Lucas part 7 Flashcards
Structure of smoot muscle:
____, ____-shaped cells compared to skeletal muscle.
____ nucleus per cell. (single or multiple)
____ striations because thick and thin filaments are not organized into sarcomeres.
small, spindle, single, lacks
Key Differences from Skeletal Muscle:
1) No ____, ____, or ____.
2) Thick filaments lack a “____” allowing more flexibility in filament interactions.
T-tubules, DHPRs, or RyRs
bare zone
function of smooth muscle
Controls involuntary movements such as peristalsis, blood flow regulation, and bladder emptying.
where is smooth muscle found
blood vessels, digestive tract, bladder, uterus, and respiratory tract.
Thin and thick filaments are arranged in a ____ network rather than sarcomeres.
During contraction, thin filaments slide past thick filaments in ____ directions, shortening the cell.
lattice-like, opposite
Change of Partners During Stretch:
During stretch, myosin heads move to interact with new thin filaments. So original filaments sets no longer overlap
Stress-Relaxation Property:
Initial force from stretch decreases over time as filaments reorganize.
what is the purpose of the stress-relaxation property
accommodating changes in organ size, such as in the bladder or stomach.
Single-Unit Smooth Muscle:
Features:
Connected by ____, allowing cells to contract as a ____ unit.
____ (self-excitable).
Examples: ____, ____.
gap junctions, single myogenic, guts, bladder
Multi-Unit Smooth Muscle:
Features:
Each cell acts ____, requiring ____.
____ (controlled by nerves).
Examples: ____, iris of the eye, ____ follicles.
independently, direct neural stimulation
neurogenic
blood vessels, hair follicles
Phasic vs. Tonic Contractions:
Phasic:
____, ____ contractions (e.g., ____ in the intestines).
Tonic:
____ contractions (e.g., maintaining ____ tone).
rhytmic, intermitten, perilstasis
sustained, blood vessel
Myogenic Excitation
2 types of potentials:
Pacemaker Potentials and Slow Wave Potentials
Pacemaker Potentials:
____, ____ changes in membrane potential.
Trigger ____ and contractions.
spontaneous, rhytmic, action potentials
Slow Wave Potentials:
____ fluctuations in membrane potential, requiring ____ (e.g., ____ signals) to reach the action potential threshold.
gradual, ANS signals, additional input
Neurogenic Excitation
____:
Swellings along ____ nerve fibers release ____.
Neurotransmitters ____ across the smooth muscle, stimulating contraction.
varicosities, autonomic, neurotransmitters, diffuse
Smooth muscle relies on ____ for contraction. Calcium can enter the cell via: (3 ways)
cytoplasmic contraction
Voltage-Gated Ca²⁺ Channels:
Second-Messenger Pathways:
Store-Operated Ca²⁺ Channels:
Voltage-Gated Ca²⁺ Channels:
Opened by ____.
action potentials
Second-Messenger Pathways:
____ trigger the release of calcium from the ____
GPCRs, SR
Store-Operated Ca²⁺ Channels:
Open in response to depletion of ____.
SR calcium stores
What is found on myosin heads and control ATPase activity
myosin light chains
mechanism for smooth muscl filament contraction
Ca²⁺ binds to ____.
The Ca²⁺-CaM complex activates ____
MLCK phosphorylates ____, activating ____.
ATPase hydrolyzes ATP, powering the cross-bridge cycle and contraction.
CaM (Calmodulin), MLCK (MLC kinase), MLC, myosin atpase
Relaxation Process for smooth muscle
Process:
____ is pumped out of the cytoplasm, reducing cytosolic levels.
Low Ca²⁺ deactivates ____.
____ dephosphorylates ____, stopping the ATPase activity.
The cross-bridge cycle halts, and the muscle relaxes.
Calcium, MLCK, MLC phosphotase, MLC
Smooth Thin Filament Regulation
____:
Blocks myosin-binding sites on g actin in the absence of ____⁺.
Ca²⁺-CaM Complex:
Removes ____, exposing actin and enabling cross-bridge formation.
caldesmon, calcium, caldesmon
3 factors that promoting contraction:
para and sympathetic ANS (acth, epinephrine, norepinephrine)
serotonin
stretch
alpha 1 receptors
3 factors that promote relaxation
sympathetic ANS (nor + epi)
beta 2 receptors
inhibit mlck
hormones from blood
is there a length-tension curve in smooth muscle
no
During pregnancy, uterine smooth muscle transitions from ____-unit to ____-unit to enable coordinated contractions for childbirth.
multi to single
the hyperpolarization in pacemaker potentials is from
leaky ion channels
the hyperpolarization in slow wave potentials is in
random bursts
the increase AP in pacemaker potentials is from
calcium
the increase in AP in slow wave potentials is from
bursts
