The Muscular System Flashcards
Muscle cells
highly specialized to
convert chemical energy (ATP) into
kinetic energy.
Skeletal muscle
-Striated and tubular
-have many nuclei
-contract voluntarily
-are usually attached to the bones of the skeleton
SKELETAL MUSCLE FUNCTION
SUPPORT – contraction of muscles opposes force
of gravity.
MOVEMENT – allows for movement of bones
(arms and legs), eyes, face.
Maintain body TEMPERATURE – ATP breakdown
releases heat spread
PROTECTION – pads bones and cushions organs.
STABILIZE JOINTS – tendons help hold bones to
joints.
Smooth muscle
-Non-striated
-have one nucleus
-Contract involuntarily
-are found in the walls of internal organs
Cardiac muscle
-striated, tubular, branched
-have one nucleus
-Contract involuntarily
-are found in the walls of heart
What is the Order of Components in the skeletal muscles? (Largest to Smallest)
Muscle > Muscle Fiber Bundle > Muscle Fiber > Myofibril > Myofilaments
Muscles
An organ surrounded by connective tissue
and composed of several tissues. Largest unit;
attached to bone by tendons.
Muscle fibres
organized into larger bundles; up to
20 cm long. Connective tissue wraps fibers
Myofibrils
thousands of cylindrical subunits.
Myofilaments
protein structures responsible for
muscle contraction; two types.
Actin – thin filament
Myosin – thick filament
Sarcomere
-functional
-Composed of myofilaments.
MUSCLE FIBRE (MUSCLE CELL)
-Myoglobin
-Sarcolemma
-Sarcoplasm
-Sarcoplasmic reticulum
Myoglobin
-stores oxygen for muscle contractions.
Sarcolemma
membrane of muscle fibre;
entry and exit of materials.
Sarcoplasm
cytoplasm of muscle fibre;
site of metabolic processes; contains
myoglobin and glycogen.
Sarcoplasmic reticulum
smooth ER in
muscle fibre; stores calcium ions.
MYOFILAMENTS
Actin (thin)
composed of globular actin proteins and ion receptor proteins called troponin and tropomyosin.
MYOFILAMENTS
Myosin (thick)
composed of myosin proteins, two polypeptide chains wrapped around each other; ends have
globular heads.
MUSCLE CONTRACTION –
SLIDING FILAMENT MODEL
Major Steps:
1. Presence of calcium ions allow myosin
head to attach to actin
2. Myosin head flexes, pulling on the actin
filament
3. Myosin head releases and unflexes via
ATP
4. Myosin reattaches to actin further down
fibre
ROLW OF CALCIUM
Muscle relaxed – tropomyosin blocks
myosin binding sites along the actin
molecule.
Muscle contracted – calcium ions bind to
troponin on actin causing tropomyosin to
reposition and expose myosin binding sites.
Three mechanisms to make ATP
- Breakdown of creatine phosphate (no O2 required)
- Aerobic cellular respiration
- Fermentation (no O2 required)
CREATINE PHOSPHATE BREAKDOWN
A high-energy molecule built up during rest, CANNOT generate muscle contraction. Regenerates ATP by contributing a phosphate to sliding filaments.
AEROBIC CELLULAR RESPIRATION
Glucose or fatty acids converted to ATP. Provides majority of energy for muscles.
FERMENTATION TO LACTIC ACID
Accumulation of lactate in muscle fibre
makes sarcoplasm more acidic enzymes
stop functioning!
If fermentation continues longer than 2-3
minutes cramping, fatigue
Muscles can use glucose OR fatty acids to
make ATP; brain can only use glucose.
Atrophy
reduction of size, tone and power of muscle; often caused by disuse.
Hypertrophy
exercise-induced increase in muscle mass.
MYOGRAMS
force of a muscle contraction IN A SKELETAL MUSCLE with time. When a muscle is not allowed to relax completely between stimuli, the contraction gradually increases in intensity until it reaches a maximum (tetanus), which is sustained until the muscle fatigues
Two main muscle fibres:
Slow-twitch (Type I) – dark; contain
myoglobin and have many surrounding
capillaries.
Fast-twitch (Type II) – light; little or no
myoglobin and fewer blood vessels.
SLOW TWITCH FIBRES (long term)
Contract slowly, but resist fatigue.
Produce most ATP aerobically,
so tire only when fuel supply is gone.
FAST TWITCH FIBRES (short term)
-Produces most energy anerobiacally - putting them at risk of lactate accumulation.
-Adapted for rapid generation of
power, but fatigue quickly.
-Rich in glycogen; large number
of sarcomeres.
INTERMEDIATE FIBRES
Fast twitch but high oxidative capacity
(fatigues slowly).
Proportion can be increased by endurance
training and genetics.
FORCE & RESPONSE TIMES
Skeletal muscles have different proportions
of fast-twitch and slow-twitch fibres. Thus,
the force and response times of their
contractions differ.
