muscular and skeleton - יערה לסיים

Question 1

define glycogen

Answer 1

Glycogen is the stored form of glucose in the body, particularly in the liver and muscles. Glucose, a simple sugar, is the main source of energy for the cells. When the body doesn’t immediately need the glucose from your food, it gets converted and stored as glycogen for later use.

Question 2

define cardiac muscle

Answer 2

Cardiac muscle is also known as heart muscle or myocardium.
It forms the thick middle layer of the heart wall and is responsible for the powerful, rhythmic contractions that pump blood throughout the body. it is not possible to consciously control cardiac muscle. It contracts automatically in a coordinated rhythm dictated by the heart’s natural pacemaker.

cardiac muscle cells have a striped appearance under a microscope due to the organized arrangement of contractile proteins within them. typically have one nucleus, although some may have two. This is different from skeletal muscle which is multinucleated (many nuclei).

Question 3

define skeletal muscle

Answer 3

Skeletal muscles are the muscles that you can control voluntarily. They are responsible for all the movements of the body parts, from blinking your eyes to running a marathon. They are also known as striated muscles because of their microscopic striped appearance.

Skeletal muscle cells have a striated appearance under a microscope. This is due to the orderly arrangement of proteins within the cells. single skeletal muscle cell contains many nuclei rather than just one, located by the edge of the cell.

Question 4

define smooth muscle

Answer 4

Found in the walls of hollow organs throughout the body, including the stomach, intestines, bladder, uterus, and blood vessels.
Plays a crucial role in involuntary actions like digestion, waste elimination, blood flow regulation, and maintaining organ shape.
Unlike skeletal muscle (controlled consciously) and cardiac muscle (automatic heart function), smooth muscle contracts and relaxes involuntarily. The nervous system or hormones trigger these actions.

Smooth muscle cells are elongated and spindle-shaped, with a single centrally located nucleus. smooth muscle lacks the striped pattern of skeletal and cardiac muscle. This is because the contractile proteins (actin and myosin) are not arranged in a highly organized way within the cells.

Question 5

define excitability

Answer 5

excitability refers to the property of a cell or tissue to respond to a stimulus. This is particularly important in the context of neurons and muscle cells.

Question 6

define contractility

Answer 6

Contractility is the ability of a cell or tissue to contract and shorten in response to a stimulus.
Contractility is an essential property of muscles, allowing them to generate force and movement (actively).

Question 7

define tendon
where in the muscle does it connect?

Answer 7

A tendon is a tough, fibrous cord made of dense connective tissue. It acts as a bridge between muscles and bones, transmitting the force generated by muscle contractions to the bones, which allows for movement.
Tendons are primarily composed of collagen fibers, which are strong and flexible, allowing them to withstand significant tension.
origin - proximal side
insertion - distal side

Question 8

define extensibility

Answer 8

t’s a measure of how easily a muscles can be extended

Question 9

define elasticity

Answer 9

Elasticity refers to the ability of a muscle object to resist a distorting influence and return to its original size and shape

Question 10

define epimysium

Answer 10

Epimysium is the outermost connective tissue sheath that surrounds a skeletal muscle. It’s a tough layer protecting the muscle and separating it from neighboring muscles and bones.

Question 11

define perimysium

Answer 11

Perimysium is a layer of connective tissue that groups muscle fibers together within a skeletal muscle.
It surrounds individual bundles of muscle fibers, called fascicles (each containing 10-100+ fibers). Perimysium separates these fascicles from each other provides structural support.

Question 12

define endomysium

Answer 12

Endomysium is the innermost layer of connective tissue that surrounds and supports individual muscle fibers within a skeletal muscle. It’s a delicate sheath that provides a microenvironment for each fiber

Question 13

define fascicle

Answer 13

A fascicle refers to a bundle of muscle fibers within a skeletal muscle. These muscle fibers are grouped together by connective tissue called the perimysium. Fascicles work together to generate a stronger overall force compared to individual muscle fibers contracting alone.

