1.8. The physiology of smooth muscle. The functions of different types of smooth muscle. Flashcards
I. Physiology of smooth muscle - Smooth muscle
1A. What are the characteristics of smooth muscle?
- Uni-nucleated, narrow, spindle-shaped cells
- Lacks striations – distinct from cardiac and skeletal muscle, because thin and thick filaments are present, but are not organized in sarcomeres (no Z-lines)
- No T-tubules, but SR is present
I. Physiology of smooth muscle - Smooth muscle
1B. Where can you find smooth muscle?
- Found in walls of hollow organs: GI-tract, bladder, ureters, bronchioles, vasculature
I. Physiology of smooth muscle - Structure of myofilaments
2A. What are the 2 types of myofilaments?
Thin and thick myofilaments
I. Physiology of smooth muscle - Structure of myofilaments
2B. What are the characteristics of thin myofilaments?
They contain smooth muscle cell (SMC) actin, tropomyosin (NO TROPONIN)
I. Physiology of smooth muscle - Structure of myofilaments
2C. What are the characteristics of thick myofilaments?
Thick – myosin:
- Heavy chain – 2 heavy chains form a complex
- Light chain (MLC) – 2 light chains per heavy chain <- can be phosphorylated by MLCK
I. Physiology of smooth muscle - Types of SMCs
3A. How is the classification of SMCs based on?
Classification based on how the cells are electrically coupled
I. Physiology of smooth muscle - Types of SMCs
3B. What are the 2 types of SMCs?
1) Single-unit SMCs: (GI-tract & urogenital system)
2) Multi-unit SMCs: (iris, airways, tunica media of large vessels)
I. Physiology of smooth muscle - Types of SMCs
3C1. What are the characteristics of single-unit SMCs
- Has gap junctions which allow easy electrical conduction between cells
- Gap junctions allow large regions to contract in unison
- Characterized by spontaneous pacemaker activity – ‘’slow waves’’
I. Physiology of smooth muscle - Types of SMCs
3C2. Where can you find single-unit SMCs?
GI-tract & urogenital system
I. Physiology of smooth muscle - Types of SMCs
3D1. What are the characteristics of multi-unit SMCs?
- Each cell has its own innervation
- Neural control of contraction
- Functions are tightly regulated
I. Physiology of smooth muscle - Types of SMCs
3D2. Where can you find multi-unit SMCs?
Iris, airways, tunica media of large vessels
II. AP in smooth muscle
1. What are characteristics of AP in smooth muscle?
Exhibit continuous fluctuation of Em = slow-wave potential
- Occurs as electrical AP generated by interstitial cells of Cajal is propagated through gap junctions
- There are 2 thresholds in SMC Em
+) Threshold for contraction (without having an AP spike)
+) Electrical threshold (AP is generated)
II. AP in smooth muscle
2. What are the 2 thresholds in SMC Em?
There are 2 thresholds in SMC Em
1. Threshold for contraction (without having an AP spike)
2. Electrical threshold (AP is generated)
II. AP in smooth muscle
3. How are different types of contraction made?
Depending on the degree of depolarization, different types of contractions are made:
- Depolarization does not peak beyond electrical threshold
-> tonic contraction (basal activity)
- Depolarization does reach above electrical threshold
-> phasic contraction (↑AP frequency = ↑ contraction force)
II. AP in smooth muscle
4. What are the 4-step process of SMC AP development?
- Cationic-leak channels open -> depolarization -> Na+-influx
- Electrical threshold is reached
-> L-type VGCCs open -> a series of AP spikes - ↑[Ca2+]IC causes Ca2+-activated K+-channels to open -> repolarization occurs slowly
- VGCCs close due to repolarization -> ↓[Ca2+]IC -> Ca2+-activated K+-channels close