Metazoans are most likely a clade, that is, they all descended from one kind of protist. All metazoans originally had one cilium or flagellum per cell, for example. Metazoans also share the same kind of early development. They form into infolded balls of internal cells which are often free to move, and are covered by outer sheets of cells that form an external coating for the animal: a skin, if you like.
Among various types of organ systems, the nervous system is one of the most important one in human body. It is responsible for producing, controlling and guiding our thoughts and responses to the world around us according to James W. Pennebaker (2012). During embryological development, the cells that form nervous system are incredibly specialised and work complexly than the cells that form skin or other body parts. Neurosecretory cells are one of the examples of specialised nervous system cells that produce neurosecretions. Neurosecretions are hormones which carry information from sensor cells to target cells and they can be released directly into the bloodstream
In the summer of 1674, the Dutch scientist Antoni van Leeuwenhoek looked through a homemade microscope at a sample of rain water and revolutionized the human view of the world. What he found was “little legs” that we now know are the cilia that many single-celled protozoa use for locomotion. Almost exactly 300 years later, the observations of Swedish scientists Afzelius led to another paradigm shift, when he linked defects in the machinery required for the movement of human cilia to Kartagener’s syndrome (KS), a disease characterized by chronic sinus and respiratory infections; male infertility; and, incredibly, the misplacement of the heart and other organs (Brown & Whitman 2014). He too came up with the hypothesis that the existence of ‘so-called sensory hairs protruding from the cell surface into the extracellular space’ was to explain the poor sense of smell and decreased hearing ability in patients with KS (Pennekamp et al. Cilia 2015). Almost two decades after Afzelius presented his
The phylum Ctenophora is very intriguing, and o ur research was focused mainly on the species Mnemiopsis, otherwise known as the Sea Walnut. This species of Comb Jellies is found in freshwater and saltwater all throughout the world. They move through their habitat with cilia attached to comb rows. The Sea Walnut is thought to be one of largest organism to move with cilia. This may be because it is not the most advanced organism. Its highest level of organization is tissues. But do not mistake that for this organism being boring, it has many redeemable qualities, like bioluminescence (http://www.aquariumofpacific.org/onlinelearningcenter/species/comb_jelly).
Cnidarians share a basic body plan, but have two distinct body forms-the polyp and the medusa. The medusa plan is essentially the polyp turned upside down. By inverting same shape, cnidarians devised two distinctive ways of living. Exactly how and when the transition occurred is uncertain, but anchored cnidarians adapted a body plan for a free-swimming life (the medusa),and may have been the first animal to swim the oceans. The medusa plan allows the jellyfish to swim through the water using muscle contractions and float with the currents.
The evidence is based on the assumption that homologous structures tend to possess similar developmental properties as compared to structures that have evolved independently on both the genetic and molecular stages.
During normal development of the mammalian central nervous system (CNS), neural stem cells (NSC) give rise to neurons via process of neurogenesis (Kempermann et al., 2004; Zhao et al., 2008). Neurogenesis normally occurs in dentate gyrus (DG) region of the hippocampus and lateral ventricle of sub-ventricular zone (SVZ) (Zhao et al., 2008). Hippocampal neurogenesis plays pivotal role in neurologic and psychiatric disorder like epilepsy, depression, schizophrenia and mood disorders (Antonova et al., 2004; Keller and Roberts, 2008; Lucassen et al., 2006; Zhao et al., 2008). Development of the nervous system is complex, and includes multistep dynamic processes such as proliferation, differentiation, migration, expansion of axons and dendrites, synapse formation, myelination and programmed cell death (Rice and Barone, 2000). These processes required the coordinated expression of cellular and molecular events in a spatial and temporal manner during the brain development (Rice and Barone, 2000; Rodier, 1994). Several growth factors and signal transduction cascades have been implicated in controlling NSC behavior in the developing brain (Faigle and Song, 2013). Among these, members of the Wnt family of secreted glycoprotein thought to be variably influence proliferation and lineage decisions of NSC and their progeny (Clevers et al., 2014).
The anatomical and functional divisions of the nervous system are divided into two categories the central nervous system (CNS) and the peripheral nervous system (PNS).
The human brain is a feat of evolution: it has allowed humans to have complex thoughts, conscience, build tools, create fires, and much more. Humans did not acquire this simply by chance. Evolution throughout our ancestral past has shaped and moulded the human mind to its state. The earliest of ancestors, including apes, had very small brains, but as evolution progressed, so too did the human brain. The rapid progression of human intelligence has been attributed to environmental changes causing humans to change with their surroundings for survival. This lead to the expansion of specific areas of the brain, vastly differing maturation of humans compared to our
Instead of measuring the weight of a brain scientists measure the endocasts of brains. http://humanorigins.si.edu/human-characteristics/brains
The nervous systems of all organisms confront perturbations ranging from genetic and developmental errors to changing environmental conditions. However, following such perturbations neurons return to their set point via homeostatic regulation. To understand how neurons come back to their set point one must first realize what is meant by ‘homeostatic regulation’. Definitions differ, but a common theme is that of a system returning to a ‘set-point’, ‘target value’ or ‘previous state’ following some perturbation (Turrigiano; 1999, Turrigiano & Nelson; 2004, Davis; 2006, O’Donnell & Nolan; 2011). Such a definition can have an overly restrictive interpretation: in the most extreme form it could be construed to mean that nothing really changes in homeostatic systems. This often results in concepts such as ‘allostasis’ (‘stability through change’) – a term necessitated by the mistaken view that homeostatic processes imply static systems. Some authors have attempted to solve the problem of finding an adequate yet simple conceptual model of neuronal homeostasis by restricting the range of phenomena that homeostasis applies to (Davis; 2006), or by embellishing a static theory with the notion of ‘customizable set points’ (Turrigiano; 2008). Homeostatic signaling systems act throughout the central and peripheral nervous systems to stabilize the active properties of nerve and muscle (Davis; 2006, Marder; 2011, Turrigiano; 2011). Evidence for this has accumulated by measuring how nerve
The nervous system in a canine is made up of these three things: Brain, spinal cord and several different kinds of nerves located throughout the body. They create complex circuits through which animals experience and respond to sensations: The central nervous system includes the spinal cord and brain. The brain has three main sections: the brain stem that controls several basic life functions. The cerebrum, which is the center of conscious decision making, and lastly, the cerebellum which involves movement and motor skills in the animal. The most common type of nervous system circuit that most people are familiar with is the reflex. Reflexes are simple networks found in the nervous system of all animals. For example, if a dog goes down in
On page nine in the Blackmore article, it is stated that, “On the one hand, if consciousness is an extra added ingredient then we naturally want to ask why we have it. We want to ask what consciousness is for, what it does, and how we got it. On this view, it is easy to imagine that we might have evolved without it, and so we want to know why consciousness evolved, what advantages it gave us, and whether it evolved in other creatures too. On this view, the hard problem is indeed hard; and the task ahead is to answer these difficult questions.”
During development, neurons extend their axons and dendrites to establish proper connections in the central and peripheral nervous system (CNS and PNS). This wiring process is largely controlled by extracellular cues, which activate receptors on the responding neurons. In turn, these receptors initiate