Human Physiology - Class Notes and Study Guide Bundle
Human Physiology - Class Notes and Study Guide Bundle PCB4701
Popular in Human Physiology
verified elite notetaker
verified elite notetaker
verified elite notetaker
verified elite notetaker
verified elite notetaker
verified elite notetaker
Popular in Biology
This 132 page Bundle was uploaded by Hannah Hartman on Sunday August 14, 2016. The Bundle belongs to PCB4701 at Florida State University taught by Trombley in Fall 2016. Since its upload, it has received 10 views. For similar materials see Human Physiology in Biology at Florida State University.
Reviews for Human Physiology - Class Notes and Study Guide Bundle
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 08/14/16
Human Physiology – Exam 1 Study Guide, Chapters 6 Notes from powerpoint, Notes from in class, Important vocabulary, Important molecules and compounds (such as proteins, lipids, neurotransmitters, etc.), body part Chapter 6: Interactions between Cells and the Extracellular Environment A. Extracellular Environment: Introduction 1. The extracellular environment includes everything located outside the cells 2. Cells receive nourishment from and release wastes into the extracellular environment. 3. Cells communicate with each other by secreting chemical regulators into the extracellular environment. B. Body Fluids 1. 67% of our water is within cells in the intracellular compartment. 2. 33% is in the extracellular compartment. OF this: i. 20% is in blood plasma ii. 80% makes up what is called tissue fluid or interstitial fluid; this fluid connects the intracellular compartment with the blood plasma. C. Extracellular matrix ECM 1. Contains protein fibers of collagen and elastin, and a gellike ground substance i. Protein fibers provide structural support. ii. Ground substance is composed of glycoproteins (composed of proteins and sugars) and proteoglycans (composed of polysaccharides and hold a lot of liquid; polysaccharides make the “gel”). iii. Integrins are glycoproteins that extend from the cell cytoskeleton and bind to the extracellular matrix. 2. Functions of integrins i. Impart a polarity to the cells ii. Affect adhesion and motility – migration and movement of cells iii. Affect proliferation (cell division) D. Plasma membrane transport 1. Plasma membrane permeability i. The plasma membrane is selectively permeable, meaning it allows some molecules to cross but not others ii. Generally not permeable to proteins, nucleic acids, or other large molecules – RNA, DNA, parger molecules, proteins. iii. Generally permeable to ions, nutrients and wastes small gases 2. Categories of membrane transport i. Noncarriermediated 1. Simple diffusion of lipidsoluble molecules 2. Simple diffusion of ions through channel proteins (this uses a protein, so some consider it facilitated diffusion) 3. Simple diffusion of water = osmosis via aquaporins ii. Carrier mediated uses proteins 1. Facilitated diffusion (diffusion of ions through channel proteins is often categorized as facilitated diffusion) – diffusion DOWN the concentration gradient. 2. Active transport – diffusion from low to high concentrations. 3. Energy Involvement in Membrane Transport i. Passive transport: Molecules move from higher to lower concentration without using metabolic energy (e.g. ATP). ii. Active transport: molecules move from lower to higher concentration using ATP and specific carrier pumps. II. Diffusion and Osmosis A. Introduction 1. Solution: consists of solvent (water) and a solute (molecules dissolved in water) a. Molecules in a solution are in a constant state of motion b. If there is a concentration difference between two regions, random motion will establish equilibrium via diffusion. c. Obeys the 2 Law of Thermodynamics – diffusion increase entropy 2. Diffusion will occur without a physical separation or across a permeable membrane 3. Net diffusion – due to random movement, the net direction of diffusion is from high to low solute concentration. 4. Mean diffusion time – the average time it takes for a solute to diffuse a. Increases with the square of the distance the solute must travel (less distance, faster) b. Distances beyond 100 micrometers, diffusion time is too long to be effective. c. Diffusion rate increases with temperature, surface area of membrane, difference in concentration gradients. B. Diffusion through the plasma membrane 1. Small, nonpolar (or uncharged) lipidsoluble molecules pass easily through the lipid portion of the membrane. Includes: a. Oxygen, carbon dioxide, and steroid hormones (Cortisol and lipids) 2. Gas exchange: net diffusion of O2 into cells and CO2 out of cells due to concentration gradients. (opposite in lungs.) 3. Water can pass through using special channels called aquaporins in a process called osmosis. 4. Charged ions can pass through ion channels that span the plasma membrane tat may always be open or gated 5. Larger polar molecules cannot pass through the membrane by simple diffusion, but need special carrier proteins C. Rate of Diffusion 1. Measured by the number of diffusion particles per unit of time 2. Depends on: a. Magnitude of concentration difference – the driving force for diffusion b. Permeability of the membrane to the molecules c. Temperature of the solution; higher temperature increases the rate d. Surface area of the membrane; increased by microvilli D. Osmosis – diffusion of a solvent (not a solute!) 1. Water molecules do not carry a charge, so they can pass through the plasma membrane slowly. 