Question 14

define sarcolemma

Answer 14

The sarcolemma is the cell membrane surrounding a skeletal muscle fiber or a cardiomyocyte (heart muscle cell).

Question 15

define myofibril

Answer 15

A myofibril is the basic unit of contraction within a skeletal muscle fiber. These myofibrils are responsible for the striated (striped) appearance of skeletal muscles seen under a microscope.

Question 16

define sarcomere
what is its size? (relaxed and contracted)
what is its structure?

Answer 16

A sarcomere is the fundamental unit of contraction within a skeletal muscle fiber (rows of sarcomeres make up myofibrils). It’s the smallest functional unit that can shorten to generate force.

The length of a relaxed sarcomere is typically around 2.0 to 2.2 micrometers (µm). When a muscle contracts, the sarcomere shortens. The extent of shortening depends on the intensity of the contraction, but generally a sarcomere can shorten by about 20-30%, bringing its length to around 1.6 to 1.8 micrometers (µm).

The sarcomere is a highly organized structure composed of two main types of protein filaments:
Thick filaments (myosin): These are located in the center of the sarcomere and appear dark under a microscope. Myosin has projections called myosin heads that can bind to actin and generate force.
Thin filaments (actin): Thinner filaments flanking the myosin filaments. Actin plays a crucial role in the muscle contraction process by interacting with myosin heads.

Question 17

define sarcoplasm and sarcoplasmic reticulum

Answer 17

Sarcoplasm is the cytoplasm, or the fluid-filled interior, of a muscle cell.

The sarcoplasmic reticulum (SR) is a specialized membrane network within the sarcoplasm of a muscle cell. The primary function of the SR is to store and release calcium ions (Ca²⁺). Calcium plays a critical role in initiating muscle contraction. When a signal arrives from the nervous system, the SR releases calcium into the sarcoplasm. This increase in calcium concentration triggers a chain reaction that leads to the interaction between actin and myosin filaments within the myofibrils, ultimately causing muscle contraction.

Question 18

define filaments

Answer 18

filaments are generally long, thin, thread-like structures found within cells. They play various crucial roles in cell structure, movement, and function. Filaments are primarily composed of proteins, but the specific protein type can vary depending on the filament’s function.

can be seen in electrons microscope.

Question 19

define I band

Answer 19

lighter bands on either side of the sarcomere where only thin actin filaments are present (no overlap with myosin). These bands also narrow during contraction.

Question 20

define H band/zone

Answer 20

The lighter region in the center of the sarcomere where only thick filaments are present (no actin). This zone gets narrower during contraction as the filaments slide past each other.

Question 21

define A band

Answer 21

The A band is the darker, more prominent region in the center of the sarcomere. It appears dark because it contains both thick and thin filaments overlapping to a significant degree.

Question 22

define thick filaments

Answer 22

thick filaments are protein structures composed primarily of the protein myosin.
Thick filaments are elongated, rod-shaped structures with a tail and two globular heads at opposite ends.

Question 23

define thin filaments

Answer 23

thin filaments are thread-like structures composed primarily of the protein actin.
Thin filaments are long, double-stranded polymers made up of actin subunits that twist together to form a helical structure. Along the length of the thin filament, regulatory proteins called troponin and tropomyosin are bound.

Question 24

define tropomyosin

Answer 24

a protein twisted around actin chains.
in relaxed muscle, it hides myosin binding sites on the actin chains.

Question 25

define troponin

Answer 25

a protein linked to the actin chain at constant distances and has binding sites for Ca+2. gives "order" to the tropomyosin to move

Question 26

define cross striations

Answer 26

Cross-striations refer to the alternating dark and light bands visible under a microscope when looking at skeletal muscle tissue. This striated appearance is a defining characteristic of skeletal muscle and reflects the highly organized arrangement of proteins within the muscle cells.

Question 27

what is the difference between light and dark areas?

