Macular Edema

Macular edema is a medical condition in which there is a swelling of the macula (yellow central part of the retina of the eye). It occurs when fluid and protein deposits collect on or under the macula, causing it to thicken and swell. The swelling may distort a person's central vision, as the macula is near the center of the retina at the back of the eyeball. This area holds tightly packed cones that provide sharp, clear central vision to enable a person to see form, color, and detail that is directly in the line of sight.

Macular edema can also occurs a few days or weeks after cataract surgery, but most such cases can be successfully treated with NSAID or cortisone eye drops. Until recently there were no good treatments for macular edema caused by central retinal vein occlusion (CRVO). Laser photocoagulation has been used for macular edema caused by branch retinal vein occlusion.

Cystoid Macular Edema

Cystoid macular edema is also a thickening of the macula of the eye and is usually associated with blurred or distorted vision. It is frequently associated with various ocular conditions, such as cataract surgery, age-related macular degeneration (ARMD), uveitis, eye injury, diabetes, retinal vein occlusion, or drug toxicity. The primary cause of cystoid macular edema depends on the underlying disease process, but most pathways eventually lead to vascular instability and breakdown of the blood-retinal barrier. The Müller cells in the retina become overwhelmed with fluid leading to their lysis. This results in an accumulation of fluid in the outer plexiform and inner nuclear layers of the retina. Diabetes and retinal vein occlusion can both lead to cystoid macular edema by causing vascular instability directly (vascular endothelial cell damage).

Epiretinal Membrane

Epiretinal membrane is a layer of fibrous tissue which forms on the surface of the macula. It is a disease of the eye in response to changes in the vitreous humor or more rarely, diabetes. Also called macular pucker, epiretinal membrane develops as a result of immune system response to protect the retina, cells converge in the macular area as the vitreous ages and pulls away in posterior vitreous detachment (PVD), which can cause minor damage to the retina, stimulating exudate, inflammation, and leucocyte response. These cells can form a transparent layer gradually and, like all scar tissue, tighten to create tension on the retina which may bulge and pucker, or even cause swelling or Macular edema.

Epiretinal membrane often results in distortions of vision that are clearly visible as bowing and blurring when looking at lines on chart paper (or an Amsler grid) within the macular area, or central 1.0 degree of visual arc. Usually it occurs in one eye first, and the distortions create binocular diplopia or double vision. The distortions can make objects look different in size (usually larger = macropsia), especially in the central portion of the visual field, creating a localized or field dependent aniseikonia that cannot be fully corrected optically with glasses. Partial correction often improves the binocular vision considerably though. In the young patients, these cells occasionally pull free and disintegrate on their own; but in the majority of sufferers (over 60 years of age) the condition is permanent. The underlying photoreceptor cells, rod cells and cone cells, are usually not damaged unless the membrane becomes quite thick and hard; so usually there is no macular degeneration.

Treatment

The only treatment for epiretinal membrane is surgery. Surgeons can remove or peel the membrane through the sclera and improve vision by 2 or more Snellen lines. Usually the vitreous is replaced at the same time with clear fluid, in a vitrectomy. Surgery is not usually recommended unless the distortions are severe enough to interfere with daily living, since there are the usual hazards of surgery, infections, and a possibility of retinal detachment.

Trabecular Meshwork

The trabecular meshwork is an area of tissue lying around the base of the eye cornea, near the ciliary body. It is responsible for draining the aqueous humor from the eye via the anterior chamber (the chamber on the front of the eye covered by the cornea). The trabecular meshwork is spongy and lined by trabeculocytes, allowing fluid to drain into a set of tubes called Schlemm's canal flowing into the blood system.

The trabecular meshwork is made up of three parts: 1) inner uveal meshwork, which contains thin cord-like trabeculae, orientated predominantly in a radial fashion, enclosing trabeculae spaces larger than the corneoscleral meshwork; 2) corneoscleral meshwork, which contains a large amount of elastin, arranged as a series of thin, flat, perforated sheets arranged in a laminar pattern; 3) juxtacanalicular tissue, which lies immediately adjacent to Schlemm's canal, composed of connective tissue ground substance full of glycoaminoglycans and glycoproteins.

The trabecular meshwork is assisted to a small degree in the drainage of aqueous humour by a second outflow pathway, the uveo-scleral pathway (5-10% of outflow occurs this way). The uveo-scleral pathway is increased with the use of glaucoma drugs such as prostaglandins.

Amacrine Cells

Amacrine cells are retina interneurons which interact at the second synaptic level of the vertically direct pathways consisting of the photoreceptor-bipolar-ganglion cell chain. Amacrine cells are responsible for 70% of input to retinal ganglion cells. Bipolar cells, which are responsible for the other 30% of input to retinal ganglia, are regulated by amacrine cells.

