HTHS Mod 11

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jskunz
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HTHS Mod 11
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2014-04-22 21:23:45
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Nervous system
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Nervous system
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  1. What does the nervous system do?
    • generates electrical potentials to regulate body activities
    • detects changes in the body's internal and external environments, interprets the changes, and responds by causing muscular contractions or glandular secretions
  2. 3 basic functions of the nervous system
    • Sensory : detects internal and external stimulus 
    • integrative: processes sensory info and makes appropriate responses; perception 
    • Motor: responds to by activating effectors (muscles and glands)
  3. How does the nervous system control electrical charges?
    • Nerve cells manipulate the flow of ions
    • These ions have charges ( + and - )
    • As charged ions flow, they create electrical current and electrical potential (voltage)
  4. Electrical potential =
    • voltage
    • mean the same thing
  5. What are the ONLY TWO THINGS the nervous system can do?
    move a muscle, or change the secretion of a gland
  6. What are two types of cells found in the nervous system?
    glial cells and neurons
  7. The three required components of a homeostatic loop
    • receptor - monitors controlled condition
    • Control center - receives input and provides output
    • Effectors - bring about change in controlled condition
    • *all found in nervous system
  8. neurons
    • nerve cells = the "thinking" cells of the brain
    • Receive, Process and Transmit information by manipulating the flow of ions across their membranes
    • - receive = sensory
    • - process = integrative
    • - transmit = motor
    • Each neuron does, in miniature, what the entire nervous system does as an organ
    • Approx. 10 billion ( 1011)
  9. Common ions which neurons manipulate the flow of
    • Na+ - sodium
    • K+ - potassium
    • Cl- - cloride
  10. visceral motor vs. somatic motor
    • Visceral is autonomic
    • Somatic is motor (voluntary)
  11. sensory receptors
    • also called sensory neurons, provide input to 
    • the receptors of the nervous system (receptors of homeostasis)
    • Found on the skin surface, in the taste buds of mouth, in retina or eye, etc.
    • takes info to the control center (brain)
  12. control center of the brain
    • the central nervous system (brain and spinal cord)
    • the processing center for the info from sensory receptors
  13. What are the effectors of the brain
    • smooth muscle
    • cardiac muscle
    • skeletal (voluntary) muscle
    • glands
  14. afferent pathways
    pathways INTO the central nervous system
  15. efferent pathways
    Pathways OUT OF the central nervous system
  16. Sensory = ____________; motor = ___________
    • Sensory = afferent
    • Motor = efferent
  17. transduction
    • a process by which sensory information is converted to a form the nervous system can use
    • This info flows into the control center from the PNS
  18. PNS
    • peripheral nervous system 
    • includes the cranial nerves, spinal nerves, ganglia, enteric plexi, and sensory receptors
    • has ability to regrow nerves (functional recovery) if damaged, where the CNS does not
  19. Two groups of nervous/motor systems
    • ANS or Visceral motor System - those that are controlled automatically. Hooked up to autonomic ganglia and nerves
    • Somatic nervous/motor system - the voluntary (consciously controlled) motor system. Hooked up to motor nerves
  20. ANS
    • Autonomic nervous system 
    • comprised of those effectors which are NOT under conscious control
    • Divided into 2 systems: Sympathetic & Parasympathetic
    • *do not involve cerebral cortex, which is where consciousness resides
  21. Pathway of info from ANS
    • First structures are autonomic ganglia and nerves
    • Next info passes through one or several neurons of the ANS (can be considered the "motor") to the effectors (which "do" something): smooth muscle, cardiac muscle or glands (those effectors not under voluntary control)
  22. sympathetic nervous system
    • division of ANS
    • "fight or flight"
  23. Parasympathetic nervous system
    • division of ANS
    • "rest and digest"
  24. Somatic motor system
    • Also called SNS - Somatic nervous system
    • voluntary nervous system
    • begins in cerebral and cerebellar cortex & passes through axons to spinal cord (for body except face) or to brainstem centers controlling movement (for face)
    • From there the info is relayed to Alpha motor neurons, which make contact w skeletal muscle
  25. synapse
    synapsecontacts btwn nerve cells
  26. α motor neurons
    • alpha motor neurons
    • info from the somatic nervous system are relayed to alpha motor neurons, which make contact with skeletal muscle at the neuromuscular junction
  27. components of the central nervous system
    • brain and spinal cord
    • Extremely limited ability for regeneration and repair if damaged.  If there's any recovery at all, it's because of ability to "rewire" or patch around damaged area.
