muscle flashcards.txt

• 1. body movement
• ie walking, running
• 2. stabilizing body position
• ie posture
• 3. moving substances within body
• ie heart pumping blood, moving substances in GI tract, soleus
• 4. generating HEAT
• ie contracting muscle, shivering

• 1. excitability - ability to respond to stimuli (ie action potential)
• 2. contractility - contract when stimulated (by action potential)
• 3. extensibility - ability to STRETCH without damage
• 4. elasticity - ability to return to ORIGINal length

cells that have capacity to regenerate damaged muscle fibers

set before birth and most last a lifetime

tunnels in from plastma membrane, where action potential travels through

• cytoplasm of muscle fiber
• includes GLYCOGEN (used for ATP synthesis) and MYOGLOBIN (red colored protein w/oxygen bound - releases oxygen for ATP production)

Basic functional unit of a myofibril

• 1. Contractile
• 2. Regulatory
• 3. Structural

• actin: thin filament
• myosin: thick filament

• troponin: moves tropomyosin away from myosin-binding sites
• tropomyosin: blocking myosin-binding site, therefore blocks contraction

Titin: stabilizes position of myosin, accounts for much of the ELASTICITY and EXTENSIBILITY of myofibrils

• 1. ATP hydrolysis: reorients and energizes the myosin head
• 2. Formation of cross-bridges: myosin head attaches to myosin-binding site on actin
• 3. Power stroke: during the power stroke the crossbridge rotates, sliding the filaments
• 4. Detachment of myosin from actin: as the next ATP binds to the myosin-head, the myosin head detaches from actin

• ATP needed to power contraction cycle and to pump Ca++ into SR
• ATP inside muscle fibers will power contraction for only a FEW SECONDS
• ATP must be produced by muscle fiber after reserves used up
• 3 ways to produce ATP: creatine phosphate, anaerobic respiration and aerobic respiration

• 1st way of getting energy
• -creatine phosphate transfers its phosphate group to ADP to regenerate new ATP
• -excess ATP is used to synthesize creatine phosphate
• -Provides enough energy for about 15 SECONDS

• -Do not require Oxygen, instead GLUCOSE is used to generate ATP once creatine phosphate is depleted
• -glucose comes from the blood and from the glycogen stored in muscle fibers
• -Glycolysis breaks down glucose into molecules of pyruvic acid and 2 ATP�if oxygen present, pyruvic acid enters aerobic respiration and produces a lot of ATP
• -if oxygen is LOW, pyruvic acid is converted to lactic acid, which is carried away by the blood (occurs as a 'burn,' or fatigue during a workout)

• if activity lasts longer than 30-40 seconds, need aerobic respiration
• -pyruvic acid gets oxidized and generates a lot of ATP
• -each glucose generates 36 molecules of ATP

• from the blood, through hemoglobin (is plentiful due to respiration, get more oxygen thru breathing)
• from the muscles, through myoglobin - usually used up 1st

• Creatine phosphate: provides enough energy for the first 15 seconds
• Anaerobic respiration: provides enough energy for about 30-40 seconds of Muscle activity
• Aerobic respiration: provides over 90% of the ATP needed in activities lasting longer than 10 MIN

• due to the following
• 1. Depletion of Creatine Phosphate
• 2. Insufficient Oxygen
• 3. Build up of lactic acid and ADP
• 4. Depletion of Glycogen and other nutrients
• 5. Inadequate release of Calcium from the SR
• 6. Failure of motor neuron to release enough acetylcholine (ie ulner nerve damage)

• added oxygen helps to restore muscle cells to their resting levels by the following:
• 1. replace the oxygen removed from myoglobin
• 2. synthesize creatine phosphate and ATP
• 3. convert lactic acid into GLYCOGEN

• Dependcent on:
• 1. rate at which nerve impulse arrives
• 2. amount of stretch before contraction
• 3. nutrient and oxygen availability
• 4. size of motor unit

• depends on the size of the motor units and number that are activated
• ie the more complex the muscles, the more muscle fibers used, such as more used in arm & leg (2000-3000) vs. in the eye (10-20) and voice (2-3)

• brief contraction of muscle fibers in response to action potential
• Latent period: 2msec
• -brief delay b/w stimulus and muscular contraction
• -action potential sweeps over the sarcolemma and Ca++ is released from SR
• Contraction Period: 10-100msec
• -Ca++ binds to troponin
• -myosin binding sites on actin exposed
• -Cross-bridges form (myosin head attaches to myosin binding site on actin)
• Relaxation Period: 10-100msec
• -Ca++ is transported back to SR
• -myosin bindings sites covered by tropomyosin
• -myosin heads detach from actin
• (less complex the muscle, the less their contraction periods are)

• Isotonic Contraction: tension developed remains constant while muscle CHANGES LENGTH (ie picking book up off a table)
• Isometric Contraction: tension generated is not enough for object to be moved and muscle does NOT CHANGE LENGTH (ie holding a book with an outstretched arm)

• Red muscle fibers: high myoglobin content (dark meat)
• White muscle fibers: low myoglobin content (light meat)

• 1. Slow Oxidative Fibers (SO fibers)
• 2. Fast Oxidative-glocolytic Fibers (FOG fibers)
• 3. Fast glycolytic Fibers (FG fibers)

• -smallest in diameter
• -appear dark red (more myoglobin)
• -SLOW speed of contraction
• -ATP generated by AEROBIC respiration
• -Very resistant to fatigue
• -Maintaining posture for aerobic endurance activity, such as running a marathon

• -medium in diameter
• -dark red (lots of myoglobin)
• -ATP generated by Aerobic Respiration
• -High resistance to fatigue
• -Speed of contraction is FASTER
• -contributes to activities such as walking and Sprinting

• -Largest diameter
• -most powerful contractions
• -low myoglobin content, so low mitochondria and few blood capillaries
• -ATP generated by GLYCOLYSIS
• -Contraction strongly and quickly
• -Fatigue VERY FAST
• -used for intense aerobic movements lasting a short time, such as weight lifting or throwing a ball

• -most are a mix of all 3 types
• -neck, back and legs have high SO
• -arms and shoulders have high FG
• -legs have large SO and FOG

• These ratios are GENETICALLY determined
• -ppl with high FG fiber proportions excel in intense activities (ie sprinting, weight lifting)
• -ppl with high SO fiber proportions excel in endurance activities (ie marathon running)

• -Aerobic exercise transforms some FG fibers into FOG fibers, since endurance activities do NOT increase muscle mass
• -Exercise that requires short bursts of strength increase size of FG fibers, hence when you weight lift your muscle get BIGGER (Hypertrophy)

• -Intercalated discs connect fibers
• -contracts when stimulated by its own autorhythmic muscle fibers
• -has the same arrangement of actin/myosin as skeletal fibers
• -Many Mitochondria
• -Needs AEROBIC respiration for ATP generation, and can use Lactic Acid produced by skeletal muscle to generate ATP

• -Action potentials are spread through fibers via GAP JXNS
• -Fibers stimulated by neurotransmitter, hormone or autorhythmic signals

• -NOT arranged in orderly sarcomeres
• -SMALL amounts of Ca++ stored
• -Filaments attach to dense bodies and stretch from one dense body to the other (same way as Z discs)

• Can contract or relax in response to:
• -Action potentials from the AUTONOMIC nervous system
• -In response to stretching (ie when food enters digestive tract and intenstines stretches)
• -Hormones (ie epinephrine causes relaxation of smooth muscles in air-ways and blood vessel walls)

• Results in:
• progressive loss of skeletal muscle MASS
• decrease in maximal strength
• slowing of muscle reflexes
• loss of flexibility