Cell Communication PDF

The Cell and Its Functions 1 The Cell and Its Functions - Cells are the structural and functional units of all living organisms. - A human cell has three main parts: 1-The cell membrane (also called the plasma membrane) controls move...

The Cell and Its Functions 1 The Cell and Its Functions - Cells are the structural and functional units of all living organisms. - A human cell has three main parts: 1-The cell membrane (also called the plasma membrane) controls movement of substances both into and out of the cell. 2-The nucleus is a large, centrally located structure that controls cellular activities. 3-The cytoplasm is the portion of the cell between the nucleus and the plasma membrane. The cytoplasm contains cytosol and organelles. Cytosol, or intracellular fluid, contains dissolved nutrients, ions, soluble and insoluble proteins, and waste products. Organelles ‘little organs’– specialized structures of the cytoplasm with particular functions. 4  The cell membrane (The cell membrane surrounds the cell)  Composition of the cell membrane: - The cell membrane is made up of the following components: 1- Lipid (45%): phospholipid & cholesterol. 2- Protein (50%): integral and peripheral proteins. 3- Carbohydrate (5%): glycolipids & glycoproteins.  Membrane lipids: 1) Phospholipids: - They are shaped similar to lollipops. - Each phospholipid molecule has a head & tail. - The head is  Formed of phosphate.  Charged, polar “head”.  It dissolves in water. Thus, it is called hydrophilic (water loving).  It is placed on the outer & inner surfaces of the membrane. - The tail is  Formed of fatty acids.  Uncharged, nonpolar “tail”.  It is insoluble in water. Thus, it is called hydrophobic (water-fearing).  Present in the center or the middle of the membrane. 2) Cholesterol: - Cholesterol is an important component of plasma membranes. - Cholesterol helps to keep the membrane stable by preventing it from becoming either too rigid or too flexible. 5  Functions of membrane lipids: - Impermeable to water‐soluble molecules, and so prevents the passage of these molecules into and out of the cell. - Small lipid‐soluble molecules and gases like oxygen and carbon dioxide cross membranes rapidly. 6 Membrane proteins: - Membrane proteins are of two types: 1) Integral Proteins: - Extend through the entire thickness of the membrane “transmembrane proteins”. 2) Peripheral proteins: - Peripheral proteins can be found associated with both intracellular and extracellular plasma membrane surfaces.  Functions of proteins in the cell membrane: They act as; 1- Channels through which certain substances can enter cells. 2- Carriers (pumps) involved in the passage of molecules through the membrane. 3- Enzymes that catalyze specific chemical reactions at the inside or outside surface of the cell. 4- Specific receptors for hormones and other chemical messengers.. An example is the hormone insulin, which binds to a certain membrane receptor protein and causes an increase in cellular glucose absorption. 5- Linker proteins: binding to other proteins in the extracellular fluid (ECF) (e.g. collagen) and/or cytosol (e.g. actin). 7 Membrane carbohydrates: - Short chains of sugars are attached to the outer surface of some protein & lipid molecules (called glycoproteins and glycolipids, respectively) & form an extensive sugary adhesive coat called the glycocalyx. Functions of glycocalyx: 1) Serves as cell identity markers (cell surface antigens)  facilitating cell-cell recognition that: a) Enables a sperm cell to recognize an egg. b) Enables the cells of the immune system to recognize other cells as normal (self) or abnormal (non-self or tumor cell). c) Allows cells to be sorted into the proper places during development. 2) Enables cells to adhere to one another e.g. temporary adhesion occurs between neutrophils and endothelial cells at the site of inflammation. Cytoplasmic organelles The nucleus (The nucleus controls the cell) - The nucleus is the largest organelle in the cell. - The nucleus is the “control center” of the cell [controls the structure and function of the cell] because it contains DNA, which controls the synthesis of proteins (e.g. enzymes, hormones) according to instructions in the genes. [Often described as the ‘brain’ of the cell]. - Nucleus contains nucleoplasm which is surrounded by a double-layer nuclear membrane, having wider pores than the cell membrane. 