Chapter 1: Structure and Function of Body Systems

Question 1

What does the musculoskeletal system consist of?

Answer 1

The musculoskeletal system of the human body consists of bones, joints, muscles, and tendons.

Question 2

How do muscles exert force on the ground or other objects?

Answer 2

Muscles pull against bones that rotate about joints and transmit force to their environment. They can only pull, not push.

Question 3

What does the axial skeleton consist of?

Answer 3

The axial skeleton consists of the skull (cranium), vertebral column (vertebra C1 through coccyx), ribs, and sternum.

Question 4

What does the appendicular skeleton consist of?

Answer 4

The appendicular skeleton includes the shoulder (or pectoral) girdle (left and right scapula and clavicle); bones of the arms, wrists, and hands (left and right humerus, radius, ulna, carpals, metacarpals, and phalanges); the pelvic girdle (left and right vocal or innominate bones); and the bones of the legs, ankles, and feet (left and right femur, patella, tibia, fibula, tarsals, metatarsal, and phalanges).

Question 5

What factors affect skeletal growth in an adult?

Answer 5

Heavy loads (job tasks or resistance training) and explosive movements with impact increase bone density and bone mineral count.

Question 6

How many bones are in the human body?

Answer 6

There are 206 bones in the human body.

Question 7

What are joints?

Answer 7

Joints are junctions of bones.

Question 8

What is a fibrous joint?

Answer 8

A fibrous joint is a joint that allows virtually no movement (e.g. sutures of the skull).

Question 9

What is a cartilaginous joint?

Answer 9

A cartilaginous joint is a joint that allows limited movement (e.g. intervertebral disks).

Question 10

What is a synovial joint?

Answer 10

A synovial joint is a joint that allows considerable movement (e.g. elbow and knee).

Question 11

What is hyaline cartilage?

Answer 11

Hyaline cartilage is smooth cartilage that covers articulated bone ends.

Question 12

What fills the capsules that encloses a joint?

Answer 12

Synovial fluid

Question 13

What is a uniaxial joint?

Answer 13

A uniaxial joint, such as the elbow, operates as a hinge, essentially rotating about one axis.

Question 14

What is a biaxial joint?

Answer 14

A biaxial joint, such as the ankle and wrist, allow movement about two perpendicular axes.

Question 15

What is a multiaxial joint?

Answer 15

A multiaxial joint, including the shoulder and hip ball-and-socket joints, allow movement about all three perpendicular axes that define space.

Question 16

What is the vertebral column?

Answer 16

The vertebral column is made up of vertebral bones separated by flexible disks that allow movement to occur. The vertebrae are grouped into 7 cervical vertebrae in the neck region; 12 thoracic vertebrae in the middle to upper back; 5 lumbar vertebrae, which make up the lower back; 5 sacral vertebrae, which are fused together and make up the rear part of the pelvis; and 3 to 5 coccygeal vertebrae, which form a kind of vestigial internal tail extending downward from the pelvis.

Question 17

How many skeletal muscles does the human body have?

Answer 17

The human body has more than 430 skeletal muscles.

Question 18

What is epimysium?

Answer 18

Fibrous connective tissue of a muscle. It is contiguous with the tendons at the ends of the muscles.

Question 19

What is a tendon?

Answer 19

A tendon connects muscles to bone by way of bone periosteum.

Question 20

What is bone periosteum?

Answer 20

Bone periosteum is a specialized connective tissue covering all bones.

Question 21

What does proximal mean?

Answer 21

Closer to the trunk.

Question 22

What does distal mean?

Answer 22

Farther from the trunk.

Question 23

What does superior mean?

Answer 23

Closer to the head.

Question 24

What does inferior mean?

Answer 24

Closer to the feet.

Question 25

What are the types of connective tissue of a muscle?

Answer 25

The epimysium (outer layer), perimysium (tissue surrounding each fascicles, or group of fibers), and endomysium (tissue surrounding individual fibers).

Question 26

What are muscle cells (fibers)?

