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Questions and Answers

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.

True

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.

myogenic Signup and view all the answers

Match each type of smooth muscle with its characteristic:

Single Unit Smooth Muscle = Requires no nervous stimulation, self-excitable Multiunit Smooth Muscle = Requires motor nerve impulse for contraction Myogenic Response = Contracts when stretched Smooth Muscle Tone = Amplitude of contraction remains constant Signup and view all the answers

Which of the following is a primary characteristic of smooth muscle regeneration?

It can increase in size and number. Signup and view all the answers

Visceral muscle contracts in response to a slow increase in length.

False Signup and view all the answers

List two locations where multiunit smooth muscle can be found.

Irises of the eyes and blood vessels Signup and view all the answers

Smooth muscle is able to stretch without great increases in _____ or tightness.

tension Signup and view all the answers

What is a unique feature of single unit smooth muscle?

Fibers are well organized in sheets. Signup and view all the answers

What is the primary structural characteristic of smooth muscle cells?

Fusiform and non-striated with a single nucleus Signup and view all the answers

Smooth muscle contraction is initiated primarily by neural signals.

False Signup and view all the answers

What is the name of the calcium-binding protein that facilitates contraction in smooth muscle?

calmodulin Signup and view all the answers

Smooth muscle contraction is described as _ and _ compared to skeletal muscle.

slow, sustained Signup and view all the answers

Which of the following is NOT a function of smooth muscle?

Stabilizing joints Signup and view all the answers

Smooth muscle fibers contain troponin.

False Signup and view all the answers

List one location in the body where smooth muscle can be found.

Blood vessels Signup and view all the answers

The contractile process in smooth muscle is initiated by multiple types of _____ proteins in the membrane.

receptor Signup and view all the answers

Which type of filament does NOT directly participate in smooth muscle contraction?

Intermediate filaments Signup and view all the answers

Match the following characteristics to their respective muscle type:

Skeletal Muscle = Voluntary contraction, striated, multinucleated Smooth Muscle = Involuntary contraction, non-striated, single nucleus Cardiac Muscle = Involuntary contraction, striated, single nucleus with intercalated discs Signup and view all the answers

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