Lecture - Muscles Flashcards
What are the 4 properties of skeletal muscle?
- Excitability
- Contractility
- Extensibility
- Elasticity
What is the capacity to respond to nerve stimulation and contract called?
Excitability
What is contractibility?
The ability of muscles to contract (shorten)
How much can a muscle shorten during a contraction?
By up to 50% of the resting length
What is extensability?
A muscles ability to stretch or lengthen
When one muscle contracts, what often happens to another muscle?
Extension
A muscles ability to “spring” back into its original length after being stretched is called what?
Elasticity
What are the 3 functions of skeletal muscles?
- Movement of body
- Posture maintenance
- Heat production
How do skeletal muscles attach to bones?
Via tendons
What kind of muscle fibers subconsciously contract to keep the body upright?
Slow-twitch muscle fibers maintain posture
Which function of skeletal muscles is demonstrated by shivering in the cold?
Heat Production
What are the structural layers of a skeletal muscle from the inside out?
- Endomysium - surrounds myofiber (muscle cell)
- Perimysium - surrounds fascicle(bundle of myofibers)
- Epimysium - surrounds muscle (bundle of fascicles)
Endomysium, perimysium, and epimysium are all types of what kind of tissue?
Connective tissue
Where does a tendon insert into a bone?
Periosteum
What holds a muscle together and transmits blood vessels and nerves into the interior of the muscle?
Connective tissue/tendons
What are the components of a muscle cell from large to small?
Myofiber - bundle of myofibrils - myofilament
What is the name for the thousands of long, cylinder-shaped segments in a muscle cell?
Myofibrils
What is a sarcolemma?
The cell membrane of a muscle cell
What is the sarcoplasm?
The cytoplasm of a muscle cell
What is the tubular invagination of a sarcolemma that conducts nerve impulse deep into a muscle cell?
T-Tubule
Where in a muscle cell is calcium stored?
In the sarcoplasmic reticulum (SR) - a smooth ER
What is the name for the enlarged end of the SR that borders the T-tubule?
Terminal cisterna
What is a triad?
2 teminal cisterna + the T-tubule that runs between them; helps stimulate the release of calcium
A synapse is a site of communication between a neuron and which 3 places?
- another neuron
- a muscle - usually named a neuromuscular joint
- a gland
What is a neuromuscular junction?
The junction between a neuron and a muscle cell, there is a tiny gap
What bridges the synaptic gap in a neuron?
A neurotransmitter (think acetylcholine)
What are the two main categories of myofilaments?
- Thick filament
2. Thin filament
Actin, troponin, and tropomysoin are all examples of what kind of myofilament?
Thin filament - they are also all proteins
Example of a thick filament
myosin
What is the name of the section of muscle measured from one Z disc to the next Z disc?
Sarcomere
What is the functional unit of a skeletal muscle?
A sarcomere; contains stacks of myofilaments bound together
4 Parts of the Sarcomere
- Z disc - end of each sarcomere, attachment site of actin proteins
- A band - dark band - made of myosin and overlapping actin
- I band - light band - made up on thin filaments only
- H band - contains only myosin
What gives skeletal muscle its unique striations?
Its alternating A bands and I bands
What are the 4.5 sources of ATP?
- Stored ATP - 6 seconds
- Creatine phosphate (CP) - 10 seconds
- Myoglobin
- Aerobic metabolism - 38 ATP
.5 Anaerobic metabolism - 2 ATP
Storage form of phosphate which can be quickly provided to convert ADP into ATP
Creatine Phosphate
When is Creatine phosphate replenished?
When the muscle is at rest
What is the muscle version of hemoglobin and what does it do?
myoglobin - binds oxygen and releases it as needed (when the lungs run out)
What is the primary fuel source of actively contracting muscles?
Glucose through glycolysis
Exceeding the ability of the lungs to supply oxygen
Oxygen debt (ex. sprinting) - this is why we pant after intense exercise
What 4 things happen after exercise?