8  Structures of the Cell Nucleus: 9  The mitochondria (Extract Energy from Nutrients) - Mitochondria are membranous organelles specialized for synthesizing ATP. - They have a variety of shapes: spheroid, rod-shaped, bean-shaped. - A mitochondrion is surrounded by a double membrane. The inner membrane usually has folds called cristae, which project like shelves into the interior of the mitochondrion. The space between the cristae, called the matrix, contains oxidative phosphorylation enzymes used in ATP synthesis. In the process, mitochondria use up oxygen and give off carbon dioxide. Therefore, the process of producing ATP is called cellular respiration. -The number of mitochondria present in a cell is related to the amount of energy the cell needs; for example fat cells, have few mitochondria. The cells that use a lot of energy, for example muscle and liver cells, have many mitochondria. 10 Functions of mitochondria: 1- Generation of ATP. Mitochondria are the “powerhouses” of the cell. 2-Play an important and early role in apoptosis through release of cytochrome c which initiate a cascade of activation of enzymes known as caspases (protein-digesting enzymes) that bring about apoptosis (programmed cell death = intentional suicide of a cell that is no longer useful). The ribosomes (Ribosomes are responsible for protein synthesis) - Ribosomes are non-membranous organelles composed of proteins & rRNA. - A functional ribosome consists of two subunits. One is called a small ribosomal subunit & the other a large ribosomal subunit. -They are formed in the nucleolus & then pass to the cytoplasm to perform their functions. - Some ribosomes float freely in the cytoplasm and are called free ribosomes. Others are attached to the endoplasmic reticulum Formation of ribosomal subunits: - Ribosomal subunits are synthesized in the nucleolus from rRNA & protein. Functions of ribosomes: - Protein synthesis occurs at the ribosomes with the help of mRNA & tRNA. 11 NB: - The number of ribosomes in a particular cell varies with the type of cell and its demand for new proteins. For example, liver cells, which manufacture blood proteins, contain far more ribosomes than do fat cells (adipocytes), which primarily synthesize lipids. The Endoplasmic Reticulum -The endoplasmic reticulum (ER) is a membranous organelle [an interconnected network of tubules, vesicles, & cisternae (flattened sacs)] and extends from the outer nuclear membrane into the cytoplasm. -The ER forms transport vesicles in which large molecules are transported to other parts of the cell. Often, these vesicles are on their way to the plasma membrane or the Golgi apparatus. Rough endoplasmic reticulum (RER) - It is ER with ribosomes attached to it. - It is prominent in cells specialized for protein secretion. 12 Functions of RER: 1- Formation of secreted proteins, membrane proteins & lysosomal enzymes. 2- Organelle formation: Helps form peroxisomes. Smooth endoplasmic reticulum (SER) - It is ER without ribosomes attached to it. - It is prominent in cells synthesizing steroids, triglycerides, and cholesterol. Functions of SER: 1- Synthesis of lipid and steroid hormones e.g. sex hormones. 2- Detoxification of various chemicals such as drugs, pesticides and carcinogens. 3- Muscle contraction and relaxation involves the release and recapture of calcium ions by the sarcoplasmic reticulum (the term for SER in skeletal muscle cells). NB: - Liver hepatocytes and steroid hormone–producing cells of the adrenal cortex and gonads (ovary and testis) are rich in SER. 13  The Golgi apparatus (The Golgi apparatus refines, packages, and ships) -The Golgi apparatus (complex) is composed of a cluster of vesicles, tubules, and flattened membrane-bounded cisternae. -The Golgi apparatus is well developed in secretory cells. Function of the Golgi apparatus: - The Golgi apparatus contains enzymes that modify proteins and lipids e.g. glycosylation, sulfation, phosphorylation. - When the processing is finished, it sorts and packages proteins and lipids for delivery to the plasma membrane. - It forms lysosomes and secretory vesicles. The lysosomes (Lysosomes are the digestive system of the cell.) - Lysosomes of the cell are membranous sacs filled with 40 different hydrolase (digestive) enzymes. -They are particularly abundant in cells with great phagocytic activity (e.g., macrophages, and neutrophils). Functions of lysosomes: - Lysosomes fuse with endocytotic vesicles within the cell, digesting bacteria and other large objects. - Lysosomes dissolves and removes damaged mitochondria (autophagy = “eating self.”) and help break down protein the cell doesn’t need. 14  Besides cleaning out the cell, this allows the cell to “reuse” amino acids and sugars ‘‘recycle molecules’’. - When a cell dies the enzymes are released from the lysosomes and break down the cell itself (autolysis). The peroxisomes - Peroxisomes are membranous organelles that catalyzes the breakdown of hydrogen peroxide (H2O2) & detoxify alcohol. The proteasomes - Hollow protein cylinders with embedded enzymes. - Destroys misfolded or abnormal proteins manufactured by RER. 15  The cytoskeleton [Cell “Bone and Muscle”] - The cytoskeleton is a complex network of fibers that maintains the structure of the cell, holds the organelles in place and allows the cell to change shape and move. - The cytoskeleton is composed of microfilaments, intermediate filaments, and microtubules. 16 Transport across cell membrane 2 Transport across cell membrane 2 - Molecules pass in and out of a cell across the cell membrane through several different processes that are collectively called membrane transport. - Substances move across the plasma membrane through:  Passive processes – these do not use cellular energy.  Active processes – these use cellular energy. A) Passive processes: I) Diffusion: 1- Simple diffusion. 2- Facilitated diffusion. II) Osmosis. B) Active processes: I) Active transport: 1- Primary active transport. 2- Secondary active transport. II) Vesicular transport: 1- Endocytosis. 2- Exocytosis. 17  Passive processes - Passive diffusion needs no energy. - occurs down an electrochemical gradient (“downhill”). 18  Simple diffusion - Solutes that are small and lipid-soluble move into or out of a cell down their concentration gradient by simple diffusion. - They simply pass between the phospholipid molecules that form the plasma membrane. - Lipid soluble molecules e.g. O2 & CO2 and steroid hormones. Facilitated Diffusion - Molecules that are not lipid-soluble need help across the plasma membrane. - These molecules include ions, urea, and glucose. - Channel or transporter proteins within the membrane help these molecules across the plasma membrane. I) Channel-mediated diffusion: - It is the movement of small ions e.g. Na+ or K+ across the plasma membrane through protein channels. II) Carrier-mediated diffusion: - In carrier-mediated facilitated diffusion, a carrier (also called a transporter) moves a solute down its concentration gradient across the plasma membrane e.g., glucose uptake by cells. The solute binds to a specific carrier on one side of the membrane and is released on the other side after the carrier undergoes a change in shape. 19 Types of carrier proteins: 1- Uniport system: - A carrier that transports one substance in one direction e.g. D-glucose. 2- Co-transport or Symport system:: - A carrier that transports two substances simultaneously in the same direction. - e.g. Na+-sugar transporters (glucose, mannose, galactose). 20 3- Countertransport or Antiport system: - A carrier that transports one substance in one direction and another substance in the opposite direction. - e.g. Na+ in & Ca++ out in nerve cell. Active transport [I] Primary active transport  Characteristics of primary active transport: - Occurs against an electrochemical gradient (uphill). - Requires direct input of metabolic energy in the form of adenosine triphosphate (ATP) and so it is active. - Is carrier-mediated.  Examples of primary active transport: ♣ Na+-K+ ATPase (or Na+-K+ pump): - Na+-K+ ATPase in cell membranes transports Na+ from intracellular to extracellular fluid & K+ from extracellular to intracellular fluid. - Both Na+ & K+ are transported against their electrochemical gradients. - Na+ is pumped out of the cell & K+ into the cell in a ratio of 3:2. Functions of the Na+–K+ pump: 1. Secondary active transport. - It maintains a Na+ concentration gradient across the membrane. Just as water held back by a dam can do work as it flows downward (to generate electricity, for instance), this gradient is a source of potential 21  energy that can be tapped to do other work e. g. uptake of glucose into kidney cells. 2. Regulation of cell volume. - Since each cycle of the pump removes one ion more than it brings in  reduces intracellular ion concentration  controls osmolarity  prevents cellular swelling. 