2. This is the diffusion of solvent instead of solute, it is unique a. Given by a special name – osmosis b. Aided by channels in the membrane called aquaporins. c. Many aquaporins are found in the kidneys, eyes, lungs, salivary glands, and the brain. 3. Requirements of Osmosis a. There must be a solute concentration difference on either side of the membrane permeable to water. b. The membrane must be impermeable to the solute, or the concentration difference will not be maintained. i. Solutes that cannot cross and permit osmosis are called osmotically active. 4. Water movement in Osmosis a. The net movement of water is from the side with more water (more dilute) to the side with less water (less dilute). Water must move from the side with less moles of solute to the sidewith more solute (“high water” to “low water”) b. However, when osmosis is discussed, we say that water moves from the area of low solute concentration to the area of high solute concentration. (water moves toward the side with the higher solute concentration.) 5. Osmotic pressure a. Osmotic pressure is the force surrounding a cell required to stop osmosis. Directly proportional to solute concentration. b. Can be used to describe the osmotic pull of a solution. A higher solute concentration would require a higher osmotic pressure. i. Pure water has an osmotic pressure of zero. ii. Isotonic (equal), hypotonic (lower water pressure – less concentrated solution), hypertonic (more concentrated, higher osmotic pressure). 6. Molarity and molality a. Moles i. A mole of a compound can be measured as its molecular weight in grams. ii. The number of atoms in 1 mole is always the same no matter the substance: 6.02 *10^23 particles iii. You can make molar solutions (1M) or molal solutions (1m). b. Molarity – moles solute/L solution irrespective of molecular weight i. Glucose has a molecular weight of 180/ To make 1 molar solution of glucose, dissolve 180 g glucose in water to make 1 L solution. NaCl hasa molecular weight of 58.5. To make a 1 molar solution of NaCl, dissolve 58.5 G NaCl in water to total 1 L. ii. Not useful for a discussion of osmosis, since the solute concentration is different depending on the solute. More water is used to make the 1 molar solution of NaCl. c. Molality – moles solute/liter solvent ADD one liter – not bring up to one liter. i. 1 molal solutions take the molecular weight in grams dissolved in exactly 1 L water. ii. The amount of water never changes, so you can compare solute concentrations to predict the direction of osmosis. iii. Does not depend on the chemistry of the solute, but on how many particles are present in the solution. 7. Osmolality – The number of particles in moles/ L H2O.) a. Osmolality is the total molality of a solution when you combine all of the molecules within it. b. A 360 g (2m) glucose solution and a 180 g fructose (1m) solution would hae the same osmolality. c. These are both 2 Osm solutions d. Electrolytes that dissociate in water have to be assessed differently. i. NaCl dissociates into Na+ and Cl in water and must be counted as separate particles. ii. A 1m NaCl solution would actually be a 2 Osm solution. e. Osmolality can be measured by freezing point depression – how much the freezing point is lowered depends on the number of particles present in the solution. 8. Tonicity a. Plasma has the same osmolality as a 0.3m glucose or a 0.15m NaCl solution. i. These solutions are considered isosmotic to plasma ii. Made as 0.9g NaCl/100mL water – normal saline iii. 5% dextrose – 5g glucose/100ml water b. Tonicity is the effect of a solute concentration on the osmosis of water. i. If a membrane separates a 0.3m glucose solution and a 0.15m NaCl solution, there will be no net movement of water (isotonic). c. Tonicity takes into account the permeability of the membrane to the solutes. If the solutes can cross the membrane, the tonicity will change. i. If you place RBCs in a 0.3m solution of urea, the tonicity will not be isotonic. Urea can cross into the RBCs and draw water with it. ii. These cells will eventually burst (lyse). d. Solutions with a lower solute concentration than the cell are hypoosmotic and hypotonic. i. Will pull water into the cell; cell will swell and could lyse. e. Solutions with a higher solute concentration than the cell are hyper osmotic and hypertonic. i. Will pull water out of the cell; cell will shrivel up and could crenate. E. Regulation of Blood Osmolality 1. Constant osmolality must be maintained, or neurons will be damaged. 2. Osmoreceptors in the hypothalamus detect increases in osmolality (due to dehydration). This triggers: a. Thirst b. Decreased excretion of water in urine 3. With a lower plasma osmolality, osmoreceptors are not stimulated, so more water is excreted in urine. III. CarrierMediated Transport A. Introduction 1. Molecules that are large or polar cannot diffuse across the membrane. 2. Includes amino acids, glucose, and other organic molecules. 3. Carrier proteins within the plasma membrane move these molecules across. 4. Characteristics of the carriers a. They are specific to a given molecule. b. There may be the competition for similar carriers or molecules c. Saturation – number of carriers is limited 5. Some proteins can transport more than one molecule, but then there is a competition effect. 