* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Structural Biochemistry/Cell Signaling Pathways/Nervous System
Microneurography wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Subventricular zone wikipedia , lookup
Signal transduction wikipedia , lookup
Synaptic gating wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Multielectrode array wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Biological neuron model wikipedia , lookup
Neurotransmitter wikipedia , lookup
Optogenetics wikipedia , lookup
Axon guidance wikipedia , lookup
Neural engineering wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Synaptogenesis wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Membrane potential wikipedia , lookup
Development of the nervous system wikipedia , lookup
Psychoneuroimmunology wikipedia , lookup
Chemical synapse wikipedia , lookup
Evoked potential wikipedia , lookup
Resting potential wikipedia , lookup
Node of Ranvier wikipedia , lookup
Action potential wikipedia , lookup
Electrophysiology wikipedia , lookup
Nervous system network models wikipedia , lookup
Circumventricular organs wikipedia , lookup
Single-unit recording wikipedia , lookup
End-plate potential wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Neuroregeneration wikipedia , lookup
Structural Biochemistry/Cell Signaling Pathways/Nervous System 1 Structural Biochemistry/Cell Signaling Pathways/Nervous System The nervous system is a network of specialized cells that coordinate the actions of an animal and send signals from one part of its body to another. These cells send signals either as electrochemical waves traveling along thin fibers called axons, or as chemicals released onto other cells. The nervous system is composed of neurons and other specialized cells called glial cells (plural form glia). In most animals the nervous system consists of two parts, central and peripheral. The central nervous system contains the brain and spinal cord. The neurons of the central nervous system are interconnected in complex arrangements and transmit electrochemical signals from one to another. The peripheral nervous system consists of sensory neurons, clusters of neurons called ganglia, and nerves connecting them to each other and to the central nervous system. Sensory neurons are activated by inputs impinging on them from outside or inside the body, and send signals that inform the central nervous system of ongoing events. Motor neurons, situated either in the central nervous system or in peripheral ganglia, connect neurons to muscles or other effector organs. The interaction of the different neurons form neural circuits that regulate an organism's perception of the world and its body and behavior. The human nervous system. Nervous systems are found in most multicellular animals, but vary greatly in complexity. Sponges have no nervous system, although they have homologs of many genes that play crucial roles in nervous system function, and are capable of several whole-body responses, including a primitive form of locomotion. Radiata, including jellyfish, have a nervous system consisting of a simple nerve net. Bilaterian animals, which include the great majority of vertebrates and invertebrates, all have a nervous system containing a brain, spinal cord, and peripheral nerves. A human nerve cell is composed of various components: the soma, or cell body (which has a nucleus), the axon (by which nerve signals travel), the myelin sheath, which provides conductivity and allows electrical signals to travel through nerve cells, dendrites, which receive signals from other nerve cells, and axon terminals, which nerve cells use to communicate with each other via the release and binding of neurotransmitters. A nerve cell. Neurons communicate with each other using neurotransmitters, which travel across synapses (the space between axon terminals of one nerve cell and the dendrites of another nerve cell) and bind to their appropriate receptors. However, inter cellular communication between Structural Biochemistry/Cell Signaling Pathways/Nervous System nerve cells depends on action potentials, which are voltage differences across membranes. Action potentials are initiated by the movement of charged ions, such as potassium and sodium, across the cell membrane through voltage dependent ion gates. These gates are opened by binding of neurotransmitters to post-synaptic cells. Thus, when a neurotransmitter binds and causes the voltage dependent ion gates to open, ions flow across the membrane, causing a voltage difference which results in an action potential. These action potentials travel along the axon, and axon terminals and The propagation of an action potential. dendrites allow these potentials to move through various nerve cells. Action potentials function on the all or nothing principle. In other words, if a particular stimuli or neurotransmitter concentration does not reach required levels, no action potential will occur. Thus, if a mosquito lands