11. Chapter 12- Smooth Muscle Flashcards
Why is smooth muscle more viable that skeletal? (What are it’s functions)
- operates over range of lengths
- layers run in several directions (one layer propel food, one breaks it down)
- contract and relax slower
- use less energy
- can contract without fatigue
- controlled by autonomic nervous system
What are smooth muscles?
What’s absent in them?
Spindle shaped, uninucleate
Don’t have organized pattern of sarcomeres (smooth because under microscope there’s no binding pattern)
Troponin and T tubules absent
Intermediate filaments and dense bodies form extensive cytoskeletal structure
Myosin heads all over so when muscle stretches myosin is abundant
Slide 4 Nov 2
How are smooth muscles categorized by there LOCATION? (6 of them)
- Vascular (Blood vessel walls)
- Gastrointestinal (digestive tract walls)
- Urinary (wall of bladder and urethra)
- Respiratory (airways)
- Reproductive (uterus)
- Ocular (iris and ciliary body)
How are smooth muscles categorized by their CONTRACTION PATTERN? (4 of them)
- Phasic smooth muscle that is relaxed usually (esophagus)
- Phasic smooth muscle clucked between contraction and relaxation (intestine)
- Tonic smooth muscle usually contracted (sphincter)
- Tonic smooth muscle where contraction is varied as needed (vascular smooth muscle)
Slide 6 Nov 2
How are smooth muscles categorized by their COMMUNICATION WITH NEIGHBOURING CELLS? (2 of them)
- Unitary smooth muscle- contains gap junctions like cardiac muscle cell
(Also called visceral smooth muscle)
Majority of smooth muscle is this - Multiunit smooth muscle
- few gap junctions, not electrically coupled
- acts as individual units, each muscle contracts independently
Slides 7-8 Nov 2
How does smooth muscle contract?
In response to synaptic transmission or electrical coupling
- parasympathetic and sympathetic
- can be innervated by multiple neurons
- can be excitatory or inhibitory where cardinal and skeletal are just excitatory
Where do APs usually occur in smooth muscle?
How can they be initiated
In unitary smooth muscle usually
Can be initiated by neural, hormonal, or mechanical stimulation
Slide 11 Nov 2
How can contraction occur in smooth muscle without action potentials?
Since multiunit smooth muscle usually don’t have APs, small graded depolarizations will initiate small contractions
Since smooth muscle produce lots of membrane potentials some can lead to oscillations which can lead to tonic contractions without APs
What are the 3 types of electrical activity in smooth muscle and are they associated with single unit or multiunit smooth muscle?
Autonomic AP initiation (unitary single unit)- spikes or plateaus
Spontaneous AP (unitary single unit)- slow wave due to presence of low calcium channel potentially
-pacemaker
Graded potentials (multiunit)
-contraction due to electrical signalling is electrochemical coupling
What are the 3 ways cytosolic (Ca2+) is increased?
Extracellular entry and intracellular release of Ca activate contraction, this is increased by:
1. Ca entry through voltage gated channels or ion channels
2. Ca release from the SR
3. Ca entry through voltage independent channels
Study all 3 pics on slides 15-18 nov 2
What is pharmacomechanical coupling?
Drugs, excitatory neurotransmitters and hormones can induce smooth muscle contraction independent of AP generation
Don’t need a change in membrane potential
Picture on slide 19 Nov 2
What is stretch activated contraction?
Stretch activated ion channels in the cell membrane of some smooth muscle that when activated lead to depolarization
Stretch of smooth muscle causes internal release of Ca from SR through ryanodine receptor
What is Ca signal in smooth muscle? (Compared to cardiac and skeletal muscle)
Entirely different process
Ca initiates a slow chain of events increasing myosin ATPase activity
4 Ca ions binds to calmodulin which is a Ca binding protein similar to troponin C of striated muscle
Slide 21-23 nov 2
How is cross bridge cycling initiated in smooth muscle?
The Ca calmodulin complex activates myosin light chain kinase enzyme (MLCK)
MLCK phosphorylates light chain near myosin head and alters conformation of myosin head which increases ATPase activity and interacts with actin
Slide 24-25 summary Nov 2
How does smooth muscle relax? (2 steps)
- Ca2+ is moved back to the SR and extracellular space
- Regulatory light chain must be dephosphorylated by myosin light chain phosphatase
- even after dephosphorylation of regulatory light chain some smooth muscle can maintain force for an extended period of time with little ATP (latch state)
Slide 8 Nov 5