Amacrine cells are located at the inner plexiform layer (IPL), the second synaptic retinal layer where bipolar cells and retinal ganglion cells form synapses. There are about 40 different types of amacrine cells, most lacking axons. Like horizontal cells, amacrine cells function laterally affecting the output from bipolar cells, however, their tasks are often more specialized. Each type of amacrine cell connects with a particular type of bipolar cell, and generally has a particular type of neurotransmitter. One such population, AII, 'piggybacks' rod bipolar cells onto the cone bipolar circuitry. It connects rod bipolar cell output with cone bipolar cell input, and from there the signal can travel to the respective ganglion cells. They are classified by the width of their field of connection, which layer(s) of the stratum in the IPL they are in, and by neurotransmitter type. Most are inhibitory using either GABA or glycine as neurotransmitters.

Amacrine cells with extensive dendritic trees are thought to contribute to inhibitory surrounds by feedback at both the bipolar cell, and ganglion cell levels. In this role they are considered to supplement the action of the horizontal cells. Amacrine cells give much more input to M (Magnocellular) ganglion cells than to P (Parvocellular) ganglion cells.

Cones (retina)

Cones, or cone cells, are photoreceptor cells in the retina of the eye that function best in relatively bright light. The cones gradually become sparser towards the periphery of the retina. There are between 6 to 7 million cones in the retina, concentrated in the central yellow spot known as the macula. They provide the eye's color sensitivity.

Cones are also able to perceive finer detail and more rapid changes in images, because their response times to stimuli are faster than those of rods. There are three kind of color-sensitive cones in the retina of the human eye, corresponding roughly to red, green, and blue sensitive detectors.

Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in color in different ways, they have trichromatic vision. Being color blind can change this, and there have been reports of people with four or more types of cones, giving them tetrachromatic vision.

Mydriasis (eye)

Mydriasis is an excessive dilation of the pupil of the eye due to the use of drugs or disease. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day. A mydriatic pupil will remain excessively large even in a bright environment and is sometimes colloquially referred to as a "blown pupil". The opposite, constriction of the pupil, is referred to as miosis.

Mechanism of Mydriasis

There are two types of muscle that control the size of the iris: circular muscle and radial muscle. The former is innervated by the parasympathetic nervous system, the latter by the sympathetic nervous system. Sympathetic stimulation of a1 adrenergic receptors causes the contraction of the radial muscle, and subsequent dilation of the pupil. Conversely, parasympathetic stimulation cause contraction of the circular muscle and constriction of the pupil.

The mechanism of mydriasis depends on the agent being used. It usually involves either a disruption of the parasympathetic nerve supply to the eye (which causes contraction of the pupil), or overactivity of the sympathetic nervous system (SNS).

Rods (Human Eye)

Rods are one of the two types photoreceptor cells which are found in the retina of the eye. Being used in peripheral vision, they are activated by less intense light than are the cone cells. Rods are named for their cylindrical shape and are concentrated at the outer edges of the retina. On average, there are approximately 95 million rod cells in the human retina. Rods have a synaptic terminal, an inner segment, and an outer segment. The synaptic terminal forms a synapse with another neuron, for example a ganglion cell (bipolar cell). The inner and outer segments are connected by a cilium, which lines the distal segment. The inner segment contains organelles and the cell's nucleus, while the rod outer segment, which is pointed toward the back of the eye, contains the light-absorbing materials.

Rods are almost entirely responsible for night vision. Although they are more sensitive light than cones, rod cells are not sensitive to color. A rod is sensitive enough to respond to a single photon of light, and is about 100 times more sensitive to a single photon than cones. Rods require less light to function than cones, they are therefore the primary source of visual information at night (scotopic vision). Cone cells, on the other hand, require tens to hundreds of photons to become activated. Additionally, multiple rod cells converge on a single interneuron, collecting and amplifying the signals.

Entorhinal Cortex

The entorhinal cortex is situated in the medial temporal lobe. It functions as a hub in a widespread network for memory and navigation. The entorhinal cortex is the main interface between the hippocampus and neocortex. The EC-hippocampus system plays an important role in autobiographical/declarative/episodic memories and in particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane response of classical trace conditioning, the association of impulses from the eye and the ear occurs in the entorhinal cortex.

The entorhinal cortex functions as a relay station, linking the hippocampus with the cerebral cortex. It is through the entorhinal cortex that the hippocampus maintains interconnections with the neocortical multi-modal associations areas of the temporal, frontal, and parietal lobes. The superficial layers - layers II and III - of EC project to the dentate gyrus and hippocampus: Layer II projects primarily to dentate gyrus and hippocampal region CA3; layer III projects primarily to hippocampal region CA1 and the subiculum. These layers receive input from other cortical areas, especially associational, perirhinal, and parahippocampal cortices, as well as prefrontal cortex. EC as a whole, therefore, receives highly-processed input from every sensory modality, as well as input relating to ongoing cognitive processes.

Martinotti Cells

Martinotti cells are small, specialized, multipolar neurons with ascending axons and short branching dendrites. They are scattered throughout various layers of the cerebral cortex and send their axons up to the cortical layer I where they form axonal arborization. The arbors transgress multiple columns in layer VI and make contacts with the distal tuft dendrites of pyramidal cells. Martinotti cells express somatostatin and sometimes calbindin, but not parvalbumin or vasoactive intestinal peptide.

