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Ch. 10 Muscle Tissue and Physiology
Amerman - Human Anatomy & Physiology 2nd Edition
Amerman2nd EditionHuman Anatomy & PhysiologyISBN: 9780136873822Not the one you use?Change textbook
All textbooksAmerman 2nd EditionCh. 10 Muscle Tissue and PhysiologyProblem L3.3
Chapter 10, Problem L3.3

Ms. Sanchez was in a motorcycle accident in which she lost the use of her right upper limb muscles due to significant nerve damage. However, when an electrode is inserted into her muscles, they are able to contract. Explain specifically why nerve damage caused her to lose the use of her muscles. Why can they still respond to stimulation from an electrode?

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Understand the role of nerves in muscle contraction: Nerves are responsible for transmitting electrical signals (action potentials) from the central nervous system to muscles. These signals travel along motor neurons and stimulate the release of neurotransmitters, such as acetylcholine, at the neuromuscular junction. This triggers muscle contraction.
Explain the impact of nerve damage: In Ms. Sanchez's case, the nerve damage has disrupted the communication between her central nervous system and the muscles in her right upper limb. Without this communication, her muscles cannot receive the necessary signals to contract voluntarily.
Describe the role of electrodes in muscle stimulation: When an electrode is inserted into her muscles, it bypasses the damaged nerves and directly stimulates the muscle fibers. The electrode generates an electrical current that depolarizes the muscle cell membrane, mimicking the natural action potential that would normally come from the nerves.
Clarify why muscles still respond to electrodes: The muscle fibers themselves are still functional and capable of contracting. The issue lies in the damaged nerves, not the muscles. Since the electrode provides an external source of electrical stimulation, it can directly activate the muscle fibers, causing them to contract.
Summarize the distinction: Ms. Sanchez's inability to use her muscles voluntarily is due to the loss of nerve function, which prevents the transmission of signals from her brain to her muscles. However, the muscles remain intact and can still respond to artificial stimulation, such as that provided by an electrode.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nerve Damage and Muscle Function

Nerve damage disrupts the communication between the nervous system and muscles, leading to loss of voluntary control. Motor neurons, which transmit signals from the brain to the muscles, become impaired, preventing the brain's commands from reaching the muscles. This results in muscle weakness or paralysis, as seen in Ms. Sanchez's case.
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Electrode Stimulation

Electrodes can stimulate muscles directly by bypassing the damaged nerves. When an electrode is inserted into the muscle, it delivers electrical impulses that cause the muscle fibers to contract. This mechanism allows the muscle to respond even when the nerve supply is compromised, demonstrating that the muscle tissue itself can still function independently of nerve signals.
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Muscle Contraction Mechanism

Muscle contraction occurs through the interaction of actin and myosin filaments within muscle fibers. When stimulated, these filaments slide past each other, resulting in contraction. This process can still occur in Ms. Sanchez's muscles when stimulated by an electrode, as the muscle's intrinsic mechanisms remain intact despite the loss of nerve input.
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Related Practice
Textbook Question

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

Muscle cells are contractile, conductive, distensible cells.

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Paola is a 3-year-old girl with a disease that reduces the ability of her mitochondria to generate ATP. Explain the specific effects of this disease on the ability of Paola's muscles to function properly. What other tissues and organs are likely to be especially affected by her disease, and why?

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The primary action of the biceps brachii muscle of the anterior arm is to flex the forearm at the elbow. However, when this muscle is inflamed, pain is felt in the shoulder. Explain this finding.

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How does a skeletal muscle fiber differ structurally from typical cells?

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Some athletes will consume only protein for several days before a competition, which reduces the amount of glycogen in both the muscle fibers and the liver. What effect would this have on their ability to perform activities that require short, powerful bursts of activity? How would it affect their ability to perform endurance activities?

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Textbook Question

Jesse is a 2-year-old boy who presents with difficulty in walking and poor control of movements. When the doctor examines Jesse, she notices that when his muscles contract, they are very slow to relax and remain contracted well after the movement has been performed. She sends a sample of his tissue for genetic analysis, and the lab reports a genetic defect that causes the pumps in the SR to operate much more slowly than normal. How does a defect in DNA lead to a malfunctioning protein? How does this finding explain Jesse's symptoms?

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