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Chemoaffinity Hypothesis
The Chemoaffinity hypothesis states that neurons make connections with their targets based on interactions with specific molecular markers and, therefore, that the initial wiring diagram of an organism is (indirectly) determined by its genotype. The markers are generated during cellular differentiation and aid not only with synaptogenesis, but also act as guidance cues for their respective axon. Sperry's experiments Roger Wolcott Sperry pioneered the inception of the Chemoaffinity Hypothesis following his 1960s experiments on the African Clawed Frog. He removed the eye of a frog and rotated it 180°, Sperry then replaced the eye and the visual nervous system repaired itself. However, the frog now had inverted vision. Initial eye orientation gives that the top of the eye is Dorsal, and the bottom is Ventral. Post-operation, the "top" of the eye is now Ventral, and the bottom is Dorsal. When a food source was above the frog, it extended its tongue downwards; meaning that the Dorsal-Ve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. Non-animals like plants and fungi do not have nerve cells. Neurons are typically classified into three types based on their function. Sensory neurons respond to stimuli such as touch, sound, or light that affect the cells of the sensory organs, and they send signals to the spinal cord or brain. Motor neurons receive signals from the brain and spinal cord to control everything from muscle contractions to glandular output. Interneurons connect neurons to other neurons within the same region of the brain or spinal cord. When multiple neurons are connected together, they form what is called a neural circuit. A typical neuron consists of a cell body (soma), dendrites, and a single axon. The soma is a compact structure, and the axon and dend ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wiring Diagram
A wiring diagram is a simplified conventional pictorial representation of an electrical circuit. It shows the components of the circuit as simplified shapes, and the power and signal connections between the devices. A wiring diagram usually gives information about the relative position and arrangement of devices and terminals on the devices, to help in building or servicing the device. This is unlike a schematic diagram, where the arrangement of the components' interconnections on the diagram usually does not correspond to the components' physical locations in the finished device. A pictorial diagram would show more detail of the physical appearance, whereas a wiring diagram uses a more symbolic notation to emphasize interconnections over physical appearance. A wiring diagram is often used to troubleshoot problems and to make sure that all the connections have been made and that everything is present. Architectural wiring diagrams Architectural wiring diagrams show the app ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genotype
The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific gene depends on the number of copies of each chromosome found in that species, also referred to as ploidy. In diploid species like humans, two full sets of chromosomes are present, meaning each individual has two alleles for any given gene. If both alleles are the same, the genotype is referred to as homozygous. If the alleles are different, the genotype is referred to as heterozygous. Genotype contributes to phenotype, the observable traits and characteristics in an individual or organism. The degree to which genotype affects phenotype depends on the trait. For example, the petal color in a pea plant is exclusively determined by genotype. The petals can be purple or white depending on the alleles present in the pea plant. Howev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cellular Differentiation
Cellular differentiation is the process in which a stem cell alters from one type to a differentiated one. Usually, the cell changes to a more specialized type. Differentiation happens multiple times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types. Differentiation continues in adulthood as adult stem cells divide and create fully differentiated daughter cells during tissue repair and during normal cell turnover. Some differentiation occurs in response to antigen exposure. Differentiation dramatically changes a cell's size, shape, membrane potential, metabolic activity, and responsiveness to signals. These changes are largely due to highly controlled modifications in gene expression and are the study of epigenetics. With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself. Although metabolic composition does get altered quite dramaticall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synaptogenesis
Synaptogenesis is the formation of synapses between neurons in the nervous system. Although it occurs throughout a healthy person's lifespan, an explosion of synapse formation occurs during early brain development, known as exuberant synaptogenesis. Synaptogenesis is particularly important during an individual's critical period, during which there is a certain degree of synaptic pruning due to competition for neural growth factors by neurons and synapses. Processes that are not used, or inhibited during their critical period will fail to develop normally later on in life. Formation of the neuromuscular junction Function The neuromuscular junction (NMJ) is the most well-characterized synapse in that it provides a simple and accessible structure that allows for easy manipulation and observation. The synapse itself is composed of three cells: the motor neuron, the myofiber, and the Schwann cell. In a normally functioning synapse, a signal will cause the motor neuron to depolarize, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axon
