Biomechanics 6/10- Muscles

Muscle Structures

Types of Muscle Tissue:

  • Cardiac

    • Found in the heart

    • Involuntary muscle tissue

  • Smooth

    • Found in organs, guts, stomach, etc.

    • Mostly in viscera

    • Mostly involuntary

  • Skeletal

    • Found on skeleton

    • Voluntary

    • Biceps, triceps, etc.

Myofascial Unit

  • Muscle fibers

  • Fascia

    • Endomysium

    • Perimysium

    • Epimysium

    • Tendons

    • Fascia profunda (most superficial)

Components of Skeletal Muscle

  • Fascia profunda

  • Epi

  • Peri

  • Endo

  • Fascicles

  • Myofibrils

  • Sarcomeres (movement units, contract)

  • Myofilaments

Sarcomere (individual movement unit) **

  • Thick myofilament (myosin)

  • Thin myofilament (actin)

  • Tropomyosin

  • Troponin

  • Titin

Sliding filament theory

  • ATP and Acetylcholine activate muscles

  • Each sarcomere pulls on itself

  • There is a shortened muscle

    • It can only shorten so much

  • Steps:

    • 1. unattached myosin heads become energized

      • Calcium

    • 2. Myosin head reaches out and attaches to actin, forming a crossbridge

    • 3. Crossbridge generates force (power stroke) that pulls the thin filament one notch toward the m-line

    • Myosin head detaches from actin, then tries to attached to another actin site (pull more toward m-line)

  • Ex. Tetanus, rabies, Guillain barre syndrome

Contraction Cycle

  • Sarcomere reticulum: spacing

Myofibril

  • Sarcomeres end to end = myofibril

  • Muscle fiber = 8-10 myofibrils

  • Cell nuclei, mitochondria (ATP)

  • Sarcoplasmic reticulum = fluid filled ducts that deliver calcium ions

  • Transverse tubules = transmit nerve impulses to myofibrils

Muscle fiber

  • Sarcolemma = plasma membrane around myofibrils

  • Sarcoplasm = gel-like substance surrounding fiber’s components

  • Endomysium = fascia wrapping around sarcolemma

IMPORTANT:

  • Sliding filament

  • Length tension

  • active passive insufficiency

  • Put fascia in order

  • Breakdown of muscle in order

  • Process in order

Parallel vs Pennate muscle

  • Parallel have longer muscle fibers

  • Parallel have greater ROM

  • Parallel have less strength

  • Parallel have tendons in line with fibers

  • Pennate muscles are stronger and typically generate more force

Flat:

  • parallel fibers

  • wide, flat tendons

  • hugs surface of body

    • frontalis

    • rhomboids

    • abdominals

Sphincter:

  • tissue needs to open/close

  • eyes

    • orbicularis oculi

  • mouth

  • sphincter

REVIEW THE REST OF PARALLEL/PENNATE MUSCLE TYPES

  • bicipital: 2 attachments

  • tricipital: 3 attachments

Muscle Functions

  • Generate mobility and produce stabilizing forces

Muscle contraction

  • Origin

    • Proximal attachment

  • Insertion

    • Distal attachment

  • Many muscles have more than one attachment

Muscle Architecture

  • Origin-proximal attachment

  • Insertion-distal attachment

  • Reversal of action** test question

    • Typical action moves insertion relative to origin

    • Reverse action moves origin relative to insertion

      • Sit ups

      • Pull ups

      • Gait cycle

Function of Muscle Tissue

  • Create movement

  • Stabilize posture

  • Assist fluid circulation

    • Lymphedema

  • Thermogenesis

    • body temperature

Motor Units

  • Small motor units

    • slower impulses

      • less wave summation

Recruitment of Motor Units

  • “All or none rule”

    • once a motor unit reaches stimulation threshold, all fibers in that unit fire simultaneously and completely

  • Recruitment- number of motor units that are activated

    • Body can alter the number of active motor units for smooth movement

  • Wave summation- with each consecutive activation signal, we get more contraction and tension

    • Pace of muscle twitches

**the slower we shorten, the more speed we have

Active and Passive Insufficiency

  • Insufficiency: cannot lengthen anymore or cannot shorten anymore

  • Active insufficiency: reduced ability at end-range to generate force

    • Action is weakened or incomplete due to excessive shortness of a multi-joint agonist muscle * can’t close fist

    • Too short, cannot shorten anymore

  • Passive insufficiency: inability to increase ROM by stretching muscle further

    • Action is inhibited because the antagonist muscle cannot lengthen sufficiently to allow desired movement to occur

      • Muscle stretched to its limits

      • Ex. Tenodesis, extend knee + dorsiflex ankle (calf stretch)

  • * both happen conjunctly sometimes

  • * active on the side that is shortened, passive on side that is lengthened

** Slide 86 study terms

** Review slide 62 with examples of insufficiency