Nerve Signals The nervous system is responsible for communication and coordination of all organ systems within a body. To achieve this, the neurons – cells that make up the nervous system – must be able to pass signals from one to another. To understand how a neuron transmits a signal, it is important be reminded of the structure of the neuron. The dendrites receive chemical or electrical signals from the axon terminals of other neurons. The cell body contains the nucleus, lysosomes and ribosomes. Most neurons have a single axon which sends signals to other neurons. These signals are carried down the axon into the axon terminals which are small branches of the axon. The axon terminals form synapses, or connections, with other cells. The space between two nerve cells is called the synaptic cleft. When a neuron is not transmitting a signal, it is at rest. During this rest period, the cytoplasm just inside of the neuron contains two important molecules: positively charge potassium ions (K+) and negatively charged protein molecules. (A positively charged ion occurs when an atom loses one or more electrons. Negatively charged molecules form when the molecule gains extra electrons.) The cytosol contains more negatively charged protein molecules than potassium ions, so the inside of the neuron is negative in charge. The fluid just outside of the neuron is positively charged. This positive charge is due to the presence of positively charged ions, like sodium (Na+). The cell membrane stores energy by holding these opposite charges apart. This difference in charge is referred to as an electrical potential. When the neuron is at rest, this difference in charge is referred to as the resting potential. Sending a signal through a neuron – Action Potential A stimulus (light, sound, touch or the presence of a chemical) can generate an electrical nerve signal by reversing the charges inside and outside of the neuron’s membrane. c Action potential occurs when specialized protein channels, called ion channels, open and allow the positively charged sodium ions to diffuse into the cell. This influx of positive ions causes the inside of the cell to become more positive than the outside of the cell. This reversal of charge then triggers the sodium channels to close, blocking the diffusion of Na + . Meanwhile, another type of ion channel opens allowing potassium ions (K+) to diffuse out of the cell. This causes the charge on the inside of the cell to become negative again. The neuron has returned to resting potential. To transmit the signal throughout the neuron, the action potential must travel the length of the neuron. The changes in charge in one area of the neuron trigger the opening of Na+ channels is membrane just down-stream of the action potential. As a result, an action potential is generated in the adjacent region and is quickly followed by a return to resting potential. The action potential travels down the neuron like dominoes falling over; each reversal in charge triggers the opening of ion channels in the adjacent membrane. Action potentials are the same no matter what stimulus caused them. Your central nervous system (CNS) can detect different intensity of different stimuli by interpreting the frequency of action potentials traveling down the neuron. For example, if you tap your finger on your desk softly, your CNS will receive fewer action potentials per second than if you tapped your finger very hard Passing a signal from one neuron to another – Chemical synapse If the nervous system is going to function properly, neurons must be able to communicate with each other by passing signals to one another. This occurs at a synapse, or relay point between two cells. The most common type of synapse in the nervous system of animals is chemical synapse. Chemical synapse occurs in the narrow space between the axon terminal of the sending neuron and the dendrite of the receiving neuron. When action potential reaches the axon terminal, it is converted into a chemical signal. This chemical signal comes in the form of a neurotransmitter (a chemical that carries information from one nerve cell to another). Once the action potential arrives at the end of the neuron, it stimulates vesicles containing a neurotransmitter. The vesicle will then fuse with the cell membrane and release the neurotransmitter into the synaptic cleft using the process of exocytosis. The released neurotransmitters diffuse across the synaptic cleft and bind to receptor molecules, which are proteins attached to ion channels within the membrane of the receiving cell. The binding of the neurotransmitters to the receptor molecules causes the ion channels to open, allowing Na+ to diffuse into the cell. This influx of Na+ ions causes an action potential in the receiving neuron. The neurotransmitter is then either broken down or transported back to the sending neuron to be reused. The absence of neurotransmitters in the synaptic cleft causes the ion channels to close and the signal to end. Analysis Questions Directions: Answer question based on readings 1. Sending neuron is also known as _______Dendrite_____________ 2. Receiving neuron is also known as _______Axon_____________ 3. What term is used to describe a neuron that is not transmitting a signal? The neuron is at rest, this difference responsible is named because the resting potential. 4. Assume that the neuron is at rest, where is potassium (K+) higher, inside or outside of the cell? The inside of the cell and also the outside of the cell are separated by a membrane with K channels, that are at first closed. there's a higher concentration of potassium ions on the inside of the cell than on the surface. 5. Assume that the neuron is at rest, where is sodium (Na+) higher, inside or outside of the cell? 6. Describe the conditions inside and outside of a neuron during action potential. Inside the neuron has charged because of the presence of positively charged sodium ions and outside the neuron negatively charged due to the dearth of as several sodium ions. 7. What causes a neuron to change from resting potential to action potential? A stimulus causes metal ion-channels inside the cell membrane to open and permit sodium ions to diffuse into the cell. This changes the charge of the neuron to positive. 