Thursday, September 29, 2022

Which Organism Has A Central Brain

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Distribution Of Connection Strength

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The distribution of connection strengths has been studied in mammalian tissue, looking at specific cell types in specific brain areas. These findings, such as the log-normal distribution of connection strengths in rat cortex, do not appear to generalize to flies. Assuming the strength of a connection is proportional to the number of synapses in parallel, we can plot the distribution of connection strengths, summing over the whole central brain, as shown in Figure 21. We find a nearly pure power law with an exponential cutoff, very different from the log-normal distribution of strengths found by Song et al., 2005 in pyramidal cells in the rat cortex, or the bimodal distribution found for pyramidal cells in the mouse by Dorkenwald et al., 2019. However, we caution that these analyses are not strictly comparable. Even aside from the very different species examined, the three analyses differ. Both Song and Dorkenwald looked at only one cell type, with excitatory connections only, but one looked at electrical strength while the other looked at synapse area as a proxy for strength. In our analysis, we use synapse count as a proxy for connection strength, and look at all cell types, including both excitatory and inhibitory synapses.

Neural Circuits And Systems

The basic neuronal function of sending signals to other cells includes a capability for neurons to exchange signals with each other. Networks formed by interconnected groups of neurons are capable of a wide variety of functions, including feature detection, pattern generation and timing, and there are seen to be countless types of information processing possible. Warren McCulloch and Walter Pitts showed in 1943 that even artificial neural networks formed from a greatly simplified mathematical abstraction of a neuron are capable of universal computation.

Treatise of Man

However, experimental studies of electrophysiology, beginning in the early 20th century and reaching high productivity by the 1940s, showed that the nervous system contains many mechanisms for maintaining cell excitability and generating patterns of activity intrinsically, without requiring an external stimulus. Neurons were found to be capable of producing regular sequences of action potentials, or sequences of bursts, even in complete isolation. When intrinsically active neurons are connected to each other in complex circuits, the possibilities for generating intricate temporal patterns become far more extensive. A modern conception views the function of the nervous system partly in terms of stimulus-response chains, and partly in terms of intrinsically generated activity patternsâboth types of activity interact with each other to generate the full repertoire of behavior.

Intrinsic pattern generation

How Can Animals Function Without A Brain

Although for us humans not having a brain would be unfeasible, there are many living animals that survive without a brain. Most of these brainless species are aquatic, predominantly because these animals retain morphologies similar to that of their ancient predecessors.

But, how can animals survive without a brain? Well, each species has adapted in specific ways which allow them to exist, feed, reproduce and excrete normally. Whether we speak of an evolved medullary system, arms, tentacles, ganglia or nervous systems, every one of these below species has adapted and evolved differently, allowing them to survive.

Keep reading to discover our list of aquatic creatures without a brain and insects without a brain:

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Nervous System Development Across The Human Lifespan

As a species, humans have evolved a complex nervous system and brain over millions of years. Comparisons of our nervous systems with those of other animals, such as chimpanzees, show some similarities . Researchers can also use fossils to study the relationship between brain volume and human behavior over the course of evolutionary history. Homo habilis, for instance, a human ancestor living about 2 million years ago shows a larger brain volume than its own ancestors but far less than modern homo sapiens. The main difference between humans and other animals– in terms of brain development– is that humans have a much more developed frontal cortex .

Interestingly, a persons unique nervous system develops over the course of their lifespan in a way that resembles the evolution of nervous systems in animals across vast stretches of time. For example, the human nervous system begins developing even before a person is born. It begins as a simple bundle of tissue that forms into a tube and extends along the head-to-tail plane becoming the spinal cord and brain. 25 days into its development, the embryo has a distinct spinal cord, as well as hindbrain, midbrain and forebrain . What, exactly, is this nervous system that is developing and what does it do?

What Are The Data Types

This thing.  The human brain. The central processing unit ...

