Smooth Muscle Flashcards
Smooth muscle is under _____ control
involuntary
Smooth muscle are nonstriated b/c…
actin and myosin aren’t arranged in regular sarcomeres
Smooth muscle responds to what types of stimuli?
- electrical signal
- hormones
Contraction of smooth muscle leads to…
alteration in dimension of organ
- propels substance w/in organ
- increase resistance to flow of substance
T/F: smooth muscles are more variable than skeletal muscles
T, b/c they operate over a wide range of lengths
Smooth muscles are arranged in…
- circular
- longitudinal
- oblique
- bundles
- sheets
Differences between smooth and skeletal muscles:
- contract and relax slower
- lose less E
- have less localized receptor sites
Smooth muscle is different based on…
- location
- contractions
- arrangements
Visceral muscle:
lines walls of hollow internal organs
- organs part of gastrointestinal, urinary, respiratory, and reproductive systems
Vascular muscles are located in…
blood vessels
Types of smooth muscle that differ in location:
- visceral
- vascular
- ocular
Types of smooth muscle that differ in contractions:
- phasic
- tonic
Phasic contractions depend on…
the demands of the situation
Tonic contractions:
change diameters slowly
Tonic contractions can be…
maintained for long periods without fatigue
Tonic contractions use high/low ATP due to…
low, latch-bridge state
Smooth muscle cross-bridges cycle at…
slower rate than skeletal muscle
Different types of arrangements:
- multiunit
- unitary
Multiunit arrangement:
individual cells and small groups of cells
- not electrically coupled
Multiunits act as…
many separate units b/c fibers operate independently
Multiunits are densely innervated by…
ANS fibers
Lots of nerves provide…
separate signals, which allows for greater control
Examples of multiunit smooth muscles:
- very small blood vessels
- muscles of skin
- iris
- ciliary body of eye
Unitary (single unit):
large # of cells that function together as a single unit
- not as strictly controlled by ANS
- electronically coupled
- can be initiated by pacemaker cell
Unitary arrangements make up the bulk of…
visceral organs
Unitary arrangements control…
peristalsis (aka wave contraction)
Single unit and multiunits are both mostly…
combination of cell-cell coupling and locally produced activators/inhibitors
Innervations of smooth muscle are under…
involuntary NS control
- doesn’t need NS innervation
Smooth muscles are innervated by…
motor neurons of ANS
Motor neurons of ANS:
- have no motor end plate
- supply smooth muscle flow across tissue
- NT released at varicosities
- has electromechanical coupling like skeletal muscles
T/F: smooth muscles can also contract without innervation
T
- many have intrinsic activity
If smooth muscles can contract without innervation, what are the influenced by then?
- hormonal factors
- environmental factors
Examples of hormonal factors:
- uterine muscle response to oxytocin
- vasoactive substances (paracrine)
Environmental factors:
- under myogenic control
- contract when stretched
- ex: distention of stomach
Smooth muscles that can contract without innervation acts via…
pharmacomechanical coupling
Smooth muscle cells are generally arranged in what kind of layers:
- circular
- longitudinal
- helical (oblique)
T/F: smooth muscle cells are in antagonistic pairs
F
Smooth muscle cells around large blood vessels are arranged in…
helical/circular layers
Smooth muscle cells in arterioles are arranged in…
singular circular shape
When circular muscle is contracted…
- diameter is decreased
- stops movement
When longitudinal muscle is contracted…
- organ is shortened
- moves substance through
Varicosities:
- periodical swellings of ANS neurons
- has vesicles w/ NT
- affected cells will depolarize
- whole sheets contract as functional syncytium
APs in varicosities have…
long durations
- spread to neighboring cells via gap junctions
Smooth muscle cells don’t have:
- fast VGC Na+
- T-tubules
- troponin
- visible striated sarcomeres
Smooth muscle cells have:
- slow L type VGC Ca2+
- caveolae
- calmodulin as regulatory protein
- actin and myosin wrapped in spirals between dense bodies
T/F: smooth muscle is not myosin driven
F
Single units are connected by…
gap junctions
- forms low-resistance pathway
- allows for electrical and chemical communication
Single units are…
- small
- mononucleated
- spindle shaped
Dense bodies in single units act as…
z line because it connects actin and myosin bundles
T/F: there are the same amount of actin in skeletal muscle as smooth muscle
F, there are x2 the amount of actin in smooth muscle
Actin:
- has no troponin, so not bound to tropomyosin
- myosin binding site is exposed
Myosin:
- not in ready state
- not cocked
- 1/4 of the amount in skeletal muscle
Myosin has myosin linked regulatory proteins, which are:
- myosin light chain (MLC)
- myosin light chain kinase (MLCK)
- myosin light chain phosphatase (MLCP)
Myosin light chain (MLC) is at the…
base of myosin head
Function of myosin light chain kinase (MLCK):
phosphorylates MLC, which will activate myosin ATPase