Action Potential is the change across the membrane of the neuron when a nerve is transmitting an impulse.
NARAINO MAJIE Nabiilah3rd April 2013
Introduction• Definition• Structure of Neuron• Transmission of chemical information• Release• Receptors• Inactivation Types of neurotransmitters• Inhibitory• Excitatory Conclusion References
NEUROTRANSMITTERS are the brain chemicalsthat communicate information throughout ourbrain and body. They relay signals between nerve cells, called“neurons.” The brain uses neurotransmitters to tell• your heart to beat,• your lungs to breathe, and• your stomach to digest.• They can also affect mood, sleep, concentration, weight,and• can cause adverse symptoms when they are out ofbalance.
This is a NEURONDendrites are branchingfibers that receiveinformation from otherneuronsSoma is the cell bodyof a neuron. Itcontains anucleus, ribosomes, mitochondria, and otherstructures. This iswhere much of themetabolic work takesplaceAxon is a thinfiber whereinformation issent from theneuron to otherneuronsSomaPresynapticterminalsPresynapticterminals are thepoint where theaxon releaseschemicalsDendritesAxon
Neurotransmitter comes from somaIt travels through the axonFrom the pre-synaptic terminal it istaken through the synapse to thenext neuronRe-uptake sometimes occursTransmission of Neurotransmitters
Pre-synapticNeuronPost-synaptic NeuronNeurotransmittersare sent throughthe axon to pre-synapticterminals, and thento another neuronTransmission of Neurotransmitters
Chemical transducersreleasedBy electrical impulseInto the synaptic cleftFrom pre-synapticmembraneBy synaptic vesicles.Diffuse to the post-synaptic membraneReact and activate thereceptors presentLeading to initiation ofnew electrical signals.
Across a small gap called the synapse. An electrical impulse will trigger the migration ofvesicles containing neurotransmitters toward thepresynaptic membrane. The vesicle membrane fuse with the presynapticmembrane releasing the neurotransmitters into thesynaptic cleft. Chemicals, called neurotransmitters, are releasedfrom one neuron at the presynaptic nerve terminal.
Neurotransmitters then cross the synapse wherethey may be accepted by the next neuron at aspecialized site called a receptor. Either depolarization (an excitatory postsynapticpotential) or hyper polarization (an inhibitorypostsynaptic potential). A depolarization makes it MORE likely that anaction potential will fire; a hyper polarizationmakes it LESS likely that an action potential willfire.
It occurs in 4 steps:◦ Synthesis of transmitter◦ Storage & release of transmitter◦ Interaction of transmitter with receptor in postsynapticmembrane◦ Removal of transmitter from synaptic cleft
There are 2 types of receptors:◦ Ion-Channel linked receptor◦ G- Protein linked receptor
Inactivation of the transmitter happens in oneof three ways: Re-absorption of the neurotransmitter into theneuron. This is known as reuptake and is thenormal process. Destruction of the neurotransmitter with specialchemicals called enzymes. This is known asenzymatic degradation. By the neurotransmitter becoming detached fromthe receptor and drifting out of the synaptic cleft.This is known as diffusion.
Two types:◦ Inhibitory-inhibit nerve impulses and calm the brainand help create balance.◦ Excitatory-propagate nerve impulses and stimulatethe brain. Inhibitory neurotransmitters balance moodand are easily depleted when the excitatoryneurotransmitters are overactive.
Action of Inhibitory Neurotransmitters Action potential goes down synaptic knobs ofanother neuron Release of Inhibitory neurotransmitters Activation of receptor site on cell membrane Opening of potassium channels Flow of k⁺ out of cell Cell inside becomes –ve Leads to local hyper polarization Known as Inhibitory Post Synaptic Potential (IPSP)
SEROTONIN is an inhibitory neurotransmitter –which means that it does not stimulate the brain. Serotonin are necessary for a stable mood and tobalance any excessive excitatory (stimulating)neurotransmitter firing in the brain. Stimulant medications or caffeine can cause adepletion of serotonin over time. Serotonin also regulates many other processessuch as carbohydrate cravings, sleep cycle, paincontrol and appropriate digestion. Low serotonin levels are also associated withdecreased immune system function.
GABA (Gamma-Amino Butyric Acid) When brain experiences an abundance of nervoustension and stress, it can be caused by a surplus ofnorepinephrine or epinephrine (adrenaline). To neutralize this extra adrenaline, the brainproduces neurotransmitters, one of which is GABA. When GABA is out of range (high or low excretionvalues), it is likely that an excitatoryneurotransmitter is firing too often in the brain. GABA will be sent out to attempt to balance thisstimulating over-firing.
DOPAMINE is a special neurotransmitter because it isconsidered to be both excitatory and inhibitory. Plays a critical role in the control of movement. It has a stimulating effect on the heart, the circulation, therate of metabolism, and is able to mobilize many of thebody’s energy reserves. It helps to modulate brain activity, control coordination andmovement, and regulate the flow of information to differentareas of the brain. Dopamine is believed to release chemicals that allow us tofeel pleasure (e.g. endorphins). A massive disturbance of dopamine regulation in the braincan result in a person no longer being able to respondemotionally or express his or her feelings in an appropriateway (e.g. schizophrenia).
Action of Excitatory Neurotransmitters Action potential goes down synaptic knobs ofanother neuron Release of Excitatory neurotransmitters Activation of receptor site on cell membrane Opening of ligand-gated sodium ion channels. Flow of Na⁺ in the cell Cell becomes less –ve Leads to to a local depolarization Known as Excitatory Postsynaptic Potential (EPSP).
Norepinephrine also known as noradrenalineis a excitatory neurotransmitter that isproduced by the adrenal medulla or madefrom dopamine. High levels of norepinephrine are linked toanxiety, stress, high blood pressure, andhyperactivity. Low levels are linked to lack ofenergy, focus, and motivation.
Histamine is most commonly known for itsrole in allergic reactions but it is also involvedin neurotransmission and can affect youremotions and behavior as well. Histamine helps control the sleep-wake cycleand promotes the release of epinephrine andnorepinephrine. High histamine levels have been linked toobsessive compulsivetendencies, depression, and headaches. Low histamine levels can contribute to fatigueand medication sensitivities.
Acetylcholine same as Dopamine can be both Inhibitoryand Excitatory. Acetylcholine (often abbreviated ACh) is the mostcommon neurotransmitter. It is located in both thecentral nervous system (CNS) and the peripheralnervous system (PNS). In the central nervous system, acetylcholine acts as partof a neurotransmitter system and plays a role inattention and arousal. In the peripheral nervous system, this neurotransmitteris a major part of the autonomic nervous system andworks to activate muscles. Acetylcholine is also involved in memory and learningand is in particularly short supply in people withAlzheimers disease.
All chemical messengers in the brain have immenseinterconnectivity. Their function relies on a system of checks andbalances during each moment of life. If one part ofthe system fails, others can’t do their job properly. Panic disorder is just one of many physical andpsychological illnesses that are believed to beinfluenced by the complex interacting ofneurotransmitters. Neurotransmitter levels can now be determined bya simple and convenient urine test collected athome. Knowing your neurotransmitter levels canhelp you correct a problem today or preventproblems from occuring in the future.