ANNOUNCEMENTS Review Session this Friday : 12:20 Morrill 349 IMAGE523 Poster Team: Let’s Meet After Class Write Abstract Poster Design Discussion: Exam, Midsemester Review
Dec 19, 2015
ANNOUNCEMENTS
Review Session this Friday: 12:20 Morrill 349
IMAGE523 Poster Team: Let’s Meet After Class
Write AbstractPoster Design
Discussion: Exam, Midsemester Review
Needs Improvement
Pace of class meeting (12)
More explanation/detail on ppt slides (5)
Lab/Lecture Linkage (4)
More dental coverage (2)
Many other thoughtful ideas (1)•limit reading•more previous exams•figures in lab guide•lab more hands-on•more graded assignments
•and others
Thin filaments– Microfilaments (Actin)– Anchored to Z line by -actinin, nebulin– Associated with Troponin, Tropomyosin,
TropomodulinThick filaments
- Myosin: 2 Heavy / 4 light chains- Anchored to Z line by Titin- M line anchors: myomesin and C-proteins
Molecular Components of Sarcomere
This is an electron micrograph of a section through a sarcomere of a skeletal muscle fiber.
Where in the sarcomere is the section taken?
Striated Muscle Contraction
Thin FilamentTropomyosin: – winds around actin – obscures actin-myosin binding site
Troponin Complex – Troponin T: interacts with Tropomyosin – Troponin I: prevents myosin-actin binding – Troponin C: binds Ca++, allowing myosin-actin binding
Striated Muscle Contraction
Thin FilamentTropomyosin Troponin – Troponin T – Troponin I – Troponin C
Ca+2
Contraction of Striated Muscle
- Release of Calcium from Sarcoplasmic Reticulum
- Calcium binds to Troponin
- Tropomyosin/Troponin shift to expose binding site
- Myosin head binds to Actin; Pi released
- Release of ADP from Myosin ---> POWERSTROKE
- Binding of ATP: Myosin detaches from Actin
- Splitting of ATP---> ADP + PI; Myosin head is reset
QuickTime™ and aAnimation decompressor
are needed to see this picture.
http://www.sci.sdsu.edu/movies/actin_myosin.html
Excitation-Contraction Coupling
• T tubules• Sarcoplasmic reticulum: Calcium• Triads
Sarcoplasmic Reticulum and T-tubules
Striated Muscle Structure
• T tubules• Sarcoplasmic reticulum: Calcium• Triads: juncture of T-tubules & SR
- Must release calcium from sarcoplasmic reticulum to initiate the contraction process.
Excitation-Contraction Coupling
Excitation-Contraction Coupling
Muscle Action Potential
Transverse Tubules
Sarcoplasmic Reticulum
Calcium release
Smooth Muscle Contraction
- No organized sarcomere structure
- Actin filaments are associated with tropomyosin but
Not Troponin
What controls actin-myosin interaction?
Smooth Muscle Contraction
-Myosin interacts with actin only when the myosin light chains are phosphorylated
Smooth Muscle Excitation-Contraction1) Excitation=> Ca++ influx
2) Ca++ binds Calmodulin
3) Ca++-Calmodulinactivates myosin light chain kinase (MLCK )
4) MLCK phosphorylates myosin light chains
5) Myosin binds actin => contraction
Regulation of Smooth Muscle Contraction
Nonneural regulation
Hormonal: Oxytocin- uterine contraction
Nitric Oxide (NO):
Produced by endothelial cells of
arterioles
Relaxes smooth muscle
Mice have been produced whose eNOS (endothelial cell NO synthase) genes been "knocked out”. Predict the blood pressure levels of these mice.
Nitric Oxide ----> increased [cGMP]
activates a kinase
inhibits Ca++ influx into smooth muscle cell
decreased calcium-calmodulin stimulation of
MLCK
decreased phosphorylation of myosin light
chains decreased smooth muscle tension
development
vasodilation (expansion of vessel lumen)
Nitric Oxide ----> increased [cGMP]
activates a kinase
inhibits Ca++ influx into smooth muscle cell
decreased calcium-calmodulin stimulation of
MLCK
decreased phosphorylation of myosin light
chains decreased smooth muscle tension
development
vasodilation (expansion of vessel lumen)
What would be the effect of drugs that inhibit the breakdown of cGMP ?
Drugs that inhibit the breakdown of cGMP potentiate (increase) the effects of
NO actions on target cells.
EXAMPLE: Viagra and other inhibitors of cGMP-dependent phosphodiesterase
Innervation of Muscle
Smooth Muscle
Innervation: boutons en passant acetylcholine
Stimulation spread by gap junctions
Innervation of Smooth Muscle
A multiunit system: fine innervation for regulation of individual cells; cells that control the iris opening
A single unit system:1 neuromuscularJunction serves asheet of muscle fibers; stimulus transmitted to otherMuscle cells via gapjunctions; wall of intestine
Innervation of Striated Muscles
Skeletal Muscle: each muscle fiber has at least 1 neuromuscular
junction
Cardiac Muscle: contract spontaneously
rate governed by innervation
excitation spread by gap
junctions
Motor Neuron
Nerve Action Potential
Synapse
Neuromuscular Junction
Neurotransmitter (ACh)
Receptors (AChR)
Muscle Action Potential
Transverse Tubules
Sarcoplasmic Reticulum
Calcium release
Neuromuscular Junction• Nerve stimulation
• Action potential
• Opening of calcium channels
• Exocytosis of synaptic vesicles
• Acetylcholine release
• Binding to Acetylcholine receptors
(AChR)
• Muscle depolarization including T-
tubules
• Opening of Calcium channels in SR
Motor endplate=Neuromuscular Junction
• Synaptic vesicles
• Active zones
• Junctional folds
• AChR (acetylcholine receptor)
clusters
• Schwann cell
Types of skeletal muscles
Fast muscles– Strong and rapid contraction; rapid fatigue– ATP from anaerobic glycolysis– Phasic motor neuron
Slow muscles– Slower but sustained contraction– ATP from oxidative respiration (mitochondria)– Tonic motor neuron