ANSWER THE ESSAYS AND THE BULLET (-) QUESTIONS
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APLECTURE14SkeletalMuscleActivity.pptSkeletal Muscle Activity
Functional Properties of Muscle Cells
- Irritability
- Ability to receive and respond to stimuli
- Contractility
- Ability to shorten when adequate stimuli received
Nerve Stimulus and Action Potential
- Skeletal muscle must be stimulated by nerve impulses to contract
- Motor neuron stimulate many muscle cells
- Motor unit
- One motor neuron
- All muscle cells it stimulates
Nerve Stimulus and Action Potential
- Axon neuron reaches muscle branches into axonal terminals
- Forms junctions w/ sarcolemma muscle cells = neuromuscular junctions
- Synaptic cleft – gap between nerve ending and muscle cell
Nerve Stimulus and Action Potential
- Nerve impulse reaches axon terminal
- Neurotransmitters released
- Acetylcholine (ACh)
- ACh diffuses across synaptic cleft
- Attaches receptors on sacrolemma
Nerve Stimulus and Action Potential
- Enough ACh released
- Sacrolemma permeable to Na+
- Na+ rushes into muscle cell
- Inside cell excess + ions
- Generates action potential
- Unstoppable once begun
- Travels along sacrolemma
- Conducts impulse from one cell to another
- Result = contraction muscle cell
Nerve Stimulus and Action Potential
- K+ diffuses out cell
- Na+/K+ pump transports Na+ and K+ to normal positions
- Muscle back at resting state
Mechanism of Muscle Contraction
- Sliding filament theory
- Cross bridges (myosin heads) ends of thick filaments
- Muscle fibers activated by nervous system
- Cross bridges attach to myosin binding sites on thin filaments
- Sliding begins
- ATP provides energy
Mechanism of Muscle Contraction
- Cross bridge attaches and detaches during contraction
- Pulls thin filaments toward sarcomere center
- Occurs simultaneously throughout cell
- Muscle cell shortens
Mechanism of Muscle Contraction
- Attachment of myosin cross bridges to actin requires calcium ions
- Action potential causes sarcoplasmic reticulum to release Ca+ into sarcoplasm
- Action potential ends Ca+ reabsorbed into SR
- Muscle cell relaxes
- ACh broken down by enzymes on sarcolemma
- Single nerve impulse produces 1 contraction
Sarcomere
- Relaxed
- Fully Contracted
- Light H zone center A band disappeared
- Z discs closer to thick filaments
- I bands nearly disappeared
- A bands move closer but do not change length
Sliding Filament Theory
Graded Responses
- All or none law
- Muscle cell not to whole muscle
- Muscle cell will contract to fullest when stimulated adequately
- Skeletal muscles organs w/ thousands muscle cells
- React to stimuli w/ graded responses
- Different degrees of shortening
Graded Responses
- Produced by
- Changing frequency of muscle stimulation
- Changing # of muscle cells being stimulated
Muscle Response to Increasingly Rapid Stimulation
- Muscle twitch
- Single, brief, jerky contractions
- Nerve impulses delivered to muscle rapid rate
- Cells do not get to relax in between stimuli
- Successive contractions added together
- Contractions stronger and smoother
- Fused or complete tetanus
- Muscle stimulated rapidly
- No evidence relaxation
- Contractions smooth and sustained
- Unfused or incomplete tetanus
- Until reaches complete tetanus
Muscle Response to Stronger Stimuli
- How forcefully muscle contracts depends on how many muscle cells stimulated
- Muscle contractions slight or vigorous
- Soothing hand vs. hand that slaps
Energy for Muscle Contraction
- Muscle contracts
- Bonds ATP hydrolyzed
- Releases needed energy
- Muscles only store 4-6 seconds worth energy
- ATP regenerated continuously
Pathways for ATP Regeneration in Muscles
- Direct phosphorylation of ADP by creatine phosphate
- Aerobic respiration
- Anearobic respiration
Direct Phosphorylation
- Creatine phosphate (CP)
- High energy molecule
- Found in muscle fibers
- ATP depleted
- Interaction between CP and ADP
- Transfer high-energy phosphate from CP to ADP
- Get more ATP
- 5x more CP stored than ATP
- CP supplies exhausted in 20 sec
Aerobic Respiration
- Rest during light exercise
- How 95% ATP used generated
- Mitochondria
- Metabolic pathways that use O2
- Oxidative phosphorylation
- Glucose broken down to CO2 and H2O
- Energy released bonds broken
- 36 ATP per 1 glucose
- Slow requires O2
Anaerobic Glycolysis and Lactic Acid Fermentation
- Without oxygen
- Glycolysis
- Glucose broken down to pyuvic acid
- 2 ATP per glucose
- Cytosol
- Intense muscle activity
- Pyruvic acid converted to lactic acid
- 5% as much ATP as aerobic
- 2.5x faster
- Lactic acid promotes muscle fatigue and muscle soreness
Muscle Fatigue
- Unable to contract even though it is stimulated
- Result of oxygen debt
- Prolonged periods muscle activity
- Inadequate oxygen
- Lactic acid builds up
- Muscle contracts less and less effectively
- Recovery period breath rapidly and deeply
- Continues until oxygen debt paid back
Types of Muscle Contractions
- Muscles do not always shorten when they contract
- Tension develops in muscle as actin and myosin interact
- Myosin cross bridges attempt to slide the actin filaments past them
Isotonic Contractions
- Myofilaments successful in sliding
- Muscle shortens
- Movement occurs
- Bending knee
- Rotating arms
- Smiling
Isometric Contractions
- Muscles do not shorten
- Myosin filaments skidding
- Tension keeps building
- Trying to slide
- Muscle against immovable object
- Lift something heavy
- Push against wall
Muscle Tone
- State of continuous partial contractions
- Cannot be consciously controlled
- Even when voluntarily relaxed
- Fibers contracting
- Helps muscle remain firm, healthy
Effect of Exercise on Muscles
- Use it or lose it
- Aerobic exercise
- Endurance
- Stronger, more flexible muscles
- Greater resistance to fatigue
- Blood supply increases
- Muscle cells form more mitochondria and store more oxygen
- Do not cause muscles to increase in size
- Resistance
- Isometric exercises
- Increased muscle size and strength
- Enlargement of individual muscle cells
- More contractile filaments