Answer 27

Dark areas (A bands): These appear darker because they contain a dense overlap of both thick filaments (myosin) and thin filaments (actin). This dense overlap allows for a greater number of potential interactions between myosin heads and actin binding sites, which is crucial for force generation during muscle contraction. Light areas: I bands (light): These flank the A band on either side and appear lighter because they contain only thin actin filaments. There's no overlap with the thick filaments in this region. H zone (lighter within A band): This is a faint, lighter zone in the middle of the A band. It appears lighter because it contains only thick filaments, with no overlap of thin filaments in this specific region within the A band.

Question 28

define M line

Answer 28

A lighter line in the middle of the sarcomere that holds the thick myosin filaments together.

Question 29

what is Z line? another name for the Z line

Answer 29

Dark lines that mark the boundaries of the sarcomere. They anchor the thin actin filaments. aka disc.

Question 30

define cross bridge cycle (Steps)

Answer 30

The cross-bridge cycle, also known as the actomyosin cycle, is the fundamental process that drives muscle contraction in skeletal muscle [National Institutes of Health, Muscle Contraction]. It involves the intricate interaction between thick filaments (myosin) and thin filaments (actin) within the sarcomere. Steps in the Cycle: 1. Attachment: When a signal triggers muscle contraction, calcium ions (Ca²⁺) flood the sarcoplasm (cell interior). Calcium binding to troponin on the thin filament causes a conformational change that removes tropomyosin from the actin binding sites. With the binding sites exposed, a myosin head with high affinity for actin can attach to a specific site on the thin filament. 2. Power Stroke: Once attached, the myosin head undergoes a conformational change using the energy from ATP hydrolysis (breaking down ATP into ADP and phosphate). This conformational change is like a power stroke, pulling the thin filament towards the center of the sarcomere. 3. Detachment and Reattachment: After the power stroke, the myosin head detaches from the actin binding site. The myosin head then binds a new ATP molecule, which resets it to a high-affinity state ready to attach to another actin binding site further down the thin filament. 4. Recycling: The cycle of attachment, power stroke, detachment, and reattachment continues as long as calcium levels remain high and sufficient ATP is available. This repetitive cycle leads to the sliding filament mechanism: the thin filaments appear to slide past the thick filaments within the sarcomere, even though the filaments themselves are stationary.

Question 31

define motor unit

Answer 31

consists of nerve fiber and the muscle fiber/s it innervates. one neuron can innervate several muscle fibers in parallel.

Question 32

define neoromuscular junction

Answer 32

NMJ / motor end plate a chemical synapse between nerce ending of motor neuron and muscle fiber. the neurotransmitter is acetylcholine. ......

Question 33

define end plate action potential

Answer 33

generated and then propaghated in the muscle fiber.

Question 34

define sarcoplasmic reticulum

Answer 34

The sarcoplasmic reticulum (SR), often abbreviated as SR, is a specialized organelle found within skeletal and cardiac muscle cells. It's essentially a network of interconnected membranes that acts as a storage tank for calcium ions (Ca2+). The primary function of the SR is to store and release calcium ions. Calcium plays a crucial role in muscle contraction. When a muscle needs to contract, the SR rapidly releases calcium ions into the surrounding sarcoplasm (the fluid inside the muscle cell). This surge in calcium triggers a series of events within the myofibrils, ultimately leading to muscle fiber shortening and contraction.

Question 35

define triad

Answer 35

a triad is a tiny but critical structure found in skeletal muscle. It's like a microscopic communication hub that coordinates the process of muscle contraction. The triad acts as a bridge between the nervous system's signal and the muscle's response. When a nerve impulse arrives, it travels through the T-tubule. This triggers the release of calcium from the terminal cisternae of the SR. T-tubule: A tiny invagination (inward fold) of the muscle cell membrane. Terminal cisternae: Two sac-like structures from the sarcoplasmic reticulum (SR), a network that stores calcium within the muscle cell.

