Chapter 9: Muscle Types and Aging

Smooth Muscle

• Involuntary Muscles: Controlled by the nervous system.
• Structure: Spindle-shaped, not multinucleated, more actin than myosin.
• Function: Slow, organized, and relaxed contractions.
• Contractions: Occur in a wave-like or spiral pattern, not parallel like skeletal muscles.
• Calcium Source: Calcium comes from both extracellular fluid and sarcoplasmic reticulum.
• Essential Protein: Uses calmodulin instead of troponin for calcium binding.
• Examples: Found in hollow organs like the stomach, urinary bladder, uterus.
• Peristalsis: Auto-rhythmic contractions that move food through the digestive system.
• Autonomic Nervous System: Controls smooth muscles involuntarily, involving neurotransmitters like acetylcholine and norepinephrine.

Cardiac Muscle

• Location: Found only in the heart.
• Structure: Striated with closely packed sarcomeres, branching muscle fibers, and intercalated discs.
• Function: Enables rhythmic heartbeats.

Effects of Aging on Muscles

• Sarcopenia: Age-related muscle atrophy starting around age 25.
• Muscle Mass Reduction: Up to 50% by age 80 if not active.
• Importance of Activity: Staying active with walking, weightlifting, and exercise is crucial for maintaining muscle mass and overall health.
• Bone Health: Muscle activity helps in remodeling and maintaining bone health.
• Posture and Walking: Important to keep these muscles strong to avoid falls and maintain mobility.

Summary

• Review: Recap available through highlighted notes, outlines, and questions at the end of the chapter.
• Critical Thinking Questions: Provide deeper understanding and application of the concepts.