smooth and cardiac muscle Flashcards
descibe the Non-Neural Regulation of Smooth Muscle Contraction
Some smooth muscles are able to actively exert tension in absence of external stimulus:
* Intracellular Ca2+ levels high enough to maintain constant level of crossbridge activity
what type of muscle is cardiac
striated and involuntary
why is their no summation in cardiac muscle
summation would not allow the heart to relax after each beat to fill up with blood
due to long refractory period
what is the difference between tonic and phasic smooth muscle
Phasic smooth muscle contracts in bursts; tonic smooth muscle maintains tone
why is high Ca2+ concentration needed for Smooth Muscle Excitation-Contraction Coupling
smooth muscle lacks troponin. Instead, Ca²⁺ binds to calmodulin, a regulatory protein.
This Ca²⁺-calmodulin complex activates myosin light chain kinase (MLCK), which is necessary for phosphorylation of myosin which must be phosphorylated to interact with actin.
describe smooth muscle
unstriated and involuntary
what is the function of smooth muscle
movement of contents within hollow organs
what is the location of smooth muscle
walls of hollow organs and tubes e.g. stomach and blood vessels
why does skeletal muscle have no gap junctions
each fiber is activated by a specific motor neuron at the neuromuscular junction.
If gap junctions were present, electrical signals would spread uncontrollably between fibers, leading to uncoordinated contractions.
what is the function of gap junctions
allow transmission of electrical signal from one cell
to neighboring cells
contraction in smooth muscle requires
Ca2+ but not troponin
describe a single unit smooth muscle
- tonic or phasic
- myogenic
- fibres connected by gap
junctions
digestive, reproductive and urinary tracts, small
blood vessels
what is smooth muscle innervated by
autonomic nervous system (Sympathetic and/or
parasympathetic)
May be excitatory or inhibitory
what are the steps of Excitation-Contraction Coupling in smooth muscle
- Opening of calcium channels in plasma membrane
- Calcium triggers release of calcium from sarcoplasmic reticulum
- Calcium binds to calmodulin
- Ca2+
-Calmodulin activates MLCK enzyme (Myosin Light Chain Kinase) - MLCK phosphorylates myosin
- Cross-bridge cycling
what are the steps of smooth muscle relaxation
- Phosphatase enzyme removes phosphate from myosin
- Calcium removed from cytoplasm
* Ca2+ -ATPase, Calcium Pumps
* Ca2+ - Na+ exchanger (NCX), (antiport)
how is cardiac muscle similar to smooth muscle
- gap junctions
- pacemaker cells
- innervated by autonomic nervous system
- calcium comes from extracellular fluid and SR
describe multiunit smooth muscle
phasic and neurogenic; discrete units function independently.
walls of large blood vessels, small airways of lung, muscles of eye, base of
hair follicles.
how is cardiac muscle similar with skeletal muscle
- both striated - sarcomeres
- have troponin and tropomyosin regulation
- myoglobin and mitochondria
- T tubules