Question 36

define terminal cisternae

Answer 36

Terminal cisternae are specialized regions within muscle cells that play a vital role in muscle contraction. They are like tiny calcium storage tanks located next to specialized channels called T-tubules. Terminal cisternae, along with T-tubules, form a crucial part of the excitation-contraction coupling (ECC) mechanism in muscles. This mechanism translates the electrical signal from the nervous system into the mechanical response of muscle contraction. By storing and releasing calcium in a controlled manner, terminal cisternae ensure precise and efficient muscle function.

Question 37

define agonist muscle

Answer 37

An agonist muscle, also sometimes called the prime mover, is the main muscle responsible for producing a specific movement at a joint.

Question 38

define antagonist muscle

Answer 38

An antagonist muscle, also sometimes called the opposing muscle, is the counterpart to the agonist muscle. It works in opposition to the agonist, relaxing and lengthening to allow for the agonist's contraction and movement at a joint.

Question 39

define synergists

Answer 39

In the world of muscles, synergists are teammates! They work together with another muscle, the agonist, to produce a specific movement at a joint.

Question 40

define endurance

Answer 40

fast type 1a low ATP, long periods slow type 1

Question 41

define explosive

Answer 41

fast type 2b high ATP, short periods

Question 42

define intermediate

Answer 42

type 2a

Question 43

define creatine phosphate

Answer 43

stores of phosphocreatine in sarcoplasm

Question 44

define myoglobin in muscels איפה ממוקם? למה מתפקד?

Answer 44

located in the sarcoplasm of striated muscle function as mobile carrier of O2 and oxygen storage in muscles

Question 45

define hydroxyapatite

Answer 45

Hydroxyapatite (HA) is a naturally occurring mineral found in the human body. It's the main inorganic component that gives bones and teeth their hardness and structure. Ca5(PO4)3(OH)

Question 46

define osteon

Answer 46

An osteon, also known as a Haversian system, is the fundamental functional unit of mature compact bone. They are cylindrical structures, typically between 0.25 and 0.35 millimeters in diameter and several millimeters to a centimeter long . Each osteon consists of several key components: Haversian canal: A central canal that runs along the long axis of the osteon. This canal contains blood vessels and nerves that supply nutrients and remove waste products from the bone tissue. Lamellae: Concentric rings of hard, calcified bone matrix that surround the Haversian canal. These lamellae are made up of collagen fibers and hydroxyapatite, a calcium phosphate mineral that gives bones their strength and rigidity. The lamellae are arranged in layers, with the newest bone tissue located closest to the Haversian canal and the older bone tissue located further away. Lacunae: Tiny cavities within the lamellae that house osteocytes, mature bone cells. Osteocytes are responsible for maintaining bone tissue. Canaliculi: Microscopic channels that radiate outward from the lacunae. These channels connect the osteocytes to each other and to the Haversian canal, allowing nutrients and waste products to pass through. Cement line: A thin layer of mineralized material that separates each osteon from its neighbors. Osteons are formed through a process called bone remodeling. In this process, old bone tissue is continuously removed by osteoclasts (bone-resorbing cells) and replaced with new bone tissue formed by osteoblasts (bone-forming cells). The new bone tissue is deposited in concentric layers around a blood vessel, eventually forming an osteon.

Question 47

define central canal

Answer 47

The central canal, also known as the spinal foramen or ependymal canal, is a fluid-filled channel that runs longitudinally through the entire length of the spinal cord . The central canal has two main functions: Transport of cerebrospinal fluid (CSF): The CSF acts as a protective cushion for the brain and spinal cord, removes waste products, and delivers nutrients. The central canal plays a vital role in transporting CSF throughout the spinal cord. Potential nutrient delivery: While the exact role is still being explored, the central canal might also play a part in delivering nutrients to the spinal cord tissues.

Question 48

define lamellae

Answer 48

lamellae are the concentric rings of hard, calcified bone tissue that surround the Haversian canal (central canal) in compact bone. These layers are made of collagen fibers and hydroxyapatite, a mineral that gives bones their strength. The arrangement of lamellae, with newer layers closer to the canal and older ones further away, contributes to the overall strength and structure of the bone.