6. Transport rates increase with increased molecules concentration until saturation is met; this is transport maximum where all carriers are in use. B. Facilitated Diffusion 1. Powered by the random movement of molecules (no ATP used) 2. Net movement from high to low concentration 3. Requires specific carriermediated proteins 4. Transport proteins may always exist in the plasma membrane or be inserted when needed. 5. Facilitated diffusion – glucose a. Transport carriers for glucose are designated GLUT followed by the number of the isoform b. GLUT1 – CNS c. GLUT2 – pancreatic beta cells and hepatocytes d. GLUT3 – neurons e. GLUT4 – adipose tissue and skeletal muscles; can be inserted into the plasma membrane of skeletal muscle when stimulated. C. Active Transport 1. Sometimes molecules must be moved from an area of low concentration to an area of high concentration (move uphill) a. This requires the expenditure of ATP. b. Often, these carriermediated proteins are called pumps. 2. Primary active transport a. Occurs when the hydrolysis of ATP is directly responsible for the carrier protein function. b. The transport protein is also an ATPase enzyme that will hydrolyze ATP c. Pump is activated by phosphorylation using a Pi from ATP. 3. The Ca2+ Pump a. Located on all cells and in the endoplasmic reticulum of striated muscle cells b. Removes Ca2+ from the cytoplasm by pumping it into the extracellular fluid or cisternae of the ER c. Creates a strong concentration gradient for rapid movement of Ca2+ back into the cell d. Aids in the release of neurotransmitters in neurons and in muscle contraction 4. Na+/K+ pump a. Found in all body cells b. ATPase enzyme pumps 3 Na+ out of the cell and 2 K+ into the cell c. Serves 3 functions: i. Provides energy for coupled transport of other molecules ii. Helps to maintain membrane potentials iii. Maintains osmolality d. Steps of the Na+/K+ pump i. 3 Na+ from the cytoplasm move into the pump and bind ii. ATPase activated to hydrolyze ATP to ADP and Pi which blocks both openings iii. ADP released causing a shape change that allows 3 Na+ to exit pump to outside cell iv. 2K+ enter carrier from the outside, releasing the Pi v. Pump returns to original shape and releases 2K+ to the inside. 5. Secondary active transport a. Also called coupled transport b. The energy needed to move molecules across their concentration gradient is acquired by moving sodium back into the cell. c. Since the sodium was originally pumped out of the cell using ATP, this is considered active transport. d. Cotransport or symport – the other molecule is moved with sodium. This is the common way to transport glucose. e. Countertransport or antiport – the other molecule is moved in the opposite direction from sodium. i. An example is the uphill extrusion of Ca2+ from a cell. 6. Transport across Epithelial membranes a. Absorption – transport of digestive products across intestinal epithelium into the blood b. Reabsorption – transport of molecules out of the urinary filtrate back into the blood c. Involves transcellular transport: movement of molecules through the cytoplasm of the epithelial cells d. May also involve paracellular transport: movement across the tiny gaps between cells e. Involves many different types of carrier – mediated proteins at both ends of the epithelial cells such as the Na+/K+ pump or the Na+/H+ pump. f. Paracellular transport is limited by junctional complexes: i. Tight junctions: do not allow easy diffusion ii. Adherens junctions iii. desmosomes D. Bulk transport 1. Large molecules such as proteins, hormones, and neurotransmitters are secreted via exocytosis. a. Involves fusion of a vesicle with the plasma membrane b. Requires ATP 2. Movement of large molecules such as cholesterol into the cell requires endocytosis. a. Usually a transport protein interacts with plasma membrane proteins to trigger endocytosis. IV. The Membrane Potential A. Introduction 1. There is a difference in charge on each side of the plasma membrane due to: a. Permeability of the membrane b. Action of Na+/K+ pump c. Negatively charged molecules inside the cell 2. This difference in charge is called a potential difference 3. The potential difference makes the inside of the cell is negative compared to the outside. 4. Membrane Potential: K+ a. K+ accumulates at high concentrations in the cell because: b. The K+ concentration inside is 150 mM and outside it is 5mM. B. Equilibrium Potentials 1. Even with all the K+ inside the cell, the negative molecules inside and all of the sodium outside, the cell is more negative inside compared to outside. i. This potential difference can be measured as a voltage ii. Because the membrane is so permeable to K+, this difference is often maintained by K+, concentration gradient. 2. K+ Equilibrium a. Addressing just K+, the electrical attraction would pull K+ into the cell until it reaches a point where the concentration gradient drawing K+ out matches this pull in. i. K+ would reach an equilibrium, with more K+ inside than outside. ii. Normal cells have 150 mM K+ inside and 5mM K+ outside. b. The resulting potential difference measured in voltage would be the equilibrium potential (Ek) for K+; measured at 90 mV. i. This means the inside has a voltage 90mV lower than the outside. ii. This is the voltage needed to maintain 150 mM K+inside and 5mM K+ outside. 3. Na+ equilibrium a. Sodium is also an important ion for establishing membrane potential b. The concentration of sodium in a normal cell is 12mM inside and 145mM outside. c. To keep so much sodium out, the inside would hae to be positive to repel the sodium ions. d. The equilibrium potential for sodium is +66mV. e. The membrane is less permeable to Na+, so the actual membrane potential is closer to that of the more permeable K+. 