Function

Recent research suggests that Martinotti cells are associated with a cortical dampening mechanism. When the pyramidal neuron, which is the most common type of neuron in the brain, starts getting overexcited, Martinotti cells start sending inhibitory signals to the surrounding neurons, representing crucial interneurons for feedback inhibition in and between neocortical layers and columns (Wang et al, 2004). Martinotti cells have been proposed to be involved in memory formation and storage (Eccles, 1983) and in neurodegenerative diseases (Beal et al. 1988).

Martinotti cells were discovered by Carlo Martinotti, a student of Camillo Golgi.

Bipolar Neuron

A bipolar neuron is a nerve cell which has two processes; a dendrite and an axon. Bipolar neurons are sensory nerve cells specialized for the transmission of special nerve impulses. As such, they are part of the sensory pathways for smell, sight, taste, hearing and vestibular functions. The most common examples are the bipolar neuron of the retina, and the ganglia of the vestibulocochlear nerve. When used without further detail, the term usually refers to the retinal cells.

The bipolar neuron of the retina exists between photoreceptors (rod cells and cone cells) and ganglion cells. Their function is the transmission signals from the photoreceptors to the ganglion cells. Bipolar cells receive synaptic input from either rods or cones, but not both, and they are designated rod bipolar or cone bipolar cells respectively. There are roughly 10 distinct forms of cone bipolar cells, however, only one rod bipolar cell, due to the rod receptor arriving later in the evolutionary history than the cone receptor.

Bipolar neurons are also found in the spinal ganglia, when the cells are in an embryonic condition. They are best demonstrated in the spinal ganglia of fish. Sometimes the processes, come off from opposite poles of the cell, and the cell then assumes a spindle shape; in other cells both processes emerge at the same point. In some cases where two fibers are apparently connected with a cell, one of the fibers is really derived from an adjoining nerve cell and is passing to end in a ramification around the ganglion cell, or, again, it may be coiled spirally around the nerve process which is issuing from the cell.

Multipolar Neuron

A multipolar neuron is a type of neuron which has long axon and many dendrites, allowing it to link up with many other neurons and to transmit and receive a great deal of information. These dendritic branches can also emerge from the nerve cell body. Multipolar neurons constitute the majority of neurons in the cerebral cortex and include motor neurons and interneurons.

Diagram of a multipolar neuron

Interneurons

Interneurons, also called relay neurons, are multipolar nerve cells whose axons are limited to a single brain area. They connects afferent neurons and efferent neurons in neural pathways and integrative areas of the central nervous system. Principal neurons and their networks, such as the Betz cells, underlie local information processing/storage and represent the major sources of output from any brain region, whereas interneurons, by definition, have local axons that govern ensemble activity. While principal cells are mostly excitatory, using glutamate as a neurotransmitter, interneurons most often use gamma-aminobutyric acid (GABA) to inhibit their targets. Like motor neurons, interneuron cell bodies are always located in the central nervous system.

In the central nervous system, the term interneuron is used for small, locally projecting neurons, in contrast to larger projection neurons with long-distance connections. Central nervous system interneurons are typically inhibitory. Examples of interneurons include the sensory neuron and motor neuron also connecting to the brain through the association neurons. The 6-layered neocortex, as the center of the highest nervous functions such as conscious perception or cognition, has the largest number of interneuron types.

Alpha Motor Neurons

Alpha motor neurons (a-MNs) are large lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.

While their cell bodies are found in the central nervous system (CNS), alpha motor neurons are also considered part of the somatic nervous system—a branch of the peripheral nervous system (PNS)—because their axons extend into the periphery to innervate skeletal muscles. An alpha motor neuron and the muscle fibers it innervates is a motor unit. A motor neuron pool contains the cell bodies of all the alpha motor neurons involved in contracting a single muscle.

Alpha motor neurons which contract the head and neck muscles are located in the brainstem. The remaining alpha motor neurons innervate the rest of the body muscles and are situated in the anterior horn of the spinal cord. Because there are fewer muscles in the head and neck than in the rest of the body, there are more a-MNs in the spinal cord than in the brainstem. Alpha motor neurons on one side of the brainstem or spinal cord innervate muscles on that same side of body. The one exception is the trochlear nucleus in the brainstem, which innervates the superior oblique muscle of the eye on the opposite side of the face.

Renshaw Cells

Renshaw cells are inhibitory interneurons which are located in the gray matter of the spinal cord. They are associated in two ways with an alpha motor neuron.

Renshaw cells receive an excitatory collateral from the alpha neuron's axon, as they monitor how vigorously that neuron is firing. They also send an inhibitory axon to synapse with the cell body of the initial alpha neuron and/or an alpha motor neuron of the same motor pool. Thus, Renshaw cell inhibition represents a negative feedback mechanism. A Renshaw cell may be supplied by more than one alpha motor neuron collateral and it may synapse on multiple motor neurons.