  28. components of the peripheral nervous system
    • cranial nerves 3 - 12
    • spinal nerves
    • ganglia
    • enteric plexi
    • sensory receptors
    • *unlike CNS, has ability to regenerate and "re-nerve" areas of damage
  29. Divisions of PNS
    • SNS (Somatic Nervous System)
    • ANS (Autonomic Nervous System)
    • ENS (Enteric Nervous System)
    • *Each has a sensory and motor component
  30. ganglia
    • singular - ganglion  
    • a collection of nerve cells in the PNS
  31. nucleus
    • plural - nuclei
    • a collection of nerve cells in the CNS
  32. basal ganglia
    • one CNS structure
    • *neuroscientists are trying to change the name to basal nuclei
  33. ANS
    • Autonomic Nervous System
    • Include autonomic receptors that detect BP, blood glucose, blood oxygen, etc. 
    • Send info to CNS to be processed, comes out of autonomic motor neurons (involuntary) to either sympathetic or parasympathetic divisions (which target smooth muscle, cardiac muscle, or glands)
    • also sends info to ENS
  34. ENS
    • enteric nervous system
    • controls the motility and functions of the digestive organs
    • receives info from ANS and other enteric motor neurons in enteric plexuses
    • Has sensory receptors in the GI tract and enteric plexuses, which sends info to CNS & the motor neurons
    • Motor neurons lead to smooth muscle, glands, and endocrine cells of GI tract
  35. plexus
    • plural - plexuses or plexi
    • found in the walls of digestive organs
    • clusters of neurons.
  36. enteric means...
    guts
  37. neuroscientist
    scientist who studies the nervous system (brain, spinal cord, nerves)
  38. peripheral nervous system
    can be divided into: somatic, autonomic, and enteric nervous systems
  39. Two cell types of the nervous system
    Neurons and glial cells
  40. Glia
    • Glial cells
    • Major role in support and nutrition of brain
    • Do not manipulate info
    • Maintain the structural and chemical environment of the brain, so that neurons can do their jobs
    • 4 types in CNS & 2 types in PNS
  41. soma
    • also called cell body
    • the metabolic center of a neuron
    • aids in processing information
  42. dendrites
    • gathers information for neuron
    • also used in initial stages of information processing
    • the shape of the dendrite tree can tell us what the neuron does
    • The bigger the dendrite tree, the more information that neuron gathers and processes
  43. Three different shapes of neurons
    • unipolar, bipolar, and multipolar
    • *structurally, neurons are classified according to the # of processes extending from the cell body (as in # of dendrites and axons)
  44. multipolar neurons
    • has an extensively branched tree of dendrites surrounding the cell body
    • usually has several dendrites and one axon
    • picks up information over a large area and does lots of processing
    • Most neurons in brain and spinal cord are this type
  45. Bipolar neurons
    • have one main dendrite and one axon
    • their dendrite tree and axonal branches look like mirror images of each other
    • "Relay" cell; passes info from one cell to another
    • found in places where information is relayed like in retina of eye, inner ear, and olfactory area of brain
  46. Unipolar neurons
    • also called pseudounipolar neurons
    • move the cell body off to the side, so information can bypass the cell body and not be processed or transformed
    • have dendrites and one axon that are fused together to form a continuous process 
    • Sensory cell; picks up info about environment and passes it along to CNS
    • found in skin
  47. axon that is myelinated
    • *the output of a neuron travels through it's axon
    • If the info must travel a long distance, the axon is myelinated (covered by an insulated sheath)
    • the insulated sheath is comprised of a thin sheet of lipids, wrapped around the axon several times
  48. axon terminals
    • where an axon ends
    • axons can end in one or more terminals
    • the sites where information is sent to the next neuron in line, or to muscles or glands
  49. terminal knobs
    another name for axon terminals
  50. terminal boutons
    another name for axon terminals
  51. Purkinje cell
    • one type of neuron found in the cerebellum
    • has a large and elaborate dendritic tree
  52. 4 types of glial cells in CNS
    • astrocytes
    • oligodendrocytes
    • microglia
    • ependymal cell
  53. Astrocytes
    • (think of Astronaut) 
    • also called astroglia; type of glial cell in CNS
    • make up the pia mater  (the borders of CNS)
    • cooperate w/ blood vessels to form BBB, which protects brain from chemical or microbiological damage
    • End feet of astrocytes make up pia mater
    • "sponge up" access ions, toxins, and waste products
  54. BBB
    • blood-brain barrier
    • permits only lipid-soluble substances, certain amino acids, and glucose to pass into brain 
    • helps protect the brain from chemical or microbiological damage, but also makes it hard for the body to mount a defense against something that circumvents the BBB
  55. pia mater
    • made up of the end-feet of astrocytes
    • a thin membrane covering of the brain
  56. oligodendrocytes
    • also called oligodendroglia
    • cells that form wrappings around the axon
    • only have one job: form myelin sheaths (layers of thin lipid sheets wrapped) to insulate nerve axons that must send info over long distances
    • *only found in CNS. CANNOT regrow if cut or damaged
  57. nodes of Ranvier
    the gaps in the myelin sheaths every hundred micrometers
  58. monocytes
    immune cells of the blood that, when activated, turn into macrophages
  59. macrophages
    type of cell that swallows and digests invaders and waste products
  60. microglia
    • type of glial cell in CNS
    • the brains equivalent of monocytes
    • *since the brain is termed an "immunologically privileged site", no immune cells can pass the BBB
    • ONLY MICROGLIA are normally allowed to carry out immune functions in the brain
  61. ependymal cells
    • make up a single layer of border cells lining the ventricles which make cerebrospinal fluid
    • have cilia that continuously "row" CSF through the ventricular system
    • *only found in CNS
  62. ventricles
    open spaces in the brain which are filled with CSF (cerebrospinal fluid)
  63. CSF
    • cerebrospinal fluid
    • bathes, floats and cushions the brain.
