Lecture 6: Neuromuscular Aspects of Movement I Flashcards
Muscles and motion
Muscles produce a motion when it creates tension and tries to shorten
Skeletal muscle
- overlap over each other
- striated (tells which way it will pull)
Origin
Proximal attachment of a muscle
- closer to axial skeleton
Distal
Distal attachment of a muscle
Wrapping points/retinacula
redirect muscle pull btwn origin and insertion
Wrapping points change direction (can be negative or positive)
Negative angle is held down by retinacula
Aponeuroses
Wide bands of connective tissue (wide tendon)
Attach muscle to bones like tendons
Layers of muscle
myofirbils (smallest unit) –> muscle fibres –> fascicle –> muscle (biggest)
Endomysium
covers muscle fibres
Fascicles
bundles of muscle fibres
covered by perimysium
Perimysium
covers fascicles
Epimysium
covers whole muscle AND tendon
- like cling flim
Sarcomere
Smallest contractile unit of muscle
- connected together in series
- Z-disc to Z-disc
Has actin and myosin
When stimulated by motor nerve, the sarcomere shortens
Actin
thin filament
Myosin
thick filament
Muscle contraction
Z-Discs get closer and I-band gets narrower
- A-band does NOT change
Light/dark bands and muscle
Myosin (thick) = dark band (absorbs lots of light)
Light bands - I band
Dark bands - A band
Rigor mortis
NO ATP
- can’t hydrolyze to form ADP and disconnect crossbridges
Small muscles go into rigor first and big muscles last (big muscles have higher ATP stores)
Length-tension curve
Best scenario (2): 2.20-2.25 microns
- produces 100% of tension (ideal)
worst case (1): longest sarcomere (no actin for crossbridges to connect) = no contraction
1 (longest) –> 6 (shortest)
shortest sarcomere = overlap in actin = decrease in tension
Pennation angle
Angle btwn muscle fibres and the line of pull of the muscle
Smaller angle = more direct pull = LESS force and more excursion
- fatigues easily
Larger angle = less direct pull = greater force and smaller excursion (small movement)
- force multiplier = can put more muscle fibres in parallel
Small pennation
Large excursion, small force, easily fatigued, quick rxn. time
Ex. Tibialis anterior (small angle)
- only needed for dorsiflexion when walking (small excursion)
Fusiform muscle
Fusiform muscle
Little to no pennation angle
Large pennation
Small excursion, large force (can stack more in parallel), goof endurance, slower rxn. time
Ex. Gastrocnemius
Pennation arrangements
Longitudinal
Unipennate
Bipennate
Multipennate
Longitudinal pennation
Fusiform muscle
- little to no pennation angle
Muscle fibres travel in direction of muscle pull
Ex. sartorius and tib ant.
Unipennate
single pennation angle btwn muscle fibres and direction of pull
pulls in one direction
more likely to see aponeuroses
Bipennate
pulls equally both ways
tracks to one side b/c there are 2 slightly different pennation angles
Ex. vastus intermedius
Multipennate
pulls in multiple directions
jack of many trades, master of none
- likely to pull or tear b/c it doesn’t do any one thing well
Ex. rotator cuff
CHARACTERISTICS OF A MUSCLE
- Flexibility: how much ROM does the muscle allow at the jt
- Strength: maximum FORCE that can be created
- Power: how FAST can the muscle produce force (force x velocity)
- explosive starts - Endurance: how LONG can the muscle produce force?
- fusiform muscles tire out quickly
Knee extensor group
Quads (anterior)
- vastus lateralis
- vastus intermedius
- vastus medialis
- rectus femoris (also a hip flexor)
Elbow flexor group
Anterior
- biceps brachii
- brachialis
- brachioradialis
Brachialis and brachioradialis fill in ROM to allow usable power when biceps are too short/long
Uniarticulate muscle
One-joint muscle
only cross one joint = only affect one joint when they contract
Ex. soleus in calf group (only crosses ankle)
Multiarticulate muscles
Multi-joint muscles
Cross two or more joints = affect several jts SIMULTANEOUSLY when they contract
Ex. gastrocenemius in calf (crosses ankle and knee)
Drawback of multi-joint muscles
They can’t get full ROM at both joints simultaneously
Active and passive insufficiency
Ex. semimembranosus and semitendinosus are vulnerable b/c they cross hip and knee
- both thrown into passive insufficiency = too long = tear
Active insufficiency
muscle CAN’T SHORTEN enough
too short = active part in making it too short (you do action)
Passive insufficiency
muscle CAN’T LENGTHEN enough
Steps of movement
- Agonist starts moving
- Antagonist stops moving
- Co-contraction (slow and fix mistakes)
Agonists
Muscles that pull together to produce the DESIRED motion at a joint
Ex. trying to lift a glass of water to mouth: elbow flexors are agonists
Antagonists
Muscles that pull in OPPOSITE DIRECTION at a joint
Ex. elbow extensors
Agonist-antagonist relationship
When agonists are active, antagonist group is inhibited to allow motion
In some situations, there is CO-CONTRACTION (both groups are active)
- used to stabilize of slow the jt.
What happens when a muscle is activated by a motor nerve?
The sarcomeres ATTEMPT to shorten (not always able to)
Concentric contraction
Muscle is activated and SHORTENS
External loading is insufficient
Isometric contraction
Muscle is activated and REMAINS THE SAME LENGTH
External loading exactly balances internal force produced by muscle
Ex. planks, holding yoga pose
Eccentric contraction
Muscle is activated and LENGTHENES
Produces more force than other ways
FACTORS THAT DETERMINE AMOUNT OF TENSION FROM MUSCLE ACTIVATION
- The AMOUNT of activation (does the brain want full or partial power)
- LENGTH of muscle (muscle has an ‘ideal length’ for max tension. Tension drops off if longer or shorter)
- SPEED of muscle (as muscle shortens faster, its tension drops quickly)
- lengthening muscle (eccentric) = tension goes up
Velocity-Tension Curve
Power is a parabolic function
In concentric phase, force drops off exponentially as velocity increases (force stays below 1)
At isometric contraction, force is at 1
At eccentric contraction, force goes above 1 then plateaus at max
- some fusiform muscles can go up to 180% with external load
- external load is needed to lengthen
Velocity and force
Inverse relationship
As velocity increases, force decreases
