Flashcards in CV Week 2 Deck (395)
_________ is located in the hollow organs of the body and all vasculature except for capillaries and endothelial cells
Describe structures that have smooth muscle
trachea and airways, vasculature, bladder, female reproductive organs, epididymis and vas deferences, musculature through GI tract, lymphatic vasculature
True or false - Because smooth muscle is responsible in a diverse group of organs, it requires a diverse range of regulatory mechanisms to perform specific functions
In __________, smooth muscle cells all behave independently. Few gap junctions are found in these types of cells because there is no great need to electrically couple.
In __________, smooth muscles behave as one unit which is accomplished by having many gap junctions interconnecting cells.
Describe body structures that contain
a) multiunit smooth muscle cells
b) single unit smooth muscle cells
a) airways, vasculature, neural regulation
b) GI tract
_________ smooth muscle tends to be multiunit, whereas _________ smooth muscle tends to be single-unit
Tonically active, rhythmically active
Describe how ADH regulates smooth muscle
ADH is released by posterior pituitary and causes vasoconstriction of smooth muscle (and increased water reabsorption of the kidney)
_________ cause contraction, proliferation and remodeling of blood vessels
Nitric oxide is an example of ______________. It is produced in the immediate environment of the muscle and causes vasodilation of the blood vessels.
Humoral or paracrine signaling
Describe key differences between smooth muscle and skeletal muscle
Myofilaments in skeletal muscle are more highly ordered and produce bands whereas actin and myosin filaments are arranged differently. Smooth muscle contains dense bodies. Smooth muscles also contract more slowly than skeletal muscle.
Why do smooth muscle cells contract more slowly than skeletal muscle?
Cross bridge attachment.detachment is much slower thus rate of contraction is much slower.
True/False - although smooth muscle cells contract more slowly than skeletal muscle, smooth muscle cells can achieve equivalent (or greater) peak contractions
How does slower cross-bridge cycling in smooth muscle affect energy efficiency?
Since cycling of cross-bridges is slower, energy expenditure decreases. This energy efficiency is particularly important to generate sustained contractions over minutes or hours (ie tone)
Describe the different types of myogenic activity (intrinsic to the musculature)
phasic with tone (anal sphincter), phasic (colon), tonic (some blood vessels)
Describe the steps in activating cross-bridge cycling in smooth muscle.
1) Myosin binds to actin filament and an inorganic phosphate is released
2) Power stroke where actin gets pulled towards middle of sarcomere
3) Rigor (myosin in low energy form). ADP is released and new ATP binds to myosin head.
4) Myosin unbinds from actin. ATP is hydrolyzed.
5) Cocking of myosin head (myosin in high energy form) and ready to bind again.
Describe MLCK's role in cross-bridge cycling
MLCK phosphorylates MLC20 (myosin) and facilitates its binding to actin. This facilitates cross-bridge cycling.
Describe MLCP's role in cross-bridge cycling
MLCP dephosphorylates MLC20 and reduces cross-bridge cycling --> muscle relaxation
What is MLCP activity regulated by?
pathways that in effect regulate Ca++ sensitivity of contractile apparatus
What determines the force and duration of contraction?
The balance between myosin phosphorylation and dephosphorylation; therefore, the balance btwn activity of MLCK and MLCP
How does Ca++ vary in when there are a) high MLCK levels; b) high MLCP levels
a) high MLCK - high Ca++; b) high MLCP - low Ca++
_________ (2) are examples of excitatory agonists that cause Ca++ sensitization and thus greater force by inhibiting MLCP
Rho Kinase and PKC
_________ (2) are examples of inhibitory agonists that reduce Ca++ sensitization and thus relax muscle, reducing the force by aggravating MLCP activity
cAMP and cAMP dependent mechanisms
What are three pharmacological agents that are excitatory agonists in regulation of contraction via pharmacochemical coupling?
Ach, norepinhephrine, substance P
What are two pharmacological agents that are inhibitory agonists in regulation of contraction via pharmacochemical coupling?
adenosine, vasoactive inhibitory peptide
How do ROCK and PKC inhibit MLCP activity and thus stimulate contraction?
ROCK phosphorylates MYPT1 subunit of MLCP and PKC via Ca++ and PLC-b mechanism phosphorylates CPI-17,(inhibitory proteins)
Smooth muscle cells contains transport proteins and organelle membranes that set and regulate membrane potential, generate excitable events and ___________________
Ca++ entry into and removal from the cytoplasm
Like other excitable cells, the PM has some level of permeability of each ion species present. The dominant membrane permeability in smooth muscle is due to ______________
RMP is smooth muscle is usually _________ mV
-40 to -80