Smooth Muscle Flashcards
(18 cards)
How are cells different in Smooth muscle in comparison to Skeletal Muscle?
- Cells are smaller
- Single, centrally located nuclei
- Less developed Sarcoplasmic reticulum
- Contain Actin & Myosin, but
- These myofilaments are:
- Thinner
- More randomly distributed
- Not organized in “True” sarcomeres
- These myofilaments are:
Smooth Muscle: Structure
Action & Myosin compared to Skeletal Muscle
- Fewer overall myofilaments
- Actin/Myosin ratio - 16:1
- Myofilaments not as well organized
- Have longer Actin filaments
- Do not attach to Z-lines
- Attach to the Sarcolemma or to Sarcoplasmic proteins called Dense Bodies
- Dense Bodies analogous to the z disc
- Not considered a “true” sarcomere
“Smooth” muscles are involuntary
They are under the control of:
- Thalamus and hypothalamus
- Brainstem
- Spinal cord
Smooth muscles can be found in:
- Viscera
- Glands
- Blood vessels
- others
Impulses to Smooth Muscles are carried via the
Autonomic Nervous System
How many neurotransmitters are used in the Autonomic Nervous System?
What are they?
2 Neurotransmitters
- Acetylcholine
- Norepinephrine
This is different from Skeletal Muscle
Smooth Muscle structure is necessary for function..
In many structures with Smooth Muscle..
- The condition of being stretched is present
- Still must be able to generate tension
- Bladder stretches 2-3x resting length
- Uterus: Stretches 8x resting length
Smooth Muscle:
Accomodation
- Property not seen in Skeletal muscle
- As smooth muscle cells stretch
- the muscle fibers “relax” to Accomodate the increase in length
- Able to keep the tension steady
Smooth Muscle Contraction
How is Smooth Muscle triggered?
- Triggered by impulses from the Nervous system (same as skeletal muscle)
- Stretching can trigger smooth muscle contraction
Smooth Muscle Contraction:
Sliding Filament Theory:
uses…
- Interaction between Actin and Myosin
- Uses calcium and ATP
Both same as Skeletal Muscle
Smooth Muscle Contraction
Smooth Muscle lacks..
Smooth Muscle lacks Troponin
Uses a different protein to bind calcium
Smooth Muscle is slower to
__________ & _________, so
it is more resistant to _______
contract & relax
fatigue
Smooth muscle can change length without losing tension
Accomodation
2 Major Functional Categories
Found in the various organs/structures of the body
- Unitary (visceral)
- Multi-Unit
Unitary
- Cells contact as a single unit
- Only some of the cells in the unit have direct contact with a neuron
- motor neurons from the autonomic nervous system
- Have gap junctions
- specialized connections between cells
- allows nerve impulses to spread from cell to cell
- without a direct neuronal connections to every cell
- All the cells in the unit work simutaneously
- Examples
- Stomach, intestines, bladder
*
- Stomach, intestines, bladder
Unitary
Because cells contract as a single unit
This gives the ability to
- This ability of one cell to stimulate the next cell
- Gives some Smooth Muscle with Unitary structure and a feature called Rhymicity
- Smooth muscle cells with a Unitary structure and Rhythmicity
- can produce a wave-like motion
- termed Peristalsis
Unitary
Peristalsis
- The alternation between contraction and relaxtion in the different layers of smooth muscle in an organ
- In a tubular structure (like the intestine)
- Helps move the contents in the tubular structure in one direction
- i.e. moving digesting food down the intestinal tract
Multi-Unit
- Contains units similar to Skeletal muscle
- units are variable in size
- All cells must be stimulated by individual nerve fibers
- Each cell has direct contact with a neuron from the Autonomic Nervous System
- Units can work independently
- Very few gap functions, if any
- Examples:
- Walls of blood vessels
- Iris
- Examples:
