Podcast
Questions and Answers
Which neurotransmitter is NOT associated with smooth muscle contraction?
Which neurotransmitter is NOT associated with smooth muscle contraction?
- Acetylcholine
- Norepinephrine
- Dopamine
- Serotonin (correct)
Multiunit smooth muscle requires stimulation by a motor nerve impulse to contract.
Multiunit smooth muscle requires stimulation by a motor nerve impulse to contract.
True (A)
What type of smooth muscle is also known as visceral smooth muscle?
What type of smooth muscle is also known as visceral smooth muscle?
Single Unit Smooth Muscle
The _____ response occurs when smooth muscle contracts upon being stretched.
The _____ response occurs when smooth muscle contracts upon being stretched.
Match each type of smooth muscle with its characteristic:
Match each type of smooth muscle with its characteristic:
Which of the following is a primary characteristic of smooth muscle regeneration?
Which of the following is a primary characteristic of smooth muscle regeneration?
Visceral muscle contracts in response to a slow increase in length.
Visceral muscle contracts in response to a slow increase in length.
List two locations where multiunit smooth muscle can be found.
List two locations where multiunit smooth muscle can be found.
Smooth muscle is able to stretch without great increases in _____ or tightness.
Smooth muscle is able to stretch without great increases in _____ or tightness.
What is a unique feature of single unit smooth muscle?
What is a unique feature of single unit smooth muscle?
What is the primary structural characteristic of smooth muscle cells?
What is the primary structural characteristic of smooth muscle cells?
Smooth muscle contraction is initiated primarily by neural signals.
Smooth muscle contraction is initiated primarily by neural signals.
What is the name of the calcium-binding protein that facilitates contraction in smooth muscle?
What is the name of the calcium-binding protein that facilitates contraction in smooth muscle?
Smooth muscle contraction is described as _____ and _____ compared to skeletal muscle.
Smooth muscle contraction is described as _____ and _____ compared to skeletal muscle.
Which of the following is NOT a function of smooth muscle?
Which of the following is NOT a function of smooth muscle?
Smooth muscle fibers contain troponin.
Smooth muscle fibers contain troponin.
List one location in the body where smooth muscle can be found.
List one location in the body where smooth muscle can be found.
The contractile process in smooth muscle is initiated by multiple types of _____ proteins in the membrane.
The contractile process in smooth muscle is initiated by multiple types of _____ proteins in the membrane.
Which type of filament does NOT directly participate in smooth muscle contraction?
Which type of filament does NOT directly participate in smooth muscle contraction?
Match the following characteristics to their respective muscle type:
Match the following characteristics to their respective muscle type:
Study Notes
Smooth Muscle Functions
- Fusiform, non-striated cells
- Contains one nucleus located in the center
- Involuntary contractions
- Modulated by the neuroendocrine system
- Found in:
- Walls of blood vessels
- Gastrointestinal and urogenital organs
- Dermis of skin
Smooth Muscle Microscopic Anatomy
-
Three types of filaments:
-
Thick myosin filaments: Longer than in skeletal muscle
-
Thin actin filaments: Contain tropomyosin and calmodulin (no troponin)
-
Intermediate filaments: Do not participate in contraction, support cell shape
-
No striations:
-
Actin and myosin are randomly arranged
-
Dense bodies: Analogous to Z lines in skeletal muscle
- Actin filaments insert here
-
Contraction: Pulls dense bodies together, resulting in slow and sustained contractions
-
No T-tubules
-
Poorly developed sarcoplasmic reticulum
Functional Anatomy
- Uses calmodulin: Binds calcium, activates actin and myosin cross-bridge formation
- Calcium source: Mainly from the extracellular fluid
- Resistant to fatigue: Sustained contraction for longer periods
- Energy efficiency: Can maintain force with less ATP than skeletal muscle
- Multiple stimuli: Can contract in response to:
- Nervous signals
- Hormonal stimulation
- Stretch
- Receptors: Located on the smooth muscle membrane
- Autonomic nervous system control:
- Unconscious control of contraction
- Uses neurotransmitters: acetylcholine and norepinephrine
- Effects can be excitatory or inhibitory depending on the smooth muscle receptors
Smooth Muscle Types
- Single Unit (Visceral) Smooth Muscle:
- Found in hollow organs (stomach, intestines, bladder, uterus)
- Cells connected by gap junctions
- Self-excitable, contracts as a single unit
- Multiunit Smooth Muscle:
- Fibers are less organized, scattered
- Requires stimulation by the autonomic nervous system
- Found in:
- Iris of the eyes
- Arrector pili muscles
- Blood vessels
- Large airways
Intrinsic Control of Smooth Muscle Contraction
- Myogenic Response:
- Smooth muscle contracts when stretched
- Allows organs to distend without significant tension changes
- Contraction forces contents out when stretching capacity reached
Functional Properties
- Autorhythmic contractions: Some visceral muscle exhibits this
- Stretch response: Contracts in response to sudden stretching but not slow increases in length
- Smooth muscle tone: Relatively constant tension
- Amplitude of contraction is constant even with changes in length
Electrical Properties
- Slow conduction velocity: Compared to skeletal muscle
Smooth Muscle Regeneration and Growth
- Hypertrophy: Increase in size of muscle cells
- Regeneration/Proliferation: Increase in the number of muscle cells
- Smooth muscle cells can divide
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