8. What causes a neuron to return to a resting potential from an action potential? Sodium channels close, preventing any additional Na from getting into the neuron. Meanwhile, K channels open, permitting positively charged K ions to diffuse out. 9. How is a signal transmitted through a single neuron? The action potential is generated within the adjacent region and is quickly followed by a come back to potential drop. The action potential travels down the neuron like dominoes falling over; every reversal in charge triggers the gap of ion channels within the adjacent membrane. 10. What is a neurotransmitter? Neurotransmitter is a chemical that carries info from one nerve cell to a different. 11. How are neurotransmitters secreted into the synaptic cleft? Through exocytosis 12. How does a neurotransmitter cause an action potential in a receiving neuron? The neurotransmitter binds to a receptor on the particle channel. once the neurochemical is sure to the receptor, the particle channel opens and permits Na+ to diffuse into the cell, inflicting associate action potential. 13. How is the signal between neurons stop? The neurotransmitter is either reabsorbed by the causation somatic cell or with chemicals countermined within the conjunction cleft. 14. What is saltatory conduction? Saltatory conduction describes the method associate degree electrical impulse skips from node to node down the complete length of an axone, dashing the arrival of the impulse at the nerve terminal as compared with the slower continuous progression of change spreading down associate degree unmyelinated axone. Use the lecture slides and/or Julien’s Primer of Drug Action text to help answer the following questions. Use the diagram (numbers) to identify the stages of an action potential. 12. Which section of the graph represents depolarization? ________3______ 13. Which of the following segments of the graph shows a phase where the neuron will be less likely to fire an action potential? ________2______ 14. Which of the following segments of the graph shows repolarization? _______4_______ 15. Which section of the graph represents a neuron at rest? 16. At what membrane voltage is a neuron at rest? Use the Y axis on graph to answer. ______-55_______mV 17. Na+ has the highest concentration ____________ the cell while K+ has the highest concentration of _______1_______ the ______________ of the cell. 18. What membrane potential is considered threshold membrane potential? ________5________ mV 19. When all the K+ Voltage-Gated channels are open (-90mV), the cell is considered to be hyperpolarized. Which segment of the graph represents this? ________5________ 20. At what stage are all the Na+ Voltage-Gated Channels open? ___________2____________ Match each term to the appropriate description. A. Action potential E. Refractory period B. Depolarization F. Potassium ions (K+) C. Polarized G. Repolarization D. Sodium-potassium pump H. Sodium ions (Na+) ____E_____ Period of repolarization of the neuron during which it cannot respond to a second stimulus __B_______ State in which the resting potential is reversed as sodium ions rush into neuron ____C_____ Electrical condition of the plasma membrane of a resting neuron ____G_____ Period during which potassium ions rush out of the neuron ____A_____ Transmission of the depolarization wave along a neuron's membrane ____F_____ The chief positive intracellular ion in a resting neuron ____D_____ Process by which ATP is used to move sodium ions out of the cell and potassium ion back into the cell; restores the resting conditions of the neuron Directions: The diagram represents the final stages of synaptic transmission. Answer the following questions related to synaptic transmission ! Answers: 1.Synaptic vesicles store varied neurotransmitters that are released at the synapse. the discharge is regulated by a voltage-dependent Ca channel. Vesicles are essential for propagating nerve impulses between neurons and are perpetually recreated by the cell. 2.Voltage gated Ca channels play crucial roles in several bodily functions including: cardiac action potentials, neurotransmitter release, contraction. throughout neurological functions, these Ca channels produce action potentials. At resting state,voltage-gated Ca channels are during a closed conformation. 3. The message travels from the presynaptic terminal of 1 synapse to the synaptic cleft to the postsynaptic terminal of following synapse. The synaptic cleft is principally used to transport neurotransmitters from one synapse to a different in order to continue carrying the nerve impulse till it reaches its destination. 4. Calcium channels are membrane-spanning proteins that regulate the intracellular concentration of Ca ions (Ca2+). once getting into the cell, Ca2+ activates specific Ca receptor proteins, calmodulin, troponin-C, or Caactivated calcium, potassium, and chloride channels. 5. Neurotransmitter vesicles store numerous neurotransmitters that are free at the conjunction. the discharge is regulated by a voltage-dependent metallic element channel. Vesicles are essential for propagating nerve impulses between neurons and are constantly recreated by the cell. 6.Neurotransmitter receptors transmit the actions of sure neurotransmitters, therefore enabling cell-to-cell communication within the nervous system. Most receptors are integral membrane proteins classified as ligand-gated ion channels or G protein-coupled receptors . Neurotransmitters (NTs: How Does the Brain Communicate? The brain contains billions of nerve cells (neurons) that are always talking to each other. Neurons pass messages back and forth within the brain and the spinal column. These nerve networks control everything we feel, think, and do. ! Neurotransmitters—The Brain's Chemical Messengers To make messages jump from one nerve cell to another it creates chemical messengers, called neurotransmitters. The end of one nerve cell releases neurotransmitters that travel to nearby nerve cell. Then the transmitter binds to receptors on the nearby nerve cell, giving Directions: Use your textbook