LEC-4 Smooth Muscle Physiology Flashcards
Elevated blood pressure in the systemic circulation is referred to as _____________.
Hypertension
Chronic hypertension may lead to _______________.
Cardiovascular disease
In atherosclerotic vessels, smooth muscle surrounding the vessel is known to (regress/proliferate)
Proliferate
Vascular smooth muscle may grow by (hypertrophy/hyperplasia/both).
Both
Smooth muscle cells range anywhere from ___ - ___ μm in length and ___ - ___ μm in diameter.
20-500 μm in length 1-5 μm in diameter
(T/F) Smooth muscle utilizes the same proteins and complexes as skeletal muscle for muscle contraction.
False. Skeletal muscle uses an actin/tropomyosin/troponin complex to complete muscle contraction. Smooth muscle, on the other hand, utilizes the following:
- Actin/tropomyosin/calmodulin/caldesmon complex.
Adjacent smooth muscle cells make use of _____________, low-resistance electrical pathways between cells.
Gap junctions
______________ serve as attachment points for thin actin filaments in smooth muscle cells, making them akin to Z-bands.
Dense bodies
The sarcoplasmic reticulum in smooth muscle cells is (smaller/larger/the same size) in relation to the sarcoplasmic reticulum of skeletal muscle.
Smaller
Small invaginations of the smooth muscle cell membrane are referred to as __________.
Caveolae
The absence of structure regularity in smooth muscle cells is noted as the reason for the absence of __________.
Striations
Myosin filaments within smooth muscle often have side-polar crossbridges, allowing for contraction of up to ___% of the fiber length versus the 30% that is possible in skeletal muscle.
80%
Smooth muscle cells possess a (more/less) efficient ATPase than that of skeletal muscle. This results in (faster/slower) cycling of myosin cross-bridges.
- Less efficient
- Slower cycling
Smooth muscle requires markedly (more/less) energy to complete a contraction than skeletal muscle.
Less
- Requires 1/10 - 1/300th the amount of energy as skeletal muscle
Smooth muscle possesses a “latch mechanism” that facilitates (shortened/prolonged) contraction.
Prolonged
(T/F) Due to the latch mechanism, once full contraction is achieved in smooth muscle, the amount of excitation and energy consumed to maintain contraction is greatly reduced.
True.
The maximum force of smooth muscle contraction is (greater/less) than that of skeletal muscle.
Greater
(T/F) It takes smooth muscle a considerable amount of time to return to its original state after being contracted or lengthened.
False. One of smooth muscle’s key characteristics is its ability to quickly return to its original state after contraction or lengthening. This allows smooth muscle to maintain the same amount of force within hollow organs.
______________ is the activating kinase used within smooth muscle cells. It is bound by calmodulin and calcium to convert it to its active state, in which it phosphorylates myosin regulatory light chains, allowing for muscle contraction.
Myosin light chain kinase (MLCK)
(T/F) Smooth muscle does not use sodium as its primary depolarizing agent. Instead, it uses calcium and calcium-activated proteins to conduct muscle contraction. Calcium also extracellularly enters the smooth muscle cell fairly often, instead of just from the sarcoplasmic reticulum during contraction.
True.
Smooth muscle utilizes Ca2+-dependent ATPases along with the enzyme _______________ for muscle relaxation.
Myosin light chain phosphatase (MLCP)
_________________ serves to dephosphorylate myosin chains in smooth muscle when relaxation is necessary.
Myosin light chain phosphatase
(Visceral/Multi-unit) smooth muscle consists of hundreds to thousands of smooth muscle fibers organized into bundles or sheets that can contract as a single unit. Their membranes are adherent at multiple contact points and are joined via gap junctions for transmission of contractile forces and ion flows
Visceral (or unitary)
(Visceral/Multi-unit) smooth muscle consists of discrete separate smooth muscle fibers that are each innervated by a single nerve ending and operate independently of the others. Their cellular surface is covered by matrix for insulation purposes.
Multi-unit
Smooth muscle cell innervation is from (motor units/autonomic nerves).
Autonomic nerves
What do visceral and multi-unit smooth muscle cells have in common?
- Contractions are slow in onset but are sustained for long periods of time with little energy input required
- Innervation is autonomic, either from sympathetic or parasympathetic
- Both superimpose their own contractions on an intrinsic “tone”, or basal resting tension within the muscle
(Visceral/Multi-unit) smooth muscle is capable of spontaneous activity initiated by pacemaker cells.
Visceral
(T/F) Visceral smooth muscle is most often stimulated to contract by nerve impulses.
False. Visceral smooth muscle is not usually initiated by nerve impulses.
What would the action potential of visceral smooth muscle look like in a non-pregnant uterus?
Image
What would the action potential of visceral smooth muscle look like in a ureter?
Image
What would the action potential of visceral smooth muscle look like in longitudinal muscle of the intestine or myometrium during parturition?
Image
_____________ refers to the time between an action potential and the start of contraction.
Latent period
Smooth muscle has a markedly (longer/shorter) latent period than does skeletal muscle.
Longer
(Visceral/Multi-unit) smooth muscle is most often activated by motor nerve stimulation, but it depolarizes without action potential.
Multi-unit
(T/F) Multi-unit smooth muscle does not respond to stretch by developing tension.
True.
What are the two possibilities of multi-unit smooth muscle contraction in the absence of action potentials?
- Local tissue chemical factors
- Lack of oxygen, excess CO2, increased hydrogen ion concentration, increased lactic acid, increased body temp.
- Various hormones
- Epinephrine, norepinephrine, angiotensin, vasopressin, oxytocin, serotonin, or histamine.
(Visceral/Multi-unit) smooth muscle utilizes contact junctions.
Multi-unit
(Visceral/Multi-unit) smooth muscle utilizes diffuse junctions.
Visceral
(Diffuse/Contact) junctions consist of vesicle-filled varicosities in the vicinity of smooth muscle cells. They possess a 1-5μm distance between cells along with a widely varying number of innervated cells.
Diffuse (Visceral smooth muscle)
(Diffuse/Contact) junctions are morphologically similar to the neuromuscular junction of a skeletal muscle. They possess a 20nm synaptic cleft along with innervation for every cell.
Contact (Multi-unit smooth muscle)
(T/F) Skeletal muscle has mitotic activity.
False. Skeletal muscle has no mitotic activity. Skeletal muscle regenerates through the use of satellite cells, which are considered to be adult muscle stem cells.
Skeletal muscle regenerates through the use of _______________, which are considered to be adult muscle stem cells.
Satellite cells
(T/F) Cardiac muscle is hardly capable of any regeneration. Upon cellular injury, such as during a myocardial infarction, fibroblasts invade the damaged tissue, resulting in scarring.
True.
(T/F) Smooth muscle cells possess no mitotic activity.
False. Smooth muscle cells retain their mitotic activity. They are capable of forming more smooth muscle cells.
____________ is an endothelial cell-produced signaling molecule that allows for smooth muscle relaxation.
Nitric oxide (NO)