Question 49

define lacunae

Answer 49

lacunae are small spaces within the lamellae (layers) of compact bone. These cavities house osteocytes, mature bone cells responsible for maintaining bone tissue. Osteocytes reside in lacunae and send out tiny channels called canaliculi to connect with each other and the blood vessels in the central canal.

Question 50

define canaliculi

Answer 50

Canaliculi are microscopic channels in bone that radiate outward from the lacunae (tiny cavities). They play a crucial role in keeping bone tissue healthy.

Question 51

define medullary cavity

Answer 51

The medullary cavity, also known as the marrow cavity, is the hollow space found in the center of long bones and some flat bones. It's essentially the inner core where important processes happen. Function: Holds bone marrow: The medullary cavity acts as a housing unit for bone marrow, which is a soft, connective tissue responsible for two critical functions: Blood cell production: Red bone marrow in the cavity manufactures red blood cells, white blood cells, and platelets. Fat storage: Yellow bone marrow, also found in the cavity, primarily stores fat but can convert back to red bone marrow when the body needs to increase blood cell production.

Question 52

define spongy bone

Question 53

define trabeculae

Answer 53

delicate network of interconnecting bony rods/plates each consist of...

Question 54

define resorptional

Answer 54

remove of existing bone by osteoclast

Question 55

define deposition

Answer 55

the formal of new bone by osteoblast

Question 56

define compact bone

Question 57

define parathyroid hormone (Ca+2 homeostasis)

Question 58

define calcitonin (Ca+2 homeostasis)

Question 59

define vitamin D (Ca+2 homeostasis)

Question 60

define axial skeleton

Question 61

define appendicular skeleton

Question 62

define articulation

Answer 62

= joint

Question 63

define ligament

Question 64

define epiphysis

Question 65

define articular certilage

Question 66

define diaphysis

Question 67

define epiphyseal/growth plate

Question 68

define yellow marrow

Question 69

define red marrow

Question 70

define periosteum

Question 71

define endoosteum

Question 72

What main functions are served by muscle?

Answer 72

The muscular system is involved in four main functions: -movement - Muscles are responsible for all voluntary movements of the body, from blinking your eyes to running a marathon. -Posture - Skeletal muscles help to maintain your posture by constantly contracting and relaxing to keep your body upright. -thermoregulation (Heat production) - Skeletal muscles produce heat when they contract. This helps to maintain your body temperature. -contraction of the heart - contraction of cardiac muscle in the heart allow propels of blood from the heart to the body. constriction of organ and vessels - which help to propel and mix food in the digestive tract, release substances and regulate blood flow. communication - allowing speaking, writing, gesturing and facial expressions. -respiration - muscles within the thorax are necessary for respiration.

Question 73

briefly explain the role of skeletal muscle in circulation.

Answer 73

Skeletal muscles in the legs contract to compress nearby veins, assisting venous blood as it returns to the heart. Specifically, blood returning from the lower regions of the body must counteract gravity. Since venous pressure is relatively low, the function of skeletal muscle is vital.

Question 74

Briefly explain the role of smooth muscle in circulation.

Answer 74

Smooth muscle lines arteries, arterioles, and veins. In response to a variety of factors, this muscle can contract (promoting vasoconstriction) or relax (promoting vasodilation).

Question 75

Name the three major types of muscle.

Answer 75

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

Question 76

What features characterize smooth muscle?

Answer 76

Smooth muscle is: mononucleated, meaning that a single cell contains only one nucleus rounded and irregular in appearance, not striated generally controlled involuntarily

Question 77

What features characterize skeletal muscle?

Answer 77

Skeletal muscle is: multinucleated, meaning that a single cell contains more than one nucleus striated, or striped in appearance generally controlled voluntarily

Question 78

in what way(s) does cardiac muscle resemble smooth muscle?

Answer 78

Cardiac muscle is controlled involuntarily. In general, its cells are also mononucleated. (However, a small proportion of cardiac muscle cells do contain two nuclei.)

