Lecture 1: The Nervous System

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  1. What is the function of the Nervous System?
    It helps the body structures and functions to control and communicate w/each other through three mechanisms.
  2. What three mechanisms does the Nervous system use to control and communicate body structures and functions with one another?
    • Sensory Input
    • Integration
    • Motor output
  3. What is Sensory Input?
    Information gather by sensory receptors about internal and external changes
  4. What is Integration?
    Interpretation of sensory input
  5. What is Motor output?
    Activation of effector organs (muscles and glands) which produce a response
  6. Into what two divisions is the Nervous System divided?
    • Central Nervous System (CNS)
    • Peripheral Nervous System (PNS)
  7. What makes up the CNS?
    Brain and the spinal cord
  8. What does the PNS consist of?
    Paired Spinal and Crainal nerves
  9. How is the PNS further divided?
    • Afferent (sensory) division
    • Efferent (motor) division
  10. What does the Afferent division of the PNS do?
    carries impulses to the CNS
  11. What does the Efferent division of the PNS do?
    I carries impulses from the CNS to effector organs
  12. How is the Affernet (sensory) dvision further divided and what does each division do?
    • Somatic-carries impulses from the skin, skeletal musclesl, and joints
    • Visceral- carries impulses formt eh visceral (internal) organs.
  13. How is the Efferent (motor) division further divided and what does each division do?
    • Somatic (voluntary) - concscious control of skeletal muscles.
    • Autonomic (invouluntary) - Visceral motor fibers-Regulates Smooth muscle, cardiac muscle, and glands
  14. How is the Autonomic Efferent division of the PNS further divided?
    • Sympathetic - (flight or fight)
    • Parasympathetic (Rest, Restore, Digest)
  15. What are the two principle cell types of the Nervous System?
    • Neurons
    • Neuroglia
  16. What are neurons?
    excitalbe cells that transmit eletrical signals
  17. What are neurogalia?
    supporting cells
  18. How many Neurogalia (glial) cells are there? State the Names and locations in the Nervous System ( CNS or PNS).
    • SIX
    • Astroyctes (CNS)
    • Mircogalia (CNS)
    • Epindymal (CNS)
    • Oligodendrocytes (CNS)
    • Satellite (PNS)
    • Schwan Cells (PNS)
  19. Describe Astrocytes.
    • Most abundant and highly branced glial cells
    • Support neurons
    • Help determine capillary premeability
    • Guid migration of young neurons
    • Control the chemical enviroment
  20. Describe Microglia (microphages)
    • Migrate toward injured neurons
    • Phagocytize microorganisms and neuronal debris
  21. Describe Ependymal Cells.
    • Line the central cavities of the brain and spinal column
    • Separate the CNS interstitial fluids from the cerebrospinal fluids in the cavities
  22. Describe Oligodendrocytes
    • Branced cells
    • Processes wrap CNS nerve fibers, forming insulating myelin sheaths
  23. Describe Satellite Cells
    Surrond neuron cell bodies in the PNS
  24. Describe Schwan Cells (neurolemmocytes)
    • Surround peripheral nerve fibers and form myelin shealths
    • Vital to regeneration of damaged peripheral nerve fibers
  25. What are the special characteristics of Neurons
    • Long-lived (100yrs+)
    • Amitoitc
    • High metabolic rate
    • Plasma membrane functions in : Electrical signaling
  26. Describe the Cell body ( Perikaryon or Soma)
    • Biosyntheic center of a neuron
    • Spherical nucleus with nucleolus
    • Well-developed Golgi apparatus
    • Rough ER called Nissl Bodies
    • Network of neruofibrils (neurofilaments)
    • Axon hillock- cone shaped area from which axon arises
    • Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS
  27. What are clusters of cell bodies called in the CNS?
  28. What are clusters of cell bodies called in the PNS?
  29. Name the processes
    Dendrites and axons
  30. What are Bundles of processes called in the CNS?
  31. What are Bundles of processes called in the PNS?
  32. Describe a Dendrite
    • Short, tapering, and diffusely branched
    • Receptive (input) region of a neuron
    • Convey electrical signals toward the cell body
  33. Describe the Axon
    • One axon per cell arising from the axon hillock
    • Long axons (nerver fibers)
    • Occasional branches (axon collaterals)
    • Knoblike axon terminals (synaptic knobs): 1.secretory region of neurons 2. release neurotransmitters to excite or inhibit other cells
  34. Describe Axon functions
    • Conducting region of a neuron
    • Generates and transmits nerve impulses (action potentials) away from the cell body
    • Molecules and organelles are moved along axons by motor molecules (protien carriers) in two directions: 1. Anograde-toward axon terminal 2. Biograde- toward the cell body
  35. What is Anterograde
    • the movement of molecules and organelles by motor molecules toward axonal terminal
    • ex: mitochondria, membrane componenets, enzymes
  36. What is Retrograde
    • the movement of molecules and organelles by motor molecules toward the cell body
    • ex: organelles to be degraded, signal molecules, viruses, and bacterial toxins
  37. What is a Myelin Shealth?
    Segmented protein-lioid sheath around most long or large-diameter axons
  38. What is the function of a Myelin Sheath?
    • Protects and electrically insulates the axon
    • Increases speed of nerve impulse transmission
  39. Describe Myelin Shealths in the PNS
    Concentric layers of Schwann cells that wrap many times around the axon.
