Smooth muscle Flashcards
How is smooth muscle more variable then skeletal muscle?
-Must operate over a range of lengths
-Layers may run in several directions
-Contract and relax much more slowly
-Use less energy to generate and maintain force
-Can sustain contraction without fatigue
-Contraction initiated electrically or chemically
-Controlled by autonomic nervous system
-Ca2+ from extracellular space and/or SR
-Ca2+ initiates cascade eventually turning on myosin ATPase
Describe the structure of smooth muscle
How can smooth muscle be categorized?
-Location
-Contraction pattern
-Communication with neighboring cells
Describe the location of smooth muscles
In humans smooth muscle can be divided into 6 major groups
-Vascular: blood vessel walls
-Gastrointestinal: walls of digestive tract and associated organs i.e. gallbladder
-Urinary: wall of bladder and ureters
-Respiratory: airway passages
-Reproductive: uteris in females and other reproductive structures in males and females
-Ocular (iris and ciliary body)
Describe the contraction pattern of smooth muscle
Describe communication with neighboring cells in Unitary (single unit) smooth muscle
Describe the communication with neighboring cells in multiunit smooth muscle
What are the contractile responses in smooth muscle?
May contract in response to synaptic transmission or electrical coupling
-Smooth muscle is usually innervated by the autonomic nervous system (sympathetic and parasympathetic)
-Can be innervated by multiple neurons, capable of releasing different neurotransmitters
-Receptor subtype differences in muscle (a-adrenergic: Gi vessel constriction vs B-adrenergic: airway dilation)
-Circulating hormones, stretch and local factors, including paracrine signals, acidity, oxygen and carbon dioxide concentration, and osmolarity, can also alter smooth muscle tensions
Explain action potentials of smooth muscle
What is the difference between slow wave potentials and pacemaker potentials?
Explain contraction without action potentials in smooth muscle
summarize electrical activity in smooth muscle
What are the three mechanisms that increase cytosolic calcium?
- Calcium entry through voltage gated channels or chemically gated ion channels
- calcium release from the SR
-Ca2+-induced Ca2+ release from RyR
-IP3 Ca2+ release from IP3R - Calcium entry through voltage-independent channels
-Store operated Ca2+ channels
-Strech activated channels
Explain Ca2+ entry through voltage-gated channels
Explain Ca2+ release from SR
a1 adrenergic receptor
Explain Ca2+ entry through voltage-independent channels
What is pharmacomechanical coupling?
What is stretch activated contraction?
Describe the calcium signal that activates myosin ATPase in smooth muscle
In smooth muscle, myosin ATPase must be activated
Explain the initiation of cross bridge cycling in smooth muscle
-Occurs more slowly than skeletal or cardiac
-Myosin hydrolyzes ATP slowly
-Myosin releases ADP at the end of the power strike very slowly
What is the process of relaxation in smooth muscle?
How can smooth muscle calcium sensitivity be altered?
How can smooth muscle increase contractile force?
Name the controllers of smooth muscle contraction and their roles
