Anatomy and Physiology Answer Key

Anatomy and Physiology Answer Key

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Unformatted text preview: ize and engulf foreign material. (d) Astrocytes are supportive cells anchoring neurons to capillaries and supporting the blood-brain barrier. They also help repair brain tissue after injury. They have many processes to connect the neurons and capillaries. Transmission of Nerve Impulses (page 78) 1. An action potential passes along a nerve because the depolarization occurring in one region of the axon makes the next region of the axon more permeable to sodium ions (and more likely to conduct the impulse). 2. Because the refractory period makes the neuron unable to respond for a brief period after an action potential has passed, the impulse can pass in only one direction along the nerve (away from the cell body). 3. The nervous system interprets nerve impulses correctly because it records where they have come from and “knows” where they go to. Different regions of the brain are responsible for sorting out, interpreting, and integrating the nerve impulses from different sources. Chemical Synapses (page 79) 1. A synapse is a junction between the end of one axon and the dendrite or cell body of a receiving neuron. Biozone International 2009 Photocopying Prohibited 13 Note: A synapse can also occur between the end of one axon and a muscle cell (neuromuscular junction). 2. • Arrival of a nerve impulse at the end of the axon causes an influx of calcium. This induces the vesicles to release their neurotransmitter into the cleft. • 2. Any one of: • Drug can act as an indirect agonist, preventing the reuptake of norepinephrine by the presynaptic cell, thereby prolonging the response in the postsynaptic cell, e.g. cocaine and amphetamines. • Drug can act as a direct antagonist, competing for adrenergic β receptors on the postsynaptic membrane and blocking impulse transmission, e.g. β blockers used to treat hypertension. Delay at the synapse is caused by the time it takes for the neurotransmitter to diffuse across the gap (synaptic cleft) between neurons. 4. (a) Neurotransmitter (NT) is degraded into component molecules by enzyme activit...
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This document was uploaded on 01/28/2014.

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