    • circulates continuously, being made by specific tissue in special locations, traveling through the chambers of the brain and spinal cord, and finally being absorbed into veins at another location
  64. Two types of glial cells in the peripheral nervous system
    • satellite cells
    • schwann cells
  65. satellite cells
    • similar to what astrocytes do in the CNS:
    • type of glial cell
    • maintenance of borders, favorable chemical environment and mechanical/structural support
    • "sponge up" excess ions, toxins and waste products
    • found mostly in ganglia (collections of nerve cells in PNS)
  66. Schwann cells
    • similar to what oligodendrocytes do in CNS
    • type of glial cell
    • Can insulate in two ways:
    • 1.forms axon sheaths (insulating wrappings around axons)
    • 2. completely surrounding unmyelinated axons (like pigs-in-a-blanket)
    • *axons ensheathed by oligodendrocytes in the CNS cannot regrow if cut or damaged, while those surrounded by Schwann cells in the PNS can regenerate
  67. nerve
    • a bundle of axons all traveling together in the PNS
    • have limited capacity to regenerate
    • can be myelinated or unmyelinated
    • *Naming: usually named by location or function
    • Ex: vagus nerve = in latin, vagus means "wandering all over the place". This nerve wanders all over the thoracic and abdominal cavity
  68. tract
    • a group or bundle of axons in the CNS all originating in one place and traveling to another
    • can be myelinated or unmyelinated
    • *Naming: may be named by appearance or location, or by where they start and end up
  69. gray matter
    • clusters or sheets of neuronal cell bodies
    • makes up part of the CNS
  70. white matter
    • cylinders or sheets of neuronal axons wrapped in lipid-rich myelin
    • Makes up part of the CNS
  71. Naming of nerves and tracts
    • Used to be (like in 15th, 16th century) nerves were usually named by location or function, how they appeared
    • Tracts may be named by appearance or location
    • Now names are mostly where they start and end up
  72. fasciculus gracilis
    • 'fasciculus' in Latin means "bundle of sticks"
    • 'gracilis' in latin means "thin"
    • in posterior column
    • a CNS tract
  73. corona radiata
    • Latin for "ray-filled crown"
    • a CSN tract
  74. arbor vitae
    • Latin for "tree of life"
    • a CNS tract
  75. corticospinal tract
    the pathway btwn the cortex and spinal cord
  76. recall concept of permeability
    • permeability tell us how easily a substance can cross the plasma membrane (some things can pass, others cannot)
    • Gases, small uncharged molecules, and lipid-soluble substances can pass through the cell membrane (lipid bilayer)
    • charged ions and large molecules (water-soluble substances such as glucose) don't pass w/o assistance
  77. recall concept of membrane proteins
    • recall the non-polar tails of lipid molecules (in the cellular membrane) prevent charged molecules, like ions, from crossing
    • Ion channels allow ions to pass down their concentration gradient (from high concentration to low concentration)
    • *Some are open all the time; some are gated
  78. potential energy
    • energy being stored
    • *think of archer; bow is drawn back but being held.
