Chapter 11 - Musculoskeletal System

Question 1

What are the three types of muscle?

Answer 1

Cardiac, skeletal, and smooth muscle

Question 2

Skeletal muscle is innervated by the ___________.

Answer 2

Somatic nervous system

Question 3

What is the function of the skeletal muscle?

Answer 3

Controls voluntary movement

Question 4

What is the function of smooth muscle?

Answer 4

Control involuntary movement

Question 5

Characteristics of skeletal muscle

Answer 5

Striated, multinucleated, contains actin and myosin in repeating units called sarcomeres, mature cells are suspended in G0 phase (don’t divide)

Question 6

What are the two types of fibers in skeletal muscle?

Answer 6

1. Red fibers/slow-twitch - high myoglobin and high iron, many mitochondria, use aerobic respiration
2. White fibers/fast-twitch - low myoglobin, low iron

Question 7

Characteristics of smooth muscle

Answer 7

Uninucleated, no striations, myogenic activity, actin and myosin not in organized units; control the gut, viscera, blood vessels

Question 8

Characteristics of cardiac muscle

Answer 8

1-2 nuclei per cell, striated, myogenic activity, innervated by autonomic NS, contains actin & myosin units in repeating units of sarcomeres, cardiac cells can undergo mitosis

Question 9

Nerves that innervate the heart are responsible for _______?

Answer 9

Regulating the rhythm of the heart. The parasympathetic (vagus) nerve lowers HR while the sympathetic nerves increase HR.

Question 10

Cardiac muscle cells are connected via _________. What is the purpose of this?

Answer 10

Intercalated discs, these discs house gap junctions which allow ions to flow directly from one cell to another for a rapid action potential.

Question 11

What is the basic contractile unit of skeletal muscle?

Answer 11

A sarcomere

Question 12

What makes up a sarcomere?

Answer 12

Thick myosin filaments and thin actin filaments that are connected to the proteins: troponin and tropomyosin

Question 13

Troponin and tropomyosin attach to what part of the sarcomere?

Answer 13

To the thin filaments (actin)

Question 14

Myosin is (always/sometimes) bound to actin unless the actin binding sites are blocked by tropomyosin.

Answer 14

always, myosin has a high affinity for actin such that it will always be bound unless blocked by tropomyosin

Question 15

Multiple sarcomeres form a _________.

Answer 15

Myofibril

Question 16

What is the outline of the gross structure of muscle cells starting from sarcomere?

Answer 16

Sarcomere —> myofibril —> muscle fiber —> fascicle —> skeletal muscle

Question 17

What are the Z lines in a sarcomere?

Answer 17

They are zigzag lines at the end of both sides within each sarcomere unit, which define the boundaries of an individual sarcomere. Think “Z” is the end of the alphabet, just like the end of the sarcomere.
They shorten with contraction.

Question 18

What is the A band?

Answer 18

It includes the total length of the myosin filaments as well as part of the actin filaments that overlap. Think “A” band as in it contains ALL of the myosin filament.
The distance STAYS the same with contraction.

Question 19

What is the H zone?

Answer 19

Includes only a portion of myosin thick filaments. Think “H” is a thick letter, so it only contains the thick filament and NONE of the actin filaments.
H zone distance decreases with contraction.

Question 20

What are the I bands?

Answer 20

They are the portion of the sarcomere which contain only thin actin filaments. Think of “I” as a thin letter which contains only thin filaments.
These also shorten with contraction.

Question 21

What is the M line?

Answer 21

It is a line that runs down the middle of the sarcomere, that is the middle of the myosin filaments.
The distance between M lines in 2 sarcomeres decreases during contraction.

Question 22

During contraction what part of the sarcomere stays the same?

Answer 22

A band

Question 23

How does an action potential travel in a sarcomere?

Answer 23

The sarcolemma, cell membrane of a muscle fiber, is capable of propagating an action potential and distributing that action potential to all the sarcomeres in the myofibril though the T tubules which are perpendicular to the myofibril itself.

Question 24

True or false:
Without calcium, muscle contraction wouldn’t occur.

Answer 24

True, calcium is necessary to bind to troponins which allows for bound tropomyosins configuration to change. This exposes actin binding sites to which myosin binds to.

Question 25

Just like action potential, muscle fibers contain an _________.

Answer 25

all of nothing response, meaning they either contract or they don’t

Question 26

How can you obtain a stronger muscle force?

Answer 26

Your nerve cells will recruit more muscle fibers to contract.

Question 27

A simple twitch (response of a single muscle fiber) can be divided into 3 phases:

Answer 27

Latent period - AP spreads to muscle and calcium gets released from the sarcoplasmic reticulum Contraction period - calcium binds to troponin, allowing myosin to bind to actin, muscle contracts Relaxation period - calcium unbinds stopping contraction from occurring

Question 28

What is the function of osteoclasts?

