Card Set Information

2014-03-12 04:28:32
ch11 test: nervous system
Show Answers:

  1. How do cells in the nervous system communicate
    via electrical and chemical signals
  2. What are the functions of the Nervous System
    • Sensory Input
    • Integration
    • Motor output
  3. Sensory Input
    Information gathered by sensory receptors about internal and external changes
  4. Integration
    Processing and interpretation of sensory input
  5. Motor output
    Activation of effector organs (muscles and glands) produces a response
  6. Central Nervous System (CNS)
    • Brain and spinal cord of dorsal body cavity
    • Integration and control center (interprets sensory input and dictates motor output)
  7. Peripheral Nervous System (PNS)
    • The portion of the nervous system outside CNS
    • Consists mainly of nerves that extend form brain and spinal cord (spinal nerves and cranial nerves)
  8. Spinal nerve
    Nerves to and from spinal cord
  9. Cranial nerves
    To and from brain
  10. What are the two functional divisions of the PNS
    Sensory (afferent division) and motor (efferent) division
  11. Sensory (afferent) division
    • Somatic sensory fibers: convey impulses form skin, skeletal muscles, and joints to CNS
    • Visceral sensory fibers: convey impulses from visceral organs to CNS
  12. Motor (efferent) division
    • Transmits impulses from CNS to effector organs (muscles & glands)
    • Two divisions: somatic nervous system & autonomic nervous system
  13. Somatic Nervous System
    • Somatic motor nerve fibers
    • Conducts impulses from CNS to skeletal muscle
    • Voluntary nervous system (conscious control of skeletal muscles)
  14. Autonomic Nervous System
    • Visceral motor nerve fibers
    • Regulates smooth muscle, cardiac muscle, and glands
    • Involuntary nervous system
    • Two functional subdivisions: Sympathetic & Parasympathetic (work in opposition to each other)
  15. Is nervous tissue highly cellular and tightly packed, with little extracellular space
  16. What are the two principal cell types
    Neuroglia & neurons
  17. Neuroglia
    small cells that surround and wrap delicate neurons
  18. Neurons
    excitable cells that transmit electrical signals
  19. Name the six types of neuroglia
    • Astrocytes (CNS)
    • Microglial cells (CNS)
    • Ependymal cells (CNS)
    • Oligodendrocytes (CNS)
    • Satellite cells (PNS)
    • Schwann cells (PNS)
  20. Astrocytes
    • Most abundant, versatile and highly branched glial cell
    • Cling to neurons, synaptic endings, and capillaries

    • Functions:
    • -Support and brace neurons
    • -Play role in exchanges between capillaries and neurons
    • -Guide migration of young neurons
    • -Control chemical environment around neurons
    • -Respond to nerve impulses and neurotransmitters
    • -Influence neuronal functioning
  21. Microglial cells
    • Small, ovoid cells with thorny processes that touch and monitor neurons
    • Migrate toward injured neurons
    • Can transform to phagocytize microorganisms and neuronal debris
  22. Ependymal cells
    • Range in shape from squamous to columnar
    • May be ciliated
    • Line the central cavities of the brain and spinal column
    • Form permeable barrier between cerebrospinal fluid in cavities and tissue fluid bathing CNS cells
  23. Oligodendrocytes
    • Branched cells
    • Processes wrap CNS nerve fibers, forming insulating myelin sheaths thicker nerve fibers
  24. Satellite cells
    • Surround neuron cell bodies in PNS
    • Function similar to astrocytes of CNS
  25. Schwann cells (neurolemmocytes)
    • Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers (similar function to oligodendrocytes)
    • Vital to regeneration of damaged peripheral nerve fibers
  26. what are neurolemmocytes
    Schwann cells
  27. Neurons
    • Structural units of nervou system
    • Large, highly specialized cells that conduct impulses
    • Extreme longevity (100+ years)
    • Amitotic (few exceptions)
    • High  metabolic rate (requires continuous supply of oxygen and glucose)
    • All have cell body and one or more processes
  28. Neuron Cell Body (perikaryon or soma)
    • Biosynthetic center of neuron (synthesizes proteins, membranes, etc. best rough ER in the body)
    • Spherical nucleus with nucleolus
    • Some contain pigments
    • In most, plasma membrane part of receptive region
    • Most neuron cell bodies in CNS
    • Ganglia lie along nerves in PNS
  29. Nuclei
    Clusters of neuron cell bodies in CNS
  30. Tracts
    Bundles of neuron processes in CNS
  31. Nerves
    Bundles of neuron processes in PNS
  32. What are the two types of processes
    Dendrites and axons
  33. Dendrites
    • In motor neurons (100s of short, tapering, diffusely branched processes; same organelles as in body)
    • Receptive (input) region of neuron
    • Convey incoming messages toward cell body as graded potentials 