  40. What is the Neurilemma?
    It is the peripheral bulge of Schwann cells, the outermost layer. In the PNS
  41. What is the Nodes of Ranvier?
    • Myelin sheath gaps between adjacent Schwann cells
    • Sites where axon collaterals can emerge (ocassional)
  42. Are there unmyelinated Axons?
    There are some thin and small nerve fibers which are unmyelinated without affection of the function
  43. What are Myelin Sheaths in the CNS formed by?
    Formed by processes of oligodendrocytes, not whole cells
  44. True or False, there is a Neurilemma in the Myelin Sheaths of the CNS.
    False: there is no neurilemma in the myelin sheath in the CNS as the whole oligodendrocyte is not used.
  45. True or False, Node of Ranvier are present in Myelinated Axons in the CNS.
  46. White matter is made up of what?
    A dense collection of myelinated fibers
  47. Gray matter is made up of what?
    Mostly neuron cell bodies and unmyelinated fibers
  48. What are the three types of neurons (Classified by function) ?
    • Sensory
    • Motor
    • Interneurons
  49. What do Sensory Neurons do?
    Transmit impulses from sensory receptors toward the CNS
  50. True or False, Sensory neurons are Efferent.
    False, they are afferent
  51. What do Motor Neurons do?
    Cary impulses from the CNS to effectors
  52. True or False, Motor Neurons are Efferent.
  53. What do Internuerons (association neurons) do?
    Shuttle signal through CNS pathways, most are entirely within the CNS
  54. True or False: Neurons are highly irritable
    True, neurons are excitable
  55. If a neuron has an adequate stimulus what does it do
    It responds to adequate stimulus by generating and action potential ( nerve impulse)
  56. What serves as membrane ion channels?
    Protiens serve as membrane ion channels
  57. What are the two main types of ion channels?
    • Leakage (nongated) channels- always opened
    • Gated Channels: open and close
  58. What are the three types of gated channels?
    • Chemically gated (ligand-gated) channels
    • Voltage-gated channels
    • Mechanically gated channels
  59. Do Chemically Gated Channels open, close or both, and how?
    open with binding of a specific neurotransmitter
  60. Do Voltage-gated channels opem, close, or both, and how?
    open and close in response to changes in membrane potential
  61. Do Mechanically gated channels open, close or both, and how?
    open and close in response to physical deformation of receptors
  62. What happens when gated channels are open
    • Ions diffuse quickly across the membrane along their electrochemical gradients
    • Along chemcial concentration gradients from higher concentration to lower concentration
    • Along electrical gradients toward opposite electrical charge
    • Ion flow creates an electrical current and voltage changes across the membrane
  63. What is the potential difference across the membrane of a resting cell?
    Approximately -70mV in neurons (cytoplasmic side of membrane is negatively charged relative to outside)
  64. What are the Potential differences genertated by?
    • Differences in ionic makeup of ICF and ECF
    • Selective premeability of the plasma membrane
  65. What are the differences in ionic makeup in the cell membrane?
    • ICG has lower cncentration of Na+ and Cl- than ECF
    • ICF has higher concentration of K+ and negatively charged proteins (A-) than ECF
  66. Describe the Premeabiltiy of the Cell membrane
    • Impremeable to A-
    • Slightyly premeable to Na+ (through leakage channels)
    • 75 times more premeable to K+ ( more leakage channels)
    • Freely permeable to Cl-
  67. What stabilizes the resting membrane potential?
    the Sodium-potassium pump stabilizes the resting membrane potential by maintaining the concentration gradeints for Na+ and K+
  68. Membrane potential changes when
    • Concentrations of ions across the membrane change
    • Permeability of membrane to ions changes
  69. What are changes in membrane potentials used for?
    the changes are signals which are used to receive, integrate and send information
  70. What are the two types of signals in Membrane potentials?
    • Graded ptentials - Incoming short-distance signals
    • Action potentials- Long- distance signals of axons
  71. What happens during depolarization?
    The membrane potential goes toward ZERO point and then becomes positve
  72. What happens during depolarization?
    • The membrane potential goes towards the ZERO point and then becomes more and more positive.
    • Increases the probability of producing a nerve impulse.
