The human ability to feel, reproduce, and even see the very text on this
page is controled, in computer like calculations, by the magical nervous
system. Yes, the nervous system is quite like magic because you can't see
it, but its working through electric impulses through your body. Although
it seems magical , you can comprehend it all by keeping your eyes glued
to this very web page.
One of the worlds most "intricately organized" electron mechanisms is the nervous system. Not even engineers have come close to making circuit boards and computers as delicate and precise as the nervous system. To understand this system, one has to know the tree simple functions that it puts into action: sensory input, integration, motor output.
Sensory inputWhen your eyes see something or your hands or touch a warm surface, the sensory cells, also known as Neorons, send a message straight to your brain. This action of getting information from your surrounding environment is called sensory input because your putting things in your brain by way of your senses.
IntegrationIntegration is best known as the interpretation of things you have felt, tasted, and touched with your sensory cells, also known as neurons, into responses that the body recognizes. This process is all accomplished in the brain where many, many neurons work together to understand the environment.
Motor OutputOnce your brain has interpreted all that you have learned, either by touching, tasting, or using any other sense, then your brain sends a message through neurons to effecter cells, muscle or gland cells, which actually work to perform your requests and act upon your environment. The word motor output is easily remembered if one should think that your putting something out into the environment through the use of a motor, like a muscle which does the work for our body.
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The two kinds of cells in the nervous system are: neurons and support cells.
NeuronsWe all have the common idea that neurons make up the majority of the nervous cells. However, this idea is wrong since support cells which reinforce or help the neurons are more in number. Nevertheless, neuron cells are the primal cells of the system because they transmit messages. Neuron cells differ in size and shape depending on where they are found in the body, but the structure of neurons stays constant. The three basic structures of the neuron are: the dendrite, cell body, and axon.
DendriteDendrites are short, thick branched extensions which extend like the roots of a tree over other neurons or body cells. The dendrites all branch off dendritic spines, which in turn branch of the cell body. Dendrites are the receptive sites of the neurons. Here, the neurons receive electric messages from other neurons or body cells. The site where one dendrite meets another neuron's impulse is called the synapse. Usually, neurons have hundreds of dendrite extensions. These extensions are spread over a large area, giving the neuron better reception of signals. Some dendrites are specialized for the accumulation of information. These cells are finer than other dendrites and found near the brain.
Cell BodyAlso called the perikaryon or soma, the cell body contains a spherical nucleus with a nucleolus and lots of cytoplasm. Like many cells, the neuron cell body of the neuron contains the usual cellular particles or organells, except centrioles. Centrioles are the basis by which cells are able to divide and form new cells. Because the neurons lack centrioles , they are unable to divide and reproduce themselves. Therefore, if one should damage nerves, then they are not able to be replaced. Nevertheless, neurons do have specialized hardworking endoplasmic reticulum (ER), which help transport proteins and molecules at high speeds due to the fact that neurons work at lightning speeds. Also, the neurofibrils, bundles of micro filaments and micro tubules, which are important in intracellular transport, are seen through the body. A pigment called lipofuscin, which is yellow-brown, is one of the many pigments believed to be in the neuron.
This one particular pigment is believed to be the cause of aging because it is found mostly neurons of elderly individuals.
AxonThe axon is a long cylindrical tube, with the same consistent diameter, which runs through the body for long or short lengths. For example, the axon of your neuron controlling your toe, extends all the way from the lumbar back area. The axon branches off a cone shaped region of the cell body called the axon hillock Axons diameters differ in many parts of the body, but the ruel is the thicker the axon, the more message it transmits through the neurons. The main purpose of the axon is to send impulses away from the cell body to neuron dendrite or other body cells called effecter cells. A nerve impulse travels from a dendrite, to the cell body, and down the axon to thousands of branches called telondria which connect at a synapse to dendrites from other neurons. Once the impulse reaches the synapse, neurotransmitters, chemicals, which excite or calm effecter or neurons, diffuse into the extra cellular space and reach the dendrite, once again turning into an impulse. Protecting and insulating electric fibers from one another is the myelin sheath. It is a whitish, fatty, segmented sheath which covers the majority of nerve fibers and helps transmit nerve impulses faster. Throught the axon of the neuron, cells which protect the neuron envelope . These cells forms slope like structures with indents in between them called a Node of Ranvier. The myelin sheath is exceedingly important because one can lose control of your muscles due to the uncoordinated fibers of an axon without myelin sheath.Back to the top.
