Why do summation and integration occur in postsynaptic cells? Why is it important that synapses exist rather than different neurons having a continuous plasma membrane and/or cytoplasmic connections?
131260
is this a trick question?
66084
This may seem like a silly suggestion, but try representing the elements mentioned in your textbook (which I'm sure has some illustrations) with pieces of paper, matches, beans or something like that, so you can understand the events and the outcome. \nNow, if you _really_ want an explanation, here it comes (I've ommited the names of the phases, they'll be in your textbook).\n\nMeiosis includes 2 cell divisions with different characteristics. \nWe start with a diploid (2 n) cell, in which DNA duplication has occurred so that each DNA strand is double. These strands do not yet appear as chromosomes (condensed bodies); in fact, the chromatin strands have to be "relaxed" in order to duplicate. \n\n***Meiosis I: (in which the nº of chromosomes decreases to half)\n1. The chromatin (DNA strands) starts to condense and appears as small dense dots (the chromosomes) within the cell nucleus. These chromosomes will each have 2 "arms" (they look like an X or a V) because the DNA in each has been duplicated.\n2. Now all these chromosomes align in homologous pairs, with the aid of a transparent structure formed by tiny intracellular fibers (the spindle) that has formed and will help them to move in orderly fashion within the nucleus.\n3. While they keep condensing, each homologous chromosome contacts its "brother", and they exchange some fragments of their DNA ("crossing over"). Usually only one "arm" of each  chromosome participates in crossing over. \n4. In the meantime, the nuclear membrane is disintegrating...\n5. The pairs of homologues, still united, align at the middle (equator) of the spindle... \n6... and then each pair of homologues is divided, one chromosome of each pair goes toward each "pole" of the spindle. \n7. New nuclear membranes form around the 2 groups of chromosomes. Each of these groups will only have ONE of each pair of homologues. Essentially the information in each new nucleus is the same, BUT has some differences because, as you recall, there has been crossing over i.e. partial exchange of DNA between homologues. \n8. The original cell with the 2 nuclei divides and forms 2 cells, with half the nº of chromosomes of the original cell (haploid or n). Each of the chromosomes still has a duplicate DNA strand.\n\n... the cell takes a short break (you can take a break too!)... but the chromatin does not duplicate this time (it's already done that)\n\n***Meiosis II: (in which each double DNA strand becomes single again, this phase is similar to a normal mitosis).\n1. The chromatin condenses again, so that it appears as chromosomes.\n2. This time the spindle aligns the center of each chromosome at its equator.\n3. The central part of the chromosome is duplicated and the sister "arms" (chromatids) separate, each migrating to opposite poles.\n4. Now you have two groups of chromosomes, each group still has the haploid (n) nº of chromosomes (the same amount with which they started this 2nd meiosis) but now, each chromosome has a single DNA strand. \nA new nuclear membrane forms around each of these groups of chromosomes.\n5. The rest of the cell divides.\n\nSo, to sum up: you started with ONE diploid cell. You end with FOUR haploid cells. In animals, this process only happens during the production of gametes. \nIf we're talking about the formation of female gametes, then only ONE of the 4 resulting cells will become an ovule (and that only after more maturation), the other 3 cells form "polar bodies".\nIn contrast, when it's spermatozoids being produced, all FOUR resulting cells will become spermatozoids. \nThat's one of the reasons sperm is cheaper than ovules! There's just more of them in the entire animal kingdom.\n\nNow, what is the purpose of this extremely complicated (the above is a very simplified version) process? The result will be cells that have half the chromosomes of the normal body cells. These cells
568393
Millions of sensory receptors detect changes, called stimuli, which occur inside and outside the body. They monitor such things as temperature, light, and sound from the external environment. Inside the body, the internal environment, receptors detect variations in pressure, pH, carbon \ndioxide concentration, and the levels of various electrolytes. All of this gathered information is called sensory input. \nSensory input is converted into electrical signals called nerve impulses that are transmitted to the brain. There the signals are brought together to create sensations, to produce thoughts, or to add to memory; Decisions are made each moment based on the sensory input. This is integration. \n\nBased on the sensory input and integration, the nervous system responds by sending signals to muscles, causing them to contract, or to glands, causing them to produce secretions. Muscles and glands are called effectors because they cause an effect in response to directions from the nervous system.
471528
glycolysis-occur in the cytoplasm\nelectron transport chain-occur in the mitochondria\nkrebs cycle-occur in the mitochondria.\nif you consider mitochondria as part of the cytoplasm then all of the above..\nbut if not then it will be (a)
157127
I read somewhere that your neurons in your brain fire, and register the information, then they fire again, registering the same information milliseconds later.  Your brain interprets this as a faint memory.