    • Image Upload 1
  73. What happens during Hyperpolarization?
    • The membrane potential becomes more negative than RMP
    • Reduces the probability of producing a nerve impulse
    • Image Upload 2
  74. What are Graded potentials?
    • Short-lived localized changes in membrane potentials
    • Depolarizations or Hyperpolarizations
    • Graded potential spreads as local currents change the membrane potential of adjacent regions
    • Occur when astimulus causes gated ion channels to open
    • Magnitude varies directly (graded) with stimulus strength
    • Decrease in magnitude with distance
    • Short-distance signals
    • Image Upload 3
  75. What is Action Potential (AP) ?
    • Brief reversal of membrane potential with a total amplitude of about 100mV (from -70mV to +30mV)
    • Principal means of long-distance neural communication
    • Image Upload 4
  76. Where does Action Potential occur?
    in muscle cells and axons of neurons
  77. True or False, Action Potential decreases in magnitude over distance
    False it does not decrease in magnitude over distance
  78. During the Resting state in the Generation of Action Potential what happens?
    • Only Leakage channels for Na+ and K+ are open
    • All gated Na+ and K+ channels are closed
    • Image Upload 5
  79. Describe the Na+ Channel
    • Closed at rest
    • Open fast with depolarization
  80. Describe K+ Channels
    • Close at rest
    • Opens slowly with depolerization
  81. What Happens During the Depolarizing Phase?
    • The depolarized local currents open voltage-gated Na+ Channesl
    • Na+ influx causes more depolarization
    • At threshold (-55to -50mV) positive feedback leads to opening of all Na+ channels, and a reversal of membrane polarity to +30mV(spike of action potential)
    • Image Upload 6
  82. What happens during Repolarization?
    • Na+ Channel closes
    • Membrane premeability to Na+ declines to resting levels
    • Slow voltage-sensitive K+ gates open
    • K+ exits the cell and internal negativity is restored
    • Image Upload 7
  83. What happens during Hyperpolarization
    • Some K+ channels remain open, allowing excessive K+ efflux
    • Image Upload 8
    • *NOTE: Hyperpolarization occurs below -70mV(resting potential)
  84. True or False, Sodium-Potassium pumps always restore the origninal resting membrane potential by maintaing the concentration gradients for Na+ and K+
  85. Give a brief summary of Action Potential.
    • Na+ influx causes a patch of the axonal membrane to depolariz
    • Local currents occur
    • Na+ channels toward the point of origin are inactivated and not affected by the local currents
    • Local currents affect adjacent areas in the forward direction
    • Depolarization opens voltage-gated channels and triggers an AP
    • Repolarization wave follows the depolarization wave
  86. Threshold
    • Membrane is depolarized by 15 to 20mV( around -55 to -55 mV)
    • Na+ permeability increases
    • Na influx exceeds K+ efflux
    • the positive cycle begins
  87. What is the All or none phenomenon?
    It is action potentials either completely happening or not based on it reaching or not reaching the threshold
  88. Graded or Action Potentials?
    Ligand or mechanically gated
  89. Graded or Action Potentials?
    Voltage gated
  90. Graded or Action Potentials?
  91. Graded or Action Potentials?
    Long distances
  92. Graded or Action Potentials?
    Not propagated
  93. Graded or Action Potentials?
    Short distances
  94. Graded or Action Potentials?
    Depends on strenght of stimulus
  95. Graded or Action Potentials?
    All or none
  96. What effect does the axon diameter have on conduction?
    The larger the diameter fibers the faster the impulse of conduction
  97. What effect does myelination have on the conduction velocity?
    Continuous conduction in unmyelinated axons is slower than saltatory conduction in myelinated axons
  98. True of False: Myelin Sheaths insulate and prevent leakage of charge
  99. How much faster is conduction in myelinated axons?
    Saltatory conduction in myelinated axons is about 30 times faster
  100. Where are voltage gated Na+ channels located?
    they are in the nodes
  101. True or false:
    APs jump slowly from node to node
    False, APs appear to jump rapidly from node to node
  102. What is a synapse?
    A junction that mediates information transfer from one neuron to A) another neuron or B) an effector cell
  103. What is a presynaptic Neuron
    Conducts impulses toward the synapse
  104. What is a postsynaptic Neuron?
    transmits impulses away from the synapse
  105. What is an Axodenrtic Synapse?
    A sypase b/w the axon of one neuron and the dendrite of another
  106. What is an Axosomatic synape?
    A synapse b/w the axon of one neuron and the soma of another
  107. What are Electical Synapases?
    • Less common than chemical synapses
    • Neurons ar eelectrically coupled (joined by gap junctions)
