BIOL 4160 Test 1

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  1. Basic Cell Functions
    • - Obtain nutrients and oxygen from surrounding environment
    • - Perform chemical reactions that provide energy, and eliminate carbon dioxide and other wastes to surrounding environment
    • - Synthesize needed cellular components
    • - Cell-specific transport
    • - Sensing & responding to changes in the environment
    • - Reproduction (exception: nerve cells and muscle cells)
  2. Tissues
    Groups of cells with similar structure and specialized function
  3. Four Primary Types of Tissues
    • - Muscle tissue
    • - Nervous tissue
    • - Epithelial tissue
    • - Connective tissue
  4. Muscle tissue
    • - Specialized for contracting
    • - Generate tension to produce movement
  5. Three Types of Muscle Tissue
    • Skeletal Muscle: moves the skeleton
    • Cardiac Muscle: pumps blood out of the heart
    • Smooth Muscle: encloses and controls movement of contents through hollow tubes and organs
  6. Nervous Tissue
    • Consists of cells specialized for initiating and transmitting electrical impulses
    • Found primarily in brain, spinal cord, and nerves
    • Sympathetic & Parasympathetic
  7. Epithelial Tissue
    • Consists of cells specialized for exchanging materials between the cell and its environment
    • Organized into two general types of structures:
    • - epithelial sheets (lungs, intestines, kidneys)
    • - secretory glands
  8. Connective Tissue
    • Connects, supports, and anchors various body parts (collagen or elastic fibers)
    • Distinguished by having relatively few cells dispersed within an abundance of extracellular material
    • Examples: tendons, bone, blood
  9. Organs
    Consist of two or more types of primary tissues that function together to perform a particular function or functions
  10. Body Systems
    • Groups of organs that perform related functions and interact to accomplish a common activity essential to survival of the whole body
    • Do not act in isolation from one another
    • Human body has 11
  11. Claude Bernard
    • Put forth the idea of constant internal milieu
    • Noted that mammals are able to regulate their internal environment within a narrow range
  12. Walter Cannon
    • Extended Bernard's notion to the organization of cells, tissues, and organs
    • First to coin the term "homeostasis"
    • "The maintenance of static or constant conditions in the internal environment" in face of constant environmental changes (temperature and salinity)
  13. Extracellular fluid
    • Fluid environment in which the cells live (fluid outside the cells)
    • Two components: plasma & interstitial fluid
  14. Intracellular fluid
    Fluid contained within all body cells
  15. "internal milieu"
    body cells within a multicellular vertebrate are contained in a watery internal environment through which life-sustaining exchanges are made
  16. Homeostatically-regulated variables (in ECF)
    • Concentration of water, salt, and other electrolytes
    • Concentration of nutrient molecules
    • Concentration of O2 and CO2
    • Concentration of waste products
    • pH
    • Extracellular volume & pressure
    • Temperature
  17. Hypoosmotic
    • Below normal range of osmolality
    • Less that ~295 mOsM
  18. Hyperosmotic
    • Above normal osmolality range
    • Higher than ~295 mOsM
  19. Normal Range of Osmolality
    ~295 mOsM
  20. Hyponatremia
    • Below normal range of Na+
    • Less than 138-146 mM
  21. Hypernatremia
    • Above normal range of Na+
    • Higher than 138-146 mM
  22. Normal Range of Na+
    138-146 mM
  23. Hypokalemia
    • Below normal range of K+
    • Less than 3.8 - 5.0 mM
  24. Hyperkalemia
    • Above normal range of K+
    • Higher than 3.8 - 5.0 mM
  25. Normal Range of K+
    3.8 - 5.0 mM
  26. Hypoxemia
    • Below normal range of O2 (at capillaries)
    • Less than 35-45 mm Hg
  27. Hyperoxemia
    • Above normal range of O2 (at capillaries)
    • Higher than 35-45 mm Hg
  28. Normal range of O2 (at capillaries)
    35-45 mm Hg
  29. Hypocapnia
    • Below normal range of CO2 (at capillaries)
    • Less than ~40-46 mm Hg
  30. Hypercapnia
    • Above normal range of CO2 (at capillaries)
    • Higher than ~40-46 mm Hg
  31. Normal range of CO2 (at capillaries)
    ~40-46 mm Hg
  32. Acidosis
    • Below normal range of pH
    • Less than 7.3 - 7.5
    • More acidic
  33. Alkalosis
    • Above normal range of pH
    • Higher than 7.3 - 7.5
    • More basic
  34. Normal range of pH
    7.3 - 7.5
  35. Hypothermia
    • Below normal range of temperature
    • Less than 37-38°C
  36. Hyperthermia
    • Above normal range of temperature
    • Higher than 37-38°C
  37. Normal range of temperature
  38. Hypoglycemia
    • Below normal range of glucose
    • Less than 80-120 mg/mL
  39. Hyperglycemia
    • Above normal range of glucose
    • Higher than 80-120 mg/mL
  40. Normal range of glucose
    80-120 mg/mL
  41. Homeostasis
    • Internal constancy
    • Maintenance of a relatively stable internal environment
    • Does NOT mean that composition, temperature, and other characteristics are absolutely unchanging
    • Essential for survival and function of all cells
  42. Extracellular Fluid Conditions
    • Isotonic: no net movement of water; no change in cell volume
    • Hypotonic: water diffuses into cells; cells swell
    • Hypertonic: water diffuses out of cells; cells shrink
  43. Compensatory Response