Purkinje Cells

Purkinje cells, also called Purkinje neurons, are a type of GABAergic neurons located in the cerebellar cortex. They are named after their discoverer, Czech anatomist Jan Evangelista Purkynje. They are among the biggest nerve cells of the cerebellum.

Purkinje cells are found within the Purkinje layer in the cerebellum. They had an intricately elaborate dendritic arbor, characterized by a large number of dendritic spines. Their large dendritic arbors form nearly two-dimensional layers through which parallel fibers from the deeper-layers pass. These parallel fibers make relatively weaker excitatory (glutamatergic) synapses to spines in the Purkinje cell dendrite, whereas climbing fibers originating from the inferior olivary nucleus in the medulla provide very powerful excitatory input to the proximal dendrites and cell soma.

Each Purkinje cell receives a synapse from only a single climbing fiber. Both basket and stellate cells (found in the cerebellar molecular layer) provide inhibitory (GABAergic) input to the Purkinje cell, with basket cells synapsing on the Purkinje cell axon initial segment and stellate cells onto the dendrites. Purkinje cells send inhibitory projections to the deep cerebellar nuclei, and constitute the sole output of all motor coordination in the cerebellar cortex.

Purkinje cells show two distinct forms of electrophysiological activity: 1) simple spikes occur at rates of 17 – 150 Hz (Raman and Bean, 1999) either spontaneously, or when Purkinje cells are activated synaptically by the parallel fibers, the axons of the granule cells; 2) complex spikes are rapid (>300 Hz) bursts of spikes caused by climbing fiber activation, and can involve the generation of calcium-mediated action potentials in the dendrites. Following complex spike activity simple spikes can be suppressed by the powerful complex spike input. Purkinje cells show spontaneous electrophysiological activity in the form of trains of spikes both sodium- as well as calcium-dependent was initially shown by Rodolfo Llinas (Llinas and Hess (1977) and Llinas and Sugimori (1980). P-type calcium channels were named after Purkinje cells where they were initially encountered (Llinas et al. 1989), which are crucial in cerebellar function.

Betz Cells

Betz cells are pyramidal neurons which are situated in the fifth layer of the primary motor cerebral cortex. They are named after Vladimir Alekseyevich Betz, who described them in his work published in 1874. These neurons are the largest in the central nervous system, sometimes reaching 100 µm in diameter, and have the longest axons.

Betz cells send their long axons down to the spinal cord where they establish synapses directly with spinal cord anterior horn cells, which in turn synapse directly with their target muscles. While Betz cells have one apical dendrite typical to pyramidal neurons, they have more primary dendritic shafts, and these do not leave the soma only at basal angles but rather branch out from almost any point asymmetrically. These perisomatic and basal dendrites project into all cortical layers, but most of their horizontal arbors populate layers V and VI, some reaching down into the white matter. According to one study, Betz cells represent about 10% of the total pyramidal cell population in layer Vb of the human primary motor cortex.

Cro-Magnon

The Cro-Magnon were the first early Homo sapiens sapiens of the European Upper Paleolithic in Europe. The earliest known remains of Cro-Magnons were radiometrically dated to 35,000 years ago. The French geologist Louis Lartet discovered the first five skeletons of Cro-Magnon in March 1868 in a rock shelter named Abri de Crô-Magnon, at Les Eyzies, Dordogne, France. The type specimen from this find is Cro-Magnon 1, carbon dated to about 28,000 14C years old. Similar specimens were subsequently discovered in other parts of Europe and neighboring areas.

The condition and placement of the remains of Cro-Magnon 1, along with pieces of shell and animal tooth in what appear to have been pendants or necklaces raises the question whether they were buried intentionally. Analysis of the pathology of the skeletons shows that the humans of this period led a physically difficult life. In addition to infection, several of the individuals found at the shelter had fused vertebrae in their necks, indicating traumatic injury; the adult female found at the shelter had survived for some time with a skull fracture. As these injuries would be life threatening even today, this suggests that Cro-Magnons believed in community support and took care of each other's injuries.

Like Neanderthals, the Cro-Magnon were primarily big-game hunters, killing mammoth, cave bears, horses and reindeer. In Mezhirich village in Ukraine, several huts built from mammoth bones have been unearthed. Cro-Magnon artifacts suggest that they knew how to make woven clothing. Apart from the mammoth bone huts mentioned, they constructed shelter of rocks, clay, branches, and animal hide. These early humans used manganese and iron oxides to paint pictures and may have created the first calendar around 15,000 years ago.

The Cro-Magnon shared the European landscape with Neanderthals for some 15,000 years or more. Recent genetic studies of a wide selection of modern humans indicate some form of hybridization took place between Neanderthals and Cro-Magnon. About 3 to 6 percent of the DNA in Europeans and Asians appears to be derived from Neanderthals.

Homo Rhodesiensis

Homo rhodesiensis, also known as Rhodesian man, was a hominid of the Genus Homo, whose fossil skull was discovered in Broken Hill Northern Rhodesia (now Kabwe, Zambia) in 1921 by Tom Zwiglaar, a Swiss miner. Rhodesian Man is dated to be between 125,000 and 300,000 years old. The cranial capacity of the Broken Hill skull has been estimated at 1,100 cm³.

