Chapter 12 - Muscular and Skeletal Systems

Question 1

What does the musculoskeletal system form?

Answer 1

It forms the basic internal framework for the vertebrate body

Question 2

What produces voluntary movement?

Answer 2

Muscles and bones work in close coordination to produce voluntary movement

Question 3

Describe the skeletal system:

• What serves as the framework?
• What are muscles attached to? What do they do?
• What parts protect certain areas of the body?
• What are the two components of this system?

Answer 3

• Endoskeleton serves as framework within vertebrate organisms
• Muscles are attaches to bones which permit movement
• Ribcage protects thoracic organs and skull/vertebral column protect brain/spinal cord
• Two major components are 1) cartilage and 2) bone

Question 4

What is cartilage? Where is it found?

Answer 4

It is a type of connective tissue that is softer and more flexible than bone

• Retained in adults in places where firmness and flexibility is needed
• Ex. Ear, nose, joints, etc.

Question 5

What is bone? What does it do?

Answer 5

Specialized type of mineralized connective tissue that has ability to withstand physical stress
- Body support

Question 6

What two types of bone is there?

Answer 6

1) Compact: Dense bone that does not appear to have cavities when observed with the naked eye
- Bony matrix is deposited in osteons, each consisting of a Haversian canal that is surrounded by concentric circles (lamellae)

2) Spongy: Less dense and consists of interconnecting lattice of bony spicules (trabeculae)
- Cavities are filled with yellow or red bone marrow
- Yellow - inactive and infiltrated by adipose tissue
- Red - blood cell formation

Question 7

What are osteocytes?

Answer 7

Two different types of bone tissues

1) Osteoblasts: Synthesize and secrete constituents of bone matrix; once surrounded by matrix they mature into osteocytes
2) Osteoclasts: Large, multi-nucleated cells involved in bone reabsorption; bone is broken-down and minerals released into the blood

Question 8

How does bone formation occur?

Answer 8

Occurs by:

1) Endochondral ossificaition: Existing cartilage is replace by bone; long bone formation
2) Intramembranous ossification: Mesenchymal (embryonic or undifferentiated) connective tissue is transformed into and replaced by bone

Question 9

How is the axial skeleton organized, and what is its point of attachment?

Answer 9

The axial skeleton is the basic framework of the body that consists of the body, skull, vertebral column, and rib cage
- Point of attachment for the appendicular skeleton which consists of the bones of the appendages (limbs), and pectoral and pelvic girdles

Question 10

How are bones held together?

Answer 10

1) Sutures or immovable joints hold the skull together
2) Movable joints hold together relative bones and are additionally supported/strengthened by ligaments (bone-bone connectors)
3) Tendons attach skeletal muscle to bones and bend the skeleton at movable joints

Question 11

Describe the point of attachment (muscle-bone):

Answer 11

Point of attachment of a muscle to a stationary bone (proximal) is the origin; point of attachment of muscle to bone (distal) that moves is the insertion

Question 12

Describe flexion vs. extension

Answer 12

Flexion refers to bending of a joint and extension indicates straightening of a joint

Question 13

What does the muscular system consist of?

Answer 13

Muscle tissue consists of bundles of specialized contractile fibers held together by connective tissues

Question 14

What are the three morphology and functionally distinct types of muscles in mammals?

Answer 14

1) Skeletal
2) Smooth
3) Cardiac

Question 15

How is the muscle system controlled?

Answer 15

By nervous control which involves the axons of the pyramidal cells of the motor cortex, these descend from the brain to synapse on lower motor neurons in the brain stem and spinal cord

Question 16

What occurs because there are no intervening synapses?

Answer 16

Pyramidal system is able to provide rapid commands to the skeletal muscles and various other organs

• The extrapyramidal system can issue somatic motor commands as a result of processing performed at the unconscious, involuntary level
• Red nucleus in this system located in the mesencephalon controls the skeletal muscle tone

Question 17

Describe skeletal muscle:

• What is it responsible for?
• What is a fiber?
• What are myofibrils and sarcomeres?
• What is the sarcoplasmic reticulum?
• What is the sarcolemma?
• What does the T-system do?
• What is abundant in muscle cells? Why?
• What is striated muscle?

Answer 17

• Responsible for voluntary movements and innervated by somatic nervous system
• Each fiber is multinucleate cell created by the fusion of several mononucleated embryonic cells
• Embedded in fibers are filaments (myofibrils) which are further divided into contractile units (sarcomeres)
• Myofibrils enveloped by modified endoplasmic reticulum storing Ca-ions is called the sarcoplasmic reticulum
• The cytoplasm of a muscle fiber is the sarcoplasm and the cell membrane is the sarcolemma which is capable of propagating an AP
• The sarcolemma is connected to the transverse tubules (T-system) which is organized perpendicular to the myofibrils; it provides channels for ion flow throughout muscle fibers and can propagate AP
• Mitochondria are abundant in muscles cells due to high energy requirements for contraction
• Skeletal muscle has striations of light and dark bands (striated muscle)

Question 18

What is a sarcomere composed of?

Answer 18

Composed of:

• Thin filament = chains of actin
• Thick filament = bundles of myosin

Question 19

How is a sarcomere organized?

Answer 19

1) Z-lines = define boundaries of a single sarcomere and anchor thin
2) M-line = runs down centre of sarcomere
3) I-band = region containing thin filaments only
4) H-zone = region containing thick filaments only
5) A band = spans entire length of thick filaments, and any overlapping thin filaments

Question 20

What happens in the sarcomere when muscles contract?