    • In many brain area fine dendrites specialized
    • Collect information with dendritic spines (appendages with bulbous or spiky ends)
  34. Graded Potentials
    Short distance signals
  35. Axon: structure
    • One axon per cell arising from axon hillock
    • In some axon short or absent
    • In others most of length of cell ( some 1 m long)
    • Occasional branches
    • Branches profusely at end
    • Can be 10,000 terminal branches
  36. What are other terms for distal endings for Axons
    Axon terminals or Terminal boutons
  37. What are long axons called
    Nerve fibers
  38. Axon: functional characteristics
    • Conducting region of neuron
    • Generates nerve impulses
    • Transmits them along axolemma to axon terminal
    • Carries on many conversations with different neurons at same time
    • Lacks rough ER and golgi apparatus
  39. Axolemma
    Neuron cell membrane
  40. Neurotransmitters released into extracellular space
    Either excite or inhibit neurons with which axons in close contact
  41. What happens because the axon lacks rough ER and golgi apparatus
    • Relies on cell body to renew proteins and membranes
    • Efficient transport mechanisms
    • Quickly decay if cut or damaged
  42. How are molecules and organelles moved along axons
    By motor proteins and cytoskeletal elements
  43. Anterograde
    • Away from the cell body
    • Ex. mitochondria, cytoskeletal elements, membrane components, enzymes
  44. Retrograde
    • Toward the cell body
    • Ex. organelles to be degraded, signal molecules, viruses, bacterial toxins
  45. Myelin sheath
    • Composed of myelin 
    • Segmented sheath around most long or large diameter axons (myelinated fibers)
  46. What is myelin
    whitish protein-lipid substance
  47. what are the functions of myelin
    • Protects and electrically insulates axon
    • Increases speed or nerve impulse transmission
  48. Do nonmyelinated fibers conduct impulses more slowly
  49. Myelination in the PNS
    • Formed by schwann cells (wrap around axon in jelly roll fashion, one cell forms one segment of myelin sheath)
    • Myelin sheath (concentric layers of schwann cell plasma membrane around axon)
    • Outer collar of perinuclear cytoplasm (peripheral bulge of schwann cell containing nucleus and most of cytoplasm)
    • Plasma membranes of myelinating have cells less protein (no channels or carriers, good electrical insulators, interlocking proteins bind adjavent myelin membranes)
    • Nodes of rangier (myelin sheath gaps between adjacent schwann cells, sites where axon collaterals can emerge)
    • Nonmyelinated fibers (thin fibers not wrapped in myeline, surrounded by schwann cells but no coiling, one cell may surround 15 different fibers)
  50. Myelin sheaths in CNS
    • Formed by multiple flat processes of oligodendrocytes, not whole cells
    • Can wrap up to 60 axons at once
    • Nodes of ranvier present
    • No outer collar of perinuclear cytoplasm
    • Thinnest fibers are unmyelinated (covered by long extensions of adjacent neuroglia)
    • White matter & Gray matter
  51. White matter
    Regions of brain and spinal cord with dense collections of myelinated fibers, usually fiber tracts (tract=PNS)
  52. Gray matter
    mostly neuron cell bodies and nonmyelinated fibers
  53. Structural classification of neurons
    • Grouped by number of processes; 3 types
    • Multipolar, Bipolar & Unipolar
  54. Multipolar Neurons
    • 3 or more processes
    • 1 axon, others dendrites
    • most common; major neuron in CNS
  55. Bipolar Neurons
    • 2 processes
    • 1 axon and 1 dendrite
    • rare e.g. retina and olfactory mucosa
  56. Unipolar Neurons
    • 1 short process
    • Divides T-like with both branches now considered axons (distal (peripheral) process is associated with sensory receptor and proximal (central) process enters CNS
  57. What are the functional classifications of neurons
    • Grouped by direction in which nerve impulse travels relative to CNS; 3 types
    • Sensory (afferent), Motor (Efferent), Interneurons
  58. Sensory Neurons
    • Transmit impulses from sensory receptors toward CNS
    • Almost all are unipolar
    • Cell bodies in ganglia in PNS
  59. Motor Neurons
    • Carry impulses from CNS to effectors
    • Multipolar
    • Most cell bodies in CNS (except some autonomic neurons)
  60. Interneurons (association neurons)
    • Lie between motor and sensory neurons
    • Shuttle signals through CNS pathways; most are entirely within CNS
    • 99% of body's neurons
    • Most confined in CNS
  61. How do neurons respond to adequate stimulus
    by generating an action potential
  62. what is an action potential
    a nerve impulse
  63. is the impulse always the same
    yes; regardless of stimulus
  64. if opposite charges are separated the system has what kind of energy
    potential energy
  65. voltage
    a measure of potential energy generated by separated charge