- “repayment” of oxygen debt through labored breathing
- Restoration of levels of Creatine phosphate
- Restoration of myoglobin levels
- lactic acid accumulated in muscles sent to liver where it is re-synthesized into glucose
Why must lactic acid be quickly re-synthesized?
It dangerously lowers blood pH
What 3 factors contribute to the strength of a muscle contraction?
- The size of the load (as told to the muscles by the brain’s guesstimate)
- The initial length of the muscle fibers (optimal length = optimal contraction strength)
- Frequency of stimulation (muscle memory)
What are the 3 types of muscle contractions?
- Muscle twitch - single contraction 7-100 msec.
- Temporal summation - staircase phenomenon, 10-40 stimuli per second = stronger contractions
- Complete Tetanus - 40-50 stimuli per second, locked in contraction, very painful, cramp
Which type of muscle contraction has only partial relaxation between contractions and builds on itself?
Incomplete Tetanus/Temporal Summation
A classification of muscles that maintain the same tension throughout the contraction
Isotonic contraction (iso=same, tonic=tension)
What are the two types of isotonic contraction?
- Concentric - muscle shortens (upward bicep curl)
2. Eccentric - muscle lengthens (lower bicep curl)
What is an isometric contraction?
A contraction where the muscle maintains the same length throughout
Your arm is extended and holding 5 pounds, someone adds an additional 5 pounds to your arm and you maintain the same position. What kind of contraction is this?
Isometric contraction
You pick up a book from a table. What kind of contraction is this?
Isotonic contraction
What are some cellular markers of slow-twitch fibers?
More mitochondria and myoglobin
What kind of exercise stimulates cell enlargement by synthesizing additional myofilaments?
Resistance training (weight lifting)
Hypertrophy
Cell enlargement
Stimulates an increase in mitochondria and glycogen
Endurance training (aerobic exercise)
What is a hereditary disease in males that causes skeletal muscle to degenerate and be replaced by adipose?
Muscular dystrophy
What causes muscular dystrophy?
Loss of dystrophin, a protein that connects actin filaments with the cell membrane. Myofilaments slide over each other, but the membrane remains the same length causing membrane tears
In which autoimmune disease do antibodies block receptors for acetylcholine (ACh) on the muscle cell at the neuromuscular junction (NMJ)?
Myasthenia Gravis
What are the 3 different types of muscle cells?
- Skeletal - long, cylindrical
- Cardiac - striated, involuntary, branches, aerobic respiration
- Smooth - unstriated, spindle-shaped, small myocytes across fine control of small tissues like the iris of the eye
Which type of muscle cell contracts slowly?
Smooth muscle - can maintain single contraction for a long time
What has many calcium channels that allow extensive extracellular calcium to enter?
The sarcolemma in smooth muscle cells
Why does the body need tendons and fascia?
For strong attachment of muscle to bone
What causes post-workout soreness?
Lactic acid buildup from anaerobic respiration and microtears in the muscles
How long does a skeletal muscle contraction last?
Up to 100 milliseconds (an eye twitch, 0.1 of a second)
Why do skeletal muscles have more than one nucleus?
The nucleus codes protein using DNA and muscle cells have a lot of protein to code, manage, and replace
How does a muscle shorten (does it “bunch up”)?
No, the actins slide over the myacins
What is the stiffening of the muscles caused by lack of ATP called?
Rigor mortis
How do creatine phosphate supplements work?
They give a little extra energy (ATP) in the form of phosphate
What is a muscle cramp?
A cramp is complete tetanus, full extended contraction
What is a muscle twitch?
It’s a single muscle contraction, a full contraction of relaxation
Why are we only able to sprint for a short length of time?
We burn through our ATP and creatine phosphate, then we are stopped by our oxygen debt
What makes “dark meat” dark?
It’s high concentration of myoglobin and mitochondria and oxygen; white meat is glycolytic
