SLIDE 1 Muscle Physiology
Bio 219
Napa Valley College
SLIDE 2 Muscle tissue
- Muscle is an excitable tissue capable of force production
- Three types
- Skeletal- striated, voluntary
- Cardiac- non-striated, involuntary
- Smooth- striated, involuntary
SLIDE 3
Structure of Skeletal Muscle
SLIDE 4
Neuromuscular Junction
SLIDE 5
NMJ- Micrograph
SLIDE 6
Nicotinic Acetylcholine Receptor
SLIDE 7
nAChR
SLIDE 8 Events at NMJ
- Action potential causes Ach release
- Ach binds to nAChR
- Allows Na+ to enter muscle cell (EPSP)
- Depolarization from Na+ causes opening of voltage-gated Na+ channels
- Leads to AP in muscle which spreads via T-Tubules*
- *(will come back to this shortly)
- ACh is brokendown by acetylcholinesterase (AChE)
- Also pumped back into presynaptic neuron
SLIDE 9 Structure of Skeletal Muscle
- Epimysium surrounds entire muscle
- Fascia surrounds individual fascicles
- Fasicle is made up of individual muscle fibers
SLIDE 10
Structure of skeletal muscle fiber
SLIDE 11 The Sarcomere
- Functional unit of skeletal muscle
- Smallest unit that retains all the functional properties
- Easy way to understand what the whole muscle is doing is to focus on
- ne sarcomere
- In most cases (all in this class) all sarcomeres are doing the same thing within
a single muscle
SLIDE 12
The sarcomere
SLIDE 13 The Sarcomere
- Major Functional Proteins:
- Actin: Thin filament
- Myosin: Thick filament
- Troponin + Tropomyosin : Block Actin from interacting with Myosin
- Other important structures:
- Sarcoplasmic reticulum
- Contains calcium
- T-Tubule
- Carries depolarization (from motor neuron) across entire muscle fiber
SLIDE 14
Skeletal Muscle Fiber
SLIDE 15
T-Tubule/ Sarcoplasmic Reticulum
SLIDE 16 T-Tubule/ Sarcoplasmic Reticulum
- * T-Tubule is depolarized by AP from NMJ (from earlier)
- That depolarization spreads across the muscle fiber and depolarizes
the S.R.
- Causes calcium efflux from S.R. into the sarcoplasm
- Conformational change of troponin/tropomyosin complex caused by
Ca2+ binding to Troponin
- Opens the myosin binding site on actin *(more on this soon)
SLIDE 17
Molecular Basis for Contraction
SLIDE 18
Sliding Filament Theory
SLIDE 19
Sarcomere micrograph
SLIDE 20 Basic Events of Muscle Contraction
- Depolarization spreads across T-Tubules
- Causes calcium release from S.R.
- Calcium binds to troponin
- Causes conformational change in troponin-tropomyosin complex
- Myosin binds to actin
- ATP is used
- Myosin head pulls Z-lines closer together
SLIDE 21
Actin and Myosin (Thin and Thick Filaments)
SLIDE 22
Skeletal Muscle Contraction
SLIDE 23
Length-Tension Relationship (Sarcomere)
SLIDE 24 Muscle-Bone-Tendon Systems
- Muscle is attached to bone by tendons.
- Force produced by muscle pulls on tendon, which pulls on bone
- Creates movement around a fixed point (joint)
- Muscles can only pull (not push)
- Muscles are in antagonistic pairs
- Ie biceps and triceps OR Quadriceps and hamstring
SLIDE 25 Types of Contraction
- Isometric
- No change in length of muscle
- Eccentric
- Muscle is lengthening
- Concentric
- Muscle is shortening
SLIDE 26 Muscle Twitch
- Smallest single contraction possible from a single motor unit
- If muscle is not allowed enough time to relax, twitches can summate
SLIDE 27 Motor Units
- Single motor neuron and all fibers it innervates
- All fibers activated at same time
- Different size motor units:
- Small: precise, delicate movement- fingertips
- Large: less delicate, for posture, movement- muscles in trunk, lower back
- Motor units are recruited by size:
- Smallest to largest
- Picking up keys vs. picking up 50lb bag of groceries
- Idea is to use as little energy as possible
- Recruitment results in additional force production (more fibers to contract)
SLIDE 28
Motor Unit
SLIDE 29 Summation in Skeletal Muscle
- Spatial
- Recruitment of motor units
- Temporal
- APs fire at faster rate
- Tetanic contraction
- Results from summation of a single fiber/ motor unit
SLIDE 30 Muscle Fiber Types
- Glycolytic
- Rely on glycolysis for energy (Glycolysis)
- Oxidative
- Rely on aerobic metabolism and need oxygen
- Twitch
- Fast
- Slow
- Tonic
SLIDE 31
Human Twitch Muscle Fiber Types
SLIDE 32 Regulation of Muscle Size
- Balance of hypertrophy and atrophy
- Gene expression plays a large role
- Steroids cross membrane and bind to receptors to alter gene expression
- Presence or absence of protein in diet can affect muscle growth
- Aging causes muscle loss
- Sarcopenia- 0.5%-1% loss per year after age 50
- Muscles that are used grow
- Increase fiber size, not number of fibers
- Muscles that are not used will atrophy
- Muscle atrophy can exacerbate symptoms in elderly bed ridden patients
SLIDE 33 Disorders of Skeletal Muscle
- Amyotrophic Lateral Sclerosis (ALS or Lou Gehrig’s Disease)
- Lack of muscle growth due to removal of myelin on motor neurons
- Myasthenia Gravis
- “Grave muscle weakness”
- Caused by overactive acetylcholine esterase