Question 79

In what way(s) does cardiac muscle resemble skeletal muscle?

Answer 79

Like skeletal muscle, cardiac muscle appears striated due to the presence of sarcomeres. However, the two muscle types differ in the shapes of their cells. Striated muscle contains ordered, cylindrical cells, while cardiac muscle cells are more branched and irregular.

Question 80

Which muscle types require calcium for proper contraction?

Answer 80

All three muscle types—skeletal, cardiac, and smooth—require calcium ions to contract. Note that these types use different mechanisms of contraction. In short, skeletal and cardiac muscle require calcium to bind to troponin, while smooth muscle needs the ion to trigger a signaling cascade.

Question 81

How does the role of calcium in skeletal and cardiac muscle contraction differ from its function in smooth muscle?

Answer 81

Skeletal and cardiac muscle require calcium to bind to troponin, exposing the myosin binding site. Smooth muscle contains no troponin, but still relies on calcium for a signaling cascade that promotes contraction.

Question 82

A certain tissue sample displays three nuclei in a single cell. This sample is likely which type of muscle?

Answer 82

The sample is probably skeletal muscle. In humans, skeletal muscle is the only one of the three types that is generally multinucleated.

Question 83

A certain tissue sample displays numerous mitochondria and large amounts of microfilament-based structures. This sample is likely which type of muscle?

Answer 83

This information is inconclusive. All three muscle types contain mitochondria and substantial amounts of actin, a motor protein composed of microfilaments. While skeletal muscle does tend to possess more mitochondria than the other types, we do not know enough to answer this question.

Question 84

Which division of the nervous system is involved in the control of involuntary muscles?

Answer 84

The autonomic nervous system controls muscles that are not under voluntary influence. These include both smooth and cardiac muscle. The autonomic nervous system is a division of the peripheral nervous system, or PNS.

Question 85

Which division of the nervous system is involved in the control of voluntary muscles?

Answer 85

The somatic nervous system controls muscles that are influenced consciously, or voluntarily. This category includes skeletal muscles. The somatic nervous system is a division of the peripheral nervous system, or PNS.

Question 86

A biopsy is taken from the lining of an artery wall. Which type(s) of muscle might be found in this process?

Answer 86

Smooth muscle would likely be found. Arteries, veins, arterioles, and larger venules contain smooth muscle in addition to endothelium and connective tissue. Note that capillary walls contain only a single layer of endothelial cells.

Question 87

A tissue sample is taken from the diaphragm. Which type(s) of muscle could this sample contain?

Answer 87

The sample would likely contain skeletal muscle. The diaphragm is the main muscle involved in respiration. It is composed of skeletal muscle, but can be controlled either voluntarily or involuntarily.

Question 88

Muscle cells are likely to have large amounts of which eukaryotic organelle?

Answer 88

In general, muscle cells are likely to contain high numbers of mitochondria. These organelles provide the ATP needed for contraction. Some types of muscle fiber, generally those specialized for aerobic respiration, are higher in mitochondria than others. For example, slow-twitch or red muscle fibers contain extremely high numbers of the structures.

Question 89

define sarcomere

Answer 89

A sarcomere is a highly organized unit within striated muscle. Sarcomeres are composed of alternating thick filaments (myosin) and thin filaments (actin). Together, many sarcomeres make up a myofibril, and many myofibrils form a muscle cell.

Question 90

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

Answer 90

Thick filaments are composed of 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.

Question 91

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

Answer 91

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

Question 92

Muscle cells can also be called by which alternative term?

Answer 92

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 93

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

Answer 93

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 94

define myoglobin

Answer 94

Myoglobin is the 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 95

Describe the structural difference between myoglobin and hemoglobin.

Answer 95

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 96

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

Answer 96

Muscle fibers can be grouped into either red or 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.

Question 97

What basic features characterize red muscle fibers?

Answer 97

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 98

What basic features characterize white muscle fibers?

Answer 98

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 99

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?

Answer 99

This condition is known as 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.