  66. current
    flow of electrical charge (ions) between two points
  67. resistance
    is a hindrance to charge flow; an be an insulator or conductor
  68. insulator
    substance with high electrical resistance
  69. conductor
    substance with low electrical resistance
  70. Ohms Law
    • current (I)=voltage (V)/resistance (R)
    • *current is directly proportional to voltage
    • *no net current flow between points with same potential
    • *current inversely related to resistance
  71. what is the role of membrane ion channels
    large proteins serve as selective membrane ion channels; there are two types; leakage (nongated) or gated
  72. leakage channels
    nongated channels that are always open
  73. gated channels
    part of protein changes shape to open/close channel
  74. what are the three types of gated channels
    • chemically gated
    • voltage-gated
    • mechanically gated
  75. chemically gated (ligand-gated) channels
    open with binding of a specific neurotransmitter
  76. voltage-gated channels
    open and close in response to changes in membrane potential
  77. mechanically gated channels
    open and close in response to physical deformation of receptors, as in sensory receptors
  78. explain what happens when gated channels are open
    • -ions diffuse quickly across membrane along electrochemical gradients
    • -ion flow creates an electrical current and voltage changes across membrane
  79. resting membrane potential
    • -potential difference across membrane of resting cell (-70)
    • -membrane is polarized
    • -generated by differences in ionic makeup of ICF and ECF/differential permeability of the plasma membrane
  80. ECF
    extracellular fluid
  81. ICF
    intracellular fluid
  82. which has a higher concentration of Na+ (ICF or ECF)
  83. which has a higher concentration of K+ (ICF or ECF)
  84. What chemical compound plays the most important role in membrane potential
  85. Explain the difference in plasma membrane permeability with K+ Na+ and Cl-
    • -slightly permeable to Na+ through leakage channels
    • -25 times more permeable to K+ than sodium (more leakage channels)
    • -Very permeable to Cl-
  86. what happens to chloride when it goes into the cell
    it becomes hyperpolarized
  87. More potassium diffuses out than sodium diffuses in (true or false)
    True; cell more negative inside and establishes resting membrane potential
  88. is the sodium-potassium pump always going
    Yes; it stabilizes resting membrane potential, maintains concentration gradients for Na+ and K+

    -for every 3 Na+ pumped out of cell 2 K+ pumped in
  89. When does membrane potential change
    • -when concentrations of ions across membrane change
    • -membrane permeability to ions change
  90. what are the two types of signals changes in the membrane potential produce
    graded potentials and action potentials
  91. what is graded potential
    incoming signals operating over short distances
  92. action potentials
    long-distance signals of axons
  93. what are changes in the membrane potential used as
    signals to receive, integrate, and send information
  94. Depolarization
    • -decrease in membrane potential (toward zero and above)
    • -inside of membrane becomes less negative than resting membrane potential
    • -increases probability of producing a nerve impulse
  95. is the inside of a cell positive of negative and why
    it is negative because of protein
  96. what is the membrane potential threshold
    -55; -55 and above is called action potential & -54 and below is graded potential
  97. do you have to have graded potential to have action potential
  98. hyperpolarization is the opposite of what in terms of resting membrane potential
  99. hyperpolarization
    • -an increase in membrane potential (away from zero)
    • -inside of cell more negative than resting membrane potential
    • -reduces probability of producing a nerve impulse
  100. graded potentials
    • -short-lived, localized change sin membrane potential (magnitude varies with stimulus strength; stronger stimulus=father current flow)
    • -either depolarization of hyperpolarization
    • -triggered by stimulus that opens gated ion channels
    • -current flows but dissipates quickly and decays (graded potentials are signals only over short distances)
  101. change of voltage of 100 mV --> how do you get this number
    -70 resting membrane potential --> +30 =100
  102. what is the principle way neurons send signals
    action potentials
  103. what is the principal means of long-distance neural communication
    action potentials
  104. what kind of potential only occur in muscle cells and axons of neurons
    action potentials
  105. do action potentials decay over distance
    No they don't; graded potentials do though
  106. each Na+ channel has two voltage-senstive gates, what are they?