3. Heat production. - When the weather turns cold, Thyroid hormone stimulates cells to produce more Na+–K+ pumps. As these pumps consume ATP, they release heat from it, compensating for the body heat we lose to the cold air around us. 1) H+-ATPase: - H+-ATPase (or proton pump) in renal α-intercalated cells transports H+ into the lumen of renal tubule against its electrochemical gradient. 22  [II] Secondary active transport  Characteristics of secondary active transport: a) The transport of two or more solutes is coupled. b) One of the solutes (usually Na+) is transported “downhill” & provides energy for the “uphill” transport of the other solute (s). c) Metabolic energy is not provided directly, but indirectly from the Na + gradient, which is maintained across cell membranes via primary active transport (Na+-K+ pump). NB: - Poisoning the Na+-K+ pump decreases the transmembrane Na+ gradient & consequently inhibits Na+-glucose cotransport.  Example of secondary active transport: ♣ Na+-glucose cotransport: - This occurs in intestinal mucosal & renal proximal tubule cells. 1) At the basolateral membrane (A Na+-K+ pump creates a concentration gradient of sodium ions): - From the cytosol, sodium ions bind to the Na+-K+ primary active transport pump. - ATP is hydrolyzed, and sodium ions are transported out of the cell, into the ECF, against their concentration gradient. 23 2) At the luminal membrane (A carrier protein uses the potential energy of the sodium ion gradient to power the transport of glucose): - From the lumen, both a sodium ion and a glucose molecule bind to another carrier protein (which is a symporter). - The carrier protein transports the sodium ion and glucose molecule into the cell—the sodium ion with its concentration gradient and the glucose molecule against its gradient. (II) Vesicular Transport - The two major types of vesicular transport are endocytosis and exocytosis. - Vesicular transport requires the energy from ATP hydrolysis to fuel several steps of the process, including vesicle formation. - Endocytosis  Definition: - It is the uptake (internalization) of material by cells, includes phagocytosis, pinocytosis, & receptor-mediated endocytosis.  Types of endocytosis: a) Phagocytosis: for particles ("cell eating") - It is a nonspecific process that occurs when a cell engulfs or captures a large particle (such as a bacterium) external to the cell by forming membrane extensions that are called pseudopodia to surround the particle. Once the particle is engulfed by the pseudopodia, it is enclosed within a membrane sac. When the sac is internalized, its contents are broken down chemically (digested) after it fuses with a lysosome. - Phagocytosis is carried out especially by white blood cells. b) Pinocytosis: for droplets of fluid ("cell drinking") - This process occurs when the cell internalizes droplets of ECF that contain dissolved solutes. 24 a) Receptor-mediated endocytosis: - It is more selective. - Specific molecules in the ECF bind to specific receptor proteins on the plasma membrane. The membrane sinks in at this point, creating a pit. The pit soon pinches off to form a vesicle in the cytoplasm. Exocytosis - Substances exit the cells through exocytosis, a process in which the vesicles fuse with the plasma membrane to release their contents into the extracellular fluid. 25  The body fluids 3 The body fluids - Water is the most important molecule in the human body because it is the solvent for all living matter. As we look for life in distant parts of the solar system, one of the first questions scientists ask about a planet is, “Does it have water?” Without water, life as we know it cannot exist.  Distribution of total body water (TBW): - The total body water (TBW) is approximately 60-70% of body weight (42 liters). - The percentage of TBW is highest in newborns (80%) and adult males (70%) and lowest in adult females (60%) & old age persons (50%). ֍ In adult male: There is more muscle & less fat. ֍ In adult female: There is more fat & less muscle. ֍ In baby: There is reduction in body solids and the fat content. 26 ֍ In old age: loss of muscle mass (sarcopenia) associated with aging, an increase in adipose tissue, & kidneys’ ability to reabsorb water decreases with age. TBW is distributed as follows: (1) Intracellular fluid (ICF): [28 liters] This constitutes about 2/3 of the TBW (about 40% of the body weight). The major cations of ICF are K+ and Mg2+. The major anions of ICF are protein and organic phosphates ( [ATP], [ADP], and [AMP]). (2) Extracellular fluid (ECF): [14 liters] This constitutes about 1/3 of TBW (about 20% of the body weight). The major cation of ECF is Na+. The major anions of ECF are Cl- and HCO3-. - It includes the following subdivisions: a) Intravascular fluid (the plasma): [3.5 liters] - This constitutes about 5% of the body weight. b) Interstitial fluid: [10.5 liters] - This includes water resides outside the vasculature and occupies spaces between cells (the interstitium). - It constitutes about 15 % of the body weight. 