104889
Great Question!Here is some information about how the brain works:\n\nHow does your brain work?\n\nYour brain is the hub of your nervous system. It is made up of 100 billion nerve cells - about the same as the number of trees in the Amazon rainforest. Each cell is connected to around 10,000 others. So the total number of connections in your brain is the same as the number of leaves in the rainforest - about 1000 trillion.\nYour brain is made up of 100 billion nerve cells - about the same as the number of trees in the Amazon rainforest.\n\nHow does your nervous system work?\n\nThe nervous system is a network of cells called neurones which transmit information in the form of electrical signals. Your brain has around 100 billion neurones, and each communicates with thousands of others - as many connections as in the world's telephone system, the biggest machine on the planet. Neurones communicate with each other at special junctions where chemicals help to bridge the gap between one neurone and the next. \nThe nervous system is a vast network of interconnecting neurones.\n\nMore about nervous connuections:\n\nThe electrical signals (nerve impulses) carried by neurones are passed on to other neurones at junctions called synapses. The signal may be directly transferred at electrical synapses or, if there is no physical link between adjacent neurones, the signal is carried across the gap by chemicals called neurotransmitters. By using neurotransmitters, the nervous system can alter the way a message is passed on. Each neurone communicates with many others and this contributes to the amazing complexity of the brain.Each neurone communicates with many others.\n\nHope it helps.
671762
The photoreceptor cells in the deepest (surprisingly!) layer of the retina encode the light image into electrical signals.  There is NO form of fibre optic light pipe.  The signal is purely electrical, not light, from the first cell in the system onwards.\n(When I say purely electrical, I mean not light, ie electrical and chemical neurotranmitter/receptor, of course.)\n\nNeural synapses occur through a sequence of several cells before the pattern of neural impulses reaches the optic nerve. Oddly, the light has to pass through these neurons in order to reach the photoreceptors.\n\nI understand these synapses are arranged so as to identify and encode contrasting edges and lines, providing initial processing of the image within the eye. \n\nI claim no more than the most elementary knowledge, so hopefully further answers will detail what processing exactly is performed before the optic nerve takes the messages to the temporal cortex and tectum.\n\nPerhaps more chance of this if not under "Engineering".
80959
I'm not quite sure what you are asking, but I think the answer you want is that each ganglion contains the cell bodies of the sensory neurones.\nUnipolar motor neurones have their cell bodies within the spinal cord.
398821
Plant cells have a rigid cell wall so during telephase (cytokinesis), they use a different method of divergence ('splitting' of the cell). The process is complicated, so state that plant cells do not cleave like animal cells and that they produce a cell plate from the Golgi apparatus. Also, plant cells don't have centromeres and instead use astral fibres.\n\nBefore mitosis begins, chromosomes are replicated so that their numbers are doubled.\n\nAfter a cell undergoes mitosis, the two new cells are completely identical and have the same DNA. A difference which may occur, but is of little importance, is that one cell may receive more organelles then the other when division occurs by chance.\n\nIt's important for the nuclear membrane to disintegrate during mitosis so that the chromosomes can attach to the spindle fibres and allign at the metaphase plate (or the 'equator'). It's also required so that the chromosomes can be pulled apart from each other during anaphase, and allow the division of the cell.
453974
tough questions... here is an explanation of part of your questions:\n\nA number of physiological mechanisms appear to be involved in the formation of memories, and the mechanisms may differ for short-term and long-term memory. There is both direct and indirect evidence suggesting that short-term memory involves the temporary circulation of electrical impulses around complex loops of interconnected neurons. A number of indirect lines of research indicate that short-term memories are eradicated by any event that either suppresses neural activity (for example, a blow to the head or heavy anesthesia) or causes neurons to fire incoherently (for example, electroconvulsive shock). More direct support for the electric circuit model of short-term memory comes from observing electrical brain activity. By implanting electrodes in the brain of experimental animals, researchers have observed that changes in what an animal is watching are associated with different patterns of circulating electrical activity in the brain. These results suggest that different short-term memories may be represented by different electrical patterns. However, the nature of these patterns is not well understood. \n\nLong-term memories appear to involve some type of permanent structural or chemical change in the composition of the brain. This conclusion is derived both from general observations of the imperviousness of long-term memories and from physiological studies indicating specific changes in brain composition. Even in acute cases of amnesia where massive deficits in long-term memory are reported, often, with time, all long-term memories return. Similarly, although electroconvulsive therapy is known to eliminate recent short-term memories, it has practically no effect on memories for events occurring more than an hour prior to shocking. Thus the transfer from a fragile short-term memory to a relatively solid long-term memory occurs within an hour. This process is sometimes called consolidation. \n\nThe nature of the “solid” changes associated with long-term memories appears to involve alterations in both the structural (neural connections) and chemical composition of the brain. One study compared the brains of rats that had lived either in enriched environments with lots of toys or in impoverished environments with only an empty cage. The cerebral cortices of the brains of the rats from the enriched environment were thicker, heavier, endowed with more blood vessels, and contained significantly greater amounts of certain brain chemicals (such as the neurotransmitter acetylcholine). Other researchers have observed that brief, high-frequency stimulation of a neuron can produce long-lasting changes in the neuron's communications across synapses.\n\nResearchers believe that different brain structures may be involved in the formation and storage of long-term memories. The hippocampus, thalamus, and amygdala are believed to be critical in the formation of long-term memories. Individuals who have had damage to these structures are able to recall memories prior to the damage, indicating that long-term memory storage is intact; however, they are unable to form new long-term memories, indicating that the long-term memory formation process has been disrupted. It is not known where long-term memories are stored, but they may be localized in the same areas of the brain that participated in the actual learning.