Grayscale data correspond to traditional electron microscope images. This is written only once, after alignment, but often read, because it is required for segmentation, synapse finding, and proofreading. We store the grayscale data, eight bits per voxel, in Google buckets, which facilitates access from geographically distributed sites.

Segmentation, synapses, and identifying regions annotate and give biological meaning to the grayscale data. For segmentation, we assign a 64 bit neuron ID to each voxel. Despite the larger size per voxel compared with the grayscale, the storage required is much smaller since segmentation compresses well. Although the voxel level segmentation is not needed for connectivity queries, it may be useful for tasks such as computing areas and cross-sections at the full resolution available, or calculating the distance between a feature and the boundary.

Synapses are stored as point annotations – one point for a presynaptic T-bar, and one point for each of its postsynaptic densities . The segmentation can then be consulted to find the identity of the neurons containing their connecting synapses.

The compartment map of the brain is stored as a volume specified at a lower resolution, typically a 32 × 32 × 32 voxel grid. At 8 nm voxels, this gives a 256 nm resolution for brain regions, comparable to the resolution of confocal laser scanning microscopy.

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The Brain And Nervous System

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The brain is the most complex part of the human body. It is the center of consciousness and also controls all voluntary and involuntary movement and bodily functions. It communicates with each part of the body through the nervous system, a network of channels that carry electrochemical signals.

Ability To Recognise People

Jon adds, ‘Octopuses appear to be able to recognise individuals outside of their own species, including human faces. It’s not unique behaviour – some mammals and crows can do it too – but it is rather unusual.’

Scientific American reported a story from the University of Otago in New Zealand where a captive octopus apparently took a dislike to one of the staff. Every time the person passed the tank, the octopus squirted a jet of water at her.

Biologists at the Seattle Aquarium designed an experiment to test the recognition abilities of the giant Pacific octopus.

Over the course of two weeks, one person fed a group of octopuses regularly, while another person touched them with a bristly stick. At the end of the experiment, the octopuses behaved differently to the ‘nice’ keeper and the ‘mean’ one, which confirmed the octopuses could distinguish the two individuals, despite the fact they wore identical uniforms.

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What Does A Synapse Look Like

The axon terminal of the presynaptic neuron conducts electrical signals called action potentials towards the synapse. The end of the axon terminal has a slight swelling known as the synaptic knob. This is where chemical messengers called neurotransmitters are made and strored. The synaptic knob of the presynaptic neuron is located near the postsynaptic neuron. The space between the two neurons is called the synaptic cleft, and is too wide to allow current to pass directly from one cell to another, preventing the transference of action potentials between neurons.

Synapses only operate in one direction. Presynaptic neurons influence the cell membrane voltage of postsynaptic neurons, but postsynaptic neurons cannot directly affect presynaptic neuron membrane potentials.

Triploblasty: Three Tissue Layers

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Many, but not all, animals produce three embryonictissue tissue layers as they develop: theendoderm,mesoderm,and ectoderm.Some animals, most notably sponges, lack these tissue layers.Cnidarians have only two ofthese layers, and are termed diploblastic. Flatworms, ribbon worms,humans, etc. have all three tissue layers, and are triploblastic.

Table 1. Animal embryonic tissue layers.

Tissue layer

skin, brain, and nervous system

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Animals That Lack Cephalization

Cephalization doesn’t offer an advantage to free-floating or sessile organisms. Many aquatic species display radial symmetry. Examples include echinoderms and cnidarians . Animals that can’t move or are subject to currents must be able to find food and defend against threats from any direction. Most introductory textbooks list these animals as acephalic or lacking cephalization. While it’s true none of these creatures has a brain or central nervous system, their neural tissue is organized to allow rapid muscular excitation and sensory processing. Modern invertebrate zoologists have identified nerve nets in these creatures. Animals that lack cephalization are not less-evolved than those with brains. It’s simply that they are adapted to a different type of habitat.