Answer 26

Muscle cells (fibers) are long, cylindrical cells 50 to 100 um in diameter (about the diameter of a human hair).

Question 27

What are fasciculi?

Answer 27

Fasciculi are grouped bundles of muscle fibers (may consist of up to 150 fibers).

Question 28

What is perimysium?

Answer 28

Perimysium is connective tissue that surrounds the fasciculi.

Question 29

What surrounds each individual muscle fiber?

Answer 29

Connective tissue called endomysium, which is encircled by and is contiguous with the fiber’s membrane, or sarcolemma.

Question 30

What is a motor neuron?

Answer 30

A nerve cell within a muscle.

Question 31

What is a neuromuscular junction?

Answer 31

A junction between a motor neuron and the muscle fibers it innervates. Also called a motor end plate.

Question 32

What is a motor unit?

Answer 32

A motor neuron and the muscle fibers it innervates.

Question 33

What is the sarcoplasm?

Answer 33

Sarcoplasm is the cytoplasm (living material inside a cell) of a muscle fiber and contains contractile components consisting of protein filaments, other proteins, stored glycogen and fat particles, enzymes, and specialized organelles such as mitochondria and the sarcoplasm is reticulum.

Question 34

What is a myofibril?

Answer 34

A myofibril is a thin fiber within the sarcoplasm that contain the apparatus that contracts the muscle cell, consisting of two types of myofilament: myosin and actin.

Question 35

How do myosin and actin interact with each other?

Answer 35

The myosin filament consists of a globular head, a hinge point, and a fibrous tail. The globular heads protrude away from the myosin filament at regular intervals, and a pair of myosin filaments forms a cross bridge, which interacts with the actin. The actin filaments consist of two strands arranged in a double helix.

Question 36

What is a sarcomere?

Answer 36

A sarcomere is the smallest contractile unit of skeletal muscle containing myosin and actin filaments organized longitudinally.

Question 37

How are the bands of a myofibril laid out?

Answer 37

Myofibril is maid up of repeating segments including Z-lines, M-lines, I-bands, A-bands, and H-zones.

The dark A-band corresponds with the alignment of myosin filaments, whereas the light I-band corresponds with the areas in two adjacent sarcomere that contain only actin filaments

Actin is anchored to the Z-lines which is in the middle of the I-band and appears as a think, dark line running longitudinally through the I-band.

The H-zone is the area in the center of the sarcomere where only myosin filaments are present.

Question 38

What happens to the areas of the sarcomere during a muscle contraction?

Answer 38

The H-zone decreases as the actin slides over the myosin toward the center of the sarcomere. The I-band also decreases as the Z-lines are pulled toward the center of the sarcomere.

Question 39

What is the sarcoplasmic reticulum?

Answer 39

The sarcoplasmic reticulum is a system of tubules parallel to and surrounding each myofibril which terminates as vesicles in the vicinity of the Z-lines.

Question 40

What are T-tubules?

Answer 40

T-tubles, or transverse tubules, run perpendicular to the sarcoplasmic reticulum and terminate in the vicinity of the Z-line between two vesicles.

Question 41

What is action potential?

Answer 41

Action potential is an electrical nerve impulse that arrives nearly simultaneously from the surface to all depths of the muscle fiber because due to T-tubules running between outlying myofibrils which are contiguous with the sarcolemma at the surface of the cell.

Calcium is released during action potential producing a coordinated contraction.

Question 42

What is the Sliding-Filament Theory of Muscular Contraction?

Answer 42

The sliding-filament theory states that the actin filaments at each end of the sarcomere slide inward on myosin filaments, pulling the Z-lines toward the center of the sarcomere and thus shortening the muscle fiber.

As actin filaments slide over myosin filaments, both the H-zone and I-band shrink. The action of myosin crossbridges pulling on actin filaments is responsible for the movement of the actin filament.

Because only a very small displacement of the actin filament occurs with each flexion of the myosin crossbridge, very rapid, repeated flexions must occur in many crossbridges throughout the entire muscle for measurable movement to occur.

