Biology: Musculoskeletal Flashcards
Red fibers (skeletal muscle)
Slow-twitch fibers in skeletal muscles that contract slowly. Red.
White fibers (skeletal muscle)
Fast-twitch fibers in skeletal muscles that contract rapidly (but fatigue quickly). Lighter than red.
Sarcomere (skeletal muscle)
Thick filaments + thin filaments + 2 proteins (troponin, tropomyosin).
Sarcomere: Z-M-I-H-A (skeletal muscle)
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)
Myocytes (skeletal muscle)
Muscle fiber/cells.
Myofibril –> myocytes –> muscle.
Myofibril (skeletal muscle)
Arrangements of many sarcomeres in series. Surrounded by SR (a modified ER w/ high [Ca2+]).
T-tubules (skeletal muscle)
Transverse tubules. Form a system that is used by sarcolemma to propagate and distribute AP to all sarcomeres in muscle.
Skeletal muscle
Voluntary movement. Innervated by SNS. Appears striated. Multinucleated.
Smooth muscle
Involuntary movement. Innervated by ANS. Not striated. Single nucleus.
Myogenic activity (smooth and cardiac muscle)
Can contract w/o nervous system input.
Cardiac muscle
Involuntary movement. Innervated by ANS. Appears striated.
Intercalated discs (cardiac muscle)
Connect cardiac muscle cells. Contain gap junctions –> rapid coordinated muscle cell depolarization and efficient contraction.
Muscle contraction (3 steps)
- Initiation
- Shortening of Sarcomere
- Relaxation
Each of these has their own flashcard.
Muscle contraction: Initiation
- At NMJ’s motor end plate, signal causes ACh release into synapse.
- ACh binds to sarcolemma receptors –> depolarization –> AP –> spreads down to T-tubules –> travels into muscle tissues to SR.
- Ca2+ released, binds to regulatory subunit in troponin –> conformational change of tropomyosin to expose myosin-binding sites on actin thin filament.
Muscle contraction: Shortening of sarcomere
Use this to explain rigor mortis!
Actin-myosin cross-bridge cycle / sliding filament model:
- Resting stage: hydrolyzed ATP.
- Myosin carrying hydrolyzed ATP binds to actin. Ca2+ binds to troponin.
- Release of Pi and ADP in rapid succession gives energy for powerstroke. Sliding actin filament over myosin filament ~ sarcomere contracts.
- 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.
Muscle contraction: Relaxation
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.
Simple twitch stimulation
Response of single muscle fiber to brief stimulus @ or above threshold.
Latent –> contraction –> relaxation.
Frequency summation
If muscle is exposed to frequent, prolonged stimulation, there’s insufficient time to relax. Contractions combine and become stronger and more prolonged.
Muscle fatigue (what happens?)
Overwhelmed muscle fibers switch to anaerobic metabolism and produce lactic acid.
Energy reserves in muscle (2)
- Creatine phosphate
2. Myoglobin
Bone
Connective tissue. Derived from embryonic mesoderm. Hard, but lightweight.
Types of bone (3)
- Compact (dense, strong)
- Spongy/cancellous (lattice structure)
- Long (diaphyses that swell at each end to form metaphyses and terminate in epiphyses)
Tendons
Attach muscle to bone.
Ligaments
Pieces of fibrous tissue that hold bones together at joints.
Bone remodeling 1
Osteoblasts vs. Osteoclasts
OsteoBLASTS: build bone.
OsteoCLASTS: multinucletated resident macrophages; reabsorb bone.
Bone remodeling 2
Parathyroid hormone
Promote bone resorption, therefore, affects osteoclasts. Results in increased calcium ion, decreased phosphate ion.
Bone remodeling 3
Calcitonin
Promote bone formation, therefore, affects osteoblasts. Results in decreased calcium ion.
Cartilage
Consists of firm elastic matrix (chondrin). Secreted by chondrocytes. Avascular. Not innervated.
Flexor vs. Extensor Muscles
Flexor: decrease angle across a joint.
Extensor: increase or straighten angle across a joint.
Abductor vs. Adductor Muscles
Abductor: moves part of body away from midline.
Adductor: moves part of body toward midline.
Medial vs. Lateral Rotator Muscles
Medial: rotates of axis of limb toward midline.
Lateral: rotates axis of limb away from midline.
Immovable vs. Movable Joints
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).