Opportunistic Infections Associated With Hiv Infection

Despite the marked improvement in outcomes and outlook for HIV-infected patients with the introduction of highly active antiretroviral therapy in 1995, there are still approximately 50,000 new cases of HIV infection per year in the United States . HIV infection predisposes individuals to a variety of opportunistic infections of the brain, including infections caused by Cryptococcus spp., Toxoplasma gondii, CMV, or the polyomavirus that causes progressive multifocal leukoencephalopathy . In addition, the virus itself is associated with a variety of neuropathologic manifestations.

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Interactions Between The Central And Peripheral Nervous Systems

The peripheral nervous system is made up of nerves and ganglia . The PNS and CNS work together to send information between the brain and the rest of the body. Nerves emerge from the CNS through the skull and vertebral column, using the PNS to carry information to the rest of the body.

The PNS is made up of two divisions sensory and motor. The sensory division carries signals from all over the body back to the CNS to be decoded, while the motor division carries signals from the CNS to cells all over the body to carry out the bodys responses to this information.

Neural Plasticity And Therapy

Brain Organism

Regardless of whether it is synaptic efficacy that is altered for long periods, or some other long-lasting form of neural plasticity, the net effect of the stimulation protocols described above is an increase in output from the neocortex. Repetitive stimulation of the brain can exert long-lasting functional effects, as demonstrated by the increased muscle activity in the hand in response to TMS directed at primary motor cortex. Treatment could potentially be provided for neurological disorders that arise from a reduction in the output of particular regions of the brain, as in Parkinson’s disease and depression, using remote stimulation to induce long-lasting increases in excitatory drive. Currently available therapies using electrical stimulation rely upon invasive surgery. A non-invasive method of achieving the same end would obviously be preferable.

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Do Cockroach Bites Hurt

Cockroach Bites Are Powerful You may not feel them when biting you, but the aftermath might give you a painful sensation. Cockroaches bite force is 50 times powerful than their body weight. The pain might depend on your tolerance, but if you have low pain tolerance, then you might find it too excruciating.

Circulatory And Respiratory Systems

Caffeine is absorbed from your stomach. It reaches its highest levels in your bloodstream within an hour or two.

Caffeine can make your blood pressure go up for a short time. This effect is thought to be attributed to either an increase in adrenaline or a temporary block on the hormones that naturally widen your arteries. In most people, there is no long-term effect on blood pressure, but if you have irregular heart rhythms, caffeine may make your heart work harder. If you have high blood pressure or heart-related problems, ask your doctor if caffeine is safe for you to consume.

An overdose of caffeine may cause rapid or irregular heartbeat and breathing trouble. In rare cases, caffeine overdose can result in death due to convulsions or irregular heartbeat.

Caffeine in large amounts may interfere with absorption and metabolism of calcium. This can contribute to bone thinning .If you consume too much, caffeine may cause also your muscles to twitch.

If experiencing caffeine withdrawal, a symptom may include achy muscles.

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Class Anthozoa: Sea Anemones And Corals

Sea anemones, shown in Figure 12, are solitarypolyps 5-100 mm in height and 5-200 mm in diameter or larger. Theyare often brightly colored and look like flowers on the seafloor. You might remember them from the filmFinding Nemo. The anemone’s thick, heavy body rests on a pedaldisk and supports an upward-turned mouth surrounded by hollowtentacles. Sea anemones feed on various invertebrates and fish. Theyattach to a variety of substrates, or may be mutualistic with hermitcrabs, living attached to crab’s shell.

Figure 12. Anatomy of a polyp. These animals have an almost plant-like appearance, being anchored in place.Image from Purves et al.,Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman , used with permission.