Question 43

What happens in the resting phase of a muscle?

Answer 43

Little calcium is present so very few of the myosin crossbridges are bound to actin, though the myosin and actin still interact in a weak bond.

Question 44

What happens during the Excitation-Contraction Coupling Phase?

Answer 44

The sarcoplasmic reticulum is stimulated to release calcium ions. The calcium binds with troponin, a protein that is situated at regular intervals along actin filament and has high affinity for calcium ions.

This causes a shift to occur in another protein molecule, tropomyosin, which runs along the length of the actin filament in the groove of the double helix.

The myosin crossbridge now attaches more rapidly to the actin filament, allowing force to be produced as the actin filaments are pulled toward the center of the sarcomere.

The amount of force produced by a muscle at any instant in time is directly related to the number of myosin crossbridges bound to actin filaments cross-sectionally at that instant in time.

Question 45

What happens during the Contraction Phase?

Answer 45

The energy for pulling action, or power stroke, comes from hydrolysis (breakdown) of adenosine triphosphate (ATP) to adenosine diphosphate (ADP) and phosphate, a reaction catalyze by the enzyme myosin adenosine triphosphatase (ATPase).

Another molecule of ATP must replace the ADP on the myosin crossbridge globular head in order for the head to detach from the active actin site and return to its original position.

This allows the contraction process to continue (if calcium is available to bind to troponin) or relaxation to occur (if calcium is not available).

Calcium plays a role in regulating a large number of events in skeletal muscle besides contraction. These include glycolitic and oxidative energy metabolism, as well as protein synthesis and degradation.

Calcium and ATP are necessary for crossbridge cycling with actin and myosin filaments.

Question 46

What happens during the Recharge Phase?

Answer 46

Measurable muscle shortening transpires only when this sequence of events — binding of calcium to troponin, coupling of myosin crossbridge with actin, power stroke, dissociation of actin and myosin, and resetting of the myosin head position — is repeated over and over again throughout the muscle fiber.

This occurs as long as calcium is available in the myofibril, ATP is available to assist in uncoupling the myosin from the actin, and sufficient active myosin ATPase is available for catalyze great the breakdown of ATP.

Question 47

What happens during the Relaxation Phase?

Answer 47

Relaxation occurs when the stimulation of the motor nerve stops. Calcium is pumped back into the sarcoplasmic reticulum, which prevents the link between the actin and myosin filaments. Relaxation is brought about by the return of the actin and myosin filaments to their unbound state.

Question 48

What are the Steps of Muscle Contraction?

Answer 48

1. Initiation of ATP splitting (by myosin ATPase) causes myosin head to be in an “energized” state that allows it to move into a position to be able to form a bond with actin.
2. The release of phosphate from the ATP splitting process then causes the myosin head to change shape and shift.
3. This pulls the actin filament in toward the center of the sarcomere and is referred to as the power stroke; ADP is then released.
4. Once the power stroke has occurred, the myosin head detaches from the actin but only after another ATP binds to the myosin head because the binding process facilitates detachment.
5. The myosin head is now ready to bind to another actin (as described in step 1), and the cycle continues as long as ATP and ATPase are present and calcium is bound to the troponin.

Question 49

What is the connection of the Neuromuscular System to muscle fibers?

Answer 49

Muscle fibers are innervates by motor neurons that transmit impulses in the form of electrochemical signals from the spinal cord to muscle. A motor neuron generally has numerous terminal branches at the end of its axon and thus innervates many different muscle fibers.

The whole structure is what determines the muscle fiber type and its characteristics, function, and involvement in exercise.

Question 50

What role does acetylcholine play in muscle contraction?

Answer 50

Acetylcholine is a neurotransmitter that diffuses across the neuromuscular junction, causing excitation of the sarcolemma, when an action potential is sensed at the nerve terminal of a muscle.