    • Regulatory Volume Increase OR Decrease
    • Cells return to a very specific cell size when they are perturbed
    • Cells regulate volume by changing the intracellular ion concentrations - water follows isosmotically
  44. Homeostatic Control System Levels
    • Cellular level: cells are responsible for regulating their own physiological state
    • Intrinsic level control: regulation at the local tissue or organ level (i.e. stretch of the heart controlling stroke volume)
    • Extrinsic level control: regulatory mechanisms initiated outside an organ (i.e. stroke volume increased by nervous & endocrine systems)
  45. Nervous System
    • Controls & coordinates bodily activities that require rapid responses (turning on/off lights)
    • Detects & initiates reactions to changes in external environment
    • Will only change things that are "hard-wired" or already have nerves in place
  46. Endocrine System
    • Secreting glands regulate activities that require duration rather than speed
    • Controls concentration of nutrients & controls internal environment's volume and electrolyte composition (by adjusting kidney function)
  47. Feedforward
    • Term using for responses made in anticipation of a change
    • Example: visual stimulation of digestive hormones before food is consumed
  48. Feedback
    • Responses made after change has been detected
    • Types of feedback systems: negative & positive
  49. Negative Feedback System
    • Primary type of homeostatic control
    • Opposes initial change
    • Components:
    • Sensor - monitors magnitude of a controlled variable
    • Control center - compares sensor's input with a set point
    • Effector - makes a response to produce a desired effect
  50. Positive Feedback System
    • Amplifies an initial change
    • Do not occur as often as negative feedback systems
    • Example: uterine contractions become increasingly stronger until the birth of the baby
  51. Lipid bilayer
    core of all biological membranes
  52. phospholipid-only bilayers
    • selectively permeable: impermeable to charged molecules; do not exclude lipid soluble materials
    • compartmentalization
    • barrier to free diffusion
  53. membrane permeability of a lipophilic substance
    (Mostly) a function of the membrane's solubility in lipids
  54. permeability across a lipid-only membrane
    • occurs passively
    • dependent on lipid solubility and size
  55. How do substances cross the phospholipid membrane?
    • Charged molecules: move down electrochemical gradient based on electric charge passively
    • Lipophillic substances or small hydrophillic solutes (no charge): move down concentration from [high] to [low]
    • Hydrophillic substances: move across both actively and passively
  56. Passive Diffusion
    • molecules have kinetic energy & will move spontaneously in a random fashion
    • tendency for lipophilic or small, non-charged molecules to move randomly from an area of high concentration to an area of low concentration
    • Ex: oxygen and carbon dioxide can dissolve in a phospholipid bilayer and diffuse across it
  57. Fick's Law
    • quantifying the rate of passive diffusion across a membrane
    • dQ/dt = A x D x dC/dx OR dQ/dt = A x P/mw x dC/dx
    • dQ/dt: rate of diffusion (quantity of substance per time) (mole/s)
    • A: cross-section area through which membrane diffuses; surface area of membrane available for transport (cm2)
    • D: diffusion coefficient of substance (cm2/s); OR P/mw (permeability of membrane to substance/molecular weight of molecule)
    • dC: concentration difference of substance between two points (moles/cm3)
    • dx: distance substance is diffusing (cm)
  58. Increased concentration gradient across membrane (dC) effect on rate of net diffusion?
    increase dC, increase dQ/dt
  59. Increased permeability of membrane to substance (P) effect on rate of net diffusion?
    increase P, increase dQ/dt
  60. Increased surface area of membrane (A) effect on rate of net diffusion?
    increase A, increase dQ/dt
  61. Increased molecular weight of substance (mw) effect on rate of net diffusion?
    increase mw, decrease dQ/dt
  62. Increased thickness of membrane (dx) effect on rate of net diffusion?
    increase dx, decrease dQ/dt
  63. osmosis
    net diffusion of water down its own concentation gradient
  64. tonicity of a solution
    determines whether cell remains same size, swells, or shrinks when a solution surrounds the cell
  65. Isotonic solution effect on cell
    cell remains the same size
  66. hypotonic solution effect on cell
    cell will swell
  67. hypertonic solution effect on cell
    cell shrinks
  68. osmolality
    dissolved solutes (K+, PO4-, acids, amino acids, glucose)/ solvent (water)
  69. channel protein function
    • tubular structures
    • allow passage of molecules through membrane
    • "door"
  70. carrier protein function
    • combine with substance to be transported
    • assist passage of molecules through membrane
  71. receptor protein function
    • binds with messenger molecule
    • causes cell to respond to message
  72. enzymatic protein function
    carry out metabolic reactions directly
  73. What is channel selectivity based on?
    • charge of ion
    • size of ion
    • ease of dehydration of ion (molecule is dehydrated to pass through pore)
    • charged amino acids lining the channel allow oppositely charged particles to permeate through membrane; repel like charges