on your hand, you may not feel it because the pressure changed caused by the mosquito landing on you is not significant enough to generate an action potential. However, the pressure of, for example, a handshake, does, and therefore generates an action potential, causing you to feel the other hand. Under the all or nothing principle, action potentials either occur or they do not- an amplitude difference is irrelevant so long as the threshold for an action potential is reached. Instead, the varying feeling you get depends on the rate, or frequency, of action potentials. In other words, if someone threw a pencil at you, it would hurt less than if someone hit you with a car not because the amplitude of the action potential is higher when you are hit by a car, but because nerves are transmitting action potentials much faster. The myelin sheath surrounding axons is critical to the propagation of action potentials. It essentially serves to maintain conductivity; without it, action potentials would travel much more slowly (so, for example, you would not be able to feel something hit you until after several seconds). This also improves efficiency and decreases the amount of energy required for nerve signaling. Multiple sclerosis is an example of disease caused by the degradation of the myelin sheath in nerve cells. The degradation of this sheath prevents nerve cells from communicating with each other by reducing the effect and velocity of action potentials. Because many important functions depend on a healthy nervous system, such as speech, movement, coordination, sensation, and vision, the degradation of the myelin sheaths can have a debilitating effect. Action Potentials Action potentials are a means of communicating between neurons. An action potential is started when the membrane is depolarized to a certain threshold. Action potentials are all or none, so depolarizations that do not meet the threshold do not do anything for the neuron. The threshold is a point when the charge is -55 mV. The resting potential of a neuron, which is the charge at equilibrium, is around -70 mV. The threshold is 15 mV above the resting potential, and only when the cell depolarizes to this point will the action potential initiate. The action potential starts when voltage gated sodium channels are activated. These channels allow an influx of sodium. Potassium channels also open up, which causes an efflux of potassium ions. The efflux of potassium ions causes the membrane to hyperpolarize (makes more negative) the cell. If the current of potassium exceeds the current of sodium, then the voltage of the cell returns to -70 mV, which is the resting potential. If the voltage increases past the threshold level, then the sodium current is larger than the potassium current. This induces a positive feedback, where more sodium channels are opened (slowly) from this effect, and even more sodium ions enter the cell. This sharp increase in the flow of sodium ions causes the cell to depolarize rapidly, which results in the cell “firing”, which produces an action potential. The rapid depolarization is ended when the sodium channels open all the way. This causes the membrane voltage to reach a maximum. The voltage shuts the sodium channels off, and the channels are inactivated. At the same time, the voltage opens voltage gated potassium channels. The result of these two actions is the repolarization of the membrane. As potassium ions leak out and sodium channels can no longer diffuse across the membrane, the cell is brought the its equilibrium potential. 2 Structural Biochemistry/Cell Signaling Pathways/Nervous System 3 Various phase of the action potential An action potential consists of various phases. Starting from the resting potential, the cell slowly depolarizes due to the opening of sodium and potassium channels. However, when the voltage reaches the threshold, there is a rapid influx of sodium due to the opening of more sodium channels. This is the rising phase. At the peak, the falling phase follows immediately, which represents the closing of the sodium channels and the opening of the potassium channels. The refractory period is a result of the closing of the sodium channels, which cannot be opened again until the refractory period is over. CENTRAL NERVOUS SYSTEM The central nervous system consists of the brain and the spinal cord. The spinal cord is a long nervous tissue that extends along the vertebral column from the head to the lower back. It is composed of many distinct structures working together to coordinate the body. The most important is the brain, which has several components: The cerebrum is the largest portion of the brain and it controls consciousness. It is in control of voluntary movement, sensory perception, speech, memory, and creative thought. The cerebellum helps to fine-tune voluntary movement, but is not directly involved in it. It makes sure that movements are coordinated and balanced. action potential. The brainstem is