129653
Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. According to the dogma of the 1960s.\n\nA neurotransmitter's effect is determined by its receptor. For example, GABA can act on both rapid or slow inhibitory receptors (the GABA-A and GABA-B receptor respectively). Many other neurotransmitters, however, may have excitatory or inhibitory actions depending on which receptor they bind to.\n\nNeurotransmitters may cause either excitatory or inhibitory post-synaptic potentials. That is, they may help the initiation of a nerve impulse in the receiving neuron, or they may discourage such an impulse by modifying the local membrane voltage potential. In the central nervous system, combined input from several synapses is usually required to trigger an action potential. Glutamate is the most prominent of excitatory transmitters; GABA and glycine are well-known inhibitory neurotransmitters.\n\nMany neurotransmitters are removed from the synaptic cleft by a process called reuptake (or often simply uptake). Without reuptake, the molecules might continue to stimulate or inhibit the firing of the postsynaptic neuron. Another mechanism for removal of a neurotransmitter is digestion by an enzyme. For example, at cholinergic synapses (where acetylcholine is the neurotransmitter), the enzyme acetylcholinesterase breaks down the acetylcholine. Neuroactive peptides are usually removed from the cleft by diffusion, and eventual broken down by proteases
316380
The importance of mitosis is that body cells divide by this process.  If body cells didn't divide, first off, we would never be born because we wouldn't develop into a fetus and second, we wouldn't grow.  The kind of cells that divide by mitosis are somatic (body) cells.  Meiosis is the process by which a multicellular organism is formed.  The kind of cells that divide in meiosis are the sex cells.  The female cells are eggs and the male cells are sperm.  When these two sex cells unite, they form a multicellular zygote.  The egg and sperm are haploid (meaning they have a chromosome count of 1), and they combine to form a diploid (meaning they have a chromosome count of 2) zygote.
441246
1. I guess You think about the nexuses. Its a metabolic and ionic connection of cells in form of ionic channels (built by proteins called conexones or conexone proteins).It provides rapid transport of membrane polarization changes. Its a form of electric synapses.\n2.I guess You think about the lysosomes. They're created by Golgi's Apart ('Trans" side).Lysosomic enzymes are created by Rough Endoplasmic Reticulum and GA. Lysosomical endoenvironment's pH is about 5. Function- to connect with endosomes, phagosomes and autophagosomes and to catalyze and guide analysis reaction (some kinds of digestive reactions).
672415
An electronic structure would be a neuron, as it conducts ions along the length of the axon.  This change in ion concentration is equivalent to a difference in volts, ie electrical charge.
379561
amy is right.  this is the basis behind percieved perception.  what you see may be different than what somebody else sees however you speek of it as the same thing.\n\naarons answer is missing the part of transfering the light information into a chemical reaction inside the rod cells and then turn to electical activity.  this is where the possible problem occurs\nbetter yet heres the sequence \n\n1. Light rays enter the eyes by passing through the cornea, the aqueous, the pupil, the lens, the vitreous, and then striking the light sensitive nerve cells (rods and cones) in the retina.\n\n2. Visual processing begins in the retina. Light energy produces chemical changes in the retina's light sensitive cells. These cells, in turn, produce electrical activity.\n\n3. Nerve fibers from these cells join at the back of the eye to form the optic nerve.\n\n4. The optic nerve of each eye meets the other at the optic chiasm. Medial nerves of each optic nerve cross, but lateral nerves stay on the same side. The overlap of nerve fibers allows for depth perception.\n\n5. Electrical impulses are communicated to the visual cortex of the brain by way of the optic nerve.
284348
The distribution of ions across a cell membrane produces a concentration gradient that can be used by the cell to do various kinds of work (i.e. power non-spontaneous reactions).  \n\nFor example, in mitochondria and certain aerobic bacteria, the gradient of H+ ions powers ATP synthase, and allows it to make ATP (an extremely important energy storage molecule).  \n\nIn other cells, the concentration gradients of ions can be used to facilitate active transport across the membrane by coupling an ion moving along it's concentration gradient with another molecule moving against it.\n\nIn neurons, the difference in the concentrations of ions inside and outside the cell creates a membrane polarity that allows the action potential (i.e. the nerve firing) to occur.  When the nerve is activated by a neurotransmitter or a direct external stimulus, sodium channels open, allowing Na+ to rush into the cell, making it positive relative to the external environment.  This change in polarity moves along the cell, and causes the cell to release specific neurotransmitters at the other end.\n\nIf the ions were distributed equally, none of the processes I just mentioned would work!
20607
The human mind is associated with the brain.  The brain tends to use neurons which have previously been used over those which have never been used.  Background assumptions, beliefs, paradigms all tend to prevent new associations with old concepts.