  74. What stimulates protein-gated channels to open?
    • voltage
    • stretch
    • phosphorylation
    • ligand binding
  75. What are voltage-gated ion channels sensitive to?
    small variations in membrane potential (charge separation along the membrane)
  76. Passive transport through ion channels
    (channel-mediated transport)
    • transmembrane proteins
    • every channel contains an aqueous pore
    • ions flow down electrochemical gradients
    • are selective
    • are usually "gated" - voltage, ligands, stretch, phosphate-ligated
  77. Diseases in which ion channel impairment has been implicated
    • Secretory diarrhea: over-active potassium channels can cause too much water to exit the cell in the gastrointestinal tract
    • Insulin secretion: ion channels in beta cells of the pancreas
    • Hypertension: ion channels in vascular smooth muscle around arterioles play an important role in blood pressure regulation
    • Cardiac arrhythmias: defective channels disrupt ion balance of heart muscles, causing premature or prolonged cell firing and abnormal hearth rhythms
    • Cystic fibrosis: defective chloride channels fail to let chloride ions exit lung cells; the cells don't secrete enough fluid; thick dry mucous clogs airways
  78. pharmaceutical target
    • ion channels
    • Ex - Valium targets K+ channels to open in order to down regulate firing of neurons
  79. Carrier-mediated passive transport
    • Not a channel or pore (the protein never creates a fully open portal between ICF and ECF)
    • Substances move down existing electrochemical gradients
    • Inherently slower mechanism
    • "Turnstyle"
    • Ex - urea transporters; anion-bicarbonate exchangers
  80. Characteristics of all carrier-mediated transport
    • Carrier = transporter
    • Specificity
    • Competition - it is possible for other substrates to bind & impede transport
    • Saturation
  81. Conformations of carrier proteins
    • Uniport
    • Symport
    • Antiport
  82. Uniport
    • No directionality
    • Moves single solute down existing gradient
  83. active transport
    • carrier-mediated
    • transport against the electrochemical gradient for solute(s)
    • primary or secondary
  84. primary active transport
    • can transport up concentration gradients
    • have maximum transport rates (saturable)
    • requires ATP
    • called ATPases or PUMPS
    • creates concentration gradients
  85. P-type pump
    phosphorylation of an aspartate residue causes a conformational change of transport protein
  86. V-type proton pumps
    vacuolar localization leading to the transport of H+ from cytoplasm into organelles (that are highly acidic)
  87. Sodium-potassium pump
    • P-class primary active transporter
    • Only indirectly establishes electrochemical gradient
    • Co-transporter - 3 Na+ at once or 2 K+ at once
    • Antiporter - Na+ and K+ are transported in different directions
    • Electrogenic transporter - 3 Na+ transported out; 2 K+ transported in; net +1 charge transported OUT
  88. Na+/K+ ATPase
    • the sodium-potassium pump
    • most important active transport system
  89. co-transporter
    transports two or more solutes at once
  90. antiporter
    transports solutes in different directions
  91. ouabain
    • inhibitor of Na+/K+ ATPase
    • if ATPase is inhibited by ouabain, then secondary active transport goes down
  92. Calcium pumps
    • maintain intracellular Ca2+ levels
    • PMCA: plasma membrane calcium ATPase
    • SERCA: sarcoplasmic and endoplasmic reticulum calcium ATPases
  93. PMCA
    • P-class
    • Widely expressed
    • Low capacity, high affinity
    • maintains low cytosolic calcium levels - essential for the role of this ion in intracellular signaling
    • Calcium/calmodulin-sensitive
  94. SERCA
    • P-class
    • Widely expressed
    • Recovers calcium released from ER or SR (muscle)
  95. Secondary active transport
    • requires ATP indirectly
    • driven directly by the ion gradients established by ATP-requiring primary pump
    • can transport up concentration gradients
    • have maximum transport rates (carrier can become saturated)
  96. Michaelis constant
    • Km
    • measure of transport affinity
    • not really a "constant" - concentration leading to 0.5 of Vmax
    • inversely related to the affinity of an enzyme for substrate
  97. Vmax
    maximal rate of transport
  98. vesicular membrane transport
    • material is moved into or out of the cell wrapped in membrane
    • active method of membrane transport
    • two types - endocytosis and exocytosis
  99. endocytosis
    • process by which substances move into the cell
    • pinocytosis: nonselective uptake of ECF
    • phagocytosis: selective uptake of multimolecular particle
  100. exocytosis
    • provides mechanism for secreting large polar molecules
    • enables cell to add specific components to membrane
  101. charge separation
    • membrane potential
    • only exists immediately along the plasma membrane
  102. intracellular charge balance
    • "+" is mostly K+
    • "-" is Cl- and other charged substrates
  103. extracellular charge balance
    • "+" is mostly Na+
    • "-" is mostly Cl-
  104. membrane potential
    a potential difference existing across the plasma membrane due to the unequal distribution of charge
  105. 3 main factors determining the movement of an ion across the membrane
    • Active pumps
    • Concentration gradients (if the membrane is permeable)
    • Electrical gradients (if the membrane is permeable)
  106. what does membrane potential depend on?
    • ion concentration gradients (of permeable ions) across a cell's plasma membrane
    • permeability of the plasma membrane to these ions via leak channels
  107. What ions contribute to a membrane potential?
    • Only permeable ions (e.g. Na+, Cl-, K+)
    • At rest, K+ controls potential
  108. What effect do large charged substances have on membrane potential?
    • e.g. DNA and proteins
    • do not move across membrane
    • do NOT contribute to membrane potential
  109. Goldman equation
    Vm = RT/FZ log PK[K+]out + PNa[Na+]out + PCl[Cl-]out /PK[K+]in + PNa[Na+]in + PCl[Cl-]in
