Cyclic AMP or CAMP is a molecule which is a second messenger, comprises the adenine ribonucleotide with a group of phosphate connected to oxygen molecules with positions of 3' to 5' of a sugar moiety. Its chemical formula is <span>C</span>₁₀<span>H</span>₁₂<span>N</span>₅<span>O</span>₆<span>P.</span>
The nervous system is composed of billions of specialized cells called neurons. Efficient communication between these cells is crucial to the normal functioning of the central and peripheral nervous systems. In this section we will investigate the way in which the unique morphology and biochemistry of neurons makes such communication possible.
The cell body, or soma, of a neuron is like that of any other cell, containing mitochondria, ribosomes, a nucleus, and other essential organelles. Extending from the cell membrane, however, is a system of dendritic branches which serve as receptor sites for information sent from other neurons. If the dendrites receive a strong enough signal from a neighboring nerve cell, or from several neighboring nerve cells, the resting electrical potential of the receptor cell's membrane becomes depolarized. Regenerating itself, this electrical signal travels down the cell's axon, a specialized extension from the cell body which ranges from a few hundred micrometers in some nerve cells, to over a meter in length in others. This wave of depolarization along the axon is called an action potential. Most axons are covered by myelin, a fatty substance that serves as an insulator and thus greatly enhances the speed of an action potential. In between each sheath of myelin is an exposed portion of the axon called a node of Ranvier. It is in these uninsulated areas that the actual flow of ions along the axon takes place.
The end of the axon branches off into several terminals. Each axon terminal is highly specialized to pass along action potentials to adjacent neurons, or target tissue, in the neural pathway. Some cells communicate this information via electrical synapses. In such cases, the action potential simply travels from one cell to the next through specialized channels, called gap junctions, which connect the two cells.
Most cells, however, communicate via chemical synapses. Such cells are separated by a space called a synaptic cleft and thus cannot transmit action potentials directly. Instead, chemicals called neurotransmitters are used to communicate the signal from one cell to the next. Some neurotransmitters are excitatory and depolarize the next cell, increasing the probability that an action potential will be fired. Others are inhibitory, causing the membrane of the next cell to hyperpolarize, thus decreasing the probability of that the next neuron will fire an action potential.
The process by which this information is communicated is called synaptic transmission and can be broken down into four steps. First, the neurotransmitter must be synthesized and stored in vesicles so that when an action potential arrives at the nerve ending, the cell is ready to pass it along to the next neuron. Next, when an action potential does arrive at the terminal, the neurotransmitter must be quickly and efficiently released from the terminal and into the synaptic cleft. The neurotransmitter must then be recognized by selective receptors on the postsynaptic cell so that it can pass along the signal and initiate another action potential. Or, in some cases, the receptors act to block the signals of other neurons also connecting to that postsynaptic neuron. After its recognition by the receptor, the neurotransmitter must be inactivated so that it does not continually occupy the receptor sites of the postsynaptic cell. Inactivation of the neurotransmitter avoids constant stimulation of the postsynaptic cell, while at the same time freeing up the receptor sites so that they can receive additional neurotransmitter molecules, should another action potential arrive.
Most neurotransmitters are specific for the kind of information that they are used to convey. As a result, a certain neurotransmitter may be more highly concentrated in one area of the brain than it is in another. In addition, the same neurotransmitter may elicit a variety of different responses based on the type of tissue being targeted and which other neurotransmitters, if any, are co-released. The integral role of neurotransmitters on the normal functioning of the brain makes it clear to see how an imbalance in any one of these chemicals could very possibly have serious clinical implications for an individual. Whether due to genetics, drug use, the aging process, or other various causes, biological disfunction at any of the four steps of synaptic transmission often leads to such imbalances and is the ultimately source of conditions such as schizophrenia, Parkinson's disease, and Alzheimer's disease. The causes and characteristics of these conditions and others will be studied more closely are as we focus specifically on the four steps of synaptic transmission, and trace the actions of several important neurotransmitters.
C
A is biased
B, some people may view the assignments as easy and it doesn’t show that it was more that last year
D doesn’t strongly support it
Light waves are transmitted across the cornea and enter the eyes through the pupil.
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FURTHER EXPLANATION</h3>
The eyes and the brain are important in helping people see. Light passes through the eyes and this light gets transformed into electrical signals which are sent to the brain that helps make sense of the object that is seen.
<h3 /><h3>How People See</h3>
- Light is incident on an object (or strikes an object). Some of it get absorbed, some are reflected into a human's eye.
- Light that bounces off the object is transmitted across the cornea, the transparent outer layer of the eye. It refracts the light and makes things look sharp and clear.
- Then the light enters the pupil which is the opening in the eye controlled by the iris or the colored part of the eye. The iris changes the size of the pupil and controls the amount of light that enters the eye. When there is bright light, the pupil becomes smaller. In dim light, the opposite happens and the pupil becomes bigger.
- At the back of the pupil is the lens which again helps focus the light. Its shape changes depending on the distances of the objects that is being looked at.
- The light rays are focused by the lens so that they all converge in the retina which is at the back of the eye. The retina has many specialized cells which are sensitive to light. These cells transform light energy into electrical signals or nerve impulses which form a rough inverted image of the object the person is looking at.
- The electrical signals travel to the brain through the optic nerve. The brain turns the image upright and adds more detail to the vision.
<h3 /><h3>LEARN MORE</h3>
Keywords: eye, vision, cornea, pupil
