Smooth Muscle Physiology Flashcards
What’s different about muscle length / stretch and tension in smooth muscle vs skeletal muscle?
In skeletal muscle there’s only one curve. there’s more than one for smooth muscle because you don’t want to distend your stomach every time you eat or if you want to eat more food it stops because you can’t stretch it anymore.
same thing with the uterus
they also use relatively little ATP
What are multi-unit smooth muscle?
fibers operate individually.
they’re innervated by a single nerve
examples are the ciliary muscles of the eye
What are unitary smooth muscle?
examples?
in syncytial or visceral locations that need to work together as a unit
the smooth muscle fibers are touching each other.
they contain gap junctions
GI, Bile Ducts, Uterus
What’s a good way to think about what cell type is in the GI?
Unitary because you don’t want one cell to contract and wait 5 minutes for the others to contract, you want the whole GI tract to push food down.
Innervation in Skeletal Muscle?
Smooth muscle?
alpha motor neurons from spinal cord
intrinsic (where you have no direct innervation from CNS or PNS.. innate property of smooth muscle) and extrinsic (ANS)
Neurotransmitters in Skeletal muscle?
Smooth muscle?
Acetylcholine (excited by it)
Ach (+ or -), NE, E (inhibitory on gut, but excitatory in vascular smooth muscle), NO (cyclic GMP mechanism. it can diffuse cell membranes and directly exert its effects inside the cell)
what isn’t a true neurotransmitter and why?
NO. this is because it goes into cells and relays its effects but it doesn’t bind to a receptor
it would actually be peracrine
What are the transmission specializations of Skeletal Muscle?
Smooth Muscle?
Neuromuscular Junctions (motor neurons synapsing onto a motor cell)
Varicosities (swelling along the axon that contain neurotransmitters that release and signal to the smooth muscle)
What are the neurotransmitter receptors in Skeletal muscle?
smooth muscle?
nAChR (excitatory for Ach)
MAChR (Ach for smooth)
Adrenergic (NE + E)
Are there any other forms of activation in the skeletal muscle?
smooth muscle?
no
blood-borne (CCK, oxytocin, etc), paracrine, intrinsic
How does the contraction of smooth muscle?
- what are the 2 ways calcium enters, which is more prevalent?
- What happens next and how does this bind?
- what does this activate?
- what does this do once activated?
You need calcium to enter the cell via plasma membrane or to be released by the SR through calcium channels.. way higher membrane wise, not SR
calcium binds reversibly to calmodulin, forming the calmodulin calcium complex
This activates Myosin Light Chain Kinase (MLCK)
this phosphorylates myosin which is now activated and myosin can now bind to actin and together that causes muscle contraction
How does smooth muscle relaxation work?
- what is the big molecule to know?
- what does it do
- what happens when you’ve inactivated this
- what does calcium do?
Myosin Phosphatase
it allows phosphorylated myosin to become inactivated.
once inactivated, the reversibly binding calcium unhinges from the calmodulin, separating it
the calcium goes to the SR or outside of the cell, but know that some of them require ATP
Why does smooth muscle require more ATP than skeletal muscle?
why is this a problem?
way more ATP usage than skeletal muscle.
they need to contract for longer. your stomach cannot afford to be distended past a certain point.
it’s a problem because they have less mitochondria than skeletal muscle
How does smooth muscle fix the need for ATP problem?
Latch mechanism
how does the latch mechanism form?
Myosin phosphatase removes the phosphate group but the actin and myosin are still latched together.
the reason for this is that this combination has a low affinity for ATP. you need an ATP to come and release the two.
With this low affinity it remains latched and by remaining latched this still generates active tension without the use of ATP.
this is how they do this without tiring out.