The skull of Homo rhodesiensis belonged to an extremely robust individual, and has the comparatively largest brow-ridges of any known hominid remains. It was described as having a broad face similar to Homo neanderthalensis (ie. large nose and thick protruding brow ridges), and has been interpreted as an "African Neanderthal". However, when regarding the skulls extreme robustness, recent research has pointed to several features intermediate between modern Homo sapiens and Neanderthal. Most current experts believe Rhodesian Man to be within the group of Homo heidelbergensis though other designations such as Archaic Homo sapiens and Homo sapiens rhodesiensis have also been proposed. According to Tim White, it is probable that Rhodesian Man was the ancestor of Homo sapiens idaltu (Herto Man), which would be itself at the origin of Homo sapiens sapiens. No direct linkage of the species can so far be determined.

Other morphologically-comparable remains have been found from the same, or earlier, time period in southern Africa (Hopefield or Saldanha), East Africa (Bodo, Ndutu, Eyasi, Ileret) and North Africa (Salé, Rabat, Dar-es-Soltane, Djbel Irhoud, Sidi Aberrahaman, Tighenif). Another specimen "the hominid from Lake Ndutu" may approach 400,000 years old, and Clarke in 1976 classified it as Homo erectus. Undirect cranial capacity estimate is 1100 ml. Also supratoral sculus morphology and presence of protuberance as suggest Philip Rightmire : give the Nudutu occiput an apprence which is also unlike that of Homo Erectus but Stinger 1986 pointed that thickened iliac pillar is typical for Homo erectus.

Kenyanthropus Platyops

Kenyanthropus platyops was a type of hominid that lived in east Africa 3.2 million years ago, during the Pliocene. It was discovered in Lake Turkana, Kenya in 1999 by Justus Erus, who was part of Meave Leakey's team. In 2001, Leakey theorized that the Kenyanthropus platyops fossil perhaps represented an entirely new hominine genus, while other anthropologists has classified it as a separate species of Australopithecus, Australopithecus platyops, and yet others interpret it as an individual of Australopithecus afarensis. This fossil found in Kenya features a broad flat face with a toe bone that suggests it probably walked upright. Teeth are intermediate between typical human and typical ape forms.

Homo Antecessor

Homo antecessor is an extinct species of Homo that dates from 1.2 million to 800,000 years ago. A piece of fossil remains was discovered by Eudald Carbonell, J. L. Arsuaga and J. M. Bermúdez de Castro. It was a maxilla that belonged to a 10-year-old individual found in Spain. Homo antecessor is one of the earliest known human varieties in Europe. Various archaeologists and anthropologists have debated how H. antecessor related to other Homo species in Europe, with suggestions that it was an evolutionary link between H. ergaster and H. heidelbergensis, although Richard Klein believes that it was instead a separate species that evolved from H. ergaster. Others believe that H. antecessor is in fact the same species as H. heidelbergensis, who inhabited Europe from 600,000 to 250,000 years ago in the Pleistocene.

The average brain size of Homo antecessor was 1000 cm³ in volume. In 1994 and 1995, 80 fossils of six individuals that may have belonged to the species were found in Atapuerca, Spain. The fossils bore marks where the flesh had been torn off the bones, which indicates that H. antecessor could have practiced cannibalism. H. antecessor was about 1.6-1.8 m (5½-6 feet) tall, and males weighed roughly 90 kg (200 pounds). Their brain sizes ranged from 1000 to 1150 cm³ (61in³-70.2in³), smaller than the 1350 cm³ (82.4in³) average of modern humans. Due to its scarcity, very little more is known about the physiology of H. antecessor, yet it was likely to have been more robust than H. heidelbergensis.

According to Juan Luis Arsuaga, one of the co-directors of the excavation in Burgos, H. antecessor might have been right-handed, a trait that makes the species different to the other apes. This hypothesis is based on tomography techniques. Arsuaga also claims that the frequency range of audition is similar to Homo sapiens, which makes him believe that H. antecessor used a symbolic language and was able to reason. Arsuaga's team is currently pursuing a DNA map of H. antecessor after elucidating that of a bear that lived in northern Spain some 500,000 years ago.

Heidelberg Man

Heidelberg Man, also known as Homo heidelbergensis, is an archaic type of Homo sapiens (an extinct species of the genus Homo) which may be the direct ancestor of both Homo neanderthalensis in Europe and Cro-magnon. The best evidence found for these hominin date between 600,000 and 400,000 years ago. Heidelberg Man stone tool technology was very close to that of the Acheulean tools used by Homo erectus.

It was discovered in 1907 by gravel pit workers near Heidelberg in Germany. The estimated age of Heidelberg Man is between 400,000 and 700,000 years. This find was a lower jaw with a receding chin and all its teeth. Although the jaw is large and robust, like that of Homo erectus, the teeth are at the small end of the erectus range.