  110. Use of Goldman equation
    calculate membrane potential
  111. Nernst equation
    Eion = RT/FZ log [ion]out/[ion]in
  112. Use of Nernst equation
    • calculate the equilibrium potential for every ion
    • quantifies the energy in a concentration gradient across a membrane in mv
    • will only calculate the Eion for one ion at a time
  113. What maintains the concentration differences across a membrane?
    • at equilibrium, there is an electric potential at the surface of the membrane
    • the magnitude and the sign of the electrical potential is just great enough to counterbalance the tendency for ions to diffuse down their concentration gradients
  114. electrochemical gradient
    • the driving force available to a specific type of solute for its passive movement across a membrane
    • the amount of energy available to move an ion if a channel is available
  115. What does electrochemical gradient consider?
    • chemical potential due to an ion's concentration gradient
    • electrostatics - tendency to move relative to the membrane potential
  116. calculation of electrochemical gradient
    • Δµion = Vm - Eion
    • Membrane potential minus equilibrium potential for an ion
  117. What do neurons used to transmit electrical signals?
    stored energy in the electrical and chemical gradients
  118. When do electrical signals occur in neurons?
    when there are changes in the permeability of the membrane to specific ions (Na+ and K+ in particular)
  119. Two possible mechanisms for altering membrane permeability
    • alter the total number of protein channels on the membrane (slow process; remobilization from internal stores; gene transcription)
    • change the permeability of existing membrane-bound protein channels (alterations in protein configuration; fast)
  120. Membrane permeability at rest
    • neuron is approximately 40X more permeable to K+ than it is to Na+
    • sodium permeability is low in neurons during rest
    • -70mV resting potential
    • Vm influenced predominantly by equilibrium potential of K+
  121. Membrane permeability during action potential
    • caused by dramatic increase in permeability of neuron to Na+
    • membrane potential increase quickly to approximately +30mV
  122. anatomy of a common neuron
    • dendrites: input zone recieves incoming signals from other neurons
    • soma: cell body
    • axon hillock: trigger zone initiates action potential
    • axon: conducting zone transmits action potentials in undiminishing fashion (over varying distances)
    • axon terminals: output zone releases neurotransmitters that influence other cells
  123. depolarization
    • decrease in potential
    • membrane less negative

    Ex - increase PNa ; increase PCa ; decrease PK
  124. repolarization
    return to resting potential after depolarization
  125. hyperpolarization
    • increase in potential
    • membrane more negative

    Ex - increase PK ; decrease PNa
  126. voltage
    • electrical potential between two points
    • measured in mV in biological systems
  127. current
    • charge moved per unit time
    • amperes
  128. current clamping
    • can be used to study the passive & active properties of cell membranes
    • the current electrode generates a flow of ions
    • two voltage recording electrodes measure Vm at two points along the cell
  129. Injecting Currents: effect on Vm
    • Negative charge: make Vm more negative; hyperpolarize the membrane
    • Positive charge: make Vm less negative; depolarize the membrane
    • The more current that passes across the plasma membrane, the larger the change in Vm
  130. Graded Potentials
    • occur exclusively in the dendrites and cell bodies of neurons
    • neurotransmitters secreted by presynaptics neurons bind at receptors or ion channels in postsynaptic neuron
    • causes ion channels on postsynaptic neuron to open
    • results in "local" depolarization/hyperpolarization
    • the magnitude of depolarization/hyperpolarization is graded (depends on strength of stimulus and integration)
  131. resistance
    • function of ability of a current to pass across a membrane
    • stays constant
    • properties of a medium that retard current flow
    • measured in Ohms

  132. propagation of a current pulse
    when current pulses that elicit only passive responses are injected across a plasma membrane, the size of the potential change decreases the further away it is from the current source
  133. Depolarizing Graded Potentials
    • depolarize the cell
    • make it less negative
    • bring it closer to threshold potential
    • excitatory post-synaptic potentials (EPSPs)
    • increase the chance of exciting the axon to "fire" causing an action potential
  134. Hyperpolarizing Graded Potentials
    • hyperpolarize the cell
    • make it more negative
    • take it farther away from threshold potential
    • inhibitory post-synaptic potentials (IPSPs)
    • decrease the change of exciting axon to fire - they inhibit the action potential
  135. Initiation of Action Potentials
    • signals collected by dendrites and cell bodies are integrated towards the axon hillock
    • the sum of these responses determines wheter an action potential is produced
    • action potentials start at the axon hillock (trigger zone - highest density of voltage-gated sodium channels) in afferent neurons; in sensory neurons, the trigger zone is adjacent to the receptor
    • threshold depolarization is required to produce action potential
  136. Integration of Graded Potentials
    • stimuli are integrated in the dendrites and cells bodies of post-synaptic neurons
    • graded potentials degrade further away from source
    • no action potential will be produced if the amount of depolarization at the trigger zone is below threshold potential required to open VG Na+ channels
  137. Start of an Action Potential
    • combined action of stimuli is greater in strength
    • depolarization at trigger zone is above threshold even after diffusion
    • action potential is started when VG Na+ channels respond to the amount of depolarization within the cell
  138. passive electrical properties of cells
    universal (inherent) responses of all cells to current infusion
  139. active electrical properties of cells
    i.e. action potentials in excitable cells (neurons, muscle cells, etc.)
