged cation. Chlorine accepts an electron and is therefore reduced to from a negatively charged anion, forming NaCl. Sodium chloride is a brittle solid due to its ionic lattice. NaCl crystals, like many other ionic compounds (e.g. salts and acids) are soluble in water. Aqueous or molten ionic compounds are conductive.

Figure 3; Three-dimensional ionic lattice in sodium chloride

Intermolecular Forces

Circular visualisations of electron orbitals are a simplification. The actual path of an electron is defined by its orbital An orbital is in fact a cloud of the probable position of an electron, in effect the density of the cloud signifies where an electron is likely to be. An electron has the potential to deviate from its predicted position quite dramatically! Therefore in an atom electrons are not completely evenly distributed across the orbitals - where the majority of the electrons occupy a negative charge (d-) is induced; on the opposing side the proton creates a positive charge (d+); this is called a dipole. Dipoles can have a ‘domino effect’ by causing synchronisation of charge distribution among atoms in a close vicinity- this is called an instantaneous dipole is induced dipole. These weak intermolecular forces are also known as Van Der Waals forces.

Dipoles can also be induced in molecules. Chlorine is diatomic; a chloride molecule is non-polar. Each chlorine atom has the same electronegativity therefore balanced forces of attraction allow for electrons to orbit impartially. There is an even distribution of electrostatic across their covalence orbital.

Figure 4; Polarity of a hydrogen-chloride molecule

Atoms have a force of attraction, this attracts electrons in a covalent bond, this called electronegativity. Electronegativity increases across a period and up through the groups – it would be fair to make the observation that it is related to atomic radius and levels of shielding, although evidently not completely due to irregularity in observed periodicity. In covalent compounds the constituent atoms are likely to have an imbalance in their electronegativity. This causes polarity in these molecules because the electrons will be biased to occupy one partnering atom over another. Hydrogen chloride HCL is a polar molecule – it has permanent dipole in which hydrogen is partially positively charged (d+) and chlorine is partially negative (d-). Similarly with Van Der Waals forces, permanent dipoles have influence on neighbouring particles; these are dipole-dipole interactions.

Hydrogen Bonds; Intermolecular Forces Continued

Hydrogen bonds are the strongest type of intermolecular forces and are essential for life on earth – they are present in water. Water is the medium in which all cell metabolism, interaction and biochemical synthesis is carried out. Hydrogen bonds are the present in a great deal of organic molecules.

A hydrogen bond is a relationship between a donor and an acceptor. The low electronegativity of hydrogen when bonded to a highly electronegative atom with a small physical radius  - hydrogen’s proton is left almost completely unshielded, adopting a strong partially positive charge (d+). Hydrogen acts as a donor and is strongly attracted to unpaired electrons. Hydrides of nitrogen, oxygen and fluorine and that act as both an acceptor and a donor; intermolecular hydrogen bonds.

It’s important to understand that hydrogen bonds are at dipole-dipole interaction but are individualized because of their distinct properties. There are varying strengths of hydrogen bonds. Strong hydrogen bonds are more comparable to covalent or ionic bonds but are far weaker. Strong hydrogen dipole-dipole forces, strong hydrogen bonds occur in hydride anions in specialized conditions.

Moderate and weak hydrogen bonds are electrostatic attraction weaker than ionic. Moderate hydrogen bonds are the area of the most practical interest. The presence of moderate hydrogen bonds is reasonable for the unusual boiling point of water in comparison to other hydrides. Ice has a greater volume (therefore lower density) than water because hydrogen bonds organise oxidane particles into a lattice; hydrogen bonds are often represented by a dotted line. The strong polarisation of oxidane makes it a perfect solvent for many organic and inorganic reactions.

Figure 5; Two-dimensional visualisation of water molecules in a frozen lattice

Functional groups such as ketones and esters act as acceptors where as functional groups including alcohols and primary amines act as donors. Other organic species such as carboxylic acids and nucleoside bases can do both. This can be observed in the paring of guanine and cytosine; bases from DNA the instructions in all life forms. Weak hydrogen bonds can be observed in arenes and halogenoalkanes containing fluorine.

Figure 7; Hydrogen bonding in two genetic base pairs (left guanine) (right cytosine)

By Caspar Zialor

Chemistry 1 by Brian Ratcliff, Helen Eccles, David Johnson, John Nicholson and John Raffan. 2003	http://en.wikipedia.org/wiki/Hydrogen_bond 08/11/2010
An Introduction To hydrogen Bonding by George A. Jeffrey 1997

Social Darwinism

Not publicly supported by Darwin himself. Social Darwinism has been used to support right wing political ideologies and has been used as a means to perpetuate existing stratified social structures. It main doctrine is that a factor such as intelligence or likely-hood to commit violent crime is predetermined at birth. Much of the evidence was found in concordances between monozygotic twins.

The discovery of was a revelation for social theorists. However application of selective breeding among domesticated animals is centuries old. Prior to the publications of Charles Darwin’s Origin of Species (published 1858), English political economist Robert Malthus (1766-1834) was first to suggest the potential benefits of selective breeding among human beings. Malthus is famous for his scientific contribution of Malthusian growth, which you may recognise from when we looked at ecology. Robert also devised the Malthusian catastrophe an idealised situation in which he discussed the benefits of famines and diseases in aid of wiping out the lower strata’s of society. Charles Darwin’s half cousin Francis Galton (1822-1911) coined the term eugenics and created new with it a new biosocial movement Galton feared the effects human civilisation would have on the natural selection of mankind and predicted a degeneration of the quality of the human gene pool. During World War II the grim reality of the application of human breeding programs and sterilisation, euthanasia and extermination of undesirables became realised under the rule of Adolf Hitler who became leader of the Nazi party in 1921 until his eventual suicide in 1945.

Evolution

Simple cells are thought to have evolved 3.5 billion years ago. The earth is approximately 4.6 billion years of age. The simple life forms were algae like micro-organisms and later, cyanobacteria which were responsible for the great increase in oxygen towards the end of the first era known as the Achaean. Actual algae occurred much later at the dawn of the second Proterozoic era around 2.5 billion years ago. 400 million years ago, during the Palaeozoic era, plants colonised the land. Evolution may be defined as the process by which species undergo transmutation over geological time. Evolution is a core theme of biology, all life on earth today comes from a common ancestor and incorporates genetics, systematics, palaeontology, developmental biology, behavioural psychology and ecology. The mechanisms of evolution by natural selection are variation within a population, superfluous fecundity, limits on population growth and heredity success. Individuals with the most favourable combination of characteristics are most likely to survive and reproduce therefore adaptive traits accumulate in a population. New species arise by divergence. This may due geographic, behavioural-social or physical limitation on interbreeding between populations. Comparatively the anatomy of two different species may share homologous features they have inherited from a common ancestor. The similarities between Abolocetus and the modern whale is an example of divergent evolution. Similarly two species may look very similar but only have a very distant common ancestor. By convergent evolution they have adapted to similar niches in the specific ecosystem. The fusiform shaped shared by whales and fish as result of the high density of water is an example of analogous or homoplastic features.