ELM 16 Muscles 1

Question 1

What are the three types of muscle classification?

Answer 1

Answer: The three types of muscle classification are skeletal, cardiac, and smooth muscle.

Question 2

Question: What is the primary function of skeletal muscle?

Answer 2

Answer: The primary functions of skeletal muscle are movement and generation of heat.

Question 3

Question: How is skeletal muscle connected to bone?

Answer 3

Answer: Skeletal muscle is connected to bone via tendons.

Question 4

Question: What is the name of the membrane surrounding individual muscle cells?

Answer 4

Answer: The membrane surrounding individual muscle cells is called the sarcolemma.

Question 5

Question: What is the term for an individual muscle cell?

Answer 5

Answer: An individual muscle cell is called a muscle fiber or myocyte.

Question 6

Question: How are muscle fibers formed during development?

Answer 6

Answer: Muscle fibers are multinucleate and formed by the fusion of cells during development.

Question 7

Question: What is the name of the layer of connective tissue covering muscle fibers?

Answer 7

Answer: The layer of connective tissue covering muscle fibers is called endomysium.

Question 8

Question: What are muscle fibers grouped into?

Answer 8

Answer: Muscle fibers are grouped into bundles called fascicles.

Question 9

Question: What is the name of the layer of connective tissue covering fascicles?

Answer 9

Answer: The layer of connective tissue covering fascicles is called perimysium.

Question 10

Question: How are fascicles grouped together to form a muscle?

Answer 10

Answer: Fascicles are grouped together by a sheath called epimysium to form a muscle.

Question 11

Question: What gives muscle its striped appearance?

Answer 11

Answer: The sarcomere, which is a single repeating unit, gives muscle its striped appearance.

Question 12

Question: What is the function of the M-line in the sarcomere?

Answer 12

Answer: The M-line, located in the middle of the sarcomere, is where myosin is connected.

Question 13

Question: What does the H zone of the sarcomere contain?

Answer 13

Answer: The H zone of the sarcomere contains only actin filaments and is the lightest region.

Question 14

Question: What does the A band of the sarcomere contain?

Answer 14

Answer: The A band of the sarcomere contains both actin and myosin filaments and is the darkest region.

Question 15

Question: What does the I band of the sarcomere contain?

Answer 15

Answer: The I band of the sarcomere contains actin and titin filaments only and is a lighter region.

Question 16

Question: What do the Z-lines in the sarcomere connect?

Answer 16

Answer: The Z-lines in the sarcomere connect filament proteins.

Question 17

Question: What is the function of titin in the sarcomere?

Answer 17

Answer: Titin, the largest protein in the human genome, has a spring-like function and allows muscles to return to their resting state after being stretched.

Question 18

Question: What changes in length during muscle contraction?

Answer 18

nswer: The length of the H zone and I bands change during muscle contraction.

Question 19

Question: What happens during muscle contraction at the molecular level?

Answer 19

Answer: During muscle contraction, filaments slide over each other, causing changes in the banding pattern of the sarcomere.

Question 20

Question: What is the optimum range for overlap between myosin heads and actin in muscle contraction?

Answer 20

Answer: The optimum range for overlap between myosin heads and actin in muscle contraction ensures maximal force generation; if the overlap is too compressed or stretched, the force of contraction decreases.

Question 21

Question: What is the structure of myosin?

Answer 21

Answer: Myosin is a hexamer formed from two heavy chains with large head groups and tails that coil to form an alpha helix. It also has four light chains associated with the necks of the heavy chains.

Question 22

Question: How do the heads of myosin interact with actin in thin filaments?

Answer 22

Answer: The heads of myosin form interactions with actin in thin filaments during muscle contraction.

Question 23

Question: What role do regulatory light chains play in myosin activity?

Answer 23

Answer: Regulatory light chains regulate the activity at the myosin heavy chain head groups, which is particularly important in smooth muscle.

Question 24

Question: How is muscle myosin classified?

Answer 24

Answer: Muscle myosin is classified as a member of the myosin class 2, with nine different types: eight for skeletal and cardiac muscle and one for smooth muscle.

Question 25

Question: What is the major component of the eukaryotic cytoskeleton and its form in muscle?

Answer 25

Answer: Actin is the major component of the eukaryotic cytoskeleton, with filamentous (F actin) form being found in muscle.