4. Nerst equationv a. Used to calculate equilibrium potentials b. Based on ion concentrations c. Ex=61/z log [X0]/[Xi] i. Ex = equilibrium potential in mV for ion X ii. X0 = concentration of ion outside the cell iii. Xi = concentration of ion inside the cell iv. Z = valence of ion (+1 for sodium or potassium) C. Resting Membrane Potentials 1. Membrane potential of a cell not producing any impulses. Depends on: a. Ratio of concentrations of each ion on either side of the membrane b. Specific permeability to each ion 2. K+, Na+, Ca2+, and Cl contribute to the resting potential. 3. Membrane potential of a cell not producing any impulses a. Because the membrane is most permeable to K+, it has the greatest influence. b. A change in the permeability of the membrane for any ion will change the resting potential. c. A change in concentration of any ion inside or outside the cell will change the resting potential. d. Key to how neurons work! 4. In most cells, the resting potential is between 65mV and 85mV. a. Neurons are usually at 70mV. b. Close to K+ equilibrium potential. 5. When a neuron sends an impulse, it changes the permeability of Na+, driving the membrane potential closer to the equilibrium potential for Na+. 6. Role of Na/K pump a. Acts to counter K+ leaking out b. It transports 2 K+ in for every 3 Na+ out to maintain the voltage difference. c. Keeps both the resting potential and the concentration differences stable – electrogenic effect. V. Cell Signaling A. Introduction 1. Cells communicate using chemical signals. 2. Types: a. Gap junctions: allow adjacent cells to pass ions and regulatory molecules through a channel between the cells direct electrical coupling between cells (heart and muscle cells) b. Paracrine signaling: cells within an organ secrete molecules that diffuse across the extracellular space to nearby target cells; often called local signaling (histamines in mast cells and blood vessels) c. Synaptic signaling: involves neurons secreting neurotransmitters across a synapse to target cells very very specific (just one cell) d. Endocrine signaling: involves glands that secrete hormones into the bloodstream; these can reach multiple target cells throughout the body. (insulin after a meal) 3. Receptor proteins a. A target cell receives a signal because it has receptor proteins specific to it on the plasma membrane or inside the cell i. Nonpolar signal molecules (hydrophobic) such as steroid hormones, thyroid hormone, and nitric oxide gas can penetrate the plasma membrane and interact with receptors inside the cell. – often are transcription factors (some have membrane receptors as well) ii. Large, polar signal molecules (hydrophilic) such as epinephrine, acetylcholine, and insulin bond to receptors on the plasma membrane. B. Second messengers the intermediate factor 1. Polar or large signal molecules bind to receptors on the cell surface. 2. For many of these, intermediaries called second messengers are activated inside the cell to affect change; may be ions (Ca2+) or other molecules. Calcium is common because it has a high concentration outside in comparison to the inside, and a small change can be significant. 3. Second messengers – cAMP a. Cyclic adenosine monophosphate (cyclic AMP or cAMP) is a common second messenger. b. Steps to activate i. A signaling molecule binds to a receptor. ii. This activates an enzyme that produces cAMP from ATP iii. cAMP activates other enzymes. iv. Cell activities change in response C. GProteins 1. Receptor proteins that bind to a single and enzyme proteins that produce a second messenger are rarely together. They require something to shuttle between them. 2. Gproteins are made up of 3 subunits – alpha, beta, and gamma 3. Subunits dissociate when a signal molecule binds to the receptor and travel to the enzyme or ion channel. More active than not, the alpha is the active subunit. To inactive, they dissociate from their effectors and wait for the next signal molecule to come by Human Physiology – Chapter 7 Study Guide Notes from powerpoint, notes from in class, Important vocabulary, important molecules and compounds (such as proteins, lipids, neurotransmitters, etc.), Specific body part (cellular level and up). Disease The Nervous System: neurons and Synapses I. Neurons and Supporting Cells A. Introduction to the Nervous System 1. Divided into: a. Central nervous system: brain and spinal cord everything encased in bone b. Peripheral nervous system: cranial and spinal nerves 2. Tissue is composed of two types of cells: a. Neurons that conduct impulses excitable, command motor responses b. Glial cells (neuroglia) that support the neurons. “glue” that holds the brain together. Some astrocytes are a bit more active than people thought…. B. Neurons 1. Structural and functional units of the nervous system 2. General functions: a. Respond to chemical and physical stimuli b. Conduct electrochemical impulses – the electro part is due to the movement of ions, aka action potentials. Similar to electrons in wires, but moves via ions. We will get to this more later. c. Release chemical regulators d. Enable perception of sensory stimuli, learning, memory, and control of muscles and glands – responsible for everything we do. 3. Most cannot divide, but may be able to be repaired some places in the brain (e.g. the hippocampus) have been shown to generate new neurons. 