Homo heidelbergensis is probably descended from the morphologically very similar Homo ergaster from Africa. But since Heidelberg Man had a larger cranium (cranial capacity of 1100–1400 cm³ overlapping the 1350 cm³ average of modern humans) and had more advanced tools and behavior, it has been given a separate species classification. The species was tall, 1.8 m (6 ft) on average, and more muscular than modern humans.

Recent findings in Atapuerca, Spain, suggest that Homo heidelbergensis may have been the first species of the Homo genus to bury their dead, even offering gifts. Some experts believe that Heidelberg Man, like its descendant H. neanderthalensis, had the brain capacity to produce and understand a type of language. Large temporal and frontal lobes are essential to produce and understand spoken language, and Heidelberg Man's were large enough. Well finished stone tools were uncovered at Terra Amata excavations in the south of France, along with red ochre, a mineral that can be used to create a red pigment which is useful as a paint.

Australopithecines

The australopithecines were hominids that belonged to genera Australopithecus or Paranthropus. These species occurred in the Plio-Pleistocene era, and were bipedal and dentally similar to humans, but with a brain size not much larger than modern apes, lacking the encephalization characteristics of the genus Homo.

Australopithecines are classified within the Hominina subtribe of the Hominini tribe. Australopithecus appeared about 4 million years ago; Paranthropus, appeared about 2.7 million years ago. The term "Australopithecine" refers to both genera together. Australopithecus is sometimes referred to as the "gracile (slender) australopithecines", while Paranthropus are also called the "robust australopithecines".

The ancestor of the Australopithecines is the Ardipithecus genus, who lived 4.4 million years ago. The Homo genus appeared about 2.4 million years ago with Homo habilis and seems to be descended from australopithecine ancestors, more precisely from Kenyanthropus platyops branching off Australopithecus some 3.5 million years ago. An alternative possibility is the derivation of Homo directly from Ardipithecus with an as yet undiscovered link connecting Ardipithecus and Homo habilis existing in parallel to the Australopithecines in the period 4 to 2.5 million years ago.

Zinjanthropus Boisei

Paranthropus boisei, also known Zinjanthropus boisei, was an early type of hominid that was described as the largest of the Paranthropus species. It lived from about 2.6 until about 1.2 million years ago during the Pliocene and Pleistocene epochs in Eastern Africa.

Zinjanthropus boisei had the largest teeth found in any hominid group, with teeth similar in size to gorillas (who weigh as much as 10 times as much). They are often referred to as hyper-robust due to the massive postcanine megadontia. The features of boisei are best described in relation to the other "robusts" (including aethiopicus), since this best shows some of the features that exclude aethiopicus from the "robust" lineage in favor of africanus. Nevertheless, its cranial capacity was 550 cm3, larger than that of a modern gorilla.

Paranthropus b. was discovered by anthropologist Mary Leakey on July 17, 1959, at Olduvai Gorge, Tanzania, the well-preserved cranium, which was nicknamed "Nutcracker Man," was dated to 1.75 million years old and had characteristics distinctive of the robust australopithecines. Mary and her husband Louis Leakey classified the find as Zinjanthropus boisei: "Zinj" for the medieval East African region of Zanj, "anthropus" meaning ape or ape-human, and "boisei" for Charles Boise (the anthropologists team’s funder at the time).
Paranthropus boisei (as the species was eventually categorized) proved to be a treasure especially when the anthropologists' son Richard Leakey considered it to be the first hominin species to use stone tools. Another skull was unearthed in 1969 by Richard at Koobi Fora near the Lake Turkana region, in Kenya.

Homo Habilis

Homo habilis is a species of the genus Homo, which lived from approximately 2.3 to 1.4 million years ago at the beginning of the Pleistocene period. The discovery and description of this species is credited to both Mary and Louis Leakey, who found fossils in Tanzania, East Africa, between 1962 and 1964. Homo habilis is the earliest known species of the genus Homo and the earliest known species to show novel differences from the chimpanzee and australopithid skulls. In its appearance and morphology, H. habilis is thus the least similar to modern humans of all species in the genus. Homo habilis was short and had disproportionately long arms compared to modern humans; however, it had a less protruding face than the australopithecines from which it is thought to have descended. H. habilis had a cranial capacity slightly less than half of the size of modern humans. Despite the ape-like morphology of the bodies, H. habilis remains have often been found along with primitive stone tools, such as in Olduvai Gorge, Tanzania and Lake Turkana, and Kenya.

The jaw of Homo habilis is pulled under the brain, with smaller molars (though still much larger than in modern humans), and the skull is thinner, with a distinctive rounded shape, vertical sides and a small forehead above the brows. The first humans have arrived on the scene. A male habilis may have stood at around 1.3 meters and weighed 37 kilos, and females 1.2 meters and 32 kilos. However, some forms of habilis were apparently smaller, and may have stood little more than a meter tall.

Homo habilis has often been thought to be the ancestor of the more gracile and sophisticated Homo ergaster, which in turn gave rise to the more human-appearing species, Homo erectus. Debates continue over whether H. habilis is a direct human ancestor, and whether all of the known fossils are properly attributed to the species.