Question 26

Question: What are the components of the troponin complex and their functions?

Answer 26

Answer: The troponin complex consists of three different proteins: troponin T, which associates with tropomyosin; troponin I, which inhibits the binding of myosin; and troponin C, which binds calcium, allowing the regulation of muscle contraction by calcium.

Question 27

Question: Describe the process of muscle contraction involving myosin and actin.

Answer 27

Contraction:
1. Myosin heads bonded to actin.
2. Myosin head binds ATP –> dissociation of bond.
3. Myosin hydrolyses ATP, keeps ADP + Pi. Head tilits + enters “cocked state”.
4. Formation of weak bond between actin + myosin head.
5. Dissociation of phosphate -> stronger bond forms + myosin head returns to starting position = moves the filaments relative to each other.
6. ADP dissociates + back to start, but myosin head has moved further along actin chain.

Question 28

Question: How is calcium pumped out of the cytoplasm and into the sarcoplasmic reticulum (SR)?

Answer 28

Answer: Calcium is pumped out of the cytoplasm and into the sarcoplasmic reticulum (SR) using ATP hydrolysis, which is important to maintain a low concentration of calcium in the cytoplasm.

Question 29

Question: Why is it necessary to raise calcium levels in muscle cells during contraction?

Answer 29

Answer: It is necessary to raise calcium levels in muscle cells to activate troponin C, which allows for muscle contraction. This can be achieved by action potentials activating voltage-gated calcium channels (L-type dihydropyridine channels) present in the muscle membrane.

Question 30

Question: Where does the calcium come from for muscle contraction?

Answer 30

Answer: Calcium for muscle contraction primarily comes from the sarcoplasmic reticulum (SR), which contains calcium channels called ryanodine receptors (RyR) that release calcium into the cytoplasm when activated.

Question 31

Question: Describe the mechanism by which calcium is released from the sarcoplasmic reticulum (SR) during muscle contraction.

Answer 31

Answer: When an action potential occurs, the conformational change of dihydropyridine receptors (DHP Rs) in the muscle membrane is transmitted to ryanodine receptors (RyR) in the SR membrane. This causes the RyR channels to open, allowing calcium to flood into the cytoplasm from the SR.

Question 32

Question: How is calcium balance restored in muscle cells after contraction?

Answer 32

Answer: Calcium balance is restored in muscle cells after contraction by the sarcoplasmic reticulum calcium ATPase (SERCA) pump, which actively pumps calcium from the cytoplasm back into the SR.

Question 33

Question: What is a motor unit in skeletal muscle?

Answer 33

Answer: A motor unit in skeletal muscle consists of a single motor neuron and all the muscle fibers it innervates.

Question 34

Question: Describe the structure of the neuromuscular junction (NMJ) in skeletal muscle.

Answer 34

Answer: At the neuromuscular junction (NMJ) of skeletal muscle, each motor neuron can make synapses with several muscle fibers. The motor neuron axon splits into finely branched presynaptic nerve terminals or boutons. The region where these terminals make contact with the muscle fiber is called the end plate region. Under each presynaptic terminal, the muscle fiber membrane has a series of folds called junctional folds, where nicotinic acetylcholine receptors (nAChRs) are located.

Question 35

Question: What is myasthenia gravis (MG) and what are its symptoms?

Answer 35

Answer: Myasthenia gravis (MG) is an autoimmune disorder characterized by an attack on skeletal muscle, leading to muscle weakness and fatigue. Symptoms can include drooping eyelids, difficulty smiling, difficulty swallowing, slurred speech, and overwhelming fatigue.

Question 36

Question: What is the role of the nicotinic acetylcholine receptor (nAChR) in muscle contraction, and what are its structural features?

Answer 36

Answer: The nicotinic acetylcholine receptor (nAChR) is a pentameric transmembrane protein that serves as the “molecular switch” that triggers muscle contraction. It consists of two alpha subunits, one beta, one delta, and one epsilon subunit. In fetal receptors, the epsilon subunit is replaced by a gamma subunit. The subunits have similar structures, with four transmembrane domains and a large extracellular N terminus. Antibodies in MG often target the main immunogenic region (MIR), which is in the extracellular part of the alpha subunits, specifically amino acids 67-76.