    activation gates and inactivation gates

    *they shut out unnecessary stimuli
  107. activation gates
    closed at rest; open with depolarization allowing Na+ to enter the cell
  108. inactivation gates
    open at rest; block channel once it is open to prevent more Na+ from entering cell
  109. what are the properties of K+ gated channels
    • -each K+ channel has one voltage-senstive gate
    • -closed at rest
    • -opens slowly with depolarization
  110. generation of an action potential: resting state
    • -all gated Na+ K+ channels are closed
    • -Only leakage channels for Na+ and K+ are open; which maintains the resting membrane potential
  111. generation of an action potential: depolarizing phase
    • depolarizing local currents opens voltage-gated Na+ channels
    • Na+ influx causes more depolarization which then opens more channels making ICF less negative
    • at threshold, positive feedback causes opening of ALL Na+ channels; creates a spike of action potential
  112. generation of an action potential: repolarizing phase
    • Na+ channel slow inactivation gates close
    • membrane permeability to Na+ declines (AP spike stops rising)
    • slow voltage-gated K+ channels open and K+ exits the cell so internal negativity is restored
  113. generation of an action potential: hyperpolarization
    • some k+ channels remain open, allowing excessive K+ efflux (membrane becomes more negative than -70)
    • this causes hyperpolarization of the membrane
    • Na+ channels begin to reset
  114. role of sodium-potassium pump
    • repolarization resets electrical conditions no ionic conditions
    • after depolarization Na+/K+ pumps restore ionic conditions
  115. threshold
    • -55
    • not all depolarization events produce APs
    • for the axon to "fire" signals, depolarization must reach threshold

    • @ threshold:
    • membrane has been depolarized by 15-20 mV
    • Na+ permeability increases
    • Na+ influx exceeds K+ efflux
    • the positive feedback cycle begins
  116. all or none phenomenon
    an AP either happens completely or not at all
  117. propagation of an action potential
    • propagation allow AP to serve as a signaling device
    • Na+ influx causes local currents, which causes depolarization of adjacent cells in the direction AWAY from the AP origin
    • Na+ channels closer to AP origin are inactivated so no new AP is generated there
    • once initiated, AP is self-propagating
  118. propagation of an action potential in nonmyelinated axons
    each successive segment of membrane depolarizes and then repolarizes
  119. coding for stimulus intensity
    • all APs are alike, regardless of stimulus intensity
    • CNS differentiates between weak and strong stimuli by frequency of impulses sent per second.