Once a sufficient amount of acetylcholine is release, an action potential is generated along the sarcolemma, and the fiber contracts. All of the muscle fibers in the motor unit contract and develop force at the same time.

Question 51

What is the all-or-none principle?

Answer 51

There is no evidence that a motor neuron stimulus causes only some of the fibers to contract. Similarly, a stronger action potential cannot produce a stronger contraction. This is the all-or-none principle of muscle.

Question 52

What is a twitch?

Answer 52

Each action potential traveling down a motor neuron results in a short period of activation of the muscle fibers within the motor unit. The brief contraction that results is referred to as a twitch.

Question 53

How does a contraction reach maximal force?

Answer 53

Activation of the sarcolemma results in the release of calcium within the fiber, and contraction proceeds as previously described. Force develops if there is resistance to the pulling interaction of actin and myosin filaments. Although calcium release during a twitch is sufficient to allow optimal activation of actin and myosin, and there by maximal force of the fibers, calcium is removed before force reaches its maximum, and the muscle relaxes.

If a second twitch is elicited from the motor nerve before the fibers completely relax, force from the two twitches summaries, and the resulting force is greater than that produced by a single twitch.

Decreasing the time interval between the twitches results in greater summation of crossbridge binding and force.

Question 54

What is tetanus?

Answer 54

Tetanus is a condition where muscle stimuli may be delivered at so high a frequency that the twitches begin to merge and eventually completely fuse.

This is the maximal amount of force the motor unit can develop.

Question 55

What are the different types of muscle fibers?

Answer 55

Muscle fibers are categorized as slow and fast-twitch, which can be further broken down into Type I (slow twitch), Type IIa (fast-twitch), and Type IIx (fast twitch).

Question 56

What characteristics do Type I muscle fibers have?

Answer 56

Type I fibers are generally efficient and fatigue resistant and have a high capacity for aerobic energy supply, but they have limited potential for rapid force development, as characterized by low myosin ATPase activity and low anaerobic power.

Question 57

What characteristics to Type II muscle fibers have?

Answer 57

Type II motor units are characterized as inefficient and fatiguable and as having low aerobic power, rapid force development, high myosin ATPase activity, and high anaerobic power.

Type IIa and IIx fibers differ mainly in their capacity for aerobic-oxidative energy supply. Type IIa fibers have greater capacity for aerobic metabolism and more capillaries surrounding them than Type IIx and therefore show greater resistance to fatigue.

Type IIx fibers in general have slightly higher force production/power output than Type IIa.

Question 58

What are proprioceptors?

Answer 58

Proprioceptors are specialized sensory receptors located within joints, muscles, and tendons that are sensitive to pressure and tension and relay information concerning muscle dynamics to the conscious and subconscious parts of the central nervous system.

Question 59

What are muscle spindles?

Answer 59

Muscle spindles are proprioceptors that consist of several modified muscle fibers enclosed in a sheath of connective tissue. These modified fibers, called intramural fibers, run parallel to the normal, or extrafusal, fibers.

Muscle spindles provide information concerning muscle length and the rate of change in length. When the muscle lengthens, spindles are stretched. This deformation activates the sensory neuron of the spindle, which sends an impulse to the spinal cord, where it synapse (connects) with motor neurons.

This results in the activation of motor neurons that innervates the same muscle. Spindles thus indicate the degree to which the muscle must be activated in order to overcome a given resistance.

Question 60

How can athletes improve force production?

Answer 60

-Incorporate phases of training that use heavier loads in order to optimize neural recruitment.
-Increase the cross-sectional area of muscle involved in the desired activity.
Perform multimuscle, multijoint exercises that can be done with more explosive actions to optimize fast-twitch muscle recruitment.

Question 61

What are golgi tendon organs (GTOs)?

Answer 61

Golgi tendon organs are proprioceptors located in tendons near the myotendinous junction and are in series, that is, attached end to end, with extrafusal muscle fibers.

