1 Big Neuron and Synapse Foldable – Answer Key What you expect your students to produce will depend on their grade level and their academic level. The detailed information provided in the answer key is to give you a more thorough understanding about this topic. You most likely do not require your students to know all the details, so for your ease of use, highlight which details you would like students to know and use these to guide your lessons. Note: Structures with an asterisk * next to it are not found in plant cells. Step Function 1. The action potential arrives at the axon terminal and depolarizes the pre-synaptic membrane. 2. The action potential triggers voltage-gated Ca2+ channels to open on the pre-synaptic membrane. 3. Ca2+ enters the pre-synaptic neuron. 4. The presence of Ca2+ within the pre-synaptic neuron activates synaptic vesicles. 5. Synaptic vesicles containing neurotransmitters (e.g. acetylcholine) to migrate to and fuse with the pre-synaptic membrane. 6. Vesicles are released into the synaptic cleft through exocytosis. 7. Neurotransmitters diffuse across the cleft (20nm wide) and bind to receptors (e.g. acetylcholine receptor) on the post-synaptic membrane. This either excites (acetylcholine excites) or inhibits the post-synaptic membrane by generating excitatory post-synaptic potentials (EPSPs) or inhibitory post-synaptic potentials (IPSPs) respectively. 8. In some pre-synaptic neurons, autoreceptors are present that help regulate the function of the pre-synaptic neuron. Autoreceptors bind to the neurotransmitters to provide a feedback loop that regulates the amount of neurotransmitter that is released. The more the autoreceptors bind, the less neurotransmitters are released. 9. Transporter proteins on the pre-synaptic membrane help with the reuptake of neurotransmitters from the cleft back into the pre-synaptic neuron. This helps to reverse the effects of the neurotransmitter. 10. Enzymes (e.g. acetylcholinesterase) in the synaptic cleft break down the neurotransmitter to reverse its effects. The products of this breakdown (e.g. acetate and choline) will get reabsorbed back into the pre-synaptic neuron to get reformed into active neurotransmitters again. Structure 11. dendrites Function These are branched projections off of the cell body that receive information from the axon terminals of other neurons through synaptic transmissions. The dendritic tree (post-synaptic membrane surface) provides a large surface area for communication with other neurons and it is here that EPSPs and IPSPs are generated. © Tangstar Science 2 12. axon hillock This is a specialized part of the cell body that connects to the axon. This is where post-synaptic potentials (the EPSPs and IPSPs) are summated before being transmitted down the axon. Summation determines whether or not an action potential will be triggered by the combined effects of the post-synaptic potentials. 13. Schwann cell These are the primary glial (non-neuronal) cells of the nervous system. There are two types of Schwann cells – myelinating and non-myelinating. The myelinating type wraps itself around the axons of sensory and motor neurons and produce a fatty white substance called myelin. This forms the myelin sheath. 14. axon terminals These are the terminal branch points at the end of an axon. They are also called synaptic boutons. Between an axon terminal and the surface of the next neuron/cell is a small gap called the synaptic cleft. These three structures together form the synapse. The axon helps promote the electrical transmission of the nerve impulse, and the synapse promotes the chemical transmission of the nerve impulse through the use of neurotransmitters. 15. cell body This is the part of a neuron that contains the nucleus and the majority of the organelles. It is also called the soma. 16. nodes of Ranvier These are the gaps found in the myelin sheath (between Schwann cells) and are 1 micrometer wide. Only in these areas, where the axon is not insulated by the myelin sheath, can the electrical impulse jump from node to node. This is called salutatory conduction and it speeds up the conduction of the electrical impulse down the axon. 17. myelin sheath This is formed by the numerous myelinating Schwann cells wrapped around peripheral (sensory and motor) neurons. It functions to support and conserve the electrical impulse generated down an axon, it provides nutrients to the neuron and it plays a role in nerve development and regeneration. 18. axon A long projection away from the cell body that conducts electrical impulses away from the cell body and towards another neuron or an effector (e.g. muscle/gland). Axons can be either myelinated or unmyelinated. Some cells do not have axons and transmit electrical impulses through their dendrites. Note: Nerve impulse and electrical impulse are synonymous. Neuron and nerve cell are also synonymous. © Tangstar Science 3 Created by Anh-Thi Tang – Tangstar Science Copyright © 2015 Anh-Thi Tang (a.k.a. Tangstar Science) All rights reserved by author. TERMS OF USE: This document is for personal use only and may only be used by the original purchaser. Copying for more than one teacher, classroom, department, school, or school district is prohibited. Additional licenses can be purchased at a discount for others to use in your department. This entire document, or any parts within, may not be reproduced or displayed for public viewing. You may NOT electronically post this product online including to teacher blogs, classroom websites or school networks. Failure to comply is a copyright infringement and a violation of the Digital Millennium Copyright Act (DMCA). http://www.teacherspayteachers.com/Store/Tangstar-Science © Tangstar Science