An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body. The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons (pseudounipolar neurons), such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the periphery to the cell body and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction can be the cause of many inherited and acquired neurological disorders that affect both the peripheral and central neurons. Nerve fibers are classed into three typesgroup A nerve fibers, group B nerve fibers, and group C nerve fibers. Groups A and B are myelinated, and group C are unmyelinated. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Roger Wolcott Sperry
Roger Wolcott Sperry (August 20, 1913 – April 17, 1994) was an American neuropsychologist, neurobiologist, cognitive neuroscientist, and Nobel laureate who, together with David Hunter Hubel and Torsten Nils Wiesel, won the 1981 Nobel Prize in Physiology and Medicine for his work with split-brain research. A ''Review of General Psychology'' survey, published in 2002, ranked Sperry as the 44th most cited psychologist of the 20th century. Early life and education Sperry was born in Hartford, Connecticut, to Francis Bushnell and Florence Kraemer Sperry. His father was in banking, and his mother trained in business school. He was raised in an upper middle-class environment, which stressed academic achievement. Roger had one brother, Russell Loomis. Their father died when Roger was 11. Afterwards, his mother became assistant to the principal in the local high school. Sperry went to Hall High School in West Hartford, Connecticut, where he was a star athlete in several sports, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
African Clawed Frog
The African clawed frog (''Xenopus laevis'', also known as the xenopus, African clawed toad, African claw-toed frog or the ''platanna'') is a species of African aquatic frog of the family Pipidae. Its name is derived from the three short claws on each hind foot, which it uses to tear apart its food. The word ''Xenopus'' means 'strange foot' and ''laevis'' means 'smooth'. The species is found throughout much of Sub-Saharan Africa (Nigeria and Sudan to South Africa),Weldon; du Preez; Hyatt; Muller; and Speare (2004). Origin of the Amphibian Chytrid Fungus.' Emerging Infectious Diseases 10(12). and in isolated, introduced populations in North America, South America, Europe, and Asia. All species of the family Pipidae are tongueless, toothless and completely aquatic. They use their hands to shove food in their mouths and down their throats and a hyobranchial pump to draw or suck things in their mouth. Pipidae have powerful legs for swimming and lunging after food. They also use the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dorsal (anatomy)
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes. The meaning of terms that are used can change depending on whether an organism is bipedal or quadrupedal. Additionally, for some animals such as invertebrates, some terms may not have any meaning at all; for example, an animal that is radially symmetrical will have no anterior surface, but can still have a description that a part is close to the middle ("proximal") or further from the middle ("distal"). International organisations have determined vocabularies that are often used as standard vocabularies for subdisciplines of anatom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ventral
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axis, anatomical axes. The meaning of terms that are used can change depending on whether an organism is bipedal or quadrupedal. Additionally, for some animals such as invertebrates, some terms may not have any meaning at all; for example, an animal that is radially symmetrical will have no anterior surface, but can still have a description that a part is close to the middle ("proximal") or further from the middle ("distal"). International organisations have determined vocabularies that are often used as standard vocabular ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optic Nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, Pretectal area, pretectal nuclei, and superior colliculus. Structure The optic nerve has been classified as the second of twelve paired cranial nerves, but it is technically part of the central nervous system, rather than the peripheral nervous system because it is derived from an out-pouching of the diencephalon (optic stalks) during embryonic development. As a consequence, the fibers of the optic nerve are covered with myelin produced by oligodendrocytes, rather than Schwann cells of the per ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tectum
The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', "middle", and ''enkephalos'', "brain". Structure The principal regions of the midbrain are the tectum, the cerebral aqueduct, tegmentum, and the cerebral peduncles. Rostrally the midbrain adjoins the diencephalon (thalamus, hypothalamus, etc.), while caudally it adjoins the hindbrain (pons, medulla and cerebellum). In the rostral direction, the midbrain noticeably splays laterally. Sectioning of the midbrain is usually performed axially, at one of two levels – that of the superior colliculi, or that of the inferior colliculi. One common technique for remembering the structures of the midbrain involves visualizing these cross-sections (especially at the level of the superior colliculi) as the upside-down face of a bear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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