    • more impulses per second=stronger stimulus
  120. absolute refractory period
    • when voltage-gated Na+ channels open neuron cannot respond to another stimulus
    • time from opening of Na+ channels until resetting of the channels
    • ensures that each AP is an all-or-none event
    • enforces one-way transmission of nerve impulses
  121. relative refractory period
    • -follows absolute refractory period
    • -Most Na+ channels have returned to their resting state
    • -some K+ channels still open
    • -repolarization is occuring

    • -threshold for AP generation is elevated
    • -inside of the membrane is more negative than resting state

    -only exceptionally strong stimulus could stimulate an AP
  122. conduction velocity
    • varies widely
    • rate of AP propagation depends on the axon diameter and degree of myelination
    • axon diameter: larger diameter fibers have less resistance to current flow so a fast impulse conduction
    • degree of myelination: continuous conduction in unmyelinated axons is slower than saltatory conduction in myelinated axons
  123. saltatory conduction
    • faster than continuous conduction
    • happens in myelinated axons
    • 30x faster
    • myelin sheaths insulate and prevent leakage of charge
  124. continuous conduction
    • slower than saltatory conduction
    • happens in unmyelinated axons
  125. how are nerve fibers classified
    • diameter
    • degree of myelination
    • speed of conduction
  126. what are the three nerve fiber classifications
    group A, group B, group C
  127. group A fibers
    • large diameter
    • myelinated somatic sensory and motor fibers of skin, skeletal muscles, joints
    • transmit at 150 m/s
  128. group B fibers
    • intermediate diameter
    • lightly myelinated
    • transmit at 15 m/s
  129. group C fibers
    • smallest diameter
    • unmyelinated ANS fibers
    • transmit at 1 m/s
  130. what are the cell bodies and processes for neurons called in the CNS
    • body: nuclei
    • process: tract
  131. what are the cell bodies and processes for neurons in the PNS called
    • body: ganglia
    • process: nerve
  132. how are neurons functionally connected
    • through synapses
    • they mediate information transfer from neuron to neuron or neuron to effector cell
  133. what are the two main synapse classifications
    • axodendritic: between axon terminals of one neuron and dendrites of others
    • axosamatic: between axon terminals of one neuron and soma of others
  134. presynaptic neuron
    • neuron conducting impulses towards the synapse
    • sender of the information

    most cells function as both post & pre synaptic neurons
  135. postsynaptic neuron
    • neuron transmitting electrical signals away from the synapse
    • receives the information

    most cells function as both post & pre synaptic neurons
  136. electrical synapses
    • less common than chemical synapses
    • neurons electrically coupled
    • communication very rapid
    • may be unidirectional or bidirectional
    • synchronize activity
    • more abundant in nervous tissue
    • nerve impulse remains electrical
  137. chemical synapse
    • specialized for release and reception of chemical neurotransmitters
    • composed of two parts: axon terminal of presynaptic neuron and neurotransmitter receptor region of postsynaptic neuron's membrane
    • two parts separated by synaptic cleft
    • electrical impulse changed to chemical across synapse, then back to electrical
  138. axon terminal of presynaptic neuron
    contains synaptic vesicles filled with neurotransmitters
  139. neurotransmitter receptor region on postsynaptic neuron's membrane
    usually on dendrite or cell body
  140. the synaptic cleft
    • fluid-filled space
    • 30-50 nm wide
    • prevents nerve impulses form directly passing from one neuron to the next
  141. transition across the synaptic cleft
    • chemical event (not electrical)
    • depends on release, diffusion, and receptor binding of neurotransmitters
    • ensures unidirectional communication between neurons
  142. information transfer across chemical synapses
    • AP arrives at axon terminal of presynatic neuron
    • causes voltage gated Ca2+ channels to open (Ca2+ floods into cell)
    • synaptotagmin protein binds Ca2+ and promotes fusion of synaptic vesicles with axon membrane
    • exocytosis of neurotransmitter into synaptic cleft occurs (the higher the impulse frequency, the more neurotransmitters released)
    • neurotransmitter diffuses across synapse
    • binds to receptors of postysnaptic neuron (chemically-gated ion channels)
    • ion channels are opened
    • causes an excitatory or inhibitory event (graded potential)
    • neurotransmitter effects terminated
  143. whats the name of the protein that binds Ca2+ and fuses the synaptic vesicles with the axon membrane
  144. what are the three ways neurotransmitter effects are terminated