27 28  Forces affecting exchange of body fluids [I] Osmosis -This is the movement of water through a selectively permeable membrane from an area of higher water concentration (lower solute concentration) into an area of lower water concentration (higher solute concentration), either by crossing the plasma membrane directly or by moving through a channel protein (aquaporin channels). NB: - The concentration of water is determined by the amount of solutes dissolved in the water. For example, a higher concentration of salt on one side of the cell membrane means that there is less space for water molecules. - A selectively permeable membrane allows only water molecules to move across it. 29 The osmotic pressure of a solution: - It is the pressure that must be exerted on the side containing the higher solute concentration to prevent the diffusion of water (by osmosis) from the side containing the lower solute concentration. - The osmotic pressure of solution (side B in the figure) is equal to the amount of hydrostatic pressure required to stop the osmotic flow. - Osmosis is driven by a force called osmotic pressure, which is the “pulling” force that solutes exert on water molecules. - The osmotic pressure is determined by the numbers of particles (molecules or ions) per unit volume of solvent and not on the valence, weight, or size of the particle. The number of particles in a solution (i.e., ions, molecules) determines its osmotic pressure; the greater the number of particles, the higher the osmotic pressure. 30 Tonicity - Tonicity is the ability of a solution to change the volume or “tone” of a cell by adding or subtracting water through the process of osmosis. -Tonicity refers to the relative concentrations of solutes in two fluids. ♣When cells are placed in a isotonic solution, one that has the same solute concentration as the intracellular fluid. - Cells maintain a normal volume in isotonic extracellular solutions because the concentration of water is the same inside and out. - In humans, isotonic extracellular fluid is equivalent to about 9 grams of salt dissolved in a liter of solution. ♣When cells are placed in a hypertonic solution, one with a concentration of solutes higher than the intracellular fluid,  water diffuses out of the cells, and the cells shrink. 31 ♣When cells are placed in a hypotonic solution with a lower concentration of solutes than intracellular fluid,  water enters the cells and causes them to swell. [II] Filtration - Filtration is the transfer of water and dissolved substances from a region of high pressure to a region of low pressure; the force behind it is hydrostatic pressure (hydro = water; static = fluid not moving). - The filtration rates depend on the amount of hydrostatic pressure. - Hydrostatic pressure is the pressure exerted by a fluid against a wall or membrane. In the body, filtration is powered by blood pressure. NB: - Pressure within our cardiovascular system is usually called hydrostatic pressure even though it is a system in which fluid is in motion. textbooks are beginning to replace the term hydrostatic pressure with the term hydraulic pressure. Hydraulics is the study of fluid in motion. 32 - Filtration promotes the transfer of fluids & dissolved materials from the blood across the capillaries into the interstitial fluid. 33  Homeostasis 4 Homeostasis - Cells are surrounded by the interstitial fluid which constitutes the “internal environment” for these cells. Life is compatible within narrow limits of change in the in the chemical or physical properties of the internal environment. - Homeostasis means keeping the composition of the internal environment constant, physically & chemically, in response to changing internal or external conditions, such that the cells can survive. - By contrast, the “external environment” of the body is the space that surrounds the entire body. Basic components of homeostatic mechanisms: 1- Receptors = detectors = sensors. 2- Afferent pathways. 3- Control center “decision-maker”. 4- Efferent pathways. 5- Effector organs. 34 1- The receptors detect changes in the environments both outside & inside the body, and they give signal information to the control center. 