  140. How do action potentials differ from graded potentials?
    • the magnitude of secondary depolarization is identical in action potentials
    • action potentials do NOT diminish in strength as they travel along the cell (high fidelity signal transmission)
    • transmit over long distances
  141. Common Features of Action Potentials
    • Temporary: typically only a few ms in neurons
    • Threshold: specific membrane voltage must be reached for an action potential to occur
    • All or Nothing: occur fully or not at all; independent of the strength of initial stimulus
    • Self-propagating: once begun, travels throughout the cell unless physiologically blocked
    • Transmission without decrement (same level of depolarization)
  142. Steps of an Action Potential
    • Resting membrane potential
    • Depolarizing stimulus (graded potential)
    • Membrane depolarizes to threshold; Voltage-gated Na+ channels open and Na+ enters the cell; Voltage-gated K+ channels begin to open slowly
    • Rapid Na+ entry depolarizes cell
    • Na+ channels close and slower K+ channels open
    • K+ moves from cell to extracellular fluid
    • K+ channels remain open and additional K+ leaves the cell' hyperpolarizing it
    • Voltage-gated K+ channels close; some K+ enters the cell through leak channels
    • Cell returns to resting ion permeability
  143. Voltage-gated Sodium Channel
    • regulated by two gates
    • Na+ will only move through if both gates are open
    • at rest, activation gate blocks channel (closed)
    • depolarization causes opening of activation gate (open)
    • inactivation gate is closed after conformational change of activation gate (inactive)
    • no level of stimulation will open inactivation gate - ensures one-way propagation of action potential
  144. Voltage-gated Potassium Channel
    Activation gate has delayed opening triggered at threshold
  145. Na+ channel events during action potential
    • Resting membrane potential
    • Depolarizing stimulus
    • Voltage-gated Na+ channels open
    • Na+ enters the cell
    • Causes further depolarization
    • More voltage-gated Na+ channels open
  146. Role of K+ and Na+ Permeability in Setting Membrane Potential
    • Resting Vm is primarily set by K+ leak channels
    • Na+ permeability is minimal in resting neuron
    • Na+ permeability increases during an action potential (activation of voltage-gated channels)
    • K+ permeability also increases, but the increase is small in comparison to Na+ changes
  147. States of the voltage-gated Na+ channel
    • Open
    • Closed
    • Inactive
  148. What causes Na+ permeability to decrease after Na+ activation?
    • In addition to the voltage-sensitive activation gate, there is a time-dependent inactivation gate on the VG Na+ channel
    • Inactivation gate stops Na+ diffusion after a specified period of time until membrane potential returns to normal
    • Inactivation gate prevents entry of Na+ into cell even if voltage-sensitive gate is still open
  149. Absolute Refractory Period
    • Period when Na+ inactivation gate is blocking Na+ permeability
    • Neuron is unable to produce an action potential
    • 1 ms in duration
    • Ensures action potential fires only in one direction
  150. Relative Refractory Period
    • Na+ inactivation gate is no longer blocking channel
    • Na+ activation gate (voltage gate) is blocking Na+ permeability, but can be opened
    • A stronger than normal stimulus is required to produce a second action potential (of less strength)
  151. Directionality in Action Potential Movement
    • Na+ ions enter cell and travel longitudinally along neuron, causing Na+ channels in adjacent Nodes of Ranvier to open
    • Previously depolarized areas remain in a refractory period
  152. Role of voltage-gated K+ channels during repolarization
    • Voltage-gated potassium channels open at around +30mV
    • VG-K+ channels open more slowly than VG-Na+ channels
    • Potassium permeability increases (potassium leaves the cell at a higher rate)
    • Leak channels & VG-K+ channels make the permeability to potassium higher than in normal resting cells
  153. Ohm's Law
    • V = I x R
    • I = V/R
    • R =V/I

    describes the passive & active properties of neurons
  154. conductance
    • properties of a medium that promote current flow
    • "g"
  155. myelinated fibers
    • primarily composed of lipids
    • formed by oligodendrocytes in CNS
    • formed by Schwann cells in PNC
    • characteristic of many axons
    • reduces membrane current loss
  156. Effects of Myelination
    • increased membrane resistance
    • passive spread of current is faster and decreases less with distance

    membranes need to be insulated or they need to be larger in diameter
  157. Saltatory Conduction
    • propagates action potential faster than contiguous conduction because action potential does not have to be regenerated at myelinated section
    • myelinated fibers conduct impulses about 50X faster than unmyelinated fibers of comparable sizes
    • impulse jumps over sections of the fiber covered with insulating myelin
  158. Contiguous Conduction
    • conduction in unmyelinated fibers
    • action potential develops (spreads) along every portion of the membrane
  159. 2 types of action potential propagation
    • contiguous conduction
    • saltatory conduction
  160. Increasing Resistance of Axon Membrane
    • reduce leakiness of the membrane to ion loss
    • increases speed of propagation (if charges leak out, they no longer contribute to the longitudinal movement of ions along axon)
    • vertebrates insulate their axons with a myelin sheath
  161. Axon Diameter & Resistance
    • The greater the diametere of the axon, the lower is its resistance to ion movement
    • Increased speed of conduction
    • Reduces leakiness of membrane to ion loss
  162. nerve fascicle
    many axons bundled in connective tissue
  163. neuron cell body
    houses the nucleus and organelles
  164. dendrites
    • project from cell body
    • increase surface area available for receiving signals from other nerve cells
    • signal toward the cell body
  165. neuron input zone
    dendrites + cell body
  166. axon hillock
    • first portion of the axon plus region of the cell body from which the axon leaves
    • neuron's trigger zone
  167. axon
    • nerve fiber
    • single, elongated tubular extension that conducts action potentials away from the cell body
    • conducting zone of the neuron
    • collaterals - side branches of axon
  168. axon terminals
    • release chemical messengers that simultaneously influence other cells with which they come into close association
    • output zone of the neuron
  169. electrical synapse
    • current flows from one cell to another through gap junctions - direct communication
    • only excitatory (depolarizing)
    • current usually flows equally well in either direction
    • very rapid transmission - synchronize activity between cells
    • Ex: heart (cardiac myocytes)
  170. types of synaptic transmission
    • electrical synapse
    • chemical synapse
  171. chemical synapse
    • chemical messenger is transmitted across the junctio separating two neurons - NOT in direct contact
    • action potential at presynaptic neuron causes neurotransmitter release
    • neurotransmitters bind to receptors on postsynaptic membranes
    • excitatory OR inhibitory
  172. gap junctions
    • hexameric protein complexes
    • 6 units form pore in each cell & join
    • charge moves through; large proteins are excluded
  173. active zones
    regions of the presynaptic membrane where synaptic vesicles are allowed to fuse to release neurotransmitters through exocytosis