Answer 20

Z lines move toward each other

• A-band does NOT reduce in size
• H-zone does reduce in size
• I-band does reduce in size

Question 21

What is muscle contraction stimulated by?

Answer 21

Message from somatic nervous system sent via a motor neuron

Question 22

What is the neuromuscular junction?

Answer 22

The link between the nerve terminal and sarcolemma of the muscle fiber

Question 23

What causes the release of neurotransmitters ?

Answer 23

Depolarization of the motor neuron

Question 24

What happens to the neurotransmitter once it is released?

Answer 24

It crosses the synaptic cleft and binds to special receptor on the sarcolemma

Question 25

How is an AP generated?

Answer 25

IF enough of the receptors are stimulated then the the permeability of the sarcolemma is altered and an AP is generated

Question 26

What occurs after the AP?

Answer 26

The AP is conducted only the sarcolemma and the T system into the interior of the muscle iffier which causes the sarcoplasmic reticulum to released Ca-ions into the sarcoplasm

• Ca-ions initiate contraction of sarcomere by binding to troponin C on the actin filaments
• Allosteric changes allow myosin heads to bind to these sites on actin
• Use of energy allows power stroke to occur = z-bands pull closer together and actin/myosin slide past one another = sarcomere contracts

Question 27

What occurs after death to the muscle cells? How/Why?

Answer 27

Several hours after death, muscle of the body become rigid and contract even without AP (rigor mortis)
- Causes by absence of ATP required for myosin heads to be released and therefore muscles remain rigid 12-24h after death until muscle proteins degrade

Question 28

Describe the 5 types of muscle contraction:

Answer 28

1) Isotonic: Contraction occurs when muscle shortens against a fixed load while tension on the muscle remains constant
2) Dynamic: Includes both concentric and eccentric types of contractions - Results in change in length of the muscle with a corresponding change in tension on the muscle
3) Concentric: Type of dynamic contraction; muscle fibers shorten and tension on the muscles increases
4) Eccentric: Type of dynamic contraction; muscle fiber lengthens and the tension on the muscle increases
5) Isometric: Contraction occurs when both ends of the muscle are fixed and no change in length occurs during contraction BUT the tension increases

Question 29

What stimulus do muscles exhibit?

Answer 29

All-or-none response

- Only a stimulus above a minimal value (threshold value) can elicit a contraction

Question 30

Can the strength of a single muscle fiber be increased?

Answer 30

No, regardless of a stimulus

- However, strength of an entire muscle can be increased by recruiting more muscle fibers

Question 31

What are the different types of muscle responses?

Answer 31

1) Simple Twitch: Response of single muscle fiber to a brief stimulus at or above the threshold stimulus and consists of a latent period, a contraction period, and a relaxation period
- Latent = time between stimulation and onset of contraction; during this time lag the AP spreads along the sarcolemma and Ca-ions are released
- Relaxation = muscle is unresponsive to a stimulus (absolute refractory period)

2) Temporal Summation: When fibers are exposed to frequent stimuli, the muscle cannot fully relax; the contractions begin to combine becoming stronger and prolonged
- They become continuous when the stimuli are so frequent that the muscle cannot relax (tetanus) which is stronger than a simple twitch of a single fiber - if maintain, the muscle will fatigue and the contraction will weaken

3) Tonus: State of partial contraction
- Muscles are never completely relaxed and maintain a partially contracted state at all times

Question 32

What occurs during strenuous activity?

• Enables?
• Produces?
• Allows?

Answer 32

Skeletal muscles convert glucose to pyruvic acid through glycolysis

• Enables muscles to contract in the absence of oxygen
• Produces lactic acid which reacts with enzyme lactate dehydrogenase
• Allows pyruvate to enter Krebs (Citric) Cycle

Question 33

What is the purpose of the Cori Cycle?

• Once in the blood?
• What is necessary for ATP creation during strenuous exercise that does not involve the Cori Cycle? What does this increase?

Answer 33

Convert lactic acid in the liver to glucose for discharge into the bloodstream

• Once in the blood, muscles are able to use glucose as immediate source of energy or to rebuild glycogen reserves
• Conversion of glucose into pyruvate in the muscle cells; increases lactic acid

Question 34

What is smooth muscle responsible for?

• Innervated by?
• Where is it located?
• Structure?
• Lacks?

Answer 34

Involuntary actions

• Autonomic nervous system
• Digestive tract, bladder, uterus, and blood vessel walls
• One centrally located nucleus
• Lacks striations of skeletal muscle

Question 35

What is cardiac muscle composed of?

- Structure?

Answer 35

Composed of cardiac muscle fibers
- Characteristics of both skeletal and smooth muscle fiber; actin and myosin are arranged in sarcomeres, giving striated appearance; one or two centrally located nuclei

Question 36

What us the primary source of energy for muscle contraction?

- Stored?

Answer 36

ATP

• Very little stored in muscles
• Other forms muscle be stored and rapidly converted

Question 37

What types of energy storage is there other than ATP?

Answer 37

1) Creatine phosphate: Temporarily in vertebrates (high energy compound)
2) Myoglobin: A hemoglobin-like protein in muscle tissue that has high oxygen affinity and maintains oxygen supply in muscles by tightly binding to oxygen