{"id":2247,"date":"2016-05-16T17:56:25","date_gmt":"2016-05-16T17:56:25","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/biologyxwaymakerxmaster\/?post_type=chapter&#038;p=2247"},"modified":"2024-04-26T22:25:31","modified_gmt":"2024-04-26T22:25:31","slug":"reading-types-of-signals","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology1\/chapter\/reading-types-of-signals\/","title":{"raw":"Types of Signals","rendered":"Types of Signals"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Identify the types of signals used by multicellular organisms<\/li>\r\n<\/ul>\r\n<\/div>\r\nThere are four categories of chemical signaling found in multicellular organisms: paracrine signaling, endocrine signaling, autocrine signaling, and direct signaling across gap junctions (Figure\u00a01). The main difference between the different categories of signaling is the distance that the signal travels through the organism to reach the target cell. Not all cells are affected by the same signals.\r\n<figure data-id=\"fig-ch09_01_01\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"798\"]<img id=\"22150\" class=\"\" src=\"https:\/\/openstax.org\/resources\/a38d3e4b11d54233a89abf33a4eb4ac3dc323f51\" alt=\"The illustration shows four forms of chemical signaling. In autocrine signaling, a cell targets itself. In signaling across a gap junction, a cell targets a cell connected via gap junctions. In paracrine signaling, a cell targets a nearby cell. In endocrine signaling, a cell targets a distant cell via the bloodstream\" width=\"798\" height=\"767\" data-media-type=\"image\/jpg\" \/> Figure\u00a01.\u00a0In chemical signaling, a cell may target itself (autocrine signaling), a cell connected by gap junctions, a nearby cell (paracrine signaling), or a distant cell (endocrine signaling). Paracrine signaling acts on nearby cells, endocrine signaling uses the circulatory system to transport ligands, and autocrine signaling acts on the signaling cell. Signaling via gap junctions involves signaling molecules moving directly between adjacent cells.[\/caption]<\/figure>\r\n<h2>Paracrine Signaling<\/h2>\r\n[caption id=\"attachment_1640\" align=\"alignright\" width=\"400\"]<img class=\"wp-image-1640\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/02233201\/Figure_09_01_02.jpg\" alt=\"This illustration shows closely juxtaposed bulbous protrusions of presynaptic and postsynaptic cells. The presynaptic cell stores neurotransmitter in synaptic vesicles. When signaling occurs, the vesicles fuse with the cell membrane, thereby releasing the neutrotransmitter, which then binds to receptors on the postsynaptic cell. An enzyme on the surface of the postsynaptic cell destroys the neurotrasmitter, thereby terminating the signal.\" width=\"400\" height=\"506\" \/> Figure\u00a02. The distance between the presynaptic cell and the postsynaptic cell\u2014called the synaptic gap\u2014is very small and allows for rapid diffusion of the neurotransmitter. Enzymes in the synaptic cleft degrade some types of neurotransmitters to terminate the signal.[\/caption]\r\n\r\nSignals that act locally between cells that are close together are called <strong>paracrine signals<\/strong>. Paracrine signals move by diffusion through the extracellular matrix. These types of signals usually elicit quick responses that last only a short amount of time. In order to keep the response localized, paracrine ligand molecules are normally quickly degraded by enzymes or removed by neighboring cells. Removing the signals will reestablish the concentration gradient for the signal, allowing them to quickly diffuse through the intracellular space if released again.\r\n\r\nOne example of paracrine signaling is the transfer of signals across synapses between nerve cells. A nerve cell consists of a cell body, several short, branched extensions called dendrites that receive stimuli, and a long extension called an axon, which transmits signals to other nerve cells or muscle cells. The junction between nerve cells where signal transmission occurs is called a synapse. A\u00a0<strong>synaptic signal<\/strong> is a chemical signal that travels between nerve cells. Signals within the nerve cells are propagated by fast-moving electrical impulses. When these impulses reach the end of the axon, the signal continues on to a dendrite of the next cell by the release of chemical ligands called <strong>neurotransmitters<\/strong> by the presynaptic cell (the cell emitting the signal). The neurotransmitters are transported across the very small distances between nerve cells, which are called <strong>chemical synapses<\/strong> (Figure\u00a02). The small distance between nerve cells allows the signal to travel quickly; this enables an immediate response, such as, Take your hand off the stove!\r\n\r\nWhen the neurotransmitter binds the receptor on the surface of the postsynaptic cell, the electrochemical potential of the target cell changes, and the next electrical impulse is launched. The neurotransmitters that are released into the chemical synapse are degraded quickly or get reabsorbed by the presynaptic cell so that the recipient nerve cell can recover quickly and be prepared to respond rapidly to the next synaptic signal.\r\n<h2>Endocrine Signaling<\/h2>\r\nSignals from distant cells are called\u00a0<strong>endocrine signals<\/strong>, and they originate from <strong>endocrine cells<\/strong>. (In the body, many endocrine cells are located in endocrine glands, such as the thyroid gland, the hypothalamus, and the pituitary gland.) These types of signals usually produce a slower response but have a longer-lasting effect. The ligands released in endocrine signaling are called hormones, signaling molecules that are produced in one part of the body but affect other body regions some distance away.