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Psychology 304: Brain and Behaviour

Lecture 14

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Following last class, a number of students expressed concern about the amount of content in Chapters 1-5 of the textbook. Accordingly, I have modified the chapters that will be included on the midterm exam. The midterm exam will cover Chapters 1-4 of the textbook and all related content discussed in class.

Given this modification, we will not discuss Chapter 6 in the first term of this course. The December exam will cover Chapters 5 and 7-10 of the textbook and all related content discussed in class.

Reminder

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Exam Preparation Tips

• The exam will include questions unique to the textbook content, questions unique to the lecture content, and questions that reflect overlap between the two sources of information. You are encouraged to study both sources of information thoroughly.

• The goal of the exam is to assess your mastery of thecourse content. Accordingly, the more thoroughly you know the course content, the stronger your performance will be.

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Identify the primary points of each section with key words or phrases and use these key words or phrases to test yourself.

• With respect to the textbook:

Familiarize yourself with all terms that are bolded or italicized.

Create questions with the title and subtitles of each section. Use the content of each section to answer the questions that you have generated.

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• You should familiarize yourself with the functions of brain structures and the cranial nerves. Note that you will not be asked to label the locations of the cranial and spinal nerves.

• The exam questions will assess your ability to recall, synthesize, and apply course content. Examples:

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Recall:

The cranial nerve that controls the movement of the tongue muscles is the:

(a) vagus nerve.(b) abducens nerve. (c) trigeminal nerve. (d) hypoglossal nerve.(e) trochlear nerve.

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Synthesize:

Research has demonstrated that epilepsy is associated with excessive neuronal excitation. Accordingly, epilepsy may be treated by inhibiting the excitation or “firing” of neurons. Which of the following would be most effective in reducing neuronal firing among individuals with epilepsy?

(a) A calcium (Ca2+) agonist.(b) A calcium (Ca2+) antagonist. (c) A glutamate agonist.(d) A GABA antagonist.

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Apply:

You are a biological psychologist who has discovered a new brain structure. The structure contains a small cluster of nuclei and is situated beneath the hypothalamus. You are interested in determining the function(s) of this structure. Identify two techniques that you would use to determine the function(s) of this structure. Limit your response to techniques for determining function discussed in class or in the textbook. In your response, describe the procedure associated with each technique.

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• In order to correctly respond to questions that require synthesis and application, recall of information is

necessary. The correlation between recall questions and synthesis/application questions typically exceeds .70.

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Transmission of Electrochemical Neural Signals

1. What is the structure of the synapse between two neurons?

2. How are neurotransmitters released from presynaptic neurons?

3. How do neurotransmitters generate electrochemical signals in postsynaptic neurons?

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By the end of today’s class, you should be able to:

1. describe the structure and function of the 7 types of synapses.

2. explain the process by which neurotransmitters are released from neurons.

3. distinguish between ionotropic and metabotropic receptors.

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• Action potentials arriving at terminal buttons trigger the release of neurotransmitters. The neurotransmitters are released into the synapses (i.e., “synaptic clefts”) between neurons, allowing neurons to communicate.

What is the structure of the synapse between two neurons?

• Most communication between neurons occurs across axodendritic synapses.

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Synaptic cleft

Synapsticcleft

Structure of an Axodendritic Synapse

14Electron Micrograph of an Axodendritic Synapse

Synaptic cleft

Vesicles

Presynaptic membrane

Postsynaptic membrane

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• Several other synaptic arrangements, however, have been identified: axosomatic synapses, dendrodendritic synapses, axoaxonic synapses, directed synapses, nondirected synapses, and gap junctions.

16An Axoaxonic Synapse

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Figure 4.9

A Nondirected Synapse

18Gap Junctions

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How are neurotransmitters released from presynaptic neurons?

• When stimulated by an action potential, voltage-activated calcium channels open and Ca2+ ions enter the terminal

button. This causes vesicles in the button to fuse with the presynaptic membrane and release their contents into the synaptic cleft.

20Release of Neurotransmitters into the Synaptic Cleft

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Presynaptic membrane

Release of Neurotransmitters into the Synaptic Cleft

Synaptic cleftNeurotrans-mitter

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How do neurotransmitters generate electrochemical signals in postsynaptic neurons?

• Neurotransmitters produce signals in postsynaptic neurons by binding to receptors in the postsynaptic membrane.

• A neurotransmitter that binds to a receptor is referred to as a ligand.

• Most neurotransmitters can bind to a number of receptor subtypes. Among these subtypes are:

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Ionotropic receptors (IRs): When activated by a neurotransmitter, IRs cause ligand-activated ion (e.g., Na+, K+, Cl-) channels to open or close, producing an immediate change in potential (EPSP or IPSP) on the postsynaptic membrane.

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Ionotropic Receptor Activity

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Metabotropic receptors (MRs): When activated by a neurotransmitter, MRs cause a subunit of an associated G protein to break away. The subunit either:

1. binds to a ligand-activated ion (e.g., Na+) channel, causing the channel to open or close, producing an immediate change in potential (EPSP or IPSP) on the postsynaptic membrane (Figure A).

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2. triggers the synthesis of a second messenger which: (a) binds to a ligand-activated ion channel, causing the channel to open or close, or (b) diffuses through the cytoplasm where it influences the activities of the neuron (Figure B).

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Metabotropic Receptor Activity

Figure A Figure B

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Transmission of Electrochemical Neural Signals

1. What is the structure of the synapse between two neurons?

2. How are neurotransmitters released from presynaptic neurons?

3. How do neurotransmitters generate electrochemical signals in postsynaptic neurons?