Muscle Physiology

1.) Sorry for any spelling errors lol 2.) Notes recommended for flashcard mode only 3.) Any bolded card means it was not on the study guide but felt important to me

Draw the skeletal muscle structure from whole muscle to thick and thin filaments

Sarcomere (Hint: 3)

Functional unit of skeletal muscle

Composed of thick filaments (myosin), thin filaments (actin)

From z disk to z disk

Thick Filaments (Hint: 3)

Bundles of proteins

Composed of only myosin

Anchored in place by titin (elastic) fibers

Thin Filaments (Hint: 2)

Made up of several structural proteins (major one is actin) anchored to z-lines

Polymer of myosin molecules, each of which has a flexible cross-bridge that binds ATP and actin

What two proteins have important roles in regulating contraction and relxation of skeletal muscle?

Troponin

Tropomyosin

Troponin

Calcium binds and induces a conformational change moving tropomyosin and exposing the myosin binding site on actin

Tropomyosin

Blocks the myosin binding site on the thin filament

Titin (Hint: 3)

Spring-like protein

Anchor thick filaments to z-disk

Key role in relaxation by springing the sarcomere back to resting length

When is muscle contraction triggered?

When a nerve impulse travels down a motor neuron until it reaches the neuromuscular junction

Neuromuscular Junction (Hint: 2)

Synapse between motor neuron and muscle fiber

Signals Ca2+

Describe the Excitation-Contraction Coupling Process (Hint: 7)

Somatic motor neuron releases Ach at neuromuscular junction

Net entry of Na+ through Ach receptor-channel initiates a muscle action potential

Action potential in t-tubule alters conformation of DHP receptor

DHP receptor opens Ca2+ release channels in sarcoplasmic reticulum and Ca2+ enters cytoplasm

Ca2+ binds to troponin, allowing strong actin-myosin binding

Myosin heads execute power stroke

Actin filament slides toward center of sarcomere

List the Process for Muscle Relaxation (Hint: 5)

Acetylcholinesterase removes Ach from synapse

Depolarization of motor end plate and muscle fiber action potentials cease

Calcium is pumped out of the myofibrils back into the sarcoplasmic reticulum via Ca2+-ATPase

Tropomyosin shifts back in position to block binding sites on actin

Filaments slide back into resting position (elastic elements- titin)

Describe Length-Tension Relationships (Hint: 2)

Most well known skeletal muscle graph

Structure of sarcomeres determines length of skeletal muscle

Length-Tension Relationship: Optimal Length (Hint: 2)

Sarcomere is in perfect position

Filaments have good overlap but still have plenty of space for filaments to slide

Length-Tension Relationship: Too Short (Hint: 2)

Z disks will physically hit thick filaments (why it goes to 0)

Not enough room for filaments to slide

Length-Tension Relationship: Too Long (Hint: 2)

Filaments have little to no overlap

Cannot cross bridge

List the 3 types of skeletal muscle fibers

Slow-oxidative (Type 1)

Fast-oxidative-glycolytic (Type 2A)

Fast-glycolytic (Type 2B)

Fast-Glycolytic Fibers (Type 2B) (Hint: 5)

White fibers

Largest in size

Most thick and thin filaments

Contract 2-3 times faster than slow-twitch (Faster uptake of Ca2+; Faster ATP splitting (more myosin ATPase))

Anaerobic/fatigue easily (power lifting; fast/delicate actions; Sprint)

Slow-Oxidative Fibers (Type 1) (Hint: 6)

Red fibers

Aerobic, less fatigue

More mitochondria (where we have oxidative phosphorylation done)

More capillaries (need to deliver more O2)

Abundant myoglobin (shuttles O2 from blood to mitochondria in muscles (gives red color))

Endurance activities; postural muscles (core and low back muscles)

Fast-Oxidative-Glycolytic Fibers (Type 2A) (Hint: 3)

Pink fibers

Intermediate speed

Anaerobic and aerobic- most adaptable to training

How does smooth muscle contraction differ from skeletal muscle?

• Skeletal Muscle:

  • DHP

  • Calcium comes from sarcoplasmic reticulum

  • No CaM

  • No MLCK

• Smooth Muscle

  • No DHP

  • Calcium comes from sarcoplasmic reticulum and extracellular sources

  • CaM

  • MLCK

Describe the Smooth Muscle Contraction Process (Hint: 5)

• Intracellular Ca2+ concentrations increase when Ca2+ enters cell and is released from sarcoplasmic reticulum

  • Initially Ca2+ comes from extracellular source

• Ca2+ binds to calmodulin (CaM)

• Ca2+-calmodulin activates myosin light chain kinase (MLCK)

  • MLCK only in smooth muscle; phosphorylates myosin n thick filament

  • Smooth muscle must be phosphorylated before it will bind to actin

• MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity

  • To relax, myosin must be dephosphorylated

• Active myosin cross bridges slide along actin and create muscle tension

  • Only in smooth muscle

Calmodulin (CaM)

A cytoplasmic protein not found on the thin filament