a part of the medulla oblongata and is responsible for the control and regulation of involuntary functions. These functions include breathing , cardiovascular regulation, and swallowing. The medulla oblongata is needed to sustain life and processes a great deal of information. The hypothalamus is responsible for homeostasis maintenance, which includes regulation of temperature, hunger, thirst, water balance, and generation of emotion. The spinal cord is divided into 4 distinct regions. These distinct regions in the spinal cord organize neurons segmentally. Within a single segment, neurons are grouped and located according to their function throughout the rest of the body. These four segments are the cervical region (8 segments), thoracic region (12 segments), lumbar region (5 segments), and the sacral region (5 segments). Axons usually enter the nerves near each segment in this innervated structure (e.g. fibers that innervate the arm run in the cervical spinal nerves while fibers that innervate the leg run in the lumbosacral spinal nerves). Sensory and motor neurons lie in separate portions of the spinal cord. In general, cells in the dorsal spinal cord and axons in the dorsal spinal nerves serve an afferent function (sensory fibers), while the cells in the ventral spinal cord and axons in the ventral spinal nerves serve as motor in function (efferent fibers). In specific, however, position of ascending pathways carrying fine touch, pressure, and information about the position of muscles and joints are found in the dorsal and lateral columns of each spinal segment. The position of fibers carrying pain information and pressure information are found in the anterolateral pathway. For motor information (efferent information), positions of descneding fibers are found in the dorsolateral and ventromedial columns. The Spinal cord Segments of a human body. Structural Biochemistry/Cell Signaling Pathways/Nervous System THE PERIPHERAL NERVOUS SYSTEM This system consists of a sensory system that carries information from the senses to the central nervous and then back to the body. It also consists of a motor system that branches out from the central nervous system, so it targets certain muscles or organs. The motor system can be divided into the somatic system and the autonomic system. The somatic nervous system is responsible for voluntary movement. Cross-cut diagram of a spinal segment. Thus, the neurons will only target skeletal muscles because these are the only ones responsible for voluntary movement. All of the neurons in the somatic system release acetylcholine, which is an excitatory neurotransmitter that causes skeletal muscles to contract. None of the neurons in this system will cause inhibitory effects. On the other hand, the autonomic system controls tissues other than skeletal muscles, such as cardiac muscle, glands, and organs. This system controls processes that are involuntary, such as heartbeat, movements in the digestive tract, and contraction of the bladder. Autonomic neurons are able to either excite or inhibit target muscles or organs. This nervous system is subdivided into sympathetic division and parasympathetic division. These 2 systems work antagonistically and usually have opposite effects. The Autonomic Nervous System The autonomic nervous system is a part of the peripheral nervous system that controls visceral functions. The autonomic nervous system affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, urination, and sexual arousal. Although most of this system's actions are voluntary, some actions, such as breathing, are involuntary. The autonomic nervous system is divided into the sympathetic nervous system and the parasympathetic nervous system. These two subsystems work together to produce homeostasis. Both subsystems are made up of a two-neuron chain between the central nervous system and the peripheral nervous system. In the sympathetic and parasympathetic nervous systems, pre-ganglionic neurons are in the central nervous system, but they synapse to post-ganglionic neurons in the peripheral nervous system. These post-ganglionic neurons will then synapse to the target cells. In the sympathetic nervous system, the preganglionic transmitter is acetylcholine, and they bind to nicotinic cholinergic receptors on post-ganglionic cells. Post-ganglionic cells transmit nor-epinephrine, which bind to adrenergic receptors on target cells. The parasympathetic nervous system releases acetylcholine as well as the pre-ganglionic transmitter, and bind to nicotinic cholinergic receptors on post-ganglionic cells. The transmitter from these cells is acetylcholine, and they bind to muscarinic cholinergic receptors on target cells. Increased activity in the sympathetic nervous system includes increase of heart rate, increase in blood pressure of smooth muscles, and decrease of gut motility. Parasympathetic activity decrease heart rate and increases gut motility. Sympathetic Nervous System The sympathetic nervous system controls the body's resources under stress, otherwise known as the fight-or-flight response. However, the sympathetic nervous system is constantly active in order to maintain homeostasis. 