    • *Another example is the energy you have when your at the top of a ski slope and your about to slide or ski down the hill)
  79. voltage (with electric current flow)
    • used interchangeably with potential energy
    • describes the potential energy of charged particles (energy that is available but not yet released) - like a ball on top of a hill
    • *the higher the voltage "hill", the more potential energy a charged particle has
  80. recall kinetic energy
    • what potential energy turns into when you chose to use that stored energy
    • energy in motion
    • *so in example with skiing, the potential energy you have at the top of the hill turns into kinetic energy when you begin to ski down. OR the archer releases the bow and arrow is set in motion
  81. current (with electric current flow)
    • kinetic energy, the flow of ions or electrons
    • in the biological system, the number of electrolyte ions passing by a point in the cell in a given period of time OR # of charges that flow per second
    • Symbolized by I , measured in amperes
  82. resistance (with electric current flow)
    • resistance to current flow
    • *in skiing analogy, resistance from the air, from the snow against your skis
    • resistance to kinetic energy
    • measured in ohms
  83. Ohm's Law
    • defines the precise mathematical relationship between voltage (V), current (I), and resistance (R)
    • works only for direct current circuits (DC), which is what the human body uses
    • says that voltage (V) equals the current (I) x resistance (R):
    • V = I R
  84. What exactly is electric current flow
    • when electrons move as a group
    • *just as when water molecules move as a group you have water flow
    • The same thing can happen to ions inside a cell, but it is much slower (ions are formed and move as a group)
  85. comparing the movement of ion & water
    • Just as water flow happens in a pipe, ions have their current flow in the axons of neurons
    • the ions move in the same way as water, just much slower - 100 m/sec or 223 mph
  86. current in the human body is carried in...
    • a water-based solution by electrolytes
    • instead of flowing electrons (in non-living systems) biological (living) "wires" have ions (like Na+) flowing within them
  87. conductance
    • symbolized by g
    • the inverse of resistance; so the measure of how easy it is for electrolytes/ions to move in an axon
    • measured in Siemens:
    • where (g = 1/R);   V x g = I
  88. Why do neurons have electrical potential
    because ions are distributed differently inside the cell than outside, and the membrane is selectively permeable only to certain ions
  89. What is the extracellular fluid?
    • a filtrate of blood (blood with cells removed)
    • mostly salt water = sodium chloride (table salt dissolved in water)
    • NaCl → Na+ + Cl-
    • therefore, extracellular fluid is mostly comprised of sodium ions and chloride ions
    • *this side of cell membrane has a positive charge
  90. What is the cytosol?
    • the intercellular fluid
    • what you have when you take cytoplasm and remove the organelles, and what you have left is the soluble part... left with proteins, phosphate ions and potassium ions
    • *Phosphate and proteins have negative charge, so cant pass through membrane (trapped inside cell since inside wall of cellular membrane is negative, they repel each other)
    • *potassium ions are in high concentration in cell, and low concentration outside cell
  91. Why are protein and phosphate ions stuck inside the cytosol?
    • They both have a negative charge and can not pass through the cell membrane (which has a neg charge = neg repels neg)
    • trapped inside the cell
    • Their negative charge is what gives the inside of the cell and cell membrane it's negative charge
  92. relative concentration of Na+ inside vs. outside the neuronal membrane
    • sodium ions
    • inside: 10
    • Outside: 140
  93. relative concentration of K+ inside vs outside the neuronal membrane
    • potassium ions
    • inside: 140
    • outside: 4
  94. relative concentration of Cl- inside vs. outside the neuronal membrane
    • chloride ion
    • inside: 20
    • outside: 103
  95. relative concentration of Ca++ inside vs. outside the neuronal membrane
    • calcium ion
    • inside: zero
    • outside: 5
  96. Ions that differ in concentration btwn the inside and outside of a neuron are subject to two independent forces:
    • Concentration forces
    • Electrical forces
  97. Concentration forces on ions
    All atoms, including sodium, potassium, chloride and calcium ions, want to move from where they are in high concentration to where they are in low concentration

    also called chemical forces or diffusional forces
  98. Electrical forces on ions
    • describes the "pull" of a positively charged ion exerts on a negatively charged ion. 
    • * Particles with the same charge repel each other, and opposites attract
  99. What happens when protein gates in the cell membrane open?
    • It allows ions to flow; voltage turns to current
    • In terms of Ohm's Law, resistance is going from almost infinity to a measurable number
    • *REMEMBER these channels are selective for only one type of ion!
  100. At rest, what charges are a neuron inside vs. outside
    • the neuron is always negative inside relative to outside.
    • based on electrical forces, positively charged ions always want to flow in, and negatively charged ions always want to flow out
  101. How do ions pass through the cell membrane
    • must have channels or "doorways"
    • must be open for passage
  102. "leakage" channels
    • channels that can be open all the time
    • Ion SPECIFIC
  103. Concentration and electrical forces on K+
    • Potassium is present at much higher concentration inside neuron.
    • *K+ has positive charge, inside is negative
    • Therefore, concentration force pushes K+ out.
