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View the University of Michigan Webscope (http://openstaxcollege.org/l/nervefiber) to see an electron micrograph of a cross-section of a myelinated nerve fiber. The axon contains microtubules and neurofilaments, bounded by a plasma membrane known as the axolemma. Outside the plasma membrane of the axon is the myelin sheath, which is composed of the tightly wrapped plasma membrane of a Schwann cell. What aspects of the cells in this image react with the stain that makes them the deep, dark, black color, such as the multiple layers that are the myelin sheath?
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- Assume presynaptic excitatory neuron A terminates on a postsynaptic cell near the axon hillock and presynaptic excitatory neuron B terminates on the same postsynaptic cell on a dendrite located on the side of the cell body opposite the axon hillock. Explain why rapid firing of presynaptic neuron A could bring the postsynaptic neuron to threshold through temporal summation, thus initiating an action potential, whereas firing of presynaptic neuron B at the same frequency and the same magnitude of EPSPs may not bring the postsynaptic neuron to threshold.arrow_forwardIdentify and label the following structures on the neuron model figure below: cell body, dendrites, neuron nucleus, neurolemma, axon hillock, nucleus of Schwann cell, Nissl bodies, myelin sheath, axon, node of Ranvier, axon terminals (of neurons synapsing with model neuron), endoneurium (refer to Figure 10.6). 3) 11arrow_forwardDemyelination is the loss of myelin from neurones that are normally myelinated. Multiple sclerosis is a disease in which demyelination occurs in neurones involved in coordinating muscle movement. Using your knowledge of nerve impulse generation and propagation, explain how nerve impulse generation and propagation would be affected in people who have multiple sclerosis. The explanation needs to be in the form of a step by step sequence of annotated drawings. This could be in the form of an annotated cartoon/picture strip. Compare this to nerve impulse generation and propagation in an individual who does not have multiple sclerosis.arrow_forward
- Regardless of type, all neurons transfer signals between each other or to effectors (muscles or glands) at a synapse. The neuromuscular junction that we talked about with the muscular system is one example of a synapse. The diagram below shows the general features of a synapse Match each term or description with the appropriate letter in the diagram. You may use terms more than once. 1. Synaptic knob in axon terminal of pre-synaptic cell: 2. Synaptic cleft: 3. Neurotransmitter: 4. Dendrite of post-synaptic cell: 5. Cell body of post-synaptic cell: 6. Receptor in plasma membrane of post-synaptic cell: 7. Chemical released by neurons that stimulates or inhibits other neurons, muscles, or glands: 8. Cell that sends the signal: 9. Dendrite of cell that receives the signal: 10. Space between cells that must be crossed by neurotransmitters: 11. Structure that opens, like a "protein door", when neurotransmitters attach to it:arrow_forwardCystic fibrosis is a degenerative disease that causes the progressive breakdown of the myelin sheaths around the axons of neurons. Which of the following best describes the likely effect of cystic fibrosis on neuronal function? A B C D an inhibition in the release of neurotransmitters at the synaptic terminal a decrease in the conduction speed of the action potential along neuronal axons an unstoppable generation of action potential in affected neurons an inhibition in the generation of action potentials at neuronal dendritesarrow_forwardThe following are characteristics of the myelin sheath EXCEPT: A formed by the oligodendrocytes in the CNS B lipid- rich C covers the body or dendrites of a neuron D insulates the axonsarrow_forward
- Explain what happens when an action potential reaches the axon terminus (terminal) by activating the receptors on the postsynaptic membrane. Explanation addressing the question above When an action potential, or nerve impulse, arrives at the axon terminal, it activates voltage-gated calcium channels in the cell membrane. Which is present at a much higher concentration outside the neuron than inside, rushes into the cell. The Ca2+ allows synaptic vesicles to fuse with the axon terminal membrane, releasing neurotransmitters into the synaptic cleft. The molecules of neurotransmitters diffuse across the synaptic cleft and bind to receptor proteins on the postsynaptic cell. Activation of postsynaptic receptors leads to the opening or closing of ion channels in the cell membrane. This may be depolarizing, making the inside of the cell more positive, or hyperpolarizing making the inside more negative depending on the ions involved. The excitatory and inhibitory postsynaptic potentials…arrow_forwardDescribe how an action potential in the presynaptic neuron is generated in the postsynaptic neuron. Label the presynaptic neuron, postsynaptic neuron and synapse. Explain what is happening in figure on the left. Use key terms in order AND label on diagram: presynaptic axon terminal, action potential, calcium, vesicle, neurotransmitters, synapse Explain what is happening in the figure on the right. Use key terms in order AND label on diagram: neurotransmitter, postsynaptic receptor, sodium ions, excitatory postsynaptic potential (EPSP), depolarization, action potential, postsynaptic neuronarrow_forwardSmall intestine (or other visceral organ) CNS (spinal cord) Skeletal muscle Figure 14.1 Using Figure 14.1, match the following: 11) Myelin sheath. 11) 12) Cell body of ANS preganglionic neuron. 12) - 13) Cell body of ANS postganglionic neuron. 13) 14 14) Cell body of the somatic neuron. TIPLE CHOICE. Choose the one alternative that best completes the statement or answers the qu 15) Which of the following is not a function of astrocytes? A) guide the migration of young neurons, synapse formation, and helping to determine ca permeability B) support and brace neurons C) anchor neurons to blood vesselsarrow_forward
- Photoreceptor cells form glutamatergic synapses onto bipolar cells and when photoreceptor cells are depolarized the release of glutamate into the synapse is increased. One class of bipolar cells, (called OFF bipolar cells) have excitatory glutamate receptors in their post-synaptic specialization. What happens to the membrane potential of OFF bipolar cells when photoreceptors are illuminated?arrow_forwardRead the following statements (a) The resting nerve membrane is freely permeable to Na*, K* ions and negatively charged proteins. (b) The activity of Na* - K* pump is responsible for maintaining resting membrane potential. (c) The resting membrane is impermeable to negatively charged proteins present in the axoplasm. Choose the option representing correct statements. b only a and b b and c a, b and carrow_forwardWhich of the following statements best describes the properties of a myelinated axons? The axon has an even distribution of ion channels but it is covered by layers of myelin apart from short sections termed the nodes of Ranvier where there is no myelin. The action potential is able to jump from node to node because the myelin sheath increases the length constant. There are very few ion channels underneath the myelin. The density of Na+ channels at the nodes of Ranvier is very high but there are no K+ channels in myelinated axons. The myelin sheath increases the rate of action potential conduction because the action potential underneath the myelin sheath travels faster than an action potential in an unmyelinated axon.arrow_forward
- Anatomy & PhysiologyBiologyISBN:9781938168130Author:Kelly A. Young, James A. Wise, Peter DeSaix, Dean H. Kruse, Brandon Poe, Eddie Johnson, Jody E. Johnson, Oksana Korol, J. Gordon Betts, Mark WomblePublisher:OpenStax CollegeHuman Physiology: From Cells to Systems (MindTap ...BiologyISBN:9781285866932Author:Lauralee SherwoodPublisher:Cengage Learning