Biology 101 - Muscle and Skeletal System Part 2

Question 1

Which protein or proteins are present in the thick filaments of skeletal muscle?

Accepted Answer

myosinEach myosin molecule consists of a rounded head and a long tail. The myosin head can function as an ATPase, a role that is vital during a contraction cycle.

Question 2

Which protein or proteins are present in the thin filaments of skeletal muscle?

Accepted Answer

actin, tropomyosin, troponin Microfilaments are composed of two long chains of actin monomers.

Question 3

Muscle cells can also be called by which alternative term?

Accepted Answer

myocytes While this term can refer to a muscle cell of any type, it is generally used when referring to the cells of the heart: cardiac myocytes.

Question 4

Order the following terms from largest to smallest: myofibril, sarcomere, muscle, myocyte.

Accepted Answer

Muscle > myocyte > myofibril > sarcomere The sarcomere is the functional unit of striated muscle. Together, many sarcomeres form a myofibril, and many myofibrils form a myocyte. Myocytes, or muscle cells, then make up larger muscles.

Question 5

Define: myoglobin

Accepted Answer

It is an iron-containing protein that binds oxygen in skeletal muscle cells. Because it picks up the oxygen that hemoglobin releases in the tissues, myoglobin has a higher O2 affinity than hemoglobin.

Question 6

Describe the structural difference between myoglobin and hemoglobin.

Accepted Answer

While myoglobin is very similar to hemoglobin in its tertiary structure, it contains only one monomer instead of four.

For this reason, hemoglobin can undergo cooperative binding, while myoglobin cannot.

Question 7

Skeletal muscle fibers can be characterized by their color into which two groups?

Accepted Answer

red fiberswhite fibersRed, or "slow-twitch," fibers gain their color from large amounts of myoglobin; they also contain many mitochondria. White, or "fast-twitch," fibers contain less myoglobin and fewer mitochondria.

Question 8

What basic features characterize red muscle fibers?

Accepted Answer

Red fibers gain their color from large amounts of myoglobin. They also contain many mitochondria and are thinner than white fibers.

As components of "slow-twitch" muscle, red fibers are specialized for sustained aerobic activity.

Question 9

What basic features characterize white muscle fibers?

Accepted Answer

White fibers are thicker than red fibers, but contain less myoglobin and fewer mitochondria.As components of "fast-twitch" muscle, white fibers are specialized for short bursts of intense contraction.

Question 10

Near the end of an intense workout, an athlete's muscles display a lowered amount of ATP, a buildup of lactic acid, and a decrease in the frequency of neuron signaling. What term is given to this condition?

Accepted Answer

fatigueFatigue is generally accompanied by muscle soreness, caused by high lactic acid levels in the cells. Lactic acid is a product of anaerobic respiration.

Question 11

What structure is shown in the image below?

Accepted Answer

neuromuscular junction| (NMJ)The NMJ is the synapse that separates a motor neuron and a skeletal muscle. Here, vesicles containing neurotransmitters are released from the neuron, promoting contraction in the muscle.

Question 12

Name the main neurotransmitter at the neuromuscular junction.

Accepted Answer

acetylcholineRemember that acetylcholine promotes multiple responses. At the neuromuscular junction, it acts on a muscle to promote contraction. As part of the autonomic nervous system, however, it also triggers parasympathetic responses in effector organs.

Question 13

Curare, a plant-based toxin, blocks nicotinic acetylcholine receptors at the neuromuscular junction. What symptom might be seen in a person poisoned with curare?

Accepted Answer

The person would likely be paralyzed.For skeletal muscle contraction to be initiated, acetylcholine must bind to receptors at the NMJ. If these receptors are blocked, no contraction can occur.

Question 14

A certain disorder causes a person to overproduce acetylcholinesterase (AChE) at the neuromuscular junction. What symptom might be seen in such an individual?

Accepted Answer

The person would likely be paralyzed or at least experience weakened muscle contraction.

The primary enzymatic function of AChE is to break down acetylcholine at the synapse or NMJ. Normally, this serves to prevent extended muscle contraction. However, overly high amounts of AChE would hydrolyze acetylcholine before it could reach its receptors, inhibiting contraction.

Question 15

Define: motor unit

Accepted Answer

It consists of a single motor neuron and the muscle fibers upon which it synapses. Note that some neurons innervate only a few muscle fibers, while others innervate dozens.

Question 16

What term is given to the specialized endoplasmic reticulum found in muscle cells?

Accepted Answer

This organelle is the sarcoplasmic reticulum, or SR. Specifically, the SR is a type of smooth, not rough, ER.

The SR plays a crucial role in the contraction of skeletal and cardiac muscles. It stores calcium ions and releases them in response to an action potential, which then allows contraction to occur.

Question 17

In muscle cells, which specific term is given to the cytoplasm?

Accepted Answer

sarcoplasmIn general, cytoplasm contains both a cell's cytosol and its non-nuclear organelles. In particular, sarcoplasm generally contains large amounts of myoglobin, myofibrils, and stored glycogen.

Question 18

In muscle cells, which specific term is given to the plasma membrane?

Accepted Answer

sarcolemmaThe sarcolemma resembles a normal plasma membrane, but is specially suited to receive an action potential from adjacent motor neurons. It also contains structural adaptations.

Question 19

In skeletal muscle, which ion can be found in high concentrations in the sarcoplasmic reticulum?

Accepted Answer

It contains large amounts of calcium; in fact, it functions as a storage center for Ca2+ ions.

Question 20

Briefly describe the process that triggers calcium release from the sarcoplasmic reticulum.

