Test II: Cardiac and Smooth Muscle

Question 1

Structural Characteristics of Cardiac

Muscle Tissue

Answer 1

Cardiocytes are:
• Are small
• Have a single nucleus
• Have short, wide T tubules
• Have SR with no terminal cisternae (calcium
storage site)
• Are aerobic (high in myoglobin, mitochondria)
• Have intercalated discs

Question 2

– Are specialized contact points between
cardiocytes
– Join cell membranes of adjacent cardiocytes
(gap junctions, desmosomes)

Answer 2

Intercalated Discs

Question 3

Functions of intercalated discs

Answer 3

• Maintain structure
• Enhance molecular and electrical connections
• Conduct action potentials
• Coordination of cardiocytes
- link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

Question 4

Functional Characteristics of Cardiac Muscle

Tissue

Answer 4

– Automaticity
• Contraction without neural stimulation
• Controlled by pacemaker cells
– Variable contraction tension
• Controlled by nervous system
– Extended contraction time
• Ten times as long as skeletal muscle

Question 5

Different options of circulatory assist

Answer 5

– Transplant (limited supply)
– Ventricular assist device
– Total artificial heart (not needed in general)

Question 6

Why Heart Substitutes Fail

Answer 6

• Immune response “rejects” transplant or
side effects due to immune suppression
• Infection due to tubes and wires passing
through skin
• Formation of clots
• Damage to red blood cells
• Lack of pulsatile blood flow?

Question 7

Smooth Muscle in Body Systems

Answer 7

– Forms around other tissues
• In integumentary system
– Arrector pili muscles cause “goose bumps”
• In blood vessels and airways
– Regulates blood pressure and airflow
• In reproductive and glandular systems
– Produces movements
• In digestive and urinary systems
– Forms sphincters
– Produces contractions

Question 8

Structural Characteristics of Smooth

Muscle Tissue

Answer 8

– Nonstriated tissue
– Different internal organization of actin and
myosin
– Different functional characteristics

Question 9

Characteristics of Smooth Muscle Cells

Answer 9

– Long, slender, and spindle shaped
– Have a single, central nucleus
– Have no T tubules, myofibrils, or sarcomeres
– Have no tendons
– Have scattered myosin fibers
– Myosin fibers have more heads per thick
filament
– Have thin filaments attached to dense bodies
– Dense bodies transmit contractions from cell
to cell

Question 10

Functional Characteristics of Smooth

Muscle Tissue

Answer 10

1. Excitation–contraction coupling
2. Length–tension relationships
3. Control of contractions
4. Smooth muscle tone

Question 11

Excitation–Contraction Coupling

Answer 11

– Free Ca2+ in cytoplasm triggers contraction
– Ca2+ binds with calmodulin
• In the sarcoplasm
• Activates myosin light–chain kinase
– Enzyme breaks down ATP, initiates
contraction

Question 12

Length–Tension Relationships

Answer 12

– Thick and thin filaments are scattered
– Resting length not related to tension
development
– Functions over a wide range of lengths
(plasticity)

Question 13

Muscle cell connected to motor neurons

Answer 13

Multiunit smooth muscle cells

Question 14

Muscle cell not connected to motor neurons
• Rhythmic cycles of activity controlled by pacesetter
cells

Answer 14

Visceral smooth muscle cells