  174. How do chemical synapses operate?
    by the release of chemical transmitters contained in synaptic vesicles, triggered via Ca++ entry through voltage-gated channels (initiated by membrane depolarization)
  175. SNARE molecules
    proteins involved in synaptic vesicle targeting, docking, and release
  176. Post-Synaptic Potentials
    • Excitatory Post-Synaptic Potentials
    • Inhibitory Post-Synaptic Potentials
  177. EPSPs
    • excitatory post-synaptic potentials
    • increase the probability of an action potential
    • depolarizing effect
    • Ex: Na+ channel, Ca++ channel
  178. IPSPs
    • inhibitory post-synaptic potentials
    • decrease the probability of an action potential
    • hyperpolarizing effect
    • Ex: K+ channel
  179. No Summation
    • if an excitatory post-synaptic input is stimulated a second time after the first EPSP in the postsynaptic cell has dies off, a second EPSP of the same magnitude will occur
    • no action potential is produced
  180. Temporal Summation
    • If an EPSP is stimulated a second time before the first EPSP has died off, the second EPSP will add on to or "sum" with the first EPSP
    • may bring the postsynaptic cell to threshold
  181. Spatial Summation
    • EPSPs of equal magnitude are initiated simultaneously
    • the postsynaptic cell may be brought to threshold
  182. EPSP-IPSP Cancellation
    • simultaneous activation of an excitatory and an inhibitory postsynaptic input does not change the postsynaptic membrane potential
    • EPSP and IPSP cancel each other out
  183. Possible Results of the Sum of Activity in Presynaptic Inputs
    • No summation
    • Temporal summation
    • Spatial summation
    • EPSP-IPSP cancellation
  184. presynaptic inhibition
    prevention of release of neurotransmitter through synapse of inhibitory neuron with excitatory neuron at the axon terminal
  185. Convergence
    • on cell is influenced by many others
    • multiple neurons synapsing on one neuron
  186. Divergence
    • one cell influences many others
    • axon terminals may send depolarizing current to many other neurons
  187. neurotransmitters
    substances that mediate chemical signaling between neurons or between neurons & effector cells

    • must be present in the presynaptic terminal
    • must be released upon depolarization of presynaptic neuron
    • specific receptors must exist in the postsynaptic membrane
  188. Role of Neurotransmitters in Chemical Synapses
    • Depolarize or hyperpolarize postsynaptic cells
    • Increase and decrease the number of ion channels in postsynaptic membranes
    • Alter the rate of opening and closing of ion channels
    • Alter the sensitivity of channels to activating signals
    • Affect membrane potential of postsynaptic cell
  189. 2 broad classes of neurotransmitters
    • Small molecules: i.e. acetylcholine or dopamine; packaged in small vesicles; released by exocytosis at active zones due to an increase in intracellular calcium
    • Large molecules made up of chains of amino acids: packaged in large vesicles; released by exocytosis anywhere from the presynaptic membrane
  190. Neurotransmitter action in the synaptic cleft
    • Ca2+ enters the presynaptic cell because its concentration is greater outside the cell than inside
    • The neurotransmitter diffuses through the synaptic cleft and bind with receptor channel membranes that are located in both presynaptic and postsynaptic membranes
    • The time period from neurotransmitter release to receptor channel binding is less than a millionth of a second
  191. ionotropic channel receptor
    • direct action on the ion channels
    • alterations to Vm are fast
    • ligand-gated channel
    • binding of neurotransmitter to channel controls gating
  192. membrane delimited metabotropic ion channel
    • G protein-coupled receptor
    • when neurotransmitter is bound, the metabotropic ion channel activates a G protein
    • when activated G protein complex dissociates, part of the G protein directly interacts with the ion channel
  193. diffusible second messenger metabotropic ion channel
    • G protein-coupled receptor
    • when bound, activates a G protein that then activates an enzyme - adenylyl cyclase
    • the activated enzyme generates a diffusible second messenger (cAMP) from ATP
    • cAMP interacts to modulate ion channels
  194. 2 types of cholinergic receptors
    • nicotinic cholinergic receptors
    • muscarinic cholinergic receptors
  195. nicotinic receptors
    • activated by nicotine
    • found in postganglionic cell bodies in all autonomic ganglia
    • fast - ionotropic ion channels
  196. muscarinic receptors
    • activated by the muschroom poison muscarine
    • found on effector cell membranes
    • bind Ach released from parasympathetic postganglionic fibers
    • slow - metabotropic receptors
    • use intracellular "second messengers"
    • Ex: muscarinic AChR on cardiac muscle
  197. nicotinic AChR
    • pentamer
    • two alpha, one beta , one delta, and one gamma units
    • two acetylcholine binding sites

    • ionotropic receptor (receptor is an ion channel)
    • channel is equally permeable to Na+ and K+ cations
    • electrochemcial gradients of cations determines net movement of cations through the channel
  198. States of Neuromuscular AChR
    • open: activated (gate open)
    • closed: resting (gate closed)
    • desensitized: gate closed
  199. acetylcholine
    • NOT an amino acid, nor is it derived from one
    • precursor - choline
    • motor neurons - excitatory neurotransmitter in spinal cord (enervate skeletal muscle)
    • neuromuscular junction - excitatory neurotransmitter to influence muscle activation
