M2 L7 Flashcards
What are the components of smooth muscle?
contain gap junctions and desmosomes
How does smooth muscle differ from skeletal muscle
- smaller than skeletal muscle cells
- mononuceuleated
contains thin and thick filaments
what is electrochemical coupling
the process by which electrical signals (action potentials) are translated into a chemical signal that triggers physiological responses, such as muscle contraction
What are gap junctions in smooth muscle cells
structure between smooth
muscle cells that allow for electrochemical communication
What are desmosomes in smooth muscle?
binding structures,
mechanically bind smooth muscle cells
hold adjacent cells together, providing mechanical strength and resistance to stress. They are especially important in tissues that experience significant mechanical stress, such as the skin, heart, and epithelial layers.
size of smooth muscles?
2-5 micrometers wide
100-400 micrometers long
Membrane specializations
- contains gap junctions
- no NMJ
- no T-tubules
- has a SR
What does the inside of a hollow organ contain? (the layers)
- endothelium on outside facing lumen
- smooth muscle cells in the middle
- connective tissue on the inside
what do smooth muscle cells longitudinal and circumferential do?
longitudinal: affects length
circumferential: controls size/cross sectional area of lumen (ex: blood vessel size)
How do they classify smooth muscles?
With function and organization:
1) Function
* phasic
* tonic
2) Organization
* multi-unit
* single-unit
How do they classify skeletal muscle?
With MHC isoform type and metabolic processes used:
1) MHC isoform type
* Slow
* Fast
2) Metabolic process used
* Oxidative
* Glycolytic
* Oxidative/Glycolytic
For smooth muscle function, describe phasic muscles
Phasic muscles are muscles that primarily generate movement and are involved in short bursts of activity.
These muscles are typically responsible for fast, powerful contractions.
- fast
- brief
- synchronized
- mostly single unit
For smooth muscle function, describe tonic
Tonic muscles are responsible for sustained contractions and are primarily involved in posture and stability.
- slow
- prolonged contraction
- not very synchronized
- multi unit
Describe single unit organization
* ex:
Muscle fibers connected by gap junctions, so they contract together as a single unit.
- rapid and highly synchronized
- rhythmic contraction
- action potentials
- ex: intestines, uterus
Describe multi unit organization
* ex:
Muscle fibers contract independently because they are not connected by gap junctions.
- fine tubed and prolonged control
- graded potentials
- ex: arteries, airways, blood vessels
What is phasic and tonic contractions?
Phasic and tonic refer to different types of muscle activity or muscle contractions, describing how muscles respond to stimuli or maintain tension.
- Phasic muscles: Involved in quick, powerful movements (fast or slow-twitch, typically Type II).
- Tonic muscles: Involved in sustained, low-force contractions for posture and stability (mainly slow-twitch, Type I).
Describe the different parts of the esophagus in terms of skeletal vs smooth and tonic/phasic
1)First 1⁄3 = skeletal muscle, voluntary
2) Latter 2⁄3 = smooth muscle, autonomic
* Phasic contractions: fairly fast, brief, synchronized
3) Esophageal sphincter (tonic)
* Can maintain contraction for hours
* Not necessary for it to be synchronized
* Mix of multi & single unit types
List the factors that explain why smooth muscle contraction varies depending on location and function:
- Multiple neurotransmitters – Different nerves release different signals
- Distribution of receptors – Different smooth muscle cells have different receptors
- Soluble factors (hormones) – Hormones like epinephrine or oxytocin can influence contraction or relaxation.
- Density of voltage-gated channels – More channels mean stronger or faster contractions in response to electrical signals.
- Cell-to-cell communication & gap junctions – (single unit: gap junctions to communicate as a unit, multi unit: no gaps they each do their own thing w finer contraction)
- Proximity to nerves – (multi needs direct nerve input bc they dont communicate, single dont need everyone to have nerve signal bc if one contracts they all follow)
Explain whats present here, what type of unit it is, and how things work
This is a multi unit
- has varicosities at each smooth muscle cell
- the NT release opens the VG channels but there aren’t many
- the hormones diffuse and bind to affect the cell
- no direct cell to cell communication
- graded potential
Explain whats present here, what type of unit it is, and how things work
This is single unit
- fewer varicosities per smooth muscle cell
- has more gap junctions to allow for rhythmic contractions
- more voltage gated ions to allow for more depolarization and lead to an action potential