Question 100

define neuromuscular junction, or NMJ.

Answer 100

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 101

Name the main neurotransmitter at the neuromuscular junction.

Answer 101

The neurotransmitter released at the NMJ is 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.

Question 102

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

Answer 102

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 103

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

Answer 103

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 104

define motor unit

Answer 104

A motor unit 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 105

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

Answer 105

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 muscle. It stores calcium ions and releases them in response to an action potential, which then allows contraction to occur.

Question 106

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

Answer 106

The cytoplasm of a muscle cell is called the 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.

Question 107

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

Answer 107

The plasma membrane of a muscle cell is called the 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.

Question 108

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

Answer 108

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

Question 109

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

Answer 109

1. Acetylcholine is released from an adjacent motor neuron and binds to receptors on the muscle cell membrane. 2. Ion channels open, causing a large influx of sodium ions and a depolarization of the cell. 3. Calcium release channels in the SR membrane are activated and open; Ca2+ flows down its gradient into the sarcoplasm.

Question 110

How do Ca2+ ions facilitate actin-myosin binding?

Answer 110

Each calcium ion binds to troponin, causing tropomyosin to change its shape. This frees the myosin binding site on the relevant actin molecule. When calcium is not present, tropomyosin is bound to actin in a position that blocks the myosin binding site. For contraction to occur, this site must be open for the head of a myosin molecule to attach.

Question 111

What is the function of the T-tubule system in skeletal muscle?

Answer 111

T tubules are deep folds in the sarcolemma of muscle cells. Since they bring the cell membrane closer to the central regions of the cell, they allow action potentials to quickly propagate to the sarcomeres.

Question 112

What name is given to the current model of skeletal muscle contraction?

Answer 112

Skeletal muscle is thought to contract according to the sliding filament model. According to this theory, myosin heads bind to actin molecules, then undergo a quick stroke to shorten the sarcomere. The filaments themselves do not change in length during this process; they simply overlap.

Question 113

Which of the following does not change in length during contraction: the A band, the I band, or the H zone?

Answer 113

The length of the A band remains unchanged. In a sarcomere, the A band refers to the length of an entire myosin fiber. Since actin and myosin do not actually shorten during contraction, the A band’s length is always constant.

Question 114

Which of the following does change in length during contraction: the A band, the I band, or the H zone?

Answer 114

Both the I band and the H zone change in length during contraction. In a sarcomere, the I band refers to the unoverlapped actin region, while the H zone refers to the region that contains myosin alone. Contraction involves the overlapping of filaments, so both of these regions shorten as the actin and myosin pull together.

Question 115

In skeletal muscle, how does the role of tropomyosin differ from that of troponin?

Answer 115

Tropomyosin directly attaches to actin. In the absence of calcium, it physically blocks the myosin binding site. Troponin binds to tropomyosin. It binds to calcium (when the ion is present) and triggers a conformational change in the tropomyosin molecule.

Question 116

Briefly list the steps involved in skeletal muscle contraction, beginning with the influx of Ca2+ into the sarcoplasm.

Answer 116

- Ca2+ binds troponin on actin molecules; on each one, tropomyosin is moved away from the myosin binding site. - Myosin heads have already bound ATP and are situated in a high-energy position. Now, they can freely bind actin, forming cross-bridges. - ATP is hydrolyzed; the myosin pulls back in a “power stroke,” shortening the sarcomere. - A new ATP molecule is required to remove myosin from its bound position and reset the cycle.

Question 117

What main functions are served by the skeletal system?

Answer 117

The skeletal system is involved in four main functions: protection of internal organs structure and support calcium storage immune cell and erythrocyte production

Question 118

Name the two major types of bone.

Answer 118

The two main types are compact and spongy bone. Compact bone is also called cortical bone; spongy bone is also called cancellous bone.

Question 119

What features characterize compact bone?

Answer 119

Compact bone is hard and dense. It is mainly composed of the minerals, salts, and collagen that form the bony matrix. Compact bone is comprised of cylindrical subunits called osteons.

