Chapter 1: Structure and Function of Body Systems

Question 1

Myofilaments?

Answer 1

Myosin is the thick filament and contains up to 200 myosin molecules. Contains a head that comes off the filament and forms a cross-bridge that interacts with actin. Actin filaments consist of 2 strands arranged in a double helix. There are 6 actin filaments around each myosin filament and 3 myosin filaments around each actin filament. Actin and myosin are arranged longitudinally in the smallest contractile unit of the muscle, the sarcomere. There are about 4,500 per centimeter of muscle length.

Question 2

Type IIa vs IIx fibers?

Answer 2

Type IIa have greater capacity for aerobic metabolism and more capillaries surrounding them than type IIx and therefore show greater resistance to fatigue.

Question 3

GTO’s?

Answer 3

Proprioceptors in tendons near the myotendinous junction and are attached in series with extrafusal muscle fibers. They are activated when the tendon is stretched and as tension increases discharges from GTO increase. The sensory neuron of the GTO synapses with an inhibitory interneuron in the spinal cord which synapses with and inhibits a motor neuron serving the same muscle. The GTO’s inhibitory process is though to provide a mechanism to protect against the development of excessive tension.

Question 4

How is quiet breathing accomplished?

Answer 4

The diaphragm contracts during inspiration and creates a negative pressure to bring air in. During expiration the diaphragm simply relaxes.

Question 5

Muscle Fiber Types?

Answer 5

Fast twitch motor units both develop force and relax rapidly and thus has a short twitch time. Slow twitch motor units develop force and relax slowly and thus have a long twitch time. The fiber types are type I (slow twitch), type IIa (fast twitch), type IIx (fast twitch)

Question 6

Range for bradycardia and tachycardia?

Answer 6

Resting heart rate less than 60 and greater than 100, respectively

Question 7

Muscle cells?

Answer 7

Also called muscle fibers, sometimes running entire length of muscle, and have many nuclei situated on the periphery of the cell.

Question 8

Motor Nerve, Neuromuscular Junction, etc.?

Answer 8

The junction between the motor nerve and muscle fiber is the neuromuscular junction. Each muscle cell has only one neuromuscular junction but a single motor nerve innervates many muscle fibers. The motor nerve and all the nerves it controls is the motor unit and all fibers contract together when stimulated by motor neuron.

Question 9

Sliding-filament theory?

Answer 9

Actin filaments at each end of the sarcomere slide inwards on myosin filaments, pulling the z-lines together, to shorten the muscle fiber. Only a very small displacement of actin occurs with each flexion of myosin so repeated flexions must occur in many crossbridges throughout the entire muscle.

Question 10

What part of the brain influences rhythm and conduction of the hear?

Answer 10

The cardiovascular center of the medulla, which transmits signals to the heart through the sympathetic and parasympathetic nervous systems.

Question 11

Conduction system of the heart?

Answer 11

The sinoatrial node is the intrinsic pacemaker, where rhythmic electrical impulses are normally initiated, and is located in the right atrium and is contiguous with the muscle fibers here. The electrical impulse spreads into the atria. The conduction system does not allow the impulse to spread to rapidly into the ventricles, allowing blood to empty from the atria before the ventricle contracts. The atrioventricular node will delay this and is located in the posterior septal wall of the right atrium. The AV bundle conducts the impulse to the ventricles via the left and right bundle branches and they then turn into purkinje fibers. These fibers transmit impulses much faster than the AV node fibers where impulses are delayed. The quick impulse into both ventricles causes them both to contract at the same time.

Question 12

Fibrous connective tissue?

Answer 12

Also known as epimysium and it covers the body’s more than 430 skeletal muscles. The epimysium in contiguous with the tendon that attaches to the periosteum (a specialized connective tissue covering all bones)

Question 13

Ways that muscle force can be graded?

Answer 13

The first is through variation of the frequency which the motor unit is activated. This is particularly important for small muscles, like that in the hand. The other method is through the number of motor units activated. This is more important in larger muscles, such as the thigh. Complete activation of the available motor neuron pool is probably no possible in untrained people.

Question 14

Axes of Joints

Answer 14

Uniaxial - rotates around one axis/hinge (elbow)
Biaxial - Moves about 2 perpendicular axes (wrist/ankle)
Multiaxial - Allow movement about all 3 perpendicular axes (shoulder/hip)

Question 15

Parts of the heart?

Answer 15

The right-side pumps to the lungs and the left side pumps to the rest of the body. The atrium is on top and the blood goes from the atrium to the ventricle and then to the lungs or the body.

Question 16

What transports oxygen in the blood?

Answer 16

Hemoglobin, which is an iron-protein carried by red blood cells

Question 17

Interior of myofibril?

Answer 17

Hundreds of myofibrils make up a muscle fiber and contains the apparatus that contracts the muscle cell and primarily consists of 2 types of myofilaments: myosin and actin.

Question 18

Type I Fibers?

Answer 18

Slow twitch fibers that are efficient and fatigue resistant. They have a high capacity for aerobic energy but they have a limited potential for rapid force development, as characterized by low myosin ATPase activity and low anaerobic power.

Question 19

Cytoplasm of a muscle fiber?

Answer 19

The sarcoplasm is the cytoplasm of a muscle fiber and contains protein filaments, other proteins, stored glycogen/fat, enzymes, and organelles (mitochondria and sarcoplasmic reticulum)

Question 20

What are the waves of the ECG?

Answer 20

P-wave is the depolarization of the atria. The QRS complex is the depolarization of the ventricles. The T wave is the repolarization of the ventricles. Atrial repolarization occurs as well but its wave is masked by ventricular depolarization.

Question 21

Type II Fibers?