2- The afferent pathway is the component through which signal information are sent from the sensor to the control center. 3- The control center receives the signal information from the sensors about the change, and it generates the signal commands necessary for correction of the error. - The control center is usually a part of the brain, that includes a set point, which is a particular value [normal range the body tries to stay within] e.g. body temperature = (36.5 - 37.5) 37 oC. Control center depends on comparing the received information (the change that occur in the internal environment) to the set value. 4- Efferent pathways: - This is the components through which the signal commands pass from the center to the effector organs. Efferent pathway may be neural or hormonal. 5- Effector organs: - They respond to signals from the center, to correct the error. - They are mainly muscles & glands. NB: - The factor that is being controlled (regulated) is referred to as the variable 35 Examples of homeostatic mechanisms: Regulation of body temperature: (Thermostasis) - Body temperature in man is maintained within a fraction of a degree both sides of 37oC. If the body temperature starts to rise even by a small fraction of a degree, homeostatic regulation is immediately called for and the error in body temperature immediately corrected. - The temperature rise is measured by means of thermoreceptors situated in the skin & in the hypothalamus. These receptors send signals to the heat regulatory centers in the hypothalamus, which in turn respond so as to reduce the rise in body temperature. The output of the heat regulating centers consists of responses which tend to promote heat loss e.g.: a) Vasodilatation of skin blood vessels   blood flow to the skin  loss of heat from the surface of the body by radiation. b) Stimulation of sweat glands  sweat evaporates from the surface of the skin  cooling effect. 36 37 ֍ Control of glucose levels in the blood by negative feedback: - The stimulus (either high or low blood-glucose levels) is sensed by cells of the pancreas (β cells or α cells) and triggers a response (secretion of insulin or of glucagon, bringing blood-glucose levels back to the set point). - Note that in each case the response feeds back to the secreting cells to reduce further hormone secretion. Feedback control of the homeostatic mechanism: - Homeostatic control systems are separated into two broad categories based on whether the system maintains the variable within a normal range by moving the stimulus in the opposite direction, or amplifies the stimulus in the same direction. These two types of feedback control are called negative feedback and positive feedback, respectively 38  [I] Negative feedback systems: - It opposes change & maintain stability. (The effect is opposite to the change). - They are very common in mammals & in the human body, and play an important role in many physiological functions: 1- Regulation of body temperature. 2- Regulation of body water & electrolytes. 3- Regulation of arterial blood pressure. 4- Regulation of blood glucose level. 5- Regulation of hormones. [II] Positive feedback: -The initial disturbance in a system sets off a train of events that increases the deviation from the desired level even further. - It magnifies the effect of a disturbance & results in instability. - Some important examples for physical phenomena utilizing positive feedback are: 1- In blood clotting mechanisms. 2- During excitation of membranes. 3- During birth of baby. - As the fetus head pushes into the cervix of uterus, nerve impulses pass from cervix to hypothalamus causing release of oxytocin hormone from the pituitary gland leading to stronger uterine contractions causing further stretch of cervix & further release of oxytocin and so on. 39 40  Cell Communication 5 Cell communication - Cell communication is essential to orchestrate the activities of cells in the body. - Our bodies are made up of approximately 100 trillion (1014) cells, and each depends on the others for survival, because they must work together to maintain homeostasis. To do so, cells must be able to communicate with each other to carry out coordinated activities such as the maintenance of body temperature…etc. - Communication occurs not only between neighboring cells but also between cells at different locations within the body. Types of Cell Communication: I- Direct contact communication: 1- Gap junctions: - Adjacent cells have direct channels (gap junctions) linking their cytoplasm. - The main role of gap junctions is to synchronize metabolic activities or electrical signals between cells in a tissue. - For example, gap junctions play a key role in spreading electrical signals from one cell to the next in cardiac muscle. 