009 Muscle function in health and disease Flashcards
describe the feedforward/feedback process of controlling movement
idea/need/motivation —> plan/intrinsic/extrinsic/posture —> execution/commant to muscles/force/length —> appraisal/sensory feedback/adjust if needed
-prevents movements from being jerky
what are the 3 different types of muscle contraction?
- concentric
- eccentric
- isometric
what is concentric contraction?
- when force > load
- the muscle shortens during contraction
what is isometric contraction?
- when force = load
- muscle stays at the same length during the contraction
what is eccentric contraction?
- when force < load
- the muscle lengthens during contraction
what type of muscle contraction produces the most force?
- eccentric
what are the neural factors that influence muscle contraction (2)?
- descending drive = how drive arrives at the spinal cord and how motor neurone innervates muscle fibre
- motor neurone/motor unit recruitment/coding
what are the biomechanical factors that influence muscle contraction (7)?
- cross sectional area = direct relationship between CSA and tension produced
- muscle fibre type
- visco elastic properties
- muscle architecture
- length-tension
- load velocity
- contraction time
name 3 factors other than neural and biomechanical that influence muscle contraction
- temperature
- fatigue
- pre stretching
what are the 2 main ways you can alter motor neurons to increase tension produced?
- recruit more motor neurones/units to send a larger drive and give a strong stimulus to motor neurone pool
- increase rate of firing of motor unit (summation) = rate coding
what is rate coding with motor neurones?
- increasing the firing rate of the motor neurone to generate greater force
what is the definition of muscle strength?
- maximum force or tension output generated by a single muscle or related muscle groups (isometric)
- measured in different ways such as repetition maximum, hand held dyanometer, isokinetics (special training machine that creates different levels of resistance based on the force you give)
- muscle torque = angular motion = the force applied by the muscle through a movement arm of a given length, at given angle to the joint
what is the definition of muscle power?
- product of force and velocity of muscle action
- power = work/time
- work = force x distance
what are the 2 key relationships when talking about muscle functioning?
- length-tension relationship
- force-velocity relationship
what is the difference between ACSA and PCSA?
- ACSA = anatomical cross-sectional area = straight coronal or saggital CSA, only looking at muscle in 1 directon
- PCSA = physiological cross-sectional area = bigger, perpendicular to muscle fibre direction, takes into account all the different layers and directions and angles of muscle fibres
describe the length-tension relationship of muscles
- tension is proportional to the extent of overlap of actin and myosin filaments, the greater the overlap, the more cross bridges that form
- as the muscle contracts, there is greater tension, and greater overlap of actin and myosin
- if overlapping exceeds a certain point, fewer cross bridges are formed, so tension decreases
- (graph looks like a hill, up, peak then down)
describe the force-velocity relationship
- graph is a backwards s
- force on y axis, shortening velocity on x axis
- eccentric lengthening = upper left on graph = increasing force, increasing lengthening velocity
-maximum isometric force = where it crosses y axis, when velocity = 0 (as the muscle is neither shortening or lengthening) - concentric shortening = lower right on graph = increase shortening velocity, decreases force
describe the power-velocity relationship graph
- hill/curve
- as velocity increases, power increases until a maximum and then power decreases
what are the 4 types of muscle fibres in animals?
- type 1 = slow twitch
- type 2a = fast twitch
- type 2x/d = fast twitch
- type 2b = fast twitch = just animal models
what is the fatigue resistance in the different types of muscles fibres?
- type 1 = resistant
- type 2a = moderately resistant
- type 2x/d = not resistant, very fatigable
what is the myoglobin content in the different types of muscle fibres?
- type 1 = high = appears red
- type 2a = moderate
- type 2x/d = low = appears white
what muscle fibre types do we have most common and least common in the human body?
most common = type 2x/d
least common = type 1
what type of muscle fibre is best for long distance running?
- type 1 = slow twitch = less quickly fatigued
what type of muscle fibre is best for sprinting?
- type 2 = fast twitch = quickly fatigued but produce stronger contractions
on a normal force/power and velocity graph, where is the Fmax, Pmax and Vmax?
- Force curve = downwards slope from y axis, Fmax = y intercept at top
- power curve = positive hill curve, Pmax is the top of the curve/peak
- Vmax = x axis intercept, greatest velocity
what happens to the power and the velocity if the sarcomeres are in parallel or series?
- same power produced (Pmax), but different optimal velocities (Vmax)
- parallel has a lower Vmax than series
what is the difference between the force and muscle CSA for men and women?
- women have a lower MCSA and lower force than men, but the strength per MCSA is the same in women as men (proportional)
how does ageing affect our muscles(6)?
- neural activation decreases (decreased motor recruitment and rate coding)
- muscle CSA decreases (atrophy, turns into fat)
- muscle architecture (decreased angle of pennation)
- muscle fibre type (greater loss of type 2)
- length-tension relationship ( loss of elasticity)
- agonist/antagonist coactivation (ineffective)
describe how cerebral palsy develops
- UMN lesion
- leads to loss of inhibition of lower motor neurons, which gives positive UMN features, e.g. spasticity. hyper-reflexia
-loss of connection to lower motor neurons, which gives negative UMN features e.g. weakness, fatigability, poor balance - leads to musculoskeletal pathology = muscle shortening, bony torsion, joint instability, degenerative arthritis
