skeletal and cardiac muscle anatomy, contraction, and physiology

Skeletal muscles are characterized by what

Large size

Multinucleate structure

What does the multinucleate structure do

Allows for greater surface area for muscle contraction

Motor neurons control skeletal muscle through what

Spinal reflex arcs

Spinal reflex arcs are…

Excitatory or inhibitory

Primary commands for muscle movement originate from

The motor cortex

Where does coordination occur

Cerebellum and brain stem

What’s the final common pathway

Motor neuron

What does the motor neuron do

Transmits signals to the muscle fibers

The neurotransmitter junction site binds to two things

Acetylcholine (ACh) and Nicotinic acetylcholine receptors (nAChRs)

ACh and nAChRs lead to…

Excitatory postsynaptic potentials (ESPs)

Muscle contraction occurs through…

Shortening

What is shortening

Muscle fibers generate force in response to stimulation

Stretch reflexes are important because…

Prevents overstretching of muscles

Overstretching leads to

Injury or weakening

What are the mechanisms to muscle contraction

Twitch contractions

Tetanus

Isotonic contractions

Isometric contractions

Twitch contractions are…

Single stimulus results in quick contraction followed by relaxation

Multiple stimuli leads to…

Incomplete tetanus, where muscles don’t fully relax between contractions

Tetanus is…

When multiple stimuli are delivered in rapid succession

Rapid succession leads to…

Smooth and sustained contraction without relaxation

Isotonic contractions are…

When muscle length changes while maintaining constant tension

Isotonic contraction is…

Muscle length remains constant while tension increases

An example of isotonic contractions

Bicep curl

Example of isometric contraction

Lifting a weight too heavy

What is a sarcomere

Functional unit of skeletal muscle

What do sarcomeres consist of

Thin actin filaments

Thick myosin filaments

During contractions A bands

Remain the same length

During contraction I bands

Shorten

During contraction H bands

Shorten

The shortening of I and H bands allow…

Muscle shortening

What is cross-bridging for sliding filaments

Actin and myosin

Why is cross-bridging important

Initiated by the binding of calcium ions to troponin

Excitation contraction coupling from nerve to muscle starts…

Action potential from a somatic motor neuron

What does the somatic motor neuron lead to

Release of ACh into the synapse

ACh binds to…

Sarcolemma

Sarcolemma causes…

Depolarization and the opening of voltage-gated sodium channels

What does ACh binding result in

Action potential in the muscle fiber

How does AP travel along the Sarcolemma into the muscle fibers through…

Transverse tubules

Through the transverse tubules, this triggers…

Release of calcium ions from the sarcoplasmic reticulum

Calcium ions released into the…

Cytoplasm

Calcium ions released bind to…

Troponin

When calcium ions bind to troponin it causes…

Conformational change

Conformational change exposes…

Binding sites on actin for myosin heads

calcium’s roles in muscle contraction cycle continues…

As ATP binds to myosin

As ATP binds to myosin…

Allows release from actin and reset for other contractions

Energy sources for muscle contraction is…

Anaerobic glycolysis

Aerobic respiration

Anaerobic glycolysis generates…

ATP quickly but produce lactic acid

Lactic acid can lead to…

Muscle fatigue

Anaerobic glycolysis is primarily used…

During first 45-90 seconds of intense exercise

Aerobic respiration involves…

Krebs cycle and electron transport chain

Krebs cycle and electron transport chain produces…

High yield of ATP and requires oxygen as the final electron acceptor

How many ATP per glucose

38

Creatine phosphate serves as a rapid source of…

Energy by donating a phosphate group to ADP

ADP regenerates…

ATP during short bursts of activity

Oxygen debt is…

The amount of oxygen required to metabolism lactic acid post-exercise

Why is oxygen debt important

Recovery and restoring normal muscle function

Oxygen debt allows…

Muscles to consume oxygen after exercise to replenish ATP and clear lactic acid

Upon replenishing ATP to clear lactic acid…

It is converted back to pyruvate and used in aerobic metabolism

Endurance training leads to…

Increased mitochondrial density

Enhanced glycolytic enzyme activity

Greater myoglobin content in muscle cells

Endurance training improves…

Blood flow through new vasculature

Better oxygen delivery

Nutrient supply

Endurance training can shift…

Energy source preference from carbohydrates to fatty acids

Reduce lactic acid production

Enhance endurance performance

Muscle plasticity refers to…

Muscles ability to adapt to change in activity level

Muscle atrophy refers to…

Muscles not being used

Decrease in muscle mass and strength

Muscle atrophy is seen in…

Sedentary lifestyles or immobilization