Answer 28

They break down bone tissue

Question 29

Would the hormone calcitonin released by the thyroid support or inhibit the proliferation of osteoclasts?

Answer 29

Calcitonin would inhibit the proliferation of osteoclasts. Calcitonin acts to decrease blood calcium levels, therefore less osteoclasts would mean less bone breakdown, and less calcium released from the bone.

Question 30

What constitutes a motor unit?

Answer 30

The nerve axon terminal and the myocytes (muscle fibers) it innervates.

Question 31

What is the role of the sarcoplasmic reticulum?

Answer 31

To release calcium.

Question 32

When calcium is released by the sarcoplasmic reticulum, it binds to (troponin/tropomyosin) which triggers a change in the conformation of (troponin/tropomyosin).

Answer 32

Troponin, tropomyosin

Question 33

Troponin and tropomyosin are both bound to (myosin filaments/actin filaments).

Answer 33

Actin filaments

Question 34

Explain the cross bridge cycle (myosin binding to actin) in steps.

Answer 34

1. Calcium binds to troponin, inducing conformational change and exposing actin filaments. 2. Myosin which has ADP+Pi attached to it, binds to the exposed actin site. 3. ADP+Pi are released from myosin, causing the power stroke to occur. 4. A new ATP binds to myosin, causing myosin to be released from actin. 5. Finally the attached ATP is hydrolyzed to ADP which allows the myosin head to cock back into a straight position.

Question 35

What is summation in terms of muscle contraction?

Answer 35

This is when the muscle fibers are exposed to frequent stimulation by the nerve axons, so it doesn’t give the muscle time to relax. Contractions therefore end up combining to become longer without a relaxation period.

Question 36

Tetanus occurs when ….?

Answer 36

Muscle contraction is so frequent that the muscle can’t relax at all and it just looks like one big slope on a graph.

Question 37

How does an action potential travel from a neuron to a muscle cell and reach the sarcoplasmic reticulum so calcium can be released?

Answer 37

AP travels across the axon of a neuron —> post-synaptic potential across at the muscle cell which causes Na channels to fire across the muscle cell membrane —> those AP reach a long indent in the membrane called a T tubule —> t tubule contains protein complexes which bridge with the sarcoplasmic reticulum —> cause Calcium ions to release

Question 38

What types of muscles contain gap junctions?

Answer 38

Smooth and cardiac muscles

Question 39

What is creatine phosphate?

Answer 39

A substance that is used by the body to make ATP from during strenuous exercise after all the ATP stores have been depleted in the muscle. It starts to be used about 10sec into a strenuous exercise.

Question 40

After the first 60secs of strenuous exercise, how does the body supply muscles with ATP?

Answer 40

It utilizes glycolysis by breaking down glycogen stores to glucose, which is oxidized to generate ATP.

Question 41

Glycolysis is more likely to be used by which type of muscle fiber?

Answer 41

Fast-twitch (white) muscle fibers because they have very few mitochondria so they utilize ways to make ATP outside mitochondrial use.

Question 42

A side effect of anaerobic metabolism is …?

Answer 42

Lactic acid

Question 43

Aerobic cellular respiration is likely to be used during a (sprint/2 mile jog).

Answer 43

2 mile jog

Question 44

The human skeletal system is divided into two parts, what are they?

Answer 44

Axial - Skull, vertebral column, ribcage, and hyoid bone (in the neck used for swallowing) Appendicular - bones of the limbs, humerus, radius, ulna, carpals, etc, pelvic bones, and scapula, and clavicle

Question 45

What is the function of tendons?

Answer 45

They attach muscle to bone

Question 46

What is the function of ligaments?

Answer 46

They attach bone to bone.

Question 47

Shivering is a (voluntary/involuntary) response controlled by what region of the brain?

Answer 47

Involuntary, hypothalamus

Question 48

What happens physiologically while shivering?

Answer 48

Core muscle groups under the skin undergo rapid contractions which generate heat.

Question 49

Spongy bone contains (red or yellow bone marrow) in its interwoven pocket like spaces.

Answer 49

Red bone marrow

Question 50

The site of blood cell production occurs in the red or yellow bone marrow?

Answer 50

Red bone marrow

Question 51

What kind of tissue is the bone made of?

Answer 51

Connective tissue derived from embryonic mesoderm.