    • The electrical force (neg. inside cell) pushes positively charged K+ in
    • When K+channels are open, the two forces work in opposite directions
  104. Concentration and electrical forces on Na+
    • Sodium is present at higher concentration outside neuron
    • electrical forces pull sodium into cell, where it's more negative
    • Since Na+ outside the cell is so much greater than inside, the concentration forces act to push Na+ into the neuron
    • *Both concentration and electrical forces act in the same direction when Na+ channels open, pushing sodium into the neuron
  105. equilibrium potential
    the point at which the voltage btwn the two forces (concentration and electrical) are exactly equal and opposite
  106. Equilibrium Potential for K
    • Forces on potassium are equal and opposite at about -80mV  ( -0.08 Volts)
    • In reality, it varies somewhat cause of differences in concentrations and permeability btwn different neurons
  107. Whats different btwn the equilibrium potentials of sodium and potassium?
    *Recall equilibrium is defined as the point the concentration and electrical forces are exactly equal and opposite

    • Potassium forces already work in opposite directions
    • Sodium forces both work in the same direction. Concentration can't be changed, so the electrical charge must be changed. This is where we say (or imagine) the inside of the cell membrane has positive charge
  108. sodium equilibrium potential
    • is about +20 mV for a typical neuron, but again, the exact number will vary per different type of neuron
    • *This is where we imagine a positive force inside cell membrane... in order to reach equilibrium (forces are equal and OPPOSITE)
  109. Resting potential of a neuron
    • "resting voltage" is maintained by passive ("leak") channels
    • At rest, there are about 9 Kleak channels open for every 1 Na+ leak channel
    • Since Kequilibrium is about -80mV, and Na+ is at +20mV, resting potential is at -70 mV
    • -70mV simply means there is an excess of negative charges inside cell membrane
  110. Action potential
    • When the neuron is actively trying to manipulate the flow of charges across cell membrane
    • used by neurons that need to send information over long distances through axons (takes place along axonal membrane)
    • results from active opening and closing of voltage-gated channels
  111. Steps in the action potential
    • resting potential - begins here
    • threshold - stimulus causes depolarization
    • depolarization: Na+ channels open, Peak, Na+ channels inactivate & Kchannels open
    • Repolarization
    • After-hyperpolarization (hyperpolarization)
    • return to resting potential
  112. polarization & depolarization
    • polarization simply refers to negativity
    • DEpolarization means something is losing some of its negativity
  113. Special property of axonal membrane voltage-gated sodium channels
    • When voltage becomes less negative, the sodium channels open.
    • Because of driving forces (concentration & electrical) on sodium pushing it into the cell, Nabegin rushing in and make cell membrane less negative inside.
    • This opens up more and more voltage-gated sodium channels.
    • Is a self regenerating, explosive, positive feedback
    • When all sodium channels are opened, reaches "tipping point" called threshold
  114. Threshold
    • the point at which depolarization will trigger an action potential
    • reached when all sodium voltage-gated channels have been opened
    • means that the sodium current now overwhelms the leak current and axonal membrane reaches sodium equilibrium potential
  115. How do the proteins which block the voltage-gated channels changed to allow Nato pass
    • *So initial depolarization of threshold changed shape of proteins in sodium channels, causing them to go from closed state to open state
    • (*recall shape of proteins (mod 3) as primary, secondary, tertiary, and quaternary structures. Voltage can change the shape by changing charges on amino acids)
    • So the change in voltage at threshold is enough for the proteins in the gated channels to change and openAs sodium begins to rush in, and the charge inside the cell becomes more positive, more gates open allowing more sodium in
  116. How is action potential stimulated
    by the opening of voltage-gated Nachannels, causing depolarization
  117. What two things happen when threshold (and sodium equilibrium potential) is reached
    • 1. sodium channel inactivation
    • 2. voltage-gated Kchannels are activated, but slowly

    • Both of these events cause the axonal membrane to become more negative. 
    • Therefore, Na+ quits flowing in, K+ flows out
  118. sodium channel inactivation
    • *Voltage-gated sodium channels can open only for about 1 msec. 
    • The process by which a second Na+ "gate" closes, triggered by initial voltage change but swinging more slowly than first one
  119. How is potassium equilibrium reached?
    • When the voltage-gated K+ channels are triggered by the same voltage change that affected Na+, but like the 2nd inactivation gate of Na, they are slow to react. 
    • When they do, all channels open
    • This pulls the axonal membrane potential back down toward potassium equilibrium (-80 mV)
    • also referred to as hyperpolarizing phase, or after-hyperpolarizing
  120. refractory period - during the action potential
    • The time during which the sodium channels are inactivated, and potassium channels are open
    • Nothing can change the state of these channels, therefore the axonal membrane is said to be resistant to change
  121. absolute refractory period
    • the time during which firing an action potential is impossible
    • When the voltage-gated Nachannel activation gates are open 
    • & when the voltage-gated K+ channels are open & Na+ channels are inactivating
  122. relative refractory period
    • The time during which it's merely difficult to fire an action potential, cause not all of the voltage-gated channels are reset
    • it's not impossible, but relatively difficult to fire a new spike
    • During which voltage-gated Kchannels are still open; Na+channels are in the resting state
  123. Recap on Action potential
    Start w resting potential. Change in voltage which reaches threshold. Causes depolarization as voltage-gated sodium channels open. At peak (sodium equilibrium), sodium channels close, Potassium channels slowly start to open. Potassium leaks out of cell, making inside more negative (repolarization). Overshoots resting potential (hyperpolarization). When we re-establish 9-1 ratio (9 Kto 1 Na+ leakage), we achieve resting potential