4 Structural Biochemistry/Cell Signaling Pathways/Nervous System 5 Examples of sympathetic system action. Organ Effect Eye Dilates pupil Heart Increases rate and force of contraction Lungs Dilates bronchioles Digestive tract Inhibits peristalsis Kidney Increases renin production Penis Promotes ejaculation Parasympathetic Nervous System The parasympathetic nervous system controls activities that occur when the body is at rest such as salivation, lacrimation, urination, digestion, and defecation. It's actions are often described as "rest and digest." It works in conjunction with the sympathetic nervous system to maintain homeostasis in the body. Examples of parasympathetic system action. Organ Effect Eye Constricts pupil Heart Decreases rate and force of contraction Liver Glycogen synthesis Digestive system Increases activity Kidney Increases urine production Tear Glands Secretion What is Mental Inertia and what causes this symptom. It is the involuntary or the unwillingness to perform something. In the other hands, we can say it is slacking in people’s mind to think of something or come up with a plan. People usually call that in a normal way is laziness that is hidden somewhere inside each of us. And based on each person’s function, it will display different level of the laziness. Therefore, the immunity is also different. So when we can break this slacking and laziness, we can create the impulse. There are many types that that cause by mental inertia: - By incorrectly established result - By adherence to a faulty technique - By the incorrect understanding of mechanism of action - By improper controls Now we know what causes this symptom so we can find a way to overcome it. Here is just an example of how to overcome it. There are several ways to handle it. By mentally, try to see the result of our action and capture it. Then we will start moving to physically and let our brains follow the suit. We just try to start very slow to see the actual result from the small step. The most important thing is just believe in ourselves that we can do everything. It is very easy to break and control once we know how to overcome it. Nervous system disorders Depression is a disorder characterized by depression mood, for example, appetite, sleep and energy level. There are two forms of depressive illness: major depressive disorder and bipolar disorder. Major depressive disorder maybe last many months with no pleasure and no interest. Bipolar disorder involves swings of mood form high to low and affects very rarely to people. Schizophrenia is a very rare yet severe mental disturbance characterized by psychotic episodes in which patients have a distorted perception of reality. People with this illness usually suffer from hallucination and delusions. Structural Biochemistry/Cell Signaling Pathways/Nervous System Alzheimer’s disease is a mental deterioration, or dementia characterized by confusion and many other symptoms. This disease is progressive, with patients gradually becoming less able to function. This could lead to the death of neurons in many areas of the brain. Parkinson’s disease is characterized by difficulty in initiating movement and slowness of movement. Its symptoms result from the death of neurons in the midbrain. At present, there is no cure for Parkinson’s disease. 6 Article Sources and Contributors Article Sources and Contributors Structural Biochemistry/Cell Signaling Pathways/Nervous System Source: http://en.wikibooks.org/w/index.php?oldid=1986043 Contributors: Adrignola, Crlu, Dhalim, F4yang, Ghou, Jol034, Leifu, Mlesaca, Nvuong, Rehwang, Rmhsu, T5zhou Image Sources, Licenses and Contributors Image:Nervous system diagram.png Source: http://en.wikibooks.org/w/index.php?title=File:Nervous_system_diagram.png License: Public Domain Contributors: ¤~Persian Poet Gal (talk) Image:Nerve.nida.jpg Source: http://en.wikibooks.org/w/index.php?title=File:Nerve.nida.jpg License: Public Domain Contributors: ArnoldReinhold, Juliancolton, Krinkle, TommyBee, 2 anonymous edits File:Action potential propagation animation.gif Source: http://en.wikibooks.org/w/index.php?title=File:Action_potential_propagation_animation.gif License: GNU Free Documentation License Contributors: John Schmidt File:Action_potential.JPG Source: http://en.wikibooks.org/w/index.php?title=File:Action_potential.JPG License: Public Domain Contributors: Jol034 Image:SpinalCord.jpg Source: http://en.wikibooks.org/w/index.php?title=File:SpinalCord.jpg License: unknown Contributors: EugeneZelenko, Rmhsu Image:SpinalSegment.jpg Source: http://en.wikibooks.org/w/index.php?title=File:SpinalSegment.jpg License: unknown Contributors: Silverthorn License Creative Commons Attribution-Share Alike 3.0 Unported http:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/ 7