41 2. Cell–cell recognition. - In this process, animal cells with particular membrane-bound cell- surface molecules dock with one another, initiating communication between the cells. - For example, cell–cell recognition of this kind activates particular cells in the immune system in order to mount an immune response. II- Local signaling communication: - In local signaling, a cell releases a signal molecule that diffuses through the aqueous fluid surrounding and between the cells and causes a response in nearby target cells. - The signal molecule is called a local regulator &the process is called paracrine signaling. In some cases, the local regulator acts on the same cell that produces it; this is called autocrine signaling. 42 - For example, many of the growth factors that regulate cell division are local regulators that act in both a paracrine and autocrine fashion. - Another, more specialized type of local signaling called synaptic signaling occurs in the nervous system. An electrical signal along a nerve cell triggers the secretion of neurotransmitter molecules carrying a chemical signal. These molecules diffuse across the synapse, the narrow space between the nerve cell and its target cell (often another nerve cell), triggering a response in the target cell. III- Long-distance signaling communication: - In this form of communication, a controlling cell secretes a long- distance signaling molecule called a hormone which produces a response in target cells that may be far from the controlling cell. - This method is the most common means of cell communication.. - Hormones secreted by controlling cells enter the circulatory system where they travel to target cells elsewhere in the body. 43  References Barrett KE, Brooks HL, Barman SM, and Yuan JX (2019). Ganong’s Review of Medical Physiology (26th ed.) New York: McGraw- Hill Education. Boron WF, and Boulpaep EL (2017). Medical physiology (3rd ed.) Philadelphia, PA: Elsevier. Boston, Cengage Learning. Chandar N and Viselli S (2019): Cell and molecular biology (2nd ed.) Philadelphia: Wolters Kluwer Health. Costanzo LS (2021). Physiology (7th ed.) Philadelphia, PA: Elsevier. Fox SA (2021). Human physiology (16th ed.) New York: McGraw-Hill Education. Hall JE, and Hall ME (2021). Guyton and Hall Textbook of Medical Physiology (14th ed.) Philadelphia, PA: Elsevier. Kibble J D (2020). The big picture Physiology (2nd ed.) New York: McGraw-Hill Education. Koeppen BM, and Stanton BA (2018). Berne & Levy physiology (7th ed.) Philadelphia, PA: Elsevier. Lodish H et al., (2016). Molecular Cell Biology (8th ed.) W. H. Freeman and Company. Marieb EN and Hoehn K (2023). Human Anatomy and Physiology (12th ed.) New Jersey: Pearson Education. Silverthorn D U (2019). Human Physiology: An Integrated Approach (8th ed.) Pearson Education. Stanfield CL (2017). Principles of Human Physiology. (6th ed.) Pearson Education. Tortora GJ and Derrickson BH (2020). Principles of Anatomy and Physiology (16th ed.) John Wiley & Sons. 44 Section II Autonomic Nervous System 45 Introduction 6 The nervous system -The nervous system serves as the body’s primary communication and control system. It provides a rapid means of integrating and regulating body functions through electrical signals transmitted along specialized nervous tissue cells called neurons. Functions of the nervous system: -The nervous system has three overlapping functions, illustrated by the example of a thirsty person seeing and then lifting a glass of water 1) Sensory function. -The nervous system uses its millions of sensory receptors to monitor changes occurring both inside and outside the body. The gathered information is called sensory input. 2) Integrative function. -The nervous system processes and interprets sensory input and decides what should be done at each moment—a process called integration. 3) Motor function. -The nervous system activates effector organs—the muscles and glands— to cause a response, called motor output. Here’s another example: You are driving and see a red light ahead (sensory input). Your nervous system integrates this information (red light means “stop”), and your foot hits the brake (motor output). 46