Accepted Answer

Acetylcholine is released from an adjacent motor neuron and binds to receptors on the muscle cell membrane.
Ion channels open, causing a large influx of sodium ions and a depolarization of the cell.
Calcium release channels in the SR membrane are activated and open; Ca2+ flows down its gradient into the sarcoplasm.

Biology 101 - Muscle and Skeletal System Part 2

Which protein or proteins are present in the thick filaments of skeletal muscle?

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Term	Definition
Which protein or proteins are present in the thick filaments of skeletal muscle?	myosin Each myosin molecule consists of a rounded head and a long tail. The myosin head can function as an ATPase, a role that is vital during a contraction cycle.
Which protein or proteins are present in the thin filaments of skeletal muscle?	actin, tropomyosin, troponin Microfilaments are composed of two long chains of actin monomers.
Muscle cells can also be called by which alternative term?	myocytes While this term can refer to a muscle cell of any type, it is generally used when referring to the cells of the heart: cardiac myocytes.
Order the following terms from largest to smallest: myofibril, sarcomere, muscle, myocyte.	Muscle > myocyte > myofibril > sarcomere The sarcomere is the functional unit of striated muscle. Together, many sarcomeres form a myofibril, and many myofibrils form a myocyte. Myocytes, or muscle cells, then make up larger muscles.
Define: myoglobin	It is an iron-containing protein that binds oxygen in skeletal muscle cells. Because it picks up the oxygen that hemoglobin releases in the tissues, myoglobin has a higher O2 affinity than hemoglobin.
Describe the structural difference between myoglobin and hemoglobin.	While myoglobin is very similar to hemoglobin in its tertiary structure, it contains only one monomer instead of four. For this reason, hemoglobin can undergo cooperative binding, while myoglobin cannot.
Skeletal muscle fibers can be characterized by their color into which two groups?	red fibers white fibers Red, or "slow-twitch," fibers gain their color from large amounts of myoglobin; they also contain many mitochondria. White, or "fast-twitch," fibers contain less myoglobin and fewer mitochondria.
What basic features characterize red muscle fibers?	Red fibers gain their color from large amounts of myoglobin. They also contain many mitochondria and are thinner than white fibers. As components of "slow-twitch" muscle, red fibers are specialized for sustained aerobic activity.
What basic features characterize white muscle fibers?	White fibers are thicker than red fibers, but contain less myoglobin and fewer mitochondria. As components of "fast-twitch" muscle, white fibers are specialized for short bursts of intense contraction.
Near the end of an intense workout, an athlete's muscles display a lowered amount of ATP, a buildup of lactic acid, and a decrease in the frequency of neuron signaling. What term is given to this condition?	fatigue Fatigue is generally accompanied by muscle soreness, caused by high lactic acid levels in the cells. Lactic acid is a product of anaerobic respiration.
What structure is shown in the image below?	neuromuscular junction \| (NMJ) The NMJ is the synapse that separates a motor neuron and a skeletal muscle. Here, vesicles containing neurotransmitters are released from the neuron, promoting contraction in the muscle.
Name the main neurotransmitter at the neuromuscular junction.	acetylcholine Remember that acetylcholine promotes multiple responses. At the neuromuscular junction, it acts on a muscle to promote contraction. As part of the autonomic nervous system, however, it also triggers parasympathetic responses in effector organs.
Curare, a plant-based toxin, blocks nicotinic acetylcholine receptors at the neuromuscular junction. What symptom might be seen in a person poisoned with curare?	The person would likely be paralyzed. For skeletal muscle contraction to be initiated, acetylcholine must bind to receptors at the NMJ. If these receptors are blocked, no contraction can occur.
A certain disorder causes a person to overproduce acetylcholinesterase (AChE) at the neuromuscular junction. What symptom might be seen in such an individual?	The person would likely be paralyzed or at least experience weakened muscle contraction. The primary enzymatic function of AChE is to break down acetylcholine at the synapse or NMJ. Normally, this serves to prevent extended muscle contraction. However, overly high amounts of AChE would hydrolyze acetylcholine before it could reach its receptors, inhibiting contraction.
Define: motor unit	It consists of a single motor neuron and the muscle fibers upon which it synapses. Note that some neurons innervate only a few muscle fibers, while others innervate dozens.
What term is given to the specialized endoplasmic reticulum found in muscle cells?	This organelle is the sarcoplasmic reticulum, or SR. Specifically, the SR is a type of smooth, not rough, ER. The SR plays a crucial role in the contraction of skeletal and cardiac muscles. It stores calcium ions and releases them in response to an action potential, which then allows contraction to occur.
In muscle cells, which specific term is given to the cytoplasm?	sarcoplasm In general, cytoplasm contains both a cell's cytosol and its non-nuclear organelles. In particular, sarcoplasm generally contains large amounts of myoglobin, myofibrils, and stored glycogen.
In muscle cells, which specific term is given to the plasma membrane?	sarcolemma The sarcolemma resembles a normal plasma membrane, but is specially suited to receive an action potential from adjacent motor neurons. It also contains structural adaptations.
In skeletal muscle, which ion can be found in high concentrations in the sarcoplasmic reticulum?	It contains large amounts of calcium; in fact, it functions as a storage center for Ca2+ ions.
Briefly describe the process that triggers calcium release from the sarcoplasmic reticulum.	Acetylcholine is released from an adjacent motor neuron and binds to receptors on the muscle cell membrane. Ion channels open, causing a large influx of sodium ions and a depolarization of the cell. Calcium release channels in the SR membrane are activated and open; Ca2+ flows down its gradient into the sarcoplasm.