lesson 12 transcript+ study guide Flashcards
hydrostatic skeleton
A fluid-filled cavity under pressure, with muscles working against it for movement (e.g., earthworms).
exoskeleton
A rigid outer covering made of chitin that protects internal organs and limits growth (e.g., insects).
endoskeleton
An internal skeleton of bone/cartilage that forms a framework for muscle attachment and support.
osteocytes
Mature bone cells that maintain the bone matrix.
osteoblasts
Initiate bone development by secreting matrix.
osteoclasts
Break down and resorb bone tissue
Haversian system
Structural unit of compact bone with layers (lamellae) around central Haversian canals containing blood vessels, nerves, and lymphatics.
two types of bone development
Intramembranous (flat bones)
endochondral (long bones from cartilage models).
cartilage
made up of collagen and glycoprotein
it’s flexible, avascular, and heals slowly
How do skeletal muscles produce movement?
By pulling on bones at joints when they contract.
What are antagonistic muscle pairs
Pairs of muscles where one contracts to move a limb one way, and the other contracts to move it back (e.g., biceps and triceps).
sarcomere
The basic contractile unit of a muscle fiber, from one Z-line to the next.
sarcomere during contraction
Actin and myosin filaments slide past each other, shortening the sarcomere
What bands shorten during contraction
I band and H zone; A band remains the same length
What triggers myosin to attach to actin
ATP hydrolysis energizes the myosin head
What is a power stroke
When ADP and Pi are released, the myosin head pulls actin inward
How is the cross-bridge broke
A new ATP binds to myosin, causing it to release actin.
What causes rigor mortis
No ATP is made after death, so cross-bridges can’t detach, leading to muscle stiffness.
What blocks myosin from binding actin in a relaxed muscle
Tropomyosin
What role does troponin play in contraction
Binds Ca²⁺, causing tropomyosin to move and expose actin binding sites
Where is Ca²⁺ stored in muscle cell
Sarcoplasmic reticulum
What neurotransmitter is released at the neuromuscular junction
Acetylcholine (ACh
How does the signal for contraction travel into the cell?
Via T-tubules, which carry depolarization to the sarcoplasmic reticulum.
What is a motor unit
A motor neuron and all the muscle fibers it innervates
How does motor unit size relate to precision?
Small units = precise movements (e.g., fingers)
large units = powerful movements (e.g., legs).
What is a muscle twitch
A single contraction from one action potential
What is summation?
Stronger contractions when multiple stimuli occur before full relaxation.
What is incomplete tetanus
Sustained but wavering contraction from frequent stimulation
What is complete tetanus
A smooth, sustained contraction with no relaxation—maximum tension.
What are characteristics of fast-twitch fibers
Rapid contraction, anaerobic, low endurance, fewer mitochondria/myoglobin (appear white)
What are characteristics of slow-twitch fibers?
Slow contraction, aerobic, high endurance, rich in mitochondria/myoglobin (appear dark).
Can fiber types be modified?
Yes, by genetics, body region, and training
