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HUMAN EMBRYOGENESIS (STEP 1-4)

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Embryogenesis, the first eight weeks of development after fertilization, is an incredibly complicated process. It’s amazing that in eight weeks we’re transforming from a single cell to an organism with a multi-level body plan. The circulatory, excretory, and neurologic systems all begin to develop during this stage. Luckily, like with many complex biological concepts, fertilization can be broken down into smaller, simpler ideas. The big idea of embryogenesis is going from a single cell to a ball of cells to a set of tubes.  Starting from the very beginning Step 1 : a  zygote  is the single cell formed when an egg and a sperm cell fuse; the fusion is known as fertilization Step 2 : the first 12-to 24-hours after a zygote is formed are spent in  cleavage  – very rapid cell division The zygote’s first priority is dividing to make lots of new cells, so it’s first few days are spent in rapid mitotic division. With each round of division, it doubles in c...
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MUSCULAR CONTRACTION

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The process of muscular contraction occurs over a number of key steps, including: Depolarisation and calcium ion release Actin and myosin cross-bridge formation  Sliding mechanism of actin and myosin filaments Sarcomere shortening (muscle contraction) 1.    Depolarisation and Calcium Ion Release An action potential from a motor neuron triggers the release of acetylcholine into the motor end plate Acetylcholine initiates depolarisation within the sarcolemma, which is spread through the muscle fibre via T tubules  Depolarisation causes the sarcoplasmic reticulum to release stores of calcium ions (Ca 2+ ) Calcium ions play a pivotal role in initiating muscular contractions 2.    Actin and Myosin Cross-Bridge Formation On actin, the binding sites for the myosin heads are covered by a blocking complex (troponin and tropomyosin) Calcium ions bind to troponin and reconfigure the complex, exposing the binding sites for the myosin hea...
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HUMAN EMBRYOGENESIS (STEP 5-7)

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Making Tubes Step 5 : During  gastrulation  the three germ layers form; the cell mass is now known as a gastrula Step 5a : The  primitive streak  forms Step 6 : The  notochord   is formed Week 3 of development is the week of  gastrulation . A germ layer is a layer of cells that will go on to form one of our organizational tubes. Our anatomy can really be boiled down to an inner tube (our digestive tract), and a series of tubes that wrap around it. The three germ layers that will translate into these tubes are the  ectoderm , the  mesoderm , and the  endoderm . Germ Layer What does the prefix mean? Goes on to form: Ectoderm Outer, external Epidermis (outer layer of skin), hair, nails, brain, spinal cord, peripheral nervous system Mesoderm Middle Muscle, bone, connective tissue, notochord, kidney, gonads, circulatory system Endoderm Within Epithelial lining of the digestive tract; Stomach, colon, liver, pancreas, bladd...
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ANATOMY OF THE EYE

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Your  eye  is a slightly asymmetrical globe, about an inch in diameter. The front part (what you see in the mirror) includes: Iris : the colored part Cornea : a clear dome over the iris Pupil: the black circular opening in the iris that lets light in Sclera : the white of your eye Conjunctiva : a thin layer of tissue that covers the entire front of your eye, except for the cornea Just behind the iris and pupil lies the lens, which helps focus light on the back of your  eye . Most of the eye is filled with a clear gel called the vitreous. Light projects through your pupil and lens to the back of the eye. The inside lining of the eye is covered by special light-sensing cells that are collectively called the retina. It converts light into electrical impulses. Behind the eye, your optic nerve carries these impulses to the  brain . The macula is a small extra-sensitive area in the retina that gives you central vision.
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