Homo habilis may have mastered the Olduwan era (Early Paleolithic) tool case which utilized stone flakes. These stone flakes were more advanced than any tools previously used, and gave H. habilis the edge it needed to prosper in hostile environments previously too formidable for primates. Whether H. habilis was the first hominin to master stone tool technology remains controversial, as Australopithecus garhi, dated to 2.6 million years ago, has been found along with stone tool implements at least 100,000 - 200,000 years older than H. habilis.

Most experts assume the intelligence and social organization of H. habilis were more sophisticated than typical australopithecines or chimpanzees. Yet despite tool usage, H. habilis was not the master hunter that its sister species (or descendants) proved to be, as there is ample fossil evidence that H. habilis was a staple in the diet of large predatory animals such as Dinofelis, a large scimitar-toothed predatory cat the size of a jaguar. H. habilis used tools primarily for scavenging, such as cleaving meat off carrion, rather than defense or hunting. Homo habilis is thought to be the ancestor of the lankier and more sophisticated Homo ergaster, which in turn gave rise to the more human-appearing species Homo erectus. Debates continue over whether H. habilis is a direct human ancestor, and whether all of the known fossils are properly attributed to the species.

Homo habilis co-existed with other Homo-like bipedal primates, such as Paranthropus boisei, some of which prospered for many millennia. However, H. habilis, possibly because of its early tool innovation and a less specialized diet, became the precursor of an entire line of new species, whereas Paranthropus boisei and its robust relatives disappeared from the fossil record.

Homo Erectus

Homo erectus is an extinct Genus of homo who originated in Africa and spread out as far as China and Java—from the end of the Pliocene epoch to the later Pleistocene, about 1.8 to 1.3 million years ago. There is still disagreement on the subject of the classification, ancestry, and progeny of Homo erectus, with two major alternative hypotheses: erectus may be another name for Homo ergaster, and therefore the direct ancestor of later hominids such as Homo heidelbergensis, Homo neanderthalensis, and Homo sapiens; or it may be an Asian species distinct from African ergaster.

H. erectus originally migrated from Africa during the Early Pleistocene, possibly as a result of the operation of the Saharan pump, around 2.0 million years ago, and dispersed throughout much of the Old World. Fossilized remains 1.8 and 1.0 million years old have been found in Africa (Lake Turkana and Olduvai Gorge), Europe (Georgia, Spain), Indonesia, Vietnam, and China.
Dutch anatomist Eugene Dubois, who was fascinated especially by Darwin's theory of evolution as applied to man, set out to Asia to find a human ancestor in 1886. In 1891, his team discovered a human fossil on the island of Java, Indonesia. Dubois described the species as Pithecanthropus erectus, based on a calotte (skullcap) and a femur like that of H. sapiens found from the bank of the Solo River at Trinil, in East Java. This species is now regarded as Homo erectus. This find became known as Java Man.

Throughout much of the 20th century, anthropologists debated the role of Homo erectus in human evolution. Nevertheless, early in the century, due to discoveries on Java and at Zhoukoudian, it was believed that modern humans first evolved in Asia. Only a few naturalists, such as Charles Darwin, predicted that humans' earliest ancestors were African: he pointed out that chimpanzees and gorillas, obviously human relatives, live only in Africa.

From 1950s to 1970s, however, numerous fossil finds from East Africa yielded evidence that the oldest hominins originated there. It is now believed that H. erectus is a descendant of earlier genera such as Ardipithecus and Australopithecus, or early Homo Genuses, such as H. habilis or H. ergaster. H. habilis and H. erectus coexisted for several thousand years, and may represent separate lineages of a common ancestor.

Man of La Chapelle-aux-Saints

Man of La Chapelle-aux-Saints, also called the Old Man, was a fossilized skull of a Neanderthal which was discovered in La Chapelle-aux-Saints, France, by A. and J. Bouyssonie, and L. Bardon in 1908. The physical traits included a 1,600cm3-capacity cranium and heavy thick browridge typical of Neanderthals. Estimated to be about 60,000 years old, the specimen was severely arthritic and had lost all his teeth, with evidence of healing. For him to have lived on would have required that someone process his food for him, one of the earliest examples of Neanderthal altruism.

The remains of La Chapelle-aux-Saints were first studied by Marcellin Boule, whose reconstruction of Neandertal anatomy based on la Chapelle-aux-Saints material shaped popular perceptions of the Neandertals for over thirty years. The La Chapelle-aux-Saints specimen is typical of 'classic' Western European Neandertal anatomy.

This specimen had lost many of his teeth, with evidence of healing. All of the mandibular molars were absent and consequently, some researchers suggested that the 'Old Man' would have needed someone to process his food for him. This was widely cited as an example of Neanderthal altruism, similar to Shanidar 1. However, later studies have shown that La Chapelle-aux-Saints had a number of incisors, canines and premolars in place and therefore would have been able to chew his own food, although perhaps with some difficulty.