Corals may be solitary but most today arecolonial. The majority of corals occur in warm shallow waters theaccumulation of their calcium-carbonate remains builds reefs. Somecorals occur in colder waters, so the mere presence of coral does notnecessarily indicate a tropical environment. Modern scleractiniancoral, dominant reef-builders since the Triassic period , have symbioticphotosynthetic dinoflagellatesliving within the coral body. These dinoflagellates are in the genusSymbiodinium, and are termed collectively zooxanthellae, shownin Figure 13a. Figure 13b illustrates several living coral tyypes.

Thephylum Nemertea: Ribbon Worms

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The phylum Nemertea include approximately 650species of marine ribbon worms. Ribbon worms have a distinctiveeversible proboscis stored in a rhynchocoel. When the walls of therhynchocoel contract, the proboscis extends out of the body. Theproboscis is a long, hollow tube that can be everted and shot outwardthrough a pore located just above the mouth. It is used primarily forprey capture, and for defense, locomotion, and burrowing. This phylumis included as the organisms are also triploblastic. Several of thefossils from the Cambrian-aged Burgess Shale are interpreted asribbon worms, and some extremely long worms have been found in theMediterranean and in the ocean under theAntarctic ice shelves.

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Hiv Encephalopathy And Dementia

HIV is a neurotropic virus that appears to enter the brain via infected macrophages early in the course of infection. HIV infection itself causes CNS complications, including encephalitis and dementia. Encephalopathy usually develops as part of the acute HIV syndrome during the seroconversion phase. Two pathogenic mechanisms are thought to underlie these CNS conditions. In the first mechanism, HIV and its fragments induce damage directly or indirectly through the accumulation of infected or activated macrophage and microglia cells that release neurotoxic mediators including both cellular activation products and viral proteins . The accumulation of these activated macrophage/microglia cells, some of which are infected, release a number of cytokines and small molecule mediators and viral proteins that act on bystander cells. These viral proteins and cellular products have neurotoxic properties and act directly and through induction of astrocyte dysfunction, leading to neuronal injury . The second, less predominant, pathogenic mechanism is the ability of HIV to impair neurogenesis . Kaul suggests that both proposed pathogenic mechanisms occur side by side with other host-virus interactions .

Organizationof The Animal Body

Animals are characteristically multicellularheterotrophswhose cells lack . At some point during their lives,animals are capable of movement. In the most commonly encounteredanimals, this stage is the adult, although some animals havesessile adult phases and mobile juvenile forms. Animaland plant evolutionary history both show the development ofmulticellularity and the move from water to land .

Animals developed external or internalto provide support, skin to prevent or lessen water loss, musclesthat allowed them to move in search of food, brains and nervoussystems for integration of stimuli, and internal .

Most animals have a life cycle with a preadultstage, a predominance of the diploid stage, and a series of embryonicdevelopmental stages.

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Bilateralsymmetry And Cephalization: Phylumplatyhelminthes

The phylum Platyhelminthes contains about 13,000species of flatworms subdivided into three classes: two parasitic andone free-living.The planaria and relativesare freshwater animals placed in the class Turbellaria. Flukes areexternal or internal parasites belonging to the the Class Trematoda.Tapeworms are internal parasites and form the Class Cestoda.The phylum as a whole has adult bilateral symmetryand cephalization .

Flatworms have three tissue layers: ectoderm,mesoderm and endoderm and a body plan that is acoelomate and sac-likewith a single opening. The mesoderm layer gives rise to muscles andreproductive organs. Free living forms have muscles, a nerve cord,and digestive organs, but lack both the and common to the so-called “higher”animals . Flatworms, as shown inFigure 18, have a branched gastrovascular cavity that is the site of and which distributes nutrientsthroughout the body. Gas exchange occurs by diffusionthrough the skin. Platyhelminths have an that also functions as anosmotic-regulating system. Flatworms have a ladder-style composed of paired gangliathat form a brain connected via nerve cells to sensory cells in thebody wall.

Figure 19. Anatomy of a flatworm. Note the sensory lobes and digestive system.Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman , used with permission.

Parasitic members of this phylum, such as flukesand tapeworms, are characterized by these modifications:

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