Unit 4 Lecture 26 Flashcards
What does smooth muscle control?
pressure and tension within organ layers
Where is smooth muscle present?
Sheets???, bundles or sheaths around tissues
What nervous system controls smooth muscle?
Mostly the autonomic (involuntary) nervous system
What are the transmitters of smooth muscle?
ACh and NE
What are the 2 smooth muscle cell types based on excitation?
- Single/ unitary (visceral)
- multi-unit
Where are unitary smooth muscle cells found?
Walls of digestive tract, gall bladder and urinary bladder
How do adjacent unitary SM cells connect?
gap junctions
What occurs in gap junctions?
Transmission of APs from one fiber to another
How do unitary SM cells contract?
AUTORHYTHMIC and
“graded” contractions
Define autorhythmic and graded contractions
Autorhythmic - contract on their own
Graded contractions - contractions vary in intensity and degree
Define function syncytium
The ability to perform rapid, coordinated contractions of smooth muscle along an entire length of fibers
What types of nerve fibers innervate onto smooth muscle?
Autonomic nerve fibers
What is a major component of autonomic nerve fibers found on smooth muscle?
Varicosities
What are found in viscosities of autonomic nerve fibers?
Mitochondria and synaptic vesicles
What do viscosities do?
Release neurotransmitters into DIFFUSE JUNCTIONS in the area of the SM fiber
What is scarce in smooth muscle vs. skeletal muscle?
Sarcoplasmic reticulum
What is the importance of the sarcoplasmic reticulum?
It is the main intracellular calcium store in muscle and it plays regulates excitation contraction-coupling (ECC)
What does the calcium released from the SR effect?
Thick and thin filaments
What is found on thick filaments?
Actin-gripping myosin heads that connect to actin on thin filament to make a crossbridge
How are thin and thick filaments arranged and how do they contract?
Arranged diagonally and contract w twisting motion….. like ringing out a towel
Describe the energy used during contractions of smooth muscle
sustained contraction without fatigue and little energy cost
Describe tension or TONE during contractions of smooth muscle
low levels of tension or tone even without action potentials
List the steps of the stress-relaxation response
Stretch causes initial increase in tension -> tension decreases within 1-2 minutes -> allows SM to change length but maintain ability to contract (important for storage organs)
What is the relationship between length and tension in smooth muscle?
broader length-tension relationship in smooth muscle vs. skeletal
How does smooth muscle operate?
operates over a wider range of resting lengths
