Chapter 17 Flashcards
What are the general functions of skeletal muscle?
- movement
- heat production
- posture
What functional characteristics are unique to skeletal muscles?
- excitability
- contractility
- extensibility
What are the unique characteristics of muscle cells?
- sarcolemma
- sarcoplasm
- sarcoplasmic reticulum
- multinucleated
- many mitochondria
- t-tubules
- myofibrils
What is a t-tubule? Function?
- an inward extension of the sarcolemma
- conduct impulses from the surface of the sarcolemma
What is a triad? Purpose?
- the sarcoplasmic reticulum butting up on either side of the t tubule
- allows the electrical impulse traveling along at tubule to stimulate the membranes of adjacent sacs of sarcoplasmic reticulum
What is a sarcomere?
- segment of myofibril
- one group of contractile units
What are the different portions of a sarcomere?
- z discs
- a band
- i band
- h zone
- m line
What portions of a sarcomere change during contraction?
- h zone
- i band
What kinds of proteins make up a myofibril? Function? Where are they found?
- Contractile: myosin and actin
- Regulatory: tropomyosin and troponin
- Structural: titin and dystrophin
What is the general mechanism of contraction?
-myosin heads attach to and walk along the thin filaments at both ends of the sarcomere
How is contraction initiated?
- nerve impulses reach the end of a motor neuron
- ach stimulates receptors
- Ca+ is released and binds to troponin
- troponin causes tropomyosin to shift
What is the contraction cycle?
- ATP hydrolysis
- Formation of cross-bridges
- Power stroke
- Detachment of myosin from actin
What are the steps to relaxation?
- sarcoplasmic reticulum begins pumping Ca+ into sacs
- tropomyosin moves back into place
How does the muscle generate ATP while contracting?
- creatine phosphate
- anaerobic cellular respiration
- aerobic cellular respiration
What is muscle fatigue?
-inability of a muscle to maintain force of contraction after prolonged activity
What factors contribute to muscle fatigue?
- inadequate release of calcium ions
- insufficient amounts of ATP: depletion of creatine phosphate, oxygen, glycogen, and buildup of lactic acid and ADP
- failure of the motor neuron to release enough ACH
Why does heavy breathing occur after exercise?
- it restores muscle cells to their resting level
- convert lactic acid into glycogen
- used to synthesize creatine phosphate and ATP
What is the graded strength potential?
-strength of a muscle depends on certain variables
What is strength dependent on?
- nutrient and oxygen availability
- the size of the motor unit
- the rate at which nerve impulses arrive
- the amount of stretch before contraction
- amount of load imposed on a mucle
What is a motor unit?
-a motor neuron and the muscle fibers it stimulates
How does the motor unit affect precise movements?
-the fewer the number of fibers supplied by a motor neuron, the more precise movements
How does the motor unit affect strength?
-the larger the motor unit, the more powerful the force
What is a twitch contraction?
-the brief contraction of the muscle fibers in a motor unit in response to an action potential
What are the phases of a twitch contraction? What is occurring during each phase?
- latent: delay between stimulus and contraction
- contraction
- relaxation
What is treppe?
-the gradual, steplike increase in the strength of contraction that is observed in a series of twitch contractions
How and why does treppe affect strength?
- muscle contracts more forcefully after it has contracted a few times
- Ca+ diffused easier, more actin-myosin reactions, and more calcium available because it has not been reabsorbed yet
What is tetanus?
-smooth, sustained contractions
What is the difference between incomplete and complete tetanus?
- incomplete is hilly
- complete is constant
How does sarcomere length affect strength and tension?
-if the sarcomeres are too short or too long then they will not be strong
How does load affect strength and tension?
-an increased load threatens to stretch the muscle beyond the setpoint
What happens if you pass the maximum sustainable level of load on a muscle?
-golgi tendon organs take over and force the muscle to relax
What is muscle tone? Why is it important?
- tonic contraction
- a continual, partial contraction of a muscle organ
- important for posture and keeping muscles firm
What types of contractions are there?
- isotonic: same tension
- isometric: same length
What types of skeletal muscle fibers are there?
- red
- white
Which skeletal muscle fibers are red? White? Larger? Smaller?
- red: more mitochondria and supplied by more blood capillaries; small; slow oxidative fibers
- white: low myoglobin; large; fast glycolytic fibers
What type of ATP producing reaction do muscle fibers use?
-cellular respiration
Which muscle fibers fatigue quickly? Slowly?
- quickly: white
- slowly: red
Which muscle fibers are used for long periods of time? Short bursts of energy?
- long: red
- short: white
Which types of muscle fibers are determined genetically?
-the ratio of fast glycolytic to slow oxidative
What is the anatomy of cardiac muscle?
- contains myofibrils/sarcomeres
- muscle cells branch
- muscle cells have intercalated disks
- many mitochondria
What is unique about cardiac muscle?
- self exciting
- produces rhythmic contractions on its own
What is the anatomy of smooth muscle?
- involuntary
- action potentials are spread through the muscle fibers via gap junctions
- fibers are stimulated by neurotransmitters, hormones, or autorhythmic signals
What is unique to smooth muscle? Location?
- thick and thin filaments are not arranged in orderly sarcomeres
- single unit and multi-unit
- vessels, hollow organs, airways, hair follicles, pupil, lens of eye