Question 52

Spongy bone characteristics

Answer 52

Lattice structure, cavities inside are filled with either yellow or red bone marrow, located at bulbous ends of long bones, makes up more internal parts of flat & irregular bones

Question 53

Compact bone characteristics

Answer 53

Dense and strong, no pore like appearance, it surrounds the outside of all bones, and makes up the shaft of long bones

Question 54

Anatomy of a long bone: three parts

Answer 54

Epiphysis - bulbous ends Metaphysis - connecting part to the middle Diaphysis - long cylindrical middle part shaft

Question 55

What is the epiphyseal plate made of?

Answer 55

Cartilaginous structure filled with mitotic cells that contribute to growth

Question 56

What is the function of ligaments?

Answer 56

To attach bone to bone

Question 57

What happens to muscle contraction if there is no calcium present?

Answer 57

Muscle contraction cannot occur if there is no calcium release.

Question 58

What happens to muscle contraction if there is no ATP present?

Answer 58

A condition called rigor mortis which causes the muscles to be stuck in a contracted position because the myosin heads cannot detach from actin since there is no ATP binding after the power stroke.

Question 59

To perform a delicate movement, recruitment of (few/many) motor units is necessary.

Answer 59

Few

Question 60

To perform a gross movement, recruitment of (few/many) motor units is necessary.

Answer 60

Many

Question 61

What is the role of ATP in muscle contraction?

Answer 61

1. It binds to myosin, to allow the release of the myosin head from the actin filament. 2. It must be hydrolyzed after binding to myosin, so myosin can go back to a straight position.

Question 62

What is myoglobin?

Answer 62

An iron and oxygen binding protein that contains only 1 subunit, capable of holding 1 O2 molecule

Question 63

Where is myoglobin found and what is the purpose of it?

Answer 63

It is found in cardiac muscle and skeletal muscle cells; the purpose of it is when muscles use up available oxygen, there is an additional mechanism of obtaining oxygen to keep aerobic respiration going for as long as possible

Question 64

What are osteocytes?

Answer 64

They are mature bone cells derived from osteoblast which are surrounded by a mineral matrix.

Question 65

Components of bone matrix

Answer 65

Organic - collagen, glycoproteins Inorganic - calcium, phosphate, hydroxide ions which together form a compound hydroxyapatite

Question 66

Structure of bony matrix

Answer 66

Circles called lamellae that surround a longitudinal channel called a Haversian canal (contain blood vessels and nerve fibers)

Question 67

Where are osteocytes located in the bone?

Answer 67

Between lamellar rings in small spaces called lacunae. Lacunae are connected through tiny channels called canaliculi which allow for exchange nutrients & wastes.

Question 68

What are the 4 classification of bones?

Answer 68

Long bones – femur, humerus Short bones – tarsals, carpals Flat bones – skull, sternum Irregular bones – hip, vertebrae

Question 69

What kind of tissue is cartilage composed of? Describe the characteristics of cartilage.

Answer 69

It’s composed of connective tissue mostly collagen. It is very elastic, found in the nose, ears, and vertebrae, and is avascular (no innervation of blood vessels).

Question 70

What are the two types of joints?

Answer 70

Movable and immovable

Question 71

Example of an immovable joint

Answer 71

Bones that are fused together to form sutures; joints in the skull

Question 72

Example of a movable joints

Answer 72

Hinge joints like elbow and knee, ball-and-socket joints like shoulder and hip (these contain a synovial capsule w/ synovial fluid in them

Question 73

Example of an antagonistic pair of muscles in the body

Answer 73

Biceps and triceps in the upperarm

Question 74

Which two hormones increase the resorption of bone (bone breakdown)?

Answer 74

Parathyroid hormone, and vitamin D

Question 75

AAMC FL SB #16: Which event is directly mediated by a ligand-gated ion channel? Answer is C A. Release of Ca2+ from the sarcoplasmic reticulum of a muscle fiber to initiate muscle contraction B. Influx of Na+ across the axon membrane of a somatic neuron during action potential propagation C. Influx of Na+ across the motor end plate resulting in the depolarization of the muscle fiber membrane D. Re-entry of Ca2+ back into the sarcoplasmic reticulum of a muscle fiber to end muscle contraction

Answer 75

A. Ca2+ from the sarcoplasmic reticulum is released by voltage gated Ca2+ channels on its membrane. B. Somatic neurons are those which control skeletal muscles. Key word is axon membrane which only has voltage gated Na channels. Influx of Na++ through voltage-gated Na channels allows the AP to propagate down the axon. C. This situation refers to the synapse between a neuron & muscle cell. What causes the influx of Na across the motor end plate is the binding of acetylcholine released from the presynaptic neuron to the ligand gated Na channel on the post-synaptic muscle cell, allow Na to rush in. D. Re-entry of Ca back into sarcolemma is NOT due to a ligand binding. It is due to a Ca2+ ATPase pump (primary active transport).