Lecture 11-12 Flashcards
definition of motor unit
- motor unit = motor neuron + innervated fibers
- each muscle fiber is innervated by only one motor neuron
- a single motor neuron can innervate many muscle fibers
individual muscle fibers contract in what type of response
“all-or-nothing”
describe process of motor unit recruitment
- recruitment: progressive activation of additional motor units to increase contractile strength of muscle
- under voluntary conditions- not all motor units are activated at one time
isometric contraction
- muscle develops tension but does not shorten
- NO movement
isotonic contraction
- muscle shortens
- tension remains constant
- movement
Passive vs active tension
- Passive tension: due to stretching muscle
- active tension: force developed due to cross-bridge cycling
role of Fascia
- fibrous connective tissue that binds muscle into a functional unit
- all connective tissue sheaths are continuous with each other and with tendon
- force is transfered through these connective tissues to tendon and then bone
What the length-tension relationship?
- tension developed at a particular length is proportional to the number of cross-bridges formed
- only myosin heads within the zone of overlap can bind to actin
what is the force-velocity relationship of muscle contraction
- force generated by muscle is a function of velocity
- at slower velocities more cross-bridge binding can occur
muscle twitch
- response to a single threshold stimulus
twitch summation
- increased frequency of stimulation = successive contractions with increasing force: “piggyback”
- muscle fiber does not have time to fully relax
- high frequency stimulation keeps cytosolic Ca2+ levels high
- a fused maximal contraction (tetanus) can occur
when was tissue sampling introduced? When was it re-introduced?
- 1868
- 1962
- hollow need inserted into muscle to retrieve a sample
Can the fiber type composition of a muscle be changed?
- yes, fiber type concentration of a muscle can be changed with training, but, to some extent, is limited by genetics
Charactertistics of Type I muscle fiber
- High aerobic (oxidative) capacity: MARATHON RUNNER
- lots of mitochondria, myoglobin, and capillary system -> endurance
- slow contractile velocity
- s_mall diameters than type IIa fibers_
Characteristics of Type II fibers
- high anaerobic (glycolytic) capacity
- rich in enzymes for anaerobic metabolism, high SR content, high ATPase activity
- designed for power and speed but fatigue easily
- fast contractile velocity
List the muscle fiber types in humans
- Type I: slow twitch fiber
- Type IIa: fast twitch fiber
- Type IIx: really fast fiber (rare in healthy humans)
- Hybrid: I/IIa; I/IIa/IIx; IIa/IIx
What three characteristics determines muscle fiber types
- Myofibrillar volume sets force generation
- SR volume sets frequency of operation
- Mitochondrial volume sets aerobic ATP synthesis rate
Name the Neural factors that occur early in training.
- increased motor unit recruitment = increased strength
- increased motorneuron output = increased rate of torque development
When does muscle hypertrophy occur in training
later in training
If power and contractile velocity increase in type I fibers with training, will these parameters come close to the power of velocity of type II fibers?
No
What happens to Power, contractile velocity, fiber size and % distribution of type I and type IIa fibers after 12 weeks of strength training
- type I: power increases; contractile velocity increases; fiber size increases; % distribution no change
- type IIa: power increases; contractile velocity increases; fiber size increases; % distribution: increases
What happens to Power, contractile velocity, fiber size and % distribution after 16 weeks of trianing for a marathon
- type I: power increases; contractile velocity increases; fiber size decreases; % distribution increases
- type IIa: power increases; contractile velocity remains same; fiber size decreases; % distribution: no change
older individuals, especially women rely more heavily on what type of fibers
- type I
- muscle plasticity is reduced with aging (80+)
function of tendon
- transmission of force from muscle to bone
- tendon properties influence muscle power output
- powerful muscles: short, broad tendons
- muscle for fine movement: long, thin tendons