  124. Action potentials only take place at...
    • the axonal membrane of a neuron
    • in virtually all neurons, there are no voltage-gated channels in the dendrites and cell bodies, no action potentials can occur here
    • begins at trigger point
  125. trigger zone
    • where the action potential begins
    • is near the axon hillock 
    • a point where the first set of voltage-gated channels are on a neurons axon
  126. axon hillock
    • a thickening, or bump, in axon where it meets the neuronal body
    • markes approximate location of "trigger zone"
  127. How is the voltage current spread from trigger point
    • Spreads similar to ripples in a pond
    • Since the cell membrane has no voltage-gated channels, voltage spread toward cell body"dies out"
    • Since voltage-gated sodium & potassium channels are found down axonal membrane, the voltage travels that way, passively
  128. When thinking of a nerve axon as a sort of cable, what does a bigger cable and bigger voltage entail
    • Bigger cable = more conductance = more (and faster) current
    • bigger voltage = more electrical potential = more current
  129. Propagation of the action potential in unmyelinated axon?
    • Once the action potential is triggered, the current changes spread passively through the axon
    • Behind the trigger zone, no voltage-gated channels to trigger
    • Ahead of trigger zone, there are voltage-gated channels
    • The action potential begins to move toward terminals
    • Behind the action potential, axon is in refractory period so action potential is forced to move in one direction
  130. Propagation of action potential in myelinated axons
    • Voltage-gated Na+ and K+ channels at trigger zone fire an action potential
    • The current (voltage) spread passively through axon insulated by myelin (No gated channels under sheath)
    • The myelin sheath is interrupted at nodes of Ranvier
    • At nodes, more voltage-gated Na& Kchannels trigger another action potential
    • Action potential appears to jump (saltate) from one node to the next
  131. saltatory conduction
    • the phenomenon in which the action potential appears to "jump" from node to node in myelinated axons
    • saltare: latin for "leap"
  132. What does the myelin insulation do
    • keeps leakage of ions from depleting the "wave" of voltage 
    • The neuronal axon is tuned so that the height of the depolarizing "wave" is just enough to reach threshold at the next node & trigger another action potential
  133. What is the purpose of the Na+/K+ pump
    • After several action potentials, the normal Na+ and K+ concentration gradients would be degraded
    • The Na+/K+ pump is used to restore gradients
    • The pump moves both Na/K against their concentration gradients by active transport (Na+ moves out/K+ moves in), splits ATP for energy to do it
    • 3 Naexpelled, 2 K+ are imported
  134. recall active transport
    • used to move an ion against it's concentration gradient
    • requires energy
    • Ex: Na+/K+ pump, also called Na+/K+ ATPase
  135. Digoxin
    • a drug that inhibits the Na+/K+ pump 
    • used to stop atrial fibrillation in the heart
  136. synapse
    • a point of contact btwn a neuron and another neuron or an effector cell
    • sends info only in one direction, from axon terminal which releases neurotransmitter, to the transmitter receptors on another cell
  137. presynaptic cell
    cell sending the info
  138. postsynaptic cell
    the cell, with receptors for the transmitter, that receives the info
  139. synaptic cleft
    • area btwn the two cells
    • neurotransmitter diffuses across this narrow gap and acts on the transmitter receptors on the postsynaptic cell
  140. synaptic vesicles
    • specialization of the presynaptic cell
    • tiny spheres of membrane that contain packets of neurotransmitter molecules
    • This molecules are released by exocytosis (vesicles fuse to membrane, spitting out neurotranys outside cell)
  141. quanta
    packets within synaptic vesicles that consist of an estimated 4000 acetylcholine molecules at each neuromuscular junction
  142. reuptake pumps
    removes transmitter from synaptic cleft and re-use it, Since the presynaptic cell is thrifty w energy
  143. inactivating enzymes
    • help to terminate the action of transmitter, so it doesn't hang out in the cleft and continually re-bind the receptor
    • only some neurons have it
  144. Sequence of events in chemical synapse
    • 1. Action potential arrives at synaptic end bulb
    • 2. Ca++ enters presynaptic terminal (recall Ca++ inside is zero, so opening a channel means it always enters)
    • 3. Ca++ interacts w synaptic vesicles; they move to, and fuse, w presynaptic membrane
    • 4. neurotransmitter is released from vesicles & binds to post-synaptic transmitter receptor
    • 5. Receptor protein undergoes a change in shape that allows ions to flow
    • 6. Ion flow results in PSP (post synaptic potential) - either inhibitory or excitatory
  145. omega figure
    • the resulting shape when synaptic vesicles fuse w presynaptic terminal membrane
    • during exocytosis
  146. IPSP
    • inhibitory postsynaptic potential
    • when the ion flow through the postsynaptic receptors results in the cell becoming more negative
    • moves membrane potential further away from threshold
  147. EPSP
    • Excitatory postsynaptic potential
    • when the ion flow through the postsynaptic receptors causes the cell to become more positive
    • moves membrane potential closer to threshold
  148. postsynaptic potential (PSP)
    • The change in membrane voltage of the postsynaptic cell. 