    • reuptake: by astrocytes or axon terminal
    • degradation: by enzymes
    • diffusion: away from synaptic cleft
  145. synaptic delay
    • time needed for neurotransmitter to be released, diffuses across the synapse, and bind to receptors
    • is rate-limiting step of neural transmission
  146. postsynaptic potentials
    neurotransmitter receptors cause graded potentials that vary in strength with the amount of neurotransmitter released and time neurotransmitter stays in area
  147. EPSP definition
    • excitatory postsynaptic potentials (graded potential)
    • shore-distance signaling, depolarization that spreads to axon hillock
    • moves membrane potential toward threshold for generating an AP
  148. IPSP
    • inhibitory postsynaptic potentials (graded potentials)
    • short-distance signaling
    • hyperpolarization that spreads to axon hillock
    • moves membrane potential away from threshold for generating an AP
  149. terms for output
    output, efferent, motor
  150. terms for input
    input, afferent, sensory
  151. EPSPs process
    • neurotransmitter binding opens chemically gated channels and allows simultaenous flow of Na+ and K+ in opposite directions
    • Na+ influx greater than K+ efflux --> net polarization called EPSP (not AP)
    • EPSP help trigger AP if EPSP is of threshold strength (can spread to axon hillock, trigger opening of voltage-gated channels and cause AP to be generated)
  152. IPSPs process
    • reduces postsynaptic neuron's ability to produce an action potential (by making membrane more permeable to K+ or Cl-; if K+ channel is open, it moves out of cell, if Cl- channel is open, it moves into cell)
    • neurotransmitter hyperpolarizes cell (inner surface of membrane becomes more negative, AP less likely to be generated)
  153. syanptic integration: summation
    • a single EPSP cannot induce an AP
    • EPSPs can summate to influence postsynaptic neuron
    • IPSPs can also summate
    • most neurons receive both excitatory and inhibitor inputs from thousands of other neurons
    • Action potential only happens if EPSPs predominate and bring to threshold
  154. what are the two types of summation
    • temporal summation: one or more presynaptic neurons transmit impulses in rapid-fire order
    • spatial summation: postsynaptic neuron stimulated simultaneously by large number of terminals at same time
  155. integration: synaptic potentiation
    • repeated use of synapse increases ability of presynaptic cell to excite postsynaptic neuron: Ca2+ concentration increases in presynaptic terminala nd postsynaptic neuron
    • brief high-frequency stimualtion partially depolarizes postsynaptic neuron: chemically gated channels allow Ca2+ entry, Ca2+ activates kinase enzymes that promote more effective responses to subsequent stimuli
  156. integration: presynaptic inhibition
    • excitatory neurotransmitter release by one neuron inhibited by another neuron via axoaxonic synapse
    • less neurotransmitter released
    • smaller EPSPs formed
  157. neurotransmitters
    • language of nervous system
    • 50 or more have been identified
    • most neurons make 2 or more neurotransmitters
    • usually released at different stimulation frequencies
    • classified by chemical structure and function
  158. acetylcholine (ACh)
    • first identified; best understood
    • released at neuromuscular junctions by some ANS neurons, by some CNS neurons
    • synthesized from acetic and choline by enzyme choline acetyltransferase
    • degraded by enzyme acetylcholinesterase (AChE)
  159. what are the two categories of biogenic amines
    • catecholamines: dopamine, norepinephrine (NE) and epinephrine; synthesized from amino acid tyrosine
    • indolamines: serotonin and histamine; serotonin synthesized from amino acid tryptophan, histamine synthesized from amino acid histidine
  160. biogenic amines (catecholamines and indolamines) traits
    • broadly distributed in the brain
    • plays roles in emotional behavior and biological clock
    • some ANS motor neurons (esp. NE)
    • imbalances associated with mental illness
  161. GABA
    • gamma aminobutyric acid (amino acid)
    • primarily inhibitory 99.9% of time
    • amino acid of neurotransmitters
  162. peptides of neurotransmitters
    • substance P: mediator of pain signals
    • endorphins: beta endorphin, dynorphin and enkaphalins; act as natural opiates and reduce pain perception (e.g. tattoos)
  163. gasotransmitters (gases and lipids)
    • nitric oxide (NO), carbon monoxide (CO) hydrogen sulfide gases (H2S)
    • bind with G protein-coupled receptors in the brain
    • lipid soluable
    • synthesized on demand
    • NO involved in learning and formation of new memories; brain damage in stroke patients, smooth muscle relaxation in intestine
    • H2S acts directly on ion channels to alter function