4. General structure of neurons a. Neurons vary in size and shape, but they all have: 1) A cell body that contains the nucleus and other organelles; cluster in groups called nuclei in the CNS and ganglia in the PNS 2) Dendrites: receive impulses and conducts a graded impulse toward the cell body 3) Axon: conducts action potentials away from the cell body b. Axons 1) Vary in length from a few millimeters to a meter 2) Connected to the cell body by the axon hillock where action potentials are generated at the initial segment of the axon. High concentration of ion channels. 3) Can form many branches called axon collaterals 4) Covered in myelin with open spots called nodes of Ranvier. Wrapping of glial cells creates these nodes. Myelination helps action potentials move faster. 5. Axonal transport a. An active process needed to move organelles and proteins from the cell body to axon terminals b. Fast component moves membranous vesicles c. Slow components move microfilaments, microtubules and proteins d. Anterograde transport – from cell body to dendrites and axon; uses kinesin molecular motors e. Retrograde transport from dendrites and axon to the cell body; uses dynein molecular motors. How viruses infect the brain. Picked up by synaptic terminals and used to change the genetic properties of neurons. C. Classification of Neurons and Axons 1. Functional classification of neurons – based on direction impulses are conducted a. Sensory neurons: conduct impulses from sensory receptors to the CNS (e.g. rotational acceleration, blood pressure, etc.) these pick up information and transfer it to association neurons. b. Motor neurons: conduct impulses from the CNS to target organs (muscles or glands) c. Association/interneurons: located completely within the CNS and integrate functions of the nervous system 2. Motor neurons a. Somatic motor neurons: responsible for reflexes and voluntary control of skeletal muscles b. Autonomic motor neurons: innervate involuntary targets such as smooth muscle, cardiac muscle, and glands – these are things you do not usually think about (e.g. Peristalsis in GI system, changes in vasodilation, etc.) 1) Sympathetic – emergency situations; “fight or flight” (or freeze); activation of epinephrine – tends to activate the whole system. 2) Parasymphathetic – normal functions; “rest and digest”; decreases activity of most systems, except for GI activity. 3. Structural classification of neurons a. Based on the number of processes that extend from the cell body. b. Pseudounipolar: single short process that branches like a T to form 2 longer processes; sensory neurons c. Bipolar neurons: have two processes, one on either end; found in retina of eye d. Multipolar neurons: several dendrites and one axon; most common type. 4. Classification of axons a. Nerves are bundles of axons located outside the CNS b. Most are composed of both sensory and motor neurons and are called mixed nerves. c. Some of the cranial nerves have sensory fibers only (e.g. olfactory, optic). d. A bundle of axons in the CNS is called a tract. D. Neuroglia (glial cells) 1. Cells that are nonconducting (mostly) but support neurons 2. Two types are found in the PNS: a. Schwann cells (neurolemocytes): form myelin sheaths around peripheral axons – only influences one axon at a time. b. Satellite cells (ganglionic gliocytes): support cell bodies within the ganglia of the PNS 3. Four types are found in the CNS: a. Oligodendrocytes: form myelin sheaths around the axons of CNS neurons – analogous to Schwann cells. Can wrap around multiple axons at once. b. Microglia: migrate around CNS tissue and phagocytize foreign and degenerated material. 510% of brain cells. Important for immuoprotection of the brain, and engulfs dying neurons and other glial cells, as well as pathogens. c. Astrocytes: regulate the external environment of the neurons cell body with projections and end feet that associate with neurons and blood vessels. d. Ependymal cells: line the ventricles and secrete cerebrospinal fluid. (via cilia like projections) E. Neurilemma and Myelin 1. Myelin sheath in the PNS a. All axons in the PNS are surrounded by a sheath of Schwann cells called the neurilemma, or sheath of Schwann. b. These cells wrap around the axon to form the myelin sheath in the PNS. c. Gaps between Schwann cells, called nodes of Ranvier, are left open. d. Small axons (2 micrometers in diameter) are usually unmyelinated. e. Even unmyelinated axons in the PNS have a neurilemma but lack the multiple wrappings of the Schwann cell plasma membrane f. Myelinated axons conduct impulses more rapidly. 2. Myelin Sheath in CNS a. In the CNS, the myelin sheath is produced by oligodendrocytes. b. One oligodendrocyte sends extensions to several axons and each wraps around a section of an axon. c. Produces the myelin sheath but not a neurilemma d. Myelin gives these tissues (axons) a white color = white matter. e. Gray matter is cell bodies and dendrites which lack myelin sheaths small axons are usually unmyelinated. 3. Regeneration of a cut neuron a. When an axon in the PNS is cut, the severed part degenerates, and a regeneration tube is reformed by Schwann cells; normal regrowth occurs. Initially schwann factors produce factors that inhibit growth. When there is damage to the cell, neurotrophic factors are released to help cause the cell to grow. 1) Growth factors are released that stimulate growth of axon sprouts within the tube. 2) New axon eventually connects to the undamaged axon or the effector. b. CNS axons are not as able to regenerate. 