X-Ray Prodcution

Over a century ago in 1895, Roentgen discovered the first example of ionizing radiation, x-rays. The key to Roentgens discovery was a device called a Crooke’s tube, which was a glass envelope under high vacuum, with a wire element at one end forming the cathode, and a heavy copper target at the other end forming the anode. When a high voltage was applied to the electrodes, electrons formed at the cathode would be pulled towards the anode and strike the copper with very high energy. Roentgen discovered that very penetrating radiations were produced from the anode, which he called x-rays.
X-ray production whenever electrons of high energy strike a heavy metal target, like tungsten or copper. When electrons hit this material, some of the electrons will approach the nucleus of the metal atoms where they are deflected because of there opposite charges (electrons are negative and the nucleus is positive, so the electrons are attracted to the nucleus). This deflection causes the energy of the electron to decrease, and this decrease in energy then results in forming an x-ray.
Medical x-ray machines in hospitals use the same principle as the Crooke’s Tube to produce x-rays. The most common x-ray machines use tungsten as there cathode, and have very precise electronics so the amount and energy of the x-ray produced is optimum for making images of bones and tissues in the body.


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Calvin Cycle

The Calvin cycle is a metabolic pathway found in the stroma of the chloroplast in which carbon enters in the form of CO2 and leaves in the form of sugar.



The Calvin Cycle

The cycle spends ATP as an energy source and consumes NADPH2 as reducing power for adding high energy electrons to make the sugar. There are three phases of the cycle. In phase 1 (Carbon Fixation), CO2 is incorporated into a five-carbon sugar named ribulose bisphosphate (RuBP). The enzyme which catalyzes this first step is RuBP carboxylase or rubisco. It is the most abundant protein in chloroplasts and probably the most abundant protein on Earth. The product of the reaction is a six-carbon intermediate which immediately splits in half to form two molecules of 3-phosphoglycerate. In phase 2 ( Reduction), ATP and NADPH2from the light reactions are used to convert 3-phosphoglycerate to glyceraldehyde 3-phosphate, the three-carbon carbohydrate precursor to glucose and other sugars. In phase 3 (Regeneration), more ATP is used to convert some of the of the pool of glyceraldehyde 3-phosphate back to RuBP, the acceptor for CO2, thereby completing the cycle. For every three molecules of CO2 that enter the cycle, the net output is one molecule of glyceraldehyde 3-phosphate (G3P). For each G3P synthesized, the cycle spends nine molecules of ATP and six molecules of NADPH2. The light reactions sustain the Calvin cycle by regenerating the ATP and NADPH2.

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Autonomic Nervous System

The autonomic nervous system (ANS or visceral nervous system or involuntary nervous system) is the part of the peripheral nervous system that acts as a control system, functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiratory rate,salivation, perspiration, pupillary dilation, micturition (urination), and sexual arousal. Most autonomous functions are involuntary but they can often work in conjunction with the somatic nervous system which gives voluntary control. Everyday examples includebreathing, swallowing, and sexual arousal, and in some cases functions such as heart rate.


Within the brain, the ANS is located in the medulla oblongata in the lower brainstem. The medulla's major ANS functions include respiration (the respiratory control center, or "rcc"), cardiac regulation (the cardiac control center, or "ccc"), vasomotor activity (the vasomotor center or "vmc"), and certain reflex actions (such as coughing, sneezing, vomiting and swallowing). These then subdivide into other areas and are also linked to ANS subsystems and nervous systems external to the brain. The hypothalamus, just above the brain stem, acts as an integrator for autonomic functions, receiving ANS regulatory input from the limbic system to do so.

The ANS is classically divided into two subsystems: the parasympathetic nervous system (PSNS) and sympathetic nervous system (SNS), which operate independently in some functions and interact co-operatively in others. In many cases, the two have "opposite" actions where one activates a physiological response and the other inhibits it. An older simplification of the sympathetic and parasympathetic nervous systems as "excitory" and "inhibitory" was overturned due to the many exceptions found. A more modern characterization is that the sympathetic nervous system is a "quick response mobilizing system" and the parasympathetic is a "more slowly activated dampening system", but even this has exceptions, such as in sexual arousal andorgasm, wherein both play a role. The enteric nervous system is also sometimes considered part of the autonomic nervous system, and sometimes considered an independent system[by whom?].


In general, ANS functions can be divided into sensory (afferent) and motor (efferent) subsystems. Within both, there are inhibitory and excitatory synapsesbetween neurons. Relatively recently, a third subsystem of neurons that have been named 'non-adrenergic and non-cholinergic' neurons (because they usenitric oxide as a neurotransmitter) have been described and found to be integral in autonomic function, in particular in the gut and the lungs.

Video Link: http://www.dailymotion.com/video/x1avpa0_autonomic-nervous-system_school

Joints in Human Skeleton

Types of Joints

A need for strength makes the bones rigid, but if the skeleton consisted of only one solid bone, movement would be impossible. Nature has solved this problem by dividing the skeleton into many bones and creating joints where the bones intersect. Joints, also known as articulations, are strong connections that join the bones, teeth, and cartilage of the body to one another. Each joint is specialized in its shape and structural components to control the range of motion between the parts that it connects

Joints may be classified functionally based upon how much movement they allow.

• A joint that permits no movement is known as a synarthrosis. The sutures of the skull and the gomphoses that connect the teeth to the skull are examples of synarthroses.
• An amphiarthrosis allows a slight amount of movement at the joint. Examples of amphiarthroses include the intervertebral disks of the spine and the pubic symphysis of the hips.
• The third functional class of joints is the freely movable diarthrosis joints. Diarthroses have the highest range of motion of any joint and include the elbow, knee, shoulder, and wrist.

Joints may also be classified structurally based upon what kind of material is present in the joint.

• Fibrous joints are made of tough collagen fibers and include the sutures of the skull and the syndesmosis joint that holds the ulna and radius of the forearm together.
• Cartilaginous joints are made of a band of cartilage that binds bones together. Some examples of cartilaginous joints include joints between the ribs and costal cartilage, and the intervertebral disks of the spine.
• The most common type of joint, the synovial joint, features a fluid-filled space between smooth cartilage pads at the end of articulating bones. Surrounding the joint is a capsule of tough dense irregular connective tissue lined with synovial membrane. The outer layer of capsule may extend into thick, strong bands called ligaments that reinforce the joint and prevent undesired movements and dislocations. Synovial membrane lining the capsule produces the oily synovial fluid that lubricates the joint and reduces friction and wear.

There are many different classes of synovial joints in the body, including gliding, hinge, saddle, and ball and socket joints.

• Gliding joints, such as the ones between the carpals of the wrist, are found where bones meet as flat surfaces and allow for the bones to glide past one another in any direction.
• Hinge joints, such as the elbow and knee, limit movement in only one direction so that the angle between bones can increase or decrease at the joint. The limited motion at hinge joints provides for more strength and reinforcement from the bones, muscles, and ligaments that make up the joint.
• Saddle joints, such as the one between the first metacarpal and trapezium bone, permit 360 degree motion by allowing the bones to pivot along two axes.
• The shoulder and hip joints form the only ball and socket joints in the body. These joints have the freest range of motion of any joint in the body – they are the only joints that can move in a full circle and rotate around their axis. However, the drawback to the ball and socket joint is that its free range of motion makes it more susceptible to dislocation than less mobile joints.
  
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