    • ANS (smooth muscles of heart) - inhibitory neurotransmitter in postganglionic parasympathetic neurons; also in all ANS preganglionic neurons
    • brain - used EVERYWHERE (i.e. memory systems of CNS)
  200. choline
    • precursor of acetylcholine
    • cannot be synthesized in the body
    • must be obtained from external food sources
  201. Direct Action of Acetylcholine at Synapses
    • acts on cholinergic receptors
    • diffuses away from the synaptic cleft if not bound by cholinergic receptors
    • either taken up at presynaptic terminal and recycled or hydrolyzed by acetylcholinesterase
  202. AChE
    • acetylcholinesterase
    • hydrolyzes ACh

    inhibition of AChE will INCREASE activity
  203. glutamate
    • most important excitatory neurotransmitter (most prevalent in CNS)
    • excites about 90% of the postsynaptic terminals it contacts
    • derived from a-ketoglutarate
    • binds to ionotropic receptors causing depolarization by opening Na+ ion channels
    • at metabotropic receptors, it is modulatory
  204. Glutamate Receptors
    • AMPA: glutamate-ligated Na+ channel
    • NMDA: voltage and ligand gated channel
  205. Action of Glutamate
    • Glutamate is released from activated presynaptic neuron
    • Glutamate binds with both AMPA and NMDA receptors
    • Binding opens AMPA receptor-channel
    • Na+ entry through open AMPA channel depolarizes postsynaptic neuron, producing EPSP
    • Binding opens gate of NMDA receptor, but Mg2+ still blocks channel
    • Sufficient depolarization from AMPA opening plus other EPSPs drive Mg2+ out
    • Ca2+ entry through open NMDA channel activates Ca2+ second messenger pathways
    • Second messenger pathways promote insertion of additional AMPA receptors in postsynaptic membrane (increases sensitivity to glutamate)
    • Second messengers also stimulate release of nitric oxide (stimulates increase of glutamate release)
  206. mechanism to remove glutamate from synapse
    glutamate is take up by glial cells and eventually recycled
  207. GABA
    • g-Aminobutyric Acid
    • synthesized directly from glutamate
    • most important inhibitory neurotransmitter
    • present in high concentrations in CNS - prevents brain from becoming overexcited
    • binds to both ionotropic and metabotropic receptors
    • causes hyperpolarization by opening Cl- channels
    • used by inhibitory interneurons in spinal cord
  208. biogenic amine based neurotransmitters
    • tyrosine - dopamine, norepinephrine, epinephrine
    • tryptophan - serotonin
    • histidine - histamine
  209. catecholamines
    • dopamine
    • epinephrine
    • norepinephrine
    • serotonin
    • histamine
  210. Indirect action of norepinephrine in synaptic transmission
    • NE is synthesized from the amino acid tyrosine
    • the final stage of NE production occurs in the synaptic vesicles
    • NE is released into the synaptic cleft; acts on adrenergic receptors
    • NE acts through second messengers
    • NE is deactivated at synapse by methylation or reabsorbed by the presynaptic neuron
  211. conversion of norepinephrine to epinephrine
    • norepinephrine is released from all postganglionic neurons of autonomic sympathethic nervous system
    • conversion occurs in the adrenal medulla
    • enzyme is only found in the adrenal medulla
    • synthesis of the enzyme is activated by glucocorticoids made in adrenal cortex
  212. Adrenergic Receptor Subtypes
    • Alpha1: IP3/DAG
    • Alpha2: inhibits adenylyl cyclase; autoreceptors
    • Beta1: stimulate adenylyl cyclase; heart & kidneys
    • Beta2: stimulate adenylyl cyclase; lungs, GI tract, liver, uterus, vascular smooth muscle
    • Beta3: stimulate adenylyl cyclase; adipose tissue
  213. dopamine
    • synthesized in three steps from the amino acid tyrosine
    • direct precursor to norepinephrine
    • enzyme converts tyrosine L-DOPA
    • generally involved in regulatory motor activity
    • in basal ganglia: mood, sensory perception, & attention
    • schizophrenics - too much dopamine
    • Parkinson's Disease - too little dopamine
  214. direct forms of intracellular communication
    • gap junctions
    • transient direct linkup of cells' surface markers
  215. indirect forms of intracellular communication
    • paracrine secretion
    • neurotransmitter secretion
    • hormonal secretion - hormones reach & bind to receptors of target cells via circulating blood
    • neurohormone secretion - integrates neural system with endocrine system
  216. paracrine intracellular communication
    • products of cells (paracrine, local chemical messengers) diffuse in the ECF to affect neighboring cells in the immediate environment of their site of secretion
    • distributed by simple diffusion
    • do not enter the blood in any significant quantity because they are rapidly inactivated by locally existing enzymes
    • action is restricted to short distances
  217. properties of communication by gap junctions
    • Message transmission directly from cell to cell
    • local action
    • specificity depends on anatomic location
  218. properties of communication by synaptic transmission
    • message transmission across synaptic cleft
    • local action
    • specificity depends on anatomic location & receptors
  219. properties of communication by paracrine and autocrine secretion
    • message transmission by diffusion in interstitial fluid
    • locally diffuse
    • specificity depends on receptors
  220. properties of communication by endocrine secretion
    • message transmission by circulating body fluids
    • general action
    • specificity depends on receptors
  221. neuronal intercellular communication
    • information received as chemical signals, mainly by dendrites
    • processed electrically in dendritres, cell body, axon hillock