Golgi tendon organs are activated when the tendon attached to an active muscle is stretched. As tension is the muscle increases, disc rage of the GTOS increases. The sensory neuron of the GRO synapses with an inhibitory interneuron in the spinal cord, which in turn synapses with and inhibits a motor neuron that serves the same muscle.

The result is a reduction in tension within the muscle and tendon. Thus, whereas spindles facilitate activation of the muscle, neural input from GTOs inhibits muscle activation. The GTOs’ inhibitory process is through to provide a mechanism that protects against the development of excessive tension.

Therefore the GTOs’ effect is low at low forces and increase as the load placed on the muscle increases.

The ability of the motor cortex to override this inhibition may be one of the fundamental adaptations to heavy resistance training.

Question 62

What is the primary roles of the cardiovascular system?

Answer 62

The roles of the cardiovascular system are to transport nutrients and remove waste and by-products while assisting with maintaining the environment for all the body’s functions.

The cardiovascular system plays key roles in the regulation of the body’s acid-base system, fluids, and temperature, as well as variety of other physiological functions.

Question 63

What is the heart?

Answer 63

The heart is a muscular organ composed of two interconnected but separate pumps; the right side of the heart pumps blood through the lungs,and the left side pumps blood through the rest of the body.

Each pump has two chambers: an atrium and a ventricle. The right and left atria deliver blood into the right and left ventricles. The right and left ventricles supply the main force for moving blood through the pulmonary and peripheral circulations, respectively.

Question 64

What are the valves of the heart?

Answer 64

The tricuspid valve and mitral valve (bicuspid valve), collectively called atrioventricular (AV) valves, prevent the flow of blood from the ventricles back into the atria during ventricular contraction (systole).

The aortic valve and pulmonary valve (collectively, the semilunar valves) prevent backflow from the aorta and pulmonary arteries into the ventricles during ventricular relaxation (diastole).

Each valve opens and closes passively; that is, each closes when a backward pressure gradient pushes blood back against it, opening when a forward pressure gradient forces blood in the forward direction.

Question 65

Describe the nodes and bundles of the Conduction System.

Answer 65

A specialized electrical conduction system controls the heart. The conduction system is composed of:

• the sinoatrial (SA) node - the intrinsic pacemaker - where rhythmic electrical pulses are normally initiated
• the intermodal pathways that conduct the impulse from the SA node to the atrioventricular node
• the atrioventricular (AV) node, where the impulse is delayed slightly before passing into the ventricles
• the atrioventricular (AV) bundle, which conducts the impulse to the ventricles
• the left bundle branch and right bundle branch, which further divide into the Purkinje fibers and conduct impulses to all parts of the ventricles

Question 66

What is one of the main differences in characteristics between AV nodes and AV bundles?

Answer 66

The AV bundles are large and transmit impulses at a much higher velocity than the AV nodal fibers. Because these fibers give way to the Purkinje fibers, which more completely penetrate the ventricles, the impulse travels quickly throughout the entire ventricular system and causes both ventricles to contract at approximately the same time.

Question 67

What is the myocardium?

Answer 67

The myocardium is the heart muscle.

Question 68

What are the effects of the sympathetic and parasympathetic nervous systems?

Answer 68

Stimulation of the sympathetic nerves accelerates depolarization of the SA node (the chronograph effect), which causes the heart to beat faster.

Stimulation of the parasympathetic nervous system slows the rate of SA node discharge, which slows the hear rate.

Question 69

What are the resting heart rate ranges for bradycardia and tachycardia?

Answer 69

The resting heart rate normally ranges from 60 to 100 bpm; fewer than 60 bpm is called bradycardia and more than 100 bpm is called tachycardia.

Question 70

What is an electrocardiogram (ECG)?

Answer 70

An electrocardiogram is a graphical representation of the electrical activity of the heart recorded at the surface of the body.

Question 71

What are the components of an ECG?

Answer 71

A normal ECG is composed of a P-wave, a QRS complex (often in three waves: a Q-wave, an R-wave, and an S-wave), and a T-wave.

