D4. Muscles Flashcards
Smooth Muscle
- Long and tapered at each end
- Only one nucleus
- Lines the internal organs
- Involuntary
- Slower to contract than skeletal
- Sustain prolonged contractions
- Does not fatigue easily
Cardiac (heart) muscle
- Forms the walls of the heart
- Tubular and striated (bands of light and dark)
- Cells have one nucleus
- Branched, creating a net-like structure
- Involuntary
Skeletal (striated) muscle: Function
- Allow body to move
- Atached to the bone with tendons
- Protects internal organs
- Stabilize joints
- Supports body
- Helps maintain a constant body temperature
Skeletal (striated) muscle: Structure
- Very long
- Many nuclei
- Voluntary - it’s contraction is consciously controlled by the nervous system
- Striated/tubular
Hierarchy of Muscle Structure
- Muscle
- Muscle-fibre bundle
- Muscle fibre
- Myofibrils
- Myofilaments
Two types of myofilaments
- Actin: Light, thin filaments
- Myosin: Dark, thick filaments
Sliding Filament Model
- Muscles contract when coordinated sliding and pulling motions occur between Z bands
- When a muscle is relaxed, myosin heads are not bound to actin
Sacromere
- Section of a myofibril from one Z-line to the next
- The arrangement of these sacromeres next to each other produces the striations of the skeletal muscle fibers
The Sliding Filament Model
- Muscles contract when coordinated sliding and pulling motions occur between Z bands
- When a muscle is relaxed, myosin heads are not bound to actin
The Role of Calcium and Regulatory Proteins
- An increase in Ca2+ levels trigger changes that expose binding sites for myosin
- The myosin heads bind to actin filaments
- Once bound, the myosin heads will tilt towards the sacromere’s center, sliding the bound actin filament with them
- The myosin head contains ATPase
- When ATP binds to a myosin head, the head releases its grip on actin
- The ATP is hydrolyzed to ADP and the myosin head reverts to its original position
- If Ca2+ and ATP are still present, the procecss may be repeated
Energy Sources for Contraction
- ATP reserves: Small amount found around myofilbrils/can provide only a brief contraction
- Creatine Phosphate: Initial source of energy to regenerate ATP from ADP and P; only lasts about 10 seconds
- Cellular Respiration: Produces up to 38 ATP per glucose molecule (requires O2)
Types of Skeletal Muscle Fibers
Slow-Twitch
- Sustain long contractions, often found in muscles that maintain posture
- Rely on aerobic respiration
- Break down ATP slowly, but efficiently to release energy
- Found in greater abundance in distance runners
Types of Skeletal Muscle Fibers
Fast-Twitch
- Brief, rapid, powerful contractions
- Rely on glycolysis (anaerobic respiration)
- Found in abundance in sprinters
Muscle Fatigue
- The inability of the muscles to contract
- Causes:
- Lack of oxygen
- Lack of ATP
- Accumulation of wastes (lactic acid, pyruvic acid, etc.) → lowered pH is caused by acids, results in increased heart rate
Nerve Control of Muscle Tension
Muscle Twitch
- Skeletal muscles are stimulated by nerves
- The arrival of nerve impulse causes a muscle fibre to undergo a single contraction or a twitch
Nerve Control of Muscle Tension
Muscle Tonus
- A slightly sustained contraction whereby a muscle is ready for any activity (posture tonus)
Nerve Control of Muscle Tension
Summation
If a muscle fiber is restimulated before it has completely relaxed, the second twitch is added on to the first, resulting in summation
Nerve Control of Muscle Tension
Tetanus
A sustained contraction of a muscle (continous muscle contraction b/c of activity)
Hypertrophy
- Growth and increase in the size of muscle cells
- Achieved through specific exercises
Muscle atrophy
Muscle gets weaker, smaller caused by dormancy
Muscular Dystrophy
- Can’t use muscle (paralyzed)
- Caused by genetic disorders
Antagonistic Muscles
- Skeletal muscles that work in pairs and oppose each other