\r\n\r\nHormones travel the large distances between endocrine cells and their target cells via the bloodstream, which is a relatively slow way to move throughout the body. Because of their form of transport, hormones get diluted and are present in low concentrations when they act on their target cells. This is different from paracrine signaling, in which local concentrations of ligands can be very high.\r\n<h2>Autocrine Signaling<\/h2>\r\n<strong>Autocrine signals<\/strong> are produced by signaling cells that can also bind to the ligand that is released. This means the signaling cell and the target cell can be the same or a similar cell (the prefix\u00a0<em>auto-<\/em> means self, a reminder that the signaling cell sends a signal to itself). This type of signaling often occurs during the early development of an organism to ensure that cells develop into the correct tissues and take on the proper function. Autocrine signaling also regulates pain sensation and inflammatory responses. Further, if a cell is infected with a virus, the cell can signal itself to undergo programmed cell death, killing the virus in the process. In some cases, neighboring cells of the same type are also influenced by the released ligand. In embryological development, this process of stimulating a group of neighboring cells may help to direct the differentiation of identical cells into the same cell type, thus ensuring the proper developmental outcome.\r\n<h2>Direct Signaling Across Gap Junctions<\/h2>\r\nGap junctions in animals and plasmodesmata in plants are connections between the plasma membranes of neighboring cells. These water-filled channels allow small signaling molecules, called\u00a0<strong>intracellular mediators<\/strong>, to diffuse between the two cells. Small molecules, such as calcium ions (Ca<sup>2+<\/sup>), are able to move between cells, but large molecules like proteins and DNA cannot fit through the channels. The specificity of the channels ensures that the cells remain independent but can quickly and easily transmit signals. The transfer of signaling molecules communicates the current state of the cell that is directly next to the target cell; this allows a group of cells to coordinate their response to a signal that only one of them may have received. In plants, plasmodesmata are ubiquitous, making the entire plant into a giant communication network.\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/b4642d24-2e51-4a6f-a3d2-6d0c097655d1\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Identify the types of signals used by multicellular organisms<\/li>\n<\/ul>\n<\/div>\n<p>There are four categories of chemical signaling found in multicellular organisms: paracrine signaling, endocrine signaling, autocrine signaling, and direct signaling across gap junctions (Figure\u00a01). The main difference between the different categories of signaling is the distance that the signal travels through the organism to reach the target cell. Not all cells are affected by the same signals.<\/p>\n<figure data-id=\"fig-ch09_01_01\">\n<div style=\"width: 808px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"22150\" class=\"\" src=\"https:\/\/openstax.org\/resources\/a38d3e4b11d54233a89abf33a4eb4ac3dc323f51\" alt=\"The illustration shows four forms of chemical signaling. In autocrine signaling, a cell targets itself. In signaling across a gap junction, a cell targets a cell connected via gap junctions. In paracrine signaling, a cell targets a nearby cell. In endocrine signaling, a cell targets a distant cell via the bloodstream\" width=\"798\" height=\"767\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a01.\u00a0In chemical signaling, a cell may target itself (autocrine signaling), a cell connected by gap junctions, a nearby cell (paracrine signaling), or a distant cell (endocrine signaling). Paracrine signaling acts on nearby cells, endocrine signaling uses the circulatory system to transport ligands, and autocrine signaling acts on the signaling cell. Signaling via gap junctions involves signaling molecules moving directly between adjacent cells.<\/p>\n<\/div>\n<\/figure>\n<h2>Paracrine Signaling<\/h2>\n<div id=\"attachment_1640\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1640\" class=\"wp-image-1640\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/02233201\/Figure_09_01_02.jpg\" alt=\"This illustration shows closely juxtaposed bulbous protrusions of presynaptic and postsynaptic cells. The presynaptic cell stores neurotransmitter in synaptic vesicles. When signaling occurs, the vesicles fuse with the cell membrane, thereby releasing the neutrotransmitter, which then binds to receptors on the postsynaptic cell. An enzyme on the surface of the postsynaptic cell destroys the neurotrasmitter, thereby terminating the signal.\" width=\"400\" height=\"506\" \/><\/p>\n<p id=\"caption-attachment-1640\" class=\"wp-caption-text\">Figure\u00a02. The distance between the presynaptic cell and the postsynaptic cell\u2014called the synaptic gap\u2014is very small and allows for rapid diffusion of the neurotransmitter. Enzymes in the synaptic cleft degrade some types of neurotransmitters to terminate the signal.<\/p>\n<\/div>\n<p>Signals that act locally between cells that are close together are called <strong>paracrine signals<\/strong>. Paracrine signals move by diffusion through the extracellular matrix. These types of signals usually elicit quick responses that last only a short amount of time. In order to keep the response localized, paracrine ligand molecules are normally quickly degraded by enzymes or removed by neighboring cells. Removing the signals will reestablish the concentration gradient for the signal, allowing them to quickly diffuse through the intracellular space if released again.