smooth muscles Flashcards
1
Q
types of smooth muscles (2)
A
- multi-unit smooth muscles- fibers can act independently
- unitary/ visceral smooth muscle- mass of hundreds or thousands of muscle fibers that contract together as a single unit
2
Q
unitary smooth muscles (5)
A
- mass of hundreds or thousands of fibers that act as a single unit
- arranged in sheets or bundles that adhere together
- gap junctions
- visceral- found in body viscera, gi tract, bile ducts, ueters, BV
- syncytical- multinucleate mass of cytoplasm that is not separated into individual cells
3
Q
size of smooth muscle compared to skeletal
A
smooth muscle is composed of cells 2-5um in diameter and 100-400um in length, skeletal can have 20x > diameter and 1000x longer
4
Q
caveoli
A
tiny sac-like invaginations of sarcolemma arranged in rows along cell that communicate with extracellular space
5
Q
sarcoplasmic reticulum
A
less developed than skeletal muscle
6
Q
differences from skeletal muscle (5)
A
- no t-tubles or motor endplate
- neurotransmitters are released from enlarged variscosities and diffuse to receptors in sarcolema
- myosin :actin 1:16; much lower than skeletal muscle, however myosin has heads along the entire length
- troponin complex is not present
- no sarcomeres, thick and thin filament spiral down long axis of smooth muscle like a barber pole
7
Q
smooth muscle contraction (4)
A
- contractile unit = actin filaments attached to dense bodies, filaments overlap where a single myosin is located.
- these sidepolar myosin allow it to pull two actins towards it at the same time,
- this is what gives smooth muscle ability to contract 80% (vs skeletal which can contract 30%)
- generally prolonged and isometric which can last for hours to days
8
Q
why smooth muscle is more economical than skeletal (7)
A
- slow bridge cross cycling
- low energy requirement (1/10-1/300th amt)
- slow onset of contraction and relaxation
- increased maximum force of contraction
- latch mechanism
- stress-relaxation of smooth muscle
- contractile units of smooth muscle allow optimal contraction length
9
Q
regulation of contraction by calcium (4)
A
- calcium ions combine iwht calmodulin (instead of troponin)
- calmodulin-calcium combo joins w/ and activates myosin kinase, a phosphorylating enzyme
- one of the light chains of myosin (regulatory chain) becomes phosphorylated- when this happens is can bind to actin
- when Ca ion falls below certain concentration it reverses process except phosphorylation, need myosin phosphate for this
10
Q
latch mechanism (2)
A
- when myosin kinase and phosphate enzymes are both activated, the cycling frequency of myosin heads and velocity of contraction are great. as activation decreases, cycling frequency decrease but myosin heads are allowed to stay on actin longer => more myosin attached to actin at any given time.
- ATP is only used when attaching or detaching
11
Q
action potentials of unitary smooth muscle (3)
A
- spike potentials- (most of single unit) - e;icited by electrical stim, stretch or action of hormones
- action potentials w/ plateaus- same but repolarization is delayed by several hundred milliseconds
- slow wave potentials
12
Q
slow wave potentials (4)
A
- caused by oscillations in membrane potential (singel unit)
- cause spontaneous generation of action potential- they themselves are not action potentials and cannot create contraction
- when potential of s.w. hits -35 action potential begins
- pacemaker contraction = at the peak of each slow wave, at least 1 action potential occurs which starts rhythmical contractions (ie gut)
13
Q
contraction w/o action potential (4 in response to chemicals, 1 other cause)
A
- response to local tissue chemicals - vasodialtion in blood vessles
- lack of O2 causes relaxation => vasodilation
- excess Co2 => vasodilation
- increased H => vasodilation
- hormones
14
Q
Cross-bridge cycling definition
A
- Rate of myosin cross bridge attaching and releasing actin