    • Communication is very rapid, and may be unidirectional or bidirectional
    • Are important in: Embyronic nervous tissue
  108. Whate are Chemical Synapses?
    • they are specialized for the release and reception of neurotransmitters
    • Typically composed of two parts : A) Axon terminal of the presynaptic neureon, which contains synaptic vesicles B) Receptor region on the postsynaptic neuron
  109. What is the Synaptic Cleft?
    • It is a fluid-filled space separating the presynaptic and postsynaptic neurons
    • Prevents nerve impulses from directly passing from one neuron to the next
  110. Describe the Transmission across the synaptic cleft:
    • It is a chemical event (as oppesed to an electrical one)
    • Involves release, diffusion and binding of neurotransmitters
    • Ensures unidirection communication b/w neurons
  111. Describe Information Transfer
    • AP arrives at axon terminal of the presynaptic neuron and opens voltage -gated Ca2+ channels
    • Ca2+ ions promote fusion of synaptic vesicles with axon membrane
    • Exocytosis of neurotransmitter occurs
    • Neurotransmitter diffuses and bind to receptors (often chemically gated ion channels) on the postsynaptic neuron
    • Ion channels are opened, causing and excitatory or inhibitory event
  112. Describe the termination of Neurotransmitter Effects
    • Within a few milliseconds the neurotransmitter effect is terminated
    • Degradation by enzymes
    • Reuptake by astrocytes or axon terminal
    • Diffusion away form the synaptic cleft
  113. Describe Synaptic Delay
    • Neurotransmitter must be released, diffuse across the synaps, and bind to receptors
    • Synaptic delay-time needed to do this (0.3-5.0 ms)
  114. How is the strength of Postsynaptic Potentials determined?
    • Amount of neurotransmitters released
    • Time the neurotransmtter is in the area
  115. What are the types of postsynaptic potentials
    • EPSP- Excitatory Postsynaptic Potentials
    • IPSP- Inhibitory Postsynaptic Potentials
  116. Describe Excitatory Synapes and EPSPs
    • Neurotransmitter binds to and opens chemically gated channes that allow simultaneous flow of Na+ and K+ in opposite directions
    • Na+ influx is greater than the K+ efflux, causing a net DEPOLARIZATION
    • EPSP helps trigger AP at axon hillock if EPSP is of threshold strength and opens the voltage-gated channels
  117. Describe Inhibitory Synapses and IPSPs and its function.
    • Neurotransmitter binds to and opens channeslfor K+ or Cl_
    • Causes a HYPERPOLARIZATION (the inner surface of membrande becomes more negative)
    • Reduces the postsynaptic neurons ability to produce an action potential
  118. What are Neurotransmitters?
    • Most neurons make two or more neurotransmitters, which are released at diffenent stimulation frequencies
    • 50 or more neurotransmitters have been identified
  119. How are neurotransmitters classified?
    by the chemical structure and by function
  120. Describe Acteylcholine ( Ach)
    • Excitatory in skeletal muscles and inhibitory in cardiac muscles
    • Synthesized by enzyme choline acetyltransferase
    • Degraded by the enzyme acetylcholinesterase (AChE)
  121. Describe Amies, what do they include?
    • Include: Dopamine, Norepinephrine (NE), Epinephrine, Serotonin, and Histamine
    • Broadly distrubuted in the brain
    • Plays key roles in brain function
  122. Describe Amion Acids, and what they include.
    • GABA- Gamma (y)-aminobutyric acid
    • Glycine
    • Aspartate
    • Glutamate
  123. Describe Peptides (neuropeptides) and what they include.
    • Substance P: mediatior of pain signals
    • Endorphins: Act as natural opiates; reduce pain perception
    • Gut-brain peptides:somatostatin and cholecystokinin
  124. Purines such as ATP do what?
    • Act in both the CNS and PNS
    • Produce fast or slow responses
    • Induce Ca2+ influx in astrocytes
    • Provoke pain sensation
  125. If a neurotransmitter is Depolarizing what type of effect does it have? Excitatory or Inhibitory?
  126. If a neurotransmitter is Hyperpolarizing what type of effect does it have? Excitatory or Inhibitory?
  127. What determines whether a neurotransmitter is inhibitory or excitatory?
    The receptor type of the postsynaptic neuron
  128. True or False, GABA and glycine are usually excitatory.
    False they are usually inhibitory
  129. True or False, Glutamate is usually Excitatory.
  130. Where is Acetylcholine excitatory, and where is it inhibitory?
    • Its Excitatory @ neuromuscular junctions in skeletal muscle
    • Inhibitory in cardiac muscle
  131. Describe the Direct Action of a neurotransmitter.
    • Neurotransmitter binds to channel-linked receptor and opens ion channels
    • Promotes rapid responses
    • Ex: ACh and amino acids
  132. Describe the Indirect Action of a neurotransmitter.
    • It needs a sendary messenger
    • Neurotransmitter binds to a protein-linked receptor and acts through an intracellular second messenger
    • Promotes long-lasting effects
    • Examples: biogenic amines
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Lecture 1: The Nervous System
The Nervous System
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