Question 37

Question: What are the three pathological mechanisms of myasthenia gravis (MG)?

Answer 37

Answer: The three pathological mechanisms of MG are: 1) internalization of receptors, 2) destruction and simplification of the end plate, and 3) blockage of acetylcholine binding sites by antibodies.

Question 38

Question: How is myasthenia gravis diagnosed?

Answer 38

Answer: Myasthenia gravis is diagnosed based on the pattern of muscle weakness, presence of antibodies against nAChR (revealed through serum testing), electromyography findings (showing decline in size of action potentials with repeated stimulation), and response to the Tensilon/edrophonium test, where improvement in symptoms after administration of acetylcholinesterase inhibitors can confirm the diagnosis.

Question 39

Question: What are the mainstays of treatment for myasthenia gravis?

Answer 39

Answer: The mainstays of treatment for myasthenia gravis include acetylcholinesterase inhibitors to increase acetylcholine concentration in the synapse, immunosuppressants (such as steroids or other drugs) to suppress the immune response, and plasma therapy (plasmapheresis or plasma exchange) to remove autoantibodies from circulation in severe cases.

Question 40

Question: What is the primary target of sarin within the body?

Answer 40

Answer: Sarin inhibits acetylcholinesterase at the neuromuscular junction (NMJ), synapses in the autonomic nervous system (ANS), and in the brain.

Question 41

Question: What are some symptoms of sarin exposure?

Answer 41

Answer: Sarin exposure can lead to difficulty breathing, drooling, paralysis, convulsions, coma, and respiratory failure.

Question 42

Question: How does sarin affect acetylcholine levels in synapses?

Answer 42

Answer: Sarin acts as an irreversible inhibitor of acetylcholinesterase, leading to an uncontrollable rise in acetylcholine concentration in synapses.

Question 43

Question: Why do muscles become limp after initial contractions despite increased acetylcholine levels?

Answer 43

Answer: Muscles become limp due to two factors: (1) desensitization of nicotinic acetylcholine receptors (nAChRs) and (2) continuous depolarization of muscles leading to inactivation of voltage-gated sodium channels.

Question 44

Question: What are the key amino acids involved in the molecular mechanism of sarin?

Answer 44

Answer: The molecular mechanism of sarin centers around three amino acids: serine, glutamate, and histidine.

Question 45

Question: What are the antidotes for sarin poisoning?

Answer 45

Answer: Antidotes include injections of the muscarinic antagonist atropine and the drug pralidoxime, which can recycle acetylcholinesterase back to its active form.

Question 46

Question: How can troops protect themselves from sarin exposure?

Answer 46

Answer: Troops are issued with autoinjectors containing intramuscular doses of atropine, which can save lives in the event of sarin exposure.

Question 47

Question: How do certain fish, like electric rays and eels, stun their prey?

Answer 47

Answer: Certain fish use electrical fields generated by specialized electric organs to stun their prey.

Question 48

Question: What are the electric organs in fish comprised of?

Answer 48

Answer: The electric organs are made up of stacks of flat cells called electrocytes.

Question 49

Question: What is the function of the electric organs in fish?

Answer 49

Answer: The electric organs act like mini batteries, producing tiny currents that, when combined, can generate discharges of up to 220V at 30A, allowing fish to stun their prey.

Question 50

Question: What is the structure of the electroplaques in the Torpedo electric ray?

Answer 50

Answer: The electroplaques of the Torpedo electric ray are kidney-shaped organs located on either side of the body, consisting of flat, disc-like cells called electrocytes.

Question 51

Question: What is the role of nicotinic acetylcholine receptors (nAChRs) in the electric organs of the Torpedo electric ray?

Answer 51

Answer: The electroplaques in the Torpedo electric ray are rich in nAChRs, which are innervated by cholinergic neurons and play a crucial role in generating electric discharges.

Question 52

Question: How have Torpedo nAChRs been utilized in research?

Answer 52

Answer: It is possible to obtain milligram quantities of nAChRs from Torpedo, which has been extensively used in studying these receptors and understanding diseases like myasthenia gravis (MG).

Question 53

Question: How has injecting animals with purified nAChR from Torpedo been used in research?

Answer 53

Answer: Injecting animals with purified nAChR from Torpedo can provoke an immune response leading to experimental myasthenia gravis, providing a model for studying the disease.