HORMONES AND BEHAVIOR Psychology

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Synapses and Neurotransmitters

• What is a Synapse? (3.1)
• the properties of a synapse
• relationship between APs, EPSPs, and IPSPs
• Chemical Events of the Synapse (3.2)
• sequence of events
• neurotransmitters

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Action potentials are due to __________ channels
opening. A) sodium (Na) B) calcium (Ca2) C)
chloride (Cl-) D) two of the above
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Which of the following statements is false? A)
resting potential is -70 mV B) the amplitude
of an action potential increases as the
stimulus increases C) Na concentration is
greater outside than inside the
membrane D) K concentration is greater inside
than outside the membrane
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Synapses
How do neurons communicate with each other ???
Cajal (late 1800s) neurons do not physically
merge into each other there appeared to be a gap
between neurons (anatomical studies) Sherrington
(1906) described a specialized form of
communication that occurs with the gap
between adjacent neurons, he called this the
synapse (behavioral studies of stretch
reflexes)
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Sherrington discovered that reflexes are slower
than conduction along the neuron.
Evidence for Synaptic Delay
Same Distance
Faster
Slower
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Sherrington discovered that multiple weak stimuli
can produce a stronger reflex than a one stronger
stimulus.
Temporal Summation Repeated stimuli occurring
within a brief time can have a cumulative effect.
Spatial Summation Several synaptic inputs
originating from separate locations can have a
cumulative effect.
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Recording from a Postsynaptic Neuron During
Synaptic Activation
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Excitatory and Inhibitory Synapses
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Chemical Events at the Synapse
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Neurotransmitters

• Neurotransmitters chemicals that are released by
  one neuron at the synapse and affect another
  neuron
• each neuron synthesizes its neurotransmitters
  from materials in the blood
• the functions of many neurotransmitters have
  been identified
• Types of Neurotransmitters
• 1) acetylcholine
• 2) monoamines (serotonin, dopamine, epinephrine,
  norepinephrine)
• 3) amino acids (glutamate, GABA)
• 4) peptides (neuropeptide Y, endorphin)
• 5) purines (ATP, adenosine)
• 6) gases (nitric oxide)

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Neurotransmitters
Synthesis of Neurotransmitters neurotransmitters
are synthesized from precursor molecules that are
derived from the food we eat
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Neurotransmitters

• Transport of Neurotransmitters
• neurotransmitters can be synthesized in the cell
  body or in the
• presynaptic terminals
• they are then stored in vesicles so they will be
  available for transport/release
• the process of secreting the neurotransmitter
  into the synaptic cleft is called
• exocytosis

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Neurotransmitters

• Activation of Receptors
• neurotransmitter receptors are protein
  structures embedded in the membrane
• neurotransmitters bind to the active site of
  specific receptors
• this binding opens a channel and can produce
  ionotropic or metabotropic effects on the
  postsynaptic neuron

Ionotropic Effects gate opens and permits entry
of an ion rapid effect short lived Metabotropic
Effects gate opens and initiates a sequence of
metabolic reactions slower effect long lasting
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Ionotropic Effect Ion Channels
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Metabotropic Effect Second Messenger Systems
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Release and Disposal of Neurotransmitters
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Factors Influencing the Release and Disposal of
Neurotransmitters