    • As ions flow through the opened gates, the voltage across the membrane of the postsynaptic cell changes
    • Depending on which ions are admitted, the postsynaptic potential may be depolarization or hyperpolarization
  149. What two conditions can cause the structure of protein channels in neurons to change?
    • When a chemical, such as a neurotransmitter, outside the neuron binds to a special site on the channel (ex: ligand-gated channel)
    • When the voltage (electric potential) across the membrane changes, changing the distribution of charges surrounding the channel protein (ex: voltage-gated channels)
  150. Different kinds of protein (ion) channels in neurons
    • leakage channels
    • ligand-gated channels
    • mechanically gated channels
    • voltage-gated channels
  151. ligand-gated channel
    • when ligand (a neurotransmitter) outside the neuron binds to it's receptor, the receptor changes shape and opens a pore
    • Found on dendrites of some sensory neurons, dendrites and cell bodies of interneurons and motor neurons
    • chemical stimulus (such as a neurotransmitter or drug) opens the channel
    • used when neurons signal each other, or when neurons signal muscle cells
  152. voltage-gated channel
    • when the voltage (electrical potential) across the membrane changes, changing the distribution of charges surrounding the channel protein
    • Change in membrane potential opens the channel
    • essential for action potentials and synapses
    • used to move info within a single neuron, from cell body to axon terminals
    • *has one of only two special conditions that can change the structure of a protein channel
    • found on axons of all types of neurons
  153. leakage channels
    • gated channels that randomly open and close
    • found on nearly all parts of nerve cells
  154. mechanically-gated channels
    • gated channels that open in response to mechanical stimulus (such as pressure receptor, being pressed on)
    • opened when they are mechanically forced to change shape
    • found on dendrites of some sensory neurons such as touch, pressure, or pain receptors
  155. recall facilitated diffusion
    • type of passive transport (no energy needed)
    • For larger molecules and charged molecules that must be "escorted" across the membrane, even if the concentration is higher outside than in
    • protein channels or carriers in the membrane "facilitate" the diffusion of substances
    • Ex: K+
  156. inhibition
    • any change in the neuron which makes it more difficult to reach threshold
    • most common form is a stimulus that makes membrane more negative
  157. What causes IPSP?
    • Ligand-gated ion channels
    • By opening Clor K+ channels, it makes the neuronal membrane more negative
    • (inhibitory postsynaptic potential)
  158. excitation
    • any change in the neuron which makes it easier to reach threshold
    • most common type is one that makes membrane more positive (depolarization)
  159. What causes EPSP?
    • Ligand-gated ion channels
    • by opening a Na+ channel, it makes the neuronal membrane more positive
    • (excitatory postsynaptic potential)
  160. Neurotransmitters
    • signaling molecules used btwn neurons
    • 6 categories:
    • amino acids
    • modified amino acids
    • polypeptides
    • purines
    • fatty acids
    • gases
    • "Are My Ponies Properly Feed, Gus?"
  161. Amino Acid neurotransmitters
    • Glutamate - major excitatory NT for brain
    • Aspartate - is excitatory in most cases
    • Glycine - inhibitory, in most cases
  162. Modified amino acid neurotransmitters
    • Acetylcholine 
    • GABA
    • Norepinephrine (noradrenaline)
    • epinephrine (adrenaline)
    • dopamine
    • serotonin
  163. Polypeptide neurotransmitters
    • "Neuropeptides"
    • Substance P
    • Enkephalins
    • Endorphins
    • Dynorphins
    • Hypothalamic Releasing Hormones
    • Hypothalamic Inhibiting Hormones
    • Angiotensin II
    • CCK (Cholecystokinin)
    • "Every SurPrise Ends Doing Happy Hugs And Crying"
  164. Purines as neurotransmitters
    ATP
  165. gases
    • Only one we'll learn is NO - Nitric Oxide
    • Made by nitroglycerin (Nitro to give heart pts)
    • Used to create Viagra & similar drugs
    • Able to freely diffuse across the cell membrane; therefore, doesn't get released from vesicles and doesn't act on receptors.