1) Death receptors form that promote apoptosis of oligodendrocytes. 2) Inhibitory proteins in the myelin sheath prevents regeneration. 3) Glial scars from astrocytes form that also prevent regeneration. 4) Demyelination diseases: multiple sclerosis – motor control problems, visual impairment, etc. 4. Neurotrophins a. Promote neuronal growth in the fetal brain 1) Nerve growth factor (NGF) 2) Brainderived neurotrophic factor (BDNF) 3) Glialderived neurotrophic factor (GDNF) 4) Neurotrophin3, neurotrophin4/5 b. In adults, neurotrophins aid in the maintenance of sympathetic ganglia and the regeneration of sensory neurons. F. Astrocytes 1. Most abundant glial cell 2. Processes with endfeet associate with blood capillaries and axon terminals. 3. Influences interactions between neurons and between neurons and blood – influences the amount of transmitter, or releases other cofactors. 4. Astrocyte functions a. Take up K+ from the extracellular environment to maintain ionic environment for neurons. b. Take up extra neurotransmitter released from axon terminals, particularly glutamate. Chemicals are recycled. (can affect the duration of a synaptic event). c. Endfeet around capillaries take up glucose from blood for use by neurons to make ATP; converted first to lactic acid d. Can store glycogen and produce lactate for neurons to use. e. Needed for the formation of synapses in the CNS. f. Regulate neurogenesis in regions of the adult brain g. Form the bloodbrain barrier h. Release transmitter molecules (gliotransmitters) that can stimulate or inhibit neurons; includes glutamate, ATP, adenosine, Dserine. (interacts with glutamate to enhance glutamate receptors). Regulates receptors that can change the function of ion channels. 5. Astrocytes and neural activity a. Although astrocytes do not produce action potentials, they can be excited by neurons via release of ATP. b. This causes a rise intracellular Ca2+, which can cause the astrocyte to release prostaglandin E2, from the endfeet on the blood capillary, increasing blood flow. (prostaglandin release) 6. Bloodbrain barrier a. Capillaries in the brain do not have pores between adjacent cells, but are joined by tight junctions. b. Substances can only be moved by very selective processes of diffusion through endothelial ells, active transport, and bulk transport. c. Movement is transcellular not paracellular. d. Astrocytes influence the production of ion channels and enzymes that can destroy toxic substance by secreting glialderived neurotrophic factor. e. Creates problems with chemotherapy of brain diseases because many drugs cannot penetrate the bloodbrain barrier. E.g. Parkinson’s disease treatments (Ldopa is used in place of dopamine). II. Electrical Activity in Axons A. Resting membrane potential 1. Neurons have a resting potential of 70mV. a. Established by large negative molecules inside the cell b. Na/K pumps c. Permeability of the membrane to positively charged, inorganic ions. 2. At rest, there is a high concentration of K+ inside the cell and Na+ outside the cell. 3. Altering membrane potential a. Neurons and muscle cells can change their membrane potentials. b. Called excitability c. Caused by changes in permeability to certain ions d. Ions will follow their electrochemical gradient = combination of concentration gradient and attraction to opposite charges. e. Flow of ions are called ionic currents which occur in limited areas where ion channels are located (hydration shell). 4. Changes in membrane potential a. At rest, a neuron is considered polarized when the inside is more negative than the outside. b. When the membrane potential inside the cell increases (becomes more positive), this is called depolarization. c. A return to resting potential is called repolarization. d. When the membrane potential inside the cell decreases (becomes more negative), this is called hyperpolarization. e. Depolarization occurs when positive ions enter the cell (usually Na+). f. Hyperpolarization occurs when positive ions leave the cell (K+) or negative ions (Cl) enters the cell. g. Depolarization of the cell is excitatory. (stimulation) h. Hyperpolarization is inhibitory. i. Usually it is sodium, but sometimes potassium and chloride can be used to alter the electrochemical gradient. B. Ion gating in axons 1. Changes in membrane potential are controlled by changes in the flow of ions through channels. a. K+ has two types of channels: 1) Not gated (always open); sometimes called K+ leakage channels help to maintain the resting membrane potential. 2) Voltagegated K+ channels; open when a particular membrane potential is reached; closed at resting potential At least 12 different families. b. Na+ has only voltagegated channels that are closed at rest; the membrane is less permeable to Na+ than K+ at rest. c. Nerst equation for K and Na 1) E(K) = 90mV 2) E(Na) = +66 mV 2. VoltageGated Na+ Channels a. Na+ channels open if the membrane potential depolarizes to 55mV (threshold potential). 1) The protein is made of 1 long string of amino acids. It changes due to a binding of the positively charged side change. When the inside is negative, it holds the sides down. When it becomes positive, the side chains pop open. 2) Ball and chain model. 