Answer 21

Fast twitch fibers that are inefficient and fatigable. They have low capacity for aerobic power. They allow rapid force development, high myosin ATPase activity, and high anaerobic power.

Question 22

Force Development of a motor unit?

Answer 22

Activation of the sarcolemma results in release of calcium within the fiber and a contraction develops. Calcium is removed before force reaches the maximum though and the muscle relaxes. If a second twitch is elicited from the motor nerve before the fibers completely relax, force from the 2 twitches summates and the resulting force is greater than that produced by a single twitch. Decreasing the time between twitches results in greater summation of crossbridge binding and force. If the stimuli is developed at such a high frequency that the twitches merge and eventually completely fuse, causing tetanus (maximal force the motor unit can develop).

Question 23

Number of Bones In Body

Answer 23

206

Question 24

Muscles to help breathing?

Answer 24

The muscles that elevate the ribs can help with inspiration and the muscles that depress the ribs can help with expiration (abdominals).

Question 25

Phases for muscle contraction?

Answer 25

Resting - Little calcium is present in the myofibril so very few of the myosin crossbridges are bound to actin. Even with the actin binding site covered, myosin and actin still interact in a weak bond.
Excitation - Contraction Coupling- The sarcoplasmic reticulum is stimulated to release calcium ions, the calcium binds to troponin (a protein situated at regular intervals along the actin filament) and causes a shift 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 to the actin if ATP and calcium are present.
Contraction – Once myosin/actin bind, myosin ATPase breaks ATP down into ADP and phosphate which releases energy for the “power stroke” (pulling of actin).
Recharge – ATP binds to the myosin head and facilitates detachment from the actin and is ready for myosin ATPase the change the break down the ATP to release energy if calcium is still present to bind to the troponin
Relaxation – When the motor nerve is no longer stimulated and calcium is pumped back into the sarcoplasmic reticulum

Question 26

Number of vertebrae at each leve

Answer 26

Sacral - 5 (fused)

Coccygeal - 3-5

Question 27

Sarcoplasmic Reticulum?

Answer 27

This surrounds each myofibril and is an intricate system of tubules. It terminates as vesicles near the z-line and calcium is stored here. T-tubules run perpendicular to the sarcoplasmic reticulum between the vesicles of the sarcoplasmic reticulum. The t-tubule is contiguous with the sarcolemma so an action potential arrives nearly simultaneously at all depths of the muscle fiber and the sarcoplasmic reticulum releases calcium throughout to get a coordinated contraction.

Question 28

Heart valves?

Answer 28

The tricuspid valve (right side of heart) and mitral valve (left side of heart) (collectively called the atrioventricular valves) prevent blood from flowing back into the atrium during ventricular contraction (systole). The aortic valve and pulmonary valves (collectively the semilunar valves) prevent backflow from aorta/pulmonary arteries during ventricular relaxation (diastole).

Question 29

Muscle Spindles?

Answer 29

Proprioceptors that consist of several modified muscle fibers (intrafusal fibers) enclosed in a sheath of connective tissue and run parallel to extrafusal fibers. They provide information about muscle length and rate of length change. The deformation of the intrafusal fibers activates the sensory neuron of the spindle, which sends a signal to the spinal cord, where it synapses with motor neurons. These motor neurons can activate the same muscle. As load increases the muscle is stretched to a greater extent and results in greater activation of the muscle. Muscles that perform precise movements have many spindles per unit of mass to help ensure exact control of their contraction.

Question 30

Types of Joints

Answer 30

Fibrous - allows virtually no movement (skull)
Cartilagenous - Allow limited movement (growth plates, IVD)
Synovial Joints - Allow considerable movement (elbow, knee)

Question 31

Different layers of a muscle?

Answer 31

1. The epimysium covers muscles and is contiguous with the tendon
2. Muscle fibers are grouped into bundles known as fasciculi (has about 150 fibers)
3. Perimysium surrounds the fasciculi and is contiguous with the tendon
4. Endomysium surrounds the muscle fiber and is contiguous with the tendon
5. The sarcolemma is the muscle fiber’s outer membrane and is contiguous with the endomysium
6. Hundreds of myofibrils make up muscle cell and each one surrounded by sarcoplasmic reticulum

Question 32

Respiratory system passages?

Answer 32

The trachea divides into left/right bronchi, which then divide into bronchioles. These are defined as “generations”. The trachea is first generation, the bronchi is second generation. There are about 23 generations before the air finally reaches the alveoli.

Question 33

Parts of a sarcomere?

Answer 33

1. Z-line is the end of a sarcomere, so 1 sarcomere goes from z-line to z-line, and these are repeated across the entire myofibril. Also, the center of the I-band.
2. The H-zone is the center of the sarcomere where only myosin filaments exist
3. At the center of the h-zone (center of sarcomere) there are perpendicular bridges call M-bridges that connect adjacent myosin filaments
4. The A-band is the entire portion of the myosin filament (will probably encompass some of the actin as well)
5. The I-band encompasses 2 sarcomeres and contains the area of only actin filaments

Question 34

How can athletes improve force production?

Answer 34

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

Question 35

What dictates the amount of force produced by a muscle?

Answer 35

The number of myosin crossbridges bound to actin filaments cross-sectionally at a given time.

Question 36

Motor units firing?

Answer 36

When a motor unit fires an impulse, all of the fibers that it serves are simultaneously activated. Muscles with great precision have motor units with as few as one muscle fiber per motor neuron. Muscles like the quads with less precision may have several hundred fibers for one motor neuron. All of the fibers in the motor unit contract and develop force at the same time, not just some. Similarly, a stronger action potential cannot produce a stronger contraction.