This means that it takes an impulse of greater intensity to activate these sensory neurons, hence, the person tends not
6. 7. 8. 9.
(c) (b) (c) (c)
Chapter 9 Review (Page 458–459)
Understanding Concepts 1.
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In 1791, an Italian scientist, Luigi Galvani, discovered that the calf muscle of frog could be made to twitch under electrical stimulation. Galvani concluded that the muscle produced the “animal electricity.” Although Galvani’s conclusion was incorrect, it spawned a flood of research that led to the development of theories about how electrical current is generated in the body. For instance, in 1840, Emil DuBois-Reymond attempted to refine instruments that could be used to detect the movement of electrical impulses in nerves and muscles. Willem Einthoven recorded the movement of electrical impulses of the heart using an early form of the electrocardiogram (ECG) in 1906. The EEG has been refined since then and is still used to diagnose heart problems. In 1929, Hans Berger developed the electroencephogram (EEG) by placing electrodes on the head of a patient to measure the electrical activity of the brain. This has also been refined since then and is still in use today. Individuals with nerves that have a higher threshold level are not as easily activated. This means that it takes an impulse of greater intensity to activate these sensory neurons, hence, the person tends not to feel pain as easily. Neuron X is an excitatory neuron. Its neuron transmitter causes the depolarization of neuron Y, making it easier to reach threshold level. Neuron W is an inhibitory neuron. Its neuron transmitter causes the hyperpolarization of the resting membrane Y, making it more difficult to achieve threshold level. Without acetylcholine being produced, postsynaptic membranes would not be depolarized. Nerve transmission would be severely inhibited, because although sensory nerves would respond to stimuli, motor neurons could not be excited. Walking, sitting, and other movements that require motor nerves could not occur. Even breathing movements would stop. The cerebellum. The cones are high light-intensity photoreceptors that detect colour. This enables the chicken to distinguish tiny objects on the ground, such as a seeds or small insects. Subtle differences in colour and texture can be detected. However, because the chicken’s eyes have so many cones, they do not have many rods. This means that they have very poor night vision and are therefore susceptible to predation at night or when there is very little light. The lens hardens as you age, as extra protein layers are added. This decreases the near-point accommodation and people tend to become farsighted. Only certain specialized hair cells along the basilar membrane of the cochlea have been destroyed. Each frequency or pitch excites a specific part of cochlea. Violent vibration may dislodge the specialized hairs.
Applying Inquiry Skills 9.
Simple colour discrimination tests might be suggested. It is important to consider light intensity and distance from the object. A control should also be introduced. Students might suggest testing younger and older subjects with a variety of paintings. The paintings should be varied in their colour content—some primarily blue, some primarily green, purple, yellow, and so on. They could ask the subjects to describe which paintings were more vivid. Alternatively, students could obtain a simple colour filter (made from cellophane) from an art supply store, or find a pair of yellow sunglasses. They could then show several paintings as above to their peers, asking them how vivid the colours in the paintings were. Subjects would probably have trouble distinguishing blues and purples, but would find the yellows and oranges to be very intense. 10.(a) Force of muscle contraction is 4 N. The all-or-none response indicates that once the neuron has been excited, it experiences force with the same speed and intensity. (b) Threshold level is 20 mV 11.(a) Neuron B (b) An action potential in neuron C will not cause a response in D because sufficient neurotransmitter chemicals are not released. However, if an action potential in C and another excitatory neuron, such as A, are combined, then an action potential in neuron D will be produced. 12.(a) How does age affect near point accommodation? (b) Hypothesis: As age increases, near-point accommodation decreases. (c) 50 years. (d) The lens becomes thicker and less flexible with age due to a build up of protein over the lens. When this occurs, the lens can no longer adjust to objects that are near the eye and reading glasses become necessary.