3) Closed (deactivated) – open – inactivated: MUST GO IN THIS ORDER! b. Sodium rushes in due to the electrochemical gradient. c. Membrane potential climbs toward sodium equilibrium potential. d. These channels are deactivated at +30mV. 3. VoltageGated K+ Channels a. At around +30mV, voltagegated K+ channels open, and K+ rushes out of the cell following the electrochemical gradient. b. This makes the cell repolarize back toward the potassium equilibrium potential. C. Action potentials 1. At threshold membrane potential (55mV), voltagegated Na+ channels open, and Na+ rushes in. As the cell depolarizes, more Na+ channels are open, and the cell becomes more and more permeable to Na+. a. This is a positive feedback loop. b. Causes an overshoot of the membrane potential (overshoots 0 mV). Cell tries to get up to the sodium potential (+66). c. Membrane potential reaches +30mV. Sodium channels are deactivated. d. This is called depolarization. 2. At +30mV, Na+ channels close, and K+ channels open. a. Results in repolarization of the membrane potential. b. This is a negative feedback loop. 3. AfterHyperpolarization a. Repolarization actually overshoots resting potential and gets down to 85mV. b. This does not reach potassium equilibrium potential because voltagegated K+ channels are deactivated as the membrane potential falls. Important: channels become DEACTIVATED, not inactivated. (mistake in slides) c. Na/K pumps quickly reestabilish resting potential. 4. AllorNone Law a. Once threshold has been reached, an action potential will happen. b. The size of the stimulus will not affect the size of the action potential; it will always reach +30mV. c. The size of the stimulus will not affect action potential duration 5. Coding for Stimulus Intensity a. A stronger stimulus will make action potentials occur more frequently. (frequency modulated) b. A stronger stimulus may also activate more neurons in a nerve. This is called recruitment. 6. Refractory Periods a. Action potentials can only increase in frequency to a certain point. There is a refractory period after an action potential when the neuron cannot become excited again. b. The absolute refractory period occurs during the action potential. Na+ channels are inactive (not just closed). c. The relative refractory period is when K+ channels are still open. Only a very strong stimulus can overcome this. d. Each action potential remains a separate, allornone event. 7. Cable properties of neurons a. Cable properties refer to the ability of neurons to conduct charges through their cytoplasm b. Poor due to high internal resistance to the spread of charges and leaking of charges through the membrane c. Neurons could not depend on cable properties to move an impulse down the length of an axon. D. Conduction of Nerve Impulses 1. When an action potential occurs at a given point on a neuron membrane, voltagegated Na+ channels open as a wave down the length of the axon. 2. The action potential at one location serves as the depolarization stimulus for the next region of the axon. 3. Conduction in an unmyelinated neuron a. Action potentials are produced down the entire length of the axon at every patch of membrane. b. This makes the conduction rate slow c. The amplitude of the action potential in each patch of membrane is the same – conducted without decrement 4. Conduction in a myelinated neuron a. Myelin provides insulation, improving the speed of action potential conduction. Myelin acts like duct tape on a water hose, blocking leakage of the current up through the sides of the membrane. b. Nodes of Ranvier allow Na+ and K+ to cross the membrane every 12 mm. c. Na+ ion channels are concentrated at the nodes. d. Action potentials “leap” from node to node. e. This is called salutatory conduction. 5. Action Potential Conduction Speed a. Increased by 1) Increased diameter of the neuron. This reduces resistance to the spread of charges via cable properties 2) Myelination because of salutatory conduction. b. Examples 1) Thin, unmyelinated neuron speed – 1.0 m/sec 2) Thick, myelinated neuron speed 100 m/sec III. The synapse A. Introduction 1. A synapse is a functional connection between a neuron and the cell it is signaling. a. In the CNS, this second cell will be another neuron. b. In the PNS, the second cell will be in a gland or muscle (neuromuscular junctions) 2. If one neuron is signaling another neuron, the first is called the presynaptic neuron, and the second is called the postsynaptic neuron. a. A presynaptic neuron can signal the dendrite, cell body, or axon of a second neuron b. There are axodendritic (axon makes contact with dendrite), axosomatic (axon to body), and axoaxonic (axon to axon) synapses. c. Most synapses are axodendritic and are 1 direction. B. Electrical synapses: electrical synapses occur in smooth muscle and cardiac muscle (think of organized contractions), between some neurons of the brain (especially during development) , and between glial cells. 1. Cells are joined by gap junctions. 2. Stimulation causes phosphorylation of connexin proteins to open or close the channels C. Chemical synapses 1. Most synapses involve the release of a chemical called a neurotransmitter from the axon’s terminal buttons. 2. The synaptic cleft is very small, and the presynaptic and postsynaptic cells are held together by cell adhesion molecules. 3. Release of neurotransmitters a. Neurotransmitters are enclosed in synaptic vesicles in the axon terminal. 