Muscles Flashcards
What are the three types of muscles?
- cardiac
- skeletal
- smooth
What is the most abundant tissue in the human body?
- skeletal tissue is responsible for about 40-45% of total body weight
- human body has more than 430 pairs of skeletal muscle
What is the structural unit of skeletal muscle?
the multinucleated muscle cell or fiber
What is the basic contractile unit of the muscle?
muscle fibers consist of myofibrils
Myofibrils consists of _____
myofilaments (actin and myosin)
What is a thin filaments?
actin
What is a thick filaments?
myosin
What is the functional unit of muscle contraction?
- Composed of motor neuron and all muscle cells (fibers) innervated by motor neuron
- Follows “all-or-none” principle
What is the size principle?
- smallest motor units recruited first & w/ smaller stimulation frequencies
- larger motor units recruited later w/ increased frequency of stimulation and increased need for greater tension
What are tonic units?
smaller, slow twitch, rich in mitochondria, highly capillarized, high aerobic metabolism, low peak tension, long time to peak (60-120 ms)
What are phasic units?
larger, fast twitch, poorly capillarized, rely on anaerobic metabolism, high peak tension, short time peak (10-50 ms)
What is the weakest voluntary contraction?
a twitch
Wha determines the force of contraction in a single fiber?
the overlap of actin and myosin
What accounts for the force of contraction for the whole muscle?
active (contractile) and passive (series and parallel elastic elements) components
What are parallel connective tissue?
- tissues surrounding contractile elements
- acts like elastic band
- slack when muscle at resting length of less
What are series elastic tissue?
- tissues in series with contractile component
- tendon forms series elastic element of skeletal muscle
What are musculotendinous unit?
-tendon and connective tissues in muscle are viscoelastic
What does viscoelastic structures help with?
They help determine mechanical characteristics of muscles during contraction and passive extension
What are the functions of elastic elements of muscle?
- Keep “ready” state for muscle contraction
- Contribute to smooth contraction
- Reduce force buildup on muscle and help prevent muscle injury
- Helps muscle absorb, store, and return energy
How does synchronization affects force potential?
- number of motor units active at one time
- the more –> greater force potential
How does the size of motor units affects force potential?
motor units with larger number of fibers have greater force potential
How does the type of motor units affects force potential?
type IIA and IIB increases force potential, type I decreases force potential
How does summation affects force of contraction?
increase frequency of stimulation, to some limit, increases the force of contraction
What is the size principle - tension decrease?
Last recruited motor units drop out first
What are the four types of muscle contraction?
- concentric
- eccentric
- isokinetic
- isometric
What is concentric muscle contraction?
Force of the muscle contraction, greater resistance;
positive work; muscle movement and angular velocity of joint in the same direction
What is eccentric muscle contraction?
Force of muscle contraction, lesser resistance;
negative work;
muscle moment and angular velocity of joint in opposite direction
What is isokinetic muscle contraction?
Force of muscle contraction is equal to resistance;
constant angular velocity; positive work; muscle movement and angular velocity of joint in the same direction
What is isometric muscle contraction?
Force of muscle contraction is lesser resistance; series elastic component stretch
no mechanical work; physiological work
What is length-tension relationship?
-difficult to isolate single agonist
When does concentric contraction (muscle shortening) occur?
Occurs when the force of contraction is greater than the resistance (positive work)
When does eccentric contraction (muscle lengthening) occur?
Occurs when the force of contraction is less than the resistance
What is a fusiform muscle?
- fibers parallel to long axis of muscle
- Many sarcomeres make up long myofibrils
- advantage for length of contraction
- tends to have a smaller PCSA
What is a pennate muscle?
- fibers arranged obliquely to long axis of muscle
- uni-, bi-, and multi-pennate
- advantage for force of contraction
- tends to have larger PCSA