    • conducted electrically along axon
    • passed along as chemical signals to other neurons
  222. neurohormones
    • hormones produced by nerve cells
    • specialized for secretion rather than for conduction
    • may be released directly into circulatory system or stored temporarily in neurohemal organ
    • longer half-lives than neurotransmitters (mechanisms in synapse promote degradation)
    • site of action is some distance away from site of release
  223. nervous system function
    • NS plays a major role in regulation of homeostasis (other key control structure is the endocrine system)
    • involved in long distance communication
    • uses a combination of chemical and electrical signals
    • transmission takes place by highly discrete lines of communication (hardwiring)
    • transmits signals that are rapid & finely controlled
    • system gives good spatial and temporal control on effectors
  224. types of receptors
    • mechanoreceptors: sensitive to mechanical energy
    • osmoreceptors: detect changes in concentration of solutes in body fluids and resultant changes in osmotic activity
    • chemoreceptors: sensitive to specific chemicals; include receptors for smell and taste; detect O2 and CO2 concentrations in the blood & chemical content of digestive tract
    • photoreceptors: responsive to visible wavelengths of light
    • thermoreceptors: sensitive to heat and cold
    • nociceptors: pain receptors that are sensitive to tissue damage or distortion of tissue
  225. functional classes of neurons
    • afferent neurons
    • interneurons
    • efferent neurons
  226. afferent neurons
    • inform CNS about conditions in both the external and internal environment
    • at its peripheral ending, there is a sensory receptor that generates action potentials in response to stimulus
  227. interneurons
    • found entirely within CNS
    • lie between afferent and efferent neurons
    • responsible for integrating afferent information & formulating an efferent response
    • responsible for higher mental function associated with the mind
  228. neuroglia
    • make up ~90% of the cells within the brain
    • ~50% of the volume of the brain
    • AKA glial cells
    • do NOT initiate or conduct nerve impulses
    • COMMUNICATE with neurons & among themselves via chemical signals
    • serve as connective tissue of CNS - physically, metabolically, and functionally support interneurons
  229. 4 major types of glial cells
    • astrocytes
    • oligodendrocytes
    • microglia
    • epedymal cells
  230. oligodendrocytes
    form myelin sheath around axon in CNS
  231. microglia
    • immune defense of the CNS
    • in resting state, release low levels of growth factors that help neurons and other glial cells survive
    • Ex - nerve growth factor
  232. ependymal cells
    • line internal fluid-filled cavities of the CNS
    • in ventricles of brain, help form and circulate cerebrospinal fluid
  233. astrocytes
    • named for starlike shape
    • most abundant glial cells
    • main "glue" of CNS - holds neurons together
    • guide neurons during fetal brain development
    • induce capillaries of the brain to establish blood-brain barrier
    • important in repair of brain injuries & neural scar formation
    • takes up & degrades glutamate & GABA
    • takes up excess K+ from brain ECF - helps maintain optimal ion conditions for neural excitability
    • enhances synapse formation & modifies synaptic transmission
  234. CNS
    • central nervous system
    • brain & spinal cord
  235. PNS
    • peripheral nervous system
    • consists of nerve fibers that carry information between the CNS and other parts of the body (the periphery)
    • divided ito afferent & efferent systems
  236. Afferent division of PNS
    carries information to the CNS
  237. Efferent division of the PNS
    • carries information away from CNS to effector organs (muscles and glands that carry out orders to bring about the desired effect)
    • divided into somatic nervous system & autonomic nervous system
  238. Somatic Nervous System
    • consists of fibers of motor neurons that supply skeletal muscles
    • relays information to (efferent) and from (afferent) skin & skeletal muscles
    • largely voluntary
    • Exception - phrenic nerve
    • one motor neuron extends from CNS to skeletal muscle
    • axons are well myelinated
    • conducts impulses rapidly
  239. Autonomic Nervous System
    • consists of fibers that innervate smooth muscle, cardiac muscle, & glands (internal viscera)
    • involuntary
    • two divisions - sympathetic & parasympathetic
    • conduction is slower due to thinly or unmyelinated axons
  240. efferent neurons
    • carry instructions from CNS to effector organs (muscles & glands)
    • lie primarily in PNS (cell body & dendrites within CNS)
  241. Sympathetic Nervous System
    • controls organs during times of exercise, excitement, and emergencies
    • "fight, flight, fright"
    • thoracolumbar division of the ANS
    • long postganglionic fibers
    • highly branched axons - influence many organs
  242. Parasympathetic Nervous System
    • controls organs when body is at rest & digestion
    • concerned with conservation of energy
    • craniosacral division of the ANS
    • short postganglionic fibers
    • few branches on axons - localized effect
  243. neurotransmitters of autonomic nervous system
    • ALL autonomic PREganglionic axons - release acetylcholine
    • sympathetic postganglionic axons - release norepinephrine
    • parasympathetic postganglionic axons - release acetylcholine
Card Set
BIOL 4160 Test 1
Vertebrate Physiology Exam 1
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