Biology: Musculoskeletal

Question 1

Red fibers (skeletal muscle)

Answer 1

Slow-twitch fibers in skeletal muscles that contract slowly. Red.

Question 2

White fibers (skeletal muscle)

Answer 2

Fast-twitch fibers in skeletal muscles that contract rapidly (but fatigue quickly). Lighter than red.

Question 3

Sarcomere (skeletal muscle)

Answer 3

Thick filaments + thin filaments + 2 proteins (troponin, tropomyosin).

Question 4

Sarcomere: Z-M-I-H-A (skeletal muscle)

Answer 4

Z-lines: boundaries of each sarcomere (z @ ends)
M-line: runs down center of sarcomere (midline)
I-band: only thin filaments (I is a thin letter)
H-zone: only thick filaments (H is a thick letter)
A-band: contain thick filaments in their entirety, including overlap w/ thin filaments (A for all)

Question 5

Myocytes (skeletal muscle)

Answer 5

Muscle fiber/cells.

Myofibril –> myocytes –> muscle.

Question 6

Myofibril (skeletal muscle)

Answer 6

Arrangements of many sarcomeres in series. Surrounded by SR (a modified ER w/ high [Ca2+]).

Question 7

T-tubules (skeletal muscle)

Answer 7

Transverse tubules. Form a system that is used by sarcolemma to propagate and distribute AP to all sarcomeres in muscle.

Question 8

Skeletal muscle

Answer 8

Voluntary movement. Innervated by SNS. Appears striated. Multinucleated.

Question 9

Smooth muscle

Answer 9

Involuntary movement. Innervated by ANS. Not striated. Single nucleus.

Question 10

Myogenic activity (smooth and cardiac muscle)

Answer 10

Can contract w/o nervous system input.

Question 11

Cardiac muscle

Answer 11

Involuntary movement. Innervated by ANS. Appears striated.

Question 12

Intercalated discs (cardiac muscle)

Answer 12

Connect cardiac muscle cells. Contain gap junctions –> rapid coordinated muscle cell depolarization and efficient contraction.

Question 13

Muscle contraction (3 steps)

Answer 13

1. Initiation
2. Shortening of Sarcomere
3. Relaxation

Each of these has their own flashcard.

Question 14

Muscle contraction: Initiation

Answer 14

1. At NMJ’s motor end plate, signal causes ACh release into synapse.
2. ACh binds to sarcolemma receptors –> depolarization –> AP –> spreads down to T-tubules –> travels into muscle tissues to SR.
3. Ca2+ released, binds to regulatory subunit in troponin –> conformational change of tropomyosin to expose myosin-binding sites on actin thin filament.

Question 15

Muscle contraction: Shortening of sarcomere

Use this to explain rigor mortis!

Answer 15

Actin-myosin cross-bridge cycle / sliding filament model:

1. Resting stage: hydrolyzed ATP.
2. Myosin carrying hydrolyzed ATP binds to actin. Ca2+ binds to troponin.
3. Release of Pi and ADP in rapid succession gives energy for powerstroke. Sliding actin filament over myosin filament ~ sarcomere contracts.
4. New ATP binds to myosin, leading to myosin detachment from actin. ATP is hydrolyzed to Pi and ADP. Recock the myosin head to be in position to initiate another cycle.

Question 16

Muscle contraction: Relaxation

Answer 16

ACh-esterase degrades ACh in synapse –> terminate signal at NMJ.
Sarcolemma repolarizes. Stop Ca2+ release. SR takes up Ca2+ from sarcoplasm. ATP binds to myosin heads –> free from actin. Sarcomere return to OG width.

Question 17

Simple twitch stimulation

Answer 17

Response of single muscle fiber to brief stimulus @ or above threshold.
Latent –> contraction –> relaxation.

Question 18

Frequency summation

Answer 18

If muscle is exposed to frequent, prolonged stimulation, there’s insufficient time to relax. Contractions combine and become stronger and more prolonged.

Question 19

Muscle fatigue (what happens?)

Answer 19

Overwhelmed muscle fibers switch to anaerobic metabolism and produce lactic acid.

Question 20

Energy reserves in muscle (2)

Answer 20

1. Creatine phosphate

2. Myoglobin

Question 21

Bone

Answer 21

Connective tissue. Derived from embryonic mesoderm. Hard, but lightweight.

Question 22

Types of bone (3)

Answer 22

1. Compact (dense, strong)
2. Spongy/cancellous (lattice structure)
3. Long (diaphyses that swell at each end to form metaphyses and terminate in epiphyses)

Question 23

Tendons

Answer 23

Attach muscle to bone.

Question 24

Ligaments

Answer 24

Pieces of fibrous tissue that hold bones together at joints.

Question 25

Bone remodeling 1

Osteoblasts vs. Osteoclasts

Answer 25

OsteoBLASTS: build bone.
OsteoCLASTS: multinucletated resident macrophages; reabsorb bone.

Question 26

Bone remodeling 2

Parathyroid hormone

Answer 26

Promote bone resorption, therefore, affects osteoclasts. Results in increased calcium ion, decreased phosphate ion.

Question 27

Bone remodeling 3

Calcitonin

Answer 27

Promote bone formation, therefore, affects osteoblasts. Results in decreased calcium ion.

Question 28

Cartilage

Answer 28

Consists of firm elastic matrix (chondrin). Secreted by chondrocytes. Avascular. Not innervated.

Question 29

Flexor vs. Extensor Muscles

Answer 29

Flexor: decrease angle across a joint.
Extensor: increase or straighten angle across a joint.

Question 30

Abductor vs. Adductor Muscles

Answer 30

Abductor: moves part of body away from midline.
Adductor: moves part of body toward midline.

Question 31

Medial vs. Lateral Rotator Muscles

Answer 31

Medial: rotates of axis of limb toward midline.
Lateral: rotates axis of limb away from midline.

Question 32

Immovable vs. Movable Joints

Answer 32

Immovable: consist of bones that fuse together to form sutures (similar fibrous joints). Found in head to anchor bones of skull together.
Movable: hinge joints (elbow, knee), ball-&-socket joints (hip, shoulder).