  164. classification of neurotransmitters based on function
    • diverse functions
    • effects: excitatory versus inhibitory
    • actions: direct versus indirect
  165. neurotransmitters classification: effects
    • excitatory vs inhibitory
    • neurotransmitter effects can be excitatory (depolarizing) and/or inhibitory (hyper polarizing)
    • effect determined by receptor to which it binds e.g. GABA usually inhibitory vs glutamate usually excitatory
  166. neurotransmitters classification: actions
    • direct vs indirect
    • direct: neutrotransmitter binds to and opens ion channels, promotes rapid responses by altering membrane potential (ACh and amino acids)
    • indirect: neurotransmitter acts through intracellular second messengers usually G protein pathways, broader long-lasting effects similar to hormones (epinephrine and norepinephrine)
  167. what are the two types of neurotransmitter receptors
    • channel-linked: mediate fast synaptic transmission
    • g protein-linked: oversee slow synaptic responses
  168. channel-linked receptors
    • ligand-gated ion channels
    • action is immediate and brief
    • excitatory receptors are channels for small cations (Na+ influx contributes most to depolarization)
    • inhibitory receptors allows Cl- influx that causes hyper polarization
  169. g protein-linked receptors
    • responses are indirect, complex, slow and prolonged
    • transmembrane protein complexes
    • cause widespread metabolic changes
    • examples ACh receptors
    • neurotransmitters binds to g protein-linked receptor, activates g protein, and activated g protein controls production of second messengers (Ca2+)
  170. second messenger proteins functions
    • open or close ion channels
    • activate kinase enzymes
    • phosphorylate channel proteins
    • activate genes and induce protein synthesis
  171. basic concepts of neural integration
    • neurons function in groups
    • groups contribute to broader neural functions
    • there are billions of neurons in CNS, so there must be integration so the individual parts fuse to make a smoothly operating whole
  172. neuronal pools
    • functional groups of neurons:
    • integrate incoming information received from receptors or other neuronal pools
    • forward processed information to other destinations

    • simple neuronal pool:
    • single presynaptic fiber branches and synapses with several neurons in pool
    • discharge zone:neurons most closely associated with incoming fiber
    • facilitated zone:neurons farther away form incoming fiber
  173. circuits (definition and 4 types)
    • patterns of synaptic connections in neuronal pools
    • four types: 
    • diverging: away from
    • converging: together
    • reverberating: again and again and again
    • parallel after discharge: parallel
  174. patterns of neural processing: serial processing
    • input travels along one pathway to a specific destination
    • system works in all-or- none manner to produce specific anticipated response
    • e.g. spinal reflexes -5 steps (receptor, sensory neuron, CNS integration center, motor neuron, effector)
  175. patterns of neural processing: parallel processing
    • input travels along several pathways
    • different parts of circuitry deal simultaneously with the information
    • important for higher-level mental functioning
    • e.g. certain scent may remind one of an odor and associated experiences
  176. neuronal cell death
    • about 2/3 of neurons die before birth
    • if they do not make a connection, they die
    • also due to apoptosis
  177. comparing AP to GP
    • GP:
    • location of event: cell body and dendrites
    • distance traveled: short (cell body to axon hillock)
    • size: various sizes; decays with distance
    • stimulus for opening ion channels: chemical or sensory (temp, light)
    • positive feedback: absent
    • repolarization: voltage independent, occurs when stimulus is no longer present
    • summation: stimulus can summate to increase amplitude of graded potential (temporal or spatial)
    • function: EPSP or IPSP
    • initial effect: opens chemically gated channels that allow NA+ K+ fluxes or opens chemically gated K+ or Cl- channels
    • peak membrane potential: depolarizes and hyperpolarizes

    • AP:
    • location of event: axon hillock and axon
    • distance traveled: long, entire length of axon
    • size: always the same, all or none
    • stimulus for opening ion channels: voltage (depolarization triggered by GP reaching threshold)
    • positive feedback: present
    • repolarization: voltage regulated; occurs when Na+ channels inactivate and K+ channels open
    • summation: does not occur, all or none phenomenon
    • function: long distnce signaling; constitutes the nerve impulse
    • initial effect of stimulus: opens voltage-gated channels; first Na+ channels then K+ channels
    • peak membrane potential: +30 -- +50