Question 72

What is depolarization?

Answer 72

Depolarization is the reversal of the membrane electrical potential, whereby the normally negative potential inside the membrane becomes slightly positive and the outside becomes slightly negative.

The P-wave is generated by the changes in the electrical potential of cardiac muscle cells that depolarize the atria and result in atrial contraction.

The QRS complex is generated by the electrical potential that depolarizers the ventricles and results in ventricular contraction.

Question 73

What is repolarization?

Answer 73

The T-wave is cased by the electrical potential generated as the ventricles recover from the state of depolarization; this process, called repolarization, occurs in ventricular muscle shortly after depolarization. Although atrial repolarization occurs as well, its wave formation usually occurs during the time of ventricular depolarization and is thus masked by the QRS complex.

Question 74

What makes up the central and peripheral circulation?

Answer 74

The central and peripheral circulation form a single closed-circuit system with two components: an arterial system, which carries blood away from the heart, and a venous system, which returns blood toward the heart.

Question 75

What is the function of arteries?

Answer 75

The function of arteries is to rapidly transport blood pumped from the heart.

Because blood pumped from the heart is under relatively high pressure, arteries have strong, muscular walls.

Question 76

What are arterioles?

Answer 76

Small branches of arteries called arterioles act as control vessels through which blood enters the capillaries.

Arterioles play a major role in the regulation of blood flow to the capillaries. Arterioles have strong, muscular walls that are capable of closing the arterioles completely or allowing it to be dilated many times their size, thus vastly altering blood flow to the capillaries in response to the needs of the tissues.

Question 77

What is the function of capillaries?

Answer 77

The function of capillaries is to facilitate exchange of exogenous, fluid, nutrients, electrolytes, hormones, and other substances between the blood and the interstitial fluid in the various tissues of the body. The capillary walls are very thin and are permeable to these, but not all, substances.

Question 78

What are veins and venules?

Answer 78

Venules collect blood from the capillaries and gradually converge into the progressively larger veins, which transport blood back to the heart.

Because the pressure in the venous system is very low, venous walls are thin, although muscular. This allows them to constrict or dilate to a great degree and thereby act as a reservoir for blood, either in small or in large amounts.

In addition, some veins, such as those in the legs, contain one-way valves that help maintain venous return by preventing retrograde blood flow.

Question 79

What is the Skeletal Muscle Pump?

Answer 79

The skeletal muscle pump is the assistance that contracting muscles provide to the circulatory system. The muscle pump works with the venous system, which contains the one-way valves for blood return to the heart.

The contracting muscle compresses the veins, but since the blood can flow only in the direction of the valves, it is returned to the heart.

This mechanism is one of the reasons that individuals are told to keep moving around after exercise to avoid blood pooling in the lower extremities. On the flip side, it is important to periodically squeeze muscles during prolonged sitting to facilitate blood return to the heart.

Question 80

How does the blood facilitate the transport of oxygen?

Answer 80

The transport of oxygen is accomplished by hemoglobin, the iron-protein molecule carried by the red blood cells.

Hemoglobin also has an additional important role as an acid-base buffer, a regulator of hydrogen ion concentration, which is crucial to the rates of chemical reactions in cells.

Question 81

Wha is the role of red blood cells?

Answer 81

Red blood cells contain a large quantity of carbonic a hydrate, which catalyze the reaction between carbon dioxide and water to facilitate carbon dioxide removal.

Question 82

What components make up the respiratory system and what are their functions?

Answer 82

The primary function of the respiratory system is the basic exchange of oxygen and carbon dioxide. As air passes through the nose, the nasal cavities perform three distinct functions: warming, humidifying, and purifying the air.

Air is distributed to the lungs by way of the trachea, bronchi, and bronchioles. The trachea is called the first generation respiratory passage, and the right and left main bronchi are the second generation passages.

Each division thereafter is an additional generation (bronchioles). There are approximately 23 generations before the air finally reaches the alveoli, where gases are exchanged in respiration.