Neurons communicate or send impulses through an action potential., This takes place from the dendrite and all the way to the axon ends. An action potential is a change of voltage within the axon. In other words, the negative state off the inner axon turns positive when the impulses comes by. This happens by the use of a sodium and potassium pump. Sodium [Na] surrounds the axon with a positive charge, while the potassium [K] is within the axon. As an impulse enters at the axon hillock, the sodium, potassium pump puts positive sodium into the axon while it puts negative potassium out of the axon. As more sodium enters the potential of the impulse changes from -70 mV to +30 mV, (a difference of 100 mV) This change is called an action potential. The sodium, potassium pump works furiously to pass the impulse through the axon. As the impulse leaves the axon, it is reverted to a normal state which is called the resting potential. At the end of the axon, the impulse or stimulus enters the synapses and is called a post synaptic potential. From here, the impulse is transferred into neurotransmitters, some of which are chemicals called epinephrine and dopamine. These neurotransmitters flow into the fluid filled gap called the synaptic cleft and enter the dendrites. And, again, the process is repeated.
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Nine times more numerous than neurons, supporting cells assist, segregate and insulate neurons. Each supporting cell has its specific function and location. The majority of the central nervous system (CNS) support cells are referred to as glial cells which wrap around the nerves of the space to protect them. Other specific support cells are also very recognizable. Astrocyles are specific supporting cells which anchor neurons to capillaries for energy and regulate the ions around the nerve. Microgelia are a specific macrophage-hyp immune which help protect the central nervous system by engulfing invading microorganisms and dead nerve tissue. Ependymal cells form cerebral spinal fluid and help circulate the fluid by the beating of their cilia. Scwhuan cells are massive cells which cover the mylein sheath and protect neurons by acting as a phagocyte-hyp immune to clean damaged nerves. Satellite cells help control the chemical environment around nerve cells.
Nervous systemThe human nervous system is diagramed into two separately different system: peripheral nervous system (PS) and central nervous system (CNS).
Central Nervous SystemThe central nervous system is the central of the nervous. The two and only organs included in this system are of utmost importance: the spinal cord and the brain.
Spinal cordWithin the spinal cord one finds the association neuron. This neuron composes the majority of the spinal cord, and serves as an integration center or interpretation center, of sensory neurons and motor neurons. A sensory neuron informs the body of its environment, the association neuron interprets the information, and responds to the environment with the motor neuron.
BrainThe brain is divided into three segments: the forebrain, midbrain, and hind brain. The chart and diagram below will help you understand the brain.
Peripheral Nervous SystemThe peripheral nervous system is divided into two main groups of neurons: sensory and motor.
SensorySensory neurons or afferent neurons provide information from the environment to the body. For example, when you touch a hot surface, a sensory neuron informs your body that the temperature near your skin is rising.
MotorMotor neurons or efferent neurons are the neurons the body uses to react to the environment. For example, if you touch a hot surface, then your body will make your hand move away from that surface by a motor neuron. Motor neurons also send impulses to your m=muscles. These neurons are called somatic neurons. Another motor neuron is the auitomomic neuron. This neuron control your organs and heart. Usually the Vegas nerve controls and divides this power in two ways: sympathetic and parasympathetic.
Sympatheticdilate eye pupils
stops secretion of glands
makes medulla secrete eponephrine
produces goose bumps
and stimulate hair
causes high blood pressure
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Parasympatheticconstricts eye pupils
starts secretion of saliva
causes erection of sex organs
decreases heart rate
NoseThe olfactory or smell action is quite simple. Once the smell of food has reached your nose, which is lined with hairs, it travels to an olfactory bulb, a set of sensory nerves. The nerve impulses travel through the olfactory tract, around, in a circular way, the thalamus, and finally to the smell sensory cortex of your brain, located between your eye and ear, where it is interpreted to be understood and memorized by the body.
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EyeSeeing is one of the most pleasing senses of the nervous system. This cherished action primarily conducted by the lens, which magnifies a seen image, vitreous disc, which bends and rotates an image against he retina, which translates the image and light by a set of cells. The retina is at the back of the eye ball where rods and cones structures along with other cells and tissues covert the image into nerve impulses which are transmitted along the optic nerve to the brain where it is kept for memory.
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TongueA set of microscopic buds on the tongue divide everything you eat and drink into four kinds of taste: bitter, sour, salty, and sweet. These buds have taste pores, which convert the taste into a nerve impulse and sends the impulse to the brain by a sensory nerve fiber. Upon receiving the message, your brain classifies the different kinds of taste. This is how you can refer the taste of one kind of food to another.
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EarMost people only relate the ear drum or tympanic membrane as the only structure in the ear. However, this is not true. The cartilage over the cell ear is called the auricle. This area serves as a protective member to guard the inner ear where the famous ear drum is located. The typmanic membrane is divided into two layers. One that goes to the pharynx and the other is a mucus membrane. By putting pressure of both membranes is the only way the ear drum receives sound. Once the sound or sound wave has entered the drum, it goes to a large structure called the cochlea. In this snail like structure, the sound waves are divided into pitches. The brvration of the pitches in the cochlea are measured by the Corti. This organ transmits the vibrational information to a nerve, which sends it to the brain for interpretation and memory.
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