Question 120

What features characterize spongy bone?

Answer 120

Spongy bone is softer and less dense than compact bone. It contains many blood vessels, as well as gaps in its structure that are filled with bone marrow. Spongy bone is comprised of thin, sharp subunits called trabeculae.

Question 121

define ligament

Answer 121

A ligament is a strip of tough connective tissue that connects a bone to another bone. Ligaments are composed of collagen. Ligaments generally function to stabilize joints. For example, the anterior cruciate ligament, or ACL, stabilizes the knee.

Question 122

What is cartilage, and what substances does it include?

Answer 122

Cartilage is a form of connective tissue that is less rigid than bone. It includes elastin protein fibers, proteoglycan, and collagen. The collagen in cartilage is produced by specialized cells called chondrocytes.

Question 123

What functions does cartilage serve in the human body?

Answer 123

During development, cartilage solidifies into bone in a process known as ossification. It also provides soft, flexible protection for certain parts of the anatomy. For example, the trachea, nose, and ears contain cartilage.

Question 124

The human skeleton can be split into which two major divisions?

Answer 124

The skeletal system is generally divided into the axial skeleton and the appendicular skeleton. The axial skeleton is relatively central; it contains the vertebrae, ribcage, and skull. The appendicular skeleton is more peripheral and includes the bones of the appendages and the pelvis.

Question 125

Regulation of which ion involves both the skeletal and endocrine systems?

Answer 125

These systems are involved in the regulation of calcium. Plasma Ca2+ concentration is controlled by two hormones: calcitonin and parathyroid hormone (PTH). Calcitonin lowers plasma calcium by promoting its storage in bone, while PTH has the opposite effect.

Question 126

How does the role of an osteoclast differ from that of an osteoblast?

Answer 126

Osteoclasts break down bone and release its calcium content into the plasma. As a result, osteoclast activity increases blood calcium levels. Osteoblasts promote the synthesis of bone, removing calcium from the plasma in the process. As a result, osteoblast activity decreases blood calcium levels.

Question 127

What is the main mineral component of bone, and what is its chemical formula?

Answer 127

Bone is composed of hydroxyapatite (Ca5(PO4)3OH).

Question 128

define acetylcholinesterase

Answer 128

Acetylcholinesterase (AChE), also known as AChase or acetylhydrolase, is an enzyme found in the nervous system and muscle tissues. It is responsible for breaking down acetylcholine (ACh).

Question 129

from what ATP can be generated?

Answer 129

aerobic production of ATP under normal condition. anaerobic production of ATP during intensive short-term work. conversation of a molecule of creatine phosphate to ATP. conversation of 2 molecules of ADP to ATP and AMP during heavy exercise.

Question 130

what are the types of muscles fibers?

Answer 130

Slow Oxidative (SO) Fibers: Also known as Type I fibers. Contract slowly and fatigue slowly. Primarily rely on oxygen (aerobic respiration) to generate ATP using fats and some carbohydrates. Well-suited for endurance activities like marathons or long-distance swimming. Contain a rich network of capillaries for efficient oxygen delivery. Have a reddish color due to the presence of myoglobin, a protein that stores oxygen. Fast Oxidative-Glycolytic (FOG) Fibers: Also known as Type IIA fibers. Contract faster than SO fibers and have moderate fatigue resistance. Generate ATP through a combination of aerobic respiration and anaerobic respiration (glycolysis) using carbohydrates. Can switch between energy sources depending on exercise intensity. Found in muscles used for activities requiring both speed and endurance, like cycling or mid-distance running. Fast Glycolytic (FG) Fibers: Also known as Type IIB fibers. Contract very quickly but fatigue easily. Primarily rely on anaerobic respiration (glycolysis) using carbohydrates for rapid ATP generation. Produce lactic acid as a byproduct, which can contribute to muscle burning and fatigue. Adapted for short bursts of high-intensity activities like sprinting or weightlifting. Have a whitish color due to lower myoglobin content.