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Making Connections 13. If a leg had been severed, but the cell body of the sensory neuron remained intact, the neuron continues to send information to the CNS. The area of the CNS that was stimulated by the nerve was for the severed area of the leg. Although the section of the leg was removed, the sensory neuron continues to indicate that the area was irritated. 14. Student answers will vary depending on their research. Students can go to several Web sites to find out about the latest research on Parkinson’s disease: Parkinson’s Disease Links http://www.nlm.nih.gov/medlineplus/parkinsonsdisease.html National Institute of Neurological Disorders and Stroke http://www.ninds.nih.gov/health_and_medical/pubs/parkinson_disease_htr.html Some possible new forms of research include • gene therapy • investigating the role of mitochondria • investigating the role of folic acid; some studies have linked a deficiency of folic acid with Parkinson’s disease • some studies suggest that a virus may cause Parkinson’s disease. The virus combined with a genetic make-up that makes a person susceptible to Parkinson’s may be the reason that Parkinson’s disease tends to run in families 15.(a) Alzheimer’s disease is associated with a deficit in acetylcholine, a neurotransmitter. Cholinesterase destroys actelycholine. If too much cholinesterase lingers in the synapse, the transmitter chemical, actelycholine, would be destroyed before it could cause depolarization of the postsynaptic neuron. Reducing the amount of cholinesterase in the system could possibly help reduce the deficit in acetylcholine, thereby alleviating some of the symptoms of Alzheimer’s disease. (b) Student answers will vary. Western science is based on linking cause and effect relationships. If a single chain in the explanation is missing, it is often rejected. Just knowing that it works, usually isn’t good enough.
Extension 16.(a) The following Internet links are just a few that deal with current advances in Alzheimer’s research: Alzheimer’s Disease Education & Referral Center Web site: information on Alzheimer’s Disease and related disorders http://www.alzheimers.org/ Alzheimer’s Disease Education & Referral Center: Alzheimer’s Disease Fact Sheet http://www.alzheimers.org/pubs/adfact.html University of Kentucky Alzheimer’s Disease Review Web site: archives of the Review and links to related web sites http://www.mc.uky.edu/adreview/default.htm (b) The following online articles deal with current studies in immunology, biochemistry, and neurology as relates to Alzheimer’s Disease: Alzheimer’s Disease Education & Referral Center Web site: NIA News: Alzheimer’s Disease Research Update Folic Acid Possibly a Key Factor in Alzheimer’s Disease Prevention (March 1, 2002) http://www.alzheimers.org/nianews/nianews45.html High Homocysteine Levels May Double Risk of Dementia, Alzheimer’s Disease, New Report Suggests (February 14, 2002) http://www.alzheimers.org/nianews/nianews44.html
“Use It or Lose It?” Study Suggests Mentally Stimulating Activities May Reduce Alzheimer’s Risk (February 13, 2002) http://www.alzheimers.org/nianews/nianews43.html
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Homeostasis
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Cognitive Impairment High Among Older People, Study Suggests (November 12, 2001) http://www.alzheimers.org/nianews/nianews41.html Scientists Suspect New Genetic Risk Factor for Late Onset Alzheimer’s Disease (December 21, 2000) http://www.alzheimers.org/nianews/nianews36.html (c) Students should consider the sizable amount of money that could be made by developing a cure. Students should mention the various fields of science that have something to contribute to Alzheimer’s research: • Geneticists and the role of the Apo-E4 gene in predicting Alzheimer’s Disease (AD) • Heart and stroke researchers who might explore the connection between strokes and AD • Psychologists who have developed tests to screen patients for AD • Medical imaging scientists who use sophisticated equipment to detect plaques in the brains of AD sufferers • Epidemiologists who explore correlations between various environmental factors and the incidence of AD Students should identify the benefits of the above scientists (and more) working together to understand such a complex and enigmatic disease as AD. (d) Challenges to finding a cure include the following: • What triggers Alzheimer’s disease is not well understood. • Genetic links. Three new, separate research studies suggest that a gene or genes on chromosome 10 may be risk factors for late onset Alzheimer’s disease (AD). The findings, reported in the December 22, 2000, issue of Science, are important new evidence that more than one gene may play a role in development of AD later in life. For the past several years, a particular form of the apolipoprotein E (APOE) gene on chromosome 19 has been the only widely recognized genetic risk factor in late onset Alzheimer’s disease, but scientists have long suspected that more than one gene may be involved in increasing an individual’s risk of developing late onset AD. • Environmental triggers may be involved. • Lifestyle factors may come into play.
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Chapter 9 How Nerve Signals Maintain Homeostasis 201