Brain Growth Mirrors Human Evolution

Scientists at Washington University School of Medicine in St. Louis found that the human brain regions that grow the most during infancy and childhood are nearly identical to the brain regions with the most changes when the human cerebrum are compared to those of apes and monkeys. Researchers report the finding in a detailed comparison of the brains of normal-term infants and healthy young adults published online in the Proceedings of the National Academy of Sciences.

Scientists conducted the study to help assess the long-term effects of premature birth on brain development. These can include increased risks of learning disabilities, attention deficits, behavioral problems and cognitive impairments.

"Pre-term births have been rising in recent years, and now 12 percent of all babies in the United States are born prematurely," says Terrie Inder, MD, PhD, professor of pediatrics. "Until now, though, we were very limited in our ability to study how premature birth affects brain development because we had so little data on what normal brain development looks like."

Among the questions Inder and her colleagues hope to answer is the extent to which the brain can adapt to developmental limitations or setbacks imposed by early birth. They are also helping to develop clinical strategies to promote such adaptations and normalize development.

The study used a technique for comparative brain anatomy called surface reconstruction pioneered by senior author David Van Essen, PhD, Edison Professor and head of the Department of Anatomy and Neurobiology. Surface reconstruction helps scientists more closely align comparable regions and structures in many different brains and has been used to create online atlases of brain structure.

First author Jason Hill, an MD/PhD student, analyzed the brain scans of 12 full-term infants and compared these to scans from 12 healthy young adults. Data from the two groups were combined into a single atlas to help scientists quantify the differences between the infant and young-adult brains.

They found that the cerebral cortex, the wrinkled area on the surface of the brain responsible for higher mental functions, grows in an uneven fashion. Every region expands as the brain matures, but one-quarter to one-third of the cortex expands approximately twice as much as other cortical areas during normal development.

"Through comparisons between humans and macaque monkeys, my lab previously showed that many of these high-growth regions are expanded in humans as a result of recent evolutionary changes that made the human brain much larger than that of any other primate," says Van Essen. "The correlation isn't perfect, but it's much too good to put down to chance."

The high-growth regions are areas linked to advanced mental functions such as language, reasoning, and what Van Essen calls "the abilities that make us uniquely human." He speculates that the full physical growth of these regions may be delayed somewhat to allow them to be shaped by early life experiences.

Inder notes another potential explanation for the different development rates: the limitations on brain size imposed by the need to pass through the mother's pelvis at birth may force the brain to prioritize.

"Vision, for example, is a brain area that is important at birth so an infant can nurse and learn to recognize his or her parents," Inder says. "Other areas of the brain, less important very early in life, may be the regions that see greater growth as the child matures."

Researchers are currently conducting similar scans of premature babies at birth and years later.
"This study and the data that we're gathering now could provide us with very powerful tools for understanding what goes wrong structurally in a wide range of childhood disorders, from the aftereffects of premature birth to conditions like autism, attention-deficit disorder or reading disabilities," Inder says.

Source: Science Daily

Neanderthal's Vocal Tract

Dr. Robert McCarthy, an assistant professor of anthropology in the Dorothy F. Schmidt College of Arts and Letters at Florida Atlantic University, has reconstructed a vocal tract that simulates the sound of the Neanderthal voice.

Using 50,000-year-old fossils from France and a computer synthesizer, McCarthy’s team has generated a recording of how a Neanderthal would pronounce the letter “e.” The brief recording doesn’t sound like any letter in modern languages, but McCarthy says that’s because Neanderthals lacked the “quantal vowels” modern humans use. Quantal vowels provide cues that help speakers with different size vocal tracts understand one another.

“They would have spoken a bit differently,” McCarthy said at the annual meeting of the American Association of Physical Anthropologists in Columbus, Ohio in April. “They wouldn't have been able to produce these quantal vowels that form the basis of spoken language.”

Though quantal vowels make subtle differences in speech, their absence would have limited Neanderthal speech. For example, Neanderthals would not be able to distinguish between the words ‘beat’ and ‘bit.’

For scientists, McCarthy’s work represents an exploration of life 30,000 years ago when Neanderthal humans, our closest extinct ancestor, lived in parts of Europe, Central Asia and the Middle East. The species died out mysteriously some 28,000 years ago.

Australopithecus Anamensis

Australopithecus anamensis was a species of hominid that inhabited east Africa approximately four million years ago. Nearly one hundred fossil specimens are known from Kenya and Ethiopia, representing over 20 individuals. The first fossilized specimen of the species was a single arm bone found in Pliocene strata in the Kanapoi region of East Lake Turkana by a Harvard University research team in 1965. The specimen was tentatively assigned at the time to Australopithecus and dated about four million years old.

In 1995, Meave Leakey and her associates, taking note of differences between Australopithecus afarensis and the new finds, assigned them to a new species, A. anamensis, deriving its name from the Turkana word anam, meaning "lake". Leakey determined that this species was independent of many others. It does not represent an intermediate species of any type. In 2006, a new A. anamensis find was officially announced, extending the range of A. anamensis into north east Ethiopia. These new fossils, sampled from a woodland context, include the largest hominid canine tooth yet recovered and the earliest Australopithecus femur.