Chapter 13 SYNAPSES

Chapter 13 SYNAPSES

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DOWNLOAD an Adobe Acrobat version of the chapter outline 6 slides per page

review questions

Background from Introductory Biology Courses

  1. On-Line Biology Book by M. J. Farabee 
    1. Nervous system
  2. Kimball's Biology Pages
    1. Neurons from Kimball's Biology Pages
    2. Synapses
  3. Wikipedia
  4. Neuroscience for kids
  5. Physioviva Educational Videos

  1. Hill, Wyse, and Anderson
    1. Chapter Outline
    2. Chapter Summary
    3. Flashcards


      1. pre-synaptic neurons: send signals
      2. post-synaptic neurons, muscles, glands: receive signals
    2. Two types of synapses
      1. Electrical synapses (Fig. 13.1a)
      2. Chemical synapses (Fig. 13.1b)
        1. The Chemical Synapse video from McGraw Hill
        2. Transmission across a synapse video from McGraw Hill
    3. Electrical Synapses
      1. found in high speed systems in invertebrates and (rarely) vertebrates
      2. Vertebrates: CNS, retina, and cardiac & some smooth muscle
      3. Electrical continuity between neurons: Gap junction
    4. Chemical Synapse (Fig. 13.4)
      1. Unidirectional signal
      2. Slower than electrical transmission
      3. Excitatory OR inhibitory
      4. Fast (ionotropic) or slow (metabotropic)
      5. Neurotransmitter
        1. brief effect on postsynaptic membrane
    5. Chemical Synapses
      1. gap called synaptic cleft .
      2. knob is presynaptic, dendrite is postsynaptic.
      3. knob contains hundreds of vesicles containing neurotransmitters.
    6. Figure 13.6  The function of a chemical synapse: Berkeley mcb64
      1. depolarization causes calcium channels to open (Fig. 13.6a)
      2. Calcium rushes into the presynaptic terminal.
      3. vesicles fuse with membrane and release neurotransmitters (NT) (Fg. 13.6b)
      4. NT diffuse across cleft
    7.  Ionotropic Receptors (Figure 13.6c)
      1. NT bind to ionotropic (fast synapse) ligand gated receptors (Fig.2.27a)
      2. Sodium channels open
      3. NT is removed from the synaptic cleft
      4. NT can trigger an action potential in the post synaptic cell
    8. Metabotropic Receptors (Figure 13.6d)
      1. Intracellular messengers
      2. G protein-coupled receptor activates G protein, causing metabolic cascade,
      3. Ion channels open or close
      4. Provide slow modulatory responses
      5. NTs larger and may contain amino acids
    9. Postsynaptic Potential (Fig. 13.7)
      1. EPSP,  Excitatory postsynaptic potential:
        1. Excitation: cell is depolarized
        2. Na channels open
        3. NT in neuromuscular junction (PNS) is acetylcholine
        4. NT in CNS is glutamate
      2. IPSP: Inhibitory postsynaptic potentials
        1. hyperpolarization (K channels open)
        2. NT is GABA or glycine (increases cell membrane permeability to Cl-)
    10. Postsynaptic Potentials are Graded
      1. multiple stimuli change potential
      2. Cerebellum neurons can have input from 150,000 synapses
    11. Neuromuscular junction (Figs. 13.8-13.9)
    12. Signal Transmission
      1. Summation
        1. multiple stimuli slowly increase the change in potential
        2. temporal summation
        3. spatial summation
        4. enough change triggers an action potential
    13. Acetylcholine synthesis and breakdown (Fig 13.11)
      1. enzymes (e.g., acetylcholinesterase) mop up the transmitters present in the synapse
    14. Neurotransmitters  (Table 13.2)
    15. More than 50 transmitters identified
      1. Acetylcholine (most common)
      2. Biogenic amines (derived from amino acids)
        1. Norepinephrine
        2. Dopamine
        3. Serotonin
      3. Amino acids
      4. Neuropeptides (short chains of amino acids)
        1. Endorphin
      5. Some vertebrate neurons use gas molecules as regulators
    16. Acetylcholine (Ach)
      1. Excitatory to nicotinic receptors (ionotropic) on skeletal muscle
      2. Inhibitory to muscarinic receptors (metabotropic) of the autonomic nervous system
        1. Blocked by atropine
      3. Nicotine excites acetylcholine receptors
        1. Curare replaces and blocks acetylcholine in receptor sites: flaccid paralysis
        2. Botulism blocks the release of ACh from presynaptic terminal.
        3. Black widow bite prevents release of ACh
        4. People with Alzheimer's have low levels of ACh
        5. Nerve agents : Interfere with Acetylcholine esterase
    17. Neurotransmitters: Novel Messengers
      1. Nitric oxide (NO) has role in vasodilation of blood vessel
      2. Viagra --> NO release --> cGMP --> smooth muscle relaxation --> increased blood flow --> erection

    From Wikipedia: Illustration of the major elements in chemical synaptic transmission. An electrochemical wave called an action potential travels along the axon of a neuron. When the wave reaches a synapse, it provokes release of a puff of neurotransmitter molecules, which bind to chemical receptor molecules located in the membrane of another neuron, on the opposite side of the synapse.

    Source of drawing illustrating the process of synaptic transmission in neuron :






    From Wikipedia: Schematic of a chemical synapse between an axon of one neuron and a dendrite of another. Synapses are specialised minute gaps between neurons. The electrical impulses arriving at the axon terminal triggers the release of packets of chemical messengers (neurotransmitters), which diffuse across the synaptic cleft to receptors on the adjacent dendrite temporarily affecting the likelihood that an electrical impulse will be triggered in the latter neuron. Once released the neurotransmitter is rapidly metabolised or is pumped back into a neuron.


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