1) When the action potential reaches the end of the axon, voltagegated Ca2+ channels open. 2) Ca2+ stimulates the fusing of synaptic vesicles to the plasma membrane and exocytosis of neurotransmitter. 3) A greater frequency of action potential results in more stimulation of the postsynaptic neuron. b. Ca2+ and synaptic vesicles 1) When Ca2+ enters the cell, it binds to a protein called synaptotagmin that serves as a Ca2+ sensor. 2) Vesicles containing neurotransmitter are docked at the plasma membrane by three SNARE proteins. 3) The Ca2+ synaptotagmin complex displaces part of SNARE, and the vesicle fuses. 4) Forms a pore to release the neurotransmitter. 4. Actions of Neurotransmitter a. Neurotransmitter diffuses across the synapse, where it binds to a specific receptor protein. 1) The neurotransmitter is referred to as the ligand. 2) This results in the opening of chemically regulated ion channels (also called ligandgated ion channels) many receptors are ion channels in themselves; therefore, when the transmitter binds, it causes a pore to form allowing ions in or out. b. Graded potential 1) When ligandgated ion channels open, the membrane potential changes depending on which ion channel is open. i. Opening Na+ or Ca2+ channels results in a graded depolarization called an excitatory postsynaptic signal (EPSP). ii. Opening K+ or Cl channels results in a graded hyperpolarization called inhibitory postsynaptic potential (IPSP). 2) EPSPs and IPSPs i. EPSPs move the membrane potential closer to threshold; may require EPSPs from several neurons to actually produce an action potential. 1. IPSPs move the membrane potential farther from threshold. 2. IPSPs can counter EPSPs from other neurons so summation of EPSPs and IPSPs at the initial segment of the axon (next to the axon hillock) determines whether the action potential occurs. IV. Acetylcholine – CAN’T FIND MY NOTES ON ACETYLCHOLINE. A. Acetylcholine (Ach) 1. introduction a. In some chases, Ach is excitatory, and in other cases it is inhibitory, depending on the organ involved. b. Excitatory in some areas of the CNS, in some autonomic motor neurons, and in all somatic motor neurons c. Inhibitory in some autonomic motor neurons. 2. Two types of Acetylcholine receptors a. Nicotinic ACh receptors 1) Can be stimulated by nicotine 2) Found on the motor end plate of skeletal muscle cells, in autonomic ganglia, and in some parts of the CNS. b. Muscarinic Ach receptors 1) Can be stimulated by muscarine (From poisonous mushrooms) 2) Found in CNS and plasma membrane of smooth and cardiac muscles and glands innervated by autonomic motor neurons. c. Agonists and antagonists 1) Agonists: drugs that can stimulate the receptor i. Nicotine for nicotinic ACh receptors ii. Muscarine for muscarinic ACh receptors 2) Antagonists: drugs that inhibit the receptor i. Curare is an antagonist for nicotinic receptors. ii. Atropine for muscarinic receptors. B. Chemically regulated channels 1. Binding of a neurotransmitter to a receptor can open an ion channel in one of two ways: a. Ligandgated channels b. Gprotein coupled channels 2. Ligandgated channels a. The receptor protein is also an ion channel; binding of the neurotransmitter directly opens the ion channel. b. Nicotinic ACh receptors are ligandgated channels with two receptor sites for two ACh molecules. c. Binding of 2 acetylcholine molecules opens a channel that allows both Na+ and K+ passage. 1) Na+ flows in, and K+ flows out. 2) Due to electrochemical gradient, more Na+ flows in than K+ out creating an EPSP. 3. GProtein Coupled channels a. The neurotransmitter receptor is separate from the protein that serves as the ion channel. 1) Binding at the receptor opens ion channels indirectly by using a Gprotein 2) Muscarinic ACh receptors interact with ion channels in this way as well as many other neurotransmitter receptors. b. Associated with a Gprotein 1) Gproteins have three subunits (alpha, beta, and gamma) 2) Binding of one acetylcholine results in the dissociation of the alpha subunit. 3) Either the alpha or betagamma diffuses through the membrane to the ion channel. 4) This opens or closes the channel for a short period of time. 5) The Gprotein subunits dissociate from the channel and it closes. c. Binding of acetylcholine opens K+ channels in some tissues (IPSP) or closes K+ channels in others (EPSP). 1) In the heart, K+ channels are opened by the betagamma complex, creating IPSPs (hyperpolarization) that slows the heart rate. 2) In smooth muscle of the stomach, K+ channels are closed by the alpha subunit, producing EPSPs (Depolarization) and the contraction of these muscles. C. Acetylcholinesterase (AchE) 1. AChE is an enzyme that inactivates ACh activity shortly after it binds to the receptor. 2. Hydrolyzes ACh into acetate and choline, which are taken back into the presynaptic cell for reuse. D. Ach in the PNS 1. Somatic motor neurons form interactions called neuromuscular junctions with muscle cells. 2. The area on the muscle cell with receptors for neurotransmitter is called the motor end plate. a. EPSPs formed here are often called end plate potentials. b. End plate potentials open voltagegated Na+ channels, which result in an action potential. c. This produces muscle contraction. 3. Interruption of Neuromuscular Transmission a. Certain drugs can block neuromuscular transmission. b. Curare is an antagonist of acetylcholine (Nicotinic). It blocks ACh receptors so muscles do not contract. 1) Lea
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'