to fill in information about the chemicals listed below. Indicate (1) whether each neurotransmitter is excitatory, inhibitory, or both and (2) briefly describe its function. Acetylcholine is a chemical that is observed among the nerve synapses, or gaps, among nerve cells. When activated, it causes the contraction of skeletal muscles and turns on glandular functions inside the endocrine system.Like mail persons who can each supply and select up envelopes and packages, acetylcholine capabilities inside the peripheral nervous gadget and crucial nervous device both as an activator and inhibitor. In the peripheral nervous gadget, it reasons skeletal muscle groups to contract. In the important nervous device, it inhibits the activation of the cholinergic device._____________________________________________________________________________________ Acetylcholine (ACh) Glutamate is a effective excitatory neurotransmitter that is launched with the aid of nerve cells in the brain. It is accountable for sending signals among nerve cells, and under normal situations it performs an important position in getting to know and memor_____________________________________________________________________________________ Glutamate Gamma aminobutyric acid is a naturally happening amino acid that works as a neurotransmitter in your brain. Neurotransmitters feature as chemical messengers. GABA is considered an inhibitory neurotransmitter because it blocks, or inhibits, sure brain alerts and decreases activity on your fearful system_____________________________________________________________________________________ Gamma aminobutyric acid (GABA) Collectively with adrenaline, norepinephrine will increase heart price and blood pumping from the heart. It also increases blood strain and allows ruin down fats and boom blood sugar tiers to provide more power to the body._____________________________________________________________________________________ Norepinephrine (NE) Dopamine is a chemical discovered naturally within the human frame. It is a neurotransmitter, which means it sends alerts from the body to the brain. Dopamine performs a element in controlling the movements a person makes, as well as their emotional responses. The right stability of dopamine is crucial for both bodily and mental wellbeing._____________________________________________________________________________________ Dopamine (DA) Serotonin is an critical chemical and neurotransmitter inside the human body. It is believed to assist modify mood and social behavior, appetite and digestion, sleep, memory, and sexual choice and function. There may be a link between serotonin and depression._____________________________________________________________________________________ Serotonin Endorphins act as analgesics, because of this they diminish the belief of pain. They additionally act as sedatives. They are synthetic in your brain, spinal cord, and many other elements of your body and are released in reaction to brain chemicals referred to as neurotransmitters._______________________________________________________________________________ ______ Endorphins Answer the following questions: 6. What is monoamine oxidase? Monoamine oxidase is concerned in removing the neurotransmitters catecholamine, serotonin and intropin from the brain. MAOIs prevent this from happening, that makes a lot of of those brain chemicals on the market to result changes in each cells and circuits that are wedged by depression. 7. What is an monoamine oxidase inhibitor (MOAI)? MAOIs were the primary category of antidepressants to be developed. They fell out of favor owing to issues regarding interactions with sure foods and diverse drug interactions. once MAO is restrained, noradrenaline, serotonin, and Intropin don't seem to be countermined, increasing the concentration of all 3 neurotransmitters within the brain. MAOIs are used for the treatment of Parkinson's sickness. 8. How do MOAI’s work at the synapse? MAOIs increase synaptic norepinephrine, serotonin, and dopamine by inhibiting the protein enzyme from metabolizing these amine transmitters. Adverse effects embody hypotension, weight gain, sexual disfunction, edema, and sleep disorder. 9. What is the precursor to serotonin, i.e. what amino acid is it made form? Hydroxytryptophan is associate organic compound precursor employed in the formation of 5hydroxytryptamine. 5-HTP has been used as associate oral supplement various to spice up 5hydroxytryptamine.22 it's been shown in studies to boost depression, however solely preliminary proof is offered suggesting that 5-HTP conjointly could improve anxiety. 10. 11. Serotonin can be metabolized (broken down) into what sleep related hormone? What is the precursor to dopamine i.e. what amino acid is it made form? Dopamine is one in every of the 3 main sign molecules from the hormone family. the opposite 2 are the known fight-or-flight response molecules hormone and noradrenaline.Dopamine is created within the brain. It’s additionally created in and utilized by alternative systems within the body, wherever it acts as a very important chemical courier. Dopastat is attached the center, modulating vessel perform, stimulating muscular tissue contraction, and promoting the widening of blood vessels required for correct blood flow. Dopastat is employed within the kidneys to assist them perform properly, stimulating inflated excretion, and evacuation excess Na. 12. What is the precursor to epinephrine and norepinephrine? Epinephrine and norepinephrine are two neurotransmitters that additionally function hormones, and they belong to a category of compounds called catecholamines. As hormones, they influence totally different elements of your body and stimulate your central nervous system.Chemically, epinephrine and norepinephrine are very similar. However, epinephrine works on each alpha and beta receptors, whereas catecholamine solely works on alpha receptors. Alpha receptors are only found within the arteries. Beta receptors are within the heart, lungs, and arteries of skeletal muscles. It’s this distinction that causes epinephrine and norepinephrine to have slightly totally different functions.