<\/p>\n<p>One example of paracrine signaling is the transfer of signals across synapses between nerve cells. A nerve cell consists of a cell body, several short, branched extensions called dendrites that receive stimuli, and a long extension called an axon, which transmits signals to other nerve cells or muscle cells. The junction between nerve cells where signal transmission occurs is called a synapse. A\u00a0<strong>synaptic signal<\/strong> is a chemical signal that travels between nerve cells. Signals within the nerve cells are propagated by fast-moving electrical impulses. When these impulses reach the end of the axon, the signal continues on to a dendrite of the next cell by the release of chemical ligands called <strong>neurotransmitters<\/strong> by the presynaptic cell (the cell emitting the signal). The neurotransmitters are transported across the very small distances between nerve cells, which are called <strong>chemical synapses<\/strong> (Figure\u00a02). The small distance between nerve cells allows the signal to travel quickly; this enables an immediate response, such as, Take your hand off the stove!<\/p>\n<p>When the neurotransmitter binds the receptor on the surface of the postsynaptic cell, the electrochemical potential of the target cell changes, and the next electrical impulse is launched. The neurotransmitters that are released into the chemical synapse are degraded quickly or get reabsorbed by the presynaptic cell so that the recipient nerve cell can recover quickly and be prepared to respond rapidly to the next synaptic signal.<\/p>\n<h2>Endocrine Signaling<\/h2>\n<p>Signals from distant cells are called\u00a0<strong>endocrine signals<\/strong>, and they originate from <strong>endocrine cells<\/strong>. (In the body, many endocrine cells are located in endocrine glands, such as the thyroid gland, the hypothalamus, and the pituitary gland.) These types of signals usually produce a slower response but have a longer-lasting effect. The ligands released in endocrine signaling are called hormones, signaling molecules that are produced in one part of the body but affect other body regions some distance away.<\/p>\n<p>Hormones travel the large distances between endocrine cells and their target cells via the bloodstream, which is a relatively slow way to move throughout the body. Because of their form of transport, hormones get diluted and are present in low concentrations when they act on their target cells. This is different from paracrine signaling, in which local concentrations of ligands can be very high.<\/p>\n<h2>Autocrine Signaling<\/h2>\n<p><strong>Autocrine signals<\/strong> are produced by signaling cells that can also bind to the ligand that is released. This means the signaling cell and the target cell can be the same or a similar cell (the prefix\u00a0<em>auto-<\/em> means self, a reminder that the signaling cell sends a signal to itself). This type of signaling often occurs during the early development of an organism to ensure that cells develop into the correct tissues and take on the proper function. Autocrine signaling also regulates pain sensation and inflammatory responses. Further, if a cell is infected with a virus, the cell can signal itself to undergo programmed cell death, killing the virus in the process. In some cases, neighboring cells of the same type are also influenced by the released ligand. In embryological development, this process of stimulating a group of neighboring cells may help to direct the differentiation of identical cells into the same cell type, thus ensuring the proper developmental outcome.<\/p>\n<h2>Direct Signaling Across Gap Junctions<\/h2>\n<p>Gap junctions in animals and plasmodesmata in plants are connections between the plasma membranes of neighboring cells. These water-filled channels allow small signaling molecules, called\u00a0<strong>intracellular mediators<\/strong>, to diffuse between the two cells. Small molecules, such as calcium ions (Ca<sup>2+<\/sup>), are able to move between cells, but large molecules like proteins and DNA cannot fit through the channels. The specificity of the channels ensures that the cells remain independent but can quickly and easily transmit signals. The transfer of signaling molecules communicates the current state of the cell that is directly next to the target cell; this allows a group of cells to coordinate their response to a signal that only one of them may have received. In plants, plasmodesmata are ubiquitous, making the entire plant into a giant communication network.<\/p>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_b4642d24-2e51-4a6f-a3d2-6d0c097655d1\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/b4642d24-2e51-4a6f-a3d2-6d0c097655d1?iframe_resize_id=assessment_practice_id_b4642d24-2e51-4a6f-a3d2-6d0c097655d1\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-2247\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":3,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"0057bbad-c6ea-4fc8-bd79-e647783f1a23, 3eb70e19-bdee-4454-81c0-52eae245906b","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2247","chapter","type-chapter","status-publish","hentry"],"part":3271,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2247","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":10,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2247\/revisions"}],"predecessor-version":[{"id":5925,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2247\/revisions\/5925"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/parts\/3271"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2247\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/media?parent=2247"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapter-type?post=2247"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/contributor?post=2247"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/license?post=2247"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}