  166. 4 Biogenic Amine Neurotransmitters
    • Important to human medicine
    • Made by the body (biogenic) and contain amino groups:
    • Norepinephrine
    • Epinephrine
    • Dopamine
    • Serotonin
  167. Norepinephrine as biogenic amine neurotransmitter
    • typical Function: increase blood pressure
    • source: ANS
    • target can be: smooth muscle of blood vessels
    • it binds to the β-adrenergic receptor, which causes smooth muscle in blood vessels to contract, making vessel diameter smaller, thereby increasing blood pressure
  168. Epinephrine as biogenic amine neurotransmitters
    • "adrenaline" 
    • Typical function: fight-or-flight response
    • source: adrenal medulla
    • target: widespread
  169. Dopamine as biogenic amine neurotransmitter
    • typical function: smoothing movement
    • source: substantia nigra (structure in brain stem)
    • target: basal ganglia
  170. Serotonin as biogenic amine neurotransmitters
    • typical function: regulating mood
    • Source: raphe nuclei (in brain)
    • target: widespread areas of brain
    • To increase serotonin, use SSRI (selective S reuptake inhibitor)
    • Ex: 1st discovered med was Prozac - elevates mood by blocking reuptake of S, making more avaliable at synapse
  171. Is Acetylcholine (ACh) an excitatory neurotransmitter or an inhibitory neurotransmitter?
    • BOTH~
    • at skeletal muscle it's excitatory
    • at heart muscle, it's inhibitory
  172. How can a neurotransmitter be inhibitory AND an excitatory
    • Whatever happens to the postsynaptic cell depends on the receptor NOT the transmitter
    • so technically, there are no "inhibitory" or "excitatory" neurotransmitters -- only inhibitory or excitatory receptors
  173. ionotropic neurotransmitter receptors
    • receptors which open or close ion channels, because the affect the ionic environment of the neuron
    • Therefore, allow more ions of a particular type to flow through a channel OR allow fewer ions of a particular type to flow through
    • Ionotropic, where "tropic" means acting on
  174. metabotropic neurotransmitter receptors
    • receptors which change the biochemistry of a neuron by affecting the metabolism of the neuron
    • When activated, can cause a long term biochemical change in the postsynaptic cell
    • acts through second messenger systems
  175. 3 categories of metabotropic neurotransmitter receptors
    • 1~Some, when activated, change the properties of nearby ion channels by chemically modifying the receptor protein
    • 2~Some activate themselves by adding a phosphate group to amino acid tyrosine
    • 3~G Protein receptors
    • *all 3 types ultimately act by adding a phosphate group onto 1 or more amino acids on 1 or more proteins
  176. G protein receptors
    • a large category of metabotropic receptors
    • ALWAYS span the membrane 7 times
    • activate adenylate cyclase (enzyme)
  177. adenylate cyclase
    • enzyme activated by G proteins
    • make cyclic AMP (cAMP) from ATP
    • cAMP kicks off a cascade of chemical reaction that results in the adding of a phosphate group to the protein
    • (recall, when phosphate is added to protein, it changes their shape, which in turn changes their activity)
  178. kinases
    enzymes that add phosphate groups
  179. tyrosine kinase
    the enzyme which adds a phosphate group to the amino acid tyrosine
  180. tyrosine kinase-linked receptor
    the receptor for tyrosine kinase
  181. protein kinases
    a metabotropic receptor which adds a phosphate group onto one or more amino acids on one or more proteins
  182. What's the similarities and differences btwn nervous and endocrine systems?
    • The nervous system and the endocrine system "blend hormones and neurotransmitters together", sharing the same neurotransmitter/hormones, receptors and signaling pathways.
    • There are some chemicals that are both a hormone and a neurotransmitter
    • Both use chemical signaling mediated through receptors. 
    • Main difference is the distance traveled by the chemical signal: very short in most neurons, and very long in the case of hormones
  183. Types of cell signaling
    • Autocrine
    • Paracrine
    • Endocrine
  184. Endocrine signaling
    • where a hormone is released in bloodstream to act on receptors on a distant organ
    • endo = "within"
  185. Paracrine signaling
    • where a chemical signal travels a short distance to neighboring cells in the same organ
    • Neurotransmission at synapses is just a special case of this general property of tissues
    • can operate btwn cells that are not neurons
    • para = "next to"
  186. Autocrine signaling
    • where a chemical signal acts on receptors on the same cell that released the chemical signal
    • Usually this acts to turn the signal off
    • also called auto receptors; "self" signaling

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