Smooth Muscle Physiology Flashcards
Where can smooth muscle be found?
Gut, Respiratory Tract, Vasculature
What are some of the features (physiologically) of smooth muscle?
- Can maintain contractions for long period of time
- Maintain organ shape
- Continuously generate active tension
- Uses relatively little ATP
What are the key features of a multi-unit smooth muscle?
- FIbers operate individually
- Innervated by a single nerve
What are some examples of multi-unit smooth muscle?
- Ciliary muscles or eye
- Iris
- Piloerector muscles
What are the key features of unitary smooth muscle?
- Syncytial or visceral
- Work together as a unit
- Cell membranes adhere to one another and contain gap junctions
Where can you find unitary smooth muscle?
- GI Tract
- Bile Ducts
- Uterus
What type of neurons innervate skeletal muscle?
Alpha motor neurons
What is the innervation of smooth muscle?
- Can be intrinsic or extrinsic
- Intrinsic (IE: Enteric NS)
- Extrinsic (IE: Stretch)
What is the NTX of skeletal muscle?
ACh
What is the NTX of smooth muscle?
- ACh
- NE
- Epi
- NO- (more of a paracrine agent)
What is the transmission specialization of skeletal muscle?
NMJ
What is the transmission specialization of smooth muscle?
Varicosities (bumps along the axon that contain ntx vesicles)
NO NMJ*
What is the NTX receptor on skeletal muscle?
nAChR
What is the NTX receptor on smooth muscle?
mAChR or adrenergic
Does skeletal muscle have any other NTX receptors?
NO
Are there other smooth muscle receptors?
Yes
- Blood bourne (ex: hormones)
- Paracrine (ex: NO-)
- Intrinsic (ex: enteric NS)
What are the steps of smooth muscle contraction?
- Ca2+ enters cytosol thru Ca2+ channels in plasma membrane (which has much bigger effect than Ca2+ released from SR)
- Ca2+ binds to CaM and together they form REVERSIBLE Ca2+-CaM complex
- Ca2+-CaM complex activates MLCK (myosin light chain kinase)
- MLCK phosphorylates myosin
- Myosin-actin cross bridges can form and contraction can occur
What are the steps of smooth muscle relaxation?
- Myosin phosphatase dephosphorylates myosin
- Ca2+-CAM complex dissociates
- Ca2+ transported out of the cell (via Na+/Ca2+ exchanger) or pumped back into the SR (via Ca2+/ATPase)
- CAM hangs out in the smooth muscle cell
How can the smooth muscle cell maintain such long contractions?
Latch mechanism
What is the latch mechanism?`
- After phosphate is removed from myosin via Myosin phosphatase
- Actin and myosin are still latched together
- This complex has LOW affinity for ATP
- Remaining latched-the muscle can continue to generate active tension
Why does smooth muscle use ATP at a slower rate than skeletal muscle?
Cross bridge formation is slower in smooth muscle
What is active tension? (very general sense)
What the cross bridges do
There is an optimal range of active tension for both smooth and skeletal muscle
What is passive tension? (very genrally speaking)
How individual muscle cells are able to stretch their membranes
What is important about passive tension?
Limits the muscles ability to continue stretching despite increases in length (this helps prevent injury)
What is unique about smooth muscle regarding passive tension?
- Once actin and myosin release maximum passive tension, the smooth muscle cell can reduce its tension back to zero via rearrangement of the dense bodies and cell as a whole
- This enables smooth muscle to maintain contractions for long periods of time
Identify the red and blue lines on each graph. Which type of muscle is represented by each graph?
Left= Skeletal muscle cell (Blue=active tension, red=passive tension)
Right=Smooth muscle cell (Blue=active tension, red=passive tension)
