A motor neuron and all the muscle cells it stimulates

Skeletal Muscle Activity

UTILIZING THE BOOK AND THE FOLLOWING POWERPOINT SLIDES TO ANSWER THE TWO ESSAY QUESTIONS AND EACH QUESTION WITHIN EACH SECTION. YOU WILL NEED TO ANNOTATE WHERE YOU FOUND YOUR ANSWERS (VIA BOOK OR POWERPOINTS) ANNOTATE WHAT PAGE OR SLIDE NUMBER YOU FOUND EACH ANSWER ON.

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